Ethanol substitutes for the discriminative stimulus effects of m-chlorophenylpiperazine

Rats were trained to discriminate the 5-HT agonist m-chlorophenylpiperazine (mCPP, 1 mg/kg, i.p.) from saline. Ethanol (0.1 to 1 g/kg, i.p.) partially substituted for the discriminative stimulus effects of 1 mg/kg mCPP. Methysergide (10 mg/kg, i.p.), a 5-HT_1/2 receptor antagonist, blocked the ability of ethanol (1 g/kg) to substitute for mCPP. The largest dose of ethanol markedly reduced response rate. These findings suggest an important role of serotonin receptors in mediating the discriminative stimulus effects of ethanol.