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.

Trait and state binge eating predispose towards cocaine craving.

Binge eating (BE) and drug seeking share similar behavioral features, including loss of control over consumption and compulsive seeking of the craved substance. Previous studies in animal models have demonstrated a complex interaction between 'state' BE, produced by intermittent access to a palatable diet, and 'trait' BE, a phenotypical proneness towards overeating. In the present study, we examined the relationship between state and trait BE and cocaine seeking. We used Otsuka Long Evans Tokushima Fatty rats, a genetic model for obesity that demonstrates BE-like behavior, and Long Evans Tokushima Otsuka controls. They received a schedule of limited access to a palatable diet (3 days/week or 5 days/week access to Ensure for a month). Next, they underwent cocaine self-administration training (1 mg/kg, 1 hour/day for 10 days) followed by extinction sessions (7 days). We found that the degree of BE-like behavior and the state and trait BE combination predicted cocaine craving patterns. Lower levels of dopamine D2 receptors in the prefrontal cortex were correlated with increased drug craving. Moreover, restricted access to an attractive diet was found to be a risk factor for heightened cocaine craving, particularly in trait binge eaters, as rats on the 3 days/week access schedule persistently failed to cease cocaine seeking throughout extinction. Hence, we postulate a joint role of state and trait BE as risk factors for heightened cocaine craving.

Adolescent rats are more prone to binge eating behavior: a study of age and obesity as risk factors.

Binge eating (BE) is characterized by repeated, intermittent over-consumption of food in a brief period of time. This study aims to advance the understanding of potential risk factors for BE such as obesity, overeating and adolescence as an age group. We used the Otsuka Long Evans Tokushima Fatty (OLETF) rat, a genetic overeating-induced obesity model with increased preferences for sweet and fat. Adolescent and adult rats from both strains (OLETF and the lean control strain, Long Evans Tokushima Otsuka [LETO]) received limited access to a palatable liquid diet (Ensure vanilla) for three weeks. Water and chow were available throughout the study, but access to Ensure was limited to two hours, three times a week (3TW group) or every work day (5TW group). As expected, OLETF rats consumed more Ensure and were more BE-prone (BEP) than LETO rats at both ages. Adolescent rats showed a significantly larger binge size as demonstrated by a greater increase in Ensure intake, compared to adults. Furthermore, while the adults reduced their chow intake, compensating for increased Ensure intake, the adolescents increased their chow intake too. Finally, the adolescent rats showed binge like behavior earlier in the study and they tended to be BEP more than the adults. Our findings in rats suggest that adolescents and in particular obese adolescents are at risk for BE, and BE can lead to overweight, thus providing the basis for examination of biological mechanisms of this process in animal models.