Dopaminergic innervation of human basal ganglia

This paper summarises the results of some of our recent tyrosine hydroxylas e (TH) immunohistochemical studies of the dopaminergic innervation of the h uman basal ganglia. It also reports new findings on the presence of TH-immu noreactive (ir) neurons in the striatum. Our data show the existence of nig rostriatal TH-ir axons that provide collaterals arborizing in the globus pa llidus and subthalamic nucleus. These thin and varicose collaterals emerge from thick and smooth axons that course along the main output pathways of t he basal ganglia, including the ansa lenticularis, the lenticular fasciculu s and Wilsons pencils. We postulate that this extrastriatal innervation, wh ich allows nigral dopaminergic neurons to directly affect the pallidum and subthalamic nucleus, plays a critical role in the functional organisation o f human basal ganglia. The TH-ir fibres that reach the striatum arborize ac cording to a highly heterogeneous pattern. At rostral striatal levels, nume rous small TH-poor zones embedded in a TH-rich matrix correspond to calbind in-poor striosomes and calbindin-rich extrastriosomal matrix, respectively. At caudal striatal levels, in contrast, striosomes display a TH immunostai ning that is more intense than that of the matrix. A significant number of small, oval, aspiny TH-ir neurons scattered throughout the rostrocaudal ext ent of the caudate nucleus and putamen, together with a few larger, multipo lar, spiny TH-ir neurons lying principally within the ventral portion of th e putamen, were disclosed in human. This potential source of intrinsic stri atal dopamine might play an important role in the functional organisation o f the human striatum, particularly in case of Parkinson's disease. (C) 2000 Elsevier Science B.V. All rights reserved.