Behavioral supersensitivity to 5-hydroxytryptophan induced by chronic methysergide pretreatment

The administration of 5-hydroxytryptophan to intact guinea pigs results in rhythmic myoclonic behavior. This behavior is blocked acutely by methysergide, but is intensified in animals chronically pretreated with methysergide. Brain serotonin concentrations of guinea pigs pretreated with methysergide did not differ from saline-treated animals. These results are compatible with the hypothesis that prolonged methysergide administration can result in pharmacologically-induced denervation hypersensitivity at central serotonin receptors.