IMMUNOCYTOCHEMICAL LOCALIZATION OF TYROSINE-HYDROXYLASE IN THE HUMAN STRIATUM - A POSTMORTEM ULTRASTRUCTURAL-STUDY

An electron microscopic evaluation of tyrosine hydroxylase (TH) immuno cytochemistry was used to describe the synaptic organization of dopami ne innervation of the striatum in postmortem human brain tissue. TH im munoreactivity was qualitatively and quantitatively similar in the cau date and putamen. TH immunoreactivity was present mainly in unmyelinat ed axons and occasionally in myelinated axons. Both TH-immunoreactive (TH-i) varicosities (0.75-1.5 mu m) and intervaricose segments (0.2-0. 3 mu m) formed synapses with spines and dendrites. Most synapses forme d by TH-i profiles were symmetric axospinous (57-62%) or symmetric axo dendritic (33-35%). An occasional asymmetric axodendritic or asymmetri c axospinous synapse was observed. Approximately 35-50% of all symmetr ic axospinous and axodendritic synapses were formed by TH-i boutons. S ynapses formed by TH-i profiles were short in length (0.226 mu m) and had nonperforated postsynaptic densities. TH-i profiles formed synapse s with both the head (40%) and the neck (60%) of spines. Typically the TH-i bouton was apposed to both a spine and a nonlabeled terminal whi ch formed an asymmetric synapse with that spine. Direct, nonsynaptic a ppositions were often seen between TH-labeled and nonlabeled boutons f orming asymmetric synapses. The general pattern of TH immunoreactivity was similar to that of other species except for the presence of TH-i myelinated axons and the observation that the majority of TH-i synapse s were formed with spines rather than with dendritic shafts. (C) 1998 Wiley-Liss, Inc.