Serotonergic Responsivity in Male Young Adults With Autistic Disorder: Results of a Pilot Study

Altered serotonergic function has been postulated to exist in autistic disorder. Central serotonergic responsivity was assessed with a neuroendocrine challenge test in seven male young adults with autistic disorder and in seven age and gender-matched healthy controls. Binding indexes and physiologic responsivity of the platelet serotonin-2 (5-HT₂) receptor complex were also measured, as was whole-blood serotonin content. Compared with controls, autistic subjects had substantially blunted prolactin release in response to a 60-mg oral dose of fenfluramine hydrochloride, an indirect serotonin antagonist. Furthermore, the magnitude of serotonin-amplified platelet aggregation, mediated by the platelet 5-HT₂ receptor complex, was reduced in the autistic group, as was the mean number of platelet 5-HT₂ receptor sites. Among autistic subjects, fenfluramine-induced prolactin release correlated positively with the serotonin-amplified platelet aggregation response and negatively with whole-blood serotonin content. The results of the present study are compatible with the hypothesis that central serotonergic responsivity is decreased in male autistic young adults. Correlations between central and peripheral serotonergic measures in autistic subjects suggest that systemic alterations in serotonergic function may occur in autism.