The effects of aerobic exercise on cocaine self-administration in male and female rats

Rationale In drug self-administration procedures, extended-access test sessions allow researchers to model maladaptive patterns of excessive and escalating drug intake that are characteristic of human substance-abusing populations. Objectives The purpose of the present study was to examine the ability of aerobic exercise to decrease excessive and escalating patterns of drug intake in male and female rats responding under extended-access conditions. Methods Male and female Long-Evans rats were obtained at weaning and divided into sedentary (no running wheel) and exercising (running wheel) groups immediately upon arrival. After 6 weeks, rats were surgically implanted with intravenous catheters and allowed to self-administer cocaine under positive reinforcement contingencies. In experiment 1, cocaine self-administration was examined during 23-h test sessions that occurred every 4 days. In experiment 2, the escalation of cocaine intake was examined during daily 6-h test sessions over 14 consecutive days. Results In experiment 1, sedentary rats self-administered significantly more cocaine than exercising rats during uninterrupted 23-h test sessions, and this effect was apparent in both males and females. In experiment 2, sedentary rats escalated their cocaine intake to a significantly greater degree than exercising rats over the 14 days of testing. Although females escalated their cocaine intake to a greater extent than males, exercise effectively attenuated the escalation of cocaine intake in both sexes. Conclusions These data indicate that aerobic exercise decreases maladaptive patterns of excessive and escalating cocaine intake under extended-access conditions.