Ethanol consumption following acute treatment with methysergide, fluoxetine, fenfluramine, and their combination.

Methysergide (MS), a postsynaptic serotonin antagonist, was administered acutely in three experiments in relation to water or 5% ethanol solution intake of 24-hr, water-deprived male Sprague-Dawley rats. In the first experiment, MS significantly increased the consumption of ethanol at doses of 0.25, 2.0, and 4.0 mg/kg. Water intake was significantly increased by MS at the 2.0 mg/kg dose. In the second experiment, which was different from the first one in that MS was administered during the dark cycle, ethanol solution intake was again significantly increased at all three levels. In the third experiment, fenfluramine (FFL) and fluoxetine (FLU) were administered acutely (at 8 mg/kg) after MS (0.25 mg/kg) followed by measuring water or ethanol solution intake. FFL and FLU significantly decreased intake of both water and ethanol solution, a process that was significantly reversed by MS; to a greater degree for FLU (74%) than for FFL (57%). The successful use of MS in increasing ethanol intake in these studies may be due to the low doses used in comparison with earlier unsuccessful attempts. The procedure of treating 24-hr, water-deprived rats with acute doses of pre- and postsynaptic serotonin agonists and antagonists appears to be a useful model for further elucidation of their interaction in ethanol consummatory behavior.