Human striosomes are enriched in 5-HT2A receptors: autoradiographical visualization with [H-3]MDL100,907, [I-125](+/-)DOI and [H-3]ketanserin

5-HT2A receptors have been visualized with [H-3]MDL 100,907 in selected hum an brain areas by autoradiography. These areas included caudate and putamen , nucleus dentatus of the cerebellum, substantia nigra, nucleus raphe dorsa lis, locus coeruleus and inferior olive. In the striatum [H-3]MDL 100,907 l abelling was compared with the pattern obtained with [H-125](+/-)DOI and [H -3]ketanserin. [H-3]MDL100,907 and[I-125](+/-)DOI showed an identical patch y distribution which was hardly observed with [H-3]ketanserin. In the remai ning regions, [H-3]MDL100,907 and [H-3]ketanserin autoradiographical signal s and percentage of specific binding were compared. Whereas the pattern of distribution was identical for both radioligands, [H-3]MDL100,907 presented a much lower percentage of nonspecific binding compared with [H-3]ketanser in. These results confirm the presence of 5-HT2A receptors in human strioso mes and in those areas where[H-3]ketanserin presented a high nonspecific bi nding, and they highlight the advantage of using [H-3]MDL100,907 to visuali ze these receptors.