NTS neuronal response to conversion from pulsatile to nonpulsatile pressure in isolated carotid sinus baroreceptors

The purpose of this study was to demonstrate the effect of pulsatile pressure (PP) and nonpulsatile pressure (NP) on the carotid sinus baroreceptors and baroreceptor-related neurons in the nucleus tractus solitarius (NTS), using an isolated carotid sinus preparation in anesthetized rats. The baroreceptor activities were recorded from the carotid sinus nerves (CSN). Fifteen baroreceptor-related NTS neurons were recorded extracellularly. Conversion of PP to NP corresponded to a shift from phasic to irregular activity in the CSN and caused an increase in CSN activity at a mean pressure of 100 mm Hg. Under this condition, however, the discharge rate of baroreceptor-related NTS neurons was decreased and the systemic blood pressure was elevated. These results indicate that the increasing baroreceptor afferent input resulting from depulsation was not faithfully transmitted in the NTS, and suggest that the NTS is an important site for modifying the arterial baroreflex under NP.