Sustained reduction in blood pressure from electrical activation of the baroreflex is mediated via the central pathway of unmyelinated baroreceptors

Abstract

AimsThis study aims to identify the contribution of myelinated (A-fiber) and unmyelinated (C-fiber) baroreceptor central pathways to the baroreflex control of sympathetic nerve activity and arterial pressure. Main methodsTwo binary white noise stimulation protocols were used to electrically stimulate the aortic depressor nerve and activate reflex responses from either A-fiber (3V, 20–100Hz) or C-fiber (20V, 0–10Hz) baroreceptor in anesthetized Sprague-Dawley rats (n=10). Transfer function analysis was performed between stimulation and sympathetic nerve activity (central arc), sympathetic nerve activity and arterial pressure (peripheral arc), and stimulation and arterial pressure (Stim-AP arc). Key findingsThe central arc transfer function from nerve stimulation to splanchnic sympathetic nerve activity displayed derivative characteristics for both stimulation protocols. However, the modeled steady-state gain (0.28±0.04 vs. 4.01±0.2%·Hz−1, P<0.001) and coherence at 0.01Hz (0.44±0.05 vs. 0.81±0.03, P<0.05) were significantly lower for A-fiber stimulation compared with C-fiber stimulation. The slope of the dynamic gain was higher for A-fiber stimulation (14.82±1.02 vs. 7.21±0.79dB·decade−1, P<0.001). The steady-state gain of the Stim-AP arc was also significantly lower for A-fiber stimulation compared with C-fiber stimulation (0.23±0.05 vs. 3.05±0.31mmHg·Hz−1, P<0.001). SignificanceThese data indicate that the A-fiber central pathway contributes to high frequency arterial pressure regulation and the C-fiber central pathway provides more sustained changes in sympathetic nerve activity and arterial pressure. A sustained reduction in arterial pressure from electrical stimulation of arterial baroreceptor afferents is likely mediated through the C-fiber central pathway.