The effects of post-extinction exercise on cocaine-primed and stress-induced reinstatement of cocaine seeking in rats.

Rationale: Voluntary aerobic exercise has shown promise as a treatment for substance abuse, reducing relapse in cocaine-dependent people. Wheel running also attenuates drug-primed and cue-induced reinstatement of cocaine seeking in rats, an animal model of relapse. However, in most of these studies, wheel access was provided throughout cocaine self-administration and/or extinction and had effects on several parameters of drug seeking. Moreover, the effects of exercise on footshock stress-induced reinstatement have not been investigated.

Objectives: The purposes of this study were to isolate and specifically examine the protective effect of exercise on relapse-like behavior elicited by a drug prime or stress.

Methods: Rats were trained to self-administer cocaine at a stable level, followed by extinction training. Once extinction criteria were met, rats were split into exercise (24 h, continuous access to running wheel) and sedentary groups for 3 weeks, after which, drug-seeking behavior was assessed following a cocaine prime or footshock. We also measured galanin messenger RNA (mRNA) in the locus coeruleus and A2 noradrenergic nucleus.

Results: Exercising rats ran ∼4-6 km/day, comparable to levels previously reported for rats without a history of cocaine self-administration. Post-extinction exercise significantly attenuated cocaine-primed, but not footshock stress-induced, reinstatement of cocaine seeking, and increased galanin mRNA expression in the LC but not A2.

Conclusion: These results indicate that chronic wheel running can attenuate some forms of reinstatement, even when initiated after the cessation of cocaine self-administration, supporting the idea that voluntary exercise programs may help maintain abstinence in clinical populations.