Medullary catecholamine inputs to the anteroventral third ventricular cardiovascular regulatory region in the rat

Lesions in the tissue at the anteroventral end of the third ventricle (AV3V area) prevent the development of a variety of forms of experimental hypertension. This region receives afferents from several cell groups which have been implicated in cardiovascular regulation, including the nucleus of the solitary tract and neurons in the ventrolateral medulla. About 70% of the nucleus of the solitary tract neurons which could be retrogradely labeled from the AV3V area stained immunohistochemically for tyrosine hydroxylase, but not phenylethanolamine-N-methyltransferase, and were therefore presumably noradrenergic. About half of the neurons in the rostral part of the ventrolateral medulla which innervated the AV3V area stained for both enzymes, and thus were apparently adrenergic. These medullary catecholaminergic inputs to the AV3V area may be of importance in explaining recent data concerning the roles of both regions in experimental hypertension.