Updates on the neurobiology of food reward and their relation to the obesogenic environment

Control of motivation for sucrose in the paraventricular hypothalamic nucleus by dynorphin peptides and the kappa opioid receptor

The dynorphin peptides are the endogenous ligands for the kappa opioid receptor (KOR) and regulate food intake. Administration of dynorphin-A1-13 (DYN) in the paraventricular hypothalamic nucleus (PVN) increases palatable food intake, and this effect is blocked by co-administration of the orexin-A neuropeptide, which is co-released with DYN in PVN from neurons located in the lateral hypothalamus. While PVN administration of DYN increases palatable food intake, whether it increases food-seeking behaviors has yet to be examined. We tested the effects of DYN and norBNI (a KOR antagonist) on the seeking and consumption of sucrose using a progressive ratio (PR) and demand curve (DC) tasks. In PVN, DYN did not alter the sucrose breaking point (BP) in the PR task nor the elasticity or intensity of demand for sucrose in the DC task. Still, DYN reduced the delay in obtaining sucrose and increased licks during sucrose intake in the PR task, irrespective of the co-administration of orexin-A. In PVN, norBNI increased the delay in obtaining sucrose and reduced licks during sucrose intake in the PR task while increasing elasticity without altering intensity of demand in the DC task. However, subcutaneous norBNI reduced the BP for sucrose and increased the delay in obtaining sucrose in the PR task while reducing the elasticity of demand. Together, these data show different effects of systemic and PVN blockade of KOR on food-seeking, consummatory behaviors, and incentive motivation for sucrose and suggest that KOR activity in PVN is necessary but not sufficient to drive seeking behaviors for palatable food.

Sleep deprivation in development of obesity, effects on appetite regulation, energy metabolism, and dietary choices

Sleep deprivation, which is a decrease in duration and quality of sleep, is a common problem in today's life. Epidemiological and interventional investigations have suggested a link between sleep deprivation and overweight/obesity. Sleep deprivation affects homeostatic and non-homoeostatic regulation of appetite, with the food reward system playing a dominant role. Factors such as sex and weight status affect this regulation; men and individuals with excess weight seem to be more sensitive to reward-driven and hedonistic regulation of food intake. Sleep deprivation may also affect weight through affecting physical activity and energy expenditure. In addition, sleep deprivation influences food selection and eating behaviours, which are mainly managed by the food reward system. Sleep-deprived individuals mostly crave for palatable energy-dense foods and have low desire for fruit and vegetables. Consumption of meals may not change but energy intake from snacks increases. The individuals have more desire for snacks with high sugar and saturated fat content. The relationship between sleep and the diet is mutual, implying that diet and eating behaviours also affect sleep duration and quality. Consuming healthy diets containing fruit and vegetables and food sources of protein and unsaturated fats and low quantities of saturated fat and sugar may be used as a diet strategy to improve sleep. Since the effects of sleep deficiency differ between animals and humans, only evidence from human subject studies has been included, controversies are discussed and the need for future investigations is highlighted.

Combination therapy with exenatide decreases the dapagliflozin-induced changes in brain responses to anticipation and consumption of palatable food in patients with type 2 diabetes: A randomized controlled trial

AIMS

Sodium-glucose cotransporter-2 inhibitors induce less weight loss than expected. This may be explained by sodium-glucose cotransporter-2 inhibitor-induced alterations in central reward- and satiety circuits, leading to increased appetite and food intake. Glucagon-like peptide-1 receptor agonists reduce appetite and body weight because of direct and indirect effects on the brain. We investigated the separate and combined effects of dapagliflozin and exenatide on the brain in response to the anticipation and consumption of food in people with obesity and type 2 diabetes.

MATERIALS AND METHODS

As part of a larger study, this was a 16 week, double-blind, randomized, placebo-controlled trial. Subjects with obesity and type 2 diabetes were randomized (1:1:1:1) to dapagliflozin 10 mg with exenatide-matched placebo, exenatide twice-daily 10 μg with dapagliflozin-matched placebo, dapagliflozin plus exenatide, or double placebo. Using functional magnetic resonance imaging, the effects of treatments on brain responses to the anticipation of food and food receipt were assessed after 10 days and 16 weeks.

RESULTS

After 10 days, dapagliflozin increased activation in right amygdala and right caudate nucleus in response to the anticipation of food, and tended to decrease activation in right amygdala in response to actual food receipt. After 16 weeks, no changes in brain activation were observed with dapagliflozin. Dapagliflozin plus exenatide reduced activation in right caudate nucleus and amygdala to the anticipation of food, and decreased activation in the right amygdala in response to food receipt after 16 weeks.

CONCLUSIONS

The dapagliflozin-induced changes in brain activation may contribute to the discrepancy between observed and expected weight loss with dapagliflozin. Exenatide blunted the dapagliflozin-induced changes in brain activation, which may contribute to the additional weight loss with combined treatment.

Impact of Gut and Metabolic Hormones on Feeding Reward

Ingestion of food activates a cascade of endocrine responses (thereby reflecting a contemporaneous feeding status) that include the release of hormones from the gastrointestinal (GI) tract, such as cholecystokinin (CCK), glucagonlike peptide YY (PYY), peptide PP, and oleoylethanolamide, as well as suppression of ghrelin secretion. The pancreas and adipose tissue, on the other hand, release hormones that serve as a measure of the current metabolic state or the long-term energy stores, that is, insulin, leptin, and adiponectin. It is well known and intuitively understandable that these hormones target either directly (by crossing the blood-brain barrier) or indirectly (e.g., via vagal input) the "homeostatic" brainstem-hypothalamic pathways involved in the regulation of appetite. The current article focuses on yet another target of the metabolic and GI hormones that is critical in inducing changes in food intake, namely, the reward system. We discuss the physiological basis of this functional interaction, its importance in the control of appetite, and the impact that disruption of this crosstalk has on energy intake in select physiological and pathophysiological states. We conclude that metabolic and GI hormones have a capacity to strengthen or weaken a response of the reward system to a given food, and thus, they are fundamental in ensuring that feeding reward is plastic and dependent on the energy status of the organism. © 2021 American Physiological Society. Compr Physiol 11:1425-1447, 2021.

Functions of Interoception: From Energy Regulation to Experience of the Self

We review recent work on the functions of interoceptive processing, by which the nervous system anticipates, senses, and integrates signals originating from the body. We focus on several exemplar functions of interoception, including energy regulation (ingestion and excretion), memory, affective and emotional experience, and the psychological sense of self. We emphasize two themes across these functions. First, the anatomy of interoceptive afferents makes it difficult to manipulate or directly measure interoceptive signaling in humans. Second, recent evidence shows that multimodal integration occurs across interoceptive modalities and between interoceptive and exteroceptive modalities. Whereas exteroceptive multimodal integration has been studied relatively extensively, fundamental questions remain regarding multimodal integration that involves interoceptive modalities. Future empirical work is required to better understand how and where multimodal interoceptive integration occurs.

Nucleus Accumbens Functional Connectivity with the Frontoparietal Network Predicts Subsequent Change in Body Mass Index for American Children

Background: Nucleus accumbens (NAc) is a brain structure with a well-established role in the brain reward processing system. Altered function of the NAc is shown to have a role in the development of food addiction and obesity. However, less is known about sex differences in the role of NAc function as a predictor of children’s change in body mass index (BMI) over time. Aim: We used the Adolescent Brain Cognitive Development data (version 2.01) to investigate sex differences in the predictive role of the NAc functional connectivity with the frontoparietal network on children’s BMI change over a one-year follow-up period. Methods: This 1-year longitudinal study successfully followed 3784 9–10-year-old children. Regression models were used to analyze the data. The predictor variable was NAc functional connectivity with the frontoparietal network measured using resting-state functional magnetic resonance imaging (fMRI). The primary outcome was BMI at the end of the 1-year follow up. Covariates included race, ethnicity, age, socioeconomic factors, and baseline BMI. Sex was the effect modifier. Results: NAc functional connectivity with the frontoparietal network was predictive of BMI changes over time. This association remained significant above and beyond all covariates. The above association, however, was only significant in female, not male children. Conclusion: The epidemiological observation that NAc functional connectivity is associated with BMI changes in children is an extension of well-controlled laboratory studies that have established the role of the NAc in the brain reward processing. More research is needed on sex differences in the brain regions that contribute to childhood obesity.

Reframing appetitive reinforcement learning and reward valuation as effects mediated by hippocampal-dependent behavioral inhibition

Traditional theories of neuroeconomics focus on reinforcement learning and reward value. We propose here a novel reframing of reinforcement learning and motivation that includes a hippocampal-dependent regulatory mechanism which balances cue-induced behavioral excitation with behavioral inhibition. This mechanism enables interoceptive cues produced by respective food or drug satiety to antagonize the ability of excitatory food- and drug-related environmental cues to retrieve the memories of food and drug reinforcers, thereby suppressing the power of those cues to evoke appetitive behavior. When the operation of this mechanism is impaired, ability of satiety signals to inhibit appetitive behavior is weakened because the relative balance between inhibition and simple excitation is shifted toward increased retrieval of food and drug memories by environmental cues. In the present paper, we (1) describe the associative processes that constitute this mechanism of hippocampal-dependent behavior inhibition; (2) describe how a prevailing obesity-promoting diet and drugs of abuse produce hippocampal pathophysiologies that can selectively impair this inhibitory function; and (3) propose how glucagon-like peptide 1 (GLP-1), an incretin hormone that is recognized as an important satiety signal, may work to protect the hippocampal-dependent inhibition. Our perspective may add to neuroscientific and neuroeconomic analyses of both overeating and drug abuse by outlining the role of hippocampal-dependent memory processes in the control of both food and drug seeking behaviors. In addition, this view suggests that consideration should be given to diet- and drug induced hippocampal pathophysiologies, as potential novel targets for the treatment of dysregulated energy and drug intake.

Retinal functioning and reward processing in schizophrenia

Retinal responses to light, as measured by electroretinography (ERG), have been shown to be reduced in schizophrenia. Data from a prior ERG study in healthy humans indicated that activity of a retinal cell type affected in schizophrenia can be modified by the presence of a food reward. Therefore, we aimed to determine whether ERG amplitudes would be sensitive to the well-documented reward processing impairment in schizophrenia. Flash ERG data from 15 clinically stable people with schizophrenia or schizoaffective disorder and 15 healthy controls were collected under three conditions: baseline, anticipation of a food reward, and immediately after consuming the food reward. At the group level, data indicated that controls' ERG responses varied as a function of salience of the food reward (baseline vs. anticipation vs. consumption) whereas patients' ERG responses did not vary significantly across conditions. Correlations between ERG amplitudes and scores on measures of hedonic capacity (including motivation and pleasure negative symptom ratings for patients) indicated consistent relationships. These data suggest that flash ERG amplitudes may be a sensitive indicator of the integrity of reward processing mechanisms. However, several differences in the direction of findings between this and a prior study in controls point to the need for further investigation of the contributions of a number of key variables to the observed effects.

Schizophrenia and the retina: Towards a 2020 perspective

BACKGROUND

Differences between people with schizophrenia and psychiatrically healthy controls have been consistently demonstrated on measures of retinal function such as electroretinography (ERG), and measures of retinal structure such as optical coherence tomography (OCT). Since our 2015 review of this literature, multiple new studies have been published using these techniques. At the same time, the accumulation of data has highlighted the "fault lines" in these fields, suggesting methodological considerations that need greater attention in future studies.

METHODS

We reviewed studies of ERG and OCT in schizophrenia, as well as data from studies whose findings are relevant to interpreting these papers, such as those on effects of the following on ERG and OCT data: comorbid medical conditions that are over-represented in schizophrenia, smoking, antipsychotic medication, substance abuse, sex and gender, obesity, attention, motivation, and influences of brain activity on retinal function.

RESULTS

Recent ERG and OCT studies continue to support the hypothesis of retinal structural and functional abnormalities in schizophrenia, and suggest that these are relevant to understanding broader aspects of pathophysiology, neurodevelopment, and neurodegeneration in this disorder. However, there are differences in findings which suggest that the effects of multiple variables on ERG and OCT data need further clarification.

CONCLUSIONS

The retina, as the only component of the CNS that can be imaged directly in live humans, has potential to clarify important aspects of schizophrenia. With greater attention to specific methodological issues, the true potential of ERG and OCT as biomarkers for important clinical phenomena in schizophrenia should become apparent.

Parental Education and Nucleus Accumbens Response to Reward Anticipation: Minorities' Diminished Returns

Background

Considerable research has documented the effects of race and socioeconomic status (SES) on reward-seeking behaviors; however, less is known about the multiplicative effects of race and family SES on brain response to reward anticipation. Marginalization-related Diminished Returns (MDRs) suggest that family SES would show weaker effects on brain development of children in non-White families than in White families.

Objective

To test race by SES variation in Nucleus Accumbens (NAcc) response to reward anticipation (NAcc-RA) among American children.

Methods

For this cross-sectional analysis, data came from the Adolescent Brain Cognitive Development (ABCD) study which included 6,419, 9-10 year old children. The independent variable was parental education. The moderator was race. The primary outcome was the right NAcc-RA. Age, sex, ethnicity, household income, and family structure were the covariates. We used mixed effects regression models that adjusted for the nested nature of the ABCD data.

Results

While high parental education was associated with a higher amount of right NAcc-RA, this effect was stronger for White than non-White children. This finding was evident in the observed interactions between race and parental education on the right NAcc-RA.

Discussion

For American children, NAcc-RA is not shaped by race or family SES, but by their intersection. As a result of the interaction between race and SES (diminished return of SES for non-Whites), middle-class racial minority children may remain susceptible to high-risk behaviors. Disparities in high-risk behaviors in children should not be reduced to economic disparities. Structural inequalities may reduce the return of SES resources for non-White families.