Serotonergic mediation of tetrahydro-beta-carboline.

Rats were trained to discriminate between the stimulus properties of tetrahydro-beta-carboline (THBC) and its vehicle in a two-lever, food-motivated operant task. By steadily increasing the training dose, the discrimination was attained at 20.0 mg/kg THBC. Dose-response experiments subsequently indicated that decreasing doses of THBC produced decreased discrimination and generated an ED50 = 3.63 mg/kg. Administration of the serotonergically-active drug, fenfluramine, produced THBC-appropriate responding in a dose-responsive manner. In addition, LSD and yohimbine produced partial generalizations in the THBC-trained rats. These data suggest that the discriminative stimulus properties of THBC are mediated by serotonergic neurons in the central nervous system.