Differential dynamic baroreflex regulation of cardiac and renal sympathetic nerve activities

Although regional difference in sympathetic efferent nerve activity has bee n well investigated, whether this regional difference exists in the dynamic baroreflex regulation of sympathetic nerve activity remains uncertain. In anesthetized, vagotomized, and aortic-denervated rabbits, we isolated carot id sinuses and randomly perturbed intracarotid sinus pressure (CSP) while s imultaneously recording cardiac (CSNA) and renal sympathetic nerve activiti es (RSNA). The neural arc transfer function from CSP to CSNA and that from CSP to RSNA revealed high-pass characteristics. The increasing slope of the transfer gain in the frequencies between 0.03 and 0.3 Hz was significantly greater for CSNA than for RSNA (2.96 +/- 0.72 vs. 1.64 +/- 0.73 dB/octave, P< 0.01, n = 9). The difference was hardly explained by the difference in static nonlinear characteristics of CSP-CSNA and CSP-RSNA relationships or by the difference in conduction velocities in the multifiber recording. The se results indicate that the central processing in the brain stem differs b etween CSNA and RSNA. The neural arc of the baroreflex may exert differenti al effects on the heart and kidney in response to dynamic baroreflex activa tion.