Wheel-running behavior is altered following withdrawal from repeated cocaine in adult rats

The residual effects on open-field habituation and self-generated wheel running following withdrawal from repeated cocaine (COC; 30 mg/kg for 7 days) were examined in adult male rats. Control subjects received equivolumetric injections of saline (SAL) and were either allowed to feed ad libitum or pair-fed matched (PF SAL) to COC subjects to control for the drug's potential anorexic effect. Following 10 days of withdrawal, all subjects were examined twice on each of the two assessment instruments. Results indicated that COC subjects over the two test sessions failed to increase their wheel-running rates and did not show the expected habituation in the open field. However, because both COC and PF SAL groups yielded similar effects in the open field, conclusions about cocaine's consequences on habituation could not be established independent of the drug's anorexic effect. These data provide evidence for the view that repeated cocaine impairs motivational processes responsible for engaging in self-generated naturally rewarding behaviors. Speculation concerning the neurobiobehavioral substrates for this effect is presented.