Pleasurable behaviors reduce stress via brain reward pathways

Maternal caregiving stress and metabolic health: Sexual activity as a potential buffer

Chronic stress lead to dysregulation of metabolic hormones, creating risk for obesity and type 2 diabetes. Based on previous work suggesting the potential for sexual activity to relieve psychological stress and reduce stress-related neuroendocrine activity, the present research explored sexual activity as a protective factor. We focused on chronic stress in the form of caregiving stress, comparing premenopausal mothers of a child with an autism spectrum disorder vs. a neurotypical child, in relation to metabolic hormones - insulin (and insulin resistance as assessed by HOMA), leptin, and ghrelin. Then, we explored the moderating role of sexual activity. Our results showed that high-stress mothers showed higher levels of insulin, insulin resistance, and lower levels of ghrelin compared to low-stress mothers. However, sexual activity modulated these associations such that among mothers who were sexually active (as coded from their daily diaries), no significant differences in these outcomes were observed between groups. This buffering effect of sexual activity was distinguishable from the buffering effect of physical activity and independent of global relationship satisfaction. Together, our findings provide novel evidence supporting the potential protective effects of sexual activity from chronic stress-related metabolic disease risk.

Executive function, perceived stress and eating behaviours among Chinese young adults

Young adults in a transitional period may experience more stress and, hence, suffer from an increased risk of unhealthy eating. Executive function (EF) involves not only inhibitory control and mental flexibility (the 'cool' facet) to facilitate resistance to immediate temptations, but also affective decision making (the 'hot' facet) that helps to regulate emotional eating. The effects of different facets of EF and their interactions with perceived stress on eating behaviours remained underexplored. In this study, 594 young adults in their graduation year of post-secondary education were included. We used latent profile analysis to identify major patterns of eating behaviours and analysed their associations with perceived stress, and both the 'cool' and 'hot' facets of EF using multinominal logistic regression models. Latent profile analysis identified three clusters of eating patterns: non-approaching moderate eaters (N = 312, 52.5%), approaching eaters (N = 229, 38.6%), and approaching-and-avoidant eaters (N = 53, 8.9%). Logistic regression models found that the approaching-and-avoidant eating pattern was associated with higher perceived stress (OR = 3.16, p value = 0.007) and poorer affective decision-making (OR = 0.97, p value = 0.006). Stratified analysis further revealed that higher perceived stress was significantly associated with approaching-and-avoidant eating only among individuals with poorer affective decision-making. These findings suggest that individuals with poorer emotional regulation may face greater difficulties in regulating eating behaviours when experiencing higher stress. Interventions for people with a mixed pattern of approaching-and-avoidance eating should focus on providing support to regulate emotion-related eating.

Propofol Alleviates Anxiety-Like Behaviors Associated with Pain by Inhibiting the Hyperactivity of PVNCRH Neurons via GABAA Receptor β3 Subunits

Pain, a comorbidity of anxiety disorders, causes substantial clinical, social, and economic burdens. Emerging evidence suggests that propofol, the most commonly used general anesthetic, may regulate psychological disorders; however, its role in pain-associated anxiety is not yet described. This study investigates the therapeutic potential of a single dose of propofol (100 mg kg-1) in alleviating pain-associated anxiety and examines the underlying neural mechanisms. In acute and chronic pain models, propofol decreased anxiety-like behaviors in the elevated plus maze (EPM) and open field (OF) tests. Propofol also reduced the serum levels of stress-related hormones including corticosterone, corticotropin-releasing hormone (CRH), and norepinephrine. Fiber photometry recordings indicated that the calcium signaling activity of CRH neurons in the paraventricular nucleus (PVNCRH) is reduced after propofol treatment. Interestingly, artificially activating PVNCRH neurons through chemogenetics interfered with the anxiety-reducing effects of propofol. Electrophysiological recordings indicated that propofol decreases the activity of PVNCRH neurons by increasing spontaneous inhibitory postsynaptic currents (sIPSCs). Further, reducing the levels of γ-aminobutyric acid type A receptor β3 (GABAAβ3) subunits in PVNCRH neurons diminished the anxiety-relieving effects of propofol. In conclusion, this study provides a mechanistic and preclinical rationale to treat pain-associated anxiety-like behaviors using a single dose of propofol.

Evaluating the Safety and Efficacy of Capromorelin in Rhesus Macaques (Macaca mulatta)

Nonhuman primates used in biomedical research may experience clinically significant weight loss for a variety of reasons. Episodes of anorexia (complete loss of appetite) or hyporexia (decreased appetite) can result in significant weight loss, potentially altering animal welfare and scientific studies. The FDA has approved several appetite stimulants for use in domestic species, but currently none are approved for use in NHP. Treatment of inappetence and weight loss in NHP often relies on the extralabel use of these compounds. Capromorelin is a ghrelin receptor agonist. As a growth hormone secretagogue, capromorelin increases appetite, leading to weight gain. Studies in several species have shown a positive correlation between capromorelin administration and weight gain; in 2017, an oral solution of capromorelin received FDA approval for use in dogs. We tested this solution in healthy adult rhesus macaques (n = 3 males and 3 females) for its effects on body weight and insulin like growth factor-1 (IGF-1). A control group (n = 2 males and 2 females) was used for comparison. Treated macaques received a 3mg/kg oral dose daily for 7 d. Clinical signs were observed daily. Weights were collected before, during and at the end of treatment. Blood was drawn before, during and after treatment for measurement of IGF-1 levels and standard hematology and biochemistry parameters. Baseline-adjusted mean body weights and IGF-1 levels were significantly higher in treated as compared with control monkeys after 7 d of beginning treatment (body weight of 10.5±0.1kg (mean ± SEM) and 10.1±0.1kg, respectively; IGF-1 of 758±43ng/mL and 639±22ng/mL, respectively). Capromorelin administration was not associated with appreciable changes in hematologic and biochemical values in treated macaques. These findings suggest that capromorelin may be useful for treating inappetence and weight loss in NHP, and based on blood analysis, a 7-d course of treatment does not appear to cause acute toxicity.

Dietary habits, depression and obesity: an intricate relationship to explore in pediatric preventive strategies

Obesity and depression represent major health problems due to their high prevalence and morbidity rates. Numerous evidences elucidated the connections between dietary habits and the incidence or severity of depression. This overview aims to investigate the intricate relationship between dietary patterns and depression with the objective of elaborating preventive strategies for childhood obesity. Literature data recognized that there is a link between mood and food choices, with certain foods selected for their impact on the brain's reward centers. This behavior parallels the one observed in substance addiction, suggesting a specific neural mechanism for food addiction that contributes to overeating and obesity. It is important to note the significant correlation between obesity and depression, indicating a shared biological pathway influencing these conditions. Stress substantially affects also eating behaviors, often leading to increased consumption of pleasurable and rewarding foods. This can trigger a cycle of overeating, weight gain, and psychological distress, exacerbating mood disorders and obesity. In addition, consumption of certain types of foods, especially "comfort foods" high in fat and calories, may provide temporary relief from symptoms of depression, but can lead to long-term obesity and further mental health problems. Understanding these complex interactions is critical to developing preventive strategies focusing on dietary, emotional, and environmental factors, thereby reducing the risk of obesity and mood disorders.

Basolateral amygdala neuropeptide Y system modulates binge ethanol consumption

Neuropeptide Y (NPY) signaling regulation of corticolimbic communication is known to modulate binge-like ethanol consumption in rodents. In this work we sought to assess the impact of intra-BLA NPY system modulation on binge-like ethanol intake and to assess the role of the NPY1R+ projection from the BLA to the mPFC in this behavior. We used "drinking-in-the-dark" (DID) procedures in C57BL6J mice to address these questions. First, the impact of intra-BLA administration of NPY on binge-like ethanol intake was assessed. Next, the impact of repeated cycles of DID intake on NPY1R expression in the BLA was assessed with use of immunohistochemistry (IHC). Finally, chemogenetic inhibition of BLA→mPFC NPY1R+ projections was assessed to determine if limbic communication with the mPFC was specifically involved in binge-like ethanol intake. Importantly, as both the BLA and NPY system are sexually dimorphic, both sexes were assessed in these studies. Intra-BLA NPY dose-dependently decreased binge-like ethanol intake in males only. Repeated DID reduced NPY1R expression in the BLA of both sexes. Silencing of BLA→mPFC NPY1R+ neurons significantly reduced binge-like ethanol intake in both sexes in a dose-dependent manner. We provide novel evidence that (1) intra-BLA NPY reduces binge-like ethanol intake in males; (2) binge-like ethanol intake reduces NPY1R levels in the BLA; and (3) chemogenetic inhibition of BLA→mPFC NPY1R+ neurons blunts binge-like drinking in male and female mice. These observations provide the first direct evidence that NPY signaling in the BLA, and specifically BLA communication with the mPFC, modulates binge-like ethanol consumption.

Failure to mate enhances investment in behaviors that may promote mating reward and impairs the ability to cope with stressors via a subpopulation of Neuropeptide F receptor neurons

Living in dynamic environments such as the social domain, where interaction with others determines the reproductive success of individuals, requires the ability to recognize opportunities to obtain natural rewards and cope with challenges that are associated with achieving them. As such, actions that promote survival and reproduction are reinforced by the brain reward system, whereas coping with the challenges associated with obtaining these rewards is mediated by stress-response pathways, the activation of which can impair health and shorten lifespan. While much research has been devoted to understanding mechanisms underlying the way by which natural rewards are processed by the reward system, less attention has been given to the consequences of failure to obtain a desirable reward. As a model system to study the impact of failure to obtain a natural reward, we used the well-established courtship suppression paradigm in Drosophila melanogaster as means to induce repeated failures to obtain sexual reward in male flies. We discovered that beyond the known reduction in courtship actions caused by interaction with non-receptive females, repeated failures to mate induce a stress response characterized by persistent motivation to obtain the sexual reward, reduced male-male social interaction, and enhanced aggression. This frustrative-like state caused by the conflict between high motivation to obtain sexual reward and the inability to fulfill their mating drive impairs the capacity of rejected males to tolerate stressors such as starvation and oxidative stress. We further show that sensitivity to starvation and enhanced social arousal is mediated by the disinhibition of a small population of neurons that express receptors for the fly homologue of neuropeptide Y. Our findings demonstrate for the first time the existence of social stress in flies and offers a framework to study mechanisms underlying the crosstalk between reward, stress, and reproduction in a simple nervous system that is highly amenable to genetic manipulation.

A neuronal coping mechanism linking stress-induced anxiety to motivation for reward

Stress coping involves innate and active motivational behaviors that reduce anxiety under stressful situations. However, the neuronal bases directly linking stress, anxiety, and motivation are largely unknown. Here, we show that acute stressors activate mouse GABAergic neurons in the interpeduncular nucleus (IPN). Stress-coping behavior including self-grooming and reward behavior including sucrose consumption inherently reduced IPN GABAergic neuron activity. Optogenetic silencing of IPN GABAergic neuron activation during acute stress episodes mimicked coping strategies and alleviated anxiety-like behavior. In a mouse model of stress-enhanced motivation for sucrose seeking, photoinhibition of IPN GABAergic neurons reduced stress-induced motivation for sucrose, whereas photoactivation of IPN GABAergic neurons or excitatory inputs from medial habenula potentiated sucrose seeking. Single-cell sequencing, fiber photometry, and optogenetic experiments revealed that stress-activated IPN GABAergic neurons that drive motivated sucrose seeking express somatostatin. Together, these data suggest that stress induces innate behaviors and motivates reward seeking to oppose IPN neuronal activation as an anxiolytic stress-coping mechanism.

Glucocorticoid feedback paradox: a homage to Mary Dallman

As the end product of the hypothalamus-pituitary-adrenal (HPA) axis, the glucocorticoid hormones cortisol and corticosterone coordinate circadian activities, stress-coping, and adaptation to change. For this purpose, the hormone promotes energy metabolism and controls defense reactions in the body and brain. This life-sustaining action exerted by glucocorticoids occurs in concert with the autonomic nervous and immune systems, transmitters, growth factors/cytokines, and neuropeptides. The current contribution will focus on the glucocorticoid feedback paradox in the HPA-axis: the phenomenon that stress responsivity remains resilient if preceded by stress-induced secretion of glucocorticoid hormone, but not if this hormone is previously administered. Furthermore, in animal studies, the mixed progesterone/glucocorticoid antagonist RU486 or mifepristone switches to an apparent partial agonist upon repeated administration. To address these enigmas several interesting phenomena are highlighted. These include the conditional nature of the excitation/inhibition balance in feedback regulation, the role of glucose as a determinant of stress responsivity, and the potential of glucocorticoids in resetting the stress response system. The analysis of the feedback paradox provides also a golden opportunity to review the progress in understanding the role of glucocorticoid hormone in resilience and vulnerability during stress, the science that was burned deeply in Mary Dallman's emotions.

Alternative splicing in mouse brains affected by psychological stress is enriched in the signaling, neural transmission and blood-brain barrier pathways

Psychological stress increases the risk of major psychiatric disorders. Psychological stress on mice was reported to induce differential gene expression (DEG) in mice brain regions. Alternative splicing is a fundamental aspect of gene expression and has been associated with psychiatric disorders but has not been investigated in the stressed brain yet. This study investigated changes in gene expression and splicing under psychological stress, the related pathways, and possible relationship with psychiatric disorders. RNA-seq raw data of 164 mouse brain samples from 3 independent datasets with stressors including chronic social defeat stress (CSDS), early life stress (ELS), and two-hit stress of combined CSDS and ELS were collected. There were more changes in splicing than in gene expression in the ventral hippocampus and medial prefrontal cortex, but stress-induced changes of individual genes by differential splicing and differential expression could not be replicated. In contrast, pathway analyses produced robust findings: stress-induced differentially spliced genes (DSGs) were reproducibly enriched in neural transmission and blood-brain barrier systems, and DEGs were reproducibly enriched in stress response-related functions. The hub genes of DSG-related PPI networks were enriched in synaptic functions. The corresponding human homologs of stress-induced DSGs were robustly enriched in AD-related DSGs as well as BD and SCZ in GWAS. These results suggested that stress-induced DSGs from different datasets belong to the same biological system throughout the stress response process, resulting in consistent stress response effects.

Western diet-induced obesity interferes with the HPA axis-blunting effects of palatable food in male rats

Limited intermittent consumption of palatable food reduces HPA axis responses to stress in chow-fed rats, and this effect is dependent on the rewarding properties of the palatable food. However, obesity may be a state of reduced consummatory food reward, suggesting that palatable foods may be less effective at blunting HPA axis reactivity in the context of diet-induced obesity (DIO). To test this hypothesis, adult male Long-Evans rats were given unlimited access to Western (high-fat, high-sugar) diet (WD) vs. normal chow (controls). After 8 weeks of diet exposure, rats were given limited sucrose intake (LSI) consisting of additional twice-daily access to a small amount (4 ml) of either 3% or 30% sucrose drink, or water (controls) for 2 weeks. Rats then received an acute restraint stress challenge, with collection of tail blood samples for measurement of plasma corticosterone. WD-fed rats had increased caloric intake, body weight and adiposity, as expected. Rats offered LSI (3% or 30%) readily drank the maximal amount allowed (8 ml/day) and reduced their dietary intake to compensate for the sucrose calories, such that LSI did not alter body weight regardless of diet type. In chow-fed lean rats, LSI with either 3% or 30% sucrose reduced the plasma corticosterone response to restraint stress, but this effect was absent in WD-fed DIO rats. Together, these data support the hypothesis that obesity attenuates stress blunting by palatable foods and suggest the possibility that consequently, individuals with obesity may need to consume larger amounts of palatable food to obtain adequate stress relief.

Linking drug and food addiction: an overview of the shared neural circuits and behavioral phenotype

Despite a lack of agreement on its definition and inclusion as a specific diagnosable disturbance, the food addiction construct is supported by several neurobiological and behavioral clinical and preclinical findings. Recognizing food addiction is critical to understanding how and why it manifests. In this overview, we focused on those as follows: 1. the hyperpalatable food effects in food addiction development; 2. specific brain regions involved in both food and drug addiction; and 3. animal models highlighting commonalities between substance use disorders and food addiction. Although results collected through animal studies emerged from protocols differing in several ways, they clearly highlight commonalities in behavioral manifestations and neurobiological alterations between substance use disorders and food addiction characteristics. To develop improved food addiction models, this heterogeneity should be acknowledged and embraced so that research can systematically investigate the role of specific variables in the development of the different behavioral features of addiction-like behavior in preclinical models.

Impulsivity and Reactive-Proactive Aggression as Mechanisms of Alcohol-Related Sexual Intimate Partner Violence Perpetration among Romantic Partners

Background: Sexual intimate partner violence (S-IPV) commonly occurs within the contexts of committed romantic relationshops. Prior research has demonstrated the existence of a robust link between alcohol use and S-IPV. Despite this, few research studies have explored the etiological underpinnings of alcohol-related S-IPV perpetration, specifically. The present study examines the role of several key factors (i.e., problematic drinking, negative and positive urgency, proactive and reactive aggression) on S-IPV perpetration. Methods: Participants were 337 heavy drinking men and women in intimate relatinships who reported perpetrating some form of IPV toward their current partner within the past-year. A moderated-mediation model was used to determine how the key study variables interacted to predict S-IPV perpetration. Results: Results indicated that problematic drinking was positively correlated with both negative urgency and positive uregency. Findings also revealed that negative urgency, positive urgency, proactive aggression, and reactive aggression were all positively related to S-IPV perpetration. The indirect relationship between problematic drinking and S-IPV perpetration was mediated by positive urgency. Additionally, a significant main effect of proactive aggression on S-IPV perpetration was also detected. Conclusions: These findings suggest that impulsivity, specifically positive urgency, and proactive aggression may be under-appreciated constructs within the existing sexual aggression literature, and future research examining these variables as mechanisms explaining the association between the alcohol and S-IPV is warranted.

Impact of environmental enrichment on the GABAergic neurons and glucocorticoid receptors in the hippocampus and nucleus accumbens of Wistar rats: pro-resilient effects

The unpredictable chronic mild stress (UCMS) model has been used to induce depressive-like symptoms in animal models. Our work aims to evaluate the impact of environmental enrichment on male Wistar rats in an animal model for depression. For this purpose, we aim to assess changes in GR and GABAergic (PV+) density in cerebral regions related to cognitive-affective processes associated with depressive disorder, such as the dorsal- ventral hippocampus and accumbens nuclei. Three groups of rats were used: UCMs (unpredictable chronic mild stress), EE+ UCMs (enrichment + stress) and CONT (behavioral tests only). Hedonic responses elicited by sucrose solution were examined by licking behavior analysis; the anxiety level was evaluated using the elevated zero maze and the forced swimming (passive coping) tests. The environmental enrichment reduced the effects of chronic stress, promoting greater resilience. Thus, the UCMs group showed an anhedonia response, more anxiety and immobility behavior than either the control or the EE+ UCMs groups. Regarding immunochemistry results, there was a reduction in GABAergic activity coupled with increased activation of GR in UCMs in the dorsal hippocampus, but there were no differences between groups in the ventral hippocampus. These results suggest environmental enrichment could enhance greater resilience, reducing the vulnerability of the subjects to develop disorders such as depression and anxiety.

Amygdala and nucleus accumbens activation during reward anticipation moderates the association between life stressor frequency and depressive symptoms

BACKGROUND

Life stressors confer risk for depressive symptoms, but individuals vary in the extent of their sensitivity to life stressors. One protective factor may be an individual's level of reward sensitivity, e.g., a stronger neurobiological response to environmental rewards may mitigate emotional responses to stressors. However, the nature of neurobiological reward sensitivity that corresponds with stress resilience is unknown. Further, this model is untested in adolescence, when life stressor frequency and depression increase.

METHODS

We tested the hypothesis that stronger reward-related activation in the left and right nucleus accumbens (NAc), amygdala, and medial prefrontal cortex (mPFC) attenuates the strength of the stress-depression relation. We measured BOLD activation throughout Win and Lose blocks of a monetary reward task, as well as during anticipation and outcome phases of the task. Participants (N = 151, ages 13-19) were recruited to be stratified on risk for mood disorders to enhance variance in depressive symptoms.

RESULTS

Activation during anticipation of rewards in the bilateral amygdala and NAc, but not mPFC, buffered the association between life stressors and depressive symptoms. This buffering effect was not found for reward outcome activation or activation across Win blocks.

CONCLUSIONS

Results highlight the importance of reward anticipation activation of subcortical structures in attenuating the stress-depression link, suggesting that reward motivation may be a cognitive mechanism through which this stress buffering occurs.

Daily stress and eating behaviors in adolescents and young adults: Investigating the role of cortisol reactivity and eating styles

Stress-related eating has been well documented in previous literature. However, there is limited research investigating the role of cortisol reactivity in daily stress-eating associations in samples of adolescents and young adults. 123 participants completed a baseline questionnaire and the Trier Social Stress Test in groups. Four saliva samples were taken at - 10, + 00, + 10 and + 40 min during the stress-induction task. Following this, participants completed an online daily diary each evening for 14 consecutive days to record daily stress and between-meal snack consumption. Multilevel modelling indicated that daily stress was positively associated with daily snack intake, particularly for ego-threatening and work/academic stressors. Emotional and external eating styles were found to moderate the stress-snacking relationship. Cortisol reactivity also moderated stress-eating associations, such that as cortisol reactivity levels increased from lower to higher levels, the impact of stress on eating decreased. The current findings highlight the importance of cortisol reactivity status and eating styles in understanding the complex relationship between daily stress and eating behavior in adolescents and young adults. Future research should continue investigating stress-eating associations in these groups and explore the role of other aspects of hypothalamic-pituitary-adrenal axis functioning.

Relationship between polyvictimization and overweight among adolescents from São Paulo city, Brazil

This study is to identify victimization patterns and analyze the association between the experience of polyvictimization and overweight or obesity among adolescent girls and boys. The sample consisted of 2680 Brazilian ninth-graders enrolled in public and private schools, taken from the São Paulo Project for the social development of children and adolescents (SP-PROSO). Victimization was explored in two ways: (i) as per Finkelhor and (ii) by latent class analysis (LCA). The interest outcomes were overweight and obesity. Multinomial logistic regression models were used to study the relationship between victimization and overweight or obesity, controlling for confounders. LCA grouped boys and girls adolescents into three classes. These classes received the same labels, but the patterns differed between sexes. Class 1 was characterized by fewer types of victimization suffered and lower endorsement values in the analyzed items and was named bullying and indirect victimization (♀: 42.7%, n = 546; ♂: 21.6%, n = 293). Class 2 included more victimization types than Class 1 and less than Class 3. This class was labeled family violence and peer victimization (♀: 29.1%, n = 356; ♂: 47.9%, n = 652). Class 3 was named high polyvictimization (♀: 28.2%, n = 345; ♂: 30.5%, n = 418). According to Finkelhor, polyvictimization was not associated with overweight or obesity in both sexes. Only the class of high polyvictimization was associated with being overweight (OR_adj: 1.60, 95%CI: 1.01-2.54) in girls. In this study, polyvictimization was associated with being overweight only among adolescent girls. Longitudinal studies in different contexts and populations are needed to understand this relationship.

Brain Reward Circuits Promote Stress Resilience and Health: Implications for Reward-Based Interventions

From the COVID-19 global pandemic to racial injustice and the continued impact of climate change on communities across the globe, the last couple of years have demonstrated the need for a greater understanding of how to protect people from the negative consequences of stress. Here, I outline a perspective on how the brain's reward system might be an important, but often understudied, protective mechanism for stress resilience and stress-related health outcomes. I describe work suggesting that reward system engagement inhibits the stress response and is associated with improved health outcomes including reduced depressive symptomatology and slowed cancer progression. I then highlight important future directions for translational research and illustrate the value of this perspective for improving behavioral interventions in clinical psychology and beyond.

The Impact of Loosening COVID-19 Restrictions and Live-in Partner Status on Sexual and Mental Health in a Canadian Sample

Objectives

We examined changes in frequency of sexual behaviors, dyadic sexual desire, relationship satisfaction, and COVID-19 stress in Canadians across the pandemic, considering partner status.

Methods

Participants completed online questionnaires.

Results

Participants with live-in partners and single participants decreased in dyadic sexual behaviors. In August-September 2020, participants with live-in partners engaged in more dyadic sexual behaviors than single participants. In November 2021, all partnered participants engaged in more dyadic sexual behaviors than single participants. Decreases in COVID-19 stress were observed.

Conclusions

Findings suggest that despite decreases in COVID-19 stress, there may be long-lasting pandemic impacts on sexual behaviors.

Reward enhances resilience to chronic social defeat stress in mice: Neural ECs and mGluR5 mechanism via neuroprotection in VTA and DRN

INTRODUCTION

Stress often leads to emotional disorders such as depression. The reward might render this effect through the enhancement of stress resilience. However, the effect of reward on stress resilience under different intensities of stress needs more evidence, and its potential neural mechanism has been poorly revealed. It has been reported that the endogenous cannabinoid system (ECs) and downstream metabolic glutamate receptor 5 (mGluR5) are closely related to stress and reward, which might be the potential cerebral mechanism between reward and stress resilience, but there is a lack of direct evidence. This study aims to observe the effect of reward on stress resilience under different intensities of stress and further explore potential cerebral mechanisms underlying this effect.

METHODS

Using the chronic social defeat stress model, we applied reward (accompanied by a female mouse) under different intensities of stress in mice during the modeling process. The impact of reward on stress resilience and the potential cerebral mechanism were observed after modeling through behavioral tests and biomolecules.

RESULTS

The results showed that stronger stress led to higher degrees of depression-like behavior. Reward reduced depression-like behavior and enhanced stress resilience (all p-value <0.05) (more social interaction in the social test, less immobility time in the forced swimming test, etc.), with a stronger effect under the large stress. Furthermore, the mRNA expression levels of CB1 and mGluR5, the protein expression level of mGluR5, and the expression level of 2-AG (2-arachidonoylglycerol) in both ventral tegmental area (VTA) and dorsal raphe nucleus (DRN) were significantly upregulated by reward after modeling (all p-value <0.05). However, the protein expression of CB1 in VTA and DRN and the expression of AEA (anandamide) in VTA did not differ significantly between groups. Intraperitoneal injection of a CB1 agonist (URB-597) during social defeat stress significantly reduced depression-like behavior compared with a CB1 inhibitor (AM251) (all p-value <0.05). Interestingly, in DRN, the expression of AEA in the stress group was lower than that of the control group, with or without reward (all p-value <0.05).

DISCUSSION

These findings demonstrate that combined social and sexual reward has a positive effect on stress resilience during chronic social defeat stress, potentially by influencing the ECs and mGluR5 in VTA and DRN.

Real-World Intake of Dietary Sugars Is Associated with Reduced Cortisol Reactivity Following an Acute Physiological Stressor

There is increasing academic and clinical interest in understanding the nature of the relation between diet and response to stress exposure as a risk factor for mental illness. Cross-species evidence shows that conditions of chronic and acute stress increase the intake of, and preference for, caloric-dense palatable foods, a phenomenon thought to be explained by the mitigating effects of comfort foods on the activity of the stress-response network. It is largely unknown whether and how real-world dietary intake of saturated fat and sugars impacts stress responsivity in humans. Therefore, here we examined whether real-world dietary intake of saturated fat and sugars predicted salivary cortisol reactivity following an acute physiological stressor. Multilevel modelling of four salivary cortisol measures collected up to 65 min after the stressor on 54 participants (18-49 years old) were analyzed using a quadratic growth curve model. Sugar intake significantly predicted a weaker cortisol response following the Cold Pressor Test (CPT) controlling for BMI and gender, revealing an inhibitory effect of caloric-dense diets on cortisol reactivity to stress. As the consumption of sugar rose individuals had lower post-stressor cortisol levels, a smaller rate of increase in cortisol 20 and 35 min after the CPT, a lower cortisol peak, and an overall weaker quadratic effect. These observations add to a growing body of evidence reporting suppressive effects of high-energy foods on stress-associated glucocorticoids reactivity and are consistent with the comfort food hypothesis, where people are seen as motivated to eat palatable foods to alleviate the detrimental repercussions of stressor exposure.

Mesolimbic dopamine release conveys causal associations

Learning to predict rewards based on environmental cues is essential for survival. It is believed that animals learn to predict rewards by updating predictions whenever the outcome deviates from expectations, and that such reward prediction errors (RPEs) are signaled by the mesolimbic dopamine system-a key controller of learning. However, instead of learning prospective predictions from RPEs, animals can infer predictions by learning the retrospective cause of rewards. Hence, whether mesolimbic dopamine instead conveys a causal associative signal that sometimes resembles RPE remains unknown. We developed an algorithm for retrospective causal learning and found that mesolimbic dopamine release conveys causal associations but not RPE, thereby challenging the dominant theory of reward learning. Our results reshape the conceptual and biological framework for associative learning.

Restricted cafeteria feeding and treadmill exercise improved body composition, metabolic profile and exploratory behavior in obese male rats

The aim of this study was to evaluate, in male Long-Evans rats, whether a restricted-cafeteria diet (CAFR), based on a 30% calorie restriction vs continuous ad libitum cafeteria (CAF) fed animals, administered alone or in combination with moderate treadmill exercise (12 m/min, 35 min, 5 days/week for 8 weeks), was able to ameliorate obesity and the associated risk factors induced by CAF feeding for 18 weeks and to examine the changes in circadian locomotor activity, hypothalamic-pituitary-adrenal (HPA) axis functionality, and stress response elicited by this dietary pattern. In addition to the expected increase in body weight and adiposity, and the development of metabolic dysregulations compatible with Metabolic Syndrome, CAF intake resulted in a sedentary profile assessed by the home-cage activity test, reduced baseline HPA axis activity through decreased corticosterone levels, and boosted exploratory behavior. Both CAFR alone and in combination with exercise reduced abdominal adiposity and hypercholesterolemia compared to CAF. Exercise increased baseline locomotor activity in the home-cage in all dietary groups, boosted exploratory behavior in STD and CAF, partially decreased anxiety-like behavior in CAF and CAFR, but did not affect HPA axis-related parameters.

Sucrose Preference Test as a Measure of Anhedonic Behavior in a Chronic Unpredictable Mild Stress Model of Depression: Outstanding Issues

Despite numerous studies on the neurobiology of depression, the etiological and pathophysiological mechanisms of this disorder remain poorly understood. A large number of animal models and tests to evaluate depressive-like behavior have been developed. Chronic unpredictable mild stress (CUMS) is the most common and frequently used model of depression, and the sucrose preference test (SPT) is one of the most common tests for assessing anhedonia. However, not all laboratories can reproduce the main effects of CUMS, especially when this refers to a decrease in sucrose preference. It is also unknown how the state of anhedonia, assessed by the SPT, relates to the state of anhedonia in patients with depression. We analyzed the literature available in the PubMed database using keywords relevant to the topic of this narrative review. We hypothesize that the poor reproducibility of the CUMS model may be due to differences in sucrose consumption, which may be influenced by such factors as differences in sucrose preference concentration threshold, water and food deprivation, and differences in animals’ susceptibility to stress. We also believe that comparisons between animal and human states of anhedonia should be made with caution because there are many inconsistencies between the two, including in assessment methods. We also tried to offer some recommendations that should improve the reproducibility of the CUMS model and provide a framework for future research.

Interactions between emotions and eating behaviors: Main issues, neuroimaging contributions, and innovative preventive or corrective strategies

Emotional eating is commonly defined as the tendency to (over)eat in response to emotion. Insofar as it involves the (over)consumption of high-calorie palatable foods, emotional eating is a maladaptive behavior that can lead to eating disorders, and ultimately to metabolic disorders and obesity. Emotional eating is associated with eating disorder subtypes and with abnormalities in emotion processing at a behavioral level. However, not enough is known about the neural pathways involved in both emotion processing and food intake. In this review, we provide an overview of recent neuroimaging studies, highlighting the brain correlates between emotions and eating behavior that may be involved in emotional eating. Interaction between neural and neuro-endocrine pathways (HPA axis) may be involved. In addition to behavioral interventions, there is a need for a holistic approach encompassing both neural and physiological levels to prevent emotional eating. Based on recent imaging, this review indicates that more attention should be paid to prefrontal areas, the insular and orbitofrontal cortices, and reward pathways, in addition to regions that play a major role in both the cognitive control of emotions and eating behavior. Identifying these brain regions could allow for neuromodulation interventions, including neurofeedback training, which deserves further investigation.

A High-Sugar Diet Consumption, Metabolism and Health Impacts with a Focus on the Development of Substance Use Disorder: A Narrative Review

Carbohydrates are important macronutrients in human and rodent diet patterns that play a key role in crucial metabolic pathways and provide the necessary energy for proper body functioning. Sugar homeostasis and intake require complex hormonal and nervous control to proper body energy balance. Added sugar in processed food results in metabolic, cardiovascular, and nervous disorders. Epidemiological reports have shown enhanced consumption of sweet products in children and adults, especially in reproductive age and in pregnant women, which can lead to the susceptibility of offspring's health to diseases in early life or in adulthood and proneness to mental disorders. In this review, we discuss the impacts of high-sugar diet (HSD) or sugar intake during the perinatal and/or postnatal periods on neural and behavioural disturbances as well as on the development of substance use disorder (SUD). Since several emotional behavioural disturbances are recognized as predictors of SUD, we also present how HSD enhances impulsive behaviour, stress, anxiety and depression. Apart from the influence of HSD on these mood disturbances, added sugar can render food addiction. Both food and addictive substances change the sensitivity of the brain rewarding neurotransmission signalling. The results of the collected studies could be important in assessing sugar intake, especially via maternal dietary patterns, from the clinical perspective of SUD prevention or pre-existing emotional disorders. Methodology: This narrative review focuses on the roles of a high-sugar diet (HSD) and added sugar in foods and on the impacts of glucose and fructose on the development of substance use disorder (SUD) and on the behavioural predictors of drugs abuse. The literature was reviewed by two authors independently according to the topic of the review. We searched the PubMed and Scopus databases and Multidisciplinary Digital Publishing Institute open access scientific journals using the following keyword search strategy depending on the theme of the chapter: "high-sugar diet" OR "high-carbohydrate diet" OR "sugar" OR "glucose" OR "fructose" OR "added sugar" AND keywords. We excluded inaccessible or pay-walled articles, abstracts, conference papers, editorials, letters, commentary, and short notes. Reviews, experimental studies, and epidemiological data, published since 1990s, were searched and collected depending on the chapter structure. After the search, all duplicates are thrown out and full texts were read, and findings were rescreened. After the selection process, appropriate papers were included to present in this review.

Reward ameliorates depressive-like behaviors via inhibition of the substantia innominata to the lateral habenula projection

The lateral habenula (LHb) is implicated in emotional processing, especially depression. Recent studies indicate that the basal forebrain (BF) transmits reward or aversive signals to the LHb. However, the contribution of the BF-LHb circuit to the pathophysiology of depression still needs to be determined. Here, we find that the excitatory projection to the LHb from the substantia innominata (SI), a BF subregion, is activated by aversive stimuli and inhibited by reward stimuli. Furthermore, chronic activation of the SI-LHb circuit is sufficient to induce depressive-like behaviors, whereas inhibition of the circuit alleviates chronic stress-induced depressive-like phenotype. We also find that reward consumption buffers depressive-like behaviors induced by chronic activation of the SI-LHb circuit. In summary, we systematically define the function and mechanism of the SI-LHb circuit in modulating depressive-like behaviors, thus providing important insights to better decipher LHb processing in the pathophysiology of depression.

Association Between Interpersonal Violence With Inadequate Nutritional Status Among Brazilian Adolescents

Research focusing on the relationship between interpersonal violence and nutritional status in adolescence is scarce and has distinct results. The objective of this study is to investigate the association of family physical and sexual violence with inadequate nutritional status in Brazilian adolescents. We used data from the 2015 Brazilian National Survey of School Health. This study includes 11.850 students, older than 13 years, attending from sixth to ninth grade of elementary school and from the 1st to the 3rd year of high school. The exposures were family physical violence and rape. The outcome was nutritional status, assessed through body mass index. The association between exposures and outcome were investigated using a multinomial logistic regression model. These analyses were adjusted for demographic, socioeconomic, and family variables. The prevalence of family physical violence victimization was approximately 14% among adolescents for both sexes. The prevalence of rape was 4.6% and 5.7% among male and female adolescents, respectively. Family physical violence was not associated with being underweight, overweight, or obese, in either crude or adjusted models for both sexes. Sexual violence was inversely associated with being underweight only for male adolescents (OR: 0.21, CI 95%: 0.06-0.75). In female adolescents, sexual violence was associated with overweight/obesity (OR: 1.64, CI 95%:1.15-2.33). In this study, rape, but not family physical violence victimization, was associated with nutritional status in adolescents of both sexes. Nonetheless, this association was different between boys and girls. Rape was inversely associated with being underweight in male adolescents, whereas, in female adolescents, it was associated with excess body weight.

Larval Zebrafish as a Model for Mechanistic Discovery in Mental Health

Animal models are essential for the discovery of mechanisms and treatments for neuropsychiatric disorders. However, complex mental health disorders such as depression and anxiety are difficult to fully recapitulate in these models. Borrowing from the field of psychiatric genetics, we reiterate the framework of 'endophenotypes' - biological or behavioral markers with cellular, molecular or genetic underpinnings - to reduce complex disorders into measurable behaviors that can be compared across organisms. Zebrafish are popular disease models due to the conserved genetic, physiological and anatomical pathways between zebrafish and humans. Adult zebrafish, which display more sophisticated behaviors and cognition, have long been used to model psychiatric disorders. However, larvae (up to 1 month old) are more numerous and also optically transparent, and hence are particularly suited for high-throughput screening and brain-wide neural circuit imaging. A number of behavioral assays have been developed to quantify neuropsychiatric phenomena in larval zebrafish. Here, we will review these assays and the current knowledge regarding the underlying mechanisms of their behavioral readouts. We will also discuss the existing evidence linking larval zebrafish behavior to specific human behavioral traits and how the endophenotype framework can be applied. Importantly, many of the endophenotypes we review do not solely define a diseased state but could manifest as a spectrum across the general population. As such, we make the case for larval zebrafish as a promising model for extending our understanding of population mental health, and for identifying novel therapeutics and interventions with broad impact.

Sexual expression involving people with dementia living in long-term care facilities: staff's reactions

This study aims to explore and compare the reaction of long-term care staff towards situations of sexual intercourse in which one or both partners have dementia. Participants were 538 staff members at 28 Portuguese long-term care facilities. Data were collected using a printed questionnaire with seven vignettes with situations related to the sexuality of LTCF residents. In this study, three of these vignettes were analysed with situations in which residents were having relationships in their bedrooms: (1) one male resident and one female resident; (2) two residents with dementia; (3) two residents, one of them with dementia. For each of the vignettes, participants are asked what they think their 'colleagues' would do in each vignette, i.e. 'What do you think most of your colleagues would do?' The results revealed that when sexual relationships involved both partners living with dementia, the most selected reaction was 'Comment on what happened with supervision or direction', which may suggest that the situation was perceived as difficult or problematic. The most restrictive reactions were most often chosen when only one partner had dementia. This study suggests the need to improve and provide training, so that staff have knowledge and strategies that allow people living with dementia to preserve their sexual rights in long-term care facilities.

Intermittent social stress produces different short- and long-term effects on effort-based reward-seeking behavior

Previous studies show that intermittent social defeat (ISD) stress increases self-administration of psychostimulants, which suggests that ISD promotes reward-seeking behavior and, ultimately, increases vulnerability to develop drug abuse. The present study investigates whether ISD alters cost/benefit evaluations to promote reward-seeking behavior and whether these alterations are time-dependent. Male rats performed two different tasks that assessed their motivation to seek and consume food rewards. An effort-discounting task in which rats chose between less and more effortful options (i.e., 1 lever-press versus 2, 5, 10 or 20 lever-presses) associated with low- and high-reward (i.e., 1 sugar pellet versus 3 sugar pellets), respectively; and a progressive ratio task in which rats had to increase their effort (more lever presses) to obtain a sugar pellet. ISD consisted of exposing animals to social defeat once every three days for ten days (4 stress episodes). Rats were tested 24-48 h after stress episodes, and 1 week and 6 weeks after the last stress episode. In the effort-discounting task, stressed animals showed a decrease in their preference for high rewards associated with more effort (i.e., 10 and 20 lever-presses). These effects were transient and not maintained one week after stress. In the progressive ratio task, stressed animals showed an increase in the number of lever presses to obtain rewards that emerged six weeks after the last stress episode. These results suggest different short- and long-term effects on the motivation for rewards after ISD and indicate temporal dynamic adaptations in the function of the brain reward system.

Limited cheese intake reduces HPA axis and behavioral stress responses in male rats

Eating palatable foods reduces behavioral and hypothalamic-pituitary-adrenocortical (HPA) axis responses to stress - an idea referred to by the colloquial term "comfort" food. To study the underlying stress-relieving mechanisms of palatable foods, we previously developed a paradigm of limited sucrose feeding in which male rats are given twice-daily access to a small amount of sucrose drink and subsequently have reduced stress responses. Prior research in humans and rodents implicates high dietary sugars/carbohydrates with reduced stress responsivity. However, it is not clear whether the stress-relieving effects of the limited sucrose paradigm depend upon its macronutrient content. To test this idea, the current work measures stress responses in male rats following the limited intermittent intake of cheese - a highly palatable food that is low in sugar and other carbohydrates. The data show that a history of limited cheese intake (LCI) reduced HPA axis responses to acute psychological (restraint) and physiological (hypoxia) stressors. LCI also reduced behavioral struggling during restraint, increased sociability during a social interaction test, and increased open arm activity in the elevated plus-maze test. Z-score analyses evaluated the extent to which these behavioral effects extended within and across assays, and indicated that there was an overall reduction in stress-related behaviors following LCI. Finally, LCI increased immunolabeling for FosB/deltaFosB (a protein associated with repeated or chronic neuronal activation) in the nucleus accumbens. These results indicate that palatable foods can provide stress blunting regardless of their sugar/carbohydrate composition, and support the idea that food reward per se contributes to stress relief.

Association Between Family Physical Violence Victimization and Food Consumption Among Brazilian Adolescents

Few studies have evaluated the relationship between stressful events, such as child abuse and food consumption. Thus, the objective of this study is to assess whether family physical violence victimization is associated with food consumption in adolescents. We used data from the Brazilian National Adolescent School-based Health Survey, carried out in 2015, in a representative sample of 102,072 students attending ninth grade from public and private schools. We used Venn diagrams and logistic regression analysis to, respectively, graphically represent and evaluate the association between the consumption of ultra-processed food (soft drinks, sweets/candies, and salty biscuits, packaged snacks, or processed meat) and in natura food (beans, fruits and vegetables) with victimization from family physical violence. We found a lower consumption of in natura and higher consumption of ultra-processed foods among adolescent victims when compared with nonvictims of family physical violence. The probability of consuming 4 or more times a week increased by 44% for salty biscuits, packaged snacks, or processed meats; 38% for soft drinks; and 22% for sweets among adolescents who reported violence. On the contrary, the probability of consuming 4 or more times a week decreased by 25% for beans, 19% for vegetables, and 13% for fruits among adolescent victims of family physical violence. We conclude that family physical violence victimization is associated with high consumption of ultra-processed food and low consumption of in natura food among Brazilian adolescents. Therefore, issues related to violence in childhood and adolescence should be addressed in interventions aimed at altering food consumption and consequent prevention, control, and treatment of nutrition-related outcomes to increase their effectiveness.

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.

Comparison of two questionnaires for assessment of emotional eating in people undergoing treatment for obesity

PURPOSE

Emotional eating may contribute to weight gain and difficulty with weight loss. Questionnaires are currently the primary method used to identify this behaviour but there is no gold standard for detecting emotional eating, making it difficult to know which questionnaire to use for this purpose. This study assesses two questionnaires validated for assessment of emotional eating in patients with obesity, with the aim of investigating their interchangeability in the clinical setting.

METHODS

387 adult participants were recruited from the obesity treatment service at a tertiary metropolitan hospital. Responses were obtained for the 25-item Emotional Eating Scale (EES) and the 4-item coping subscale of the Palatable Eating Motives Scale (PEMS). Agreement was analysed using quadratically weighted Cohen's κ scores. Substantial agreement was defined as κ 0.61-0.80.

RESULTS

The median (interquartile range) body mass index and age of participants was 42.1 kg/m² (36.4-48.9 kg/m²) and 51.6 years (41.1-61.4 years), respectively, and 70.5% of participants were female. The EES and PEMS were found to have substantial agreement (κ 0.71; 95% CI 0.65-0.76). Agreement remained substantial when analysing responses from men (0.61; 95% CI 0.47-0.73), women (0.73; 95% CI 0.67-0.79) and post-bariatric surgery patients (0.72; 95% CI 0.62-0.82) separately.

CONCLUSION

Despite focusing on different elements of emotional eating behaviour, the substantial agreement between the EES and PEMS coping subscale suggests that they identify respondents' susceptibility to emotional eating with consistency, including in people who have undergone bariatric surgery.

LEVEL V

Opinions of respected authorities, based on descriptive studies, narrative reviews, clinical experience, or reports of expert committees.

CLINICAL TRIAL REGISTRATION

This observational study has not been registered as a clinical trial.

The influence of COVID-19-related stress on food motivation

The COVID-19 pandemic and public health measures to reduce its transmission have increased stress. Stress is associated with alterations in eating behavior which may be partly driven by effects on food-related motivation. To investigate effects of COVID-related stress on food motivation, we recruited adults (N = 429; 272 F, 157 M) to complete an online survey via Amazon MTurk in May 2020. Current COVID-related stress, retrospective pre-COVID stress, and motivation in relation to individualized preferred foods from five categories (sweet snacks, fruit, savory snacks, vegetables, and fast food) were assessed. Food motivation measures included willingness to wait, willingness to expend low effort [finger taps], willingness to expend high effort [jumping jacks], and willingness to pay for hypothetical delivery of the food item. Food motivation for each food type was assessed using a novel instrument designed for brief assessment of multiple aspects of food motivation across multiple food types. Participants were willing to pay the most for fast food followed by sweet snacks, and willing to wait longer for sweet snacks relative to other food types. While fast food and sweets also generated the most willingness to expend high and low effort, willingness to expend low effort for fruit was similar to that for fast food and sweets, and willingness to expend high effort for fruit was comparable to that for fast food. Participants were least willing to pay or expend low effort for vegetables. Higher COVID-related stress levels were associated with willingness to expend more effort and pay more for food items. These data collected during the pandemic demonstrate that highly processed and sweet foods have high motivating value across multiple measures of motivation, and COVID-related stress increases food motivation across food categories. Interventions to mitigate stress and target the link between stress and overeating may help to limit the effects of the COVID-19 pandemic on obesity.

Mind affects matter: Hindbrain GLP1 neurons link stress, physiology and behaviour

NEW FINDINGS

What is the topic of this review? This Lecture covers the role of caudal brainstem GLP1 neurons in acute and chronic stress responses. What advances does it highlight? This Lecture focuses on the recent advances in our understanding of GLP1 neurons and their physiological role in many aspects of stress. Particular focus is given to the recent elucidation, in part, of the anatomical basis for recruitment of GLP1 neurons in response to acute stress. Finally, the potential, but at this time somewhat speculative, role of GLP1 neurons in chronic stress is discussed.

ABSTRACT

The brain responds rapidly to stressful stimuli by increasing sympathetic outflow, activating the hypothalamic-pituitary-adrenal axis and eliciting avoidance behaviours to limit risks to safety. Stress responses are adaptive and essential but can become maladaptive when the stress is chronic, causing autonomic imbalance, hypothalamic-pituitary-adrenal axis hyper-reactivity and a state of hypervigilance. Ultimately, this contributes to the development of cardiovascular disease and affective disorders, including major depression and anxiety. Stress responses are often thought to be driven mainly by forebrain areas; however, the brainstem nucleus of the solitary tract (NTS) is ideally located to control both autonomic outflow and behaviour in response to stress. Here, I review the preclinical evidence that the NTS and its resident glucagon-like peptide-1 (GLP1)-expressing neurons are prominent mediators of stress responses. This Lecture introduces the reader to the idea of good and bad stress and outlines the types of stress that engage the NTS and GLP1 neurons. I describe in particular detail the recent studies by myself and others aimed at mapping sources of synaptic inputs to GLP1 neurons and consider the implications for our understanding of the role of GLP1 neurons in stress. This is followed by a discussion of the contribution of brain GLP1 and GLP1 neurons to behavioural and physiological stress responses. The evidence reviewed highlights a potentially prominent role for GLP1 neurons in the response of the brain to acute stress and reveals important unanswered questions regarding their role in chronic stress.

Chronic Isolation Stress Affects Central Neuroendocrine Signaling Leading to a Metabolically Active Microenvironment in a Mouse Model of Breast Cancer

Social isolation is a powerful stressor capable of affecting brain plasticity and function. In the case of breast cancer, previous data indicate that stressful experiences may contribute to a worse prognosis, activating neuroendocrine and metabolism pathways, although the mechanisms underlying these effects are still poorly understood. In this study, we tested the hypothesis that chronic isolation stress (IS) may boost hypothalamic–pituitary–adrenal (HPA) axis activity, leading to changes in the hypothalamic expression of genes modulating both mood and metabolism in an animal model of breast cancer. This centrally activated signaling cascade would, in turn, affect the mammary gland microenvironment specifically targeting fat metabolism, leading to accelerated tumor onset. MMTVNeuTg female mice (a model of breast cancer developing mammary hyperplasia at 5 months of age) were either group-housed (GH) or subjected to IS from weaning until 5 months of age. At this time, half of these subjects underwent acute restraint stress to assess corticosterone (CORT) levels, while the remaining subjects were characterized for their emotional profile in the forced swimming and saccharin preference tests. At the end of the procedures, all the mice were sacrificed to assess hypothalamic expression levels of Brain-derived neurotrophic factor (Bdnf), Neuropeptide Y (NpY), Agouti-Related Peptide (AgRP), and Serum/Glucocorticoid-Regulated Protein Kinase 1 (SgK1). Leptin and adiponectin expression levels, as well as the presence of brown adipose tissue (BAT), were assessed in mammary fat pads. The IS mice showed higher CORT levels following acute stress and decreased expression of NpY, AgRP, and SgK1, associated with greater behavioral despair in the forced swimming test. Furthermore, they were characterized by increased consumption of saccharin in a preference test, suggesting an enhanced hedonic profile. The IS mice also showed an earlier onset of breast lumps (assessed by palpation) accompanied by elevated levels of adipokines (leptin and adiponectin) and BAT in the mammary fat pads. Overall, these data point to IS as a pervasive stressor that is able to specifically target neuronal circuits, mastered by the hypothalamus, modulating mood, stress reactivity and energy homeostasis. The activation of such IS-driven machinery may hold main implications for the onset and maintenance of pro-tumorigenic environments.

Stress and eating behaviours in healthy adults: a systematic review and meta-analysis

Stress leads to detrimental health outcomes through direct biological and indirect behavioural changes. Stress can lead to disruption to normal eating behaviours, although the strength of these associations is unknown. This is the first meta-analysis to determine the strength of the stress-eating relationship in healthy adults and to explore the impact of potential moderators. Studies included had a clearly defined measure of stress (i.e., any noxious event or episode in one's environment with the exclusion of emotional distress) that was linked to non-disordered eating. Key terms were searched in Medline, PsycInfo and Ovid databases (23,104 studies identified). 54 studies (combined N = 119,820) were retained in the meta-analysis. A small, positive effect size was found for the stress-overall food intake relationship (Hedges' g = 0.114). Stress was associated with increased consumption of unhealthy foods (Hedges' g = 0.116) but decreased consumption of healthy foods (Hedges' g = -0.111). Only one significant moderator (restraint on stress-unhealthy eating) was identified. This meta-analysis identified the magnitude of the effect of stress on eating behaviour outcomes. Significant heterogeneity was observed that was not explained by the moderators examined. Further research on moderators of the stress-eating relationship is required and should distinguish effects for healthy versus unhealthy eating.

Converging vulnerability factors for compulsive food and drug use

Highly palatable foods and substance of abuse have intersecting neurobiological, metabolic and behavioral effects relevant for understanding vulnerability to conditions related to food (e.g., obesity, binge eating disorder) and drug (e.g., substance use disorder) misuse. Here, we review data from animal models, clinical populations and epidemiological evidence in behavioral, genetic, pathophysiologic and therapeutic domains. Results suggest that consumption of highly palatable food and drugs of abuse both impact and conversely are regulated by metabolic hormones and metabolic status. Palatable foods high in fat and/or sugar can elicit adaptation in brain reward and withdrawal circuitry akin to substances of abuse. Intake of or withdrawal from palatable food can impact behavioral sensitivity to drugs of abuse and vice versa. A robust literature suggests common substrates and roles for negative reinforcement, negative affect, negative urgency, and impulse control deficits, with both highly palatable foods and substances of abuse. Candidate genetic risk loci shared by obesity and alcohol use disorders have been identified in molecules classically associated with both metabolic and motivational functions. Finally, certain drugs may have overlapping therapeutic potential to treat obesity, diabetes, binge-related eating disorders and substance use disorders. Taken together, data are consistent with the hypotheses that compulsive food and substance use share overlapping, interacting substrates at neurobiological and metabolic levels and that motivated behavior associated with feeding or substance use might constitute vulnerability factors for one another. This article is part of the special issue on 'Vulnerabilities to Substance Abuse'.

The Impact of Chronic Stress and Eating Concern on Acylated Ghrelin Following Acute Psychological Stress in Healthy Men

Stress, mood, and eating behavior play an important role in appetite and weight regulation. In particular, ghrelin, as the only known orexigenic hormone, has been suggested to be an influential mediator in food intake responses to stress. The exact role of ghrelin in the hypothalamic–pituitary–adrenal axis is still unknown and further challenged by the psychological aspects of stress and eating behavior. This study aimed to assess the effect of chronic stress and subjective concern about eating on acute stress-induced changes in acylated ghrelin. In a 2-day study, sixteen healthy male participants were confronted with a stressful situation as well as a control situation. Additional measurements of heart rate, subjective hunger ratings, and subjective mood ratings were made to assess successful acute stress induction. The linear mixed model approach revealed a significant effect of acute stress on acylated ghrelin for a study-day*chronic-stress interaction (p < 0.001). Concern about eating did not affect acylated ghrelin levels after acute stress exposure. The significant interaction showed that lower chronic stress exposure was associated with a stronger acylated ghrelin response after acute stress exposure versus control condition. At the same time, participants with higher chronic stress exposure showed a blunted acylated ghrelin response after acute stress exposure compared to the control situation. Our findings indicate that chronic stress exposure can influence acylated ghrelin response after acute stress encounters, possibly affecting subsequent food intake and explaining the often diverse outcome in measurements of acute stress responses.

COVID-19 pandemic impact on children and adolescents' mental health: Biological, environmental, and social factors

Since the Coronavirus disease 2019 (COVID-19) pandemic, caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) was announced, we had an unprecedented change in the way we organize ourselves socially and in our daily routine. Children and adolescents were also greatly impacted by the abrupt withdrawal from school, social life and outdoor activities. Some of them also experienced domestic violence growing. The stress they are subjected to directly impacts their mental health on account of increased anxiety, changes in their diets and in school dynamics, fear or even failing to scale the problem. Our aim is to bring up a discussion under different aspects and to alert public health and government agents about the need for surveillance and care of these individuals. We hope that the damage to their mental health as a result of the side effect of this pandemic can be mitigated by adequate and timely intervention.

Brain-Gut-Microbiome Interactions and Intermittent Fasting in Obesity

The obesity epidemic and its metabolic consequences are a major public health problem both in the USA and globally. While the underlying causes are multifactorial, dysregulations within the brain–gut–microbiome (BGM) system play a central role. Normal eating behavior is coordinated by the tightly regulated balance between intestinal, extraintestinal and central homeostatic and hedonic mechanisms, resulting in stable body weight. The ubiquitous availability and marketing of inexpensive, highly palatable and calorie-dense food has played a crucial role in shifting this balance towards hedonic eating through both central (disruptions in dopaminergic signaling) and intestinal (vagal afferent function, metabolic toxemia, systemic immune activation, changes to gut microbiome and metabolome) mechanisms. The balance between homeostatic and hedonic eating behaviors is not only influenced by the amount and composition of the diet, but also by the timing and rhythmicity of food ingestion. Circadian rhythmicity affects both eating behavior and multiple gut functions, as well as the composition and interactions of the microbiome with the gut. Profound preclinical effects of intermittent fasting and time restricted eating on the gut microbiome and on host metabolism, mostly demonstrated in animal models and in a limited number of controlled human trials, have been reported. In this Review, we will discuss the effects of time-restricted eating on the BGM and review the promising effects of this eating pattern in obesity treatment.

Effects of transdermal mirtazapine on hyporexic rhesus and cynomolgus macaques (Macaca mulatta and Macaca fascicularis)

BACKGROUND

Hyporexia and weight loss are important indicators of physical and psychological well-being in macaque colonies. An FDA-approved transdermal formulated Mirtazapine (MTZ) shows effectiveness in managing feline hyporexia. This study sought to determine its effectiveness as an appetite stimulant in macaques.

METHODS

Fourteen macaques with idiopathic hyporexia, intractable to conventional management were treated with transdermal MTZ (0.5 mg/kg) topically administered to aural pinnae once daily for 14 days. Qualitative food consumption was monitored daily for 6 months. Body weights were collected prior to treatment, every 2 weeks for the first 6 weeks, 10 weeks, and 6 months post-treatment.

RESULTS

Transdermal MTZ significantly reduced the frequency of hyporexia during treatment and monthly for 6 months. No significant increase in weight noted until approximately 6 months post-treatment.

CONCLUSIONS

Results from this study indicate that a short course of transdermal MTZ is an effective way to increase food consumption in macaques chronically.

Posttraumatic stress disorder and changes in diet quality over 20 years among US women

BACKGROUND

Individuals with posttraumatic stress disorder (PTSD) are at increased risk of various chronic diseases. One hypothesized pathway is via changes in diet quality. This study evaluated whether PTSD was associated with deterioration in diet quality over time.

METHODS

Data were from 51 965 women in the Nurses' Health Study II PTSD sub-study followed over 20 years. Diet, assessed at 4-year intervals, was characterized via the Alternative Healthy Eating Index-2010 (AHEI). Based on information from the Brief Trauma Questionnaire and Short Screening Scale for DSM-IV PTSD, trauma/PTSD status was classified as no trauma exposure, prevalent exposure (trauma/PTSD onset before study entry), or new-onset (trauma/PTSD onset during follow-up). We further categorized women with prevalent exposure as having trauma with no PTSD symptoms, trauma with low PTSD symptoms, and trauma with high PTSD symptoms, and created similar categories for women with new-onset exposure, resulting in seven comparison groups. Multivariable linear mixed-effects spline models tested differences in diet quality changes by trauma/PTSD status over follow-up.

RESULTS

Overall, diet quality improved over time regardless of PTSD status. In age-adjusted models, compared to those with no trauma, women with prevalent high PTSD and women with new-onset high PTSD symptoms had 3.3% and 3.6% lower improvement in diet quality, respectively, during follow-up. Associations remained consistent after adjusting for health conditions, sociodemographics, and behavioral characteristics.

CONCLUSIONS

PTSD is associated with less healthy changes in overall diet quality over time. Poor diet quality may be one pathway linking PTSD with a higher risk of chronic disease development.

Brain-gut-microbiome interactions in obesity and food addiction

Normal eating behaviour is coordinated by the tightly regulated balance between intestinal and extra-intestinal homeostatic and hedonic mechanisms. By contrast, food addiction is a complex, maladaptive eating behaviour that reflects alterations in brain-gut-microbiome (BGM) interactions and a shift of this balance towards hedonic mechanisms. Each component of the BGM axis has been implicated in the development of food addiction, with both brain to gut and gut to brain signalling playing a role. Early-life influences can prime the infant gut microbiome and brain for food addiction, which might be further reinforced by increased antibiotic usage and dietary patterns throughout adulthood. The ubiquitous availability and marketing of inexpensive, highly palatable and calorie-dense food can further shift this balance towards hedonic eating through both central (disruptions in dopaminergic signalling) and intestinal (vagal afferent function, metabolic endotoxaemia, systemic immune activation, changes to gut microbiome and metabolome) mechanisms. In this Review, we propose a systems biology model of BGM interactions, which incorporates published reports on food addiction, and provides novel insights into treatment targets aimed at each level of the BGM axis.

Differential impact of stress and environmental enrichment on corticolimbic circuits

Stress exposure can produce profound changes in physiology and behavior that can impair health and well-being. Of note, stress exposure is linked to anxiety disorders and depression in humans. The widespread impact of these disorders warrants investigation into treatments to mitigate the harmful effects of stress. Pharmacological treatments fail to help many with these disorders, so recent work has focused on non-pharmacological alternatives. One of the most promising of these alternatives is environmental enrichment (EE). In rodents, EE includes social, physical, and cognitive stimulation for the animal, in the form of larger cages, running wheels, and toys. EE successfully reduces the maladaptive effects of various stressors, both as treatment and prophylaxis. While we know that EE can have beneficial effects under stress conditions, the morphological and molecular mechanisms underlying these behavioral effects are still not well understood. EE is known to alter neurogenesis, dendrite development, and expression of neurotrophic growth factors, effects that vary by type of enrichment, age, and sex. To add to this complexity, EE has differential effects in different brain regions. Understanding how EE exerts its protective effects on morphological and molecular levels could hold the key to developing more targeted pharmacological treatments. In this review, we summarize the literature on the morphological and molecular consequences of EE and stress in key emotional regulatory pathways in the brain, the hippocampus, prefrontal cortex, and amygdala. The similarities and differences among these regions provide some insight into stress-EE interaction that may be exploited in future efforts toward prevention of, and intervention in, stress-related diseases.