Immunohistochemical evidence for a new group of catecholamine-containing neurons in the basal forebrain of the monkey.

Using a specific antibody to the catecholamine (CA) synthesizing enzyme, tyrosine hydroxylase (TH), in combination with the avidin-biotin-peroxidase complex method, we have found evidence for the existence of a new CA-containing cell group extending from the orbitofrontal cortex through the olfactory and pyriform cortices in the brain of two species of monkey. The TH-positive perikarya, which are 4000-5000 in number, are situated within the outer layers of these cortices and also within the olfactory tubercle and horizontal limbs of the diagonal band of Broca. They have small (10-20 microns) somata of round or oval shape. A majority are bipolar with long, slender dendrites but some are small, multipolar with widely branching dendrites. The shape and laminar distribution of these TH-positive neurons suggest that they may serve functions as cortical interneurons.