Synaptic mechanisms regulating cardiovascular afferent inputs to solitary tract nucleus.

This brief review summarizes recent electrophysiological studies concerning the initial processing of cardiovascular afferent inputs within the central nervous system. This work has shown that the site of termination of baroreceptor afferent fibers, the nucleus of the tractus solitarius (nTS), is much more than a simple relay station. Interactions between afferent inputs from different reflexogenic areas and interactions that depend on the timing of the afferent inputs can influence the output of nTS neurons in either an inhibitory or facilitatory manner and thereby determine the signal that these neurons relay to subsequent central nuclei involved in cardiovascular regulation. In addition, descending inputs from more rostral structures (e.g., the hypothalamic defense area and the parabrachial nucleus) can further alter the responsiveness of nTS neurons to baroreceptor inputs. The evidence suggests that the neural substrates exist for a modulation of baroreflex gain at an early stage in the reflex pathway.