Wheel-running attenuates intravenous cocaine self-administration in rats: sex differences.
This experiment examines the effect of access to a running-wheel on intravenous cocaine self-administration in male and female rats. Rats maintained at 85% of their free-feeding body weight were first exposed to the running-wheel alone during the 6-h sessions until behavior stabilized for 14 days. Intravenous cannulae were then implanted, and the rats were trained to self-administer a low dose of cocaine (0.2 mg/kg) under a fixed-ratio (FR 1) schedule during the 6-h sessions, while the wheel remained inactive and cocaine self-administration stabilized (cocaine-only condition). Next, the wheel access and cocaine self-administration were concurrently available followed by a period of cocaine-only. Behavior was allowed to stabilize for 10 days at each phase. During wheel access, cocaine infusions decreased by 21.9% in males and 70.6% in females compared to the cocaine-only condition; the effect was statistically significant in females. Infusions increased to baseline levels when wheel access was terminated. When cocaine infusions were concurrently available, wheel revolutions were reduced by 63.7% and 61.5% in males and females, respectively, compared to the wheel-only condition. This result did not differ due to sex, but it was statistically significant when data from males and females were combined. These results indicate that wheel-running activity had a greater suppressant effect on cocaine self-administration in females than in males, and in females, wheel-running and cocaine self-administration are substitutable as reinforcers.
Cosgrove
Kelly P
KP
Department of Psychiatry, University of Minnesota, Mayo Box 392, Minneapolis 55455, USA.
Hunter
Robb G
RG
Carroll
Marilyn E
ME
D000818:Animals; D019970:Cocaine-Related Disorders / Q000523:psychology*; D005260:Female; D007262:Infusions, Intravenous; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012054:Reinforcement, Psychology; D012646:Self Administration; D012727:Sex Characteristics; D015819:Substance Abuse, Intravenous / Q000523:psychology*