Generalization of drug-seeking behavior in dogs.

Drug-naive dogs which do not spontaneously initiate morphine self-administration were given one of three treatments and tested for subsequent morphine self-administration. Neither the dogs given the treatment of response-contingent drinking water nor those given d-amphetamine by passive infusions subsequently showed significant self-administration of morphine. However, the third group which self-administered d-amphetamine did subsequently self-administer morphine. The data suggest that self-administration of one reinforcing psychoactive drug may increase the probability of subsequently self-administering another.