Participation of the area postrema in cardiovascular control in the dog

Investigations have demonstrated that the pressor effects of low-dose intravertebral angiotensin II (Ang II) in the dog are mediated by the area postrema (AP). Chronic ablation of the AP has been shown to produce both mild hypotension and blunting of the pressor effects of peripherally administered Ang II, which suggests a tonic influence by this structure on the regulation of blood pressure. These findings motivated a correlated series of neurophysiological and anatomical studies to characterize further the AP pressor pathway. The pressor response to electrical stimulation of the AP was shown to be mediated by increased central sympathetic outflow, as shown previously for the response to intravertebral Ang II, and unopposed by the central nervous system baroreflex pathways. Neuroanatomical investigations demonstrated a three-layer structure in the dog's AP, with efferent projections into the medial nucleus tractus solitarii bilaterally. These studies have provided new evidence about the functional and structural mechanisms by which the AP participates in cardiovascular regulation.