"Depression" increases "craving" for sweet rewards in animal and human models of depression and craving

Changes in food preferences and ingestive behaviors after glucagon-like peptide-1 analog treatment: techniques and opportunities

BACKGROUND

Glucagon-like peptide-1 (GLP-1) analogs are approved for the treatment of obesity in adults and adolescents. Reports have emerged that the weight loss effect of these medications may be related to changes in food preferences and ingestive behaviors following the treatment. Understanding the mechanisms which impact ingestive behavior could expand opportunities to develop more refined and personalized treatment options for obesity.

METHODS

Recent studies investigating the relationship between GLP-1 analogs and ingestive behaviors were retrieved from PubMed using the search terms: "obesity," "food preference," "taste," "ingestive behavior," "weight loss medication," "anti-obesity medication," "GLP-1 analog," "tirzepatide," "liraglutide," "semaglutide." Measurement tools were studied to compare variables used to assess food intake behavior. The main outcomes from each study were analyzed to evaluate the current standing and future directions of appetitive, ingestive, and consummatory behaviors and their association with GLP-1 analogs.

RESULTS

Thus far, studies have primarily explored the weight loss phase and report decreased short-term appetite and food intake upon treatment. However, research during the weight maintenance phase and objective measurements of food intake are notably sparse. Additionally, verbal reports have been primarily used to examine food intake, which can be susceptible to subjectivity.

CONCLUSIONS

Elucidating the relationship between GLP-1 analogs and ingestive behavior could reveal additional parameters which contribute to their anti-obesity effects. To better understand these mechanisms, it is imperative to consider objective measurements of food intake in future studies. Several measurement tools have been adapted to measure variables of food behavior in humans, and each must be carefully considered with their strengths and limitations to develop optimal investigations.

The association between soft drinks consumption and risk of mental disorders among Iranian adults: The LIPOKAP study

OBJECTIVE

With rising demand for soft drinks (SDs) in low-income countries, studies examining mental disorders in relation to SDs are rather scarce. Therefore, we aimed to explore this association in a sample of Iranian adults.

METHODS

This cross-sectional study was carried out within the framework of the multi-centric LIPOKAP project, with 1970 Iranian healthy adults. Dietary intake and symptoms of depression and anxiety were collected using validated, Persian versions of a food frequency questionnaire and a Hospital Anxiety and Depression Scale (HADS), respectively. Artificial juices were considered fruit-flavored carbonated sugar beverages, sugar-sweetened beverages (SSB) included fruit-flavored carbonated sugar beverages and carbonated colas, and soft drinks included SSB and drinks containing non-nutritive sweeteners.

RESULTS

The mean age of the participants was 39.8 ± 13.9 years. Compared to lower intake, higher intake of SDs (OR = 1.30, 95 % CI: 1.01, 1.69; P = 0.041), SSBs (OR = 1.30, 95 % CI: 1.00, 1.67; P = 0.045) and artificial juice (OR = 1.63, 95 % CI: 1.24, 2.13; P < 0.001) was associated with higher risk of depression in adjusted model. These associations were sex-specific and more evident in males. No significant association was found between any of the drinks and anxiety risk except for artificial juice in men which was directly associated with anxiety risk (OR = 1.66, 95 % CI: 1.06, 2.61; P = 0.028).

CONCLUSION

This study found a positive association between SDs, SSBs and artificial juice and depression, but not anxiety. These associations varied between men and women. Prospective cohort studies are warranted to confirm our results and reveal the causal relationship.

The odour of an unfamiliar stressed or relaxed person affects dogs' responses to a cognitive bias test

Dogs can discriminate stressed from non-stressed human odour samples, but the effect on their cognition is unstudied. Using a cognitive bias task, we tested how human odours affect dogs' likelihood of approaching a food bowl placed at three ambiguous locations ("near-positive", "middle" and "near-negative") between trained "positive" (rewarded) and "negative" (unrewarded) locations. Using odour samples collected from three unfamiliar volunteers during stressful and relaxing activities, we tested eighteen dogs under three conditions: no odour, stress odour and relaxed odour, with the order of test odours counterbalanced across dogs. When exposed to stress odour during session three, dogs were significantly less likely to approach a bowl placed at one of the three ambiguous locations (near-negative) compared to no odour, indicating possible risk-reduction behaviours in response to the smell of human stress. Dogs' learning of trained positive and negative locations improved with repeated testing and was significant between sessions two and three only when exposed to stress odour during session three, suggesting odour influenced learning. This is the first study to show that without visual or auditory cues, olfactory cues of human stress may affect dogs' cognition and learning, which, if true, could have important consequences for dog welfare and working performance.

Stress to inflammation and anhedonia: Mechanistic insights from preclinical and clinical models

Anhedonia, as evidenced by impaired pleasurable response to reward, reduced reward motivation, and/or deficits in reward-related learning, is a common feature of depression. Such deficits in reward processing are also an important clinical target as a risk factor for depression onset. Unfortunately, reward-related deficits remain difficult to treat. To address this gap and inform the development of effective prevention and treatment strategies, it is critical to understand the mechanisms that drive impairments in reward function. Stress-induced inflammation is a plausible mechanism of reward deficits. The purpose of this paper is to review evidence for two components of this psychobiological pathway: 1) the effects of stress on reward function; and 2) the effects of inflammation on reward function. Within these two areas, we draw upon preclinical and clinical models, distinguish between acute and chronic effects of stress and inflammation, and address specific domains of reward dysregulation. By addressing these contextual factors, the review reveals a nuanced literature which might be targeted for additional scientific inquiry to inform the development of precise interventions.

Total sugar intake is associated with higher prevalence of depressive symptoms in obese adults

Background

The existing literature has repeatedly assessed the association between sugar-sweetened beverages and depressive symptoms, but studies of the association of total dietary sugar with depressive symptoms and of this association in obese adults are scarce. Thus, the purpose of this cross-sectional study was to assess the association between total sugar consumption and depressive symptoms in the study population and then in the population stratified by body mass index.

Methods

This study was conducted in a nationally representative sample of 16,009 adults from the 2011-2018 National Health and Nutrition Examination Survey in the US. Total sugar intake was assessed by 24 h dietary recalls, and depressive symptoms were assessed by the nine-item Patient Health Questionnaire. Logistic regression models were used to evaluate the association between total sugar consumption and depressive symptoms.

Results

Total sugar intake was positively associated with higher prevalence of depressive symptoms, and the adjusted odds ratio (95% confidence interval) of depressive symptoms for the highest vs. lowest quintile of total sugar intake was 1.56 (1.18, 2.05). In stratified analysis, we found a positive association between total sugar intake and depressive symptoms in adults with body mass index ≥30 kg/m2 (P for trend = 0.013), whereas no association was found in normal weight or overweight adults.

Conclusions

A higher intake of total sugar was associated with increased odds of clinically relevant depressive symptoms among obese adults. Further studies are necessary to confirm the role of total sugar in depressive symptoms among obese adults.

Cyrcadian Rhythm, Mood, and Temporal Patterns of Eating Chocolate: A Scoping Review of Physiology, Findings, and Future Directions

This paper discusses the effect of chrononutrition on the regulation of circadian rhythms; in particular, that of chocolate on the resynchronization of the human internal biological central and peripheral clocks with the main external synchronizers, light-dark cycle and nutrition-fasting cycle. The desynchronization of internal clocks with external synchronizers, which is so frequent in our modern society due to the tight rhythms imposed by work, social life, and technology, has a negative impact on our psycho-physical performance, well-being, and health. Taking small amounts of chocolate, in the morning at breakfast at the onset of the active phase, helps speed up resynchronization time. The high flavonoid contents in chocolate promote cardioprotection, metabolic regulation, neuroprotection, and neuromodulation with direct actions on brain function, neurogenesis, angiogenesis, and mood. Although the mechanisms of action of chocolate compounds on brain function and mood as well as on the regulation of circadian rhythms have yet to be fully understood, data from the literature currently available seem to agree in suggesting that chocolate intake, in compliance with chrononutrition, could be a strategy to reduce the negative effects of desynchronization. This strategy appears to be easily implemented in different age groups to improve work ability and daily life.

Peripherally administered amylin inhibits stress-like behaviors and enhances cognitive performance

Amylin, a 37 amino acid peptide pancreatic hormone co-secreted with insulin, normalizes the altered eating patterns induced by chronic stress in the rat. Because these stress-induced changes are driven, in part, by brain corticotropin-releasing factor and corticosterone, and because alterations in the activity of these molecules and the stress system are commonly associated with neuropsychiatric diseases like anxiety, depression, and schizophrenia, we hypothesized that amylin might mitigate behavioral states associated with stress. Therefore, we tested the effects of rat amylin in rodent-based behavioral assays sensitive to neuropsychiatric drugs, including anxiolytic, antidepressant, antipsychotic, and cognitive enhancing drugs: stress-induced hyperthermia (SIH); marble burying; elevated plus maze (EPM)), forced swim test (FST), pre-pulse inhibition, and phencyclidine-induced locomotion. To assess the neural underpinnings of amylin's anxiolytic-like effects, we examined the effect of amylin on SIH after lesioning the area postrema (AP), which mediates amylin's metabolic effects. Amylin injection (IP, 0.1, 1.0, & 10 mg/kg) significantly (P < 0.05) decreased SIH (97% below vehicle) and AP lesions inhibited this effect. Amylin also reduced marble burying (72% below vehicle), but had no effect in the EPM. Together, these effects suggest anxiolytic-like activity or potential. Amylin injection also enhanced cognitive performance in the novel object recognition test. When administered continuously by implanted osmotic pumps, amylin (300 mg/kg/d) blocked SIH when tested at 1 and 4 weeks. Compared to vehicle, amylin infusion (1 and 3 mg/kg/d) reduced the time immobile in the FST (P < 0.05; 30% below vehicle), suggesting antidepressant-like potential. Although further testing is needed, our findings support a potential for peripherally administered amylin to access and benefit pathways that regulate memory, emotion, and mood.

A New Player in the Hippocampus: A Review on VGLUT3+ Neurons and Their Role in the Regulation of Hippocampal Activity and Behaviour

Glutamate is the most abundant excitatory amino acid in the central nervous system. Neurons using glutamate as a neurotransmitter can be characterised by vesicular glutamate transporters (VGLUTs). Among the three subtypes, VGLUT3 is unique, co-localising with other "classical" neurotransmitters, such as the inhibitory GABA. Glutamate, manipulated by VGLUT3, can modulate the packaging as well as the release of other neurotransmitters and serve as a retrograde signal through its release from the somata and dendrites. Its contribution to sensory processes (including seeing, hearing, and mechanosensation) is well characterised. However, its involvement in learning and memory can only be assumed based on its prominent hippocampal presence. Although VGLUT3-expressing neurons are detectable in the hippocampus, most of the hippocampal VGLUT3 positivity can be found on nerve terminals, presumably coming from the median raphe. This hippocampal glutamatergic network plays a pivotal role in several important processes (e.g., learning and memory, emotions, epilepsy, cardiovascular regulation). Indirect information from anatomical studies and KO mice strains suggests the contribution of local VGLUT3-positive hippocampal neurons as well as afferentations in these events. However, further studies making use of more specific tools (e.g., Cre-mice, opto- and chemogenetics) are needed to confirm these assumptions.

Diet and Anxiety: A Scoping Review

Anxiety disorders are the most common group of mental disorders. There is mounting evidence demonstrating the importance of nutrition in the development and progression of mental disorders such as depression; however, less is known about the role of nutrition in anxiety disorders. This scoping review sought to systematically map the existing literature on anxiety disorders and nutrition in order to identify associations between dietary factors and anxiety symptoms or disorder prevalence as well as identify gaps and opportunities for further research. The review followed established methodological approaches for scoping reviews. Due to the large volume of results, an online program (Abstrackr) with artificial intelligence features was used. Studies reporting an association between a dietary constituent and anxiety symptoms or disorders were counted and presented in figures. A total of 55,914 unique results were identified. After a full-text review, 1541 articles met criteria for inclusion. Analysis revealed an association between less anxiety and more fruits and vegetables, omega-3 fatty acids, "healthy" dietary patterns, caloric restriction, breakfast consumption, ketogenic diet, broad-spectrum micronutrient supplementation, zinc, magnesium and selenium, probiotics, and a range of phytochemicals. Analysis revealed an association between higher levels of anxiety and high-fat diet, inadequate tryptophan and dietary protein, high intake of sugar and refined carbohydrates, and "unhealthy" dietary patterns. Results are limited by a large percentage of animal and observational studies. Only 10% of intervention studies involved participants with anxiety disorders, limiting the applicability of the findings. High quality intervention studies involving participants with anxiety disorders are warranted.

Inpatients experiences about the impact of traumatic stress on eating behaviors: an exploratory focus group study

BACKGROUND

Unhealthy changes in eating behavior among people experiencing trauma have been observed. There is, however, a lack of in-depth knowledge regarding the impact of the after effects of traumatic life experiences on eating behavior. Because eating behavior represents important components for promotion and maintenance of good health throughout life, this study aimed to explore inpatients' lived experiences of the impact of traumatic stress on eating behavior.

METHOD

Thirteen female and two male inpatients (age range 28-62 years), recruited from a psychiatric clinic in Norway, participated in this qualitative explorative focus group study. The data analysis was performed using systematic text condensation.

RESULTS

The results in the present study describe the participants' experiences about the impact of traumatic stress on their eating behavior. Their discussions and descriptions disclosed problems that could be summarized into four main themes: "experiencing eating behaviors as coping strategies"; "experiencing being addicted to food and sweets"; "experiencing eating behaviors controlled by stress and emotions"; and "experiencing lack of appetite and reduced capacity to plan and prepare meals".

CONCLUSION

Traumatic stress can impact eating behavior in several complex ways that over time may cause adverse health consequences. The results add to an important understanding of changes in eating behavior that might appear in people struggling to cope with the after effects of traumatic life experiences to the existing literature. To better understand the complexity of how traumatic experiences may impact eating behavior, this knowledge is important and useful for health professionals offering support to those who experience struggling with eating behavior after traumatic experiences.

The Psychology of Food Cravings in Patients With First-Episode Psychosis

Objectives: Food cravings may cause weight gain in patients with schizophrenia. This study investigated psychological characteristics associated with food cravings in patients with first-episode psychosis. Methods: This study analyzed data from a clinical cohort of first-episode psychosis patients taking antipsychotics for 3 months or less. The strength of food cravings was measured using the General Food Cravings Questionnaire-Trait (G-FCQ-T). Psychological characteristics and psychiatric symptoms were investigated with the Positive and Negative Symptom Scale (PANSS), Calgary Depression Scale for Schizophrenia (CDSS), Social and Occupational Functioning Assessment Scale, Rosenberg Self-Esteem Scale (RSES), and Perceived Stress Scale (PSS). Clinical characteristics were compared according to significant weight gain (≥10% increase in body weight compared to baseline) over 3 months. Associations between the G-FCQ-T and other psychiatric scales were investigated. We conducted sex-stratified analyses. Results: In total, 182 patients (78 males and 104 females) with first-episode psychosis were enrolled in this study. In females, the G-FCQ-T total score at baseline was associated with baseline body weight and significant weight gain over 3 months. The PSS scales were significantly associated the G-FCQ-T total and all subscale scores in female participants. Scores on the RSES and CDSS were significantly associated with the G-FCQ-T total score and with the preoccupation and loss of control subscale scores. The PANSS negative and general subscales were significantly associated with the positive outcome expectancy and loss of control subscales of the G-FCQ-T, respectively. In males, the only significant association was between the loss of control subscale and RSES scores. Linear regression analysis showed significant associations of PSS scores with the total and all subscale scores of the G-FCQ-T despite the loss of significance for other variables. Conclusion: These results indicate that the food cravings in patients with first-episode psychosis, which were associated with weight gain, were influenced by perceived stress in females. To reduce food cravings in female patients with schizophrenia, interventions aimed at perceived stress should be considered.

Latent Profile Analysis of Heavy Episodic Drinking in Emerging Adults: A Reinforcer Pathology Approach

BACKGROUND

Heavy episodic drinking (HED) is a major public health problem among emerging adults (individuals 18 to 25), but with considerable heterogeneity in concurrent substance use and psychopathology. The current study used latent profile analysis (LPA) to detect discrete subgroups of HED based on alcohol, other drug severity, and concurrent psychopathology. A reinforcer pathology approach was used to understand motivational differences among the latent subgroups.

METHODS

Participants were 2 samples of emerging adults reporting regular HED, 1 Canadian (n = 730) and 1 American (n = 602). Indicators for the LPA were validated dimensional self-report assessments of alcohol severity, cannabis severity, other drug severity, nicotine dependence, depression, anxiety, posttraumatic stress disorder, and attention-deficit/hyperactivity disorder. Reinforcer pathology indicators were measures of alcohol demand, proportionate substance-related reinforcement, and discounting of future rewards.

RESULTS

The LPA yielded parallel 3-class solutions in both samples. The largest subgroup was characterized by comparatively low substance severity and psychopathology (Low overall severity). The second largest subgroup was characterized by comparatively high alcohol and other drug severity (excluding tobacco) and high levels of psychopathology (Heavy alcohol & high psychiatric severity). The third subgroup exhibited high alcohol, smoking and intermediate levels of other substance use and psychopathology (Heavy alcohol, smoking, & intermediate psychiatric severity). The Heavy alcohol & high psychiatric severity and Heavy alcohol, smoking, & intermediate psychiatric severity subgroups exhibited significantly higher alcohol demand, greater proportionate substance-related reinforcement, and steeper delay discounting.

CONCLUSIONS

Parallel latent subgroups of emerging adults engaging in HED were present in both samples, and the high-risk subgroups were significantly differentiated by the reinforcer pathology indicators. These latent profiles may ultimately inform heterogeneity in the longitudinal course of HED in emerging adults.

Suicide Attempt and Associated Factors Among Adolescents in Five Southeast Asian Countries in 2015

Background: Suicide is a major cause of death among adolescents. Aims: The study aimed to report on the prevalence and correlates of suicide attempt among in-school adolescents in five Southeast Asian countries. Method: Cross-sectional data from the 2015 Global School-Based Student Health Survey (GSHS) included 33,004 middle-school children (mean age = 14.3 years, SD = 1.6) that were representative of all students in secondary school in Indonesia, Laos, Philippines, Thailand, and Timor-Leste. Results: The overall prevalence of past 12-month suicide attempt was 9.0%, ranging from 3.9% in Indonesia to 16.2% in the Philippines. Among those with a suicide attempt in the past 12 months, almost half (49.0%) had suicidal ideation and 47.7% had a suicide plan in the past 12 months. In adjusted Poisson regression analysis, female gender, residing in Laos, Philippines, Thailand, and Timor-Leste, no close friends, loneliness, anxiety, bullying victimization, physical attack, lack of parental support, lack of peer support, current alcohol use, lifetime cannabis use, lifetime amphetamine use, soft drink consumption, truancy, and injury were associated with suicide attempt. Limitations: The correlational nature of the study limits the implications of the findings. Conclusion: Almost one in 10 students had attempted suicide in the past 12 months and several factors associated with suicide attempt were identified among adolescents in five Southeast Asian countries.

Effects of early life and current housing on sensitivity to reward loss in a successive negative contrast test in pigs

Animals in a negative affective state seem to be more sensitive to reward loss, i.e. an unexpected decrease in reward size. The aim of this study was to investigate whether early-life and current enriched vs. barren housing conditions affect the sensitivity to reward loss in pigs using a successive negative contrast test. Pigs (n = 64 from 32 pens) were housed in barren or enriched conditions from birth onwards, and at 7 weeks of age experienced either a switch in housing conditions (from barren to enriched or vice versa) or not. Allotting pigs to the different treatments was balanced for coping style (proactive vs. reactive). One pig per pen was trained to run for a large reward and one for a small reward. Reward loss was introduced for pigs receiving the large reward after 11 days (reward downshift), i.e. from then onwards, they received the small reward. Pigs housed in barren conditions throughout life generally had a lower probability and higher latency to get the reward than other pigs. Proactive pigs ran overall slower than reactive pigs. After the reward downshift, all pigs ran slower. Nevertheless, reward downshift increased the latency and reduced the probability to get to the reward, but only in pigs exposed to barren conditions in early life, which thus were more sensitive to reward loss than pigs from enriched early life housing. In conclusion, barren housed pigs seemed overall less motivated for the reward, and early life housing conditions had long-term effects on the sensitivity to reward loss.

Effect of dietary restraint and mood state on attentional processing of food cues

BACKGROUND AND OBJECTIVES

Research linking dietary restraint to attentional bias toward food cues has been equivocal, suggesting that dietary restraint may only influence attentional processing of food in certain contexts. The present study examined whether negative mood strengthens the association between dietary restraint and attention bias for food.

METHODS

Healthy female participants were randomized to either a neutral (n = 47) or negative mood (n = 49) induction. Participants then completed a visual search task featuring targets displayed adjacent to pictures of palatable food, musical instruments, or non-instrument filler objects. Attention bias for food was operationalized as shorter response latency when the target appeared adjacent to palatable food as compared to musical instruments. Attention bias was examined in a 2 (mood condition) × 2 (picture: food vs. instrument) × 2 (target location: match vs. mismatch) repeated measures ANCOVA, with dietary restraint as a continuous covariate and response latency as the dependent variable.

RESULTS

Though there was no evidence of an interaction between mood condition and dietary restraint, mood had an influence on attention allocation. Contrary to study hypotheses, individuals in the neutral mood condition, but not those in the negative mood condition, responded in a manner indicative of bias toward food.

LIMITATIONS

Additional research is necessary to validate the experimental task used in the present study to assess food-specific attentional bias.

CONCLUSIONS

Neutral mood may be associated with enhanced processing of palatable food cues. Critically, results do not support the hypothesized link between negative mood and attention bias for food.

Influence of AT1 blockers on obesity and stress induced eating of cafeteria diet

Based on findings that treatment with AT1 receptor blocker (ARB) prevents diet-induced obesity and that the activity of the hypothalamic-pituitary-adrenal (HPA) axis is stimulated by AngII and blocked by ARBs, we aimed to investigate whether ARB treatment can reduce stress-induced eating of cafeteria diet (CD) , thus contributing to alterations in eating behavior. Sprague Dawley rats were fed with chow or CD and treated with telmisartan (TEL, 8mg/kg/d) or vehicle. At weeks 2 and 12, rats were stressed over 5 consecutive days by restraint stress (RS, 4h) and by additional shaking at d5. Tail blood was sampled during RS to determine hormone levels. During the first period of RS, ACTH and corticosterone responses were diminished at d5 in CD- compared to chow-fed rats. Independently of feeding, TEL did not reduce stress hormones. Compared to food behavior before RS, the stress-induced CD eating increased in controls but remained unchanged in TEL-treated rats. After 12 weeks, TEL reduced weight gain and energy intake, particularly in CD-fed rats. Similar to the first RS period, corticosterone response was reduced in CD-fed rats at d5 during the second RS period. TEL did not further reduce stress hormones and did not lessen the CD eating upon RS. We conclude that CD feeding compensates for stress reactions. However, stress-induced CD eating was only reduced by TEL after short-term, but not after long-term drug treatment. Thus, the potency of ARBs to lower HPA activity only plays a minor role in reducing energy intake to prevent obesity.

Can Mindfulness Address Maladaptive Eating Behaviors? Why Traditional Diet Plans Fail and How New Mechanistic Insights May Lead to Novel Interventions

Emotional and other maladaptive eating behaviors develop in response to a diversity of triggers, from psychological stress to the endless external cues in our modern food environment. While the standard approach to food- and weight-related concerns has been weight-loss through dietary restriction, these interventions have produced little long-term benefit, and may be counterproductive. A growing understanding of the behavioral and neurobiological mechanisms that underpin habit formation may explain why this approach has largely failed, and pave the way for a new generation of non-pharmacologic interventions. Here, we first review how modern food environments interact with human biology to promote reward-related eating through associative learning, i.e., operant conditioning. We also review how operant conditioning (positive and negative reinforcement) cultivates habit-based reward-related eating, and how current diet paradigms may not directly target such eating. Further, we describe how mindfulness training that targets reward-based learning may constitute an appropriate intervention to rewire the learning process around eating. We conclude with examples that illustrate how teaching patients to tap into and act on intrinsic (e.g., enjoying healthy eating, not overeating, and self-compassion) rather than extrinsic reward mechanisms (e.g., weighing oneself), is a promising new direction in improving individuals' relationship with food.

Progressive ratio (PR) schedules and the sipometer: Do they measure wanting, liking, and/or reward? A tribute to Anthony Sclafani and Karen Ackroff

This paper honors the contributions made by Anthony (Tony) Sclafani and Karen Ackroff to both the Columbia University Seminar on Appetitive Behavior and to the field of ingestive behavior in general. We review their use of the progressive ratio (PR) licking paradigm, to determine whether the taste of sucrose, independent of its post-ingestive effects, is always positively reinforcing in animals. They demonstrated a monotonic increase in licking as concentration increased, and obtained results identical to those obtained with a lever-pressing paradigm, but licking was easier and more natural than lever pressing. The PR paradigm was translated to evaluate liquid food reward value in humans. An instrument (the sipometer) was devised that initially permitted a few seconds access to small amounts of a sweet beverage as the participants increased the time to obtain it in 3-5-sec increments. The device went through two refinements and currently delivers the reinforcer and measures the pressure exerted to obtain it. The sipometer is compared with other techniques for measuring motivation and reward. The use of the sipometer and the PR method are discussed in relation to the theoretical challenges inherent in measuring motivation and pleasure, from both psychological and behavioral economics perspectives, and why it is or is not important to separate these processes for both theoretical and practical applications.

Role of addiction and stress neurobiology on food intake and obesity

The US remains at the forefront of a global obesity epidemic with a significant negative impact on public health. While it is well known that a balance between energy intake and expenditure is homeostatically regulated to control weight, growing evidence points to multifactorial social, neurobehavioral and metabolic determinants of food intake that influence obesity risk. This review presents factors such as the ubiquitous presence of rewarding foods in the environment and increased salience of such foods that stimulate brain reward motivation and stress circuits to influence eating behaviors. These rewarding foods via conditioned and reinforcing effects stimulate not only metabolic, but also stress hormones, that, in turn, hijack the brain emotional (limbic) and motivational (striatal) pathways, to promote food craving and excessive food intake. Furthermore, the impact of high levels of stress and trauma and altered metabolic environment (e.g. higher weight, altered insulin sensitivity) on prefrontal cortical self-control processes that regulate emotional, motivational and visceral homeostatic mechanisms of food intake and obesity risk are also discussed. A heuristic framework is presented in which the interactive dynamic effects of neurobehavioral adaptations in metabolic, motivation and stress neurobiology may further support food craving, excessive food intake and weight gain in a complex feed-forward manner. Implications of such adaptations in brain addictive-motivational and stress pathways and their effects on excessive food intake and weight gain are discussed to highlight key questions that requires future research attention in order to better understand and address the growing obesity epidemic.

A sipometer for measuring motivation to consume and reward value of foods and beverages in humans: Description and proof of principle

New methods, derived from animal work, for measuring food reward value (i.e. reinforcing value of food), and motivation (i.e. strength of desire) to consume, in humans are described and validated. A sipping device (sipometer) was developed that permits access to a liquid food or beverage on two reward schedules: continuous reinforcement (CR) and progressively increasing time spent exerting pressure on a straw (PR-schedule). In addition, a pictorial scale showing a cup, from which the 'amount wanted' could be marked was used to pre-test potential consumption. Intake, time spent sipping, breakpoint, and pressure exerted were the main dependent variables measured. Three pilot experiments were conducted. In Experiment 1, participants (n=8) consumed yogurt shakes after a 1-h or 21-h food deprivation period on both schedules. In Experiment 2, participants (n=8) sham-consumed (i.e. spit out) sweet and non-sweet beverages, utilizing both schedules. In Experiment 3, sham-consuming sweet and non-sweet beverages on both schedules and working for shake on the PR schedule were repeated, after three nights of either habitual sleep or short sleep duration (n=7) in a crossover design. In Experiment 1, participants sipped longer after 21-h vs. 1-h of food deprivation (13±3.0 vs. 8.0±2.1s; p=0.04), on the PR schedule. In Experiment 2, sham-intake (p=0.01) and sipping time (p=0.04) were greater for sweet than non-sweet beverages on the PR schedule and a similar, though not conventionally significant, effect was observed for exerted pressure (p=0.09). In both Experiment 2 and Experiment 3 after habitual sleep, on the PR schedule, cumulative pressure difference between sweet and non-sweet beverage increased with difference in amount wanted in the taste test. In contrast, after short sleep participants were less willing to work for sweet taste as their wanting increased, suggesting that sleep deprivation raises desire, but lowers behavioral output. Taken together these results demonstrate that the sipometer and associated ratings are reliable and useful measures of motivation to consume and reward value in humans. Participants were more motivated to obtain access to sweet beverages, especially when these were better liked than to obtain access to non-sweet beverages.

Cognitive Bias in Ambiguity Judgements: Using Computational Models to Dissect the Effects of Mild Mood Manipulation in Humans

Positive and negative moods can be treated as prior expectations over future delivery of rewards and punishments. This provides an inferential foundation for the cognitive (judgement) bias task, now widely-used for assessing affective states in non-human animals. In the task, information about affect is extracted from the optimistic or pessimistic manner in which participants resolve ambiguities in sensory input. Here, we report a novel variant of the task aimed at dissecting the effects of affect manipulations on perceptual and value computations for decision-making under ambiguity in humans. Participants were instructed to judge which way a Gabor patch (250ms presentation) was leaning. If the stimulus leant one way (e.g. left), pressing the REWard key yielded a monetary WIN whilst pressing the SAFE key failed to acquire the WIN. If it leant the other way (e.g. right), pressing the SAFE key avoided a LOSS whilst pressing the REWard key incurred the LOSS. The size (0–100 UK pence) of the offered WIN and threatened LOSS, and the ambiguity of the stimulus (vertical being completely ambiguous) were varied on a trial-by-trial basis, allowing us to investigate how decisions were affected by differing combinations of these factors. Half the subjects performed the task in a ‘Pleasantly’ decorated room and were given a gift (bag of sweets) prior to starting, whilst the other half were in a bare ‘Unpleasant’ room and were not given anything. Although these treatments had little effect on self-reported mood, they did lead to differences in decision-making. All subjects were risk averse under ambiguity, consistent with the notion of loss aversion. Analysis using a Bayesian decision model indicated that Unpleasant Room subjects were (‘pessimistically’) biased towards choosing the SAFE key under ambiguity, but also weighed WINS more heavily than LOSSes compared to Pleasant Room subjects. These apparently contradictory findings may be explained by the influence of affect on different processes underlying decision-making, and the task presented here offers opportunities for further dissecting such processes.

HPA Axis Interactions with Behavioral Systems

Perhaps the most salient behaviors that individuals engage in involve the avoidance of aversive experiences and the pursuit of pleasurable experiences. Engagement in these behaviors is regulated to a significant extent by an individual's hormonal milieu. For example, glucocorticoid hormones are produced by the hypothalamic-pituitary-adrenocortical (HPA) axis, and influence most aspects of behavior. In turn, many behaviors can influence HPA axis activity. These bidirectional interactions not only coordinate an individual's physiological and behavioral states to each other, but can also tune them to environmental conditions thereby optimizing survival. The present review details the influence of the HPA axis on many types of behavior, including appetitively-motivated behaviors (e.g., food intake and drug use), aversively-motivated behaviors (e.g., anxiety-related and depressive-like) and cognitive behaviors (e.g., learning and memory). Conversely, the manuscript also describes how engaging in various behaviors influences HPA axis activity. Our current understanding of the neuronal and/or hormonal mechanisms that underlie these interactions is also summarized. © 2016 American Physiological Society. Compr Physiol 6:1897-1934, 2016.

Self-medication with sucrose

For many individuals, stress promotes the consumption of sweet, high-sugar foods relative to healthier alternatives. Daily life stressors stimulate the overeating of highly-palatable foods through multiple mechanisms, including altered glucocorticoid, relaxin-3, ghrelin and serotonin signaling in brain. In turn, a history of consuming high-sugar foods attenuates the psychological (anxiety and depressed mood) and physiological (HPA axis) effects of stress. Together the metabolic and hedonic properties of sucrose contribute to its stress relief, possibly via actions in both the periphery (e.g., glucocorticoid receptor signaling in adipose tissue) and in the brain (e.g., plasticity in brain reward regions). Emerging work continues to reveal the bidirectional mechanisms that underlie the use of high-sugar foods as 'self-medication' for stress relief.

Diminished effort on a progressive ratio task in both unipolar and bipolar depression

BACKGROUND

Amotivation, or decisional anhedonia, is a prominent and disabling feature of depression. However, this aspect of depression remains understudied, and no prior work has applied objective laboratory tests of motivation in both unipolar and bipolar depression.

METHODS

We assessed motivation deficits using a Progressive Ratio Task (PRT) that indexes willingness to exert effort for monetary reward. The PRT was administered to 96 adults ages 18-60 including 25 participants with a current episode of unipolar depression, 28 with bipolar disorder (current episode depressed), and 43 controls without any Axis I psychiatric disorders.

RESULTS

Depressed participants exhibited significantly lower motivation than control participants as objectively defined by progressive ratio breakpoints. Both the unipolar and bipolar groups were lower than controls but did not differ from each other.

LIMITATIONS

Medication use differed across groups, and we did not have a separate control task to measure psychomotor activity; however neither medication effects or psychomotor slowing are likely to explain our findings.

CONCLUSIONS

Our study fills an important gap in the literature by providing evidence that diminished effort on the PRT is present across depressed patients who experience either unipolar or bipolar depression. This adds to growing evidence for shared mechanisms of reward and motivation dysfunction, and highlights the importance of improving the assessment and treatment of motivation deficits across the mood disorders spectrum.

Differential motivational profiles following adolescent sucrose access in male and female rats

Adolescents are the highest consumers of sugar sweetened drinks. Excessive consumption of such drinks is a likely contributor to the development of obesity and may be associated with enduring changes in the systems involved in reward and motivation. We examined the impact of daily sucrose consumption in young male and female rats (N=12 per group) across the adolescent period on the motivation to perform instrumental responses to gain food rewards as adults. Rats were or were not exposed to a sucrose solution for 2 h each day for 28 days across adolescence [postnatal days (P) 28-56]. They were then trained as adults (P70 onward) to lever press for a palatable 15% cherry flavored sucrose reward and tested on a progressive ratio (PR) schedule to assess motivation to respond for reinforcement. Female rats exposed to sucrose had higher breakpoints on the PR schedule than controls, whereas male rats exposed to sucrose had lower breakpoints than controls. These results show that consumption of sucrose during adolescence produced sex-specific behavioral changes in responding for sucrose as adults.

Sugar Consumption Produces Effects Similar to Early Life Stress Exposure on Hippocampal Markers of Neurogenesis and Stress Response

Adverse early life experience is a known risk factor for psychiatric disorders. It is also known that stress influences food preference. We were interested in exploring whether the choice of diet following early life stress exerts long-lasting molecular changes in the brain, particularly the hippocampus, a region critically involved in stress regulation and behavioral outcomes. Here, we examined the impact of early life stress induced by limited nesting material (LN) and chronic sucrose availability post-weaning on an array of hippocampal genes related to plasticity, neurogenesis, stress and inflammatory responses and mitochondrial biogenesis. To examine mechanisms underlying the impact of LN and sugar intake on hippocampal gene expression, we investigated the role of DNA methylation. As females are more likely to experience adverse life events, we studied female Sprague-Dawley rats. After mating LN was imposed from days 2 to 9 postpartum. From 3 to 15 weeks of age, female Control and LN siblings had unlimited to access to either chow and water, or chow, water and 25% sucrose solution. LN markedly reduced glucocorticoid receptor (GR) and neurogenic differentiation 1 (Neurod1) mRNA, markers involved in stress and hippocampal plasticity respectively, by more than 40%, with a similar effect of sugar intake in control rats. However, no further impact was observed in LN rats consuming sugar. Hippocampal Akt3 mRNA expression was similarly affected by LN and sucrose consumption. Interestingly, DNA methylation across 4 CpG sites of the GR and Neurod1 promoters was similar in LN and control rats. In summary, early life stress and post-weaning sugar intake produced long-term effects on hippocampal GR and Neurod1 expression. Moreover we found no evidence of altered promoter DNA methylation. We demonstrate for the first time that chronic sucrose consumption alone produces similar detrimental effects on the expression of hippocampal genes as LN exposure.

Animal models of recurrent or bipolar depression

Animal models of mental disorders should ideally have construct, face, and predictive validity, but current animal models do not always satisfy these validity criteria. Additionally, animal models of depression rely mainly on stress-induced behavioral changes. These stress-induced models have limited validity, because stress is not a risk factor specific to depression, and the models do not recapitulate the recurrent and spontaneous nature of depressive episodes. Although animal models exhibiting recurrent depressive episodes or bipolar depression have not yet been established, several researchers are trying to generate such animals by modeling clinical risk factors as well as by manipulating a specific neural circuit using emerging techniques.

Beneficial Effects of Highly Palatable Food on the Behavioral and Neural Adversities induced by Early Life Stress Experience in Female Rats

This study examined the effects of highly palatable food during adolescence on the psycho-emotional and neural disturbances caused by early life stress experience in female rats. Female Sprague-Dawley pups were separated from dam for 3 h daily during the first two weeks of birth (MS) or left undisturbed (NH). Half of MS females received free access to chocolate cookies in addition to ad libitum chow from postnatal day 28. Pups were subjected to the behavioral tests during young adulthood. The plasma corticosterone response to acute stress, ΔFosB and brain-derived neurotrophic factor (BDNF) levels in the brain regions were analyzed. Total caloric intake and body weight gain during the whole experimental period did not differ among the experimental groups. Cookie access during adolescence and youth improved anxiety-/depression-like behaviors by MS experience. ΔFosB expression was decreased, but BDNF was increased in the nucleus accumbens of MS females, and ΔFosB expression was normalized and BDNF was further increased following cookie access. Corticosterone response to acute stress was blunted by MS experience and cookie access did not improve it. Results suggest that cookie access during adolescence improves the psycho-emotional disturbances of MS females, and ΔFosB and/or BDNF expression in the nucleus accumbens may play a role in its underlying neural mechanisms.

The possible relationship between expressions of TRPC3/5 channels and cognitive changes in rat model of chronic unpredictable stress

Transient receptor potential canonical channel (TRPC) is a nonselective cation channel dominantly permeable to Ca(2+). It consists of seven homologues, TRPC1-TRPC7, based on their sequence similarity. According to some researches, the expression of TRPC3/5 in hippocampus is related to the morphological changes of hippocampus, including axon length and dendritic spine density [1]. This study observed whether the expression of TRPC3/5 was changed in chronic unpredictable stress (CUS)-induced depression of rat model and can the altered TRPC3/5 expression affect the morphology of neurons in hippocampus of depressive rats as well as the cognitive ability. A total of 16 rats were equally and randomly divided into two groups: the control group and the depression model group, which underwent a process of CUS for three weeks. Western blot assay was conducted to test the content of TRPC3/5 in hippocampus, and Golgi-Cox staining was used to observe the morphological changes of neurons in hippocampus. Morris water maze (MWM) test was performed to observe the changes of spatial cognitive ability of rats while the long-term potentiation was applied to evaluate synaptic plasticity. Results showed that there was a difference in the expression of TRPC3/5 in hippocampal neurons, as well as the neuron morphology between control group and depression model group. At the same time the cognitive ability and synaptic plasticity were significantly changed. Results suggest that there is an association between expressions of TRPC3/5 and cognitive changes in CUS rat model, and the mechanism maybe that the different expressions of TRPC3/5 can cause morphological changes of the neurons in hippocampus, which has a profound impact on the spatial cognitive ability and synaptic plasticity.

Reconceptualizing anhedonia: novel perspectives on balancing the pleasure networks in the human brain

Anhedonia, the lack of pleasure, has been shown to be a critical feature of a range of psychiatric disorders. Yet, it is currently measured primarily through subjective self-reports and as such has been difficult to submit to rigorous scientific analysis. New insights from affective neuroscience hold considerable promise in improving our understanding of anhedonia and for providing useful objective behavioral measures to complement traditional self-report measures, potentially leading to better diagnoses and novel treatments. Here, we review the state-of-the-art of hedonia research and specifically the established mechanisms of wanting, liking, and learning. Based on this framework we propose to conceptualize anhedonia as impairments in some or all of these processes, thereby departing from the longstanding view of anhedonia as solely reduced subjective experience of pleasure. We discuss how deficits in each of the reward components can lead to different expressions, or subtypes, of anhedonia affording novel ways of measurement. Specifically, we review evidence suggesting that patients suffering from depression and schizophrenia show impairments in wanting and learning, while some aspects of conscious liking seem surprisingly intact. Furthermore, the evidence suggests that anhedonia is heterogeneous across psychiatric disorders, depending on which parts of the pleasure networks are most affected. This in turn has implications for diagnosis and treatment of anhedonia.

Individual differences in anhedonic and accumbal dopamine responses to chronic social stress and their link to cocaine self-administration in female rats

RATIONALE

Women are twice as likely as men to develop major depressive disorder. Exposure to chronic stress can induce depression in some vulnerable individuals, while others are resistant to depressive-like symptoms after equivalent levels of chronic stress.

OBJECTIVES

In female rats, individual differences in saccharin intake during chronic social defeat stress may predict subsequent cocaine self-administration, and may be attributed to alterations in mesolimbic dopamine activity.

METHODS

Female rats were exposed to 21 days of chronic social defeat stress, during which they were evaluated for their anhedonia-like responses in the form of saccharin intake. After chronic social defeat stress, the rats were tested for behavioral cross-sensitization to cocaine and escalated cocaine self-administration in a 24-h "binge." A separate group of animals underwent in vivo microdialysis of the nucleus accumbens (NAc) shell to assess dopamine (DA) in response to acute cocaine challenge.

RESULTS

Cluster analysis revealed two phenotypes among the stressed female rats based on their saccharin intake while being exposed to stress, termed stress-resistant (SR, 28 %) and stress-sensitive (SS, 72 %). The amount of cocaine self-administered during the 24-h "binge" was positively correlated with preceding saccharin intake. The NAc DA response to a cocaine challenge was significantly lower in SR rats than in the SS and non-stressed control rats. No other significant differences were observed in behavioral cross-sensitization or cocaine self-administration prior to the "binge."

CONCLUSION

Female rats showed individual differences in their anhedonic-like response to chronic social defeat stress, and these differences were reliably associated with subsequent cocaine-taking behavior.

Stress exposure, food intake and emotional state

This manuscript summarizes the proceedings of the symposium entitled, "Stress, Palatable Food and Reward", that was chaired by Drs. Linda Rinaman and Yvonne Ulrich-Lai at the 2014 Neurobiology of Stress Workshop held in Cincinnati, OH. This symposium comprised research presentations by four neuroscientists whose work focuses on the biological bases for complex interactions among stress, food intake and emotion. First, Dr Ulrich-Lai describes her rodent research exploring mechanisms by which the rewarding properties of sweet palatable foods confer stress relief. Second, Dr Stephanie Fulton discusses her work in which excessive, long-term intake of dietary lipids, as well as their subsequent withdrawal, promotes stress-related outcomes in mice. Third, Dr Mark Wilson describes his group's research examining the effects of social hierarchy-related stress on food intake and diet choice in group-housed female rhesus macaques, and compared the data from monkeys to results obtained in analogous work using rodents. Finally, Dr Gorica Petrovich discusses her research program that is aimed at defining cortical-amygdalar-hypothalamic circuitry responsible for curbing food intake during emotional threat (i.e. fear anticipation) in rats. Their collective results reveal the complexity of physiological and behavioral interactions that link stress, food intake and emotional state, and suggest new avenues of research to probe the impact of genetic, metabolic, social, experiential and environmental factors on these interactions.

Depressive-like behaviors in a rat model of chronic cerebral hypoperfusion

The vascular depression hypothesis suggests that there is an association between cerebrovascular pathophysiology and depression in the elderly. We investigated depressive-like behaviors and perturbations in the hypothalamus-pituitary-adrenal (HPA) axis in a rat model of chronic cerebral hypoperfusion. We modeled chronic cerebral hypoperfusion by permanent occlusion of the bilateral common carotid arteries (BCCAo) in Wistar rats. Sucrose preference, forced swim, and social interaction tests were performed to measure depressive-like behaviors. The plasma levels of adrenocorticotropic hormone and corticosterone, and the hippocampal expression of the glucocorticoid receptor (GR) were assessed. Sucrose preference (P = 0.045) and social withdrawal (P = 0.038) were significantly enhanced in BCCAo rats. Increased plasma levels of corticosterone (P = 0.034) and impaired cytosolic-to-nuclear translocation of the GR protein were observed in the hippocampus (P = 0.038) of BCCAo rats. Our experimental results support the clinical hypothesis that vascular depression can be induced by chronic cerebral hypoperfusion. Increased HPA axis activity and perturbation of the GR signaling pathway in the hippocampus may be associated with depressive-like behaviors in rats with chronic cerebral hypoperfusion.

Amotivation in schizophrenia: integrated assessment with behavioral, clinical, and imaging measures

Motivational deficits play a central role in disability caused by schizophrenia and constitute a major unmet therapeutic need. Negative symptoms have previously been linked to hypofunction in ventral striatum (VS), a core component of brain motivation circuitry. However, it remains unclear to what extent this relationship holds for specific negative symptoms such as amotivation, and this question has not been addressed with integrated behavioral, clinical, and imaging measures. Here, 41 individuals with schizophrenia and 37 controls performed a brief, computerized progressive ratio task (PRT) that quantifies effort exerted in pursuit of monetary reward. Clinical amotivation was assessed using the recently validated Clinical Assessment Interview for Negative Symptoms (CAINS). VS function was probed during functional magnetic resonance imaging using a monetary guessing paradigm. We found that individuals with schizophrenia had diminished motivation as measured by the PRT, which significantly and selectively related to clinical amotivation as measured by the CAINS. Critically, lower PRT motivation in schizophrenia was also dimensionally related to VS hypofunction. Our results demonstrate robust dimensional associations between behavioral amotivation, clinical amotivation, and VS hypofunction in schizophrenia. Integrating behavioral measures such as the PRT will facilitate translational efforts to identify biomarkers of amotivation and to assess response to novel therapeutic interventions.