CARDIAC RHYTHMICITY AMONG NTS NEURONS AND ITS RELATIONSHIP TO SYMPATHETIC OUTFLOW IN RABBITS

The caudal nucleus tractus solitarius (NTS) is the primary termination site for baroreceptor afferents, but distinct pulse phasic activity is rarely recorded from NTS neurons. In the present study cross-correlation analysis was used to identify pulse phasic activity in NTS neurons in the anesthetized rabbit. Crosscorrelation analysis demonstrated that 19 of 38 pressure-sensitive neurons had activity that correlated with the cardiac cycle, including 5 of 11 neurons activated by aortic depressor nerve stimulation, and 12 of 28 pressure-sensitive NTS neurons had activity that correlated with renal sympathetic nerve activity. Autocorrelation analysis identified 17 of 38 pressure-sensitive neurons that had rhythmic activity not related to the cardiac cycle (mean frequency 14.1 +/- 2 Hz). The results indicate that many NTS neurons do have pulse phasic activity consistent with baroreceptor input, but this activity is difficult to detect because it is distributed throughout the cardiac cycle.