Chronic ACTH treatment: influence on 5-HT2 receptors and behavioral supersensitivity induced by 5,7-dihydroxytryptamine lesions.

The capacity of the serotonin (5-HT) precursor 5-HIP to induce the ACTH-responsive myoclonic-convulsive disorder infantile spasms in patients with Down's syndrome has been cited as evidence for altered serotonergic neurotransmission in infantile spasms. Since there is no animal model of infantile spasms, the suitability of behavioral supersensitivity (myoclonus) evoked by 5-HTP in rats with 5,7-dihydroxytryptamine (DHT) lesions as a model was tested by determining the effect of chronic treatment with ACTH (40 IU/kg) on 5-HTP-evoked myoclonus. In rats treated with DHT as adults, ACTH administration did not alter the "serotonergic behaviors," such as myoclonus, induced by 30 mg/kg 5-hydroxytryptophan (5-HTP), but induced a small significant increase in Bmax of neocortical 5-HT2 sites of the DHT group, with no change in rats without lesions. In rats treated with DHT as neonates, there was also no significant difference in behaviors evoked by several doses of 5-HTP. These data suggest that ACTH minimally modifies the effects on 5-HT receptors of DHT lesions, but the intracisternal DHT model is not a suitable model for infantile spasms because chronic ACTH was not antimyoclonic.