Like drugs for chocolate: separate rewards modulated by common mechanisms?

Food selection in a buffet scenario by persons in recovery from substance use disorder: Testing a parallel mediation model including impulsivity, food craving, and breadth of drug use

Elevated food cravings and higher food consumption and body weight have been reported in studies of people in recovery from substance use disorder (SUD). In a previous study, SUD recovery status predicted the energy from selected food images in a virtual buffet meal, most strongly in those with high reward responsiveness. The present study was conducted to determine which psychological variables might mediate the relationship between SUD recovery status and food selection and to replicate the finding that reward responsiveness moderated this relationship. In an online study, 216 women and men (109 in recovery from SUD) were asked to choose from among 16 food images in an all-you-can-eat buffet scenario. Food craving, impulsivity, "food addiction", irrational food beliefs, anhedonia, and breadth of drug use were examined as potential mediators while reward responsiveness was examined as a potential moderator. The amount of energy in the selected foods was the outcome variable. Results indicated that breadth of drug use was a mediator; being in SUD recovery predicted higher variety of drug use which predicted higher food selection. However, reward responsiveness did not moderate the relationship between SUD recovery status and energy from the selected foods. Exploratory analysis indicated that lack of premeditation, a measure of impulsivity, with food craving partially mediated the relationship between breadth of drug use and energy from selected foods and that lack of premeditation fully mediated it for sweet foods. The results confirm an association between substance use and food selection and suggest a mechanism via impulsivity.

Neurogenetics and Epigenetics of Loneliness

Loneliness, an established risk factor for both, mental and physical morbidity, is a mounting public health concern. However, the neurobiological mechanisms underlying loneliness-related morbidity are not yet well defined. Here we examined the role of genes and associated DNA risk polymorphic variants that are implicated in loneliness via genetic and epigenetic mechanisms and may thus point to specific therapeutic targets. Searches were conducted on PubMed, Medline, and EMBASE databases using specific Medical Subject Headings terms such as loneliness and genes, neuro- and epigenetics, addiction, affective disorders, alcohol, anti-reward, anxiety, depression, dopamine, cancer, cardiovascular, cognitive, hypodopaminergia, medical, motivation, (neuro)psychopathology, social isolation, and reward deficiency. The narrative literature review yielded recursive collections of scientific and clinical evidence, which were subsequently condensed and summarized in the following key areas: (1) Genetic Antecedents: Exploration of multiple genes mediating reward, stress, immunity and other important vital functions; (2) Genes and Mental Health: Examination of genes linked to personality traits and mental illnesses providing insights into the intricate network of interaction converging on the experience of loneliness; (3) Epigenetic Effects: Inquiry into instances of loneliness and social isolation that are driven by epigenetic methylations associated with negative childhood experiences; and (4) Neural Correlates: Analysis of loneliness-related affective states and cognitions with a focus on hypodopaminergic reward deficiency arising in the context of early life stress, eg, maternal separation, underscoring the importance of parental support early in life. Identification of the individual contributions by various (epi)genetic factors presents opportunities for the creation of innovative preventive, diagnostic, and therapeutic approaches for individuals who cope with persistent feelings of loneliness. The clinical facets and therapeutic prospects associated with the current understanding of loneliness, are discussed emphasizing the relevance of genes and DNA risk polymorphic variants in the context of loneliness-related morbidity.

Association between body mass index and treatment completion in extended-release naltrexone-treated patients with opioid dependence

Background

Excessive consumption of opioids is associated with impaired metabolic function including increased body mass index (BMI). Opioid antagonist naltrexone (NTX) is an effective treatment for opioid use disorder (OUD) that has the potential to mitigate such metabolic disturbances. Understanding the relationship between treatment adherence and BMI in NTX-treated OUD patients may provide valuable insights into optimizing clinical outcomes.

Methods

Patients with opioid dependence were offered up to three monthly injections of extended-release (XR) NTX. Treatment completers (n = 41) were defined as those who had received all three XR-NTX injections, and non-completers (n = 20) as those missing at least one injection. Logistic regression was performed to examine the association between pre-treatment BMI and treatment completion.

Results

BMI was positively associated with treatment completion. This association remained significant after adjusting for potentially confounding variables.

Conclusion

Our findings suggest that baseline BMI may serve as a potential predictor of XR-NTX treatment adherence in patients with OUD and could help healthcare providers and policy makers alike in developing strategies to improve retention and tailor interventions for specific patient subgroups.

Patterns and Determinants of Weight Gain among People Who Use Drugs Undergoing Treatment for Recovery in Lebanon

Substance use disorder compromises the nutritional status and the eating habits of drug users, often leading to malnutrition. Once referred for treatment, hyperphagia and poor lifestyle practices leading to weight gain are observed. This study aimed to examine the patterns and extent of weight change as well as the determinants of weight gain in a sample of drug users who were receiving treatment in Lebanon. A total of 172 male participants undergoing either rehabilitation or opioid substitution treatment (OST) were included. Multivariate regression analysis was applied to assess the effect of different variables on weight gain while adjusting for potentially confounding variables. Approximately two-thirds (65.1%) of the participants gained weight (OST: 54.3%, rehabilitation: 78.2%; p < 0.05). The mean weight gain was 5.9 kg and was mainly reported among participants in the underweight, normal, and overweight pre-treatment categories and accentuated in the rehabilitation group (OST: 2 kg, Rehabilitation: 10.6 kg). Around half of the participants moved from the normal weight category to the overweight and obese categories during treatment. Weight gain was negatively associated with the number of previous treatment attempts (Odds Ratio = 0.86; Confidence Interval: 0.74-0.99), duration of current treatment (Odds Ratio = 0.98; Confidence Interval: 0.96-0.99), and pre-treatment body mass index (BMI) (Odds Ratio = 0.88; Confidence Interval: 0.80-0.96). Investigating other nutrition and lifestyle practices, neither nutrition knowledge, food addiction, physical activity level, nor sleep quality were associated with weight gain. Treatment through drug use was associated with meaningful weight gain that might lead to health risk factors. Developing health promotion programs is crucial to enhance treatment and decrease the risk of relapse.

The Role of Ghrelin/GHS-R1A Signaling in Nonalcohol Drug Addictions

Drug addiction causes constant serious health, social, and economic burden within the human society. The current drug dependence pharmacotherapies, particularly relapse prevention, remain limited, unsatisfactory, unreliable for opioids and tobacco, and even symptomatic for stimulants and cannabinoids, thus, new more effective treatment strategies are researched. The antagonism of the growth hormone secretagogue receptor type A (GHS-R1A) has been recently proposed as a novel alcohol addiction treatment strategy, and it has been intensively studied in experimental models of other addictive drugs, such as nicotine, stimulants, opioids and cannabinoids. The role of ghrelin signaling in these drugs effects has also been investigated. The present review aims to provide a comprehensive overview of preclinical and clinical studies focused on ghrelin's/GHS-R1A possible involvement in these nonalcohol addictive drugs reinforcing effects and addiction. Although the investigation is still in its early stage, majority of the existing reviewed experimental results from rodents with the addition of few human studies, that searched correlations between the genetic variations of the ghrelin signaling or the ghrelin blood content with the addictive drugs effects, have indicated the importance of the ghrelin's/GHS-R1As involvement in the nonalcohol abused drugs pro-addictive effects. Further research is necessary to elucidate the exact involved mechanisms and to verify the future potential utilization and safety of the GHS-R1A antagonism use for these drug addiction therapies, particularly for reducing the risk of relapse.

Context-Specific Tolerance and Pharmacological Changes in the Infralimbic Cortex-Nucleus Accumbens Shell Pathway Evoked by Ketamine

Like other drugs, ketamine is abused due to its ability to act as a positive reinforcer in the control of behavior, just as natural reinforcers do. Besides, through Pavlovian conditioning, tolerance to drug effects can become conditioned to specific contextual cues showing that environmental stimuli can act as powerful mediators of craving and relapse. In the present study, we shall investigate the effects of long-term ketamine administration and withdrawal on behavioral measures and emotionality, the drug-context-specific influence on the tolerance to the sedative effects of an anesthetic dose of ketamine, and the neuropharmacological events underlying this phenomenon, in rats conditioned with 10 mg/kg of ketamine and later challenged with a dose of ketamine of 80 mg/kg in a familiar and non-familiar environment. Variations in dopamine and serotonin efflux in the infralimbic cortex-nucleus accumbens shell circuitry (IL-NAcSh) was further recorded in the same conditions. Our results highlight that besides its well-known reinforcing properties, ketamine also shares the ability to induce behavioral and pharmacological conditioned tolerance, associated with increases in cortical (IL), and decreases in striatal (NAcSh) dopamine release. To our knowledge, we are presenting the first set of behavioral and neurochemical data showing that, like other drugs of abuse, ketamine can induce learned context-specific tolerance.

Binge Eating and Addictive-Like Behaviours in Males and Females

INTRODUCTION

Binge eating is a common behaviour that is strongly linked to both obesity and eating disorder. There is evidence that binge eating commonly co-occurs with other problematic and addictive-like behaviours; however, this has not been explored systematically. The present study aimed to examine the relationship between binge eating, body weight, disordered eating behaviours and associated addictive-like behaviours, with particular attention paid to gender differences.

METHOD

A community sample (N = 500; 75% female, M_age = 32.5 years) reported disordered eating behaviours (i.e. binge eating, purging, restriction of eating, compulsive exercise), body mass index (BMI), food addiction, starvation addiction, exercise dependence, tobacco use and alcohol consumption.

RESULTS

42% of females and 21% of males reported binge eating during the past four weeks. Binge eating was significantly associated with all investigated behaviours in females, and with purging, compulsive exercise and overweight/obesity in males. Controlling for BMI, self-starvation predicted binge eating in males (OR = 1.07), while food addiction (OR = 1.73) and alcohol dependence (OR = 1.11) predicted binge eating in females.

CONCLUSIONS

The multiple associations between binge eating and addictive-like behaviors supports broad screening and generalized prevention efforts. Prevention efforts should reflect gender differences.

Metabolic and Addiction Indices in Patients on Opioid Agonist Medication-Assisted Treatment: A Comparison of Buprenorphine and Methadone

Metabolic hormones stabilize brain reward and motivational circuits, whereas excessive opioid consumption counteracts this effect and may impair metabolic function. Here we addressed the role of metabolic processes in the course of the agonist medication-assisted treatment for opioid use disorder (OUD) with buprenorphine or methadone. Plasma lipids, hemoglobin A1C, body composition, the oral glucose tolerance test (oGTT) and the Sweet Taste Test (STT) were measured in buprenorphine- (n = 26) or methadone (n = 32)- treated subjects with OUD. On the whole, the subjects in both groups were overweight or obese and insulin resistant; they displayed similar oGTT and STT performance. As compared to methadone-treated subjects, those on buprenorphine had significantly lower rates of metabolic syndrome (MetS) along with better values of the high-density lipoproteins (HDL). Subjects with- vs. without MetS tended to have greater addiction severity. Correlative analyses revealed that more buprenorphine exposure duration was associated with better HDL and opioid craving values. In contrast, more methadone exposure duration was associated with worse triglycerides-, HDL-, blood pressure-, fasting glucose- and hemoglobin A1C values. Buprenorphine appears to produce beneficial HDL- and craving effects and, contrary to methadone, its role in the metabolic derangements is not obvious. Our data call for further research aimed at understanding the distinctive features of buprenorphine metabolic effects vis-à-vis those of methadone and their potential role in these drugs' unique therapeutic profiles.

Short- and long-access palatable food self-administration results in different phenotypes of binge-type eating

Binge eating disorder (BED), the most common eating disorder in the United States, is characterized by binge-type eating and is associated with higher body mass index and greater motivation for food. This disorder tends to first appear in late adolescence or young adulthood and is more common in women than men. While some animal models of BED have recapitulated both the overeating and the excessive body weight / fat of BED, very few have examined the motivational aspects of this disorder or utilized young females as subjects. In the present study, female Long-Evans rats, starting in late adolescence, were trained in operant chambers to self-administer the highly palatable Milk Chocolate Ensure Plus®, in 30-minute ("short access") or 6-hour ("long access") sessions, 5 days per week, over 6.5 weeks. For comparison, other subjects were provided with Ensure ad libitum or maintained on chow and water only. Both short and long access to Ensure led rats to develop binge-type eating, measured as greater 30-minute caloric intake than rats with ad libitum or chow access and as increasing 30-minute intake across weeks. Compared to those with short access, rats with long access demonstrated moderately increased motivation for Ensure (measured by progressive ratio testing) and, compared to those with only chow access, they eventually showed significant hyperphagia on Ensure access days and hypophagia on non-access days. Rats with long access also showed greater body weight/fat than those maintained on chow. These findings suggest that, while both short and long operant access to Ensure causes young female rats to meet the definition of binge-type eating, they lead to different phenotypes of this behavior, with long access promoting the development of a greater number of features found in clinical BED. Ultimately, both models may be useful in future studies aimed at identifying the neurobiological basis of binge eating.

Food selection, food craving, and body mass index in persons in treatment for substance use disorder

Studies of persons in treatment for substance use disorder (SUD) frequently report significant body weight gain and higher food consumption. It is unclear what psychological variables might mediate a relationship between SUD treatment status and food selection. To examine the association between SUD treatment status and food selection, 212 men and women (104 in treatment for SUD) were asked, in an online survey, to choose from among 16 food images in an imagined all-you-can-eat buffet scenario. Food craving, emotional eating (EE), impulsivity, and drugs used were examined as potential mediators while reward responsiveness (RR) was examined as a potential moderator. The amount of energy from foods selected was the predicted variable. Results indicated that those in treatment for SUD had significantly higher food cravings, positive EE, and attentional and motor impulsivity (but not RR or negative EE) which were (with the exception of RR) not correlated with energy selected from food images. Those in SUD treatment selected more energy (M = 2655.10 kcal, SEM = 156.97) from food images than those in the control group (M = 2221.52 kcal, SEM = 112.29), t(188) = -2.25, p = 0.026. In a multiple regression moderation analysis, SUD treatment status (β = 419.58, p = 0.029) and RR (β = 39.23, p = 0.016) were significant predictors of energy from foods selected. The amount of energy selected from food images predicted by SUD treatment status was dependent on values of RR. Mean BMI was not significantly higher for the SUD group but there were more participants with BMI values over 29 and fewer with BMI between 25 and 29 in the SUD treatment group. While the cause remains unclear, the results show that persons in treatment for SUD and with higher RR do select more energy from food images in a meal scenario.

Threat Response System: Parallel Brain Processes in Pain vis-à-vis Fear and Anxiety

Pain is essential for avoidance of tissue damage and for promotion of healing. Notwithstanding the survival value, pain brings about emotional suffering reflected in fear and anxiety, which in turn augment pain thus giving rise to a self-sustaining feedforward loop. Given such reciprocal relationships, the present article uses neuroscientific conceptualizations of fear and anxiety as a theoretical framework for hitherto insufficiently understood pathophysiological mechanisms underlying chronic pain. To that end, searches of PubMed-indexed journals were performed using the following Medical Subject Headings' terms: pain and nociception plus amygdala, anxiety, cognitive, fear, sensory, and unconscious. Recursive sets of scientific and clinical evidence extracted from this literature review were summarized within the following key areas: (1) parallelism between acute pain and fear and between chronic pain and anxiety; (2) all are related to the evasion of sensory-perceived threats and are subserved by subcortical circuits mediating automatic threat-induced physiologic responses and defensive actions in conjunction with higher order corticolimbic networks (e.g., thalamocortical, thalamo-striato-cortical and amygdalo-cortical) generating conscious representations and valuation-based adaptive behaviors; (3) some instances of chronic pain and anxiety conditions are driven by the failure to diminish or block respective nociceptive information or unconscious treats from reaching conscious awareness; and (4) the neural correlates of pain-related conscious states and cognitions may become autonomous (i.e., dissociated) from the subcortical activity/function leading to the eventual chronicity. Identifying relative contributions of the diverse neuroanatomical sources, thus, offers prospects for the development of novel preventive, diagnostic, and therapeutic strategies in chronic pain patients.

Heroin-induced suppression of saccharin intake in OPRM1 A118G mice

The single nucleotide polymorphism of the μ-opioid receptor, OPRM1 A118G, has been associated with greater drug and alcohol use, increased sensitivity to pain, and reduced sensitivity to the antinociceptive effects of opiates. In the present studies, we employed a 'humanized' mouse model containing the wild-type (118AA) or variant (118GG) allele to examine behavior in a model of heroin-induced devaluation of an otherwise palatable saccharin cue when repeated saccharin-heroin pairings occurred every 24h (Experiment 1) or every 48h (Experiment 2). The results showed that, while both the 118AA and 118GG mice demonstrated robust avoidance of the heroin-paired saccharin cue following daily taste-drug pairings, only the 118AA mice suppressed intake of the heroin-paired saccharin cue when 48h elapsed between each taste-drug pairing. Humanized 118GG mice, then, defend their intake of the sweet cue despite saccharin-heroin pairings and this effect is illuminated by the use of spaced, rather than massed, trials. Given that this pattern of strain difference is not evident with saccharin-cocaine pairings (Freet et al., 2015), reduced avoidance of the heroin-paired saccharin cue by the 118GG mice may be due to an interaction between the opiate and the subjects' drive for the sweet or, alternatively, to differential downstream sensitivity to the aversive kappa mediated properties of the drug. These alternative hypotheses are addressed.

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.

The rewarding effects of ethanol are modulated by binge eating of a high-fat diet during adolescence

Binge-eating is considered a specific form of overeating characterized by intermittent and high caloric food intake in a short period of time. Epidemiologic studies support a positive relation between the ingestion of fat and ethanol (EtOH), specifically among adolescent subjects. The aim of this work was to clarify the role of the compulsive, limited and intermittent intake of a high-fat food during adolescence on the rewarding effects of EtOH. After binge-eating for 2 h, three days a week from postnatal day (PND) 29, the reinforcing effects of EtOH were tested with EtOH self-administration (SA), conditioned place preference (CPP) and ethanol locomotor sensitization procedures in young adult mice. Animals in the high fat binge (HFB) group that underwent the EtOH SA procedure presented greater EtOH consumption and a higher motivation to obtain the drug. HFB mice also developed preference for the paired compartment in the CPP with a subthreshold dose of EtOH. Independently of the diet, mice developed EtOH-induced locomotor sensitization. After the SA procedure, HFB mice exhibited reduced levels of the mu opioid receptor (MOr) and increased cannabinoid 1 receptor (CB1r) gene expression in the nucleus accumbens (N Acc), and decreased of tyrosine hydroxylase (TH) gene expression in the ventral tegmental area (VTA). Taken together the results suggest that bingeing on fat may represent a vulnerability factor to an escalation of EtOH consumption.

A Shared Molecular and Genetic Basis for Food and Drug Addiction: Overcoming Hypodopaminergic Trait/State by Incorporating Dopamine Agonistic Therapy in Psychiatry

This article focuses on the shared molecular and neurogenetics of food and drug addiction tied to the understanding of reward deficiency syndrome. Reward deficiency syndrome describes a hypodopaminergic trait/state that provides a rationale for commonality in approaches for treating long-term reduced dopamine function across the reward brain regions. The identification of the role of DNA polymorphic associations with reward circuitry has resulted in new understanding of all addictive behaviors.

Increased intravenous morphine self-administration following Roux-en-Y gastric bypass in dietary obese rats

Roux-en-Y gastric bypass (RYGB) surgery is a commonly performed and very effective method to achieve significant, long-term weight loss. Opioid analgesics are primarily used to manage postoperative pain as fewer alternative medication options are available for bariatric surgery patients than for the general population. Recent clinical studies support a greater risk for substance use following bariatric surgery, including an increased use of opioid medications. The present study is the first to study morphine self-administration in a rat model of RYGB. High fat diet-induced obese (HFD-DIO) rats underwent RYGB (n=14) or sham-surgery with ad libitum HFD (SHAM, n=14) or a restricted amount that resulted in weight matched to the RYGB cohort (SHAM-WM, n=8). An additional normal-diet (ND, n=7), intact (no surgery) group of rats was included. Two months after the surgeries, rats were fitted with jugular catheters and trained on a fixed ratio-2 lick task to obtain morphine intravenously. Both morphine-seeking (number of licks on an empty spout to obtain morphine infusion) and consumption (number of infusion) were significantly greater in RYGB than any control group beginning on day 3 and reached a two-fold increase over a period of two weeks. These findings demonstrate that RYGB increases motivation for taking morphine and that this effect is independent of weight loss. Further research is warranted to reveal the underlying mechanisms and to determine whether increased morphine use represents a risk for opioid addiction following RYGB. Identifying risk factors preoperatively could help with personalized postoperative care to prevent opioid abuse and addiction.

Litter size reduction alters insulin signaling in the ventral tegmental area and influences dopamine-related behaviors in adult rats

Postnatal overfeeding is a well-known model of early-life induced obesity and glucose intolerance in rats. However, little is known about its impact on insulin signaling in specific brain regions such as the mesocorticolimbic system, and its putative effects on dopamine-related hedonic food intake in adulthood. For this study, rat litters were standardized to 4 (small litter - SL) or 8 pups (control - NL) at postnatal day 1. Weaning was at day 21, and all tests were conducted after day 60 of life in male rats. In Experiment 1, we demonstrated that the SL animals were heavier than the NL at all time points and had decreased AKT/pAKT ratio in the Ventral Tegmental Area (VTA), without differences in the skeletal muscle insulin signaling in response to insulin injection. In Experiment 2, the standard rat chow intake was addressed using an automated system (BioDAQ, Research Diets(®)), and showed no differences between the groups. On the other hand, the SL animals ingested more sweet food in response to the 1 min tail-pinch challenge and did not develop conditioned place preference to sweet food. In Experiment 3 we showed that the SL rats had increased VTA TH content but had no difference in this protein in response to a sweet food challenge, as the NL had. The SL rats also showed decreased levels of dopamine D2 receptors in the nucleus accumbens. Here we showed that early postnatal overfeeding was linked to an altered functioning of the mesolimbic dopamine pathway, which was associated with altered insulin signaling in the VTA, suggesting increased sensitivity, and expression of important proteins of the dopaminergic system.

The role of ghrelin in addiction: a review

RATIONALE

Ghrelin is a fast-acting hormone that is produced primarily by the stomach and by the brain although in smaller quantities. The regulation and the secretion of ghrelin are complex and not limited to aspects of feeding. Ghrelin exerts powerful effects on multiple processes, and it has been demonstrated that it mediates the rewarding properties of food as well as of drugs of abuse.

OBJECTIVES

The purpose of this review is to summarize the findings of preclinical and clinical studies related to ghrelin's possible role in addiction for each specific class of substances. Questions related to ghrelin's involvement in addiction are highlighted. Recurrent methodological issues that render the interpretation of the findings challenging are discussed. Also, the potential of targeting ghrelin as a pharmacologic treatment strategy for addiction is explored.

RESULTS

Ghrelin signaling is implicated in the mediation of behavioral and biochemical effects of drugs of abuse that are cardinal for the development of addiction, especially for alcohol, nicotine, and stimulants. The available literature implicating ghrelin in opioid or cannabis use disorders is currently limited and inconclusive.

CONCLUSIONS

There is intriguing, although not always consistent, evidence for the involvement of ghrelin signaling in aspects of addiction, especially in the cases of alcohol, nicotine, and stimulants. Further research, particularly in humans, is recommended to replicate and expand on the findings of the current literature. Improved and novel methodologies that take into account the volatile and complex nature of ghrelin are required to clarify the inconsistencies of the findings.

Inhibitory control effects in adolescent binge eating and consumption of sugar-sweetened beverages and snacks

Inhibitory control and sensitivity to reward are relevant to the food choices individuals make frequently. An imbalance of these systems can lead to deficits in decision-making that are relevant to food ingestion. This study evaluated the relationship between dietary behaviors - binge eating and consumption of sweetened beverages and snacks - and behavioral control processes among 198 adolescents, ages 14 to 17. Neurocognitive control processes were assessed with the Iowa Gambling Task (IGT), a generic Go/No-Go task, and a food-specific Go/No-Go task. The food-specific version directly ties the task to food cues that trigger responses, addressing an integral link between cue-habit processes. Diet was assessed with self-administered food frequency and binge eating questionnaires. Latent variable models revealed marked gender differences. Inhibitory problems on the food-specific and generic Go/No-Go tasks were significantly correlated with binge eating only in females, whereas inhibitory problems measured with these tasks were the strongest correlates of sweet snack consumption in males. Higher BMI percentile and sedentary behavior also predicted binge eating in females and sweet snack consumption in males. Inhibitory problems on the generic Go/No-Go, poorer affective decision-making on the IGT, and sedentary behavior were associated with sweetened beverage consumption in males, but not females. The food-specific Go/No-Go was not predictive in models evaluating sweetened beverage consumption, providing some initial discriminant validity for the task, which consisted of sweet/fatty snacks as no-go signals and no sugar-sweetened beverage signals. This work extends research findings, revealing gender differences in inhibitory function relevant to behavioral control. Further, the findings contribute to research implicating the relevance of cues in habitual behaviors and their relationship to snack food consumption in an understudied population of diverse adolescents not receiving treatment for eating disorders.

Dynamic interplay among homeostatic, hedonic, and cognitive feedback circuits regulating body weight

Obesity is associated with a prolonged imbalance between energy intake and expenditure, both of which are regulated by multiple feedback processes within and across individuals. These processes constitute 3 hierarchical control systems-homeostatic, hedonic, and cognitive-with extensive interaction among them. Understanding complex eating behavior requires consideration of all 3 systems and their interactions. Existing models of these processes are widely scattered, with relatively few attempts to integrate across mechanisms. We briefly review available empirical evidence and dynamic models, discussing challenges and potential for better integration. We conclude that developing richer models of dynamic interplay among systems should be a priority in the future study of obesity and that systems science modeling offers the potential to aid in this goal.

Is low BMI associated with specific drug use among injecting drug users?

Body mass index (BMI) of a sample of people who regularly inject drugs (N = 781) was examined to gauge the impact of specific types of drug use. Cross-sectional interviews were undertaken in 2010 as part of a national monitoring program funded by the Australian Government. Latent class analysis identified three groups of drug users, with heroin users at 3.4 times the risk of being underweight compared with amphetamine users, and amphetamine users were at almost twice the odds of being obese compared with lower level morphine users. Nutrition should play a part in harm minimization.

Association between the seven-repeat allele of the dopamine-4 receptor gene (DRD4) and spontaneous food intake in pre-school children

BACKGROUND

Studies in adults show associations between the hypofunctional seven-repeat allele (7R) of the dopamine-4 receptor gene (DRD4), increased eating behaviour and/or obesity, particularly in females. We examined whether 7R is associated with total caloric intake and/or food choices in pre-schoolers.

METHODS

150 four-year-old children taking part in a birth cohort study in Canada were administered a snack test meal in a laboratory setting. Mothers also filled out a food frequency questionnaire to address childrens' habitual food consumption. Total caloric and individual macronutrient intakes during the snack meal and specific types of foods as reported in the food diaries were compared across 7R allele carriers vs. non-carriers, using current BMI as a co-variate.

RESULTS

We found significant sex by genotype interactions for fat and protein intake during the snack test. Post hoc testing revealed that in girls, but not boys, 7R carriers ate more fat and protein than did non-carriers. Based on the food diaries, across both sexes, 7R carriers consumed more portions of ice cream and less vegetables, eggs, nuts and whole bread, suggesting a less healthy pattern of habitual food consumption.

CONCLUSION

The 7R allele of DRD4 influences macronutrient intakes and specific food choices as early as four years of age. The specific pattern of results further suggests that prior associations between the 7R allele and adult overeating/obesity may originate in food choices observable in the preschool years. Longitudinal follow-up of these children will help establish the relevance of these findings for obesity risk and prevention.

Co-sensitivity to the incentive properties of palatable food and cocaine in rats; implications for co-morbid addictions

Several lines of evidence suggest that there may be a shared vulnerability to acquire behaviors motivated by strong incentive stimuli. Non-food restricted male Sprague-Dawley rats (n = 78) underwent place conditioning with Oreos, and were subsequently tested on cocaine self-administration (SA) on fixed and progressive ratios, as well as extinction and reinstatement by cocaine primes and by consumption of Oreos. Although there was a group preference for the Oreo-paired compartment, at the individual level some rats (69%) displayed a preference and others did not. In cocaine SA, 'preference' rats achieved higher break points on a progressive ratio, and displayed greater responding during extinction and cocaine-induced reinstatement. Within the context of this study, Oreo-cocaine cross-reinstatement was not observed. In a control study, rats (n = 29) conditioned with a less palatable food (rice cakes) also displayed individual differences in place preference, but not on subsequent cocaine tests. These findings indicate that there is a relationship between incentive learning promoted by palatable foods and by cocaine. This supports the hypothesis that co-morbid food-drug addictions may result from a shared vulnerability to acquire behaviors motivated by strong incentives.

Compared with DBA/2J mice, C57BL/6J mice demonstrate greater preference for saccharin and less avoidance of a cocaine-paired saccharin cue

Rats avoid intake of a saccharin cue when paired with a drug of abuse. While this is true for most subjects, the degree of avoidance of the drug-paired cue depends upon many factors including an individual rat's preference for rewards. That said, the direction of this effect is complex. For example, reward-preferring Lewis rats exhibit greater cocaine-induced avoidance of a saccharin cue relative to Fischer 344 rats; while reward-preferring mice that overexpress ΔFosB (NSE-tTA × TetOp-ΔFosB) exhibit less avoidance of the drug-paired taste cue compared to controls. The aim here was to use two strains of commonly used mice, C57BL/6J and DBA/2J, to determine whether known differences in sensitivity to rewards will facilitate or attenuate drug-induced suppression of intake of a drug-paired taste cue. The results of Experiment 1 demonstrate that C57BL/6J mice, compared with DBA/2J mice, exhibit attenuated suppression of saccharin intake when it is paired with cocaine. The results of Experiment 2 demonstrate that strain differences in impulsivity are not likely to account for these differences. It is proposed that, while the C57BL/6J mice typically are more responsive to drug, they also are more responsive to natural rewards (in this case saccharin), and the stronger preference for saccharin serves to militate against drug.

Opiate agonists and antagonists modulate taste perception in opiate-maintained and recently detoxified subjects

Heroin addicts consume large quantities of refined sugars. This study investigated the effect of opiate use and antagonism on sweet taste in opiate-maintained drug users and detoxified former chronic opiate users, using a within-subject design. Seven opiate users received methadone and seven buprenorphine maintenance. Six detoxified subjects received naltrexone. Sucrose recognition thresholds and measurements of pleasantness and intensity were determined before and four hours after 1) a single dose of methadone or buprenorphine or 2) naltrexone. Control data were taken from a cohort of healthy volunteers including smokers. All measures of sweet and salt taste perception were significantly greater in opiate users and recently detoxified subjects compared to control subjects, with the exception of sweet pleasantness, which returned to control level after detoxification. Acute methadone administration reduced salt thresholds and unpleasantness to control levels. Increased sweet thresholds and salt unpleasantness in detoxified subjects were reversed by acute opioid antagonism, returning to control levels. These results suggest that opiate use and antagonism alters taste perception. Some of the alterations reverse on detoxification (sweet pleasantness), and others can be reversed by opioid antagonism (sweet threshold, salt unpleasantness). Changes in taste perception may underlie altered consumption of refined sugars in opiate users.

Pharmacotherapies for Overeating and Obesity

Obesity has become pandemic, and the annual cost in related illnesses and loss of productivity is already over $100 billion and rising. Research has shown that obesity can and does cause changes in behavior and in the brain itself that are very similar to changes caused by drugs of abuse. While food addiction is not the causal agent of all obesity, it is clear that many people no longer eat to survive, but instead survive to eat. This review considers the importance of the brain's reward system in food intake. The review also examines research developments and current treatments for obesity, including diet and exercise, psychotherapy, surgical interventions, and pharmacotherapies. Finally we discuss alterations in American society that are necessary for change to occur, and the diffculties therein.

The neurobiology of food intake in an obesogenic environment

The objective of this non-systematic review of the literature is to highlight some of the neural systems and pathways that are affected by the various intake-promoting aspects of the modern food environment and explore potential modes of interaction between core systems such as hypothalamus and brainstem primarily receptive to internal signals of fuel availability and forebrain areas such as the cortex, amygdala and meso-corticolimbic dopamine system, primarily processing external signals. The modern lifestyle with its drastic changes in the way we eat and move puts pressure on the homoeostatic system responsible for the regulation of body weight, which has led to an increase in overweight and obesity. The power of food cues targeting susceptible emotions and cognitive brain functions, particularly of children and adolescents, is increasingly exploited by modern neuromarketing tools. Increased intake of energy-dense foods high in fat and sugar is not only adding more energy, but may also corrupt neural functions of brain systems involved in nutrient sensing as well as in hedonic, motivational and cognitive processing. It is concluded that only long-term prospective studies in human subjects and animal models with the capacity to demonstrate sustained over-eating and development of obesity are necessary to identify the critical environmental factors as well as the underlying neural systems involved. Insights from these studies and from modern neuromarketing research should be increasingly used to promote consumption of healthy foods.

A model of food reward learning with dynamic reward exposure

The process of conditioning via reward learning is highly relevant to the study of food choice and obesity. Learning is itself shaped by environmental exposure, with the potential for such exposures to vary substantially across individuals and across place and time. In this paper, we use computational techniques to extend a well-validated standard model of reward learning, introducing both substantial heterogeneity and dynamic reward exposures. We then apply the extended model to a food choice context. The model produces a variety of individual behaviors and population-level patterns which are not evident from the traditional formulation, but which offer potential insights for understanding food reward learning and obesity. These include a "lock-in" effect, through which early exposure can strongly shape later reward valuation. We discuss potential implications of our results for the study and prevention of obesity, for the reward learning field, and for future experimental and computational work.

Decision-Making Deficits and Overeating: A Risk Model for Obesity

OBJECTIVE

To demonstrate that human overeating is not just a passive response to salient environmental triggers and powerful physiological drives; it is also about making choices. The ventromedial prefrontal cortex has been strongly implicated in the neural circuitry necessary for making advantageous decisions when various options for action are available. Decision-making deficits have been found in patients with ventromedial prefrontal cortex lesions and in those with substance dependence--impairments that reflect an inability to advantageously assess future consequences. That is, they choose immediate rewards in the face of future long-term negative consequences.

RESEARCH METHODS AND PROCEDURES

We extended this research to the study of overeating and overweight, testing a regression model that predicted that poor decision making (as assessed by a validated computerized gambling task) and a tendency to overeat under stress would correlate with higher BMI in a group of healthy adult women (N = 41) representing a broad range of body weights.

RESULTS

We found statistically significant main effects for both independent variables in the predicted direction (p < 0.05; R2 = 0.35). Indeed, the decision-making impairments across the 100 trials of the computer task were greater in those with high BMI than in previous studies with drug addicts.

DISCUSSION

Findings suggested that cortical and subcortical processes, which regulate one's ability to inhibit short-term rewards when the long-term consequences are deleterious, may also influence eating behaviors in a culture dominated by so many, and such varied, sources of palatable and calorically dense sources of energy.

Social 'wanting' dysfunction in autism: neurobiological underpinnings and treatment implications

Most behavioral training regimens in autism spectrum disorders (ASD) rely on reward-based reinforcement strategies. Although proven to significantly increase both cognitive and social outcomes and successfully reduce aberrant behaviors, this approach fails to benefit a substantial number of affected individuals. Given the enormous amount of clinical and financial resources devoted to behavioral interventions, there is a surprisingly large gap in our knowledge of the basic reward mechanisms of learning in ASD. Understanding the mechanisms for reward responsiveness and reinforcement-based learning is urgently needed to better inform modifications that might improve current treatments. The fundamental goal of this review is to present a fine-grained literature analysis of reward function in ASD with reference to a validated neurobiological model of reward: the 'wanting'/'liking' framework. Despite some inconsistencies within the available literature, the evaluation across three converging sets of neurobiological data (neuroimaging, electrophysiological recordings, and neurochemical measures) reveals good evidence for disrupted reward-seeking tendencies in ASD, particularly in social contexts. This is most likely caused by dysfunction of the dopaminergic-oxytocinergic 'wanting' circuitry, including the ventral striatum, amygdala, and ventromedial prefrontal cortex. Such a conclusion is consistent with predictions derived from diagnostic criteria concerning the core social phenotype of ASD, which emphasize difficulties with spontaneous self-initiated seeking of social encounters (that is, social motivation). Existing studies suggest that social 'wanting' tendencies vary considerably between individuals with ASD, and that the degree of social motivation is both malleable and predictive of intervention response. Although the topic of reward responsiveness in ASD is very new, with much research still needed, the current data clearly point towards problems with incentive-based motivation and learning, with clear and important implications for treatment. Given the reliance of behavioral interventions on reinforcement-based learning principles, we believe that a systematic focus on the integrity of the reward system in ASD promises to yield many important clues, both to the underlying mechanisms causing ASD and to enhancing the efficacy of existing and new interventions.

Translating evidence based violence and drug use prevention to obesity prevention: development and construction of the pathways program

Effective school-based obesity prevention programs are needed to prevent and reduce the growing obesity risk among youth. Utilizing the evidence-rich areas of violence and substance use prevention, translation science may provide an efficient means for developing curricula across multiple health behaviors. This paper introduces Pathways to Health, a school-based obesity prevention program that was developed by translating from evidence-based violence and drug use prevention programs, Promoting Alternative THinking Strategies and the Midwestern Prevention Project STAR (STAR). We illustrate how a hypothesized underlying behavior change mechanism in two domains of risk behavior, violence and substance use, can be applied to obesity prevention. A 4-step translational process is provided and may be relevant for use in developing other curricula to address multiple health risk behaviors. Practical application and decision points are also provided.

Depot naltrexone decreases rewarding properties of sugar in patients with opioid dependence

BACKGROUND

Opioid neurotransmission mediates hedonic value of sweet tastants; their intake may be exaggerated by the consumption of exogenous opioids (e.g., opioid dependence). Sweet Taste Test (STT) is a validated quantitative instrument assessing taste perception and hedonic features of sugar (sucrose) using a randomized and double-blind administration at five different sucrose concentrations ranging from 0.05 to 0.83 M.

METHODS

The STT and cue-induced craving procedure were administered to opioid-dependent patients (n = 15) before and 1 week after the injection of a long-acting depot naltrexone (XRNT) preparation.

RESULTS

Analyses of covariance, employing sucrose concentration and its perceived taste as covariates, showed that XRNT therapy significantly reduced the self-reported hedonic and motivational characteristics of sucrose. Greater reductions in both these characteristics were associated with more diminution in the cue-induced opioid craving.

CONCLUSIONS

Opioid antagonism in opioid-dependent subjects leads to a smaller sweet taste reward, which, in turn, may be proportional to decreased opioid craving. These pilot results support the heuristic value of the STT as a potential marker of the XRNT treatment response and call for further inquiry into potential clinical applications of the test.

Drug use is associated with elevated food consumption in college students

Higher food consumption, particularly of sweets, has been reported by substance-dependent persons in various stages of treatment but no investigation of substance use and actual food consumption has been conducted in non-dependent persons. Sixty-two male and female college students completed the Core Alcohol and Drug Survey and the amount of each of six snack foods (including both sweet and savory items) they consumed were measured. Participants also rated appetite before and after eating and rated the pleasantness of and desire to eat each food. Hierarchical multivariate regression revealed that, while controlling for the influence of BMI and intermeal interval, frequency and breadth of substance use significantly predicted elevated food consumption and elevated ratings of hunger and desire to eat. Furthermore, the link between breadth of drug use and food consumption was mediated by higher desire to eat and not by pleasantness of the food. The relationship between substance use and eating behavior may not be restricted only to those in recovery or treatment for persons diagnosed with substance use disorders.

Feeding and reward: perspectives from three rat models of binge eating

Research has focused on understanding how overeating can affect brain reward mechanisms and subsequent behaviors, both preclinically and in clinical research settings. This work is partly driven by the need to uncover the etiology and possible treatments for the ongoing obesity epidemic. However, overeating, or non-homeostatic feeding behavior, can occur independent of obesity. Isolating the variable of overeating from the consequence of increased body weight is of great utility, as it is well known that increased body weight or obesity can impart its own deleterious effects on physiology, neural processes, and behavior. In this review, we present data from three selected animal models of normal-weight non-homeostatic feeding behavior that have been significantly influenced by Bart Hoebel's 40+-yr career studying motivation, feeding, reinforcement, and the neural mechanisms that participate in the regulation of these processes. First, a model of sugar bingeing is described (Avena/Hoebel), in which animals with repeated, intermittent access to a sugar solution develop behaviors and brain changes that are similar to the effects of some drugs of abuse, serving as the first animal model of food addiction. Second, another model is described (Boggiano) in which a history of dieting and stress can perpetuate further binge eating of palatable and non-palatable food. In addition, a model (Boggiano) is described that allows animals to be classified as having a binge-prone vs. binge-resistant behavioral profile. Lastly, a limited access model is described (Corwin) in which non-food deprived rats with sporadic limited access to a high-fat food develop binge-type behaviors. These models are considered within the context of their effects on brain reward systems, including dopamine, the opioids, cholinergic systems, serotonin, and GABA. Collectively, the data derived from the use of these models clearly show that behavioral and neuronal consequences of bingeing on a palatable food, even when at a normal body weight, are different from those that result from simply consuming the palatable food in a non-binge manner. These findings may be important in understanding how overeating can influence behavior and brain chemistry.

Food reward, hyperphagia, and obesity

Given the unabated obesity problem, there is increasing appreciation of expressions like "my eyes are bigger than my stomach," and recent studies in rodents and humans suggest that dysregulated brain reward pathways may be contributing not only to drug addiction but also to increased intake of palatable foods and ultimately obesity. After describing recent progress in revealing the neural pathways and mechanisms underlying food reward and the attribution of incentive salience by internal state signals, we analyze the potentially circular relationship between palatable food intake, hyperphagia, and obesity. Are there preexisting individual differences in reward functions at an early age, and could they be responsible for development of obesity later in life? Does repeated exposure to palatable foods set off a cascade of sensitization as in drug and alcohol addiction? Are reward functions altered by secondary effects of the obese state, such as increased signaling through inflammatory, oxidative, and mitochondrial stress pathways? Answering these questions will significantly impact prevention and treatment of obesity and its ensuing comorbidities as well as eating disorders and drug and alcohol addiction.

Executive cognitive function and food intake in children

OBJECTIVE

The current study investigated relations among neurocognitive skills important for behavioral regulation, and the intake of fruit, vegetables, and snack food in children.

DESIGN

Participants completed surveys at a single time point.

SETTING

Assessments took place during school.

PARTICIPANTS

Participants were 107 fourth-grade children from a large US city. Ninety-one percent were Latino, and 4% were African-American, which represented school ethnic distribution.

MAIN OUTCOME MEASURE(S)

Independent variable included was self-reported executive cognitive function (ECF). Dependent variables included self-reported fruit, vegetable, and snack food intake.

ANALYSES

Primary analyses general linear regression models covarying for appropriate demographic variables.

RESULTS

Analyses demonstrated that ECF proficiency was negatively related to snack food intake, but was not significantly related to fruit and vegetable intake.

CONCLUSIONS AND IMPLICATIONS

Since ECF is correlated with snack food intake, future studies may consider assessing the potential of enhancing ECF in health promotion interventions.

Attention-deficit/hyperactivity disorder: associations with overeating and obesity

In the past decade, we have become increasingly aware of strong associations between overweight/obesity and symptoms of attention-deficit/hyperactivity disorder (ADHD) in children, adolescents, and adults. This review addresses the prevalence of the comorbidity and discusses some of the mechanisms that could account for their relationship. It is suggested that the inattentive and impulsive behaviors that characterize ADHD could contribute to overeating in our current food environment, with its emphasis on fast food consumption and its many food temptations. It is also proposed-based on the compelling evidence that foods high in fat, sugar, and salt are as addictive as some drugs of abuse-that excessive food consumption could be a form of self-medication. This view conforms with the well-established evidence that drug use and abuse are substantially higher among those with ADHD than among the general population.

The neurobiology of appetite: hunger as addiction

Obesity is now being recognized as a neurobehavioral disorder. Although the view of appetite as an addiction to food is controversial, there are useful lessons to be learned from the neuroscience of addiction for understanding obesity. The speakers in this symposium all addressed different aspects of the neurobiology of feeding and obesity. In this overview and the associated reviews, the behavioral, genetic and neural factors that promote over-eating in animals and humans are discussed.

The medial preoptic area is necessary for motivated choice of pup- over cocaine-associated environments by early postpartum rats

Converging evidence suggests that the motivation to seek cocaine during the postpartum period is significantly impacted by the competing incentives of offspring, a stimulus unique to this life stage. In the present study, the functional role of the medial preoptic area (mPOA), a critical site involved in maternal responsiveness, on processing incentive value of pup-associated cues and influencing response allocation for pup- over cocaine-associated environments was investigated using a concurrent pup/cocaine choice conditioned place preference (CPP) paradigm. Early postpartum females with bilateral guide cannulae aimed into the mPOA or into anatomical control sites were conditioned, from postpartum days (PPD) 4 to 7, to associate different uniquely featured environments with pups or cocaine. CPP was tested on PPD8 following intra-mPOA infusions of either 2% bupivacaine or saline vehicle. In two additional experiments, the effects of intra-mPOA infusions of bupivacaine on expression of conditioned responding induced by environments associated with either pups or cocaine were examined separately. Transient inactivation of the mPOA selectively blocked the conditioned preferences for pup-associated environments, significantly contrasting the robust pup-CPP found in non-surgical and intra-mPOA vehicle-treated females. In contrast, mPOA inactivation failed to alter cocaine-CPP in postpartum females. When given a choice between environments associated with pups or cocaine, transient functional inactivation of the mPOA altered choice behavior, biasing the preference of females toward cocaine-associated environments, such that almost all preferred cocaine- and none the pup-associated option. The anatomical specificity was revealed when inactivation of adjacent regions to the mPOA did not affect CPP responses for pups. The findings support a critical role for the mPOA in mediating pup-seeking behavior, and further suggest that the competing properties of pups over alternative incentives, including drugs of abuse, rely on mPOA integrity to provide relevant pup-related information to the circuitry underlying the choice behavior between pups and alternative stimuli.

The tempted brain eats: pleasure and desire circuits in obesity and eating disorders

What we eat, when and how much, all are influenced by brain reward mechanisms that generate "liking" and "wanting" for foods. As a corollary, dysfunction in reward circuits might contribute to the recent rise of obesity and eating disorders. Here we assess brain mechanisms known to generate "liking" and "wanting" for foods and evaluate their interaction with regulatory mechanisms of hunger and satiety, relevant to clinical issues. "Liking" mechanisms include hedonic circuits that connect together cubic-millimeter hotspots in forebrain limbic structures such as nucleus accumbens and ventral pallidum (where opioid/endocannabinoid/orexin signals can amplify sensory pleasure). "Wanting" mechanisms include larger opioid networks in nucleus accumbens, striatum, and amygdala that extend beyond the hedonic hotspots, as well as mesolimbic dopamine systems, and corticolimbic glutamate signals that interact with those systems. We focus on ways in which these brain reward circuits might participate in obesity or in eating disorders.

Reward and neurocomputational processes

The neurobiology of eating disorders (EDs) is largely unknown. However, brain imaging studies over the past decade have identified neurotransmitter alterations that could be part of dysfunctional behavior characteristics of EDs. In this chapter we focus on a specific behavioral construct, the brain reward system, and demonstrate a functional brain imaging approach toward identifying dopamine function in anorexia nervosa (AN). We demonstrate how human brain reward activation can be used in a translational approach to test whether computer models, based on basic science research, can predict expected in vivo reward system activation, and how such an approach can identify specific biologic alterations in a psychiatric population.

Overexpression of DeltaFosB is associated with attenuated cocaine-induced suppression of saccharin intake in mice

Rodents suppress intake of saccharin when it is paired with a drug of abuse (Goudie, Dickins, & Thornton, 1978; Risinger & Boyce, 2002). By the authors' account, this phenomenon, referred to as reward comparison, is thought to be mediated by anticipation of the rewarding properties of the drug (P. S. Grigson, 1997; P. S. Grigson & C. S. Freet, 2000). Although a great deal has yet to be discovered regarding the neural basis of reward and addiction, it is known that overexpression of DeltaFosB is associated with an increase in drug sensitization and incentive. Given this, the authors reasoned that overexpression of DeltaFosB should also support greater drug-induced devaluation of a natural reward. To test this hypothesis, NSE-tTA x TetOp-DeltaFosB mice (Chen et al., 1998) with normal or overexpressed DeltaFosB in the striatum were given access to a saccharin cue and then injected with saline, 10 mg/kg cocaine, or 20 mg/kg cocaine. Contrary to the original prediction, overexpression of DeltaFosB was associated with attenuated cocaine-induced suppression of saccharin intake. It is hypothesized that elevation of DeltaFosB not only increases the reward value of drug, but the reward value of the saccharin cue as well.

'Liking' and 'wanting' food rewards: brain substrates and roles in eating disorders

What brain reward systems mediate motivational 'wanting' and hedonic 'liking' for food rewards? And what roles do those systems play in eating disorders? This article surveys recent findings regarding brain mechanisms of hedonic 'liking', such as the existence of cubic-millimeter hedonic hotspots in nucleus accumbens and ventral pallidum for opioid amplification of sensory pleasure. It also considers brain 'wanting' or incentive salience systems important to appetite, such as mesolimbic dopamine systems and opioid motivation circuits that extend beyond the hedonic hotspots. Finally, it considers some potential ways in which 'wanting' and 'liking' might relate to eating disorders.

Distinct subsets of nucleus accumbens neurons encode operant responding for ethanol versus water

Subsets of nucleus accumbens (NAc) neurons process information about operant responses for drugs as well as natural rewards (food and water) by excitations and inhibitions in firing rate time-locked to the operant response. The degree to which ensembles of neurons exhibit similar firing patterns when encoding cues and operant responses across different reinforcer conditions will provide critical information regarding the functional organization of this nucleus. The present experiment evaluated the relative contribution of subsets of accumbens neurons that encode distinct features of lever press responding for ethanol vs. water. Electrophysiological recordings (n = 153 neurons) were made in the accumbens of rats trained on concurrent reinforcement schedules for ethanol and water throughout a self-administration session. During operant responding, 52% of neurons exhibited patterned discharges characterized by significant increases or decreases in firing rate of +/- 1 s relative to lever presses for ethanol and/or water. Of these phasic cells, 85% discriminated between presses for ethanol and water (i.e. exhibited firing patterns unique to one reinforcer type), while 15% exhibited identical firing patterns relative to lever presses for both reinforcers. Notably, the data revealed that both high ethanol preference and spatially distinct lever positions contributed to the reinforcer specificity. Together, these data demonstrate that subsets of NAc neurons encode conditioned and instrumental aspects of ethanol vs. water reinforcement in well-trained rats, and that reinforcer preference and spatial cues are important components of this differential information processing.

Associations between body mass index and substance use disorders differ by gender: results from the National Epidemiologic Survey on Alcohol and Related Conditions

Alcohol, illicit drugs, and nicotine can affect appetite and body weight, but few epidemiologic studies have examined relationships between body mass index (BMI) and substance use disorders. This study used logistic regression to examine effects of BMI and gender on risk for DSM-IV substance use disorders in a sample of 40 364 adults. Overweight and obesity were associated with increased risk for lifetime alcohol abuse and dependence in men but not women. Overweight and obesity were associated with decreased risk for past-year alcohol abuse in women. BMI was not associated with illicit drug use disorders. Overweight and obese men were at decreased risk for both lifetime and past-year nicotine dependence. Overweight women were at increased risk for lifetime nicotine dependence, and obese women were at decreased risk for past-year nicotine dependence. Further research is needed to identify reasons for observed gender differences in relationships between BMI and substance use disorders.

Reward Comparison: The Achilles' heel and hope for addiction

In the words of the late Charles Flaherty, reward comparison is commonplace. Rats and man, it appears, compare all rewards and this capacity likely contributes to our ability to select the most appropriate reward/behavior (food, water, salt, sex), at the most ideal level (e.g., a certain sweetness), at any given time. A second advantage of our predisposition for reward comparison is that the availability of rich alternative rewards can protect against our becoming addicted to any single reward/behavior. Thus, the potential protective effects of natural rewards/enrichment are addressed. Despite this, behavior can become inflexible when, through the development of addiction, stress, drug, or cues elicit craving, withdrawal, and ultimately, drug-seeking. Drug-seeking corresponds with a 'window of inopportunity', when even potent natural rewards have little or no impact on behavior. During this time, there is a unitary solution to the need state, and that solution is drug. The present animal model explores this 'window of inopportunity' when natural rewards are devalued and drug-seeking is engaged and considers a mode of possible intervention.