Social defeat increases food intake, body mass, and adiposity in Syrian hamsters

A hamster model for stress-induced weight gain

This review addresses the translational relevance of animal models of stress and their effects on body weight. In humans, stress, whether chronic or acute, has often been associated with increased food intake and weight gain. In view of the current obesity epidemic, this phenomenon is especially relevant. Such observations contrast with reports with commonly used laboratory animals, especially rats and mice. In these species, it is common to find individuals gaining less weight under stress, even with potent social stressors. However, there are laboratory species that present increased appetite and weight gain under stress, such as golden hamsters. Furthermore, these animals also include metabolic and behavioral similarities with humans, including hoarding behavior which is also enhanced under stress. Consequently, we propose that our comparative perspective provides useful insights for future research on the development of obesity in humans as a consequence of chronic stress exposure.

Incorporating neurological and behavioral mechanisms of sociality into predator-prey models

Consumer-resource population models drive progress in predicting and understanding predation. However, they are often built by averaging the foraging outcomes of individuals to estimate per capita functional responses (functions that describe predation rate). Reliance on per-capita functional responses rests on the assumption that that individuals forage independently without affecting each other. Undermining this assumption, extensive behavioral neuroscience research has made clear that facilitative and antagonistic interactions among conspecifics frequently alter foraging through interference competition and persistent neurophysiological changes. For example, repeated social defeats dysregulates rodent hypothalamic signaling, modulating appetite. In behavioral ecology, similar mechanisms are studied under the concept of dominance hierarchies. Neurological and behavioral changes in response to conspecifics undoubtedly play some sort of role in the foraging of populations, but modern predator-prey theory does not explicitly include them. Here we describe how some modern approaches to population modeling might account for this. Further, we propose that spatial predator-prey models can be modified to describe plastic changes in foraging behavior driven by intraspecific interaction, namely individuals switching between patches or plastic strategies to avoid competition. Extensive neurological and behavioral ecology research suggests that interactions among conspecifics help shape populations' functional responses. Modeling interdependent functional responses woven together by behavioral and neurological mechanisms may thus be indispensable in predicting the outcome of consumer-resource interactions across systems.

Selective targeting of chronic social stress-induced activated neurons identifies neurogenesis-related genes to be associated with resilience in female mice

Prolonged social stress is a major cause for depression in humans and is associated with a wide range of subsequent pathophysiological changes such as elevated blood pressure. A routinely used model for investigating this kind of stress in mice is the chronic social defeat paradigm where a smaller intruder is exposed to an aggressive inhabitant of a home cage. This model is restricted to males and includes a high proportion of physical stress that might e.g., interfere with immunological aspects of the stress. The prevalence of depression in humans is even higher in women than in men. Therefore, expanding models to female individuals is desirable. We here tested the social instability model as a tool for administering chronic social stress to female C57BL/6J mice and analyzed short-term as well as long-lasting effects. Animals were housed in groups of four and were shuffled two times a week, resulting in a permanent re-structuration of their social hierarchy. While directly after the stress exposure, serum corticosterone was elevated, increased body weight and fat deposits were observed in stressed mice even one year after discontinuation of the stress. At the behavioral level, animals could be stratified into resilient and susceptible animals directly post-stress, but those subgroups were not distinguishable any more in the long-term analysis. To identify molecular contributors to resilience in the here presented social instability induced stress model, Arc-activity dependent trapping of neurons was conducted in Arc-creERT2/sun1sfGFP mice. RNA samples derived from activated nuclei from the ventral hippocampus, a brain region involved in stress-regulation during attacks or explorative behavior of mice, were subjected to a neurogenesis pathway array. While several genes were differentially regulated by stress, in particular, artemin, a neurotrophic factor was upregulated in resilient versus susceptible individuals.

Distinct Roles of Distress and Coping Capacity in the Effects of Psychological Stress on Energy Intake and Percentage of Energy from Macronutrients

The aim of this study was to explore the association of perceived stress on energy intake and percentage of energy from macronutrients. We examined cross-sectional data from the China Health and Nutrition Survey among Chinese adults. Perceived stress scale was used to assess psychological stress, and confirmatory factor analysis was used to calculate the two latent variable scores: distress factor and coping factor of perceived stress. Combined two-level random effect model and structural equation modeling were used to explore the association between distress, coping, and energy intake. The study involved 6865 adults with an average age of 46.9 years. The intake of energy was 2047.9 ± 666.6 kcal/d, 51.1% from carbohydrate and 35.2% from fat. Neither distress nor coping capacity had an association with energy intake. The coping factor score was positively associated with the sum of percentage of energy intake from carbohydrate and fat (%C&F) in females (β = 0.149, p = 0.015) but not in males. Compared to the lowest tertile, %C&F of females with a coping factor score in the medium and top tertiles were 0.44 and 0.81 significantly higher, respectively (pmedium = 0.0013, ptop < 0.0001). Psychological stress was positively associated with %C&F in females. It was insufficient capacity to cope with stress that led to unhealthy eating behavior.

Long-term changes of parvalbumin- and somatostatin-positive interneurons of the primary motor cortex after chronic social defeat stress depend on individual stress-vulnerability

Chronic stress is a major risk factor for developing mental illnesses and cognitive deficiencies although stress-susceptibility varies individually. In a recent study, we established the connection between chronic social defeat stress (CSDS) and impaired motor learning abilities accompanied by chronically disturbed structural neuroplasticity in the primary motor cortex (M1) of mice. In this study, we further investigated the long-term effects of CSDS exposure on M1, focusing on the interneuronal cell population. We used repeated CSDS to elicit effects across behavioral, endocrinological, and metabolic parameters in mice. Susceptible and resilient phenotypes were discriminated by symptom load and motor learning abilities were assessed on the rotarod. Structural changes in interneuronal circuits of M1 were studied by immunohistochemistry using parvalbumin (PV+) and somatostatin (SST+) markers. Stress-susceptible mice had a blunted stress hormone response and impaired motor learning skills. These mice presented reduced numbers of both interneuron populations in M1 with layer-dependent distribution, while alterations in cell size and immunoreactivity were found in both susceptible and resilient individuals. These results, together with our previous data, suggest that stress-induced cell loss and degeneration of the GABAergic interneuronal network of M1 could underlay impaired motor learning, due to their role in controlling the excitatory output and spine dynamics of principal neurons required for this task. Our study further highlights the importance of long-term outcomes of chronically stressed individuals which are translationally important due to the long timecourses of stress-induced neuropsychiatric disorders.

Stress, Subordination, and Anomalies of Feeding Across the Tree of Life: Implications for Interpreting Human Eating Disorders

Eating behaviors of animals living in naturalistic environments offer unique insights into several dysregulated eating patterns observed in humans. Social subordination is a known precipitant of hyperphagia and hypophagia in human beings, and examples of similar responses have been identified in a phylogenetically widespread range of vertebral species. This points to potentially conserved, patterned responses to animals navigating lives within social hierarchies. Self-imposed food restriction in subordinate fish and hyperphagic responses in socially subordinated bird and primate individuals may represent evolved adaptations to the stress of social subordination. As such, hyperphagic and hypophagic responses to social subordination in these species may model the natural history, neurobiology, and behavioral ecology of human dieting and bingeing more accurately than some current animal models. Phylogenetically widespread similarities in eating patterns under the stress of social subordination point to potentially shared biological benefits of these behaviors across species and the role of evolutionary trade-offs, adaptations, and other processes in shaping them. The application of a broadly comparative lens to disordered eating behaviors in other species exposes important similarities and differences between neurophysiology of eating across species. In doing so, it highlights the value of phylogenetic analyses and macroevolution as tools for identifying novel, naturally occurring models for understanding disordered human eating. Moreover, this approach introduces the intriguing possibility that human cultural influences on disordered eating may have far more ancient origins than previously considered.

Exposure to food insecurity increases energy storage and reduces somatic maintenance in European starlings (Sturnus vulgaris)

Birds exposed to food insecurity-defined as temporally variable access to food-respond adaptively by storing more energy. To do this, they may reduce energy allocation to other functions such as somatic maintenance and repair. To investigate this trade-off, we exposed juvenile European starlings (Sturnus vulgaris, n = 69) to 19 weeks of either uninterrupted food availability or a regime where food was unpredictably unavailable for a 5-h period on 5 days each week. Our measures of energy storage were mass and fat scores. Our measures of somatic maintenance were the growth rate of a plucked feather, and erythrocyte telomere length (TL), measured by analysis of the terminal restriction fragment. The insecure birds were heavier than the controls, by an amount that varied over time. They also had higher fat scores. We found no evidence that they consumed more food overall, though our food consumption data were incomplete. Plucked feathers regrew more slowly in the insecure birds. TL was reduced in the insecure birds, specifically, in the longer percentiles of the within-individual TL distribution. We conclude that increased energy storage in response to food insecurity is achieved at the expense of investment in somatic maintenance and repair.

Exposure to Vicarious Social Defeat Stress and Western-Style Diets During Adolescence Leads to Physiological Dysregulation, Decreases in Reward Sensitivity, and Reduced Antidepressant Efficacy in Adulthood

A dramatic increase in the prevalence of major depression and diet-related disorders in adolescents has been observed over several decades, yet the mechanisms underlying this comorbidity have only recently begun to be elucidated. Exposure to western-style diet (WSD), high in both fats (45% kcal) and carbohydrates (35% kcal): e.g., high fat diet (HFD), has been linked to the development of metabolic syndrome-like symptoms and behavioral dysregulation in rodents, as similarly observed in the human condition. Because adolescence is a developmental period highlighted by vulnerability to both stress and poor diet, understanding the mechanism(s) underlying the combined negative effects of WSDs and stress on mood and reward regulation is critical. To this end, adolescent male C57 mice were exposed to vicarious social defeat stress (VSDS), a stress paradigm capable of separating physical (PS) versus psychological/emotional (ES) stress, followed by normal chow (NC), HFD, or a separate control diet high in carbohydrates (same sucrose content as HFD) and low in fat (LFD), while measuring body weight and food intake. Non-stressed control mice exposed to 5 weeks of NC or HFD showed no significant differences in body weight or social interaction. Mice exposed to VSDS (both ES and PS) gain weight rapidly 1 week after initiation of HFD, with the ES-exposed mice showing significantly higher weight gain as compared to the HFD-exposed control mice. These mice also exhibited a reduction in saccharin preference, indicative of anhedonic-like behavior. To further delineate whether high fat was the major contributing factor to these deficits, LFD was introduced. The mice in the VSDS + HFD gained weight more rapidly than the VSDS + LFD group, and though the LFD-exposed mice did not gain weight as rapidly as the HFD-exposed mice, both the VSDS + LFD- and VSDS + HFD-exposed mice exhibited attenuated response to the antidepressant fluoxetine. These data show that diets high in both fats and carbohydrates are responsible for rapid weight gain and reduced reward sensitivity; and that while consumption of diet high in carbohydrate and low in fat does not lead to rapid weight gain, both HFD and LFD exposure after stress leads to reduced responsiveness to antidepressant treatment.

Lifelong enhancement of body mass from adolescent stress in male hamsters

In hamsters, exposure to stress in adulthood causes increased body weight. We addressed how social stress during puberty would impact food intake and body weight. Stressed hamsters started gaining significantly more weight than controls after only two days of stress exposure. Over a two-week period, stressed subjects gained 10% more weight and consumed more food than controls. At the end of the stress period, stressed hamsters collected nearly twice as many palatable sugar pellets from an arena than controls. Stressed subjects presented 15-20% more body fat in mesenteric, inguinal, and retroperitoneal fat pads. In order to assess the duration of these effects, we analyzed data from previous studies keeping hamsters for over two months past the stress period in puberty. Our analysis shows that stressed hamsters stopped gaining more weight after the stress period, but their body weights remained elevated for over two months, consistently weighing 10% more than their non-stressed counterparts. We also analyzed conditioning training data collected after the period of stress in late puberty and early adulthood (P56 to P70) that was part of the original studies. Training consisted of lever pressing for palatable food rewards. At these times, previously stressed hamsters retrieved similar numbers of food pellets from the conditioning chambers, suggesting no difference in appetite after the stress period. These data showing a long-lasting effect of stress on body weight may be relevant to studies on the ontogeny of lifelong obesity.

Obesity and dietary fat influence dopamine neurotransmission: exploring the convergence of metabolic state, physiological stress, and inflammation on dopaminergic control of food intake

The aim of this review is to explore how metabolic changes induced by diets high in saturated fat (HFD) affect nucleus accumbens (NAc) dopamine neurotransmission and food intake, and to explore how stress and inflammation influence this process. Recent evidence linked diet-induced obesity and HFD with reduced dopamine release and reuptake. Altered dopamine neurotransmission could disrupt satiety circuits between NAc dopamine terminals and projections to the hypothalamus. The NAc directs learning and motivated behaviours based on homeostatic needs and psychological states. Therefore, impaired dopaminergic responses to palatable food could contribute to weight gain by disrupting responses to food cues or stress, which impacts type and quantity of food consumed. Specifically, saturated fat promotes neuronal resistance to anorectic hormones and activation of immune cells that release proinflammatory cytokines. Insulin has been shown to regulate dopamine neurotransmission by enhancing satiety, but less is known about effects of diet-induced stress. Therefore, changes to dopamine signalling due to HFD warrant further examination to characterise crosstalk of cytokines with endocrine and neurotransmitter signals. A HFD promotes a proinflammatory environment that may disrupt neuronal endocrine function and dopamine signalling that could be exacerbated by the hypothalamic-pituitary-adrenal and κ-opioid receptor stress systems. Together, these adaptive changes may dysregulate eating by changing NAc dopamine during hedonic versus homeostatic food intake. This could drive palatable food cravings during energy restriction and hinder weight loss. Understanding links between HFD and dopamine neurotransmission will inform treatment strategies for diet-induced obesity and identify molecular candidates for targeted therapeutics.

Prolonged chronic social defeat stress promotes less resilience and higher uniformity in depression-like behaviors in adult male mice

Chronic social defeat stress (CSDS) is widely applied to study of depression in rodents. 10-day CSDS was a most commonly employed paradigm but with high resilience ratio (∼30%), producing potential variation in depression-like behavioral symptoms. Whether prolonged period (21 days) of CSDS would promote less resilience and reduce behavioral variability remains unknown. We applied 10-day and 21-day CSDS paradigms to induce mouse model of depression and compared their resilience ratio and behavioral phenotypes. Mice under 21-day CSDS had significantly lower resilience ratio and greater changes in behavioral indicators relative to mice under 10-day CSDS. Behavioral indicators from 21-day CSDS paradigm had higher correlations and better prediction for susceptibility which indicating higher uniformity in behavioral phenotypes. Furthermore, a subset of behavioral indicators in 21-day CSDS had high prediction efficacy and should be first applied to screen susceptibility of CSDS. Thus, our study demonstrates that 21-day CSDS is a more robust paradigm inducing reliable depression-like behaviors relative to 10-day CSDS, and should be preferentially used in rodent studies of depression.

Ingestion of probiotic (Lactobacillus helveticus and Bifidobacterium longum) alters intestinal microbial structure and behavioral expression following social defeat stress

Social stress exacerbates anxious and depressive behaviors in humans. Similarly, anxiety- and depressive-like behaviors are triggered by social stress in a variety of non-human animals. Here, we tested whether oral administration of the putative anxiolytic probiotic strains Lactobacillus helveticus R0052 and Bifidobacterium longum R0175 reduces the striking increase in anxiety-like behavior and changes in gut microbiota observed following social defeat stress in Syrian hamsters. We administered the probiotic at two different doses for 21 days, and 16S rRNA gene amplicon sequencing revealed a shift in microbial structure following probiotic administration at both doses, independently of stress. Probiotic administration at either dose increased anti-inflammatory cytokines IL-4, IL-5, and IL-10 compared to placebo. Surprisingly, probiotic administration at the low dose, equivalent to the one used in humans, significantly increased social avoidance and decreased social interaction. This behavioral change was associated with a reduction in microbial richness in this group. Together, these results demonstrate that probiotic administration alters gut microbial composition and may promote an anti-inflammatory profile but that these changes may not promote reductions in behavioral responses to social stress.

Molecular and neurocircuitry mechanisms of social avoidance

Humans and animals live in social relationships shaped by actions of approach and avoidance. Both are crucial for normal physical and mental development, survival, and well-being. Active withdrawal from social interaction is often induced by the perception of threat or unpleasant social experience and relies on adaptive mechanisms within neuronal networks associated with social behavior. In case of confrontation with overly strong or persistent stressors and/or dispositions of the affected individual, maladaptive processes in the neuronal circuitries and its associated transmitters and modulators lead to pathological social avoidance. This review focuses on active, fear-driven social avoidance, affected circuits within the mesocorticolimbic system and associated regions and a selection of molecular modulators that promise translational potential. A comprehensive review of human research in this field is followed by a reflection on animal studies that offer a broader and often more detailed range of analytical methodologies. Finally, we take a critical look at challenges that could be addressed in future translational research on fear-driven social avoidance.

Protective Effect of Sphaerococcus coronopifolius Crude Extract in Combination with Bacillus Calmette-Guerin on Ligature-Induced Depression in Female Wistar Rats

OBJECTIVE

Immunomodulation is a therapeutic technique that modulates the balance of cytokines in the body. In this regard, our experiment was conducted to investigate the potential effect of S. coronopifolius crude extract in combination with low dose of Bacillus Calmette-Guerin (BCG) on depression-like behaviors in female Wistar rats.

METHODS

Sciatic nerve injury was employed to induce depression and intradermal injection of 0.02 mL of BCG per rat was administered to lead an activation of innate immune system. Daily intra-peritoneal injections of 25 mg algae extract kg-1 body weight were performed for 14 continuous days. Forced Swimming (FS) and Open Field (OF) tests were conducted to assess despairing and spontaneous behaviors. At the end of the experiment, brain was removed to determine the activities of catalase (CAT) and glutathione-S-transferase (GST), whereas spleen and adrenals were used for the histopathological study.

RESULTS

The combined treatment exhibited antidepressant-like activity in FST by reducing immobility time, without inducing any significant change in ambulatory behavior in OFT. The histological analyses of spleen and adrenal structure showed a conserved architecture.

CONCLUSION

The results suggested that algae extract produce an antidepressant-like effect in combination with low dose of BCG, which is possibly trigged by its anti-oxidant and anti-inflammatory properties.

A tale of two islands: evidence for impaired stress response and altered immune functions in an insular pit viper following ecological disturbance

The frequency and intensity of ecological perturbations affecting wild animal populations is expected to increase in the future with animals facing numerous global threats. Seahorse Key is a continental island off mainland Florida that has historically been a major rookery for several species of waterbirds. As a result of an unknown disturbance, the entire rookery abandoned Seahorse Key in April 2015 and shifted nesting activities to nearby Snake Key, resulting in an influx of food resources in the form of fish carrion to resident Florida cottonmouth snakes (Agkistrodon conanti), while snakes on Seahorse Key experienced a drastic reduction in food resources. Our objective was to assess plasma corticosterone concentrations, corticosterone negative feedback using dexamethasone, blood glucose, body condition, packed cell volume, natural antibody agglutination, white blood cell counts and ratios and erythrocyte sedimentation rate to characterize the long-term effects of differential resource availability in these two snake populations 3 years after this major ecological disturbance. We collected blood samples at three time points from cottonmouths on Seahorse Key (n = 6 individuals) and Snake Key (n = 13 individuals) in fall 2018. In due consideration of the small sample size, our study shows evidence that 3 years after the shift in waterbird nesting Seahorse Key cottonmouths exhibit a dampened acute stress response and presumptive impaired innate immune functions relative to cottonmouths on Snake Key. These results highlight the context-dependent nature of biomarkers and implicate the significant decrease in food resources on Seahorse Key in altering hormonal stress responses and innate immune functions, possibly leading to unknown long-term downstream effects. This study assessed the response of a wild population of pit viper to ecological disturbance in situ with the aim to improve our understanding of how animals cope with such perturbations and improve our capacity to make informed decisions for conservation.

Metformin ameliorates stress-induced depression-like behaviors via enhancing the expression of BDNF by activating AMPK/CREB-mediated histone acetylation

BACKGROUND

Metformin, a first-line antiglycemic drug, has been reported to have anti-depressant effects in patients with type 2 diabetes; however, its exact role and underlying mechanism still need to be investigated.

METHOD

C57BL/6J mice were subjected to the Chronic social defeat stress (SDS) and drug administration (Control + Vehicle, SDS + Vehicle, SDS + MET (200 mg kg^-1), SDS + FLUOX (3 mg kg^-1), SDS + MET + FLUOX). And the depression phenotypes were evaluated by the sucrose preference test, social interaction, tail suspension test and forced swimming test. The potential mechanisms underlying the effects of metformin on depression was discussed by using Chromatin immunoprecipitation, Quantitative real-time PCR mRNA expression analysis and Western blot in vivo and in primary cultured hippocampal neurons.

RESULT

The metformin treatment counteracted the development of depression-like behaviors in mice suffering SDS when administered alone and enhanced the anti-depressant effect of fluoxetine when combined with fluoxetine. Further RNA sequencing analysis revealed that metformin treatment prevented the transcriptional changes in the medial prefrontal cortex (mPFC) of the animals and Golgi staining indicated favorable morphological changes in the neurite plasticity of CA1 pyramidal neurons, which approximated to those found in unstressed mice. At a molecular level, metformin significantly upregulated the expression of the brain-derived neurotrophic factor (BDNF) by increasing the histone acetylation along with the BDNF promoter, which was attributed to the activation of AMP-activated protein kinase (AMPK) and cAMP-response element binding protein (CREB).

CONCLUSION

Our findings suggest that metformin can produce antidepressant effects, which provides empirical insights into the clinical value of metformin in the prevention and therapy of depression.

Foraging dynamics are associated with social status and context in mouse social hierarchies

Living in social hierarchies requires individuals to adapt their behavior and physiology. We have previously shown that male mice living in groups of 12 form linear and stable hierarchies with alpha males producing the highest daily level of major urinary proteins and urine. These findings suggest that maintaining alpha status in a social group requires higher food and water intake to generate energetic resources and produce more urine. To investigate whether social status affects eating and drinking behaviors, we measured the frequency of these behaviors in each individual mouse living in a social hierarchy with non-stop video recording for 24 h following the initiation of group housing and after social ranks were stabilized. We show alpha males eat and drink most frequently among all individuals in the hierarchy and had reduced quiescence of foraging both at the start of social housing and after hierarchies were established. Subdominants displayed a similar pattern of behavior following hierarchy formation relative to subordinates. The association strength of foraging behavior was negatively associated with that of agonistic behavior corrected for gregariousness (HWIG), suggesting animals modify foraging behavior to avoid others they engaged with aggressively. Overall, this study provides evidence that animals with different social status adapt their eating and drinking behaviors according to their physiological needs and current social environment.

Evolutionary considerations on social status, eating behavior, and obesity

Lower socioeconomic status (SES) is consistently related to higher obesity risk, especially in women living in developed countries such as the United States and Western Europe. Prevailing theories to describe this relationship have focused primarily on proximate level factors such as the generally poorer food environment (e.g. relative lack of healthy food options and higher concentrations of fast food restaurants) found in lower vs. higher SES neighborhoods and the higher financial costs associated with purchasing healthy, nutrient-dense foods compared to unhealthy, energy-dense foods. These factors are hypothesized to preclude the purchase of these foods by lower SES individuals. Unfortunately, public health interventions aimed at improving the food environment of lower SES communities and to provide financial resources for purchasing healthy foods have had limited success in reducing overall energy intake and body weight. Some evidence suggests these interventions may even exacerbate obesity. More recent hypotheses have shifted the focus to ultimate (or adaptive) factors that view increased energy intake and accrual of body fat among individuals of lower social status as adaptive strategies to protect against potential prolonged food scarcity. The purpose of this review is integrate past research at the proximate and ultimate levels with a consideration of how social status and SES during development (in utero through adolescence) may moderate the relationships between social status, eating behavior, and obesity. Utilizing an evolutionary framework that incorporates life history theory can lead to more integrative and thorough interpretations of past research and allow researchers to better elucidate the complex set of environmental, physiological, psychological, and behavioral factors that influence obesity risk among individuals of lower social status.

Social Defeat Stress, Sex, and Addiction-Like Behaviors

Social confrontation is a form of social interaction in animals where two conspecific individuals confront each other in dispute over territory, during the formation of hierarchies, and during breeding seasons. Typically, a social confrontation involves a prevailing individual and a yielding individual. The prevailing individual often exhibits aggressive postures and launches attacks, whereas the yielding individual often adopts postures of defeat. The yielding or defeated animals experience a phenomenon known as social defeat stress, in which they show exaggerated stress as well as autonomic and endocrine responses that cause impairment of both the brain and body. In laboratory settings, one can reliably generate social defeat stress by allowing a naïve (or already defeated) animal to intrude into a home cage in which its resident has already established a territory or is nursing. This resident-intruder paradigm has been widely used in both males and females to study mechanisms in the brain that underlie the stress responses. Stress has profound effects on drug reward for cocaine, methamphetamine, alcohol, and opioids. Particularly, previous experiences with social defeat can exaggerate subsequent addiction-like behaviors. The extent of these addiction-like behaviors depends on the intensity, duration, frequency, and intermittency of the confrontation episodes. This chapter describes four types of social defeat stress: acute, repeated, intermittent, and chronic. Specifically, it focuses on social defeat stress models used in laboratories to study individual, sex, and animal strain differences in addiction-like behaviors.

Diet matters: Glucocorticoid-related neuroadaptations associated with calorie intake in female rhesus monkeys

Exposure to psychosocial stressors increases consumption of palatable, calorically dense diets (CDD) and the risk for obesity, especially in females. While consumption of an obesogenic diet and chronic stress have both been shown to decrease dopamine 2 receptor (D2R) binding and alter functional connectivity (FC) within the prefrontal cortex (PFC) and the nucleus accumbens (NAcc), it remains uncertain how social experience and dietary environment interact to affect reward pathways critical for the regulation of motivated behavior. Using positron emission tomography (PET) and resting state functional connectivity magnetic resonance neuroimaging (rs-fMRI), in female rhesus monkeys maintained in a low calorie chow (n = 18) or a dietary choice condition (chow and a CDD; n = 16) for 12 months, the current study tested the overarching hypothesis that the adverse social experience resulting from subordinate social status would interact with consumption of an obesogenic diet to increase caloric intake that would be predicted by greater cortisol, lower prefrontal D2R binding potential (D2R-BP) and lower PFC-NAcc FC. Results showed that the consequences of adverse social experience imposed by chronic social subordination vary significantly depending on the dietary environment and are associated with alterations in prefrontal D2R-BP and FC in NAcc-PFC sub-regions that predict differences in caloric intake, body weight gain, and fat accumulation. Higher levels of cortisol in the chow-only condition were associated with mild inappetence, as well as increased orbitofrontal (OFC) D2R-BP and greater FC between the NAcc and the dorsolateral PFC (dlPFC) and ventromedial PFC (vmPFC). However, increased cortisol release in females in the dietary choice condition was associated with reduced prefrontal D2R-BP, and opposite FC between the NAcc and the vmPFC and dlPFC observed in the chow-only females. Importantly, the degree of these glucocorticoid-related neuroadaptations predicted significantly more total calorie intake as well as more consumption of the CDD for females having a dietary choice, but had no relation to calorie intake in the chow-only condition. Overall, the current findings suggest that dietary environment modifies the consequences of adverse social experience on reward pathways and appetite regulation and, in an obesogenic dietary environment, may reflect impaired cognitive control of food intake.

Low subjective socioeconomic status stimulates orexigenic hormone ghrelin - A randomised trial

Recent evidence suggests that lower perceived socioeconomic status is linked to increased appetite and intake of greater calories. Yet, whether insecurity of socioeconomic resources directly influences regulatory systems of appetite and energy intake is not known. Considering psychological states, mindsets and beliefs have shown to meaningfully affect physiological responses to food, the present study tested the hypothesis that low subjective socioeconomic status (SSS) will have a direct influence on physiological responses, such as appetite-related hormones (ghrelin, pancreatic polypeptide and insulin). Forty-eight healthy males were randomly (crossover, counterbalanced) assigned, to two experimental conditions where participants were either experimentally induced to feel low SSS or not (control; CON). Feelings of low SSS resulted in an increase in active ghrelin (an orexigenic hormone) following the SSS manipulation compared with baseline, while no change in active ghrelin was observed in CON. Furthermore, participants reported lower fullness and satiety following low SSS compared with CON. Our findings demonstrate that SSS may influence hunger regulation and appetite, and suggest that physiological systems regulating energy balance (i.e. caloric resources) may also be sensitive to perceived deprivation or imbalances in critical non-food resources (socioeconomic resources).

Effect of Notoginsenoside R1 on autologous adipose graft in rats

Autologous fat particle transplantation has been widely used by surgeons. The present study evaluated the effect of Notoginsenoside R1 (NR1) treatment on rat autologous fat graft, along with the quality and retention rates. Male Sprague‑Dawley rats (n=60) received fat particle auto‑transplantation from the left abdominal cavity into lateral dorsum. A total of 14 days after surgery, NR1 in different doses (50, 100 and 200 mg/kg/day) was injected into rats, following which blood and fat graft samples were harvested at days 7, 14 and 28. Assessments were carried out by hematoxylin and eosin staining, western blotting, ELISA and immunohistochemistry (IHC). The survival rate of fat grafts was increased in three experimental groups, as detected by weight measurement. Histological scoring demonstrated that there were significant differences in tissue integrity between the 100 mg/kg/day group and the other 3 groups. hepatocyte growth factor, vascular endothelial growth factor, fibroblast growth factor, angiotensin and S100 levels in the 100 mg/kg/day NR1 group was increased compared with the other 2 treatment groups; however, all 3 treatment groups demonstrated increased expression of these proteins compared with the control group. Additionally, cluster of differentiation (CD)68 exhibited negative expression and CD31 showed weakly positive expression in all three experiments, as assessed by IHC. In conclusion, 100 mg/kg/day NR1 may potentially promote the retention rate and enhance the quality of autologous fat grafts via increasing vascularity in the recipient site. These results implicate NR1 as a therapeutic strategy for the improvement of outcome following fat graft surgery.

Social housing and social isolation: Impact on stress indices and energy balance in male and female Syrian hamsters (Mesocricetus auratus)

Although Syrian hamsters are thought to be naturally solitary, recent evidence from our laboratory demonstrates that hamsters may actually prefer social contact. Hamsters increase their preference for a location associated with an agonistic encounter regardless of whether they have "won" or "lost". It has also been reported that social housing as well as exposure to intermittent social defeat or to a brief footshock stressor increase food intake and body mass in hamsters. By contrast, it has also been suggested that housing hamsters in social isolation causes anxiety-induced anorexia and reductions in body mass selectively in females. The purpose of this study was to determine the physiological consequences of housing hamsters in social isolation versus in social groups. Male and female hamsters were housed singly or in stable groups of 5 for 4weeks after which they were weighed and trunk blood was collected. In addition, fat pads and thymus and adrenal glands were extracted and weighed. Serum and fecal cortisol were measured using an enzyme-linked immunoassay. Housing condition had no effect on serum or fecal cortisol, but socially housed hamsters displayed modest thymus gland involution. Socially housed females weighed more than did any other group, and socially housed females and males had more fat than did socially isolated hamsters. No wounding or tissue damage occurred in grouped hamsters. Overall, these data suggest that Syrian hamsters tolerate both stable social housing and social isolation in the laboratory although social housing is associated with some alteration in stress-related and bioenergetic measures.

Obesity induction in hamster that mimics the human clinical condition

Although obesity is well established in hamsters, studies using diets with high levels of simple carbohydrate associated with lipids are necessary to assess the impact of this type of food in the body. In this study a high sugar and butter diet (HSB) and high temperature were employed towards this end. Obesity was successfully induced at a temperature of 30.3°C to 30.9°C after 38 days feeding the animals an HSB diet. It was shown that although diet is important for the induction of obesity, temperature is also essential because at a temperature slightly below the one required, obesity was not induced, even when the animals were fed for a longer period (150 days).The obese clinical condition was accompanied by biochemical and hematological changes, as increased cholesterol and triglyceride levels and increased leukocyte numbers, similar to alterations observed in obese humans. Furthermore, it was demonstrated that increasing the intake of simple carbohydrates associated with lipids provided evidence of inflammation in obese animals.

Increased intake of energy-dense diet and negative energy balance in a mouse model of chronic psychosocial defeat

PURPOSE

Chronic exposure to stress may represent a risk factor for developing metabolic and eating disorders, mostly driven by the overconsumption of easily accessible energy-dense palatable food, although the mechanisms involved remain still unclear. In this study, we used an ethologically oriented murine model of chronic stress caused by chronic psychosocial defeat (CPD) to investigate the effects of unrestricted access to a palatable high fat diet (HFD) on food intake, body weight, energy homeostasis, and expression of different brain neuropeptides. Our aim was to shed light on the mechanisms responsible for body weight and body composition changes due to chronic social stress.

METHODS

In our model of subordinate (defeated), mice (CPD) cohabitated in constant sensory contact with dominants, being forced to interact on daily basis, and were offered ad libitum access either to an HFD or to a control diet (CD). Control mice (of the same strain as CPD mice) were housed in pairs and left unstressed in their home cage (UN). In all these mice, we evaluated body weight, different adipose depots, energy metabolism, caloric intake, and neuropeptide expression.

RESULTS

CPD mice increased the intake of HFD and reduced body weight in the presence of enhanced lipid oxidation. Resting energy expenditure and interscapular brown adipose tissue (iBAT) were increased in CPD mice, whereas epididymal adipose tissue increased only in HFD-fed unstressed mice. Propiomelanocortin mRNA levels in hypothalamic arcuate nucleus increased only in HFD-fed unstressed mice. Oxytocin mRNA levels in the paraventricular nucleus and neuropeptide Y mRNA levels within the arcuate were increased only in CD-fed CPD mice. In the arcuate, CART was increased in HFD-fed UN mice and in CD-fed CPD mice, while HFD intake suppressed CART increase in defeated animals. In the basolateral amygdala, CART expression was increased only in CPD animals on HFD.

CONCLUSIONS

CPD appears to uncouple the intake of HFD from energy homeostasis causing higher HFD intake, larger iBAT accumulation, increased energy expenditure and lipid oxidation, and lower body weight. Overall, the present study confirms the notion that the chronic activation of the stress response can be associated with metabolic disorders, altered energy homeostasis, and changes of orexigenic and anorexigenic signaling. These changes might be relevant to better understand the etiology of stress-induced obesity and eating disorders and might represent a valid therapeutic approach for the development of new therapies in this field.

Mere experience of low subjective socioeconomic status stimulates appetite and food intake

Among social animals, subordinate status or low social rank is associated with increased caloric intake and weight gain. This may reflect an adaptive behavioral pattern that promotes acquisition of caloric resources to compensate for low social resources that may otherwise serve as a buffer against environmental demands. Similarly, diet-related health risks like obesity and diabetes are disproportionately more prevalent among people of low socioeconomic resources. Whereas this relationship may be associated with reduced financial and material resources to support healthier lifestyles, it remains unclear whether the subjective experience of low socioeconomic status may alone be sufficient to stimulate consumption of greater calories. Here we show that the mere feeling of lower socioeconomic status relative to others stimulates appetite and food intake. Across four studies, we found that participants who were experimentally induced to feel low (vs. high or neutral) socioeconomic status subsequently exhibited greater automatic preferences for high-calorie foods (e.g., pizza, hamburgers), as well as intake of greater calories from snack and meal contexts. Moreover, these results were observed even in the absence of differences in access to financial resources. Our results demonstrate that among humans, the experience of low social class may contribute to preferences and behaviors that risk excess energy intake. These findings suggest that psychological and physiological systems regulating appetite may also be sensitive to subjective feelings of deprivation for critical nonfood resources (e.g., social standing). Importantly, efforts to mitigate the socioeconomic gradient in obesity may also need to address the psychological experience of low social status.

Repeated, Intermittent Social Defeat across the Entire Juvenile Period Resulted in Behavioral, Physiological, Hormonal, Immunological, and Neurochemical Alterations in Young Adult Male Golden Hamsters

The developing brain is vulnerable to social defeat during the juvenile period. As complements of human studies, animal models of social defeat provide a straightforward approach to investigating the functional and neurobiological consequences of social defeats. Taking advantage of agonist behavior and social defeat in male golden hamster, a set of 6 experiments was conducted to investigate the consequences at multiple levels in young adulthood resulting from repeated, intermittent social defeats or “social threats” across the entire juvenile period. Male hamsters at postnatal day 28 (P28) were randomly assigned to either the social defeat, “social threat”, or arena control group, and they correspondingly received a series of nine social interaction trials (i.e., either social defeat, “social threat”, or arena control conditions) from P33 to P66. At the behavioral level (Experiment 1), we found that repeated social defeats (but not “social threats”) significantly impacted locomotor activity in the familiar context and social interaction in the familiar/unfamiliar social contexts. At the physiological and hormonal levels (Experiments 2 and 3), repeated social defeat significantly enhanced the cortisol and norepinephrine concentrations in blood. Enlargement of the spleen was also found in the social defeat and “social threat” groups. At the immunological level (Experiment 4), the social defeat group showed lower levels of pro-inflammatory cytokines in the hypothalamus and hippocampus but higher concentration of IL-6 in the striatum compared to the other two groups. At the neurochemical level (Experiment 5), the socially defeated hamsters mainly displayed reductions of dopamine, dopamine metabolites, and 5-HT levels in the striatum and decreased level of 5-HT in the hippocampus. In Experiment 6, an increase in the spine density of hippocampal CA1 pyramidal neurons was specifically observed in the “social threat” group. Collectively, our findings indicate that repeated, intermittent social defeats throughout entire adolescence in hamsters impact their adult responses at multiple levels. Our results also suggest that the “social threat” group may serve as an appropriate control. This study further suggest that the alterations of behavioral responses and neurobiological functions in the body and brain might provide potential markers to measure the negative consequences of chronic social defeats.

Stress-induced alterations in estradiol sensitivity increase risk for obesity in women

The prevalence of obesity in the United States continues to rise, increasing individual vulnerability to an array of adverse health outcomes. One factor that has been implicated causally in the increased accumulation of fat and excess food intake is the activity of the limbic-hypothalamic-pituitary-adrenal (LHPA) axis in the face of relentless stressor exposure. However, translational and clinical research continues to understudy the effects sex and gonadal hormones and LHPA axis dysfunction in the etiology of obesity even though women continue to be at greater risk than men for stress-induced disorders, including depression, emotional feeding and obesity. The current review will emphasize the need for sex-specific evaluation of the relationship between stress exposure and LHPA axis activity on individual risk for obesity by summarizing data generated by animal models currently being leveraged to determine the etiology of stress-induced alterations in feeding behavior and metabolism. There exists a clear lack of translational models that have been used to study female-specific risk. One translational model of psychosocial stress exposure that has proven fruitful in elucidating potential mechanisms by which females are at increased risk for stress-induced adverse health outcomes is that of social subordination in socially housed female macaque monkeys. Data from subordinate female monkeys suggest that increased risk for emotional eating and the development of obesity in females may be due to LHPA axis-induced changes in the behavioral and physiological sensitivity of estradiol. The lack in understanding of the mechanisms underlying these alterations necessitate the need to account for the effects of sex and gonadal hormones in the rationale, design, implementation, analysis and interpretation of results in our studies of stress axis function in obesity. Doing so may lead to the identification of novel therapeutic targets with which to combat stress-induced obesity exclusively in females.

Chronic and acute effects of stress on energy balance: are there appropriate animal models?

Stress activates multiple neural and endocrine systems to allow an animal to respond to and survive in a threatening environment. The corticotropin-releasing factor system is a primary initiator of this integrated response, which includes activation of the sympathetic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis. The energetic response to acute stress is determined by the nature and severity of the stressor, but a typical response to an acute stressor is inhibition of food intake, increased heat production, and increased activity with sustained changes in body weight, behavior, and HPA reactivity. The effect of chronic psychological stress is more variable. In humans, chronic stress may cause weight gain in restrained eaters who show increased HPA reactivity to acute stress. This phenotype is difficult to replicate in rodent models where chronic psychological stress is more likely to cause weight loss than weight gain. An exception may be hamsters subjected to repeated bouts of social defeat or foot shock, but the data are limited. Recent reports on the food intake and body composition of subordinate members of group-housed female monkeys indicate that these animals have a similar phenotype to human stress-induced eaters, but there are a limited number of investigators with access to the model. Few stress experiments focus on energy balance, but more information on the phenotype of both humans and animal models during and after exposure to acute or chronic stress may provide novel insight into mechanisms that normally control body weight.

Ecoimmunology for psychoneuroimmunologists: Considering context in neuroendocrine-immune-behavior interactions

The study of immunity has become an important area of investigation for researchers in a wide range of areas outside the traditional discipline of immunology. For the last several decades, psychoneuroimmunology (PNI) has strived to identify key interactions among the nervous, endocrine and immune systems and behavior. More recently, the field of ecological immunology (ecoimmunology) has been established within the perspectives of ecology and evolutionary biology, sharing with PNI an appreciation of the environmental influences on immune function. The primary goal of ecoimmunology is to understand immune function within a broadly integrative, organismal context, typically from an ultimate, evolutionary perspective. To accomplish this ecoimmunology, like PNI, has become a broadly integrative field of investigation, combining diverse approaches from evolution and ecology to endocrinology and neurobiology. The disciplines of PNI and ecoimmunology, with their unique yet complementary perspectives and methodologies, have much to offer one another. Researchers in both fields, however, remain largely unaware of each other's findings despite attempts at integration. The goal of this review is to share with psychoneuroimmunologists and other mechanistically-oriented researchers some of the core concepts and principles, as well as relevant recent findings, within ecoimmunology with the hope that this information will prove relevant to their own research programs. More broadly, our goal is to attempt to integrate both the proximate and ultimate perspectives offered by PNI and ecoimmunology respectively into a common theoretical framework for understanding neuro-endocrine-immune interactions and behavior in a larger ecological, evolutionary context.

To stress or not to stress: a question of models

Stress research is a rapidly evolving field that encompasses numerous disciplines ranging from neuroscience to metabolism. With many new researchers migrating into the field, navigating the hows and whys of specific research questions can sometimes be enigmatic given the availability of so many models in the stress field. Additionally, as with every field, there are many seemingly minor experimental details that can have dramatic influences on data interpretation, although many of these are unknown to those not familiar with the field. The aim of this overview is to provide some suggestions and points to guide researchers moving into the stress field and highlight relevant methodological points that they should consider when choosing a model for stress and deciding how to structure a study. We briefly provide a primer on the basics of endpoint measurements in the stress field, factors to consider when choosing a model for acute stress, the difference between repeated and chronic stress, and importantly, influencing variables that modulate endpoints of analysis in stress work.

Social overcrowding as a chronic stress model that increases adiposity in mice

Stress is a widely recognized risk factor for psychiatric and metabolic disorders. A number of animal models utilizing various stressors have been developed to facilitate our understanding in the pathophysiology of stress-related dysfunctions. The most commonly used chronic stress paradigms include the unpredictable chronic mild stress paradigm, the social defeat paradigm and the social deprivation paradigm. Here we assess the potential of social crowding as an alternative chronic stress model to study the effects on affective behaviors and metabolic disturbances. Ten-week-old male C57BL/6 mice were housed in groups of four (control) or eight (social crowding; SC) in standard cage for 9 weeks. Exploration, anxiety- and depressive-like behaviors were assessed in the open field test, the elevated T-maze, the novelty-suppressed feeding test and the forced swim test. SC mice exhibited a modest anxiety-like phenotype without change in depressive-like behaviors. Nine weeks of social crowding did not affect the body weight, but robustly increased adiposity as determined by increased mass of fat depots. Consistent with the increased fat content, serum leptin was markedly elevated in the SC mice. Specific changes in gene expression were also observed in the hypothalamus and the white adipose tissue following SC housing. Our study demonstrates the potential of social crowding as an alternative model for the study of stress-related metabolic and behavioral dysfunctions.

Rethinking animal models and human obesity

Human obesity is a complex phenomenon where economic, cultural, behavioral, and biological factors intersect in the physiological space. Developing animal models that capture several elements of the many potential interactions between these factors will only increase their translational value.

Controversies about a common etiology for eating and mood disorders

Obesity and depression represent a growing health concern worldwide. For many years, basic science and medicine have considered obesity as a metabolic illness, while depression was classified a psychiatric disorder. Despite accumulating evidence suggesting that obesity and depression may share commonalities, the causal link between eating and mood disorders remains to be fully understood. This etiology is highly complex, consisting of multiple environmental and genetic risk factors that interact with each other. In this review, we sought to summarize the preclinical and clinical evidence supporting a common etiology for eating and mood disorders, with a particular emphasis on signaling pathways involved in the maintenance of energy balance and mood stability, among which orexigenic and anorexigenic neuropeptides, metabolic factors, stress responsive hormones, cytokines, and neurotrophic factors.

Establishment of stable dominance interactions in prairie vole peers: relationships with alcohol drinking and activation of the paraventricular nucleus of the hypothalamus

Dominance hierarchies are an important aspect of group-living as they determine individual access to resources. The existence of dominance ranks in access to space has not been described in socially monogamous, communally nesting prairie voles (Microtus ochrogaster). Here, we tested whether dominance could be assessed using the tube test. We also tested whether dominance related to alcohol intake, similar to what has been demonstrated in nonmonogamous species. Same-sex pairs of unfamiliar peers were tested in a series of three trials of the tube test, then paired and allowed individual access to alcohol and water for 4 days, and then tested again in the tube test. For all pairs, the same subjects won the majority of trials before and after alcohol drinking. The number of wins negatively correlated with alcohol intake on the first day of drinking and positively correlated with levels of Fos in the paraventricular nucleus of the hypothalamus following the tube test in a separate group of voles. Dominance was not related to Fos levels in other brain regions examined. Together, these results indicate that prairie voles quickly establish stable dominance ranks through a process possibly involving the hypothalamus and suggest that dominance is linked to alcohol drinking.

Executive and modulatory neural circuits of defensive reactions: implications for panic disorder

The present review covers two independent approaches, a neuroanatomical and a pharmacological (focused on serotonergic transmission), which converge in highlighting the critical role of the hypothalamus and midbrain periaqueductal gray matter in the generation of panic attacks and in the mechanism of action of current antipanic medication. Accordingly, innate and learned fear responses to different threats (i.e., predator, aggressive members of the same species, interoceptive threats and painful stimuli) are processed by independent circuits involving corticolimbic regions (the amygdala, the hippocampus and the prefrontal and insular cortices) and downstream hypothalamic and brainstem circuits. As for the drug treatment, animal models of panic indicate that the drugs currently used for treating panic disorder should work by enhancing 5-HT inhibition of neural systems that command proximal defense in both the dorsal periaqueductal gray and in the medial hypothalamus. For the anticipatory anxiety, the reviewed evidence points to corticolimbic structures, such as the amygdala, the septo-hippocampus and the prefrontal cortex, as its main neural substrate, modulated by stimulation of 5-HT2C and 5-HT1A receptors.

Psychosocial stress induces hyperphagia and exacerbates diet-induced insulin resistance and the manifestations of the Metabolic Syndrome

Stress and hypercaloric food are recognized risk factors for obesity, Metabolic Syndrome (MetS) and Type 2 Diabetes (T2D). Given the complexity of these metabolic processes and the unavailability of animal models, there is poor understanding of their underlying mechanisms. We established a model of chronic psychosocial stress in which subordinate mice are vulnerable to weight gain while dominant mice are resilient. Subordinate mice fed a standard diet showed marked hyperphagia, high leptin, low adiponectin, and dyslipidemia. Despite these molecular signatures of MetS and T2D, subordinate mice fed a standard diet were still euglycemic. We hypothesized that stress predisposes subordinate mice to develop T2D when synergizing with other risk factors. High fat diet aggravated dyslipidemia and the MetS thus causing a pre-diabetes-like state in subordinate mice. Contrary to subordinates, dominant mice were fully protected from stress-induced metabolic disorders when fed both a standard- and a high fat-diet. Dominant mice showed a hyperphagic response that was similar to subordinate but, unlike subordinates, showed a significant increase in VO2, VCO2, and respiratory exchange ratio when compared to control mice. Overall, we demonstrated a robust stress- and social status-dependent effect on the development of MetS and T2D and provided insights on the physiological mechanisms. Our results are reminiscent of the effect of the individual socioeconomic status on human health and provide an animal model to study the underlying molecular mechanisms.

Stress and eating: a dual role for bombesin-like peptides

The current obesity “epidemic” in the developed world is a major health concern; over half of adult Canadians are now classified as overweight or obese. Although the reasons for high obesity rates remain unknown, an important factor appears to be the role stressors play in overconsumption of food and weight gain. In this context, increased stressor exposure and/or perceived stress may influence eating behavior and food choices. Stress-induced anorexia is often noted in rats exposed to chronic stress (e.g., repeated restraint) and access to standard Chow diet; associated reduced consumption and weight loss. However, if a similar stressor exposure takes place in the presence of palatable, calorie dense food, rats often consume an increase proportion of palatable food relative to Chow, leading to weight gain and obesity. In humans, a similar desire to eat palatable or “comfort” foods has been noted under stressful situations; it is thought that this response may potentially be attributable to stress-buffering properties and/or through activation of reward pathways. The complex interplay between stress-induced anorexia and stress-induced obesity is discussed in terms of the overlapping circuitry and neurochemicals that mediate feeding, stress and reward pathways. In particular, this paper draws attention to the bombesin family of peptides (BBs) initially shown to regulate food intake and subsequently shown to mediate stress response as well. Evidence is presented to support the hypothesis that BBs may be involved in stress-induced anorexia under certain conditions, but that the same peptides could also be involved in stress-induced obesity. This hypothesis is based on the unique distribution of BBs in key cortico-limbic brain regions involved in food regulation, reward, incentive salience and motivationally driven behavior.

Comparison of the effects of acute and chronic psychological stress on metabolic features in rats

This study was aimed to compare the effects of acute and chronic psychological stress on metabolic factors. Forty-two male Wistar rats were divided into control and stressed groups. Stress was applied by a communication box acutely (1 d) and chronically (15 and 30 d). Blood sampling was carried out by retro-orbital-puncture method. The plasma levels of glucose, cholesterol, triglyceride, insulin, and corticosterone were measured. In addition, feed and water intake, latency to eat and drink, adrenal and body weights were determined. Acute and chronic psychological stress did not significantly change basal plasma corticosterone levels. However, immediately (1 min) after acute exposure to stress, plasma corticosterone level increased compared to that before stress exposure. Acute stress increased plasma insulin levels significantly. Fifteen days of stress exposure resulted in plasma glucose increase. Chronic stress significantly increased feed intake, latency to eat, and adrenal weight compared to acute stress. The body weights of both control and stressed groups increased markedly during the experiment. Homeostasis model assessment of insulin resistance (HOMA-IR) index did not change significantly in the stressed group. In conclusion, application of acute and chronic psychological stress leads to different metabolic and/or behavioral changes but the metabolic changes resulting from acute exposure to stress seem to be more pronounced.