Ability of palatable food consumption to buffer against the short- and long-term behavioral consequences of social defeat exposure during juvenility in rats

Treating chronic stress and chronic pain by manipulating gut microbiota with diet: can we kill two birds with one stone?

Background: Chronic stress and chronic pain are closely linked by the capacity to exacerbate each other, sharing common roots in the brain and in the gut. The strict intersection between these two neurological diseases makes important to have a therapeutic strategy aimed at preventing both to maintain mental health in patients. Diet is an modifiable lifestyle factor associated with gut-brain axis diseases and there is growing interest in its use as adjuvant to main therapies. Several evidence attest the impact of specific diets or nutrients on chronic stress-related disorders and pain with a good degree of certainty. A daily adequate intake of foods containing micronutrients such as amino acids, minerals and vitamins, as well as the reduction in the consumption of processed food products can have a positive impact on microbiota and gut health. Many nutrients are endowed of prebiotic, anti-inflammatory, immunomodulatory and neuroprotective potential which make them useful tools helping the management of chronic stress and pain in patients. Dietary regimes, as intermittent fasting or caloric restriction, are promising, although further studies are needed to optimize protocols according to patient's medical history, age and sex. Moreover, by supporting gut microbiota health with diet is possible to attenuate comorbidities such as obesity, gastrointestinal dysfunction and mood disorders, thus reducing healthcare costs related to chronic stress or pain.Objective: This review summarize the most recent evidence on the microbiota-mediated beneficial effects of macro- and micronutrients, dietary-related factors, specific nutritional regimens and dietary intervention on these pathological conditions.

Stress in adolescence as a first hit in stress-related disease development: Timing and context are crucial

The two-hit stress model predicts that exposure to stress at two different time-points in life may increase or decrease the risk of developing stress-related disorders later in life. Most studies based on the two-hit stress model have investigated early postnatal stress as the first hit with adult stress as the second hit. Adolescence, however, represents another highly sensitive developmental window during which exposure to stressful events may affect programming outcomes following exposure to stress in adulthood. Here, we discuss the programming effects of different types of stressors (social and nonsocial) occurring during adolescence (first hit) and how such stressors affect the responsiveness toward an additional stressor occurring during adulthood (second hit) in rodents. We then provide a comprehensive overview of the potential mechanisms underlying interindividual and sex differences in the resilience/susceptibility to developing stress-related disorders later in life when stress is experienced in two different life stages.

Social adversity during juvenile age but not adulthood increases susceptibility to an immune challenge later in life

Adverse experiences in early life can increase mental vulnerability to immune challenges experienced later in life, which may induce the development of stress-related psychopathologies. Here, we investigated whether the combined effect of both events is higher if the first adverse experience occurs when the brain is still in development. Therefore, male Wistar rats were exposed to repeated social defeat (RSD, first hit) during juvenile age or adulthood and to an immune challenge consisting of a single injection of lipopolysaccharide (LPS, second hit) in adulthood. Control animals were not exposed to RSD, but only to the LPS challenge. Translocator protein density, a marker for reactive microglia, microglia cell density and plasma corticosterone levels were measured using in vivo [¹¹C]PBR28 positron emission tomography, iba1 immunostaining, and corticosterone ELISA, respectively. Anhedonia, social behavior and anxiety were measured with the sucrose preference, social interaction, and open field tests, respectively. Rats exposed to RSD during juvenile age exhibited enhanced anhedonia and social interaction dysfunction after an immune challenge in adulthood. This enhanced susceptibility was not observed in rats exposed to RSD during adulthood. In addition, exposure to RSD synergistically increased microglia cell density and glial reactivity to the LPS challenge. This increase in microglia cell density and reactivity to the LPS challenge was more pronounced in rats exposed to RSD during juvenile age than in adulthood. Exposure to RSD alone in juvenile age or adulthood induced similar short-term anhedonia, a long-lasting increase in plasma corticosterone and microglial activity, but no change in anxiety and social behavior. Our findings indicate that exposure to social stress during juvenile age, but not adulthood, primes the immune system and increases the sensitivity to an immune challenge experienced later in life. This suggests that juvenile social stress can have more deleterious effects in the long term than similar stress in adulthood.

Neurobiological Mechanisms Modulating Emotionality, Cognition and Reward-Related Behaviour in High-Fat Diet-Fed Rodents

Affective and substance-use disorders are associated with overweight and obesity-related complications, which are often due to the overconsumption of palatable food. Both high-fat diets (HFDs) and psychostimulant drugs modulate the neuro-circuitry regulating emotional processing and metabolic functions. However, it is not known how they interact at the behavioural level, and whether they lead to overlapping changes in neurobiological endpoints. In this literature review, we describe the impact of HFDs on emotionality, cognition, and reward-related behaviour in rodents. We also outline the effects of HFD on brain metabolism and plasticity involving mitochondria. Moreover, the possible overlap of the neurobiological mechanisms produced by HFDs and psychostimulants is discussed. Our in-depth analysis of published results revealed that HFDs have a clear impact on behaviour and underlying brain processes, which are largely dependent on the developmental period. However, apart from the studies investigating maternal exposure to HFDs, most of the published results involve only male rodents. Future research should also examine the biological impact of HFDs in female rodents. Further knowledge about the molecular mechanisms linking stress and obesity is a crucial requirement of translational research and using rodent models can significantly advance the important search for risk-related biomarkers and the development of clinical intervention strategies.

Social Instability Stress in Adolescence and Social Interaction in Female Rats

Adolescence is a critical time of brain development for regions governing social behaviour and social learning. Social experiences influence the ongoing maturation of the neural structures and ultimately modify the social behaviour of adults in response to social cues. Social instability stress in adolescence (SS; daily 1-hour isolation + change of cage partner in postnatal days [PND] 30-45) leads to a long-lasting reduction in social interaction in SS rats compared with non-stressed (CTL) rats in males; here we investigate females. In a first experiment, we found that female rats exposed to adolescent SS also showed the decrement in social interaction irrespective of age at which tested, and replicated the effects previously found in males. In experiment 2, which involved females only, SS and CTL rats did not differ in anxiety-like behaviour in the elevated plus maze (EPM) and the reduction in social interaction was not significant. Nevertheless, when tested in adolescence at P47 (and not at P71), SS female rats had higher corticosterone release during the social interaction test than did CTL rats, and they exhibited a different pattern of neural activation as measured by immunoreactivity to the protein products of zif268 and c-fos (SS < CTL in medial prefrontal cortex and SS > CTL in hippocampus), and reduced oxytocin immunoreactivity in the paraventricular nucleus of the hypothalamus than did CTL rats. These results extend our previous findings of effects of SS in adolescent female rats on behavioural responses to psychostimulants to social behaviour, and point to directions for investigations of the neural mechanisms involved.

Reward anticipation buffers neuroendocrine and cardiovascular responses to acute psychosocial stress in healthy young adults

Research over the last 10 years suggests that the brain's reward system plays a crucial role in stress resilience. Notably, reward processing includes both an anticipatory (cue-triggered "wanting") phase and a consummatory ("liking") phase. However, previous studies manipulated rewards via direct reward administration, which makes it difficult to isolate the buffering effect of anticipating the reward stimulus. In the current study, we designed a paradigm to manipulate participants into generating reward anticipation or not and investigated whether reward anticipation can buffer psychological, neuroendocrine, and cardiovascular responses to psychosocial stress. A sample of 78 healthy young adults underwent the Trier Social Stress Test or placebo-Trier Social Stress Test after a reward anticipation task. Results showed that reward anticipation relieved subjective stress feelings, as well as the overall cortisol secretion and the increased heart rate induced by psychosocial stress. Taken together, these findings expanded our understanding of the role the reward system plays in stress resilience, and the possible psychological mechanism of the buffering effect for future stress study was also discussed.HIGHLIGHTSReward processing includes both an anticipatory and consummatory phasesThe buffering effect of anticipating the reward stimulus requires elucidationWe examined if said anticipation buffers varied responses to psychosocial stressReward anticipation relieved subjective stress, cortisol secretion, and heart rateWe clarified the role of the reward system in stress resilience.

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.

Western Diet Consumption During Development: Setting the Stage for Neurocognitive Dysfunction

The dietary pattern in industrialized countries has changed substantially over the past century due to technological advances in agriculture, food processing, storage, marketing, and distribution practices. The availability of highly palatable, calorically dense foods that are shelf-stable has facilitated a food environment where overconsumption of foods that have a high percentage of calories derived from fat (particularly saturated fat) and sugar is extremely common in modern Westernized societies. In addition to being a predictor of obesity and metabolic dysfunction, consumption of a Western diet (WD) is related to poorer cognitive performance across the lifespan. In particular, WD consumption during critical early life stages of development has negative consequences on various cognitive abilities later in adulthood. This review highlights rodent model research identifying dietary, metabolic, and neurobiological mechanisms linking consumption of a WD during early life periods of development (gestation, lactation, juvenile and adolescence) with behavioral impairments in multiple cognitive domains, including anxiety-like behavior, learning and memory function, reward-motivated behavior, and social behavior. The literature supports a model in which early life WD consumption leads to long-lasting neurocognitive impairments that are largely dissociable from WD effects on obesity and metabolic dysfunction.

Social Defeat Stress During Early Adolescence Confers Resilience Against a Single Episode of Prolonged Stress in Adult Rats

Early-life adverse experiences (first hit) lead to coping strategies that may confer resilience or vulnerability to later experienced stressful events (second hit) and the subsequent development of stress-related psychopathologies. Here, we investigated whether exposure to two stressors at different stages in life has long-term effects on emotional and cognitive capabilities, and whether the interaction between the two stressors influences stress resilience. Male rats were subjected to social defeat stress (SDS, first hit) in adolescence and to a single episode of prolonged stress (SPS, second hit) in adulthood. Behavioral outcomes, hippocampal expression of brain-derived neurotrophic factor, and plasma corticosterone levels were tested in adulthood. Rats exposed to both stressors exhibited resilience against the development of stress-induced alterations in emotional behaviors and spatial memory, but vulnerability to cued fear memory dysfunction. Rats subjected to both stressors demonstrated resilience against the SDS-induced alterations in hippocampal brain-derived neurotrophic factor expression and plasma corticosterone levels. SPS alone altered locomotion and spatial memory retention; these effects were absent in SDS-exposed rats later exposed to SPS. Our findings reveal that exposure to social stress during early adolescence influences the ability to cope with a second challenge experienced later in life.

Food Addiction and Psychosocial Adversity: Biological Embedding, Contextual Factors, and Public Health Implications

The role of stress, trauma, and adversity particularly early in life has been identified as a contributing factor in both drug and food addictions. While links between traumatic stress and substance use disorders are well documented, the pathways to food addiction and obesity are less established. This review focuses on psychosocial and neurobiological factors that may increase risk for addiction-like behaviors and ultimately increase BMI over the lifespan. Early childhood and adolescent adversity can induce long-lasting alterations in the glucocorticoid and dopamine systems that lead to increased addiction vulnerability later in life. Allostatic load, the hypothalamic-pituitary-adrenal axis, and emerging data on epigenetics in the context of biological embedding are highlighted. A conceptual model for food addiction is proposed, which integrates data on the biological embedding of adversity as well as upstream psychological, social, and environmental factors. Dietary restraint as a feature of disordered eating is discussed as an important contextual factor related to food addiction. Discussion of various public health and policy considerations are based on the concept that improved knowledge of biopsychosocial mechanisms contributing to food addiction may decrease stigma associated with obesity and disordered eating behavior.

Behavioral Traits Associated With Resilience to the Effects of Repeated Social Defeat on Cocaine-Induced Conditioned Place Preference in Mice

The relationship between stress and drug use is well demonstrated. Stress-induced by repeated social defeat (RSD) enhances the conditioned place preference (CPP) induced by cocaine in mice. The phenomenon of resilience understood as the ability of subjects to overcome the negative effects of stress is the focus of increasing interest. Our aim is to characterize the behavior of resilient animals with respect to the effects of RSD on the CPP induced by cocaine. To this end, 25 male C57BL/6 mice were exposed to stress by RSD during late adolescence, while other 15 male mice did not undergo stress (controls). On the 2 days following the last defeat, all the animals carried out the elevated plus maze (EPM) and Hole Board, Social Interaction, Tail Suspension and Splash tests. Three weeks later, all the animals performed the CPP paradigm with a low dose of cocaine (1 mg/kg). Exposure to RSD decreased all measurements related to the open arms of the EPM. It also reduced social interaction, immobility in the tail suspension test (TST) and grooming in the splash test. RSD exposure also increased the sensitivity of the mice to the rewarding effects of cocaine, since only defeated animals acquired CPP. Several behavioral traits were related to resilience to the potentiating effect of RSD on cocaine CPP. Mice that showed less submission during defeat episodes, a lower percentage of time in the open arms of the EPM, low novelty-seeking, high social interaction, greater immobility in the TST and a higher frequency of grooming were those that were resilient to the long-term effects of social defeat on cocaine reward since they behaved like controls and did not develop CPP. These results suggest that the behavioral profile of resilient defeated mice is characterized by an active coping response during episodes of defeat, a greater concern for potential dangers, less reactivity in a situation of inevitable moderate stress and fewer depressive-like symptoms after stress. Determining the neurobehavioral substrates of resilience is the first step towards developing behavioral or pharmacological interventions that increase resilience in individuals at a high risk of suffering from stress.

Effects of oxytocin receptor antagonism on social function and corticosterone release after adolescent social instability in male rats

Oxytocin influences social behaviour and hypothalamic-pituitary-adrenal (HPA) function. We previously found that social instability stress (SS) from postnatal day 30 to 45 increased oxytocin receptor (OTR) densities in the lateral septum and nucleus accumbens of adolescent male rats. Here, we investigated social behaviour and HPA function in adolescent male SS rats compared with age- and sex-matched controls after intraperitoneal treatment with an OTR antagonist L-368,899 (OTR-A). Regardless of OTR antagonism, adolescent SS rats spent more time in social approach (investigation through wire mesh) but less time in social interaction (physical interaction) with unfamiliar same-sex and same-age peers than did controls. However, OTR-A-treatment caused SS rats to be more socially avoidant than OTR-A-treated controls and saline-treated rats of the same condition. Additionally, the predicted rise in plasma corticosterone in response to OTR-A treatment was blunted in SS rats. Fos immunoreactivity (IR) was used as a marker of neural activation in social brain regions and oxytocin-IR was examined in the paraventricular nucleus of the hypothalamus (PVN) in response to interacting with unfamiliar peers in SS and control rats after OTR-A treatment. OTR-A treatment had little effect on Fos-IR and oxytocin-IR in the analyzed brain regions, but SS rats had lower Fos-IR and oxytocin-IR in the PVN and greater Fos-IR in subregions of the prefrontal cortex, and hippocampus, and lateral septum than did controls. Finally, binding density of OTR was measured in the PVN and hippocampus, and greater OTR binding density was found in the PVN of SS rats. Together, these data demonstrate a greater influence of OTR antagonism on social behaviour and a reduced influence of OTR antagonism on HPA responses after adolescent SS in male rats. The results also suggest that differences in neural functioning in the prefrontal cortex, hippocampus and lateral septum of adolescent SS rats may be involved in their altered social behaviour relative to that of controls.

Sex-specific differences in adult cognition and neuroplasticity following repeated combinatory stress and TrkB receptor antagonism in adolescence

Evidence supports brain-derived neurotrophic factor (BDNF) and its primary receptor tyrosine-related kinase B (TrkB) as targets in the treatment of mood disorders. This study characterized the impact of a 10-day combinatory stress paradigm (alternating days of restraint stress and forced swim) and administration of the selective TrkB antagonist ANA-12 (0.5 mg/kg, i.p.) during adolescence in male and female Wistar rats on adulthood behavioral and neurochemical responses. The social interaction/preference (SIT/SP), and Y maze conditioned place preference (YMCPP) and passive avoidance tests (YMPAT), initiated on PND 62, served to determine sex-related behavioral responses. Results support reduced sociability in females in the SIT/SP, but no impact of ANA-12 to regulate sociability or social memory. Blockade of TrkB during adolescence facilitated YMCPP-related reward behavior in both sexes, and reduced YMPAT fear conditioning in females. Following behavioral testing, rats were exposed to 5-min acute forced swim and brains collected 2 h post swim to determine effects of adolescent TrkB blockade and stress exposure on neurochemical regulators of stress and plasticity. Findings show elevated glucocorticoid receptor (GR-) and TrkB-immunoreactivity (ir) in the amygdalar central nucleus, and GR-ir in the hypothalamic paraventricular nucleus of females compared to males. In the hippocampal CA1, BDNF-ir was lower in females versus males, and GR-ir was elevated in stress versus non-stress males. Together, we demonstrate that inherent sex-specific differences, which may modulate impact of adolescence stress exposure and TrkB inhibition, differentially affect male and female adulthood behavior and biochemical response profiles, suggesting that these responses are in part conditioned by prior experience.

Comparative analysis of the influence of a high-fat/high-carbohydrate diet on the level of anxiety and neuromotor and cognitive functions in Wistar and DAT-KO rats

We compared anxiety, neuromotor, and cognitive functions in mutant rats with different allelic variants of dopamine transporter DAT knockout receiving balanced or excess in fat and fructose diet. The experiments were performed in DAT-/- homozygotes, DAT+/- heterozygotes, and DAT+/+ wild type rats. The genotype of DAT-KO rats was confirmed by restriction analysis of DAT gene compared to behavioral responses in the open field test (OF). Animals in the first groups of each strain were fed a balanced AIN93M diet; and those in the second groups with a high-fat/high-fructose diet. Neuromotor function was studied as grip strength, and behavioral responses were assessed in the elevated plus maze and conditioned passive avoidance response tests. The mass of the internal organs and white and brown fat, as well as selected lipid and nitrogen metabolism parameters in blood plasma were determined at the end of the experiment. DAT-/- had the highest specific grip strength, and showed an increase in initial exploratory activity in comparison with DAT+/- and DAT +/+. The exploratory activity was significantly reduced in the second test compared to the first one in DAT-/- and DAT+/- of first but not second group. Anxiety decreased with age in the second groups of DAT+/- and DAT+/+ (but not in DAT-/-) and was higher in DAT+/+ than in DAT+/- and DAT-/-. Excess fat and fructose resulted in the deterioration of short-term memory in DAT+/+. Lipidomic indices of blood plasma were less responsive to diet in DAT-/- and DAT-/+ in comparison to DAT+/+. The increased AsAT/AlAT activity ratio in DAT-/- compared with those in DAT+/+ suggests the activation of catabolism activity in the mutants. The consumption of excess fat and fructose significantly modified the effects produced by DAT gene allelic variants presumably due to the influence on the processes of dopamine metabolism.

Effects of high fat or high sucrose diet on behavioral-response to social defeat stress in mice

Stress increases risk for psychopathology, and diet may moderate the impact of stress on mental health. A “Western” diet has been linked to psychopathology in humans; animal studies also show that diet can influence negative valence behavior in the presence or absence of stress, but findings are inconsistent. Contradictions in existing studies may result from differences in macronutrient content of diets and presence of metabolic syndrome. The present study exposed mice to 10 days of high fat or high sucrose diet concurrent with social defeat stress exposure and examined negative valence behavior at acute (<five days) and long-term (>30 days) time points after stress/diet exposure. Predictably, stress increased negative valence behavior in the social interaction, open field, elevated zero maze, and tail suspension tests at the acute time point. While most stress-induced behaviors normalized after the 30-day recovery period, social avoidance was still highly significant for stress-exposed mice, supporting the hypothesis that avoidance of a trauma-related cue persists beyond non-specific anxiety-like behaviors. Supporting the hypothesis that an unhealthy diet contributes to psychopathology, non-stressed mice fed high fat or high sucrose diets spent less time exploring the center of the open field. This effect was no longer present after a 30-day recovery. Intriguingly, mice previously fed either high fat or high sucrose diets exhibited increased rearing behavior in the elevated zero maze 30 days post stress and diet exposure. This finding could be evidence that short-term diet administration can initiate a long-term increase in risk-assessment behavior.

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Social stress increased negative valence in short-term behavioral tests.

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Social avoidance persisted for stress exposed mice thirty days post stress exposure.

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Unhealthy diet decreased exploration in the center of the open field.

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Non-stress, control diet mice had the least anxiety-like behavior in open field.

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Unhealthy diets increased rearing behavior 30 days post stress exposure.

Hyperpalatability and the Generation of Obesity: Roles of Environment, Stress Exposure and Individual Difference

PURPOSE OF REVIEW

This review investigates how exposure to palatable food and its associated cues alters appetite regulation and feeding behaviour to drive overeating and weight gain.

RECENT FINDINGS

Both supraphysiological and physiological feeding systems are affected by exposure to palatable foods and its associated cues. Preclinical research, largely using rodents, has demonstrated that palatable food modulates feeding-related neural systems and food-seeking behaviour by recruiting the mesolimbic reward pathway. This is supported by studies in adolescents which have shown that mesolimbic activity in response to palatable food cues and consumption predicts future weight gain. Additionally, stress exposure, environmental factors and individual susceptibility have been shown to modulate the effects of highly palatable foods on behaviour. Further preclinical research using free-choice diets modelling the modern obesogenic environment is needed to identify how palatable foods drive overeating. Moreover, future clinical research would benefit from more appropriate quantification of palatability, making use of rating systems and surveys.

Inhibition of TrkB at the nucleus accumbens, using ANA-12, regulates basal and stress-induced orexin A expression within the mesolimbic system and affects anxiety, sociability and motivation

Repeated stress exposure can lead to the development of anxiety and mood disorders. An emerging biological substrate of depression and associated pathology is the nucleus accumbens (NAc), which through interactions with limbic, cognitive and motor circuits can regulate a variety of stress responses. Within these circuits, orexin neurons are involved in arousal and stress adaptability, effects proposed mediated via brain-derived neurotrophic factor signaling. This study tested the hypotheses that 1) repeated exposure to heterotypic stress alters social ability and preference and passive avoidant behaviors, 2) TrkB receptors at the NAc shell regulates stress-induced behavioral responses and orexin expression within the mesocorticolimbic system. Our findings indicate that ANA-12 (0.25 μg/0.5 μl) enhanced sociability during the social interaction test, although treatment had no effect on social preference. The development of conditioned place preference, and fear retention in the passive avoidance test were also facilitated by ANA-12. Biochemical assessments on brain tissues collected within 2 h of a forced swim exposure revealed that ANA-12 increased orexin A immunoreactivity (ir) in the hypothalamic perifornical area, while expression was reduced in the ventral portion of the hippocampal CA1 layer, irrespective of the stress condition. This contrasts changes at the VTA characterized by elevated versus reduced orexin A-ir in ANA-12-treated stress and non-stress rats, respectively. Colocalized orexin A- and tyrosine hydroxylase (TH)-ir at the VTA supports a different temporal expression post stress, TH-ir being unaffected 9 days post stress. These findings support a role for TrkB receptors in regulating basal and stress-induced social, cognitive and motivational behavior, and modulatory actions of BDNF, via TrkB signaling, on orexin A signaling upon stress exposure.