Effects of Intermittent or Ad Libitum Consumption of High‐Fat Diet on the Reinforcing Effects of Cocaine in Male Rats

Abstract

Drug abuse and obesity are serious public health problems. Dopamine systems play a central role in mediating the reinforcing effects of drugs and food, and the prolonged use of drugs or consumption of foods high in fat is known to alter the function and/or sensitivity of neurotransmitter systems, including dopamine. The current studies evaluated the impact of ad libitum or intermittent (1‐hr per day; Mon, Wed, Fri) consumption of the high‐fat diet on the acquisition of cocaine self‐administration during late adolescence (PND 52–62), relative to rats that consumed a standard diet (n=10–12 male rats per condition). During adulthood (PND ≥70), dose‐response curves for cocaine self‐administration were obtained under both fixed ratio (FR) 5 and progressive ratio (PR) schedules of reinforcement. Although the rate of acquisition was comparable across the three dietary conditions, high levels of responding (≥65 infusions of 0.032 mg/kg cocaine per session) were observed more frequently (85%) in rats with intermittent access to the high‐fat food compared with rats eating only the standard (60%) or high‐fat diets (20%). Similarly, when dose‐response curves for cocaine self‐administration were evaluated under an FR 5 schedule of reinforcement, intermittent consumption of the high‐fat diet shifted the dose‐response curve leftward and/or upward relative to the dose‐response curve obtained in rats that consumed the standard diet; ad libitum consumption of the high‐fat diet did not alter the cocaine dose‐response curve. Although dose‐response curves obtained when cocaine was self‐administered under a PR schedule did not differ among the three groups of rats, a subset of rats from the intermittent high‐fat condition completed significantly more ratios than all other rats. In addition to self‐administering more cocaine under the FR 5 schedule and completing larger ratios to obtain cocaine under the PR schedule, this subset of rats also consistently consumed more high‐fat food during the 1‐hr access period than other rats from the intermittent high‐fat condition. Although it is unclear what factors account for these differential levels/patterns for consumption, the current results provide additional evidence that the abuse‐related effects of drugs, such as cocaine, can be influenced by dietary factors and suggest that patterns of food consumption (i.e., intermittent versus ad libitum) might have a greater impact than the type of foods that are consumed on vulnerability to drug abuse.Support or Funding InformationCPF is supported by a NIDA Senior Scientist Award (K05 DA017918).