Tyrosine hydroxylase-immunoreactive somata within the primate subfornical organ: species specificity

The present study describes a collection of tyrosine hydroxylase-immunoreactive (TH-ir) somata within the subfornical organ (SFO) of the Cebus monkey. In contrast, no cell bodies, and only sparse TH-ir fibers, were observed within the SFO in rats. In the monkey, these TH-ir neurons were observed throughout the rostrocaudal extent of the SFO, preferentially located at its lateral and dorsal aspects. These neurons were bipolar and multipolar with long, beaded, varicose fibers emanating from the cell soma. Cebus monkeys displayed dopamine beta hydroxylase and phenylethanolamine-N-methyltransferase- immunoreactive within established noradrenergic and adrenergic nuclei respectively, but not within the SFO, suggesting that the neurons which are immunoreactive for TH in this region contain dopamine.