COCAINE IMPAIRS ACQUISITION OF AN AUTOSHAPED LEVER-TOUCH RESPONSE

The effects of daily peripheral (IP) post-session injection of cocaine on the development of an autoshaped lever-touch response in rats were investigated. Male Spraque-Dawley rats received ten daily pairings of a retractable lever (conditioned stimulus; CS) and food delivery (unc onditioned stimulus; UCS). Food delivery occurred if the subjects cont acted the extended lever within 10 s, or, if the subjects failed to co ntact the lever, at the end of the 10-s stimulus interval. These conti ngencies resulted in increased lever-touch responses over 10 days of c onditioning. Cocaine (5.6-19.0 mg/kg) impaired development of the leve r-touch response, as compared to saline-treated control subjects. Beca use the injections were given immediately after each conditioning sess ion, we suggest that cocaine affects the neural processes involved in consolidation. Three additional control experiments support this sugge stion. The effect of cocaine an lever-touch acquisition was time-depen dent as daily injection of cocaine (5.6 mg/kg) 3 h after each conditio ning session did not affect lever-touch acquisition. In addition, the effect of cocaine was dependent upon the explicit pairing of lever ext ension (CS) and food delivery (UCS) as immediate post-session cocaine (5.6 mg/kg) administration did not alter responding when the presentat ion of both the CS and the UCS was uncorrelated. Cocaine (5.6 mg/kg) a dministered to subjects previously trained to a performance criterion did not affect lever-touch responding, indicating that cocaine adminis tration (5.6 mg/kg) impairs the development, but not the maintenance, of autoshaped lever-touch responding. In contrast, the highest dose of cocaine tested, 19.0 mg/kg, did decrease lever-touch responding in we ll-trained subjects, indicating that post-session administration of hi gher doses of cocaine can produce aversive effects that may affect bot h the acquisition and maintenance of appetitively motivated behavior i n the rat. The relative contributions of the instrumental and classica l associations inherent in the autoshaping procedure were investigated by altering response contingencies. Rats showed no evidence of learni ng the lever-touch response when lever insertion and food delivery wer e positively correlated, and no explicit response contingency was pres ent (classical conditioning); further, cocaine-treated subjects did no t differ from saline-treated subjects. However, cocaine did impair lev er-touch responding in the instrumental version of the task. Taken tog ether, these results show that the post-session administration of coca ine can impair the acquisition of a multi-trial, multi-session appetit ively motivated response.