Effects of the heterosomes and maternal environments on aggressive behavior in Mus musculus

This is a study of the offense type of aggression in males of the DBA/1Bg and C57BL/10Bg inbred strains of mice and their two reciprocal F1 hybrids. It uses three test paradigms for dyadic encounters: the homogeneous set test, an identity panel of testers, and the standard opponent test. There were no reciprocal F1 hybrid differences for any of the 12 behavioral measures of aggression in the homogeneous set test or the standard opponent test. For the panel of testers paradigm, reciprocal F1 hybrid differences occurred when the tester (opponent) was an F1 hybrid male, but not when the tester (opponent) was an RB/1 or C57BL10 male. When B10RB1F1 males were the testers (opponents), B10RB1F1 hybrid males were more aggressive than RB1B10F1 hybrid males across 10 of the 12 behavioral measures. Conversely, when RB1B10F1 males were the testers (opponents), RB1B10F1 males were more aggressive than B10RB1F1 males across 9 of the 12 behavioral measures. These results conform to the following empirical rule: A significant difference between reciprocal F1 hybrids is observed for these behavioral measures when one of the hybrids has both of its heterosomes (X and Y chromosomes) and its maternal environment identical to those of its opponent and the other hybrid has none of these identical to those of its opponent. These results are consistent with a model in which on some genetic backgrounds, but not on others, similarity of the heterosomes and maternal environments can influence the display of or response to social or other stimuli for the offense type of aggression in mice. These stimuli may be individual recognition chemosignals in urine.     

Strain-dependent differences in LTP and hippocampus-dependent memory in inbred mice

Many studies have used "reverse" genetics to produce "knock-out" and transgenic mice to explore the roles of various molecules in long-term potentiation (LTP) and spatial memory. The existence of a variety of inbred strains of mice provides an additional way of exploring the genetic bases of learning and memory. We examined behavioral memory and LTP expression in area CA1 of hippocampal slices prepared from four different inbred strains of mice: C57BL/6J, CBA/J, DBA/2J, and 129/SvEms-+(Ter?)/J. We found that LTP induced by four 100-Hz trains of stimulation was robust and long-lasting in C57BL/6J and DBA/2J mice but decayed in CBA/J and 129/SvEms-+(Ter?)/J mice. LTP induced by one 100-Hz train was significantly smaller after 1 hr in the 129/SvEms-+(Ter?)/J mice than in the other three strains. Theta-burst LTP was shorter lasting in CBA/J, DBA/2J, and 129/SvEms-+(Ter?)/J mice than in C57BL/6J mice. We also observed specific memory deficits, among particular mouse strains, in spatial and nonspatial tests of hippocampus-dependent memory. CBA/J mice showed defective learning in the Morris water maze, and both DBA/2J and CBA/J strains displayed deficient long-term memory in contextual and cued fear conditioning tests. Our findings provide strong support for a genetic basis for some forms of synaptic plasticity that are linked to behavioral long-term memory and suggest that genetic background can influence the electrophysiological and behavioral phenotypes observed in genetically modified mice generated for elucidating the molecular bases of learning, memory, and LTP.     

Differential acquisition of lever pressing in inbred and outbred mice: comparison of one-lever and two-lever procedures and correlation with differences in locomotor activity

Recent progress in mouse genetics has led to an increased interest in developing procedures for assessing mouse behavior, but relatively few of the behavioral procedures developed involve positively reinforced operant behavior. When operant methods are used, nose poking, not lever pressing, is the target response. In the current study differential acquisition of milk-reinforced lever pressing was observed in five inbred strains (C57BL/6J, DBA/2J, 129X1/SvJ, C3H/HeJ, and BALB/cJ) and one outbred stock (CD-1) of mice. Regardless of whether one or two levers (an "operative" and "inoperative" lever) were in the operant chamber, a concomitant variable-time fixed-ratio schedule of milk reinforcement established lever pressing in the majority of mice within two 120-min sessions. Substantial differences in lever pressing were observed across mice and between procedures. Adding an inoperative lever retarded acquisition in C57BL/6J, DBA/2J, 129X1/SvJ, and C3H/HeJ mice, but not in CD-1 and BALB/cJ mice. Locomotor activity was positively correlated with number of lever presses in both procedures. Analyses of durations of the subcomponents (e.g., time to move from hopper to lever) of operant behavior revealed further differences among the six types of mice. Together, the data suggest that appetitively reinforced lever pressing can be acquired rapidly in mice and that a combination of procedural, behavioral, and genetic variables contributes to this acquisition.     

Variations in the Gender-Stereotyped Content of Children's Television Cartoons Across Genres

This study examined the gender-stereotyped content of children's TV network cartoons across 4 genres: traditional adventure (e.g., "Spiderman"), nontraditional adventure (e.g., "Reboot"), educational/family (e.g., "Magic School Bus"), and comedy ("Animaniacs"). Acting negatively, showing physical aggression, and being a victim were significantly less likely in the educational/family genre cartoons than any of the other three genres. Demonstrating romantic behavior was significantly more likely in the traditional adventure and the comedy genres than the other genres. Male characters were represented in cartoons significantly more than were female characters, but only in the traditional adventure and the comedy genres. Male characters were more likely than were female characters to use physical aggression, but only in the traditional adventure genre. Behaviors that were relatively more likely among female characters across genres included showing fear, acting romantic, being polite, and acting supportive. Most of the significant differences were also associated with very large effect sizes.     

Genetic influences on digging behaviors in mice (Mus musculus) in laboratory and seminatural settings

Digging behaviors of several inbred strains of laboratory mice and some of their crosses were examined in three contexts. In laboratory burrow boxes, C57BL/6Abg mice constructed more sophisticated burrow systems than did BALB/cAbg mice. Their F1 hybrids built burrow systems more complex than either parental strain. The same pattern of genetic influence was observed in an outdoor pen. In an escape task that required digging, BALB/c mice escaped more quickly than did C57BL/6 mice; their F1 hybrids showed dominance toward the BALB/c phenotype. These results indicate that behavioral polymorphisms in digging behavior, which may relate to habitat selection, have a genetic basis. The dominance and overdominance toward the better digging parental strain in each type of task suggest the possible evolutionary importance of these digging behaviors.     

Observational learning of a left-right behavioral asymmetry in mice (Mus musculus)

B6D2F1 hybrid mice that were allowed to observe a trained female mouse open a pendulum door to the right (or to the left) to enter a food compartment later solved this problem faster than pupils that had been placed behind a visual barrier. Male pupils that had observed a "left-handed" teacher performed sinistrally; males that had observed a "right-handed" model performed dextrally. Female pupils did not exhibit their demonstrator's laterality. Observational learning may provide a means to maintain certain lateralized behaviors. Such social learning may lead to the emergence of local traditions and to the cultural diffusion of behavioral asymmetries.     

Pre-exposure to context affects learning strategy selection in mice

The multiple memory systems hypothesis proposes that different types of learning strategies are mediated by distinct neural systems in the brain. Male and female mice were tested on a water plus-maze task that could be solved by either a place or response strategy. One group of mice was pre-exposed to the same context as training and testing (PTC) and the other group was pre-exposed to a different context (PDC). Our results show that the PTC condition biased mice to place strategy use in males, but this bias was dependent on the presence of ovarian hormones in females.The participation of different brain areas in place and response learning strategies has been studied extensively (White and McDonald 2002; Gold 2004; Mizumori et al. 2004). Place strategy is an allocentric navigation strategy that depends on extramaze cues. Response strategy is an egocentric navigation strategy based on proprioceptive cues. Inactivation of the hippocampus biased animals to response strategy use, and inactivation of the striatum biased animals to place strategy use (Packard and McGaugh 1996; Lee et al. 2008). Furthermore, glutamate infusion into the hippocampus strengthened place strategy use and, conversely, glutamate infusion into the striatum enhanced response strategy use (Packard 1999). These studies suggest that the hippocampus system mediates place strategy, while the striatum system mediates response strategy.Various factors can modulate learning strategy use, including training intensity (Packard and McGaugh 1996; Martel et al. 2007). A recent study investigated the influence of training on strategy use on a probe trial conducted 1 h after training (Martel et al. 2007). Male mice displayed enhanced place strategy use when trained on 12 or 22 trials compared with four trials, suggesting an effect of training intensity on strategy choice (Martel et al. 2007). This study further investigated the effect of pre-exposure to the training and testing context (PTC). Pre-exposure enhanced place strategy use in male mice after only four trials relative to animals pre-exposed to a different context (PDC). These results suggest that a sufficient exposure to the training and testing context promotes place strategy use in mice.The type of strategy used by rats is affected by both biological sex and gonadal steroids. Male rats typically employ a place strategy, especially during the early phase of training, on both land and water T-mazes (Packard and McGaugh 1992, 1996; Packard and Teather 1997). However, strategy use by female rats depends on hormonal conditions (Dohanich 2002; Dohanich et al. 2009). Place strategy is preferred by intact female rats on the day of proestrus when estradiol levels are elevated, and by ovariectomized rats treated with estradiol (Korol and Kolo 2002; Korol 2004; Korol et al. 2004). In contrast, response strategy is more often displayed by intact females on diestrus, and by ovariectomized females that did not receive estradiol replacement (Korol and Kolo 2002; Korol et al. 2004). To date, the effects of biological sex and gonadal steroids on learning strategy have not been studied in mice.In this study, we developed a modified version of the dual-solution water plus-maze task to further investigate the role of PTC compared with PDC in male and female mice. We hypothesized that strategy choice in both sexes would be dependent on context pre-exposure, and ovarian hormones would influence strategy choice in females. Our results show that PTC significantly enhanced place strategy use in male mice. Although there was no significant difference between PTC and PDC female mice, ovariectomy significantly reduced place strategy use in the PTC females, suggesting that ovarian hormones play a significant role in strategy use in female mice.Sixteen male and 39 female 129/Sve strain mice were obtained at 2–3 mo of age from Charles River Laboratories (Boston, MA). Mice were housed in groups of four on a 12/12 light/dark cycle (lights on at 07:00 h) with free access to food and water. All protocols followed the guidelines from a protocol approved by the Animal Care and Use Committee of Tulane University in accordance with National Institutes of Health Guide for the Care and Use of Laboratory Animals.Mice were pre-exposed for 5 min to the dry plus-maze either in the context of the subsequent training and testing (PTC), or in a different context in a different room (PDC), 30 min prior to the first training trial. The maze consisted of four clear Plexiglas arms (40 cm in length, 10 cm in width, and 40 cm in height). During the pre-exposure, mice were able to visit three arms of the maze. The rooms had different visual cues surrounding the maze. No extramaze cues were placed directly at the end of any arm. After the pre-exposure, the animal was placed in its home cage. The maze was wiped clean with 70% ethanol between trials.After pre-exposures, the maze was filled to 1.5 cm above the Plexiglas escape platform (15 cm in height) with room-temperature water colored opaque with white nontoxic tempera paint. Mice were trained in the water plus-maze task (Fig. 1A). The training was ended when the animals made six correct choices or reached nine trials. The animals that made fewer than four correct choices during training were not included in the study. Trials were continued until the mouse reached the platform or a maximum of 1 min. Each trial was separated by an intertrial interval of 4 min. Throughout the training trials, one arm (north) was blocked off by a white Plexiglas shield, creating a T-shaped maze. Mice were placed in the start arm of the maze (south) and were allowed to swim to the escape platform, which was consistently located in one arm of the maze for each animal and alternated between animals (east or west). Entry of the entire animal into the maze arm that contained the escape platform was scored as a correct response during the training trials, and entry of the entire animal into the maze arm that did not contain the escape platform was scored as an incorrect response. Mice were allowed to remain on the escape platform for 15 sec before being returned to their cages. Mice that failed to find the escape platform within 60 sec were manually guided to the platform. The water was distributed across all arms of the maze and the maze walls were wiped down to reduce intramaze cues between training and probe trials. One hour after training, mice were tested on a probe trial (Fig. 1B) in order to determine their relative use of “place” and “response” strategy. On the probe trial, mice were placed into the start arm 180° opposite the start arm used during training (i.e., end of the north arm) and were allowed to make an entry into either the east or west maze arm. The white Plexiglas shield blocked the south arm during the probe trial. Mice were designated as using place or response strategy based on the probe trial. Place strategy was designated as entry of the entire animal into the arm with the platform, and response strategy was designated as entry of the entire animal into the opposite arm.Open in a separate windowFigure 1.The effects of pre-exposure to the training and testing context (PTC) or to a different context (PDC) on strategy selection of male mice. (A) Schematic diagram of the water plus-maze. Mice were released from the south arm during training trials and from the north arm during the probe test. (B) More male mice used place strategy than response strategy when pre-exposed to the same context prior to training and testing (PTC, n = 5) compared with male mice pre-exposed to a different context (PDC, n = 7, P < 0.05). (C) Latency curves show the actual latency to escape to the platform. Two-way ANOVA (non-repeated measures) revealed no significant difference across training trials in escape latencies between PDC and PTC mice (P > 0.5), although a significant effect of trial indicated that mice reduced their escape latencies across trials (P < 0.001). Values represent mean ± S.E.M.Sixteen male mice were randomly divided into two groups based on pre-exposure context, PTC or PDC. Four of the 16 males were not included in the study for failure to reach criterion (four correct out of nine trials) or failure to escape to the platform due to floating, which is a behavior commonly seen in this strain (Wolfer et al. 1997). On the probe trial PTC males used the place strategy significantly more often than PDC males (P < 0.05, χ² = 5.182, Fig. 1B). Four of five PTC males used place strategy, whereas only one of seven PDC males used place strategy. Pre-exposure of animals to the same or different context prior to training did not affect the latency to escape the platform during training. Latency to find the platform during training trials revealed a significant effect of trial (F_(8,89) = 3.830, P = 0.0007, non-repeated measures two-way ANOVA) but not pre-exposure condition (F_(1,89) = 0.103, P = 0.75, non-repeated measures two-way ANOVA; Fig. 1C). Moreover, the average swim speed of PDC male mice (6 ± 1.6 cm/sec, n = 7) was not significantly different than the average swim speed of PTC male mice (6 ± 2.5 cm/sec, n = 5; P = 0.34, t = 0.9 [t-test]). Together, these data suggest that the pre-exposure condition did not influence learning during the training period, but PTC did enhance place strategy use in the probe trial in male mice.Female mice at 3 mo of age were randomly divided into two groups: mice that would receive ovariectomy (Ovx), and a sham surgery group (Sh). Mice were anesthetized with a ketamine (80 mg/kg) and xylazine (8 mg/kg) mixture. The first group of mice (n = 20) received ovariectomy using a dorsolateral approach. The other group (n = 19) of female mice received sham surgery, which consisted of ovary exposure only. Animals were injected with the pain reliever, buprenorphine (5 mg/kg), immediately after the surgery. One week after the surgery, vaginal smears were collected from all females, including Ovx as handled controls, at the same time each morning by lavage to track their estrus cycles (Marcondes et al. 2002). After two regular cycles, Sh animals were trained and tested on the day of proestrus (high estradiol).Ovariectomy has been reported to affect anxiety levels (Walf et al. 2006), and anxiety levels may alter performance on water maze tasks. To assay possible anxiety differences between Sh and Ovx, female mice were tested on open field and elevated plus-maze (EPM) 2 wk after the surgery in a room different from the rooms used in water maze tasks. A single mouse was placed in the center of a white, Plexiglas chamber measuring 43 cm in length × 43 cm in width × 18 cm in height. The animal explored the novel environment for 15 min, and movements were monitored by a camera interfaced with a tracking system (US HVS Image). The area was divided into 16 virtual squares (10.75 × 10.75 cm) by the program, and the middle four squares were defined as the center area. The Plexiglas chamber was wiped clean with 70% ethanol between trials. The EPM consisted of four arms (5 cm in width × 30 cm in length) arranged perpendicularly in a plus shape and elevated 38 cm above the floor. Two arms were enclosed by 15.5-cm dark Plexiglas walls and two arms were open. Each animal was placed in the center of the EPM facing a closed arm and allowed to move freely for 5 min. Behavior was monitored by a camera interfaced with the tracking system.Animals with high anxiety levels tend to spend less time in the open arms of the EPM and in the center of the open field. The percent time spent in the open arms of the EPM by Ovx mice (37.9% ± 7.5%, n = 14) was not significantly different than the percent of time spent in the open arms by Sh mice (27.8% ± 6.2%, n = 15; P = 0.30, t = 1.1). The percent time spent in the center of the open field by Ovx mice (35.1% ± 7.1%, n = 14) was not significantly different from Sh mice (29.0% ± 7.1%, n = 15; P = 0.55, t = 0.61). These results indicate that ovarian hormones did not have a significant effect on the anxiety levels of the female mice tested in this study.Two weeks after the anxiety tests, the Ovx and Sh groups were divided randomly into two groups based on the pre-exposure context: Ovx PTC, Ovx PDC, Sh PTC, Sh PDC. Sh females with regular estrus cycles were trained and tested on the day of proestrus. Five Ovx and seven Sh animals were not included in the study because of floating, failing to reach criterion (four correct out of nine trials), or exhibiting irregular estrus cycles. Five of eight Sh PTC and only one of six Sh PDC females used place strategy; however, this difference was not significant (P > 0.05, χ² = 2.94, Fig. 2A). Therefore, the pre-exposure condition did not significantly affect strategy use in females at proestrus.Open in a separate windowFigure 2.The effects of ovarian hormone status and pre-exposure to the training and testing (PTC) or to a different context (PDC) on strategy selection of female mice. (A) When pre-exposed to the same context prior to training and testing (PTC), more gonadally intact female mice at proestrus (Sh, n = 8) used place strategy than response strategy compared with ovariectomized female mice (Ovx, n = 8, P < 0.05). When pre-exposed to a context different than the training and testing context (PDC), gonadally intact female mice at proestrus (Sh, n = 6) and ovariectomized mice (Ovx, n = 6) used response strategy rather than place strategy. (B) Latency curves show the actual latency to escape to the platform. Two-way ANOVA (non-repeated measures) revealed no significant differences across training trials in escape latencies between sham and ovariectomized PTC and PDC mice (P > 0.5), although a significant effect of trial indicated that mice reduced their escape latencies across trials (P < 0.0001). Values represent mean ± S.E.M.Interestingly, ovariectomy did significantly affect strategy use in PTC females. Five of eight Sh PTC and only one of eight Ovx PTC females used place strategy (P < 0.05, χ² = 4.267, Fig. 2A). One of six Sh PDC females and zero of the six Ovx PDC animals used place strategy (Fig. 2A). Therefore, both Sh and Ovx PDC females used response strategy, and ovarian hormones did not enhance place strategy use in PDC females (P > 0.05, χ² = 1.09, Fig. 2A). Ovarian hormones did enhance place strategy use in PTC females. Furthermore, PTC did not enhance place strategy use in Ovx animals. Similar to males, there was a significant effect of training trial on latency to find the platform in female animals (F_(8,189) = 10.32, P < 0.0001, Fig. 2B). Ovarian hormones or pre-exposure to either context also did not affect escape latency during training in PTC or PDC females (F_(3,189) = 0.33, P = 0.80, Fig. 2B). In addition, there was no significant difference in the average swim speed between groups (F_(3,14) = 0.15, P = 0.93, one-way ANOVA). The average swim speed for each group was as follows: Ovx PTC (5 ± 1.5 cm/sec, n = 5), Ovx PDC (5 ± 1.0 cm/sec, n = 4), Sh PTC (5 ± 1.8 cm/sec, n = 5), Sh PDC (6 ± 1.5 cm/sec, n = 4). The numbers of animals are lower because in some cases, speed was not measured. Together, these data suggest that ovarian hormones and pre-exposure condition did not influence learning during the training period, but ovarian hormones did enhance place strategy use in the probe trial in only PTC mice.Consistent with previous literature (Martel et al. 2007), we found that ∼80% of PTC males favored the use of place strategy. In addition, 63% of PTC females on proestrus also used place strategy. Ovx female mice used response strategy regardless of the pre-exposure condition. These results confirm that pre-exposure to the training and testing context significantly increased the use of place strategy or reduced response strategy in male mice, while female mice on proestrus were not significantly different than chance. Ovariectomy diminished the use of place strategy and enhanced response strategy use in our study, implicating ovarian hormones in strategy choice.Male rats rely initially on a hippocampus-dependent place strategy, and then switch to a striatum-based response strategy over training (Packard and McGaugh 1996; Packard 1999). This suggests that response strategy is incrementally learned with repeated exposure to the same task. However, a sufficient amount of time to explore the extramaze cues during or before training increased place strategy use in male mice (Martel et al. 2007). In addition, it has been proposed that the presence of an increased number of salient extramaze cues favors place strategy use in rats (Restle 1957). Therefore, it is possible that pre-exposing mice to the learning environment allowed them to build a cognitive map that facilitated the use of a spatial place strategy. Another possible advantage of pre-exposure for place strategy use is that it may reduce the impact of non-mnemonic factors, such as anxiety, on performance (Cain 1998). Indeed, it was shown that peripheral injection and infusion of anxiogenic drugs into the basolateral amygdala biased rats toward the use of response strategy (Packard 1999; Wingard and Packard 2008; Packard and Gabriele 2009).While PTC female mice were not significantly different than PDC female mice, ovariectomy did reduce place strategy choice in the PTC mice. An emerging theory proposes that estradiol modulates cognitive performance via shifts in learning strategy (Korol and Kolo 2002; Daniel and Lee 2004; Korol 2004; McElroy and Korol 2005; Zurkovsky et al. 2007). Shifts in strategy use occurred across the estrus cycle in rats such that the hippocampus-dependent strategy was favored when estradiol levels were high (Korol et al. 2004). Similarly, estradiol treatment in ovariectomized rats increased hippocampus-dependent place strategy and impaired response strategy use compared with nontreated ovariectomized females (Korol and Kolo 2002). Our results showing that the lack of ovarian hormones reduced place strategy and increased response strategy use in PTC mice are consistent with these studies.In summary, we present a new design to a traditional dual-solution land plus-maze. One issue with the land maze version of the task is that it requires food deprivation. The possible increase in the appetite as a result of ovariectomy (Wade 1975) or disruption in the estrus cycle in response to food deprivation (Daniel et al. 1999) could confound the results in females in tasks that present food reward. In order to avoid these confounds, we used a modified version of a water-escape plus-maze (Packard and Wingard 2004). In this design, compared with the water-escape plus-maze, the clear Plexiglas maze itself is filled with water, instead of placing the plus-maze into a water maze, allowing a better view of extramaze visual cues. However, unlike rats, mice tend to be prey animals when in the water; therefore they are highly motivated to escape the water (Francis et al. 1995; Van Dam et al. 2006). Consequently, the stressful nature of the task prevents mice from utilizing the spatial cues as efficiently (Frick et al. 2000). Therefore, we pre-exposed the mice to the maze while it was dry, allowing them to build a cognitive map before they were released in water. The water plus-maze is important not only for the design of future studies, but also for the evaluation of previous studies that investigated learning strategies using tasks dependent on food deprivation.     

Measurements of the behavioral effects of albino mutation in mice (Mus musculus): comparisons of coisogenic inbred and hybrid lines

The effects of the albino gene on mouse behavior were examined, in particular its possible interactions with nonallelic genes (epistasis). More generally, the possible effects of genetic background (inbreeding depression or hybrid vigor) on the effects of the mutation were also considered. Tasks requiring either predominantly motor or predominantly cognitive capacity were studied for coisogenic albino and pigmented mice from either an inbred strain (C57BL/6 c/c vs. C57BL/6 +/c) or an F1 heterozygous generation (F1 c/c vs. F1 +/c) from a BALB/c X C57BL/6 +/c cross. The results showed a clear albino gene effect in the two lines and provide further evidence that the gene is the effective factor. On the other hand, there was no significant interaction between the mutation and the genotypic group (C57BL/6 or F1), which indicates that the effects of the mutation act approximately in an additive fashion between loci in these groups.     

Electrophysiological responses to ethanol, pentobarbital, and nicotine in mice genetically selected for differential sensitivity to ethanol

Cortical electroencephalographic (EEG) changes induced by ethanol (4.3 and 1.4 g/kg, ip), pentobarbital (50 and 16 mg/kg), and nicotine (1.0 g/kg) were examined in long-sleep (LS) and short-sleep (SS) mice that were genetically selected for differential sleep times induced by a hypnotic dosage of ethanol. Ethanol (4.3 g/kg) caused EEG changes that paralleled the behavioral differences, whereas no differences between selected lines were observed following the activating dose (1.4 g/kg). Data support the notion that the known difference in ethanol sleep times is due not to greater SS sensitivity to ethanol activation but rather to greater LS sensitivity to ethanol hypnosis. No differences between selected lines were observed following 50 mg/kg pentobarbital, which again parallels previous behavioral data. The SS mice were more responsive to pentobarbital activation (16 mg/kg). Nicotine more severely reduced EEG power and heart rate in LS mice; a continuous iv infusion of nicotine elicited a distinct pattern of behavioral stereotypy for each selected line, with more profound motor and reflex depression in LS mice. The lines do not differ in rate of nicotine metabolism, hence they must differ in central nervous system sensitivity to nicotine. Thus, lines of mice selectively bred for differential sensitivity to ethanol also display marked differences in electrophysiological and behavioral responses to nicotine.     

Prelimbic cortex bdnf knock-down reduces instrumental responding in extinction

Anatomically selective medial prefrontal cortical projections regulate the extinction of stimulus–reinforcement associations, but the mechanisms underlying extinction of an instrumental response for reward are less well-defined and may involve structures that regulate goal-directed action. We show brain-derived neurotrophic factor (bdnf) knock-down in the prelimbic, but not orbitofrontal, cortex accelerates the initial extinction of instrumental responding for food and reduces striatal BDNF protein. When knock-down mice were provided with alternative response options to readily obtain reinforcement, extinction of the previously reinforced response was unaffected, consistent with the hypothesis that the prelimbic cortex promotes instrumental action, particularly when reinforcement is uncertain or unavailable.The rodent medial prefrontal cortex contains cytoarchitectonically distinct subregions that can be differentiated based on efferent and afferent projection patterns, with dorsal regions—including the dorsal prelimbic cortex (PLc)—sharing similar functions that differ from those of the ventromedial prefrontal cortex, which includes the medial orbitofrontal cortex (mOFC) and infralimbic cortex. These dorsal/ventral networks are considered “go” and “stop” systems, respectively, that coincidentally guide behavior (Heidbreder and Groenewegen 2003). For example, the PLc is essential for maintaining instrumental responding for food when reinforcement is uncertain (Corbit and Balleine 2003; Gourley et al. 2008a). By contrast, ventromedial structures are associated with response inhibition, particularly in the context of stimulus–reinforcement associations (Heidbreder and Groenewegen 2003).We explore the hypothesis that the PLc may also promote goal-directed responding in the absence of reinforcement, thereby slowing the extinction of a previously reinforced instrumental response. If this is the case, diminution of the biological factors essential for activity-dependent neuroplasticity and cytoskeletal structure within the PLc might be expected to shift the balance between a dorsal “go” network and ventral “stop” network. The consequence would be a rapid decline in instrumental responding during extinction training. Indeed, we report that such a manipulation—virally knocking down BDNF, which promotes long-term potentiation (Kang and Schuman 1995; Korte et al. 1995, 1996; Patterson et al. 1996) and neuronal outgrowth (McAllister et al. 1995, 1996; Xu et al. 2000a,b; Gorski et al. 2003)—within the PLc facilitates the extinction of instrumental action.In the first experiment, group-housed ≥10 wk-old male mice bred in-house and homozygous for a floxed bdnf gene (Rios et al. 2001) were anaesthetized with 1:1 2-methyl-2-butanol and tribromoethanol (Sigma Aldrich) diluted 40-fold with saline. Mice were infused into the PLc (+2.0AP, −2.8DV, ±0.1ML) with an adeno-associated virus (AAV) expressing enhanced green fluorescent protein (EGFP) ± Cre. With needles (Hamilton Co.) centered at bregma, stereotaxic coordinates were located using Kopf''s digital coordinate system with 1/100-mm resolution (David Kopf Instruments). Viral constructs were infused over 5 min with 0.5 μL/hemisphere; needles were left in place for an additional 4 min. Mice were allowed to recover for at least 2 wk, allowing for viral-mediated gene knock-down (Berton et al. 2006; Graham et al. 2007; Unger et al. 2007). All procedures were Yale University Animal Care and Use Committee approved.Mice were then food-restricted (90-min access/day) and trained to perform an instrumental response (nose poke) for food reinforcement using Med-Associates operant conditioning chambers controlled by Med-Associates software. These 25-min training sessions were conducted daily, and one, two, or three responses on one of three apertures were reinforced with a 20-mg grain-based food pellet (variable ratio 2 schedule of reinforcement; Bioserv). Two-factor (knock-down × session) analysis of variance (ANOVA) with repeated measures (RM) indicated bdnf knock-down did not affect the acquisition of instrumental responding (main effect of infusion and infusion × session interaction Fs < 1) (Fig. 1A).Open in a separate windowFigure 1.PLc bdnf knock-down decreases instrumental responding in extinction. (A) Viral-mediated PLc bdnf knock-down had no effects on the acquisition of an instrumental response for food. Responses made on the active aperture are shown (left). Responding in extinction was, however, diminished during the first extinction session (right). The break in the extinction curve represents the passage of 1 d. (B) A second group of mice was trained to respond for food before viral construct infusion. Responding during reacquisition reminder sessions after recovery was unaffected, but extinction was again immediately facilitated, as indicated by fewer responses made during sessions 1 and 2. Representative EGFP spread is inset. (C) As a control measure, this experiment was replicated in mice initially trained to perform the task, then given a mOFC, rather than PLc, bdnf knock-down. Although reinforced responding during reacquisition was diminished, responding during extinction was unchanged. Representative EGFP spread is inset. (D) In a reversal task, PLc bdnf knock-down mice did not differ in their ability to “reverse” their responding on an aperture on the opposite side of the chamber; response inhibition—extinction of responding on the previously active aperture—under these circumstances was also unchanged. (E) An enlarged EGFP image is shown (taken from inside the white box in C). EGFP radiates laterally from the infusion site, and the medial wall of the PFC can be seen at left. Symbols represent means (+ SEM) per group (*P < 0.05; ^†P = 0.07). Arrows indicate the time of knock-down, relative to testing sessions.Response extinction was then tested with 10 15-min nonreinforced sessions (five sessions/day). Here, responses made on the previously active aperture declined as expected (F_(9,72) = 6.7, P < 0.001). An interaction between group and session for responses on the active aperture was also identified (F_(9,72) = 2.3, P = 0.03). Tukey''s post-hoc tests indicated responses made during session 1 were reduced in knock-down mice (P = 0.002) (Fig. 1A). Responses made during session 2 were reduced at a trend level of significance (P = 0.07), but responding during other sessions did not differ (all Ps > 0.3), suggesting PLc bdnf knock-down facilitated initial response suppression, but not necessarily the consolidation or expression of extinction learning (Rescorla and Heth 1975).Because knock-down could conceivably regulate extinction processes via effects on initial instrumental conditioning, we trained another group of mice to perform the response prior to knock-down. Mice were then matched based on responses made during training, and surgery proceeded. After recovery, mice were given three “reacquisition” sessions identical to training sessions, during which no differences were found for responses made on the reinforced aperture (main effect of group and interaction Fs < 1) (Fig. 1B). When reinforcement was withheld, however, bdnf knock-down mice again made fewer responses relative to control mice during sessions 1 and 2 (interaction F_(9,135) = 2.3, P = 0.02; post-hoc Ps < 0.01) but not later sessions (Fig. 1B). These data further support our conclusion that PLc bdnf knock-down decreases instrumental responding during the early phases of extinction, but do not indicate whether this effect is behaviorally or anatomically specific. In this group, post-mortem EGFP distribution indicated two mice had only unilateral bdnf knock-down; these animals were excluded.To address anatomical specificity, we replicated this experiment with bdnf knocked down in the ventrally situated mOFC. This site was chosen over the infralimbic cortex because we had greater confidence we could achieve anatomically selective knock-down in this larger region. Viral constructs were infused over 3 min with 0.25 μL/hemisphere and needles aimed AP +2.3, DV −3.0, ML ±0.1 and left in place for an additional 4 min. During reacquisition, a main effect of group on responses made on the active aperture indicated mOFC bdnf knock-down, unlike PLc bdnf knock-down, decreased reinforced responding (F_(1,9) = 7.9, P = 0.02; interaction F < 1) (Fig. 1C). No effects of knock-down were, however, detected for responses made during extinction testing (group and interaction Fs < 1) (Fig. 1C). This profile is distinct from PLc bdnf knock-down mice, in which nonreinforced, but not reinforced, responding was affected. In this group, one animal with unilateral bdnf knock-down was excluded.To address behavioral specificity, mice from Figure 1B were retrained until responding for food on the active aperture was reinstated. Then, the location of the active aperture was “reversed,” such that the previously nonreinforced aperture on the opposite side of the chamber wall was reinforced. In other words, mice trained to respond on the right-side aperture were now reinforced for responding on the left-side aperture and vice versa. This “reversal” procedure allowed us to test whether PLc bdnf knock-down facilitates extinction when reinforcement is available upon the acquisition of an alternative response. We used a highly reinforcing variable ratio 2 schedule, and test sessions lasted 45 min.Under these conditions, bdnf knock-down and control mice did not differ, responding on both the previously reinforced and the newly reinforced apertures to the same degree as control mice (main effect of genotype on nonreinforced responding F_(1,14) = 1.9, P = 0.2; reinforced responding F < 1; group × session interaction F < 1) (Fig. 1D). In other words, PLc bdnf knock-down mice showed exaggerated response inhibition in the absence of reinforcement, but not when a competing response to obtain food reinforcement was available. Main effects of session on responses made on the active and inactive apertures indicated mice acquired the “reversal” (F_(3,45) = 15.2, P < 0.001; F_(3,45) = 5.7, P = 0.002, respectively).In a final behavioral experiment, male group-housed C57BL/6J mice (Charles River Laboratories, Kingston, New York), also ≥10 wk of age at the start of the experiment, were trained and infused with BDNF to evaluate whether acute PLc BDNF infusion produced the opposite effects of gene knock-down: slowed extinction. Human recombinant BDNF (Chemicon) dissolved in sterile saline in a concentration of 0.4 μg/μL (Gourley et al. 2008b) was used, with 0.2 μL/site at AP +2.0, DV −2.5, ML ±0.1 (Gourley et al. 2008a) infused over 2 min with needles left in place for 2 min after infusion.Several studies indicate BDNF has behavioral effects for several days after infusion into the striatum (Horger et al. 1999), ventral tegmental area (Lu et al. 2004), hippocampus (Shirayama et al. 2002; Gourley et al. 2008b), and prefrontal cortex (Berglind et al. 2007, 2009). Therefore, we utilized a single-infusion protocol: Food restriction resumed on day 5 after surgery, at which point mice appeared active. Testing resumed on day 7, at which point mice were subjected to three nonreinforced test sessions. bdnf knock-down mice were affected during the first and second sessions only, so this protocol would be expected to capture the window during which BDNF had effects, if any. These mice showed the typical reduction of responding across sessions (F_(2,14) = 8.6, P = 0.004) (Fig. 2). It is worth noting that responding in control mice was lower than in previous experiments; this is likely due to the more limited recovery and food restriction time after surgery. Nonetheless, we found no effect of BDNF on responding (F < 1; infusion × session interaction F_(2,14) = 1.4, P = 0.3).Open in a separate windowFigure 2.Effects of PLc BDNF microinfusion. Mice were initially trained to perform the nose poke response for food. Responses on the active aperture during training are shown at left. Mice were then infused with BDNF; subsequent instrumental responding during extinction was unaffected. (Inset) Adrenal glands were extracted and weighed after the last extinction session as a measure expected to be sensitive to PLc manipulations. Here, BDNF decreased gland weights (represented as the weight of both glands normalized to total body weight). Symbols represent means (+ SEM) per group, *P < 0.05.To verify a physiological response to PLc BDNF infusions (despite a lack of behavioral effect), we rapidly euthanized mice after the last session and extracted and weighed the adrenal glands, which secrete the hormone, corticosterone. Corticosterone secretion is sensitive to medial prefrontal cortex lesions (Diorio et al. 1993; Rangel et al. 2003) and noradrenergic depletion (Radley et al. 2008), and adrenal weights correlate with PLc BDNF expression levels (Gourley et al. 2008a). As expected, BDNF-infused mice had lighter adrenal glands (t₍₁₀₎ = 4.2, P = 0.002) (Fig. 2), indicating effects of BDNF infusion were detectable on this measure, though not on response diminution per se.Local bdnf knock-down could conceivably act in part by retarding anterograde BDNF transport to, or BDNF synthesis in, major PLc projections sites (Sobreviela et al. 1996; Altar et al. 1997; Conner et al. 1997; Kokaia et al. 1998). BDNF in those projection regions—the dorsal and ventral striatum and multiple hypothalamic subregions (Öngür and Price 2000)—as well as in the PLc itself, was therefore quantified by enzyme-linked immunosorbent assay (ELISA; Promega) in knock-down, control, and BDNF-infused mice.Brains were rapidly harvested from extinguished mice in Figures 1A and ​and2,2, and frozen and sliced into 1-mm-thick coronal sections. Brain regions were dissected bilaterally or with a single midline extraction by tissue punch (1.2-mm diameter). Tissue was then sonicated in lysis buffer (200 μL: 137 mM NaCl, 20 mM tris-Hcl [pH 8], 1% igepal, 10% glycerol, 1:100 Phosphatase Inhibitor Cocktails 1 and 2; Sigma) and stored at −80°C. ELISAs were conducted using 65 μL/sample/well and in accordance with manufacturer''s instructions. BDNF concentrations were normalized to each sample''s total protein concentration, as determined by Bradford colorimetric protein assay (Pierce). BDNF was analyzed by ANOVA or ANOVA-on-Ranks for non-normally distributed PLc values.In the PLc, BDNF was diminished in bdnf knock-down mice as expected (H_(2,18) = 0.2, P = 0.006, post-hoc Ps < 0.05), but BDNF expression in BDNF-infused mice did not differ from the control group (P > 0.05) (Fig. 3A). BDNF in the hypothalamus (F_(2,19) = 2.6, P = 0.1) and nucleus accumbens (F < 1) was not affected. By contrast, dorsal (primarily dorsomedial) striatal BDNF expression differed between groups (F_(2,20) = 5.4, P = 0.01), with knock-down mice expressing less BDNF than the BDNF-infused group (P = 0.01). BDNF in knock-down mice did not, however, significantly differ from control mice (P = 0.09).Open in a separate windowFigure 3.Quantification of BDNF in the PLc, dentate gyrus, and downstream projection sites. (A) BDNF was quantified in the PLc and major projection sites after viral-mediated gene knock-down or acute microinfusion. BDNF was diminished in the PLc of knock-down mice as expected. BDNF was also reduced in the dorsal striatum (dstri) of these animals, while other regions were unaffected by this manipulation. NAC refers to the nucleus accumbens. (B) To confirm the effects of acute BDNF infusion could be detected under some circumstances, tissue from mice infused with BDNF into the dentate gyrus (dentate) was also analyzed. Under these circumstances, elevated BDNF was detected in the hypothalamus. *P < 0.05 relative to control and BDNF-infused groups; ^§P < 0.05 relative to BDNF-infused mice; and P = 0.09 relative to control mice.For additional analyses, we conducted ELISAs on tissue from drug-naïve mice that had had a BDNF infusion of the same volume and concentration in the dorsal hippocampus, rather than PLc. As here, these animals had been subsequently tested in an instrumental conditioning task and were sacrificed 7 d after infusion (for behavioral reports, see Fig. 4 in Gourley et al. 2008b). Like the PLc, the hippocampus projects to the striatum and hypothalamus (Groenewegen et al. 1987; Kishi et al. 2000). In this instance of acute hippocampal infusion, BDNF expression was increased in hypothalamic samples (infusion × brain region interaction F_(3,27) = 3.5, P = 0.03, post-hoc P = 0.009), consistent with previous findings (Sobreviela et al. 1996). Other regions were not affected (Ps > 0.6) (Fig. 3B).Taken together, these data indicate long-term distal effects of acute BDNF infusion are detectable when BDNF is infused into the dorsal hippocampus, though not necessarily PLc. Our data do not preclude the possibility, however, that acute PLc BDNF infusion has long-term consequences for BDNF-regulated intracellular signaling cascades in these downstream sites. For example, extracellular-signal regulated kinase 1/2 phosphorylation in the nucleus accumbens is enhanced by single BDNF infusions aimed at the anterior cingulate/PLc border (Berglind et al. 2007).To summarize, we provide evidence for decreased responding in instrumentally trained mice with PLc-selective bdnf knock-down tested in extinction. Recall of extinction learning did not appear to be affected, as group differences were restricted to test sessions 1 and 2. Time of instrumental training was not a factor, as mice trained to respond for food both before and after knock-down showed a characteristically rapid decline in responding when reinforcement was withheld.Testing mice in a spatial “reversal” task, in which mice learn simultaneously to inhibit responding on one operant and respond instead on a previously nonreinforced operant, eliminated differences in nonreinforced responding between groups. In other words, in the presence of positive reinforcement, knock-down mice did not show exaggerated response inhibition. This behavioral pattern is consistent with the PLc''s role in maintaining goal-directed action particularly under low-reinforcement conditions (Corbit and Balleine 2003; Gourley et al. 2008a). If PLc bdnf played a more general role in extinction learning, one would expect PLc bdnf knock-down mice to show rapid response diminution regardless of whether reinforcement was readily available or not, but our reversal experiment clearly illustrated this was not the case.BDNF ELISA indicated the gene knock-down protocol utilized here results in an ∼48% reduction in BDNF within the PLc and a modest reduction in the downstream dorsal striatum, providing direct evidence for effects of bdnf knock-down on PLc projection neurons (though local interneurons would also be expected to have been infected). Such effects on striatal BDNF expression may be selective to chronic manipulations, as our acute infusion protocol had no consequences for expression in downstream regions, despite actions on a peripheral measure (adrenal gland weight) and evidence of downstream effects after hippocampal infusion.While we report bdnf knock-down rapidly decreased responding early in extinction, we found that acute BDNF infusion had no effects. How might we reconcile these findings? First, it is possible that prefrontal BDNF overexpression must be chronic to have behavioral effects in this task. Second, supraphysiological BDNF-induced structural destabilization and neuronal remodeling (Horch et al. 1999; Horch and Katz 2002) or activation of cortical interneurons (Rutherford et al. 1998) may have counteracted any effects on extinction. Cortical interneuron activation in particular—a process thought to stabilize cortical activity to maintain homeostasis in local circuits—could conceivably negate any effects of BDNF infusion on prefrontal projection neurons (cf., Turrigiano and Nelson 2004; see also Berglind et al. 2007). Last, while single prefrontal BDNF infusions have been reported to suppress cue-induced drug-seeking behavior (Berglind et al. 2007, 2009), such effects may be more acute and/or selectively mediated by Pavlovian, rather than instrumental, processes.Traditionally, extinction research has focused on Pavlovian fear extinction, in which the infralimbic cortex, and not PLc, is considered the major regulatory site (Quirk and Mueller 2008). Our findings suggest the PLc may, however, be indirectly involved in instrumental extinction, as bdnf knock-down facilitated rapid response diminution in the absence of reinforcement, but not when a competing response was reinforced. These findings are consistent with the idea that under normal circumstances, the PLc invigorates responding by maintaining sensitivity to reinforcement previously available upon completion of a particular instrumental action (Corbit and Balleine 2003) or previously associated with a Pavlovian cue (Vidal-Gonzalez et al. 2006). Future studies will address whether PLc BDNF is indeed critical to the maintenance of action–outcome behavior, since the mechanisms of goal-directedness are not well-characterized. This is despite the possibility that their identification may aid in therapeutically facilitating goal-directed action when response extinction is an unproductive behavioral choice.     

Auditory physiology and behavior in RB/1bg, RB/3bg, and their F1 hybrid mice (Mus musculus): influence of genetics, age, and acoustic variables on audiogenic seizure thresholds and cochlear functions

In the early 1950s, Frings and Frings began a process of selection for audiogenic seizure susceptibility and resistance in albino mice. The present study was conducted to examine behavioral and cochlear functions in the inbred descendants of these mice. The cochlear action potential (AP) thresholds of the susceptible RB/1bg inbred mice were abnormally high, and the resistant inbred RB/3bg mice had normal AP audiograms. The F1 hybrid showed heterosis for its cochlear function. Only the RB/1bg was susceptible to audiogenic seizures on the first acoustic exposure. Thresholds for the successive components of their audiogenic seizures were determined in response to narrow bands of noise. These paralleled the AP thresholds of RB/1bg mice (r = .89). This RB/1bg mouse showed little age-related cochlear loss, which probably accounts for its robust sensitivity to audiogenic seizures over most of its lifespan. Earlier studies had demonstrated that the susceptible RB line had a robust AP, but little or no cochlear microphonic (CM). The susceptible RB/1bg had well-defined AP and CM responses at low frequencies. The nonsusceptible RB/3bg mice were more resistant to acoustic priming than another mouse (CBA/J) strain with a similar audiometric profile.     

Vigor predicting health outcomes in a high risk occupational context

Feelings of vigor are associated with positive consequences in the work place but these relationships have not yet been assessed in a high-risk occupational context. The current study assessed the relationships between feelings of vigor on physical health symptoms, functional impairment, and depression symptoms among U.S. service members who recently returned from a combat deployment. U.S. service members were asked to complete questionnaires at 2 time points. Significant positive correlations were found between combat experiences and the 3 outcomes. Significant negative correlations were found for feelings of vigor and each outcome. Regression analyses indicated a significant effect for feelings of vigor such that higher feelings of vigor at Time 1 predicted better physical health and fewer depression symptoms at Time 2. There was no significant effect for functional impairment. Results demonstrate the potential importance of maintaining or improving feelings of vigor throughout the work day, especially for those with high risk occupations.     

The Role of Psychological Factors in Medical Presentations

Research shows that a large number of medical presentations do not result in a medical diagnosis but rather are related to behavioral health problems. Factors such as age, lower education and economic status, health beliefs, and medical and psychological factors are linked to high medical service utilization. Research consistently shows that patients with psychological problems use more services than those without diagnosable psychological problems. The purpose of this paper is to provide a more detailed analysis of the roles of psychological factors in medical presentations. We present three kinds of pathways by which psychological factors lead to medical presentations. These include the (1) primary or direct medical presentation of a clinical problem, (2) secondary presentation or the impact of the clinical problem on patients general physical, psychological, or psychosocial health, and (3) the complex presentation or the impact of multiple diagnoses on the presentation of the clinical problem. Examples of each of these pathways are presented for each axis of the DSM-IV.     

Facial attractiveness and juvenile delinquency among black and white offenders

Facial pictures of black and white delinquents were significantly less attractive than pictures of corresponding groups of high school students, as judged by same-race raters. Significant differences were found among the white delinquents, but not among the black, for Quay's four behavioral dimensions of delinquency. Black delinquents were significantly darker in skin color than the black high school students, and lightness of skin color was positively correlated with physical attractiveness ratings made by both black and white raters, indicating that neither race has yet assimilated the saying black is beautiful. This and other evidence suggest that facial attractiveness may be causal in delinquency.These studies were conducted with the cooperation of the staff of the Robert F. Kennedy Youth Center, Federal Bureau of Prisons, U.S. Department of Justice. The center is not responsible for the contents of this report; the report does not necessarily represent the Center's views. The portion of this paper dealing with the white offenders was presented at the meeting of the Eastern Psychological Association, Boston, Massachusetts, April 1972.The authors would like to thank Hayne W. Reese for his assistance.     

Effects of the "beauty is good" stereotype on children's information processing

The authors tested schematic information processing as a function of attractiveness stereotyping in two studies. An adult experimenter read children (ages 3 to 7 years) eight different stories in which a child narrator encountered two characters who varied in level of attractiveness and displayed positive or negative traits that were either consistent or inconsistent with the "beauty is good" stereotype. Following the story, the experimenter showed each child a photograph of the two characters' faces and asked the child to point to the character who displayed the positive trait. In Experiment 1, children made more errors in identifying female characters with stereotype inconsistent traits but did just the opposite with male characters. Experiment 2 replicated the findings with female characters but found no difference in errors with male characters. The findings have implications for how attractiveness and gender stereotypes affect children's information processing, how attractiveness schemata may be organized, and why physical attractiveness stereotypes are maintained.     

The genetic versus pharmacological invalidation of the cannabinoid CB(1) receptor results in differential effects on 'non-associative' memory and forebrain monoamine concentrations in mice

The endocannabinoid CB(1) receptor has been implicated in the inhibitory control of learning and memory. In the present experiment, we compared the behavioral response of CB(1) receptor knockout mice (CB(1)R(-/-)) with animals administered CB(1) receptor antagonist/inverse agonist SR141716A (rimonabant; 3 mg/kg IP, 30 min pre-trial) in terms of acquisition and retention of a habituation task and changes in cerebral monoamines. The results can be summarized as follows: (i) the acute and chronic invalidation of the CB(1) receptor resulted in an increase of behavioral habituation during the first exposure to an open field, indicative of enhanced acquisition of the task; (ii) CB(1)R(-/-) mice, but not rimonabant-treated animals, showed enhanced retention of the habituation task when re-tested 48 h and 1 week subsequent to the first exposure to the open field, respectively; (iii) the facilitation of retention of the habituation task in CB(1)R(-/-) mice was accompanied by a selective and site-specific increase in serotonin activity in hippocampus; and (iv) rimonabant-treated animals displayed 'antidepressant-like' neurochemical alterations of cerebral monoamines, that is, most parameters of monoaminergic activity were increased especially in dorsal striatum and hippocampus. Taken together, the present findings demonstrate that the genetic disruption of the CB(1) receptor gene can cause an improvement of behavioral habituation, which is considered to represent a form of 'non-associative' learning. Furthermore, our data support the assumption of a rimonabant-sensitive cannabinoid receptive site that is different from the 'classical' CB(1) receptor and which, under physiological conditions, might be involved in the inhibitory control of the acquisition but not retention of non-associative learning tasks.     

Efficacy of behavioral management and patient education on vascular access cleansing compliance in hemodialysis patients

Compared four treatment conditions to test their ability to enhance compliance with vascular access cleansing (VAC) procedures in a group of 56 hemodialysis patients. The conditions were patient education, behavioral management with monetary incentive, patient education/behavioral management, and attention control. Behavioral observers rated VAC behavior at pretreatment, posttreatment 1-month follow-up, and 1-year follow-up. Knowledge of VAC procedures was also assessed via a questionnaire at pretreatment and posttreatment. Data were analyzed using repeated-measures multivariate analyses of variance. Results indicated that the patients in the education/behavioral, behavioral, and education groups gave significantly more correct answers on our VAC knowledge questionnaires at posttreatment than did patients in the attention control group. Further, patients in the education/behavioral and behavioral groups completed significantly more VAC steps at posttreatment and 1-month follow-up than did patients in the education group and in the attention control group. Differences were not maintained at 1-year follow-up, although more than 50% of the patients were lost to follow-up. Implications of the present findings for behavioral and educational interventions are discussed.     

Memory deficits are associated with impaired ability to modulate neuronal excitability in middle-aged mice

Normal aging disrupts hippocampal neuroplasticity and learning and memory. Aging deficits were exposed in a subset (30%) of middle-aged mice that performed below criterion on a hippocampal-dependent contextual fear conditioning task. Basal neuronal excitability was comparable in middle-aged and young mice, but learning-related modulation of the post-burst afterhyperpolarization (AHP)—a general mechanism engaged during learning—was impaired in CA1 neurons from middle-aged weak learners. Thus, modulation of neuronal excitability is critical for retention of context fear in middle-aged mice. Disruption of AHP plasticity may contribute to contextual fear deficits in middle-aged mice—a model of age-associated cognitive decline (AACD).Plasticity of intrinsic neuronal excitability increases the overall storage capacity of neurons and therefore likely plays a critical role in learning and memory (Zhang and Linden 2003). Increased neuronal excitability via reductions of the post-burst afterhyperpolarization (AHP) is hypothesized as a general mechanism underlying learning and memory tasks (Disterhoft et al. 1986; Disterhoft and Oh 2006). The AHP serves to limit subsequent firing in response to excitation (Madison and Nicoll 1984; Lancaster and Adams 1986; Storm 1990; Sah and Bekkers 1996). Generally speaking, the size of the AHP is inversely related to neuronal excitability, and the measurement of the AHP is routinely used as an index of neuronal excitability.Our laboratory and others have shown that AHP reductions are observed in hippocampal neurons from animals that learn hippocampal-dependent tasks including trace eyeblink conditioning in rabbit and rat (de Jonge et al. 1990; Moyer Jr et al. 1996, 2000; Kuo 2004) and spatial water maze in rat and mouse (Oh et al. 2003; Tombaugh et al. 2005; Ohno et al. 2006b). Learning-related reductions in the AHP have also been observed in cortical neurons following odor discrimination (Saar et al. 1998) and extinction learning (Santini et al. 2008). In vitro, activity-dependent plasticity of the AHP is induced using physiologically relevant stimuli (Kaczorowski et al. 2007). Because the AHP serves to limit subsequent firing, learning-related reductions in the AHP are poised to facilitate mechanisms crucial for information storage, such as long-term potentiation (LTP), synaptic integration (Sah and Bekkers 1996), metaplasticity (Le Ray et al. 2004), and spike-timing dependent plasticity (STDP) (Le Ray et al. 2004).Hippocampal neurons from naïve aged rodents and rabbits show a decrement in basal excitability evidenced by a robust enhancement of the AHP (Landfield and Pitler 1984; Moyer Jr et al. 1992, 2000; Oh et al. 1999; Kumar and Foster 2002, 2004; Power et al. 2002; Hemond and Jaffe 2005; Murphy et al. 2006b; Gant and Thibault 2008). Enhancement of the AHP in hippocampal neurons in aged animals correlates with impaired performance on learning paradigms that depend on a functional hippocampus, such as trace eyeblink and spatial water maze (Moyer Jr et al. 2000; Tombaugh et al. 2005; Murphy et al. 2006a). Pharmaceuticals aimed at reducing the AHP and increasing basal excitability (Moyer Jr et al. 1992; Moyer Jr and Disterhoft 1994) have been successful at restoring performance of aged rats on trace eyeblink conditioning (Deyo et al. 1989; Straube et al. 1990; Kowalska and Disterhoft 1994). Interestingly, AHPs from neurons recorded from aged learners are indistinguishable from young learners; both are reduced compared to that of aged weak-learners (Moyer Jr et al. 2000; Tombaugh et al. 2005). These data suggest that mechanisms that permit learning-related modulation of the AHP are also critical determinants of learning abilities in an aged population. To date, age-related impairments in hippocampal-dependent tasks and biophysical alterations in hippocampal neurons have largely focused on studies that compare animals at extreme ends of the aging spectrum.In an effort to better understand physiological changes that underlie the onset of early cognitive decline, the development of rodent models of “normal” age-associated cognitive decline (AACD), as well as mild cognitive impairment (MCI), is critical (Pepeu 2004). Therefore, we set out to characterize the development of age-related deficits indicative of hippocampal dysfunction in middle-aged C57Bl6/SJL mice and to examine the biophysical changes in hippocampal neurons that accompany such deficits.Recently, age-related deficits in contextual fear memory following trace fear conditioning were reported in a subset of middle-aged rats (Moyer Jr and Brown 2006). Because the dorsal hippocampus is critical for trace and contextual fear conditioning in mice and rats (McEchron et al. 1998; Chowdhury et al. 2005; Misane et al. 2005), trace fear conditioning is an ideal paradigm for exploring cellular mechanisms that underlie early-age-related cognitive decline.Here we investigate the effects of “early” aging on trace fear conditioning by comparing performance outcomes of young (2 mo, n = 7; and 4 mo, n = 8) and middle-aged (8 mo, n = 22) male C57/SJL F1 hybrid mice. Mice were trained and tested singly, and the experimenter was blind to the training and retention status of the mice. All animal procedures were approved by the Northwestern University Animal Care and Use Committee. Preliminary data were reported previously (Kaczorowski 2006).To assess hippocampal function with aging, young and middle-aged mice were trained on a trace fear conditioning task followed by retention tests of the auditory conditioned stimulus (CS) and contextual CS memory. The basic protocol for trace fear conditioning has been described previously (Ohno et al. 2006a). Mice were trained in a Plexiglas conditioning chamber with a stainless-steel floor grid used for shock delivery. After the baseline period (150 sec), mice received four pairings of the CS (tone; 15 sec, 3 kHz, 75 dB) and US (shock; 1 sec, 0.7 mA). The CS and unconditioned stimulus (US) were separated by a 30-sec empty trace interval. The intertrial interval was set at 210 ± 10 sec. The training chamber was wiped with 95% ethyl alcohol, illuminated with a 10-W bulb in an otherwise dark room, and provided with 65-dB white noise to make it distinct. During training on trace fear conditioning, no effect of age was observed on measures of baseline freezing (F_(2,34) = 2.0, P = 0.15), the expression of freezing during tone (F_(2,34) = 0.6, P = 0.6), or post-shock freezing (F_(2,34) = 0.2, P = 0.8), suggesting that middle-aged and young mice do not differ in measures of anxiolysis or expression of behavioral freezing (measured index of fear) (Fig. 1A).Open in a separate windowFigure 1.Onset of early aging deficits in 8-mo-old middle-aged mice. (A) Baseline (BL) freezing and auditory CS freezing during trace fear conditioning was similar between young (2 mo and 4 mo) and middle-aged (8 mo) mice. (B1) Mean baseline freezing and retention of the auditory CS memory (tones 1–4) were comparable in young (2 mo and 4 mo) and middle-aged (8 mo) mice. (B2) Middle-aged mice showed a significant decrease in freezing compared to young (2 mo and 4 mo) mice when exposed to the original context chamber where they had been trained 1 d earlier; (*) P < 0.05.Retention of the auditory CS:US memory was tested 24 h later in a novel context that differed in its location, size, scent, lighting, background noise, and flooring (bedding) compared to the training chamber. Data from three mice (one young, two middle-aged) were excluded because of video malfunction. Following a 150-sec baseline, mice received four presentations of the tone CS in the absence of footshock. Neither baseline freezing (F_(2,31) = 2.6, P = 0.1) nor conditional freezing in response to the tone CS (F_(2,31) = 1.6, P = 0.2) differed between young and middle-aged mice (Fig. 1B1). Thus, retention of the auditory CS following trace fear conditioning was intact in middle-aged compared to young mice. Although deficits in retention of auditory trace fear have been reported in aged mice and rats (Blank et al. 2003; McEchron et al. 2004; Villarreal et al. 2004), the results herein agree with report of intact trace fear memory in middle-aged rats (Moyer Jr and Brown 2006).One hour after this testing, retention of the contextual fear memory was assessed by placing mice in the original context (in the absence of the tone and footshock) and measuring freezing for 10 min. A subtle but significant difference in freezing was observed as a function of age (F_(2,31) = 4.3, P = 0.02; Fig. 1B ​2).2). A student''s post-hoc t-test revealed that mean freezing (collapsed across 10 min) of middle-aged mice was reduced compared to 2-mo (P < 0.05) and 4-mo (P < 0.05) young mice. Contextual fear memory deficits have been similarly reported in aged mice (Fukushima et al. 2008). Studies that failed to observe contextual fear deficits in aged (>18 mo) mice may result from a floor effect because young mice showed weak conditioning to the context (∼30% freezing) (Feiro and Gould 2005; Gould and Feiro 2005) or employment of delay (Corcoran et al. 2002; Feiro and Gould 2005; Gould and Feiro 2005) compared to trace procedures (Moyer Jr and Brown 2006). Although differences in experimental parameters are plausible, heterogeneity in the performance of aged mice may make detection of age-related impairments difficult owing to increased variability.Open in a separate windowFigure 2.Selective deficits on retention of contextual fear in middle-aged weak-learner mice. (A,B) Summary plot and histogram show young mice (100%, n = 6) at 2 mo of age showed robust recall of contextual fear memory (range 75%–99%) with mean and standard deviation (SD) of 91% ± 10%, whereas retention of middle-aged mice (n = 21) varied to a much greater extent (range 21%–95%; M, SD = 74% ± 19%). Distribution of middle-aged mice relative to their mean percent freezing shows two distinct populations. Middle-aged mice with freezing levels less than 3 SD from the mean freezing in young wild-type (WT) mice (61%, dashed line) were characterized as having weak contextual fear memory (weak learners) and those with freezing levels ≥62% as having strong contextual fear memory (learners). (C) Baseline (BL) freezing, expression of post-shock freezing and freezing during retention tests for auditory CS and trace CS memories, were comparable in both weak-learners and learners. (D) Selective deficits in retention of contextual fear memories were observed in middle-aged weak learners as compared to middle-aged learners; (*) P < 0.05.Previous studies in the rat report heterogeneity in spatial water maze and contextual fear conditioning in middle-aged and/or aged rats compared to young animals (Fischer et al. 1992; Wyss et al. 2000; Moyer Jr and Brown 2006). Therefore, we determined if middle-aged impairments of context fear (Fig. 2A) were driven by a subset of impaired mice. The degree of age-related impairment in each middle-aged mouse was determined by comparison to a reference group of young mice tested concurrently (shown in Fig. 1). The behavioral criterion for retention of contextual fear in middle-aged mice was set at 61%, which was 3 standard deviations (SD) below the mean freezing in young mice (mean and SD, 91% ± 10%; Fig. 1). A bimodal distribution of freezing of middle-aged mice was observed (Fig. 2B), where 70% of middle-aged mice performed above criterion and were labeled learners (n = 14), and 30% of middle-aged mice performed below criterion and were labeled as weak learners (n = 6). Comparison on measures of baseline freezing (F_(1,18) = 1.8, P = 0.2) and expression of post-shock freezing (F_(1,18) = 2.1, P = 0.2) revealed no differences between the groups during auditory trace fear training (Fig. 2C). Similarly, no differences in baseline freezing (F_(1,18) = 0.03, P = 0.9) or acquisition/recall of conditioned auditory trace fear (tone, F_(1,18) = 0.08, P = 0.8; trace, F_(1,18) = 2.4, P = 0.1) were observed 24 h later during retention tests. Thus, deficits ascribed to middle-aged weak learners were limited to contextual processing/retention, where middle-aged weak learners responded to the contextual CS with significantly lower levels of freezing compared to middle-aged learners (F_(1,18) = 47, P = 0.001; Fig. 2D). To summarize, we found that onset of cognitive decline in the C56Bl6/SJL mice was first apparent in a subset of middle-aged mice. Middle-aged weak learners showed a mild but specific deficit in hippocampal-dependent contextual learning/memory (spatial learning) but not hippocampal-dependent auditory trace learning/memory (temporal learning), assessed following trace fear conditioning.Given that contextual fear deficits occurred in a subset of middle-age mice, we were able to directly assess age-related alterations in excitability and AHP plasticity in CA1 neurons as they relate to learning abilities (learners vs. weak learners). Within 1 h of cessation of behavioral tests, middle-aged learners and weak learners were decapitated under deep halothane anesthesia and their brains quickly removed and placed into ice-cold artificial cerebral spinal fluid (aCSF): 125 mM NaCl, 25 mM glucose, 25 mM NaHCO₃, 2.5 mM KCl, 1.25 mM NaH₂PO₄, 2 mM CaCl₂, 1 MgCl₂ (pH 7.5, bubbled with 95%O₂/5%CO₂). Naïve mice were removed from their home cage and underwent identical decapitation procedures. Slices (300 μm) of the dorsal hippocampus and adjacent cortex were made using a Leica vibratome. The slices were first incubated for 30 min at 34°C in bubbled aCSF, and held at room temperature in bubbled aCSF for 1–4 h before use. Recording electrodes prepared from thin-walled capillary glass were filled with potassium methylsulfate-based internal solution and had a resistance of 5–6 MΩ.Whole-cell current-clamp recordings were performed on CA1 hippocampal pyramidal neurons of middle-aged learners (n = 36, 14 mice) and weak-learners (n = 15, 6 mice), as well as middle-aged naïve mice (n = 35 cells, 18 mice). Neuronal excitability was compared by measuring the post-burst AHP generated by 25 action potentials at 50 Hz (Fig. 3A), a stimulus shown to reliably evoke an AHP of sizable—but not maximal—amplitude from hippocampal neurons of mice (Ohno et al. 2006b). A significant difference in the peak amplitude of the AHP from learners, weak learners, and naïve mice was observed (F_(2,83) = 5, P < 0.01). Because the peak AHP and sAHP amplitudes did not differ between neurons from weak-learners and naïve mice (Fig. 3B). No differences in membrane resistance (F_(2,83) = 1.6, P = 0.2) or action potential properties, elicited using a brief (2 msec) near threshold current step (pA), were observed (Open in a separate window^aP < 0.05 compared to Weak L.^bP < 0.05 compared to Naïve.^cP < 0.05 compared to Pooled.Open in a separate windowFigure 3.Learning-related AHP plasticity is impaired in middle-aged weak-learner mice. (A) Representative traces showing the sAHP is reduced in neurons from (black) middle-aged learners compared to (blue) weak-learner mice and (gray) naïve mice. (Inset) The medium AHP (mAHP) of neurons from (black) learner mice was decreased compared to (blue) weak-learner mice and (gray) naïve mice. (B) No differences in the AHP from naïve and weak learners were observed; therefore, their data were pooled, and mean AHP was plotted by time on a log scale. (Inset) The mean amplitude of the peak AHP (1 msec) and sAHP (600 msec) was significantly reduced in neurons from learners compared to AHPs from weak learners and naïve labeled control; (*)P < 0.05.The results presented here are important in two respects. First, we demonstrate that the successful acquisition and recall of trace fear conditioning results in a significant reduction in the AHP in CA1 hippocampal neurons from the mouse. Our data are similar to previous reports showing learning-related reductions of the AHP in hippocampal neurons following training on hippocampal-dependent tasks (Disterhoft and Oh 2007) and thus strengthen the case for neuronal excitability change as a general mechanism underlying hippocampal-dependent learning. Second, we demonstrate that the onset of age-related cognitive decline in the C56Bl6/SJL mouse (termed “weak learners”) first manifests as a specific deficit in spatial associative learning in a subset of middle-age mice. These data, combined with a previous report from middle-aged rats (Moyer Jr and Brown 2006), suggest that initiation of age-related hippocampal dysfunction results in specific spatial—as opposed to temporal—deficits in associative learning and memory during middle age. By combining trace fear conditioning with whole-cell patch-clamp recordings in middle-aged mice, we revealed that “early” age-related impairments in spatial associative learning—like those in the aged hippocampus (Tombaugh et al. 2005)—result in part from an impairment of AHP plasticity of hippocampal neurons. Because AHP reductions are poised to facilitate mechanisms crucial for information storage, it is interesting that trace fear conditioning facilitates the long-term potentiation (LTP) of field excitatory postsynaptic potentials in the CA1 region of the rat hippocampus (Song et al. 2008).Generally speaking, both LTP and activation of AHP currents (I_AHP and sI_AHP) are sensitive to changes in intracellular Ca²⁺ (Storm 1990; Sah 1996; Malenka and Nicoll 1999). Thus, dysregulation of Ca²⁺ homeostasis in the hippocampus of middle-aged rats via enhancement of Ca²⁺-induced Ca²⁺ release (CICR) is an important finding (Gant et al. 2006). Age-related enhancement of Ca²⁺-dependent AHPs has been shown to raise the threshold for induction of LTP (Kumar and Foster 2004). These data support our hypothesis that impairments in contextual fear reported herein, as well as deficits in spatial water maze reported in middle-aged rats (Frick et al. 1995; Markowska 1999; Kadish et al. 2009), result from dysfunction of AHP plasticity.Studies in middle-aged mice have important implications for the treatment of “normal” age-associated cognitive decline (AACD), as well as mild cognitive impairment (MCI) (Pepeu 2004). Further studies aim to examine alterations in cholinergic function in our middle-aged mouse model, as the cholinergic agonist carbachol suppressed the AHP in neurons from naïve middle-aged mice (Supplemental Fig. 1). Activation of cholinergic receptors shape neuronal excitability and synaptic throughput (Tai et al. 2006) through multiple Ca²⁺-dependent processes (Gahwiler and Brown 1987; Tai et al. 2006). Restoration of cholinergic function has been shown to rescue deficits on hippocampal-dependent tasks in aged rodent and mouse models of Alzheimer''s disease (AD) (Disterhoft and Oh 2006), as well as in human AD patients (Cummings et al. 1998; Morris et al. 1998; Pettigrew et al. 1998), and therefore is a potential target aimed at the rescue of early age-related cognitive decline.     

虐待与流动儿童对立违抗症状的关系:亲密度和冲突性的作用

以来自北京10所小学的369名有对立违抗障碍症状的流动儿童,349名无ODD症状的对照组流动儿童和94名有ODD症状的北京儿童为被试,探究了有ODD症状流动儿童的症状严重程度及影响因素,并进一步探讨了ODD症状流动儿童在家庭中所受情感虐待、躯体虐待对其情绪方面的ODD症状和行为方面的ODD症状的影响,以及亲子关系(包括亲密度和冲突性)在其中起的作用。研究结果发现:(1)对比ODD症状北京儿童和对照组流动儿童,ODD症状流动儿童受到更严重的虐待,亲子关系亲密度更差,冲突性更高;(2)对ODD症状流动儿童,虐待和亲密度显著负相关,虐待和冲突性显著正相关,躯体虐待、冲突性均和行为方面ODD症状显著正相关;(3)躯体虐待能直接预测ODD症状流动儿童的行为方面ODD症状,但无法直接预测其情绪方面ODD症状;(4)在躯体虐待对ODD症状的影响中,冲突性起着显著的中介作用,躯体虐待通过影响亲子关系冲突性,对流动儿童的行为方面ODD症状产生影响,而亲密度则显著调节了躯体虐待对流动儿童情绪方面ODD症状的影响。     

Exploration in outbred mice covaries with general learning abilities irrespective of stress reactivity, emotionality, and physical attributes

Across multiple learning tasks (that place different sensory, motor, and information processing demands on the animals), we have found that the performance of mice is commonly regulated by a single factor ("general learning") that accounts for 30-40% of the variance across individuals and tasks. Furthermore, individuals' general learning abilities were highly correlated with their propensity to engage in exploration in an open field, a behavior that is potentially stress-inducing. This relationship between exploration in the open field and general learning abilities suggests the possibility that variations in stress sensitivity/responsivity or related emotional responses might directly influence individuals' general learning abilities. Here, the relationship of sensory/motor skills and stress sensitivity/emotionality to animals' general learning abilities were assessed. Outbred (CD-1) mice were tested in a battery of six learning tasks as well as 21 tests of exploratory behavior, sensory/motor function and fitness, emotionality, and stress reactivity. The performances of individual mice were correlated across six learning tasks, and the performance measures of all learning tasks loaded heavily on a single factor (principal component analysis), accounting for 32% of the variability between animals and tasks. Open field exploration and seven additional exploratory behaviors (including those exhibited in an elevated plus maze) also loaded heavily on this same factor, although general activity, sensory/motor responses, physical characteristics, and direct measures of fear did not. In a separate experiment, serum corticosterone levels of mice were elevated in response to a mild environmental stressor (confinement on an elevated platform). Stress-induced corticosterone levels were correlated with behavioral fear responses, but were unsystematically related to individuals' propensity for exploration. In total, these results suggest that although general learning abilities are strongly related to individuals' propensity for exploration, this relationship is not attributable to variations in sensory/motor function or the individuals' physiological or behavioral sensitivity to conditions that promote stress or fear.