THE EFFECTS OF 3,4-DIMETHOXYPHENYLETHYLAMINE IN RATS TRAINED WITH MESCALINE AS A DISCRIMINATIVE STIMULUS

¹ Department of Pharmacology and Therapeutics, School of Medicine, State University of New York at Buffalo, New York

It is known that the effects of mescaline (3,4,5-trimethoxyphenylethylamine), a hallucinogen, can function as a discriminative stimulus. The present investigation examined the ability of 3,4-dimethoxyphenylethylamine (DMPEA), a non-hallucinogen, to substitute for mescaline in animals previously trained with mescaline and saline. Subjects were first trained on a variable interval schedule of positive reinforcement Two treatment conditions, mescaline hydrochloride (10 mg/kg) and saline, were then assigned to each animal. One treatment was S^D, the stimulus in whose presence responses were reinforced, and the other treatment was S, the stimulus in whose presence no responses were reinforced. After approximately 10 sessions in which the drug treatments were alternated on successive days, a punishment contingency was added, i.e., in the presence of S, responses were punished by the delivery of electric shock. The efficacy of the drug treatments as discriminative stimuli was established in test sessions in which responses were neither punished nor reinforced. Subsequent administration of a range of doses of DMPEA to subjects in which saline functioned as S^D and mescaline as S revealed that a dose of 10 to 30 mg/kg of DMPEA was equivalent to the training dose of mescaline. However, the same range of doses, when tested in subjects in which mescaline was S^D did not result in responding appropriate for the mescaline condition. Subsequently, direct comparisons of DMPEA and mescaline were made by substituting DMPEA for saline 1) in subjects previously trained with mescaline and saline and 2) in a second group which had previously received neither drugs nor behavioral training. Discriminated responding developed rapidly in both groups. The present results suggest that DMPEA cannot substitute for mescaline in a discriminative task and that comparable doses of the two drugs are discriminable in rats.