ABSTRACT
The nucleus tractus solitarii (NTS) is the site of termination of visceral afferent nerve fibers from numerous peripheral cardiovascular and noncardio-vascular mechano- and chemoreceptors. 1-5 Thus, neurons in NTS participate in the first synapse of a number of important polysynaptic visceral reflex pathways. Among these are high- and low-pressure arterial baroreceptor reflexes, arterial and cardiac chemoreceptor reflexes, gastric mechanoreceptor and chemoreceptor reflexes, pulmonary stretch receptor reflexes, and gustatory reflexes, to name but a few. There is a degree of topographic organization to this important nucleus, 1,2 but there is also considerable overlap of the functional organization and of the afferents that terminate in specific subnuclei. 6-9 Indeed, some neurons respond identically to two different afferent signals, while others manifest opposite responses to the same stimuli, and yet others in the same region respond to but one of the afferent signals. 10-13 Likewise, exogenous stimuli delivered to the same region of the nucleus may produce a multitude of responses ranging from gastric, through cardiopulmonary, to cerebral cortical. 8,14-16 However, composite responses from activation of any one site are clearly dependent upon the degree to which the stimulus is restricted within a certain volume of tissue 17 and to the degree of specificity of the stimulus itself. 18,19 Thus, opposing responses may occur either when identical stimuli are delivered at two distinct, though proximate, sites or when different stimuli are delivered at the same site.
