AUTORADIOGRAPHIC ANALYSIS OF 5-HT RECEPTOR SUBTYPES LABELED BY [H-3] 5-CT([H-3]5-CARBOXAMIDOTRYPTAMINE)

This work examines the autoradiographic distribution of zerotonin (5-H T) receptor subtypes in rat, guinea pig and human brain, using [H-3]5- HT and [H-3]5-CT as ligands. Different displacers were used to mask ra dioligand binding to 5-HT1A, 5-HT1B/1D and 5-HT2C receptors, in an att empt to visualize other receptor populations, which presumably would c orrespond to 5-HT1E and 5-HT1F sites. Brain areas enriched in 5-HTnon1 A/1B/1D sites in guinea pig were the hilus, dentate gyrus, striatum, c laustrum, substantia nigra and superior colliculus, among others. In h umans, however, the claustrum, a structure supposed to contain 5-HT1E sites, showed significant densities of [H-3]5-CT binding. An interesti ng finding was that blockade [H-3]5-CT binding to 5-HT1A receptors by 8-OH-DPAT could only be achieved at very high concentrations of the di splacer. This could be due to differences in the affinity of ligands i n intact tissue sections compared to membrane homogenates or cell line s. Another possibility would be that [H-3]5-CT labels 5-HT1A receptors in the low-affinity state. These hypotheses remain to be investigated .