Cross-generalization between a cocaine cue and two antihistamines.

Rats were trained to discriminate between 10 mg/kg cocaine and saline injections under a fixed ratio 10 schedule of food-motivated lever press responding. Once stimulus control was achieved, reinforced test sessions were conducted to assess the degree of generalization of a wide range of cocaine doses and the cross-generalization between the cocaine training stimulus and two over-the-counter antihistaminic drugs, diphenhydramine and doxylamine, when administered with saline or in drug combinations. Cocaine produced a dose-dependent generalization to the 10 mg/kg training stimulus. Cocaine also produced mild rate-increasing effects at low test doses and response rate suppression at higher doses. Both diphenhydramine and doxylamine produced a partial generalization to the 10 mg/kg cocaine training stimulus. Drug mixtures produced complete cross-generalization with the training cue.