Localization of dopaminergic markers in the human subthalamic nucleus

The potential role for dopamine in the subthalamic nucleus was investigated in human postmortem tissue sections by examining; (1) immunostaining for t yrosine hydroxylase, the rate-limiting enzyme in catecholamine synthesis; ( 2) binding of [H-3]-SCH23390 (D1-like), [H-3]-YM-09151-2 (D-2-like), and [H -3] mazindol (dopamine uptake); and (3) expression of dopamine D1 and D2 re ceptor mRNAs. Immunostaining for tyrosine hydroxylase was visualized in Bou in's-fixed tissue by using a monoclonal antibody and the avidin-biotin-comp lex method. The cellular localization of the dopamine D1 and D2 receptor mR NAs was visualized by using a cocktail of human specific oligonucleotide pr obes radiolabeled with S-35-dATP. Inspection of immunostained tissue reveal ed a fine network of tyrosine hydroxylase-immunostained fibers traversing t he nucleus; no immunopositive cells were detected. Examination of emulsion- coated tissue sections processed for D1 and D2 receptor mRNA revealed, as e xpected, an abundance of D1 and D2 mRNA-positive cells in the caudate nucle us and putamen. However, no D1 or D2 receptor mRNA-expressing cells were de tected in the subthalamic nucleus. Further, semiquantitative analysis of D1 -like, D2-like and dopamine uptake ligand binding similarly revealed an enr ichment of specific binding in the caudate nucleus and putamen but not with in the subthalamic nucleus. However, a weak, albeit specific, signal for [H -3]-SCH23390 and [H-3]-mazindol was detected in the subthalamic nucleus, su ggesting that the human subthalamic nucleus may receive a weak dopaminergic input. As weak D1-like binding is detected in the subthalamic nucleus, and subthalamic neurons do not express dopamine D1 or D2 receptor mRNAs, toget her these data suggest that the effects of dopaminergic agents on the activ ity of human subthalamic neurons may be indirect and mediated via interacti on with dopamine D1-like receptors. (C) 2000 Wiley-Liss, Inc.