Abstract
The present study examined the potential contribution of the arterial baroreflex to the differential responses of renal (RSNA) and lumbar sympathetic nerve activity (LSNA) and heart rate (HR) observed during freezing behavior, which was reported previously (FASEB J. 21:6 A882, 2007). Male Wistar rats were chronically instrumented with electrodes for measurements of RSNA, LSNA, and electrocardiogram, and with arterial and venous catheters. At least three days after the surgery, rats were exposed to white noise with 90dB over 10 min following a 60 min control period. The baroreflex curve for RSNA, LSNA and HR was determined by changing systemic arterial pressure using rapid intravenous infusions of vasoactive drugs and then fitted to an inverse sigmoid function curve. During the freezing behavior, the baroreflex curve for RSNA was shifted upward with a significant (P<0.05) increase in the response range of 115% compared with control level; while the baroreflex curve for LSNA remained unchanged during freezing behavior. The baroreflex curve for HR was shifted leftward with a significant (P<0.05) decrease in the midpoint pressure of 11mmHg relative to the control level. These data suggest that the differential responses of RSNA, LSNA and HR observed during freezing behavior may be explained, in part, by differential shifts in baroreflex curves for RSNA, LSNA and HR in rats.
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