Sexual differentiation of the effects of emotional stress on food intake in rats

Binge eating, overeating and food addiction: Approaches for examining food overconsumption in laboratory rodents

Overeating ranges in severity from casual overindulgence to an overwhelming drive to consume certain foods. At its most extreme, overeating can manifest as clinical diagnoses such as binge eating disorder or bulimia nervosa, yet subclinical forms of overeating such as emotional eating or uncontrolled eating can still have a profoundly negative impact on health and wellbeing. Although rodent models cannot possibly capture the full spectrum of disordered overeating, studies in laboratory rodents have substantially progressed our understanding of the neurobiology of overconsumption. These experimental approaches range from simple food-exposure protocols that promote binge-like eating and the development of obesity, to more complex operant procedures designed to examine distinct 'addiction-like' endophenotypes for food. This review provides an overview of these experimental approaches, with the view to providing a comprehensive resource for preclinical investigators seeking to utilize behavioural models for studying the neural systems involved in food overconsumption.

A review of sex differences in the mechanisms and drivers of overeating

Disordered eating is often associated with marked psychological and emotional distress, and severe adverse impact on quality of life. Several factors can influence eating behavior and drive food consumption in excess of energy requirements for homeostasis. It is well established that stress and negative affect contribute to the aetiology of eating disorders and weight gain, and there is substantial evidence suggesting sex differences in sub-clinical and clinical types of overeating. This review will examine how negative affect and stress shape eating behaviors, and how the relationship between the physiological, endocrine, and neural responses to stress and eating behaviors differs between men and women. We will examine several drivers of overeating and explore possible mechanisms underlying sex differences in eating behavior.

Sex-linked roles of the CRF1 and the CRF2 receptor in social behavior

Dysfunctional social behavior is a major clinical feature of mood, anxiety, autism spectrum, and substance-related disorders, and may dramatically contribute to the poor outcome of these diseases. Nevertheless, the mechanisms underlying social behavior deficits are still largely unknown. The corticotropin-releasing factor (CRF) system, a major coordinator of the stress response, has been hypothesized to modulate social behavior. CRF signaling is mediated by two receptor types, termed CRF₁ and CRF₂ . Using the three-chamber task for sociability (i.e., preference for an unfamiliar conspecific vs. an object), this study demonstrates that CRF₂ receptor null mutation (CRF₂ -/-) reduces sociability in female mice but increases it in male mice. Both female and male CRF₂ -/- mice display a preference for social odor cues over neutral cues, indicating that sex- and CRF₂ receptor-dependent sociability is not due to altered olfaction or impaired social cues discrimination. Moreover, treatment with the CRF₁ receptor-preferring antagonist, antalarmin, consistently induces sociability in non-social mice but disrupts it in social mice, independently of CRF₂ receptor deficiency. Sex, CRF₂ receptor deficiency, or antalarmin affect locomotor activity during the three-chamber test. However, throughout the study CRF₁ and CRF₂ receptor-linked sociability is independent of locomotor activity. The present findings highlight major functions for the CRF system in the regulation of social behavior. Moreover, they provide initial evidence of sex-linked roles for the CRF₁ and the CRF₂ receptor, emphasizing the importance of sex as a major biological variable to be taken into consideration in preclinical and clinical studies.

Oral Fat Sensitivity Is Associated with Social Support for Stress Coping in Young Adult Men

Oral fat sensitivity (OFS), the ability to taste fat, is associated with eating habits in humans, including daily fatty food consumption; namely, proper OFS is important for health. In addition, lifestyle factors, such as stress and sleep, may affect fat intake. However, correlations between OFS, stress management, and sleep are largely unknown. Thus, we investigated the associations of OFS with lifestyle factors regarding stress management and daytime sleepiness in healthy young adult men. We measured OFS, sensitivities for three prototypical tastes (sweet, salty, and sour), and BMI in 22 subjects (27.2 ± 6.0 years), who also completed a self-reported questionnaire on health, including lifestyle-related questions. The correlations of taste sensitivities with stress management and daytime sleepiness were analyzed. We thus found that the number of mentors for personal concerns (a question regarding stress management, social support) was positively associated with OFS (P = 0.041), but not the other taste sensitivities. In contrast, other lifestyle factors related to stress management (frequency of relaxation, frequency of eating when irritated or worried, and degree of satisfaction with one's sleep) and daytime sleepiness were not significantly associated with OFS, similar to that observed for other tested taste sensitivities. These results characterize the unique association of OFS with the degree of social support in healthy young men and provide novel insights into the nature of individual OFS differences. Thus, measuring the degree of social support may be helpful for the evaluation of OFS impairment, thereby contributing to the prevention of stress-induced overeating.

Effects of aging, gender, and hypogonadism on mandibular bone density

AIM

The aim of the present study was to evaluate how aging, sex, and hypogonadism influence mandibular bone density with and without the benefits of hormone treatment.

METHODS

Three-month old Wistar rats were randomly assigned to three experimental groups, with eights animals per group: controls, castrated (orchiectomized [ORX], ovariectomized [OVX]) and castrated with hormonal treatment (ORX + testosterone, OVX + estradiol benzoate). Females were previously evaluated by vaginal cytology. The corporal mass was verified weekly, and after three experimental periods (90, 120, and 150 days), the animals were killed. Blood was collected, and bones underwent densitometric and biomechanical analyses.

RESULTS

After castration, the male rats demonstrated low gain in body weight compared to females (P < .05). Male and female castrated animals presented serum concentrations of sex steroid hormones lower than the control group (P < .05). Bone mineral density and biomechanical properties of the L4 vertebrae and femur were reduced earlier in females than in males (P < .05). However, mandibles were affected only in the male rats at the most chronic experimental period.

CONCLUSION

Hypogonadism promotes alterations in the mandible over chronic periods, especially in males, and these alterations could be minimized by hormone treatment.

Sex differences in avoidance behavior after perceiving potential risk in mice

Background

Sex has been considered as a potential factor regulating individual behaviors in different contexts. Recently, findings on sex differences in the neuroendocrine circuit have expanded due to exact measurements and control of neuronal activity, while findings on sex differences in behavioral phenotypes are limited. One efficient way to determine the miscellaneous aspects of a sexually different behavior is to segment it into a set of simpler responses induced by discrete scenes.

Methods

In the present study, we conducted a battery of behavioral tests within a variety of unique risky scenes, to determine where and how sex differences arise in responses under those scenes.

Results

A significant sex difference was observed in the avoidance responses measured in the two-way active and the passive avoidance tests. The phenotype observed was higher mobility in male mice and reduced mobility in female mice, and required associative learning between an escapable risk and its predictive cue. This was limited in other scenes where escapable risk or predictive cue or both were missing.

Conclusions

Taken together, the present study found that the primary sex difference occurs in mobility in the avoidance response after perceiving escapable risks.

Electronic supplementary material

The online version of this article (doi:10.1186/s12993-017-0126-3) contains supplementary material, which is available to authorized users.

Discovery of 4-chloro-2-(2,4-dichloro-6-methylphenoxy)-1-methyl-7-(pentan-3-yl)-1H-benzimidazole, a novel CRF1 receptor antagonist

Compound 1 exhibits potent binding inhibition activity against a corticotropin-releasing factor 1 (CRF₁) receptor (IC₅₀=9.5nM) and in vitro antagonistic activity (IC₅₀=88nM) but is rapidly metabolized by human hepatic microsomes (182μL/min/mg). Here we identified metabolically stable compounds with potent CRF binding inhibitory activity. Structure-activity relationship (SAR) studies considering in vitro metabolic stability revealed that 4-chloro-2-(2,4-dichloro-6-methylphenoxy)-1-methyl-7-(pentan-3-yl)-1H-benzimidazole 24d was more stable in human microsomes (87μL/min/mg) than compound 1. Compound 24d demonstrated potent CRF binding inhibitory activity (IC₅₀=4.1nM), in vitro antagonistic activity (IC₅₀=44nM), and slow dissociation from the CRF₁ receptor. Orally administered compound 24d (6-24μmol/kg) showed ex vivo CRF₁ receptor binding in the rat pituitary, olfactory bulb, and frontal cortex and suppressed stress-induced adrenocorticotropic hormone (ACTH) secretion. In this report, we discuss SAR studies on the metabolic stability as well as CRF binding inhibitory activity of the benzimidazole series as CRF₁ receptor antagonists and the pharmacological profiles of compound 24d.

Behavioral and hormonal responses to stress in binge-like eating prone female rats

Binge eating episodes are frequently stimulated by stress. We developed a model of binge eating proneness based on individual sensitivity of young female Sprague Dawley rats to significantly increase sucrose consumption in response to stress. The rats were subjected to unpredictable intermittent 1-h access to 10% sucrose. After the stabilization of sucrose intake, rats were assessed for consistency of higher (for binge-like eating prone, BEP) or lower (for binge-like eating resistant, BER) sucrose intake in response to unpredictable episodes of foot-shock stress. The objectives of this study included demonstrating face validity of the BEP model and determining if some of the features of this model were pre-existing before exposure to intermittent access to sucrose and repeated stress. The BEP rats consumed a larger (20%>BER) amount of sucrose in a discrete (1-h) period of time compared to the BER phenotype in non-stressful conditions and significantly increased sucrose intake (50%>BER) under stress. Conversely, stress did not affect sucrose intake in BER rats. BEP rats showed higher sucrose intake compared to BER rats at the beginning of darkness as well as during the light period when they were sated and not physically hungry. Analyses of the sucrose licking microstructure revealed that BEP rats had a high motivational drive to consume sucrose in non-stressful condition and an increased hedonic value of sucrose when they were exposed to stressful conditions. BEP rats consumed sucrose much more rapidly under stressful conditions compared to BER rats. Finally, BEP rats demonstrated compulsive-like intake of sucrose (assessed in the light-dark box) and a blunted stress-induced increase in plasma corticosterone levels. Body weight and chow intake were not different between the phenotypes. Before exposure to intermittent access to sucrose and repeated stress, the BEP rats showed no clear evidence for compulsive sucrose intake. However, from the first 1-h access to sucrose, the BEP rats exhibited sucrose overeating; and from the first exposure to stress before intermittent access to sucrose, the BEP rats showed a blunted increase in corticosterone plasma levels. Innate sucrose hyperconsumption and altered reactivity of the hypothalamo-pituitary adrenal (HPA) axis to stress may be involved in the development of binge-like eating. Increased perceived hedonic value of palatable food and an increased motivation to consume this food despite aversive conditions as well as deregulated reactivity of the HPA axis may contribute to stress-induced bingeing on sucrose in BEP rats.

Estrogen involvement in social behavior in rodents: Rapid and long-term actions

This article is part of a Special Issue ("Estradiol and cognition"). Estrogens have repeatedly been shown to influence a wide array of social behaviors, which in rodents are predominantly olfactory-mediated. Estrogens are involved in social behavior at multiple levels of processing, from the detection and integration of socially relevant olfactory information to more complex social behaviors, including social preferences, aggression and dominance, and learning and memory for social stimuli (e.g. social recognition and social learning). Three estrogen receptors (ERs), ERα, ERβ, and the G protein-coupled ER 1 (GPER1), differently affect these behaviors. Social recognition, territorial aggression, and sexual preferences and mate choice, all requiring the integration of socially related olfactory information, seem to primarily involve ERα, with ERβ playing a lesser, modulatory role. In contrast, social learning consistently responds differently to estrogen manipulations than other social behaviors. This suggests differential ER involvement in brain regions important for specific social behaviors, such as the ventromedial and medial preoptic nuclei of the hypothalamus in social preferences and aggression, the medial amygdala and hippocampus in social recognition, and the prefrontal cortex and hippocampus in social learning. While the long-term effects of ERα and ERβ on social behavior have been extensively investigated, our knowledge of the rapid, non-genomic, effects of estrogens is more limited and suggests that they may mediate some social behaviors (e.g. social learning) differently from long-term effects. Further research is required to compare ER involvement in regulating social behavior in male and female animals, and to further elucidate the roles of the more recently described G protein-coupled ERs, both the GPER1 and the Gq-mER.

CRF2 Receptor Deficiency Eliminates the Long-Lasting Vulnerability of Motivational States Induced by Opiate Withdrawal

Vulnerability to stressful life events is a hallmark of drug dependence that may persist long after cessation of drug intake and dramatically fuel key clinical features, such as deregulated up-shifted motivational states and craving. However, to date, no effective therapy is available for reducing vulnerability to stressful events in former drug users and drug-dependent patients, mostly because of poor knowledge of the mechanisms underlying it. In this study, we report that genetic inactivation of the stress-responsive corticotropin-releasing factor receptor-2 (CRF2-/-) completely eliminates the reemergence of increased nonrewarded nose-pokes, reflecting up-shifted motivational states, triggered by ethological environmental stressors long after cessation of morphine administration in mice. Accordingly, CRF2 receptor deficiency completely abolishes the increase in biomarkers of synthesis of major brain motivational substrates, such as ventral tegmental area (VTA) dopamine (DA) and amygdala γ-aminobutyric acid (GABA) systems, associated with the stress-induced reemergence of up-shifted motivational states long after opiate withdrawal. Nevertheless, neither CRF2 receptor deficiency nor long-term opiate withdrawal affects amygdala CRF or hypothalamus CRF expression, indicating preserved brain stress-coping systems. Moreover, CRF2 receptor deficiency does not influence the locomotor or the anxiety-like effect of long-term opiate withdrawal. Thus, the present results reveal an essential and specific role for the CRF2 receptor in the stress-induced reemergence of up-shifted motivational states and related alterations in brain motivational systems long after opiate withdrawal. These findings suggest new strategies for the treatment of the severe and long-lasting vulnerability that inexorably follows drug withdrawal and hinder drug abstinence.

Preclinical experimental stress studies: protocols, assessment and comparison

Stress is a state of threatened homeostasis during which a variety of adaptive processes are activated to produce physiological and behavioral changes. Preclinical models are pivotal for understanding these physiological or pathophysiological changes in the body in response to stress. Furthermore, these models are also important for the development of novel pharmacological agents for stress management. The well described preclinical stress models include immobilization, restraint, electric foot shock and social isolation stress. Stress assessment in animals is done at the behavioral level using open field, social interaction, hole board test; at the biochemical level by measuring plasma corticosterone and ACTH; at the physiological level by measuring food intake, body weight, adrenal gland weight and gastric ulceration. Furthermore the comparison between different stressors including electric foot shock, immobilization and cold stressor is described in terms of intensity, hormonal release, protein changes in brain, adaptation and sleep pattern. This present review describes these preclinical stress protocols, and stress assessment at different levels.

Estrogens downregulate urocortin 2 expression in rat uterus

Urocortin 2 (Ucn2) is a member of the corticotropin-releasing factor peptide family and is expressed by various tissues, including reproductive tissues such as the uterus, ovary, and placenta. However, the regulatory mechanisms of Ucn2 expression and the physiological significance of Ucn2 in these tissues remain unclear. We previously showed that passive immunization of immature female rats by i.p. injection of anti-Ucn2 IgG induces earlier onset of puberty. Therefore, this study was designed to clarify the site and regulatory mechanisms of Ucn2 expression in the uterus. Expression levels of Ucn2 mRNA in the uterus were higher in immature (2- and 4-week-old) and aged (17-month-old) rats than in mature (9-week-old) rats in the proestrus phase. In 9-week-old rats, mRNA expression levels and contents in the uterus were lower in the proestrus phase than in the diestrus phase, while plasma Ucn2 concentrations did not differ between the two phases. Ucn2-like immunoreactivitiy was detected in the endometrial gland epithelial cells of the uterus. S.c. injection of estradiol benzoate or an estrogen receptor α (ERα) agonist significantly reduced mRNA expression levels and contents of Ucn2 in the uterus when compared with vehicle-injected ovariectomized rats. By contrast, estradiol benzoate increased Ucn2 mRNA expression levels in the lung. Thus, estrogens downregulate Ucn2 expression in the uterus in a tissue-specific manner, and Ucn2 may play a role in the regulatory mechanisms of maturation of the uterus through ERα and estrous cycle.

Bone marrow-derived microglia infiltrate into the paraventricular nucleus of chronic psychological stress-loaded mice

Background

Microglia of the central nervous system act as sentinels and rapidly react to infection or inflammation. The pathophysiological role of bone marrow-derived microglia is of particular interest because they affect neurodegenerative disorders and neuropathic pain. The hypothesis of the current study is that chronic psychological stress (chronic PS) induces the infiltration of bone marrow-derived microglia into hypothalamus by means of chemokine axes in brain and bone marrow.

Methods and Findings

Here we show that bone marrow-derived microglia specifically infiltrate the paraventricular nucleus (PVN) of mice that received chronic PS. Bone marrow derived-microglia are CX₃CR1^lowCCR2⁺CXCR4^high, as distinct from CX₃CR1^highCCR2^-CXCR4^low resident microglia, and express higher levels of interleukin-1β (IL-1β) but lower levels of tumor necrosis factor-α (TNF-α). Chronic PS stimulates the expression of monocyte chemotactic protein-1 (MCP-1) in PVN neurons, reduces stromal cell-derived factor-1 (SDF-1) in the bone marrow and increases the frequency of CXCR4⁺ monocytes in peripheral circulation. And then a chemokine (C-C motif) receptor 2 (CCR2) or a β₃-adrenoceptor blockade prevents infiltration of bone marrow-derived microglia in the PVN.

Conclusion

Chronic PS induces the infiltration of bone marrow-derived microglia into PVN, and it is conceivable that the MCP-1/CCR2 axis in PVN and the SDF-1/CXCR4 axis in bone marrow are involved in this mechanism.

Acute corticosterone sexually dimorphically facilitates social learning and inhibits feeding in mice

In numerous species social learning is predominant and adaptive, yet, we know little of its neurobiological mechanisms. Social learning is modulated by motivations and emotions, in a manner that is often sexually dimorphic. Additionally, stress hormones acutely modulate the related social cognitive process of social recognition. Whether this is true even for social learning is currently unknown. We investigated the acute effects of the stress hormone corticosterone (CORT) on the social transmission of food preferences (STFP) in male and female mice. During a brief social interaction an observer (OBS) acquires a food preference from a same-sex demonstrator (DEM). CORT (1.0, 2.5, 5.0 mg/kg), its ethanol vehicle (0.1%), and saline solution (0.9%) were administered intraperitoneally to the OBS, 10 min before a 30-min social interaction. Levels of plasma CORT were assessed in other mice that had received the same doses of CORT and either had or had not gone through a 30 min social interaction 10 min post-treatment. Exogenous CORT elicited levels of plasma level comparable to those seen at the peak of the circadian cycle and facilitated the STFP with males responding more than females both in terms of the duration of the food preference and the minimum effective dose. CORT also sexually dimorphically inhibited feeding, with females showing a greater dose-response than males. Saline solution and ethanol vehicles also sexually dimorphically facilitated the STFP and reduced feeding, but less than CORT did. These results indicate that CORT facilitates social learning, like social recognition. Hence, CORT may generally increase social information processing.

Oestradiol differentially influences feeding behaviour depending on diet composition in female rhesus monkeys

In females, cyclical changes in the ovarian hormone oestradiol are known to modulate feeding behaviour. However, what is less clear is how these behavioural effects of oestradiol are modified by the macronutrient content of a diet. In the present study, we report data showing that oestradiol treatment results in both significantly smaller meals and a reduced total calorie intake in ovariectomised, socially-housed female rhesus macaques when only chow diet is available. Conversely, during a choice dietary condition where both palatable and chow options are available, oestradiol treatment had no observable, attenuating effect on calorie intake. During this choice dietary phase, all animals consumed more of the palatable diet than chow diet; however, oestradiol treatment appeared to further increase preference for the palatable diet. Finally, oestradiol treatment increased snacking behaviour (i.e. the consumption of calories outside of empirically defined meals), regardless of diet condition. These findings illustrate how oestradiol differentially influences feeding behaviour depending on the dietary environment and provides a framework in which we can begin to examine the mechanisms underlying these observed changes.

The influence of experimental manipulations on chewing speed during in vivo laboratory research in tufted capuchins (Cebus apella)

Even though in vivo studies of mastication in living primates are often used to test functional and adaptive hypotheses explaining primate masticatory behavior, we currently have little data addressing how experimental procedures performed in the laboratory influence mastication. The obvious logistical issue in assessing how animal manipulation impacts feeding physiology reflects the difficulty in quantifying mechanical parameters without handling the animal. In this study, we measured chewing cycle duration as a mechanical variable that can be collected remotely to: 1) assess how experimental manipulations affect chewing speed in Cebus apella, 2) compare captive chewing cycle durations to that of wild conspecifics, and 3) document sources of variation (beyond experimental manipulation) impacting captive chewing cycle durations. We find that experimental manipulations do increase chewing cycle durations in C. apella by as much as 152 milliseconds (ms) on average. These slower chewing speeds are mainly an effect of anesthesia (and/or restraint), rather than electrode implantation or more invasive surgical procedures. Comparison of captive and wild C. apella suggest there is no novel effect of captivity on chewing speed, although this cannot unequivocally demonstrate that masticatory mechanics are similar in captive and wild individuals. Furthermore, we document significant differences in cycle durations due to inter-individual variation and food type, although duration did not always significantly correlate with mechanical properties of foods. We advocate that the significant reduction in chewing speed be considered as an appropriate qualification when applying the results of laboratory-based feeding studies to adaptive explanations of primate feeding behaviors.

Sex differences in behavioral and corticosterone responses to mild stressors in ICR mice are altered by ovariectomy in peripubertal period

Among rodents, females are generally considered to be highly responsive in terms of emotionality under stressful conditions, and have higher corticosterone levels and activity. In this study, we examined sex differences in mice by evaluating anxiety behaviors and corticosterone responses to mild stressors. In our first experiment, we analyzed the behavioral and corticosterone responses to the elevated plus-maze test and open-field test in male and female mice, and compared sex differences. Principal component analysis (PCA) was used to investigate the correlation of these responses between males and females. The corticosterone level was higher in females under both basal and stressed conditions. In the behavioral response, higher locomotor activity was seen in females in the elevated plus-maze test. PCA showed little association among anxiety behavior, locomotor activity, and corticosterone secretion. In our second experiment, we examined the activational effects of sex steroids on the corticosterone response to the elevated plus-maze test by gonadectomizing male and female mice and using testosterone or estrogen capsules as hormonal replacements. Sex differences at the basal corticosterone level were not altered by the hormonal milieu in adults, however the higher corticosterone level of females in response to stress was diminished by ovariectomy, although replacement with neither testosterone nor estrogen had any effect. These results suggest that the sex difference in novelty exposure observed in the form of a greater hypothalamic-pituitary-adrenal (HPA) axis response in female ICR mice is controlled by ovary-derived factors in adults.

Chronic social instability stress in female rats: a potential animal model for female depression

Epidemiological studies demonstrate that affective disorders are at least twice as common in women as in men, but surprisingly, very few preclinical studies have been conducted on female experimental animals. Therefore, the necessity of developing valid animal models for studying the pathophysiology of stress-related disorders in women is obvious. Chronic social stress has the potential to induce depression in humans and therefore we characterize here a chronic social instability stress paradigm in female rats. This consists of a 4-week period with alternating stressful social situations, including phases of isolation and crowding, in an unpredictable manner. At the physiological level, increased adrenal weight and plasma corticosterone levels indicated hyperactivity of the hypothalamus-pituitary-adrenal axis. Elevated plasma luteinizing hormone and disruption of the estrus cycle together with increased serum prolactin levels revealed disrupted regulation of the hypothalamus-pituitary-gonadal axis. Body temperature regulation was affected during the last week of stress such that stressed rats reduced their body temperature less during the rest phase than the controls, thus exhibiting a flattened temperature curve. Behaviorally, chronically stressed rats showed reduced sucrose preference and food intake. However, we did not observe any effect of stress on performance in the forced swim test and hippocampal neurotrophin levels were similarly unaffected. Our results indicate that, by using this social instability paradigm, female rats can be kept under chronic stress for weeks without habituation, and that ultimately the animals develop a depressive-like phenotype. This model may provide a valuable tool for further analyses of the neurobiology of stress-related disorders in women and has the potential to serve as a paradigm for screening novel antidepressant drugs with special efficacy in women.

Gender differences in corticotropin and corticosterone secretion and corticotropin-releasing factor mRNA expression in the paraventricular nucleus of the hypothalamus and the central nucleus of the amygdala in response to footshock stress or psychological stress in rats

Anorexia nervosa is mostly seen in adolescent females, although the gender-differentiation mechanism is unclear. Corticotropin-releasing factor (CRF), a key peptide for stress responses such as inhibition of food intake, increases in arousal and locomotor activity, and gonadal dysfunction, is thought to be involved in the pathophysiology of anorexia nervosa. CRF in the paraventricular nucleus of the hypothalamus (PVN) and CRF in the central nucleus of the amygdala (CeA) are involved in the regulation of stress responses, and gender differences in CRF mRNA expression in these regions in response to various stressors are controversial. We therefore examined CRF gene expression in the PVN and CeA as well as corticotropin (ACTH) and corticosterone secretion in response to a 60-min period of electric footshock (FS) or psychological stress (PS) induced by a communication box in both male and female rats in proestrus or diestrus in an effort to elucidate the mechanism underlying the gender difference in the activity of the hypothalamic-pituitary-adrenal (HPA) axis and the mechanism underlying the remarkable prevalence of anorexia nervosa in females. Female rats in proestrus showed higher basal plasma ACTH and CRF mRNA expression levels in the PVN and CeA than males. Females more rapidly showed higher plasma ACTH and corticosterone levels and a higher CRF mRNA expression level in the PVN in response to FS than males. Although females in both proestrus and diestrus showed significant increases in plasma ACTH and corticosterone and CRF mRNA expression in the PVN in response to PS, no significant responses of the HPA axis to PS were found in males. FS significantly increased CRF mRNA expression in the CeA in both females and males, with significantly higher peaks in females in proestrus than in males, while PS significantly increased CRF mRNA expression in the CeA only in males. These results suggest that gender affects differentially the function of the stress-related regions such as the PVN and CeA. The finding that CRF gene expression in the PVN responds to PS only in females may be a clue to elucidation of the neurobiological mechanism underlying the gender-differential prevalence of anorexia nervosa.

Chronic social stress, hedonism and vulnerability to obesity: lessons from rodents

Obesity is a current health pandemia. Determinants of this pathology are rather complex and include genetic, developmental and environmental factors only partially disclosed. Stress related neuroendocrine dysregulation and overconsumption of high palatable high caloric food and are likely to contribute to this modern health threats. Despite the evidence that psychosocial stress is one of the main sources of stress in humans and may play an important role in the development of the stress disorders, including obesity and metabolic syndrome, animal models focusing on the relationship between chronic stress and energy homeostasis are scattered and most of them encompasses physical rather than psychosocial stress. Aim of the present paper is to review rodent studies on the effect of psychosocial stress throughout life on body weight and food intake regulation. In the second part of the review special focus will be given on the mechanisms linking stress and the reward system.

Sleep deprivation-induced gnawing—relationship to changes in feeding behavior in rats

We have recently reported that food spillage increases during sleep deprivation in rats, which may lead to an overestimation of food intake in this condition. The objective of this study was to verify whether sleep deprivation induces an increase in gnawing behavior that could account for increased food spillage and apparent increase in food intake. We introduced wood blocks as objects for gnawing and determined the effects of their availability on food consumption and food spillage during sleep deprivation. Wood block availability reduced the amount of food removed from hoppers and decreased the amount of food spilled. However, weight loss still occurred during the sleep deprivation period, especially in the first 24 h, and it was related to a reduction in food intake. Sleep deprivation causes an increase in stereotyped gnawing behavior which largely accounts for increased food spillage observed during deprivation. Specifically, the observed increase in food removed from feeders seems to be due to an increase in gnawing and not to increased hunger. However, even when appropriately corrected for spillage, food intake decreased in the first 24 h of sleep deprivation, which accounted for most of the body weight loss seen during the 96 h of sleep deprivation.

Social defeat and footshock increase body mass and adiposity in male Syrian hamsters

Obesity is a world-wide epidemic, and many factors, including stress, have been linked to this growing trend. After social stress (i.e., defeat), subordinate laboratory rats and most laboratory mice become hypophagic and, subsequently, lose body mass; the opposite is true of subordinate Syrian hamsters. After social defeat, Syrian hamsters become hyperphagic and gain body mass compared with nonstressed controls. It is unknown whether this increase in body mass and food intake is limited to subordinate hamsters. In experiment 1, we asked, do dominant hamsters increase food intake, body mass, and adiposity after an agonistic encounter? Subordinate hamsters increased food intake and body mass compared with nonstressed controls. Although there was no difference in food intake or absolute body mass between dominant and nonstressed control animals, cumulative body mass gain was significantly higher in dominant than in nonstressed control animals. Total carcass lipid and white adipose tissue (WAT) (i.e., retroperitoneal and epididymal WAT) masses were significantly increased in subordinate, but not dominant, hamsters compared with nonstressed controls. In experiment 2, we asked, does footshock stress increase food intake, body mass, and adiposity. Hamsters exposed to defeat, but not footshock stress, increased food intake relative to nonstressed controls. In animals exposed to defeat or footshock stress, body mass, as well as mesenteric WAT mass, increased compared with nonstressed controls. Collectively, these data demonstrate that social and nonsocial stressors increase body and lipid mass in male hamsters, suggesting that this species may prove useful for studying the physiology of stress-induced obesity in some humans.

Anxiety and panic responses to a predator in male and female Ts65Dn mice, a model for Down syndrome

Hyperactivity is a feature frequently reported in behavioral studies on the Ts65Dn (TS) mouse, the most widely accepted model of Down syndrome, when tested in anxiety-provoking situations such as the plus-maze and the open-field tests. Although this behavior could be considered as an expression of reduced anxiety, it has been considered as a consequence of a lack of behavioral inhibition and/or reduced attention. This study addressed anxiety and panic behavior of male and female TS mice by evaluating serum biochemical parameters and behavioral responses to a predator in the Mouse Defense Test Battery. Flight, risk assessment, defensive threat/attack and escape attempts were measured during and after rat confrontation. When confronted to a rat, male TS mice showed similar biochemical and behavioral responses as control mice. However, female control and TS mice presented lower serum adrenocorticotropic hormone (ACTH) levels under basal conditions and higher corticosterone levels after predator exposure than male mice. Thus, there was a larger increase in ACTH and corticosterone levels after predator exposure with respect to the undisturbed condition in females than in males. In addition, TS females showed some alterations in defensive behaviors after predator exposure. The results emphasize the need to consider gender as a confounding factor in the behavioral assessment of TS mice.

Paradoxical sleep deprivation and sleep recovery: effects on the hypothalamic-pituitary-adrenal axis activity, energy balance and body composition of rats

Numerous studies indicate that sleep deprivation alters energy expenditure. However, this conclusion is drawn from indirect measurements. In the present study, we investigated alterations of energy expenditure, body composition, blood glucose levels, plasma insulin, adrenocorticotropic hormone (ACTH) and corticosterone levels immediately after 4 days of sleep deprivation or after 4 days of sleep recovery. Rats were sleep deprived or maintained in a control environment (groups sleep-deprived/deprivation and control/deprivation). One half of these animals were sacrificed at the end of the deprivation period and the other half was transported to metabolic cages, where they were allowed to sleep freely (groups sleep-deprived/recovery and control/recovery). At the end of the sleep recovery period, these rats were sacrificed. After sleep deprivation, sleep-deprived rats exhibited loss of body weight, augmented energy expenditure and reduced metabolic efficiency compared to control rats. These alterations were normalised during the sleep recovery period. The body composition of sleep-deprived rats was altered insofar as there was a loss of fat content and gain of protein content in the carcass compared to control rats. However, these alterations were not reversed by sleep recovery. Finally, plasma levels of insulin were reduced during the sleep deprivation period in both control and sleep deprived groups compared to the recovery period. After the deprivation period, plasma ACTH and corticosterone levels were increased in sleep-deprived rats compared to control rats, and although ACTH levels were similar between the groups after the sleep recovery period, corticosterone levels remained elevated in sleep-deprived rats after this period. By means of direct measurements of metabolism, our results showed that sleep deprivation produces increased energy expenditure and loss of fat content. Most of the alterations were reversed by sleep recovery, except for corticosterone levels and body composition.

Programming the offspring of the pig by prenatal social stress: neuroendocrine activity and behaviour

This study provides evidence in the pig that stress experienced during gestation has long-lasting effects on offspring daughters, including their maternal behaviour. Thirty-six primiparous sows were divided into control and two groups that were stressed (by social mixing) during either the second (Mix 2) or third (Mix 3) trimester of pregnancy. We found detrimental effects of mixing on the mothers' growth, body lesions, and cortisol secretion, but did not observe any significant effects on reproductive parameters including birth weight. At 60 days of age, 48 daughters were randomly selected from the three treatments: half were challenged using a restraint and isolation test. Then, all were culled and brain tissue was collected. In situ hybridisation measurements showed increased expression of CRH mRNA in the PVN in unrestrained Mix 2 and in the amygdala of Mix 2 and Mix 3 daughters. At 67 days, 24 further daughters were mixed to measure their responses to this social stress. All showed increased salivary cortisol secretion, but Mix 2 and Mix 3 daughters showed a greater and longer response than controls. Finally, all 24 were inseminated and at parturition maternal behaviour was measured. Mix 2 and Mix 3 daughters were more restless and more responsive to piglets that approached the head of the sow, traits which previously have been shown to be a component of abnormal maternal behaviour. Indeed, Mix 2 and Mix 3 daughters also tended to bite at their piglets more than control daughters.

Compulsive-like behaviour according to the sex and the reproductive stage of female rats

The aim of the present study was to explore putative differences in the responses assessed in an animal model of obsessive-compulsive disorder (OCD) according to the sex and the reproductive cycle of female rats. The model consists of the induction of perseveration (repetitive choices of the same arm in a T-maze) by 8-OH-DPAT (1.0mg/kg). Males and females (pooled in all stages of their oestrous cycle) persevered after 8-OH-DPAT administration and no differences were observed between groups. During the oestrous cycle, this 5-HT(1A) agonist induced perseveration in metoestrus, dioestrus and prooestrus and reduced levels of this behaviour in oestrus. 8-OH-DPAT provoked perseveration in mid-gestation, an effect that was reduced in late-gestation and blocked during lactation. Reproductive cycle changes in the induced perseveration are discussed from the standpoint of the ovarian steroids' action on the serotoninergic system and on the bases of the variations in stress responsiveness along the reproductive cycle of the female. Present results validate the use of females in this model of OCD and could be relevant for studying the role of reproductive hormones in the pathophysiology of this disorder.

Androgens in the hippocampus can alter, and be altered by, ictal activity

Steroid hormones, such as androgens, can modulate seizure processes. This review summarizes prior research and presents new data that support the role of androgens in modulating seizure processes. Testosterone, the primary endogenous androgen, has antiseizure effects in people and in animal models of epilepsy. Furthermore, testosterone's antiseizure effects may involve actions of its 5alpha-reduced metabolite and neuroactive steroid, 5alpha-androstane-3alpha,17beta-diol (3alpha-diol). The hippocampus is a target for androgen action and is involved in many types of seizure disorder. Data suggest that actions of androgens in the hippocampus may be important for androgens' antiseizure effects. Interestingly, there may also be a reciprocal relationship between androgens and seizures. Ictal activity can alter the gonadal responsiveness of people with epilepsy and in animal models of seizure disorder. Thus, this paper will review data in support of androgens' antiseizure effects. Further understanding of androgens' role in seizure processes is important for potential therapeutic effects.

The effect of stress on menstrual function

Historically difficult to define, stress is, in one sense, the factor that stressors have in common in their impact on the body. Menstrual function is disrupted by stressors that activate the hypothalamic-pituitary-adrenal (HPA) axis; this activation is part of a catabolic response of the whole body that mobilizes metabolic fuels to meet energy demand. Functional menstrual disorders are associated with an increase in cortisol and with a broad spectrum of other symptoms of energy deficiency. Recent experiments suggest that exercise and other stressors have no disruptive effect on reproductive function beyond the impact of their energy cost on energy availability. These studies suggest that treatments for functional menstrual disorders should aim at dietary reform and that stress is simply low energy availability. Future experiments should carefully test this hypothesis.