Differential dynamic control of cardiac and splanchnic sympathetic nerve activity by the arterial baroreflex

The arterial baroreflex is the primary negative feedback system involved in stabilizing arterial pressure from external disturbances. Determining the dynamic characteristics of the baroreflex is important for our understanding of the mechanisms involved in rapid restoration of arterial pressure. This study examined the differences in the dynamic baroreflex control of cardiac (CSNA) and splanchnic (SSNA) sympathetic nerve activity. The baroreceptor region of the right aortic depressor nerve was isolated from the systemic circulation to control baroreceptor region pressure (BRP) with a Gaussian white noise signal while simultaneously recording CSNA and SSNA in anesthetized Sprague-Dawley rats. SSNA was recorded from a postganglionic branch of the splanchnic sympathetic nerve and CSNA was recorded from a branch of the left stellate ganglion. Neural arc transfer functions from BRP to SSNA (H_SSNA) and BRP to CSNA (H_CSNA) displayed derivative characteristics. When dynamic gain below 0.03 Hz was normalized to unity, H_SSNA had a higher gain at frequencies 0.1 and 1 Hz and increasing slope from 0.1 to 1 Hz relative to H_CSNA. The peak decrease in the step response was higher for SSNA than CSNA. These data indicate differential dynamic baroreflex control of SSNA and CSNA. Rapid changes in baroreceptor pressure input would result in a larger response in SSNA compared with CSNA.