TRKA NGF RECEPTOR EXPRESSION BY NONCHOLINERGIC THALAMIC NEURONS

EXPRESSION of the trkA receptor for nerve growth factor was analyzed b y mRNA in situ hybridization in the telencephalon and diencephalon in adult rats. Two densely packed populations expressing trkA mRNA were d etected in the thalamus, in the paraventricular thalamic nucleus anter ior and reuniens thalamic nucleus. These neurons did not express mRNA coding for choline acetyltransferase. In basal forebrain and striatum, trkA and choline acetyltransferase mRNAs showed identical patterns of expression, supporting the view that trkA expression is confined to c holinergic population in these areas. In contrast, cholinergic neurons of the medial habenula did not express trkA mRNA. Our findings sugges t the existence of previously undiscovered populations of non-choliner gic, NGF responsive populations in the thalamis.