LIGHT AND ELECTRON-MICROSCOPIC CHARACTERIZATION OF CHOLINERGIC AND DOPAMINERGIC STRUCTURES IN THE STRIATAL COMPLEX AND THE DORSAL VENTRICULAR RIDGE OF THE LIZARD GEKKO-GECKO

The purpose of the present study was to visualize the morphological su bstrate underlying acetylcholine-dopamine interactions in the striatal complex of the lizard Gekko gecko and to compare the results with dat a obtained by others in mammals. The results are also discussed in the light of data obtained previously by us on neurochemical aspects of a cetylcholine-dopamine interactions in Gekko and in rats. The study is part of a large research program in which the cholinergic and dopamine rgic elements of the striatum of rats and reptiles are studied at morp hological and neurochemical levels. We employed light microscopic immu nocytochemistry, using single-label staining with antibodies against c holine acetyltransferase (ChAT) and dopamine (DA) and double-staining with antibodies against ChAT and tyrosine hydroxylase (TH). A detailed analysis of ultrastructural characteristics of ChAT- and DA-immunolab eled striatal tissue was undertaken. The morphology and synaptic relat ions of the ChAT-immunopositive neurons in the basal forebrain of the lizard Gekko gecko are very similar to those of the cholinergic cells in the striatum of mammals. Probably, the cholinergic cells are in bot h mammals and reptiles interneurons that receive inputs of intrinsic o r extrinsic origin and project upon output neurons. The location of Ch AT-immunopositive somata outside the patches of high TH- or DA-immunor eactivity is at odds with the situation in the striatum of mammals and suggests the possibility of axoaxanal or axodendritic contacts at the level of these patches. We found no essential differences between the synaptic relations of the dopaminergic fibers in the striatal complex of Gekko and the conditions described for rats. In conclusion, we fou nd little evidence for the presence of synaptic interaction between th e cholinergic and dopaminergic systems in the striatum of this reptile . The possibility of nonsynaptic interaction, however, remains open. ( C) 1994 Wiley-Liss, Inc.