Abstract

This investigation sought to test the hypothesis that those pharmacologic properties which distinguish hallucinogens and non-hallucinogens in man are reflected in distinctive stimuli in the rat. Subjects were first trained on a variable interval schedule of positive reinforcement. Two drug treatments were then assigned to each animal. One treatment was the S^D, the stimulus in whose presence responses were reinforced on the variable interval schedule and the other treatment was the S^Δ, the stimulus in whose presence no responses were reinforced. After 8 to 12 sessions in which the drug treatments were alternated on successive days, a punishment contingency was added, i.e., in the presence of S^Δ, responses were punished by the delivery of electric shock on a variable interval schedule. Approximately every fourth session was designated a test session and responses were neither reinforced nor punished during the first five minutes of these sessions. In this way the efficacy of the drug treatments as discriminative stimuli was determined. It was first established, in two separate groups of rats, that mescaline, when paired with saline and 2, 3, 4-trimethoxyphenylethylamine (2, 3, 4-TMPEA), when paired with saline, can be discriminative stimuli. In a third group, equivalent doses of mescaline and 2, 3, 4-TMPEA were compared directly. If we assume that 2, 3, 4-TMPEA is without hallucinogenic activity, the hypothesis predicts that mescaline and 2, 3, 4-TMPEA will be discriminable in the rat. No evidence of discriminated responding was obtained. The present data fail to support the hypothesis that these different pharmacologic properties of hallucinogens and non-hallucinogens in man are reflected in distinctive stimuli in the rat.