Drug discrimination in rats: the effects of phencyclidine and ditran.

Choice responding in a T-shaped maze has been made contingent upon whether or not rats experienced certain drug effects. The drug discriminative cues used in the present state-dependent (StD) model were those of phencyclidine (PCP) and ditran. The specificity of these cues and their possible drug inhibition and antagonism was studied. It was found that the lower the training dose used the slower the appearance of the drug discriminative formation. Transfer testings with ketamine and cyclohexamine showed that they were interchangeable with PCP. The order of their relative potency was: cyclohexamine greater than PCP greater than ketamine. Atropine transferred to ditran. Administration of compounds not structurally related to the training drugs did not show transfer. Pretreatment with parachlorphenylalanine (p-CPA) or tetrabenazine (TBZ) plus imipramine did not indicate inhibition or antagonism in PCP trained rats. Tacrine (THA) and especially physostigmine effectively antagonized the ditran-induced cues. Yohimbine and neostigmine did not.