DEVELOPMENTAL-CHANGES IN HETEROGENEOUS PATTERNS OF NEUROTRANSMITTER RECEPTOR-BINDING IN THE HUMAN INTERPEDUNCULAR NUCLEUS

The interpeduncular nucleus (IPN) exhibits many complex features, incl uding multiple subnuclei, widespread projections with the forebrain an d brainstem, and neurotransmitter heterogeneity. Despite the putative importance of this nucleus, very little is known about its neurochemic al development in the human. The human IPN is cytoarchitectonically si mple. unlike the rat IPN, which displays considerable heterogeneity. I n the following study, we hypothesized that the developing human IPN i s neurochemically heterogeneous despite its cytological simplicity. Th e chemoarchitecture in this study was defined by neurotransmitter rece ptor binding patterns bg using quantitative tissue autoradiography for the muscarinic, nicotinic, serotoninergic, opioid, and kainate recept ors. We examined neurotransmitter receptor binding in the developing h uman IPN in a total of 15 cases. The midbrains of five midgestational fetuses (19-26 gestational weeks) and six infants (38-74 postconceptio nal weeks) were examined. The midbrain of one child (4 years) and thre e adults (20-68 years) were analyzed as indices of maturity. At all ag es examined, high muscarinic binding was localized to the lateral subd ivision of the IPN, high serotoninergic binding tvas localized to the dorsal IPN, and high opioid receptor binding was localized to the medi al IPN. The developmental profile was unique for each radioligand. We report a heterogenous distribution of neurotransmitter receptor bindin g in the developing human IPN, which supports a complex role for it in human brain function. (C) 1998 Wiley-Liss, Inc.