CARDIOVASCULAR INFLUENCES ON RAT PARABRACHIAL NUCLEUS - AN ELECTROPHYSIOLOGICAL STUDY

The rat pontine parabrachial nucleus is a prominent recipient of autonomic-related information from the more caudal levels of the neuraxis. The present experiments examined the responsiveness of neurons within the parabrachial nucleus to the following three specific cardiovascular stimuli: the activation of peripheral arterial baroreceptors, right atrial stretch receptors, and the administration of systemic angiotensin (ANG) II. Extracellular recordings in urethan-anesthetized animals indicate the presence of cells, mostly within the lateral parabrachial nucleus, that increase (17.5%, 28 of 160 cells) and decrease (48.1%, 77 of 160 cells) their excitability consequent to baroreceptor activation. A similar profile of alteration in cellular firing rates was observed with intravenous ANG II (increase in 15.8%, 16 of 101 cells; decrease in 28.7%, 29 of 101 cells). In contrast, fewer neurons located within the medial parabrachial and the Kolliker-Fuse nuclei were activated by these stimuli. A majority of cells (80%, n = 15) displayed a lack of response to right atrial stretch receptor activation. Of ANG II-sensitive lateral parabrachial cells, 23% (n = 43) revealed an alteration in excitability that could not be explained on the basis of a response to elevation in blood pressure. It is possible that this group of cells may be activated by the actions of systemic ANG II on neurons of the area postrema, a circumventricular structure, whose central projections are directed toward the parabrachial nucleus. These findings also support the notion of a diversity of cardiovascular inputs to topographically segregated regions within the parabrachial nucleus.