LOCALIZATION OF DOPAMINE D1 RECEPTORS AND DOPAMINOCEPTIVE NEURONS IN THE CHICK FOREBRAIN

The distributions of dopamine D1 receptors, dopaminoceptive neurons, a nd catecholaminergic fibers were investigated in the forebrain of the domestic chick by using D1 receptor autoradiography and immunohistoche mical detection of D1 receptor protein (D1rp), the dopamine-and cAMP-r egulated phosphoprotein DARPP-32, and tyrosine hydroxylase (TH). Parti cular attention was paid to two forebrain regions, the mediorostral ne ostriatum/hyperstriatum ventrale (MNH) and neostriatum dorsocaudale (N dc), which have been shown to be crucially involved in filial imprinti ng. In general, there was a good, but not complete, correlation betwee n the immunohistochemical pattern of DARPP-32 positive perikarya and t he distribution of D1 receptors. Both, DARPP-32 positive neurons as we ll as D1 receptors were highly enriched in the striatal part of the ba sal ganglia including the lobus parolfactorius (LPO) and paleostriatum augmentatum. High to moderate densities were observed in the outer ri nd of the pallium. Low to moderate densities were found in the belt re gions of primary sensory areas, whereas densities in the respective co re regions were generally low Labeling in the MNH and Ndc was heteroge neous. Whereas the neostriatal part of MNH displayed both, moderate DA RPP-32 immunostaining and moderate D1 receptor densities, the hyperstr iatal part showed also moderate D1 receptor densities but was only wea kly labeled by DARPP-32. The rostral part of the Ndc was among the mos t intensely DARPP-32 labeled areas of the pallium, its caudal part rev ealed only moderate DARPP-32 immunostaining. By using D1 receptor auto radiography, a homogeneous labeling throughout the rostrocaudal extens ion of the Nde was found. Double-labeling experiments with antibodies to DARPP-32 and TH revealed that TH positive fibers in the MNH, Ndc, a nd LPO were often closely related to DARPP-32 positive perikarya. At t he ultrastructural level, both immunoreaction for D1rp and DARPP-32 in the MNH and Ndc were primarily found to be associated with postsynapt ic elements. Whereas D1rp immunoreactivity was enriched at postsynapti c densities or in their vicinity, reaction product for DARPP-32 was pr esent throughout the perikaryal cytoplasm, dendrites, and dendritic sp ines. These results indicate that DARPP-32 as well as D1 receptors in the avian forebrain reveal a distribution that is substantially simila r to that of mammals. (C) 1997 Wiley-Liss, Inc.