Organization of thoracic sympathetic afferent influences on renal nerve activity

Abstract

The specific influences of thoracic sympathetic afferent nerves on sympathetic outflow to the kidney were not clearly defined, although preliminary experiments have shown that electrical stimulation of these afferent nerves causes excitation of multifiber renal nerve activity followed by inhibition of discharge. The organization of this complex reflex was investigated further in anesthetized, vagotomized, sinoaortic-denervated cats. The apparent ability of the cardiopulmonary afferent nerves to excite and then inhibit multifiber renal nerve activity initially was attributed to opposite responses of individual renal neurons to afferent stimulation. This hypothesis was not confirmed because many single postganglionic renal fibers responded to electrical afferent stimulation with excitation followed by inhibition of discharge. Alternatively, the possibility was considered that different thoracic sympathetic afferent neurons have opposite influences on renal nerve activity. Sympathetic afferent fibers activated by stretch of the ventricles or aorta caused reflex excitation of renal nerve activity, whereas activation of afferent fibers from the pulmonary vasculature caused an inhibition of this discharge. The complexity of thoracic sympathetic afferent influences on sympathetic outflow to the kidney is likely related to heterogeneity within the afferent rather than efferent neural population.