Those cheating rats: male and female rats use odor trails in a water-escape "working memory" task.

Three-month-old Sprague-Dawley rats were trained on a working memory win-stay (spatial delayed matching-to-sample) water-escape task with the escape platform location the same for all subjects on a given trial, a procedure that maximizes the buildup of an odor trail to the escape platform. In subsequent tests during which the location of the escape platform varied randomly between subjects, the rats, especially the females, while continuing to perform above chance level, made increased errors. Varying the platform location between subjects eliminated odor trail as a nonambiguous cue for locating the escape platform. In a second experiment females performed better than males on a reference memory odor trail discrimination task which involved following the path of like-gender "pathmaker" rats to the escape platform. The relatively poor use of odor trails by the males was associated with a high frequency of choosing a preferred choice section or returning to the choice section selected first on the immediately preceding trial (perseveration). Collectively, the two experiments demonstrate that rats can use either working memory or odor trails to locate an escape platform in a water maze, and that they, especially females, will use odor trails in a working memory task if odor trails are available. Clearly, the location of the escape platform should be varied randomly between subjects in tests of working memory.     

Binge eating proneness emerges during puberty in female rats: a longitudinal study

Puberty is a critical risk period for binge eating and eating disorders characterized by binge eating. Previous research focused almost entirely on psychosocial risk factors during puberty to the relative exclusion of biological influences. The current study addressed this gap by examining the emergence of binge eating during puberty in a rat model. We predicted that there would be minimal differences in binge eating proneness during pre-early puberty, but significant differences would emerge during puberty. Two independent samples of female Sprague-Dawley rats (n = 30 and n = 36) were followed longitudinally across pre-early puberty, mid-late puberty, and adulthood. Binge eating proneness was defined using the binge eating resistant (BER)/binge eating prone (BEP) model of binge eating that identifies BER and BEP rats in adulthood. Across two samples of rats, binge eating proneness emerged during puberty. Mixed linear models showed little difference in palatable food intake between BER and BEP rats during pre-early puberty, but significant group differences emerged during mid-late puberty and adulthood. Group differences could not be accounted for by changes in nonpalatable food intake or body weight. Similar to patterns in humans, individual differences in binge eating emerge during puberty in female rats. These findings provide strong confirming evidence for the importance of biological risk factors in developmental trajectories of binge eating risk across adolescence.     

"Worthless female material": nursemaids and governesses in Freud's cases

The figure of the governess, central in Freud's own history, is present in most of his cases. Freud described his nursemaid as "the prime originator" of his neuroses. Well after Freud's abandonment of the seduction theory, female servants were consistently portrayed as seducing boys, while their relationship with girls consisted of identification and rivalry. The role of Freud's own surrogate mother in his life and writing is examined, and two cases, Lucy R. and Dora, are looked at through the lens of female caretaking. A review and integration of relevant literature is followed by an exploration of the perplexing adherence in Freud's writing to the reality of seduction by a governess, even after he had abandoned the seduction theory. It is argued that it is in the figure of the female maid that the "shadowy" early history of Freud's mothering experiences may actually be engaged, however indirectly and unconsciously. This figure, and Freud's powerful, problematic identification with her, is a thread that when pulled helps unravel struggles in Freud's early theoretical development around issues of female sexuality and analytic authority. Revisiting Lucy R. and Dora provides a new perspective on Freud's difficulty with maternal transferences, and restores to their original importance his "worthless" governesses, those first analysts.     

Chronically stressed female rats show increased anxiety but no behavioral alterations in object recognition or placement memory: a preliminary examination

Stress, depending on intensity and duration, elicits adaptive or maladaptive physiological effects. Increasing evidence shows those patterns of advantageous versus deleterious physiologic stress effects also exist for some brain functions, including learning and memory. For example, short stress enhances, while chronic stress impairs, performance on numerous cognitive tasks in male rats. In contrast, performance of female rats is enhanced, or not altered, following both short-term and long-term stress exposure on the same behavioral tasks. The current study was designed to better characterize the behavioral effects of sustained chronic restraint stress in female rats. Female Sprague Dawley rats were assigned to a stress (restraint, 6 h/day, 35 days) or control (no stress) condition, weighed weekly, and then tested on open field (OF), object recognition (OR) and object placement (OP) tasks. Stressed females gained less weight during stress than controls. On the OF, there were no group differences in locomotor activity, but stressed females made fewer inner visits than controls, indicating increased anxiety. Both groups successfully performed the OP and OR tasks across all inter-trial delays, indicating intact non-spatial and spatial memory in both control and stress females. The current results provide preliminary evidence that the commonly used chronic restraint stress model may not be an efficient stressor to female rats.     

Hoarding behaviour and the defence of body weight in adult rats, following undernutrition during different periods of early development

In Experiment I, male rats, previously undernourished by underfeeding their mothers during lactation, weighed less as adults than progeny of mothers underfed during gestation, or than normally-nourished control rats. Daily 16 h food deprivation of the adults induced weight loss and elicited hoarding of food pellets. Deprivation-induced weight losses at criterion for hoarding did not differ significantly among the groups, and the critical weight at which hoarding began was thus significantly lower in the lactationally-undernourished group than in the controls. Thus adult rats, previously undernourished during their suckling period, appear to defend their body weights in a manner similar to controls, although at a lower level. Lactationally-undernourished rats also hoarded significantly fewer pellets than controls. Similar results were obtained when the rats were partially satiated before hoarding tests, suggesting that hoarding scores were unlikely to have been significantly affected by competition with feeding. Foetal undernutrition had weaker, and less consistent effects than lactational undernutrition on the ad libitum weight of the adult, and on the critical weight for hoarding. In Experiment II, severe undernutrition after weaning did not affect adult body weight, the weight loss necessary to induce hoarding, or the number of pellets hoarded. It is concluded that the pre-weaning period is specifically sensitive to the effects of undernutrition on body weight regulation and on hoarding. The data on hoarding do not support the view that a period of undernutrition at any time in early life increases the rat's responsiveness towards food.     

Early-life stress affects extinction during critical periods of development: An analysis of the effects of maternal separation on extinction in adolescent rats

Adolescence is a period of heightened susceptibility to anxiety disorders, yet we have little experimental evidence on what factors may lead to psychopathology in adolescence. Preclinical models of extinction are commonly used to study the treatment of anxiety symptoms. Interestingly, recent research has shown that there are fundamental changes in the process of extinction across development, which may have implications for our understanding of psychopathology across the lifespan. Specifically, this research shows that the process of extinction parallels the nonlinear function of prefrontal cortex development, such that extinction behaviour is similar in juvenile and adult rats, but involves different processes in infancy and adolescence (periods of rapid growth and pruning, respectively). Our previous studies have shown that early-life stress accelerates the transition between infant and juvenile extinction systems. In the current series of experiments, we examined whether the same early-life stress, maternal separation (MS), would lead to an earlier transition between the juvenile and adolescent extinction systems, and between the adolescent and adult extinction systems. We show that MS adolescent rats exhibit more adult-like extinction behaviour, and that adolescent-like extinction emerges earlier in development (i.e. in pre-adolescent rats). These results may have important implications for the understanding and treatment of anxiety symptoms in adolescent populations.     

Inhibition of suckling in weaning-age rats: a possible serotonergic mechanism.

The nature, development, and specificity of serotonergic involvement in the control of suckling behavior in rat pups from 10 to 35 days of age were studied. During development, suckling normally declines after 10 days and is abandoned after 30 days. It was found that (a) methysergide, a serotonin (5-HT) receptor blocker, reinstated suckling behavior in pups 15 days of age and older but had no effect on the suckling of 10-day old pups, (b) quipazine, a 5-HT receptor agonist, inhibited suckling of pups 10 days of age and older, (c) methysergide pretreatment blocked the quipazine inhibition of suckling, and (d) metergoline, another 5-HT blocker, also stimulated suckling, and fenfluramine, a 5-HT releaser, blocked suckling in deprived pups. Together, these data support the hypothesis that a serotonergic inhibitory mechanism modulates the suckling of weaning-age rats. These pharmacological manipulations of 5-HT appear to alter specific components of suckling behavior involved in its initiation and maintenance but do not appear to alter a general hunger system.     

"Warmup" and "cooldown" in Sidman avoidance behavior of rats: A dual-process interpretation

The present experiment investigated relations between "warmup" in unsignalled Sidman avoidance in rats and the intensity of shock. Magnitude of shock-rate change was quantified by comparing the rat's behavior during the initial third and the final two thirds of the same session. Warmup was said to occur whenever the shock rate during the initial 20 min was higher than the shock rate during the final 40 min of a 60 min session. "Cooldown" was defined as lower shock rate during the initial 20 min than during the final 40 min. Warmup was observed when shocks were intense, cooldown was observed when shocks were low intensity, and neither was observed when medium-intensity shocks were administered. Response-rate changes were correlated with shock-rate changes, but were smaller. The results are interpreted within the framework of a dual-process theory of habituation.     

Social transmission of Pavlovian fear: fear-conditioning by-proxy in related female rats

Pairing a previously neutral conditioned stimulus (CS; e.g., a tone) to an aversive unconditioned stimulus (US; e.g., a foot-shock) leads to associative learning such that the tone alone will elicit a conditioned response (e.g., freezing). Individuals can also acquire fear from a social context, such as through observing the fear expression of a conspecific. In the current study, we examined the influence of kinship/familiarity on social transmission of fear in female rats. Rats were housed in triads with either sisters or non-related females. One rat from each cage was fear conditioned to a tone CS+ shock US. On day two, the conditioned rat was returned to the chamber accompanied by one of her cage mates. Both rats were allowed to behave freely, while the tone was played in the absence of the foot-shock. The previously untrained rat is referred to as the fear-conditioned by-proxy (FCbP) animal, as she would freeze based on observations of her cage-mate’s response rather than due to direct personal experience with the foot-shock. The third rat served as a cage-mate control. The third day, long-term memory tests to the CS were performed. Consistent with our previous application of this paradigm in male rats (Bruchey et al. in Behav Brain Res 214(1):80–84, 2010), our results revealed that social interactions between the fear conditioned and FCbP rats on day two contribute to freezing displayed by the FCbP rats on day three. In this experiment, prosocial behavior occurring at the termination of the cue on day two was significantly greater between sisters than their non-sister counterparts, and this behavior resulted in increased freezing on day three. Our results suggest that familiarity and/or kinship influences the social transmission of fear in female rats.     

Defensive burying of aversive fluids in rats: The possible role of odor

Defensive burying of flavored fluids paired with lithium chloride injections was examined. Rats showed little inclination to bury conditioned saccharin or salt solutions (Experiments 1 and 2). However, they buried tabasco sauce or dilute milk solutions readily (Experiment 3). It was hypothesized that the amount of olfactory stimulation provided by a solution may determine whether a rat engages in burying. This hypothesis received support in a final experiment which demonstrated that rats readily buried an arbitrarily selected odorous solution which was previously paired with lithium chloride. Thus the present experiments begin the process of identifying the circumstances under which burying does and does not occur.     

Effects of chronic ethanol consumption on gestation and lactation in rats

Chronic consumption of ethanol during pregnancy and lactation may lead to abnormalities in the fetus or infant. A group of female Wistar rats was submitted to ethanol treatment over a period of a month. A pair-fed control group received sucrose solution isocaloric to ethanol and the control group received water “ad libitum.” Afterward, the females were mated with males over a period of 20 days. At birth, each litter was maximized to eight pups and the remaining ones were decapitated to remove the fetal blood and brains. No significant difference was observed in fetal body and brain weight at birth. During lactation the ethanol and pair-fed groups gained less weight than the control group. After weaning, their weight became similar. Fetal blood glucose levels were decreased in the ethanol-treated group. One hundred percent of the pair-fed and control females delivered live fetuses at term and all survived; only 40% of the females in the ethanol group delivered, and one pup did not survive. Chronic ethanol treatment pointed to a possible reduction in the fertility. It seems likely that the change in body weight of ethanol-fed dams was caused by undernutrition.