ORIGIN OF CARDIAC-RELATED SYNCHRONIZED CARDIAC SYMPATHETIC-NERVE ACTIVITY IN ANESTHETIZED CATS

To study the origin of cardiac-related rhythm in cardiac sympathetic nerve activity (CSNA), 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 in anaesthetized cats. CSNA was averaged by using the R-wave of ECG, or stimulus pulse as a trigger. Delay times from arterial pulse or stimulus pulse to the onset and half amplitude of inhibition and to the maximal inhibition were measured from the averaged data. The delay of inhibition in CSNA was constant and independent of pacing interval. Stimulation of the aortic nerve with single shocks caused an inhibition in averaged CSNA. The delay of inhibition was constant and independent of stimulus frequency. These results indicate that the cardiac-related rhythm in CSNA is produced reflexly by inhibiting the transmission of the fundamental rhythmicity due to periodic baroreceptor input.