ALTERED FREQUENCY-CHARACTERISTICS OF SYMPATHETIC-NERVE ACTIVITY AFTERSUSTAINED ELEVATION IN ARTERIAL-PRESSURE

We tested the hypothesis that sustained elevation in mean arterial pre ssure (MAP) alters the frequency-domain characteristics of efferent sy mpathetic nerve discharge (SND) after the return of MAP to control lev els. Renal, lumbar, and splanchnic SND were recorded before, during, a nd after a 30-min increase in MAP produced by phenylephrine (PE) infus ion in alpha-chloralose-anesthetized, spontaneously hypertensive (SH) rats. The following observations were made. 1) The basic cardiac-locke d pattern of renal, lumbar, and splanchnic SND bursts was altered afte r sustained elevation in MAP, demonstrating prolonged effects on the n eural circuits involved in entraining efferent SND to the cardiac cycl e. Importantly, discharge bursts in afferent baroreceptor nerve activi ty remained pulse-synchronous after sustained increases in arterial pr essure. 2) The frequency-domain relationships between the activity in sympathetic nerve pairs were altered after sustained elevation in MAP, suggesting a transformation from a system of tightly coupled neural c ircuits to one of multiple generators exerting selective control over SND. 3) The most prominent reduction in SND power after sustained elev ation in MAP occurred in the frequency band containing the cardiac cyc le, indicating that the prolonged suppression of SND after sustained i ncreases in arterial pressure is due primarily to the selective inhibi tion of cardiac-related SND bursts. We conclude that sustained elevati on in MAP profoundly affects the neural circuits responsible for the f requency components of basal SND in SH rats.