Antagonism by ketanserin of the behavioral effects of quipazine but not l-5-hydroxytryptophan in squirrel monkeys.

The serotonin agonist quipazine maleate (1-10 mg/kg, IM) and the serotonin precursor l-5-hydroxytryptophan (5HTP, 3-30 mg/kg, IM) produced dose-dependent decreases in responding (lever-pressing) of squirrel monkeys maintained under a fixed-ratio 30 schedule of food presentation. The classical serotonin antagonist methysergide antagonized the behavioral effects of both quipazine and 5HTP. The behavioral effects of quipazine but not 5HTP were antagonized by the selective serotonin-2 receptor antagonist ketanserin. These results suggest that decreases in food-maintained responding may be produced independently by stimulation of either serotonin-1 or serotonin-2 receptor subtypes.