Lateral parabrachial nucleus modulates baroreflex regulation of sympathetic nerve activity.

Previous studies have demonstrated that the lateral parabrachial nucleus (LPBN) is an important site for descending modulation of baroreflex control of heart rate. In the present study it was hypothesized that the LPBN neurons may also modulate baroreflex control of arterial pressure and sympathetic nerve activity. In urethan-anesthetized rats, electrical or chemical activation of the LPBN produced a significant reduction in the magnitude of the baroreflex inhibition of mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) elicited by aortic depressor nerve stimulation. Chemical inactivation of the LPBN resulted in a small increase in baroreflex control of MAP, but baroreflex control of RSNA was not affected. The results suggest that LPBN neurons have little tonic influence over baroreflex control of MAP and RSNA in the anesthetized rat. When the LPBN is activated, however, LPBN neurons may function to reduce the capacity of the baroreflex to regulate sympathetically mediated increases in arterial pressure.