EFFECT OF PHARMACOLOGICAL INTERFERENCE WITH VARIOUS NEUROPATHWAYS ON BLOCKADE OF MORPHINE-WITHDRAWAL HYPOTHERMIA BY MORPHINE AND BY CONDITIONAL STIMULUS

Rats were given 2 equally spaced injections of morphine sulfate daily, each injection being paired with a bell sound. The morphine dose was gradually increased to 200 mg/kg per day. At 24 h after withdrawal, all rats showed hypothermia which was reversed by either the bell sound or morphine. Morphine alone also produced an overshoot hyperthermia. The bell sound-induced alleviation of withdrawal hypothermia was blocked by pretreatment with mecamylamine (2.5 mg/kg), phenoxybenzamine (2 mg/kg), haloperidol (0.2 mg/kg) and benztropine (0.625 mg/kg) but was not blocked by cyproheptadine (2 mg/kg) or propranolol (2 mg/kg). In contrast, morphine-induced hyperthermia during withdrawal was blocked by pretreatment with mecamylamine, phenoxybenzamine and cyproheptadine but was not blocked by haloperidol, benztropine or propranolol.