The effects of alcohol preexposure on cocaine, alcohol and cocaine/alcohol place conditioning

The present experiment examined the effects of alcohol preexposure on place conditioning with cocaine, alcohol or the cocaine/alcohol combination. Specifically, 91 male Sprague-Dawley rats were injected i.p. with 1.5 g/kg alcohol (n = 46) or vehicle (n = 45) every fourth day for 17 days prior to conditioning. On day 21, half of the animals from each preexposure condition were injected with 20 mg/kg cocaine, 1.5 g/kg alcohol or the cocaine/alcohol combination before being restricted for 30 min to a distinctive compartment of a place conditioning apparatus. The remaining subjects were injected with vehicle and restricted to the alternative side of the chamber. The following day, subjects previously given drug (or vehicle) were given vehicle (or drug) and placed in the alternative compartment of the chamber. Following four conditioning cycles, subjects were allowed 15-min access to the entire chamber. Both alcohol- and vehicle-preexposed animals conditioned with cocaine displayed a preference for the cocaine-paired compartment. Those conditioned with alcohol had an aversion to the alcohol-paired compartment. Consistent with our previous work, animals given the cocaine/alcohol combination displayed no compartment preference, indicating that concurrent alcohol affected the reinforcing effects of cocaine. Further, the attenuating effect of concurrent alcohol was unaffected by alcohol history. Under the present parameters, alcohol pretreatment has no effect on the rewarding (and possibly aversive) properties of cocaine alone or the cocaine/alcohol combination. Continued investigation of the conditions under which preexposure to alcohol might modulate the aversive/reinforcing properties of a cocaine/alcohol combination may be important for understanding vulnerability to the use and/or abuse of this drug combination.