Periodicity, amplitude and width of synchronized cardiac sympathetic nerve activity in anaesthetized cats

Using a recently developed method, we studied periodicity, amplitude and width of synchronized cardiac sympathetic nerve activity (CSNA) at various intervals of periodic baroreceptor input in anaesthetized cats. ECG, aortic pressure and CSNA were recorded when cardiac interval was changed by artificial pacing, or when the aortic nerve was stimulated after baroreceptor denervation. The periodicity of synchronized CSNA showed mainly two modes: one was 8-14 Hz rhythmicity (Tc) and the other was related to cardiac cycle (Tb). 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 reflected the interval of inhibition in CSNA due to pulsatile baroreceptor input. The mode of inhibitory rhythm (Ts) related to the stimulation of the aortic nerve was almost constant and independent of the stimulation interval. The probability of the Ts mode was highest at a 250-ms interval and decreased with increase in stimulus interval. The mean peak height or mean peak width did not changed significantly during pacing the heart at various intervals nor after baroreceptor denervation. The peak height and peak width had a significant linear relationship at any cardiac interval or after baroreceptor denervation, whereas no relationship between the peak-to-peak interval and the peak height or peak width was found. These results indicate that the cardiac-related rhythm is produced by inhibition of transmission of the fundamental rhythm by periodic baroreceptor input. Our results suggest also that the amplitude and periodicity of synchronized CSNA are separately regulated.