Postsynaptic localization of 5-HT1D receptor binding sites in human caudate.

5-hydroxytryptamine1D (5-HT1D) receptor binding sites were quantified by saturation studies in the postmortem caudate nucleus and frontal cortex of individuals with Huntington's disease and control individuals with no known neurological disease. 3H-5-HT was used as the radioligand in the presence of 100 nM 8-OH-DPAT and 100 nM mesulergine in order to restrict radioligand binding to 5-HT1D receptors. No alteration in KD value was detected in Huntington's disease as compared to control brain tissue. However, the density (Bmax) of the 5-HT1D site was significantly decreased (P less than 0.01) in the caudate, but not the frontal cortex, of Huntington's disease versus control individuals. By contrast, no significant difference was found in Bmax or KD of [3H]paroxetine binding between control and Huntington's caudates. These data suggest that a significant number of caudate 5-HT1D receptors are located on the intrinsic neurons of the striatum as opposed to 5-HT nerve terminals.