Catecholamine innervation of the basal forebrain IV. Topography of the dopamine projection to the basal forebrain and neostriatum

Abstract

In this study the location of dopamine (DA) neuron perikarya in the rostral mesencephalon of the rat was determined using the glyoxylic acid fluorescence histochemical technique. Subsequently the topography of the projection of these mesencephalic neurons on the basal forebrain and striatum was analyzed using the anterograde transport‐autoradiographic tracing method and the retrograde transport‐horseradish peroxidase (HRP) technique. The results of these anatomical studies were correlated with the biochemical and histochemical studies presented in previous reports (Moore, 1978; Fallon and Moore, 1978; Fallon et al., 1978) to provide the following conclusions. The topography of the DA neuron projection on the basal forebrain and neostriatum is organized in three planes, dorsal‐ventral, medial‐lateral and anterior‐posterior. DA cells are found almost exclusively in the substantia nigra (SN) and ventral tegmental area (VTA). Ventral cells of the SN and VTA project to the dorsal structures of the basal forebrain such as the septum, nucleus accumbens and neostriatum. The latter includes some DA cells located ventrally in the pars reticulata of the SN. Dorsal cells project to ventral structures. The medial‐lateral topography is organized such that the medial sectors of the SN‐VTA area project to the medial parts of nuclei in the basal forebrain and neostriatum whereas lateral sectors of the SN‐VTA area project to the lateral parts of nuclei in the basal forebrain and neostriatum. An anterior‐posterior topography also is evident such that anterior parts of the SN‐VTA project anteriorly whereas the posterior SN‐VTA projects more posteriorly in these areas. These observations are consistent with the view that the DA neurons of the SN‐VTA complex form a single nuclear group with a highly topographically organized projection innervating not only deep nuclei of the telencephalon but allocortical structures as well.