Dissociation between binge eating behavior and incentive motivation

Behavioural and physiological effects of binge eating: A systematic review and meta-analysis of animal models

Binge eating is defined as eating abnormally large amounts in a brief period of time. Many animal studies have examined the behavioural and physiological effects of binge eating of high-fat, high-sugar foods to model the consequences of human binge eating. The present systematic review of 199 rodent studies sought to identify the behavioural and physiological consequences of binge eating and determine whether changes were specific to binge eating or to general effects of exposure to a palatable diet. A meta-analysis of 18 rodent studies revealed that binge eating produces greater anxiety-like behaviour on the Elevated Plus-Maze with a small effect size and significant funnel plot asymmetry, suggesting that the true effect size is overestimated. A history of binge-like access generally increases progressive ratio breakpoint for the binged food, without altering 'liking' as measured by lick microstructure, suggesting that dissociable effects on 'wanting' but not 'liking' accompany binge eating behaviour and contribute to its persistence. Binge eating appears to enhance compulsive food-seeking behaviour and prevent stress-induced reductions in intake but does not appear to alter depression-like behaviour or locomotor activity. Notably, binge eating may produce comparable metabolic impairments to those observed after extended continuous exposure to a palatable diet despite no overall effects on body weight outcomes in most studies.

The Administration of Cannabinoid Receptor 2 Agonist Decreases Binge-like Intake of Palatable Food in Mice

Binge eating disorder (BED) is characterized by uncontrollable episodes of eating in a short period of time, with a subjective loss of control of overconsumption behavior. The role CB2 cannabinoid receptor (CB2R) plays in binge-like intake has not yet been identified. In this regard, the present study aims to evaluate the effect of the administration of CB2R agonist, antagonist, or both on binge-like intake of palatable food (PF) in adolescent mice. We used 35 C57BL6/J male mice of 30 postnatal days in this research; all animals were housed individually and had ad libitum access to a standard diet (SD) and water. Animals were evaluated for a total of 15 sessions of the Binge Eating Test (BET), which consisted of 1 h access to PF (chocolate sandwich cookies) according to intermittent diet protocol, with one-day access/one-day no-access. PF and SD caloric intake, as well as the PF binge index (defined as consuming ≥20% of total caloric intake per day during the 1 h access to PF), were analyzed. Mice were randomly assigned to one of the following treatment groups: (1) control; (2) vehicle; (3) HU308, selective CB2R agonist; (4) AM630, selective CB2R antagonist; (5) AM630+HU308 coadministration of antagonist and agonists of CB2R. All treatments were administered intraperitoneally before BET sessions. Our results show that HU308 significantly reduced binge-like intake of PF, while no significant differences were found in the rest of the groups. These results suggest that activation of the CB2R decreases the binge-like intake in adolescent mice and that chronic overconsumption in conditions of non-homeostatic feeding can be modulated by the CB2R. Furthermore, the activation of CB2R may also modulate reward pathways, reducing binge-like behavior, which could be further explored in future studies as a treatment for BED.

Differential exposure to palatable food and its effects on binge-like eating behavior in adolescent rats

Introduction

Consumption of palatable food (PF) can lead to chronic overconsumption and obesity. Furthermore, adolescents may be vulnerable to excessively reinforcing foods, which increases the probability of developing overweight and obesity in adulthood. The role of PF availability in binge-like intake among adolescents without caloric needs remains unclear. The present study aimed to evaluate which PF access protocol is the most sensitive to induce increased caloric intake and binge-like eating during adolescence.

Methods

We used 24 male Wistar rats [30 postnatal days (PND)]; standard food and water were provided ad libitum. Rats were randomly assigned to one of three groups: (a) continuous, daily access to PF; (b) intermittent, 1-day access/1-day no-access; or (c) weekend, 3 days-access/4 days no-access. All groups had 1 h access to PF (chocolate sandwich cookies). Access protocols were maintained for 6 weeks; afterward, rats underwent a 7-day withdrawal period, and were then evaluated on a binge-eating test.

Results

Chronic restricted PF access induces binge-like intake, with intermittent access resulting in the highest binge index. Additionally, caloric intake of PF increases over time during adolescence, with differential effects of intermittent and weekend access.

Conclusion

Chronic restricted access to PF during adolescence induces binge-like intake, with differences depending on PF availability. This can lead to chronic overconsumption under non-homeostatic conditions.

Comparison of progressive hold and progressive response schedules of reinforcement

Progressive ratio (PR) schedules have been widely used to study motivation to work for a reinforcer. After a post-reinforcer pause, subjects engage in pressing a lever until a reinforcer is obtained. However, the discrete nature of lever presses allows alternative behaviors during inter-response time and has led to several behavioral explanations of pauses and work time. A progressive hold-down (PH) is incompatible with alternative responses and may allow a precise estimation of work time. Performance of rats trained in both PR and PH that received sucrose or intracranial self-stimulation (ICSS) as reinforcer were compared. We observed that rats mastered the PR and PH schedules. Post-reinforcer pauses (PS^RP), work time and inter-reinforcer time increased as a function of the response or hold requirement. However, rats' performance suggested that the PH progression may be experienced by the rats as easier that the PR progression. Elimination of consummatory behavior with ICSS reduced post-reinforcer pause in accordance with predictions of explanatory models of fixed and variable schedules of reinforcement. In the case of PH performance, pauses showed little variation across intermediate requirements but increased rapidly on later requirements; since rats controlled their pause length and work time was close to the hold requirement, time allocation between PR and PH schedules diverged. Finally, the Mathematical Principles of Reinforcement model of Bradshaw and Killeen (Psychopharmacology 2012, 222: 549) rendered a good description of the performance in both PR and PH schedules.

Binge eating behavior and incentive motivation with a cafeteria diet

Binge-like eating behavior (BLE) has been characterized as an eating disorder in which subjects have an enhanced intake of food, mainly fats. However, intake of fats and carbohydrates may have differential effects on motivation. Previously it was shown that BLE produces an increase in operant responding for vegetable shortening, but others were unable to replicate the finding using sucrose as the reinforcer. Our aim was to determine if BLE behavior induced with a cafeteria-like diet (CaLD) with several options with fat content would produce an increment in performance. Male Wistar rats were trained under an exponential progressive ratio schedule of sucrose reinforcement; thereafter, the limited access model was used to induce BLE using CaLD options. Finally, subjects were tested for increments in break points (BPs) in the progressive ratio schedule. Rats with intermittent access to CaLD options showed a clear BLE with an escalation in their intake; however they showed compensatory decrements of chow intake that rendered a similar body weight gain to a continuous access group. Although we were unable to observe an increase in BPs after BLE we were able to observe a protection against the decrements of BP previously observed with sugar. Different mechanisms for processing high fat and high carbohydrate reinforcers are variables worth exploring to gain a better understanding of BLE behavior in rodent models.