Hormonal and neural mechanisms of food reward, eating behaviour and obesity

The effect of underweight on female and male reproduction

Chronic energy deficiency can impair the hypothalamic-pituitary-gonadal (HPG) axis and lead to hypothalamic anovulation in underweight women. This review presents the syndromes related to underweight status that are associated with infertility, summarizes the underlying mechanisms, and reviews the available treatment options. Eating disorders, such as anorexia nervosa (AN), constitute the most common cause of infertility in underweight women, who, in addition, experience miscarriages, and sexual dysfunction. The relative energy deficiency in sports (RED-S; former terminology: athlete's triad) involves menstrual dysfunction due to low energy availability, which results in anovulation. Moreover, lipodystrophies, malnutrition, starvation, systematic illnesses (malignancies, endocrinopathies, infectious diseases, advanced chronic diseases, neurologic illnesses), and the utilization of drugs can cause excessive weight loss. They may result in fertility problems due to the loss of adipose tissue and the subsequent hormonal disturbances. Each of these conditions requires multidisciplinary management. Nutritional counseling should target the restoration of energy balance by increasing intake and reducing output. Medical treatment, recommended only for patients who did not respond to standard treatment, may include antipsychotics, antidepressants, or leptin administration. Finally, psychiatric treatment is considered an integral part of the standard treatment.

Bidirectional relationships between appetitive behaviours and body mass index in childhood: a cross-lagged analysis in the Generation XXI birth cohort

PURPOSE

Appetitive behaviours have been associated with body mass index (BMI). However, existing data were largely derived from cross-sectional studies and cannot provide insight into the direction of associations. We aimed to explore the bidirectionality of these associations in school-age children.

METHODS

Participants are from the Generation XXI birth cohort, assessed at both 7 and 10 years of age (n = 4264; twins excluded). The Children's Eating Behaviour Questionnaire (CEBQ) was used to measure appetitive behaviours (8 subscales). Anthropometrics were measured and WHO BMI z-score was calculated. Cross-lagged analyses were performed to compare the magnitude and direction of the associations (behaviours at 7 years to BMI z-score at 10 years and the reverse) (covariates: child's sex, physical exercise, maternal age and education; plus BMI z-score at age 7 or, in the reverse direction, the subscale score).

RESULTS

In cross-lagged analyses, appetitive behaviours at 10 years of age (apart from emotional undereating) were shown to be reactive to the child BMI z-score at 7 years of age. Only slowness in eating was significantly related to subsequent BMI. However, the strongest association was from the child BMI z-score to the behaviour (β_standardized = - 0.028 compared with β_standardized = - 0.103, likelihood ratio test p < 0.001).

CONCLUSIONS

BMI at age 7 was related to appetitive behaviours at 10 years of age, rather than the reverse. This suggests that children with a higher BMI in middle childhood are at increased risk of developing an avid appetite over time.

Oxytocin in the neural control of eating: At the crossroad between homeostatic and non-homeostatic signals

The understanding of the biological substrates regulating feeding behavior is relevant to address the health problems related to food overconsumption. Several studies have expanded the conventional view of the homeostatic regulation of body weight mainly orchestrated by the hypothalamus, to include also the non-homeostatic control of appetite. Such processes include food reward and are mainly coordinated by the activation of the central mesolimbic dopaminergic pathway. The identification of endogenous systems acting as a bridge between homoeostatic and non-homeostatic pathways might represent a significant step toward the development of drugs for the treatment of aberrant eating patterns. Oxytocin is a hypothalamic hormone that is directly secreted into the brain and reaches the blood circulation through the neurohypophysis. Oxytocin regulates a variety of physiologic functions, including eating and metabolism. In the last years both preclinical and clinical studies well characterized oxytocin for its effects in reducing food intake and body weight. In the present review we summarize the role played by oxytocin in the control of both homeostatic and non-homeostatic eating, within cognitive, metabolic and reward mechanisms, to mostly highlight its potential therapeutic effects as a new pharmacological approach for the development of drugs for eating disorders. We conclude that the central oxytocinergic system is possibly one of the mechanisms that coordinate energy balance at the crossroads between homeostatic and non-homeostatic mechanisms. This concept should foster studies aimed at exploring the possible exploitation of oxytocin in the treatment of aberrant eating patterns. This article is part of the special issue on Neuropeptides.

Decreased mesolimbic dopaminergic signaling underlies the waning of maternal caregiving across the postpartum period in rats

RATIONALE

Mesolimbic dopamine (DA) signaling is essential for the high maternal caregiving characteristic of the early postpartum period, but little is known about dopamine's role in the expression of maternal caregiving thereafter.

OBJECTIVES

We tested the hypothesis that decreased mesolimbic dopaminergic signaling is particularly responsible for the natural decline in maternal caregiving that occurs as the postpartum period progresses.

METHODS

Sprague-Dawley (SD) mother rats received intraperitoneal injections of either vehicle, the DA D1 receptor agonist SKF38393, the DA D2 receptor agonist quinpirole, or both agonists twice daily from postpartum days 9 to 15. In a separate experiment involving Long-Evans (LE) rats, we examined whether DA D1 and D2 receptor mRNAs in the nucleus accumbens (NA) shell and ventral tegmental area (VTA), along with DA turnover in the VTA, decline across the postpartum period in parallel with the decreasing maternal behavior.

RESULTS

All drug treatments significantly maintained higher frequencies of active maternal behaviors (nesting, pup licking, retrieval) compared to vehicle. Furthermore, the majority of mothers treated with SKF38393 either alone or combined with quinpirole maintained full expression of maternal behavior during behavioral testing. D2 receptor mRNA levels were found to be lower in the late postpartum NA shell and VTA compared to early postpartum, but D1 receptor mRNA levels in the NA shell were higher in the late postpartum period. Furthermore, both late postpartum and recently parturient LE mothers had higher VTA DA turnover compared to nulliparae, suggesting changes in mesolimbic signal-to-noise ratio both at the end and beginning of motherhood.

CONCLUSIONS

Collectively, our results suggest that alterations in mesolimbic DA is part of the neural substrate responsible for dynamic maternal caregiving across the entire postpartum period.

Effects of oral, smoked, and vaporized cannabis on endocrine pathways related to appetite and metabolism: a randomized, double-blind, placebo-controlled, human laboratory study

As perspectives on cannabis continue to shift, understanding the physiological and behavioral effects of cannabis use is of paramount importance. Previous data suggest that cannabis use influences food intake, appetite, and metabolism, yet human research in this regard remains scant. The present study investigated the effects of cannabis administration, via different routes, on peripheral concentrations of appetitive and metabolic hormones in a sample of cannabis users. This was a randomized, crossover, double-blind, placebo-controlled study. Twenty participants underwent four experimental sessions during which oral cannabis, smoked cannabis, vaporized cannabis, or placebo was administered. Active compounds contained 6.9 ± 0.95% (~50.6 mg) ∆9-tetrahydrocannabinol (THC). Repeated blood samples were obtained, and the following endocrine markers were measured: total ghrelin, acyl-ghrelin, leptin, glucagon-like peptide-1 (GLP-1), and insulin. Results showed a significant drug main effect (p = 0.001), as well as a significant drug × time-point interaction effect (p = 0.01) on insulin. The spike in blood insulin concentrations observed under the placebo condition (probably due to the intake of brownie) was blunted by cannabis administration. A significant drug main effect (p = 0.001), as well as a trend-level drug × time-point interaction effect (p = 0.08) was also detected for GLP-1, suggesting that GLP-1 concentrations were lower under cannabis, compared to the placebo condition. Finally, a significant drug main effect (p = 0.01) was found for total ghrelin, suggesting that total ghrelin concentrations during the oral cannabis session were higher than the smoked and vaporized cannabis sessions. In conclusion, cannabis administration in this study modulated blood concentrations of some appetitive and metabolic hormones, chiefly insulin, in cannabis users. Understanding the mechanisms underpinning these effects may provide additional information on the cross-talk between cannabinoids and physiological pathways related to appetite and metabolism.

High Fat Diet Suppresses Peroxisome Proliferator-Activated Receptors and Reduces Dopaminergic Neurons in the Substantia Nigra

Although several epidemiologic and animal studies have revealed correlations between obesity and neurodegenerative disorders, such as Parkinson disease (PD), the underlying pathological mechanisms of obesity-induced PD remain unclear. Our study aimed to assess the effect of diet-induced obesity on the brain dopaminergic pathway. For five months, starting from weaning, we gave C57BL/6 mice a high-fat diet (HFD) to generate an obese mouse model and investigate whether the diet reprogrammed the midbrain dopaminergic system. Tyrosine hydroxylase staining showed that the HFD resulted in fewer dopaminergic neurons in the substantia nigra (SN), but not the striatum. It also induced neuroinflammation, with increased astrogliosis in the SN and striatum. Dendritic spine density in the SN of HFD-exposed mice decreased, which suggested that prolonged HFD altered dopaminergic neuroplasticity. All three peroxisome proliferator-activated receptor (PPAR) subtype (PPAR-α, PPAR-β/δ, PPAR-γ) levels were significantly reduced in the SN and the ventral tegmental area of HFD mice when compared to those in controls. This study showed that a prolonged HFD induced neuroinflammation, suppressed PPAR levels, caused degeneration of midbrain dopaminergic neurons, and resulted in symptoms reminiscent of human PD. To our knowledge, this is the first study documenting the effects of an HFD on PPARs in dopaminergic neurons.

Developing Insulin and BDNF Mimetics for Diabetes Therapy

Diabetes is a global public health concern nowadays. The majority of diabetes mellitus (DM) patients belong to type 2 diabetes mellitus (T2DM), which is highly associated with obesity. The general principle of current therapeutic strategies for patients with T2DM mainly focuses on restoring cellular insulin response by potentiating the insulin-induced signaling pathway. In late-stage T2DM, impaired insulin production requires the patients to receive insulin replacement therapy for maintaining their glucose homeostasis. T2DM patients also demonstrate a drop of brain-derived neurotrophic factor (BDNF) in their circulation, which suggests that replenishing BDNF or enhancing its downstream signaling pathway may be beneficial. Because of their protein nature, recombinant insulin or BDNF possess several limitations that hinder their clinical application in T2DM treatment. Thus, developing orally active "insulin pill" or "BDNF pill" is essential to provide a more convenient and effective therapy. This article reviews the current development of non-peptidyl chemicals that mimic insulin or BDNF and their potential as anti-diabetic agents.

Neuroendocrinology of reward in anorexia nervosa and bulimia nervosa: Beyond leptin and ghrelin

The pathophysiology of anorexia nervosa (AN) and bulimia nervosa (BN) are still poorly understood, but psychobiological models have proposed a key role for disturbances in the neuroendocrines that signal hunger and satiety and maintain energy homeostasis. Mounting evidence suggests that many neuroendocrines involved in the regulation of homeostasis and body weight also play integral roles in food reward valuation and learning via their interactions with the mesolimbic dopamine system. Neuroimaging data have associated altered brain reward responses in this system with the dietary restriction and binge eating and purging characteristic of AN and BN. Thus, neuroendocrine dysfunction may contribute to or perpetuate eating disorder symptoms via effects on reward circuitry. This narrative review focuses on reward-related neuroendocrines that are altered in eating disorder populations, including peptide YY, insulin, stress and gonadal hormones, and orexins. We provide an overview of the animal and human literature implicating these neuroendocrines in dopaminergic reward processes and discuss their potential relevance to eating disorder symptomatology and treatment.

Increasing Dietary Carbohydrate as Part of a Healthy Whole Food Diet Intervention Dampens Eight Week Changes in Salivary Cortisol and Cortisol Responsiveness

It is largely unknown whether and how whole food diets influence psychological stress and stress system responsiveness. To better understand the effects of whole diets on stress system responsiveness, we examined randomized control trial effects of a whole food diet based on the Dietary Guidelines for Americans (DGA) on cortisol responsiveness. A randomized, double-blind, controlled 8-week intervention was conducted in overweight and obese women to examine differentiated effects between two diet intervention groups: one based on the 2010 DGA and the other one based on a typical American diet (TAD). During a test week that occurred at baseline and again after 8 weeks of the intervention, we assessed salivary cortisol collected at 14 selected times across the day, including upon awakening, at bedtime, and during a test visit, and administered a standardized social stress task (Trier Social Stress Test, TSST). There were no statistical differences between the diet groups in salivary cortisol at baseline or after 8 weeks. However, when considering differences in dietary carbohydrate, but not fat or protein, from the pre-intervention (habitual) to the intervention period, there was a significant (P = 0.0001) interaction between diet group, intervention week, saliva sample, and level of intervention-based change in carbohydrate consumption. This interaction was reflected primarily by an 8-week reduction in salivary cortisol during a period just prior to (log Δ −0.35 ± 0.12 nmol/L) and 30 (log Δ −0.49 ± 0.12 nmol/L), 60 (log Δ −0.50 ± 0.13 nmol/L), 90 (log Δ −0.51 ± 0.13 nmol/L), and 120 (log Δ −0.4476 ± 0.1231 nmol/L) min after the TSST in the DGA group having the highest increase (90th percentile) in carbohydrate consumption. In support of this finding, we also found significant (P < 0.05) and inverse linear associations between dietary carbohydrate and log salivary cortisol, with the strongest negative association (β: −0.004 ± 0.0015, P = 0.009) occurring at 30 min post-TSST, but only in the DGA group and at week 9 of the intervention. Together, increasing dietary carbohydrate as part of a DGA-based diet may reduce circulating cortisol and dampen psychological stress-related cortisol responsiveness.

Of mice and men: incretin actions in the central nervous system

Incretins have risen to the forefront of therapies for obesity and related metabolic complications, primarily because of their efficacy and relatively few side effects. Importantly, their efficacy in altering energy balance and decreasing body weight is apparently through actions in the central nervous system (CNS); the latter may have implications beyond obesity per se, i.e. in other disease states associated with obesity including CNS-related disorders. Here, we first describe the role of the CNS in energy homeostasis and then the current state of knowledge in terms of incretin physiology, pathophysiology and efficacy in preclinical and clinical studies. In the future, more clinical studies are needed to fully map mechanistic pathways underlying incretin actions and outcomes in the human CNS. Additionally, future research will likely lead to the discovery of additional novel incretins and/or more efficacious medications with less side effects through the improvement of current compounds with properties that would allow them to have more favorable pharmacokinetic and pharmacodynamic profiles and/or by combining known and novel incretins into safe and more efficacious combination therapies leading ultimately to more tangible benefits for our patients.

RhoA in tyrosine hydroxylase neurones regulates food intake and body weight via altered sensitivity to peripheral hormones

Dopamine-producing tyrosine hydroxylase (TH) neurones in the hypothalamic arcuate nucleus (ARC) have recently been shown to be involved in ghrelin signalling and body weight homeostasis. In the present study, we investigate the role of the intracellular regulator RhoA in hypothalamic TH neurones in response to peripheral hormones. Diet-induced obesity was found to be associated with increased phosphorylation of TH in ARC, indicating obesity-associated increased activity of ARC TH neurones. Mice in which RhoA was specifically knocked out in TH neurones (TH-RhoA^-/- mice) were more sensitive to the orexigenic effect of peripherally administered ghrelin and displayed an abolished response to the anorexigenic hormone leptin. When TH-RhoA^-/- mice were challenged with a high-fat high-sucrose (HFHS) diet, they became hyperphagic and gained more body weight and fat mass compared to wild-type control mice. Importantly, lack of RhoA prevented development of ghrelin resistance, which is normally observed in wild-type mice after long-term HFHS diet feeding. Patch-clamp electrophysiological analysis demonstrated increased ghrelin-induced excitability of TH neurones in lean TH-RhoA^-/- mice compared to lean littermate control animals. Additionally, increased expression of the orexigenic hypothalamic neuropeptides agouti-related peptide and neuropeptide Y was observed in TH-RhoA^-/- mice. Overall, our data indicate that TH neurones in ARC are important for the regulation of body weight homeostasis and that RhoA is both a central effector in these neurones and important for the development of obesity-induced ghrelin resistance. The obese phenotype of TH-RhoA^-/- mice may be a result of increased sensitivity to ghrelin and decreased sensitivity to leptin, resulting in increased food intake.

Immunometabolism: Insights from the Drosophila model

Multicellular organisms inhabit an environment that includes a mix of essential nutrients and large numbers of potentially harmful microbes. Germline-encoded receptors scan the environment for microbe associated molecular patterns, and, upon engagement, activate powerful defenses to protect the host from infection. At the same time, digestive enzymes and transporter molecules sieve through ingested material for building blocks and energy sources necessary for survival, growth, and reproduction. We tend to view immune responses as a potent array of destructive forces that overwhelm potentially harmful agents. In contrast, we view metabolic processes as essential, constructive elements in the maintenance and propagation of life. However, there is considerable evidence of functional overlap between the two processes, and disruptions to one frequently modify outputs of the other. Studies of immunometabolism, or interactions between immunity and metabolism, have increased in prominence with the discovery of inflammatory components to metabolic diseases such as type two diabetes. In this review, we will focus on contributions of studies with the fruit fly, Drosophila melanogaster, to our understanding of immunometabolism. Drosophila is widely used to study immune signaling, and to understand the regulation of metabolism in vivo, and this insect has considerable potential as a tool to build our understanding of the molecular and cellular bridges that connect immune and metabolic pathways.

Obesity: global epidemiology and pathogenesis

The prevalence of obesity has increased worldwide in the past ~50 years, reaching pandemic levels. Obesity represents a major health challenge because it substantially increases the risk of diseases such as type 2 diabetes mellitus, fatty liver disease, hypertension, myocardial infarction, stroke, dementia, osteoarthritis, obstructive sleep apnoea and several cancers, thereby contributing to a decline in both quality of life and life expectancy. Obesity is also associated with unemployment, social disadvantages and reduced socio-economic productivity, thus increasingly creating an economic burden. Thus far, obesity prevention and treatment strategies - both at the individual and population level - have not been successful in the long term. Lifestyle and behavioural interventions aimed at reducing calorie intake and increasing energy expenditure have limited effectiveness because complex and persistent hormonal, metabolic and neurochemical adaptations defend against weight loss and promote weight regain. Reducing the obesity burden requires approaches that combine individual interventions with changes in the environment and society. Therefore, a better understanding of the remarkable regional differences in obesity prevalence and trends might help to identify societal causes of obesity and provide guidance on which are the most promising intervention strategies.

Sustained behaviour change in healthy eating to improve obesity outcomes: It is time to abandon willpower to appreciate wanting

The purpose of this study was to report on a nationally representative survey of the experience of Canadian adults regarding food cravings and the impact of these cravings on behaviour and quality of life. A total of 1532 respondents (16% of members of an online panel emailed an invitation and link) completed a nationally distributed survey. Almost two-thirds of the sample reported experiencing cravings, with women being more likely to report cravings than men. Of those with cravings, 83.1% reported moderate or strong cravings. Cravings impacted eating behaviours and quality of life, especially for those with strong cravings. Cravings were associated with being bored, emotional or watching TV. Those who identified themselves as overweight or as trying to lose weight were more likely to have cravings. Of those reporting to be overweight and trying to lose weight few experienced distress because of lack of access to help and rates of interest in being guided by healthcare professionals were low, except in those with strong cravings. These results reinforce the notion that eating behaviour may differ from other behaviours in that there is a strong drive to eat that is difficult to control for many individuals. Behavioural interventions targeting healthy eating should be developed to address this construct of drive to eat, that is, food cravings.

Brief communication: β-cell function influences dopamine receptor availability

We aim to identify physiologic regulators of dopamine (DA) signaling in obesity but previously did not find a compelling relationship with insulin sensitivity measured by oral-minimal model (OMM) and DA subtype 2 and 3 receptor (D2/3R) binding potential (BPND). Reduced disposition index (DI), a β-cell function metric that can also be calculated by OMM, was shown to predict a negative reward behavior that occurs in states of lower endogenous DA. We hypothesized that reduced DI would occur with higher D2/3R BPND, reflecting lower endogenous DA. Participants completed PET scanning, with a displaceable radioligand to measure D2/3R BPND, and a 5-hour oral glucose tolerance test to measure DI by OMM. We studied 26 age-similar females without (n = 8) and with obesity (n = 18) (22 vs 39 kg/m2). Reduced DI predicted increased striatal D2/3R BPND independent of BMI. By accounting for β-cell function, we were able to determine that the state of insulin and glucose metabolism is pertinent to striatal D2/3R BPND in obesity. Clinical Trial Registration Number: NCT00802204.

Neural vulnerability factors for obesity

Multiple theories identify neural vulnerability factors that may increase risk for overeating and weight gain. Early cross-sectional neuroimaging studies were unable to determine whether aberrant neural responsivity was a risk factor for or a consequence of overeating. More recent obesity risk, prospective, repeated-measures, and experimental neuroimaging studies with humans have advanced knowledge of etiologic processes and neural plasticity resulting from overeating. Herein, we review evidence from these more rigorous human neuroimaging studies, in conjunction with behavioral measures reflecting neural function, as well as experiments with animals that investigated neural vulnerability theories for overeating. Findings provide support for the reward surfeit theory that posits that individuals at risk for obesity initially show hyper-responsivity of reward circuitry to high-calorie food tastes, which theoretically drives elevated intake of such foods. However, findings provide little support for the reward deficit theory that postulates that individuals at risk for obesity show an initial hypo-responsivity of reward circuitry that motives overeating. Further, results provide support for the incentive sensitization and dynamic vulnerability theories that propose that overconsumption of high-calorie foods results in increased reward and attention region responsivity to cues that are associated with hedonic reward from intake of these high-calorie foods via conditioning, as well as a simultaneous decrease in reward region responsivity to high-calorie food tastes. However, there is little evidence that this induced reduction in reward region response to high-calorie food tastes drives an escalation in overeating. Finally, results provide support for the theory that an initial deficit in inhibitory control and a bias for immediate reward contribute to overconsumption of high-calorie foods. Findings imply that interventions that reduce reward and attention region responsivity to food cues and increase inhibitory control should reduce overeating and excessive weight gain, an intervention theory that is receiving support in randomized trials.

Uncontrolled eating: a unifying heritable trait linked with obesity, overeating, personality and the brain

Many eating-related psychological constructs have been proposed to explain obesity and overeating. However, these constructs, including food addiction, disinhibition, hedonic hunger, emotional eating, binge eating and the like all have similar definitions, emphasizing loss of control over intake. As questionnaires measuring the constructs correlate strongly (r > 0.5) with each other, we propose that these constructs should be reconsidered to be part of a single broad phenotype: uncontrolled eating. Such an approach enables reviewing and meta-analysing evidence obtained with each individual questionnaire. Here, we describe robust associations between uncontrolled eating, body mass index (BMI), food intake, personality traits and brain systems. Reviewing cross-sectional and longitudinal data, we show that uncontrolled eating is phenotypically and genetically intertwined with BMI and food intake. We also review evidence on how three psychological constructs are linked with uncontrolled eating: lower cognitive control, higher negative affect and a curvilinear association with reward sensitivity. Uncontrolled eating mediates all three constructs' associations with BMI and food intake. Finally, we review and meta-analyse brain systems possibly subserving uncontrolled eating: namely, (i) the dopamine mesolimbic circuit associated with reward sensitivity, (ii) frontal cognitive networks sustaining dietary self-control and (iii) the hypothalamus-pituitary-adrenal axis, amygdala and hippocampus supporting stress reactivity. While there are limits to the explanatory and predictive power of the uncontrolled eating phenotype, we conclude that treating different eating-related constructs as a single concept, uncontrolled eating, enables drawing robust conclusions on the relationship between food intake and BMI, psychological variables and brain structure and function.

Neuropeptides Exert Neuroprotective Effects in Alzheimer's Disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by cognitive deficits and neuronal loss. Deposition of beta-amyloid peptide (Aβ) causes neurotoxicity through the formation of plaques in brains of Alzheimer's disease. Numerous studies have indicated that the neuropeptides including ghrelin, neurotensin, pituitary adenylate cyclase-activating polypeptide (PACAP), neuropeptide Y, substance P and orexin are closely related to the pathophysiology of Alzheimer's disease. The levels of neuropeptides and their receptors change in Alzheimer's disease. These neuropeptides exert neuroprotective roles mainly through preventing Aβ accumulation, increasing neuronal glucose transport, increasing the production of neurotrophins, inhibiting endoplasmic reticulum stress and autophagy, modulating potassium channel activity and hippocampal long-term potentiation. Therefore, the neuropeptides may function as potential drug targets in the prevention and cure of Alzheimer's disease.

Diet Quality for Sodium and Vegetables Mediate Effects of Whole Food Diets on 8-Week Changes in Stress Load

Very little is known about how whole food diets, such as those based on the Dietary Guidelines for Americans (DGA), influence psychological stress and physiological stress load. To better understand the effects of whole food diets on stress, we examined in a randomized control trial the effects of a DGA-based diet on markers of psychological and physiological stress. A randomized, double-blind, controlled 8-week intervention was conducted in overweight and obese women randomly assigned to one of two diet groups: a diet based on the 2010 DGA or a diet based on a Typical American Diet (TAD). The Perceived Stress Scale and allostatic load were used to assess stress load. Eight-week change in perceived stress did not significantly (p = 0.45) differ between the DGA (+0.53 ± 0.99) and TAD (-0.57 ± 0.99) groups. Likewise, 8-week change in allostatic load did not significantly (p = 0.79) differ between the two diet intervention groups (DGA: +0.001 ± 0.26 vs. TAD: +0.105 ± 0.28). However, we did find strong inverse associations between 8-week change in stress and intervention-based improvements in diet quality (lower sodium and higher vegetable consumption). When statistically accounting for these inverse associations, we found that perceived stress and allostatic load were higher (p < 0.04) in the DGA group. These findings suggest that improvements in dietary vegetable and sodium intake mediated effects of the diet intervention on psychological and physiological stress load. That is, adopting and adhering to a diet of higher quality (DGA) for 8 weeks may have been generally more stressful in the absence of improvements in vegetable or sodium consumption. This study provides further evidence for the mental health benefits of maximizing vegetable and minimizing sodium consumption.

The Neuroendocrinology of the Microbiota-Gut-Brain Axis: A Behavioural Perspective

The human gut harbours trillions of symbiotic bacteria that play a key role in programming different aspects of host physiology in health and disease. These intestinal microbes are also key components of the gut-brain axis, the bidirectional communication pathway between the gut and the central nervous system (CNS). In addition, the CNS is closely interconnected with the endocrine system to regulate many physiological processes. An expanding body of evidence is supporting the notion that gut microbiota modifications and/or manipulations may also play a crucial role in the manifestation of specific behavioural responses regulated by neuroendocrine pathways. In this review, we will focus on how the intestinal microorganisms interact with elements of the host neuroendocrine system to modify behaviours relevant to stress, eating behaviour, sexual behaviour, social behaviour, cognition and addiction.

Predictive regulation and human design

Organisms evolving toward greater complexity were selected across aeons to use energy and resources efficiently. Efficiency depended on prediction at every stage: first a clock to predict the planet's statistical regularities; then a brain to predict bodily needs and compute commands that dynamically adjust the flows of energy and nutrients. Predictive regulation (allostasis) frugally matches resources to needs and thus forms a core principle of our design. Humans, reaching a pinnacle of cognitive complexity, eventually produced a device (the steam engine) that converted thermal energy to work and were suddenly awash in resources. Today boundless consumption in many nations challenges all our regulatory mechanisms, causing obesity, diabetes, drug addiction and their sequelae. So far we have sought technical solutions, such as drugs, to treat complex circuits for metabolism, appetites and mood. Here I argue for a different approach which starts by asking: why does our regulatory system, which evolution tuned for small satisfactions, now constantly demand 'more'?

Lateral hypothalamic GLP-1 receptors are critical for the control of food reinforcement, ingestive behavior and body weight

Increased motivation for highly rewarding food is a major contributing factor to obesity. Most of the literature focuses on the mesolimbic nuclei as the core of reward behavior regulation. However, the lateral hypothalamus (LH) is also a key reward-control locus in the brain. Here we hypothesize that manipulating glucagon-like peptide-1 receptor (GLP-1R) activity selectively in the LH can profoundly affect food reward behavior, ultimately leading to obesity. Progressive ratio operant responding for sucrose was examined in male and female rats, following GLP-1R activation and pharmacological or genetic GLP-1R blockade in the LH. Ingestive behavior and metabolic parameters, as well as molecular and efferent targets, of the LH GLP-1R activation were also evaluated. Food motivation was reduced by activation of LH GLP-1R. Conversely, acute pharmacological blockade of LH GLP-1R increased food motivation but only in male rats. GLP-1R activation also induced a robust reduction in food intake and body weight. Chronic knockdown of LH GLP-1R induced by intraparenchymal delivery of an adeno-associated virus-short hairpin RNA construct was sufficient to markedly and persistently elevate ingestive behavior and body weight and ultimately resulted in a doubling of fat mass in males and females. Interestingly, increased food reinforcement was again found only in males. Our data identify the LH GLP-1R as an indispensable element of normal food reinforcement, food intake and body weight regulation. These findings also show, for we believe the first time, that brain GLP-1R manipulation can result in a robust and chronic body weight gain. The broader implications of these findings are that the LH differs between females and males in its ability to control motivated and ingestive behaviors.

Estradiol and the control of feeding behavior

This review lays out the evidence for the role of E2 in homeostatic and hedonic feeding across several species. While significant effort has been expended on homeostatic feeding research, more studies for hedonic feeding need to be conducted (i.e. are there increases in meal size and enhanced motivation to natural food rewards). By identifying the underlying neural circuitry involved, one can better delineate the mechanisms by which E2 influences feeding behavior. By utilizing more selective neural targeting techniques, such as optogenetics, significant progress can be made toward this goal. Together, behavioral and physiological techniques will help us to better understand neural deficits that can increase the risk for obesity in the absence of E2 (menopause) and aid in developing therapeutic strategies.

Increased ethanol consumption after interruption of fat bingeing

There is a marked comorbidity between alcohol abuse and eating disorders, especially in the young population. We have previously reported that bingeing on fat during adolescence increases the rewarding effects of ethanol (EtOH). The aim of the present work was to study if vulnerability to EtOH persists after cessation of binge eating. OF1 mice binged on fat (HFB: high-fat binge) during adolescence (PND 25-43) and were tested for 15 days after the last access to HFB (on PND 59) using the self-administration paradigm, the conditioned place preference (CPP) and locomotor sensitization to ethanol. Our results showed that after 15 days of cessation of fat ingestion, mice increased their consumption of ethanol and showed greater motivation to obtain ethanol. On the other hand, no effects were observed in the CPP, while an increased locomotor response to ethanol was detected. The present results confirm and extend our previous study demonstrating that the compulsive intake of fat induces long-lasting effects on the reward system that lead to an increased consumption of EtOH.

Contrast-Enhanced Magnetic Resonance Imaging of Gastric Emptying and Motility in Rats

The assessment of gastric emptying and motility in humans and animals typically requires radioactive imaging or invasive measurements. Here, we developed a robust strategy to image and characterize gastric emptying and motility in rats based on contrast-enhanced magnetic resonance imaging (MRI) and computer-assisted image processing. The animals were trained to naturally consume a gadolinium-labeled dietgel while bypassing any need for oral gavage. Following this test meal, the animals were scanned under low-dose anesthesia for high-resolution T1-weighted MRI in 7 Tesla, visualizing the time-varying distribution of the meal with greatly enhanced contrast against non-gastrointestinal (GI) tissues. Such contrast-enhanced images not only depicted the gastric anatomy, but also captured and quantified stomach emptying, intestinal filling, antral contraction, and intestinal absorption with fully automated image processing. Over four postingestion hours, the stomach emptied by 27%, largely attributed to the emptying of the forestomach rather than the corpus and the antrum, and most notable during the first 30 min. Stomach emptying was accompanied by intestinal filling for the first 2 h, whereas afterward intestinal absorption was observable as cumulative contrast enhancement in the renal medulla. The antral contraction was captured as a peristaltic wave propagating from the proximal to distal antrum. The frequency, velocity, and amplitude of the antral contraction were on average 6.34 ± 0.07 contractions per minute, 0.67 ± 0.01 mm/s, and 30.58 ± 1.03%, respectively. These results demonstrate an optimized MRI-based strategy to assess gastric emptying and motility in healthy rats, paving the way for using this technique to understand GI diseases, or test new therapeutics in rat models.The assessment of gastric emptying and motility in humans and animals typically requires radioactive imaging or invasive measurements. Here, we developed a robust strategy to image and characterize gastric emptying and motility in rats based on contrast-enhanced magnetic resonance imaging (MRI) and computer-assisted image processing. The animals were trained to naturally consume a gadolinium-labeled dietgel while bypassing any need for oral gavage. Following this test meal, the animals were scanned under low-dose anesthesia for high-resolution T1-weighted MRI in 7 Tesla, visualizing the time-varying distribution of the meal with greatly enhanced contrast against non-gastrointestinal (GI) tissues. Such contrast-enhanced images not only depicted the gastric anatomy, but also captured and quantified stomach emptying, intestinal filling, antral contraction, and intestinal absorption with fully automated image processing. Over four postingestion hours, the stomach emptied by 27%, largely attributed to the emptying of the forestomach rather than the corpus and the antrum, and most notable during the first 30 min. Stomach emptying was accompanied by intestinal filling for the first 2 h, whereas afterward intestinal absorption was observable as cumulative contrast enhancement in the renal medulla. The antral contraction was captured as a peristaltic wave propagating from the proximal to distal antrum. The frequency, velocity, and amplitude of the antral contraction were on average 6.34 ± 0.07 contractions per minute, 0.67 ± 0.01 mm/s, and 30.58 ± 1.03%, respectively. These results demonstrate an optimized MRI-based strategy to assess gastric emptying and motility in healthy rats, paving the way for using this technique to understand GI diseases, or test new therapeutics in rat models.

Voglibose-mediated alterations in neurometabolomic profiles in the hypothalamus of high-fat diet-fed mice

The alpha-glucosidase inhibitor voglibose (VO) was recently reported to have a protective effect against weight gain as well as affect various metabolic changes related to food intake and gut-brain signaling. We hypothesized that VO prevents weight gain by altering neurometabolome profiles in the hypothalamus to reduce food intake. To test this hypothesis, we assessed metabolite profiles in the hypothalamus of standard diet- or high-fat (HF) diet-fed mice in the absence or presence of VO. In total, 29 male C57BL/6 mice were divided into 3 groups: (1) lean control, (2) HF, and (3) HF + VO. Vehicle or VO was administered for 12 weeks. The results showed that there were alterations in levels of metabolites across several metabolic pathways in the hypothalamus. VO treatment increased levels of many amino acids including arginine, glutamine, histidine, isoleucine, leucine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine in the hypothalamus. In addition, levels of 2-hydroxy-2-methyl-butyric acid in the hypothalamus were significantly increased after VO administration in HF diet-fed mice. Among lipid metabolites, levels of fatty acids were higher in the hypothalamus of VO-treated mice than in that of HF diet-fed mice. In terms of the energy status, the ATP/ADP ratio was higher in the hypothalamus of VO-treated mice (P < 0.001), thereby indicating an energy surplus. In conclusion, VO supplementation altered metabolite profiles in the hypothalamus to enhance catabolism, which is possibly responsible for the hypophagic effect of VO in HF diet-fed mice.

Cafeteria diet induces neuroplastic modifications in the nucleus accumbens mediated by microglia activation

High-palatable and caloric foods are widely overconsumed due to hedonic mechanisms that prevail over caloric necessities leading to overeating and overweight. The nucleus accumbens (NAc) is a key brain area modulating the reinforcing effects of palatable foods and is crucially involved in the development of eating disorders. We describe that prolonged exposure to high-caloric chocolate cafeteria diet leads to overeating and overweight in mice. NAc functionality was altered in these mice, presenting structural plasticity modifications in medium spiny neurons, increased expression of neuroinflammatory factors and activated microglia, and abnormal responses after amphetamine-induced hyperlocomotion. Chronic inactivation of microglia normalized these neurobiological and behavioural alterations exclusively in mice exposed to cafeteria diet. Our data suggest that prolonged exposure to cafeteria diet produces neuroplastic and functional changes in the NAc that can modify feeding behaviour. Microglia activation and neuroinflammation play an important role in the development of these neurobiological alterations.

Limited Access to a High Fat Diet Alters Endocannabinoid Tone in Female Rats

Emerging evidence suggest an impaired endocannabinoid activity in the pathophysiology of binge eating disorder (BED). Herein, we investigated whether endocannabinoid tone could be modified as a consequence of dietary-induced binge eating in female rats. For this purpose, brain levels of the endocannabinoids anandamide (AEA) and 2-arachidonoyl glycerol (2-AG), as well as two endocannabinoid-like lipids, oleoylethanolamide (OEA) and palmitoylethanolamide (PEA), were assessed in different brain areas involved in the hedonic feeding (i.e., prefrontal cortex, nucleus accumbens, amygdala, hippocampus, and hypothalamus). The brain density of cannabinoid type-1 receptors (CB₁) was also evaluated. Furthermore, we determined plasma levels of leptin, ghrelin, and corticosterone hormones, which are well-known to control the levels of endocannabioids and/or CB1 receptors in the brain. To induce binge eating behavior, rats were subject to an intermittent and limited access to a high fat diet (HFD) (margarine). Three experimental groups were used, all with ad libitum access to chow: control (CTRL), with no access to margarine; low restriction (LR), with 2 h margarine access 7 days/week; high restriction (HR), with 2 h margarine access 3 days/week. Bingeing was established when margarine intake in the HR group exceeded that of the LR group. Our results show that, compared to CTRL, AEA significantly decreased in the caudate putamen, amygdala, and hippocampus of HR group. In contrast, 2-AG significantly increased in the hippocampus while OEA decreased in the hypothalamus. Similar to the HR group, AEA and OEA decreased respectively in the amygdala and hypothalamus and 2-AG increased in the hippocampus of LR group. Moreover, LR group also had AEA decreased in the prefrontal cortex and increased in the nucleus accumbens. In both groups we found the same reduction of CB₁ receptor density in the prefrontal cortex compared to CTRL. Also, LR and HR groups showed alterations in both ghrelin and corticosterone levels, while leptin remained unaltered. In conclusion, our findings show a modified endocannabinoid tone due to margarine exposure, in several brain areas that are known to influence the hedonic aspect of food. Even if not uniquely specific to binge eating, margarine-induced changes in endocannabinoid tone could contributes to the development and maintenance of this behavior.

Food Addiction and Binge Eating: Lessons Learned from Animal Models

The feeding process is required for basic life, influenced by environment cues and tightly regulated according to demands of the internal milieu by regulatory brain circuits. Although eating behaviour cannot be considered "addictive" under normal circumstances, people can become "addicted" to this behaviour, similarly to how some people are addicted to drugs. The symptoms, cravings and causes of "eating addiction" are remarkably similar to those experienced by drug addicts, and both drug-seeking behaviour as eating addiction share the same neural pathways. However, while the drug addiction process has been highly characterised, eating addiction is a nascent field. In fact, there is still a great controversy over the concept of "food addiction". This review aims to summarize the most relevant animal models of "eating addictive behaviour", emphasising binge eating disorder, that could help us to understand the neurobiological mechanisms hidden under this behaviour, and to improve the psychotherapy and pharmacological treatment in patients suffering from these pathologies.

Obesity as a Disease

Obesity is a complex disease with many causal factors, associated with multiple comorbidities that contribute to significant morbidity and mortality. It is a highly prevalent disease that poses an enormous health and economic burden to society. This article reviews the mechanisms of obesity and its related comorbidities.

Novel Insights into How Overnutrition Disrupts the Hypothalamic Actions of Leptin

Obesity has become a worldwide health problem, but we still do not understand the molecular mechanisms that contribute to overeating and low expenditure of energy. Leptin has emerged as a major regulator of energy balance through its actions in the hypothalamus. Importantly, obese people exhibit high circulating levels of leptin, yet the hypothalamus no longer responds normally to this hormone to suppress appetite or to increase energy expenditure. Several well-known hypotheses have been proposed to explain impaired central responsiveness to the effects of leptin in obesity, including defective transit across the blood-brain barrier at the arcuate nucleus, hypothalamic endoplasmic reticulum stress, maladaptive sterile inflammation in the hypothalamus, and overexpression of molecules that may inhibit leptin signaling. We also discuss a new explanation that is based on our group's recent discovery of a signaling pathway that we named "NSAPP" after its five main protein components. The NSAPP pathway consists of an oxide transport chain that causes a transient, targeted burst in intracellular hydrogen peroxide (H₂O₂) to inactivate redox-sensitive members of the protein tyrosine phosphatase gene family. The NSAPP oxide transport chain is required for full activation of canonical leptin signaling in neurons but fails to function normally in states of overnutrition. Remarkably, leptin and insulin both require the NSAPP oxide transport chain, suggesting that a defect in this pathway could explain simultaneous resistance to the appetite-suppressing effects of both hormones in obesity.

Sugars, exercise and health

BACKGROUND

There is a direct link between a variety of addictions and mood states to which exercise could be relieving. Sugar addiction has been recently counted as another binge/compulsive/addictive eating behavior, differently induced, leading to a high-significant health problem. Regularly exercising at moderate intensity has been shown to efficiently and positively impact upon physiological imbalances caused by several morbid conditions, including affective disorders. Even in a wider set of physchiatric diseases, physical exercise has been prescribed as a complementary therapeutic strategy.

METHOD

A comprehensive literature search was carried out in the Cochrane Library and MEDLINE databases (search terms: sugar addiction, food craving, exercise therapy, training, physical fitness, physical activity, rehabilitation and aerobic).

RESULTS

Seeking high-sugar diets, also in a reward- or craving-addiction fashion, can generate drastic metabolic derangements, often interpolated with affective disorders, for which exercise may represent a valuable, universal, non-pharmachological barrier.

LIMITATIONS

More research in humans is needed to confirm potential exercise-mechanisms that may break the bond between sugar over-consumption and affective disorders.

CONCLUSIONS

The purpose of this review is to address the importance of physical exercise in reversing the gloomy scenario of unhealthy diets and sedentary lifestyles in our modern society.

Dopamine Neuron-Restricted Leptin Receptor Signaling Reduces Some Aspects of Food Reward but Exacerbates the Obesity of Leptin Receptor-Deficient Male Mice

The contribution of leptin-induced modulation of dopamine neurons to feeding behavior and energy homeostasis remains unclear. Midbrain dopamine neurons regulate the reward value of food, and direct leptin administration to the midbrain reduces food intake. However, selective deletion of leptin receptors (Leprs) from dopamine neurons has no effect on body weight, food intake, or hedonic responses, suggesting that leptin acts indirectly or demonstrating that sufficient compensation occurs to mask any direct leptin-dopamine effects. To further explore the role of direct Lepr-dopamine neuron signaling in the control of feeding behavior and energy homeostasis, we generated mice in which Leprs were expressed exclusively in dopamine transporter (DAT)-expressing neurons (LeprDAT). We then assessed weekly body weight, daily food intake, hyperphagic feeding, and leptin-induced suppression of feeding in the LeprDAT mice compared with their Lepr-deficient (LeprNULL) and wild-type control (LeprCON) littermates. We also used metabolic cages to characterize running wheel activity, home-cage activity, and total energy expenditure. As expected, LeprNULL mice exhibited increased body weight and food intake compared with LeprCON mice. LeprDAT male mice exhibited acute leptin-induced suppression of food intake and reduced hedonic feeding but also exhibited significantly increased postweaning body weight gain compared with the LeprNULL mice. This was associated with significantly reduced home-cage activity counts, although no differences in food intake were observed between the LeprDAT and LeprNULL mice. These data demonstrate that restoring Lepr signaling exclusively in dopamine neurons reduces some aspects of food reward and activity but does not ameliorate the obesity phenotype of Lepr-deficient mice.

High-fat diet-induced obesity and insulin resistance are characterized by differential beta oscillatory signaling of the limbic cortico-basal ganglia loop

The concept of brain circuit disorders has been proposed for a variety of neuropsychiatric diseases, characterized by pathological disturbances of neuronal networks including changes in oscillatory signaling of re-entrant cortico-subcortical loops in the basal ganglia system. Parts of this circuitry play a pivotal role in energy homeostasis. We therefore investigated whether high-fat diet (HFD) induced obesity is associated with changes in oscillatory signaling in the limbic cortico-basal ganglia loop. We performed multi-site in-vivo electrophysiological recordings of local field potentials within this network under urethane anesthesia in adult rats after 4 weeks of HFD feeding compared to age-matched controls. Recordings were performed at baseline and during systemic glucose challenge. Our analysis demonstrates increased oscillatory beta power in the nucleus accumbens (NAC) associated with decreased beta coherence between cortex and NAC in animals fed a HFD. Spontaneous beta oscillatory power strongly correlated with endocrine markers of obesity. The glucose challenge increased beta oscillations in control animals but not in animals receiving the HFD. Furthermore direct intracerebroventricular insulin injection increased beta oscillations in the NAC. The present study provides evidence for aberrant oscillatory signaling in the limbic cortico-basal ganglia loop that might contribute to the dysfunctional information processing in obesity.

Caloric Restriction-Induced Decreases in Dopamine Receptor Availability are Associated with Leptin Concentration

OBJECTIVE

It has been previously reported that early after Roux-en-Y-gastric bypass, dopamine (DA) type 2 and 3 receptor (D2/3R) binding potential (BP_ND ) was decreased from preoperative levels. The current study aimed to determine whether calorie restriction without weight loss modifies D2/3R BP_ND and whether such changes are explained by neuroendocrine regulation.

METHODS

Fifteen females with obesity (BMI = 39 ± 6 kg/m² ) were studied before and after ∼10 days of a very-low-calorie-diet (VLCD). Outcome measures included fasting insulin, leptin, acyl ghrelin, and glucose, and insulin sensitivity and disposition index were estimated using the oral-minimal model (OMM) method. Participants underwent positron emission tomography scanning with the displaceable radioligand [¹⁸ F]fallypride to estimate available regional D2/3R levels. Regions of interest included the caudate, putamen, ventral striatum, hypothalamus, and substantia nigra (SN).

RESULTS

With the VLCD, weight decreased slightly (-3 kg). Insulin, glucose, and leptin decreased significantly, but there was no change in acyl ghrelin or measures from OMM. SN D2/3R BP_ND decreased significantly, with trends toward decreased levels in the remaining regions. The decrease in leptin concentration strongly predicted the change in D2/3R BP_ND in all regions (all P ≤ 0.004).

CONCLUSIONS

In obesity, reductions in regional D2/3R availability after VLCD are suggestive of increased endogenous DA competing with the radioligand. Changes in regional D2/3R availability were associated with decreases in leptin concentrations that occurred before clinically significant weight loss.

Acute effects of intravenous cocaine administration on serum concentrations of ghrelin, amylin, glucagon-like peptide-1, insulin, leptin and peptide YY and relationships with cardiorespiratory and subjective responses

BACKGROUND

Food intake and use of drugs of abuse like cocaine share common central and peripheral physiological pathways. Appetitive hormones play a major role in regulating food intake; however, little is known about the effects of acute cocaine administration on the blood concentrations of these hormones in cocaine users.

METHODS

We evaluated serum concentrations of six appetitive hormones: ghrelin (total and acyl-ghrelin), amylin, glucagon-like peptide-1 (GLP-1), insulin, leptin and peptide YY (PYY), as well as acute cardiorespiratory and subjective responses of 8 experienced cocaine users who received 25mg intravenous (IV) cocaine.

RESULTS

Serum concentrations of GLP-1 (p=0.014) and PYY (p=0.036) were significantly decreased one hour following IV cocaine administration; there was a trend towards a decrease for insulin (p=0.055) and amylin (p=0.063) concentrations, while no significant IV cocaine effect was observed for ghrelin (total or acyl-ghrelin) or leptin concentrations (p's≫>0.5). We also observed associations between hormone concentrations acutely affected by IV cocaine (GLP-1, PYY, insulin, amylin) and some cocaine-related cardiorespiratory and subjective responses (e.g., increased heart and respiratory rates; feeling high and anxious).

DISCUSSION

These findings show a significant effect of acute IV cocaine administration on some appetitive hormones and suggest potential associations between these hormones and cocaine-related cardiorespiratory and subjective responses. Additional research is needed to further investigate the potential mechanisms underlining these associations.

Impact of diet-derived signaling molecules on human cognition: exploring the food-brain axis

The processes that define mammalian physiology evolved millions of years ago in response to ancient signaling molecules, most of which were acquired by ingestion and digestion. In this way, evolution inextricably linked diet to all major physiological systems including the nervous system. The importance of diet in neurological development is well documented, although the mechanisms by which diet-derived signaling molecules (DSMs) affect cognition are poorly understood. Studies on the positive impact of nutritive and non-nutritive bioactive molecules on brain function are encouraging but lack the statistical power needed to demonstrate strong positive associations. Establishing associations between DSMs and cognitive functions like mood, memory and learning are made even more difficult by the lack of robust phenotypic markers that can be used to accurately and reproducibly measure the effects of DSMs. Lastly, it is now apparent that processes like neurogenesis and neuroplasticity are embedded within layers of interlocked signaling pathways and gene regulatory networks. Within these interdependent pathways and networks, the various transducers of DSMs are used combinatorially to produce those emergent adaptive gene expression responses needed for stimulus-induced neurogenesis and neuroplasticity. Taken together, it appears that cognition is encoded genomically and modified by epigenetics and epitranscriptomics to produce complex transcriptional programs that are exquisitely sensitive to signaling molecules from the environment. Models for how DSMs mediate the interplay between the environment and various neuronal processes are discussed in the context of the food-brain axis.

Psychopharmacological advances in eating disorders

INTRODUCTION

Anorexia nervosa (AN), bulimia nervosa (BN) and binge eating disorder (BED) are the primary eating disorders (EDs). The only psychopharmacological treatment options for EDs with approval in some countries include fluoxetine for BN and lisdexamfetamine for BED. Given the high comorbidity and genetic correlations with other psychiatric disorders, it seems possible that novel medications for these conditions might also be effective in EDs. Areas covered: The current scientific literature has increased our understanding of how medication could be beneficial for patients with EDs on a molecular, functional and behavioral level. On the basis of theoretical considerations about neurotransmitters, hormones and neural circuits, possible drug targets for the treatment of EDs may include signal molecules and receptors of the self-regulatory system such as serotonin, norepinephrine and glutamate, the hedonic system including opioids, cannabinoids and dopamine and the hypothalamic homeostatic system including histamine, ghrelin, leptin, insulin, and glucagon-like peptide-1. Expert commentary: The latest research points to an involvement of both the immune and the metabolic systems in the pathophysiology of EDs and highlights the importance of the microbiome. Therefore, the next few years may unveil drug targets for EDs not just inside and outside of the brain, but possibly even outside of the human body.

Effects of nicotine on homeostatic and hedonic components of food intake

Chronic tobacco use leads to nicotine addiction that is characterized by exaggerated urges to use the drug despite the accompanying negative health and socioeconomic burdens. Interestingly, nicotine users are found to be leaner than the general population. Review of the existing literature revealed that nicotine affects energy homeostasis and food consumption via altering the activity of neurons containing orexigenic and anorexigenic peptides in the brain. Hypothalamus is one of the critical brain areas that regulates energy balance via the action of these neuropeptides. The equilibrium between these two groups of peptides can be shifted by nicotine leading to decreased food intake and weight loss. The aim of this article is to review the existing literature on the effect of nicotine on food intake and energy homeostasis and report on the changes that nicotine brings about in the level of these peptides and their receptors that may explain changes in food intake and body weight induced by nicotine. Furthermore, we review the effect of nicotine on the hedonic aspect of food intake. Finally, we discuss the involvement of different subtypes of nicotinic acetylcholine receptors in the regulatory action of nicotine on food intake and energy homeostasis.

Reward Capacity Predicts Leptin Dynamics During Laboratory-Controlled Eating in Women as a Function of Body Mass Index

OBJECTIVE

The role of leptin in mesolimbic signaling of non-food-related rewards has been well established at the preclinical level, yet studies in humans are lacking. The present investigation explored the association between hedonic capacity and leptin dynamics and whether this association differed by BMI class.

METHODS

In this cross-sectional study of 75 women (42 with BMIs in the lean range and 33 with BMIs in the obesity range), serum leptin before and after meal consumption was measured. Reward capacity was assessed using the Snaith-Hamilton Pleasure Scale (SHAPS). Multiple regression tested whether reward capacity was associated with the leptin area under the curve (AUC), with an interaction term to test differences between the lean and obesity groups.

RESULTS

The interaction of SHAPS by BMI group was robust (β = -0.40, P = 0.005); among women with obesity, a greater SHAPS score was associated with a lower leptin AUC (β = -0.35, P = 0.002, adjusted R²  = 0.66). Among those in the lean group, the association was not statistically significant (β = -0.16, P = 0.252, adjusted R²  = 0.22). Findings were above and beyond BMI and age.

CONCLUSIONS

In this sample, a robust negative association between reward capacity and circulating leptin was stronger in women with obesity compared with lean counterparts. These findings suggest that despite likely leptin resistance, inhibitory leptin functioning related to nonfood rewards may be spared in women with obesity.

Central insulin modulates food valuation via mesolimbic pathways

Central insulin is thought to act at the neural interface between metabolic and hedonic drives to eat. Here, using pharmacological fMRI, we show that intranasal insulin (INI) changes the value of food cues through modulation of mesolimbic pathways. Overnight fasted participants rated the palatability of food pictures and attractiveness of non-food items (control) after receiving INI or placebo. We report that INI reduces ratings of food palatability and value signals in mesolimbic regions in individuals with normal insulin sensitivity. Connectivity analyses reveal insulinergic inhibition of forward projections from the ventral tegmentum to the nucleus accumbens. Importantly, the strength of this modulation predicts decrease of palatability ratings, directly linking neural findings to behaviour. In insulin-resistant participants however, we observe reduced food values and aberrant central insulin action. These data demonstrate how central insulin modulates the cross-talk between homeostatic and non-homeostatic feeding systems, suggesting that dysfunctions of these neural interactions may promote metabolic disorders.

The influence of insulin on food preference and the corresponding underlying neural circuits are unknown in humans. Here, the authors show that increasing insulin changes food preference by modulating mesolimbic neural circuits, and that this pattern is changed in insulin-resistant individuals.

A Potential Animal Model of Maladaptive Palatable Food Consumption Followed by Delayed Discomfort

Introduction: Binging is the consumption of larger amounts of food in a briefer period of time than would normally be consumed under similar circumstances. Binging requires palatable food (PF) to trigger abnormal eating, probably reflecting gene × environment interactions. In this study we examined the impact of trait binge eating (BE) and its compulsive nature on the conflict between hedonic eating of PF and anticipation of a delayed aversive effect. We used female rats as an animal model similar to other models of BE. A novel aspect of this model in this paper is the use of a delayed internal aversive effect produced by lactose ingestion. Establishing this model will allow us to better understand the nature of the conflict between immediate reward and its delayed aversive implications. We hypothesized that BE prone (BEP) rats will demonstrate maladaptive decision making, presenting higher motivation toward PF even when this is associated with delayed discomfort. Method: (Phase 1) 52 female adult Wistar rats were divided to two eating profiles: resistant and prone binge eaters (BER/BEP) based on intake of liquid PF (Ensure). Next, all subjects underwent a Lactose Conditioning Protocol (LCP) that included 4 h tests, one baseline and 3 conditioning days (Phase 2), in which solid PF (Oreo cookies) was paired with glucose (control-no internal aversive effect) or lactose, dissolved in liquid PF. Index for PF motivation was PF consumption during the 4 h LCP. To test for memory of lactose conditioning, we performed another LCP with glucose only (anticipation, but no actual lactose-induced discomfort), a week after the last conditioning session. Results: Lactose conditioned BEP showed higher motivation toward PF compared to lactose conditioned BER faced with delayed aversive effects. Only lactose conditioned BER rats devaluated the PF over LCP days, indicating an association between PF and abdominal discomfort. In addition, only lactose conditioned BER presented an adaptive dynamic behavior, by varying PF intake according to consequences. Furthermore, solid PF consumption was predicted by binge size of liquid PF, only for lactose conditioned rats. Conclusions: We established an animal model for a common eating conflict in humans using delayed internal aversive unconditional stimuli.