Interaction of ethanol and tetrahydro-beta-carboline (THBC) in a discriminative task.

Rats (n = 10) were trained to discriminate between ethanol (600 mg/kg, IP) and its vehicle, or between THBC (20 mg/kg) and its vehicle in a two-lever food-motivated operant task. Once the discriminative training criterion was attained, rats in each group were administered different doses of both ethanol and THBC. The ED50 of ethanol in the ethanol-trained rats was 298.0 mg/kg and 15 mg/kg THBC produced ethanol-like responding. The ED50 of THBC in the THBC-trained rats was 3.63 mg/kg and 1200 mg/kg ethanol produced THBC-like responding. The cross-generalization between ethanol and THBC is, thus, indicated and relates to previous evidence in which both ethanol- and THBC-trained rats generalize to a common agent, TFMPP, a putatively specific 5HT1B receptor agonist. Taken together, these observations suggest that beta-carbolines may play a role in the discriminative stimulus properties of ethanol.