Actometric effects of intravenous cocaine in rats

Intravenous infusions of cocaine, in dosages which have been reported to maintain self-administration behavior, were administered to cannulated rats. Ten identical infusions were administered at 6 min intervals within a session. The activity occuriring in the initial minute following infusions was compared to that produced by saline infusions. Dosages of 200, 400, 800 and 1200 microgram/kg significantly increased activity. However, this effect was not maintained throughout the session. The tenth infusion no longer increased activity as compared to the initial infusion. Therefore these data would not support the hypothesis that cocaine-induced activity was responsible for maintaining cocaine self-administration behavior in this species. Pretreatment with agents which disrupt the synthesis of dopamine and/or norepinephrine failed to antagonize this initial increase in activity. These data would suggest that the activity effect of cocaine is not dependent on newly synthesized pools of the catecholamines.