Aerobic exercise can serve as an alternative, non-
drug reinforcer in laboratory animals and has been recommended as a potential intervention for substance abusing populations. Unfortunately, relatively little empirical data have been collected that specifically address the possible protective effects of voluntary, long-term exercise on measures of
drug self-administration. The purpose of the present study was to examine the effects of chronic exercise on sensitivity to the positive-reinforcing effects of
cocaine in the
drug self-administration procedure. Female rats were obtained at weaning and immediately divided into two groups. Sedentary rats were housed individually in standard laboratory cages that permitted no exercise beyond normal cage ambulation; exercising rats were housed individually in modified cages equipped with a running wheel. After 6 weeks under these conditions, rats were surgically implanted with venous
catheters and trained to self-administer
cocaine on a fixed-ratio schedule of reinforcement. Once
self-administration was acquired,
cocaine was made available on a progressive ratio schedule and breakpoints were obtained for various doses of
cocaine. Sedentary and exercising rats did not differ in the time to acquire
cocaine self-administration or responding on the fixed-ratio schedule of reinforcement. However, on the progressive ratio schedule, breakpoints were significantly lower in exercising rats than sedentary rats when responding was maintained by both low (0.3mg/kg/infusion) and high (1.0mg/kg/infusion) doses of
cocaine. In exercising rats, greater exercise output prior to
catheter implantation was associated with lower breakpoints at the high dose of
cocaine. These data indicate that chronic exercise decreases the positive-reinforcing effects of
cocaine and support the possibility that exercise may be an effective intervention in
drug abuse prevention and treatment programs.