EVIDENCE FOR A DOPAMINERGIC INNERVATION OF THE SUBTHALAMIC NUCLEUS INTHE RAT

The dopaminergic connection from the substantia nigra pars compacta (S Nc) and the ventral tegmental area (VTA) to the subthalamic nucleus in the rat was investigated using anterograde and retrograde tracers. Io ntophoretic injection of the retrograde tracer fluoro-gold (FG) into t he subthalamic nucleus resulted in a substantial number of labeled neu rons in the SNc. Immunohistochemistry of tyrosine hydroxylase (TH) con firmed the dopaminergic nature of these labeled neurons. Retrogradely labeled neurons were also found in the VTA. Injection of the anterogra de tracer biocytin into the SNc produced biocytin-labeled terminals in the subthalamic nucleus hence providing clear evidence for a dopamine rgic innervation of this nucleus. Quantitative analysis of labeled axo ns revealed that there were 15-38 terminal branches per axon, each bra nch being 50-150 mu m long. The overall dimensions of one terminal arb orization were 400 x 250 x 150 mu m. There was no clear-cut topographi cal organization of the projection, but a slight mediolateral differen ce in the density of terminals. This direct dopaminergic projection is thought to interact with cortical and pallidal inputs in the subthala mic nucleus, which implies that the functions of the subthalamic nucle us are more complex than previously assumed. (C) 1997 Elsevier Science B.V.