Caffeine preexposure sensitizes rats to the motor activating effects of cocaine.

Rats were preexposed to caffeine or to water vehicle with nine daily injections (20 mg/kg, i.p.). On each of the 9 days, the motor activating response to the drug was assessed in open field boxes. On the tenth day, water and caffeine preexposed rats were challenged with a single injection of cocaine HCI (10 mg/kg, i.p.) or vehicle, and the activational effect of cocaine was assessed. The rats that had been pretreated with caffeine showed a larger response to cocaine than their vehicle treated counterparts, suggesting that caffeine exposure enhanced the response to cocaine. Since caffeine-preexposed rats responded to the vehicle injection on test day in much the same manner as rats that had received chronic injections of the water vehicle, it is unlikely that the increase in cocaine effect was due to carryover effects of the caffeine pretreatment or conditioned activity due to the preexposure. These data add to the literature base describing predisposing factors in cocaine sensitivity, and suggest that readily available stimulants, like caffeine, may serve to prime central systems that mediate the response to cocaine.