EXCITATION OF BARORECEPTORS DEPRESSES A-COMPONENT AND C-COMPONENT OF THE SOMATO-CARDIAC SYMPATHETIC REFLEX IN ANESTHETIZED RATS

The effect of baroreceptor activation on somato-cardiac sympathetic re flex discharges was examined in urethane-anesthetized, vagotomized, an d artificially ventilated rats. Single shock stimulation of myelinated (A) and unmyelinated (C) fibers in the tibial nerve of the left hindl imb elicited two separate excitatory reflex discharge components in a branch of the cardiac sympathetic nerve, They are termed the A- and C- components of the somato-cardiac sympathetic reflex discharges. When a ortic nerves (AN) and carotid sinus nerves (CSN) were intact, a sudden increase in mean arterial blood pressure to about 150 mmHg induced by i.v. injection of phenylephrine (50 mu g/kg) depressed the A- and C-c omponents by up to 47 +/- 5.4 and 37 +/- 7.7% of the control values, r espectively. However, bilateral sine-aortic denervation completely abo lished the pressure-induced depression of both components. We conclude that baroreceptor afferent signals from the AN and CSN inhibit both A - and C-components of the excitatory somato-cardiac sympathetic reflex discharges. This and other previous evidence mentioned in the text in dicate that inhibitory cardiac sympathetic reflexes originating from a rterial baroreceptors and excitatory ones originating from somatic aff erents interact, probably at the brainstem.