PERIODICITY, AMPLITUDE AND WIDTH OF SYNCHRONIZED CARDIAC SYMPATHETIC-NERVE ACTIVITY IN ANESTHETIZED CATS

Using a recently developed method, we studied periodicity, amplitude a nd width of synchronized cardiac sympathetic nerve activity (CSNA) at various intervals of periodic baroreceptor input in anaesthetized cats . EGG, aortic pressure and CSNA were recorded when cardiac interval wa s changed by artificial pacing, or when the aortic nerve was stimulate d after baroreceptor denervation. The periodicity of synchronized CSNA showed mainly two modes: one was 8-14 Hz rhythmicity (Tc) and the oth er was related to cardiac cycle (To). The Tc mode was almost constant and independent of cardiac interval or stimulation. The probability of the Tc mode increased as pacing interval increased. The Tb mode refle cted the interval of inhibition in CSNA due to pulsatile baroreceptor input. The mode of inhibitory rhythm (Ts) related to the stimulation o f the aortic nerve was almost constant and independent of the stimulat ion interval. The probability of the Ts mode was highest at a 250-ms i nterval and decreased with increase in stimulus interval. The mean pea k height or mean peak width did not changed significantly during pacin g the heart at various intervals, nor after baroreceptor denervation. The peak height and peak width had a significant linear relationship a t any cardiac interval or after baroreceptor denervation, whereas no r elationship between the peak-to-peak interval and the peak height or p eak width was found. These results indicate that the cardiac-related r hythm is produced by inhibition of transmission of the fundamental rhy thm by periodic baroreceptor input. Our results suggest also that the amplitude and periodicity of synchronized CSNA are separately regulate d.