Genetic differences in the mouse defense test battery

The mouse defense test battery (MDTB) has been designed to examine anxiogenic- or anxiolytic-like properties of psychoactive drugs through effects on specific defensive behaviors. In the present study, the MDTB was used to evaluate the potential contribution of genetic factors to these behaviors. The data revealed pronounced differences in several defense reactions among four inbred strains (BALB/c, C57BL/6, CBA, DBA/2) and one outbred (Swiss) mouse line. Thus, when subjects were introduced into the apparatus, Swiss and C57BL/6 displayed the highest levels of horizontal and vertical activities, while BALB/c and DBA/2 mice showed intermediate and CBA low activity rates. When subjects were chased by the rat, C57BL/6 mice used flight as the dominant defense strategy, while the defensive responses of BALB/c, C57BL/6, and DBA/2 mice consisted of flight reactions and risk assessment activities. However, when flight or escape was not possible, risk assessment became the predominant feature of the defense repertoire in the C57BL/6 mice. When defensive threat/attack behaviors were required, Swiss, BALB/c, DBA/2, and C57BL/6 mice showed very similar reactions in terms of the magnitude of the responses observed. CBA mice were poorly defensive in all these test situations. Finally, after the rat was removed from the test apparatus, Swiss, DBA/2, and C57BL/6 mice displayed more vertical activities than BALB/c mice. These latter, however, showed an increased level of ambulation compared to the activity recorded before the rat exposure. Together, these findings indicate that genetic factors contribute to defensive behaviors in this animal model of anxiety. The different behavioral profiles displayed by the strains used here may provide the means to obtain a better insight into the neurobehavioral mechanisms involved in anxiety-related disorders. Aggr. Behav. 23:19–31, 1997. © 1997 Wiley-Liss, Inc.     

Learning strategy selection in the water maze and hippocampal CREB phosphorylation differ in two inbred strains of mice

Learning strategy selection was assessed in two different inbred strains of mice, C57BL/6 and DBA/2, which are used for developing genetically modified mouse models. Male mice received a training protocol in a water maze using alternating blocks of visible and hidden platform trials, during which mice escaped to a single location. After training, mice were required to choose between the spatial location where the platform had been during training (a place strategy) and a visible platform presented in a new location (a cued/response strategy). Both strains of mice had similar escape performance on the visible and hidden platform trials during training. However, in the strategy preference test, C57BL/6 mice selected a place strategy significantly more often than DBA/2 mice. Because much evidence implicates the hippocampus and striatum as important neural substrates for spatial/place and cued/response learning, respectively, the engagement of the hippocampus was then assessed after either place or cue training by determining levels of cAMP response element-binding protein (CREB) and phosphorylated CREB (pCREB) in these two mouse strains. Results revealed that hippocampal CREB levels in both strains of mice were significantly increased after place in comparison to cued training. However, the relation of hippocampal pCREB levels to training was strain dependent; pCREB was significantly higher in C57BL/6 mice than in DBA/2 mice after place training, while hippocampal pCREB levels did not differ between strains after cued training. These findings indicate that pCREB, specifically associated with place/spatial training, is closely tied to differences in spatial/place strategy preference between C57BL/6 and DBA/2 mice.     

Genotype modulates prenatal stress effects on aggression in male and female mice

Prenatal stress (heat and restraint) significantly increased postpartum aggression (proportion of animals fighting and/or the intensity of the behavior) in C57BL/6J female mice and reduced the behavior in DBA/2J females. For intermale aggression, prenatal stress increased the behavior (intensity of aggression) in C57BL/6J males but did not affect aggressive behavior in DBA/2J animals. Infanticidal behavior (the killing of young) exhibited by male mice was not influenced by prenatal stress in either strain. Relative anogenital distance measurements in neonates at birth did not serve as a reliable predictor of strain variation in prenatal stress effects. Prenatal stress did not influence this measure of prenatal androgen exposure in DBA/2J or C57BL/6J females. For males, prenatal stress elevated relative anogenital distance in C57BL/6J mice and decreased this measure in DBA/2J animals. Prenatal stress effects on aggressive behavior in male and female mice therefore depend upon genotype. Strain-dependent differences may be modulated by differences in endocrine reactivity to prenatal stress/and or differential central neural tissue sensitivity to hormones.     

Place avoidance learning and stress-induced analgesia in the attacked mouse: role of endogenous opioids

In this study, mechanisms of pain inhibition (tail-flick test) and memory (place avoidance paradigm) were investigated in attacked, DBA/2 and C57BL/6, mice. During training, exposure of test animals to 10 or 30 bites by an aggressive, isolated ICR mouse situated in the dark half of a bright/dark conditioning box induced a significantly higher social conflict analgesia in DBA than in C57 mice. Naltrexone (0.5 and 2.0 mg/kg) reduced this response in DBA mice that received 30, but not 10, bites and was ineffective in C57 mice. This points to different, opioid versus naltrexone-insensitive nonopioid, analgesic mechanisms. During place choice testing in the same box 24 h later, DBA mice that had received 30, but not 10, bites showed a significant, naltrexone-reversible, avoidance of the attack place. No place avoidance learning was observed in C57 mice. The data provided unequivocal evidence that place avoidance learning was a result of associative conditioning, in that neither pairing nor social conflict per se significantly changed the preference for the dark side seen in experimentally naive DBA mice. Antagonism of place avoidance conditioning was observed regardless of whether testing was carried out in the drugged or undrugged state, excluding possible state-dependent effects as an explanation for the naltrexone-induced impairment. Individual correlational analysis in saline-injected, attacked DBA mice revealed a negative relationship between the analgesic state immediately after training and the avoidance of attack place during testing. In summary, the results suggest strain-dependent analgesic and learning mechanisms and indicate that endogenous opioids released in attacked DBA mice support pain inhibition and modulate the memorization of attack place by their analgesic effects, as well as by mechanisms independent of pain inhibitory systems.     

Effects of acute and chronic stress and of genotype on oxotremorine-induced locomotor depression of mice

The locomotor behavior of unstressed and stressed mice of two inbred strains, DBA/2 and C57/BL6, was investigated. Animals were tested in a toggle-floor box apparatus, 30 min after saline or oxotremorine treatment (ip). A dose of oxotremorine that did not depress the activity of na?ve mice (0.01 mg/kg) was chosen. Stressed mice were injected 24 h after either a single 2-h stress session (acute stress) or the last of 14 daily stress sessions of tube restraining (chronic stress). Acute stress did not modify the depressant effect of oxotremorine on locomotor behavior in either strain. On the contrary, chronic stress induced a clear sensitization of DBA but not C57 mice to the depressant effect of oxotremorine. These findings show that chronic stress may result in modifications of the cholinergic function, and its behavioral correlates, and that these changes are modulated by the genetic makeup.     

Strain-dependent interactions between MK-801 and cocaine on retention of C57BL/6 and DBA/2 mice tested in a one-trial inhibitory avoidance task: involvement of dopaminergic mechanisms

Two sets of experiments were carried out with C57BL/6 (C57) and DBA/2 (DBA) mice tested in a one-trial inhibitory avoidance task. In the first set C57 and DBA mice were injected posttraining with saline or with the D1 DA receptor antagonist SCH 23390 and then with saline, cocaine (5 mg/kg), MK-801 (0.1 mg/kg), or with a combination of these two drugs. Cocaine enhanced retention in the C57 strain and impaired it in the DBA strain, and MK-801 potentiated the effects of cocaine in both strains. Furthermore, pretreatment with SCH 23390 completely antagonized the potentiation of the effects of cocaine exerted by MK-801. In the second set of experiments mice belonging to these same two strains were injected posttraining with vehicle or with the D2 DA receptor antagonist (-)-sulpiride and then with saline, cocaine (5 mg/kg), MK-801 (0.1 mg/kg), or with a combination of these two drugs. Pretreatment with the D2 DA receptor antagonist completely antagonized in both strains the potentiation of the effect of cocaine exerted by MK-801. The results of the present research show that the noncompetitive NMDA receptor antagonist MK-801 enhances the effect of cocaine on retention performance in C57 and DBA mice and that dopaminergic mechanisms are involved in this potentiation.     

Strain and sex differences on olfactory discrimination learning in C57BL/6J and DBA/2J inbred mice (Mus musculus)

In this study, the authors explored potential strain and sex differences in nonspatial cognitive ability. Beginning around 90 days of age, male and female C57BL/6J (C57) and DBA/2J (DBA) inbred mice (Mus musculus) were tested on a task of simple odor discrimination learning with 3 repeated reversals. Males learned the task more readily than females, and DBA mice learned the task more readily than C57 mice. All differences became evident after repeated testing. Similarity of perseveration measures indicated the differences were not due to inhibitory deficits. Instead, a phase analysis localized differences to a transitional period of reversal learning. Females increased transitional errors that more likely indicated adaptive sampling strategies than memory failures. C57 females used this strategy indiscriminately, but DBA females sampled as a function of environmental uncertainty.     

Strain differences in open field activity after learning in mice

Male mice of albino and pigmented strains were tested on their open field activity after maze learning and passive avoidance conditioning. The results indicated that the albino strains Balb/c, NMRI, Swiss albino and hybrids of these, reacted with an open field activity increase after maze learning in contrast to the pigmented strains C3H/He, C57BL/6J and DBA/2N. Only Swiss albino displayed an increased ambulatory level after passive avoidance conditioning for the whole experimental time. It is suggested that an ambulatory increase after learning is related to fur color and not to the initial open field activity level, nor to the learning time or the learning capacity.     

Landmark-based but not vestibular-based orientation elicits mossy fiber synaptogenesis in the mouse hippocampus

This study tries to shed light on the paradoxical finding that two inbred strains of mice C57BL/6 (C57) and DBA/2 (DBA), with differences in hippocampal function, perform similarly in the water maze (WM). Mice from both strains were trained on WM protocols permitting or preventing the use of vestibular signals. Hippocampal involvement in performance was then assessed by estimation of post-training mossy fiber (MF) synaptogenesis. We found that C57 and DBA mice performed similarly when both visual and vestibular information were available but only C57 mice exhibited new MF synapses. Disruption of vestibular inputs impaired performance in DBA mice but not in C57 mice which still exhibited a post-training increase of hippocampal MF synaptic terminals. This strain-specific dissociation indicates that DBA mice can navigate successfully by relying on vestibular signals without engaging their hippocampus. In contrast, vestibular signals are irrelevant for C57 mice since their suppression neither disrupts their behavior nor prevents the formation of new hippocampal synapses. These findings suggest some caution is required in considering performance on standard WM protocols as an index of hippocampus-based learning. Estimating the extent of post-training mossy fiber synaptogenesis would be helpful in solving this issue.     

Mice (Mus musculus) learn a win-shift but not a win-stay contingency under water escape motivation

Twenty mice (Mus musculus), the second filial generation offspring from a C57BL/6 and DBA/2J cross, received spatial win-shift and win-stay water escape training within a mixed design in which all mice received both types of training. Acquisition under win-shift was superior to win-stay with respect to errorless trials and latencies regardless of the order in which the procedures were experienced. Win-stay responding did not exceed chance levels during any training phase. These data contradict the claim that win-stay training is the more easily acquired of the 2 acquisition strategies under aversive motivation.     

Selective improvement of strain-dependent performances of cognitive tasks by food restriction

Temporary food restriction affects strain differences for behavioral phenotypes in the inbred strains of mice C57BL/6 (C57) and DBA/2 (DBA). Since food restriction is a routine procedure to motivate learning, we evaluated its influence on differences for spatial and non-spatial discrimination between these strains of mice by using two non-associative tasks: the Spatial Novelty Test (SNT) and the Spontaneous Object Recognition Test (SORT). The results confirmed the poor performance of the DBA mice in SNT. Nonetheless, DBA mice were perfectly able to recognize the novel object in SORT. By contrast, C57 mice were good performers in SNT but failed to recognize a novel object in SORT. Finally, food restriction selectively improved C57 performance in SNT and DBA performance in SORT. These results support the view that a food restricting procedure enhances strain differences for discrimination of configurational information.     

The Y chromosome, social signals, and offense in mice

Offense is one type of aggression in mice (Mus musculus/Mus domesticus). Offense was measured in a panel of testers design for two congenic strains of mice. The two congenic strains were DBA1Bg and DBA1. C57BL10-YBg. These differ in the Y chromosome. Offense was measured for the following dyadic pairs: Group 1 (DBA1 tested against a DBA1 opponent); Group 2 (DBA1 tested against a DBA1.C57BL10-Y opponent); Group 3 (DBA1.C57BL10-Y tested against a DBA1.C57BL10-Y opponent); and Group 4 (DBA1.C57BL10-Y tested against a DBA1 opponent). Group 1 was more aggressive than Group 3, whereas Group 2 was no more aggressive than Group 4. Thus, when the experimental and opponent pairs have the same Y chromosome, the congenics differ in offense, whereas when the experimental and opponent pairs have different Y chromosomes, the congenics do not differ in offense. These findings are consistent with the hypothesis that these Y chromosomes affect the display of and response to social or other stimuli for offense of mice. These stimuli may be individual recognition chemosignals in urine.     

Effect of age of habit on susceptibility to cycloheximide-induced amnesia in mice.

The amnesic effects of cycloheximide (CYC) on habits of different ages were investigated in a food-motivated, discrimination-reversal task. Groups of C57BL/6J mice were injected 30 min before training or immediately, 3 days, 6 days, or 9 days after training. Retention was tested 24 hr after CYC treatment. The usual amnesic effect of CYC occurred in animals injected before training. No amnesia was apparent in groups injected immediately, 3 days, or 9 days after training. However, a reliable and reproducible amnesia occurred in the group injected 6 days after training. This amnesia could be reversed by pretest treatment with a monoamine oxidase inhibitor, pheniprazine. Pheniprazine, given 7 days after training, also enhanced retrieval of memory in saline-injected mice.     

Alcohol-induced conditioned aversion: genotypie specificity in mice (Mus musculus).

Acetaldehyde poisoning from ethanol ingestion may lead to aversion to ethanol among DBA mice but not among C57s, since the former are relatively deficient in aldehyde dehydrogenase activity. The present study paired ingestion of saccharin with a single intraperitoneal injection of one of four concentrations of ethanol for DBA/2J and C57BL/6J mice. Subjects were then given a two-bottle saccharin versus water preference test for 10 days. Substitution of saccharin for the taste of ethanol resulted in avoidance of saccharin with all concentrations of ethanol by DBAs but not by C57s, consistent with the conditioned taste aversion paradigm as a model for genetically mediated ethanol avoidance.     

A genetic analysis of stereotypy in the mouse: dopaminergic plasticity following chronic stress

After repeated stressful experiences, DBA/2 (DBA) mice showed an increase in apomorphine-induced climbing while C57BL/6 (C57) mice showed a clear-cut decrease of this behavior. Genetic analysis involving F1 and F2 hybrids and the backcross populations (F1 X C57; F1 X DBA) indicated complete dominance of the C57 genotype and a significant genotype X environment interaction. These findings are discussed in terms of dopaminergic plasticity and of the heuristic value of this animal model in relation to disturbed behaviors triggered by stressful experiences.     

Opposite strain-dependent differences for intermale aggressive behavior elicited by individual housing and housing with a female in the mouse

Male mice of the C57BL/6 strain show a significant increase in aggression toward a nonaggressive male conspecific following 72 hr of individual housing. However, this increase was no longer evident following 2 weeks of individual housing. When housed with a female, C57BL/6 mice show significantly more aggression than singly housed mice of the same strain after 72 hr as well as 2, 4, 8 weeks of differential housing. Male C57BL/6 mice housed with a female also show significantly higher levels of aggression than DBA/2 mice living in the same housing condition after 4 or 8 weeks of differential housing. Finally, male DBA/2 mice individually housed for 8 weeks are significantly more aggressive than mice of the same strain housed with a female for the same time. These results indicate that the increase in aggressive behavior observed following isolation and cohabitation with a female in the mouse is not the same phenomenon. © 1994 Wiley-Liss, Inc.     

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.     

Effects of posttraining ethanol on an appetitive task

The present study examined the effects of posttraining ethanol administration upon retention of an appetitive task using a variety of retention behaviors associated with the task. Male C57BL/6J mice were individually trained to find a cheese pellet placed in the corner of an open field. Five behavioral measures were used including locomotor activity counts, rearings, grooming episodes, approaches to the cheese pellet, and latency to consume the cheese pellet. Immediately after training, mice were injected intraperitoneally with saline or 2.0 g/kg of ethanol and then returned to their home cage in which four "intruder" mice were added for 2 h after training. On subsequent testing days (1, 6, 14, and 51 days posttraining), mice were returned to the original training environment and the five behaviors were measured. Both saline- and ethanol-treated mice habituated to the initially novel test environment at similar rates as indicated by decreased exploratory behavior (locomotor activity and rearings). In contrast, a divergence in the latency to consume the cheese pellet was observed: Saline-treated mice behaved as though the cheese was rewarding (decreased latency to eat the pellet), while the ethanol group behaved as though the cheese was aversive (increased latency to eat the pellet). Taken with previous studies, these results demonstrate that posttraining ethanol can have strikingly different effects on retention depending on the task, the measure of retention used, and the underlying neural structures involved.     

Chronic stress-induced alterations in mouse colonic 5-HT and defecation responses are strain dependent

Mood disorders and chronic stress are frequently associated with gastrointestinal (GI) symptoms including diarrhoea or constipation. Locally produced serotonin [5-hydroxytryptamine (5-HT)] regulates GI motility and is a key factor in the pathophysiology of stress-associated GI disorders. We aimed to establish whether chronic stress can differentially affect faecal output and colon 5-HT concentration in two inbred mouse strains: BALB/c and C57BL/6 which differ in their ability to cope with stress. Adult male BALB/c and C57BL/6 mice were restrained for 2?h daily for 10 days. Defecation was monitored during each stress session. Twenty-four hours after the last session of stress, plasma corticosterone concentration was higher than control in both strains, indicative of a physiological effect of chronic stress; however, stress-induced diarrhoea was more persistent in C57BL/6 mice. Basal concentration of colon 5-HT was higher in C57BL/6 mice, and stress elicited an increase in colon 5-HT only in this strain. Finally, na?ve BALB/c mice had a higher sensitivity (incidence of diarrhoea) to 5-HT (0.33?mg/kg, i.p.) than C57BL/6 mice. Our results suggest that differential defecation responses to stress may be associated with colon 5-HT concentration, which may in turn reflect the individual sensitivity to 5-HT. In addition, C57BL/6 mice emerge as a relevant model for studying GI alterations induced by chronic stress.     

Auditory similarities associated with genetic and experimental acoustic deprivation.

Susceptibility to audiogenic seizures has been produced in otherwise non-susceptible mice by acoustic stress and by conductive hearing loss. Both procedures temporarily elevate the absolute threshold of the auditory evoked potential (AEP) and are maximally effective during a circumscribed period of early development. In the genetically SUSCEPTIBLE DBA/2J mouse, AEP thresholds indicated that its auditory system is functionally less mature during this early period than that of the nonsusceptible C57BL/6Jmouse. It was proposed that innate susceptibility found in the DBA/2J mouse results from auditory disuse supersensitivity during a critical developmental period, in support of Saunders' hypothesis for acoustically primed mice. The increased peak-to-peak AEP amplitudes, however, were not believed to be causally related to the audiogenic seizures.