THE AMPLITUDE OF SYNCHRONIZED CARDIAC SYMPATHETIC-NERVE ACTIVITY REFLECTS THE NUMBER OF ACTIVATED PRE-GANGLIONIC AND POSTGANGLIONIC FIBERS IN ANESTHETIZED CATS

In order to obtain information regarding the number of pre- and postga nglionic fibers that are firing, we measured cardiac sympathetic nerve activity (CSNA) before and after the successive sectioning of T1-T5 t horacic rami in anesthetized cats. Total activity from the area was me asured under the mean CSNA curve. Peak amplitude, width and periodicit y of the synchronized discharge was analyzed from the CSNA curve by th e method we developed. Total CSNA decreased to 91+/-6%, 63+/-6%, 27+/- 10%, 8+/-6% and < 1% of the control due to successive section of the T 5, T4, T3, T2 and TI rami, respectively. The peak amplitude of synchro nized CSNA decreased to 95+/-6%, 73+/-8%, 40+/-5% and < 10% of the con trol value, due to section of the T5, T4, T3 and T2 rami, respectively . The control width was 107+/-8 ms and decreased to 106+/-1 ms, 92+/-6 ms and 68+/-5 ms by successive section of the respective T5, T4 and T 3 rami. However, periodicities of 80-120 ms (Tc rhythm) and 140-500 ms (Tb rhythm) of synchronized CSNA remained unchanged after section of the T3-T5 rami. The total CSNA decreased gradually due to decreases in the peak amplitude and width of synchronized CSNA with the successive section of preganglionic fibers. These results indicate that the peak amplitude of synchronized CSNA reflects the number of pre- and post-g anglionic fibers that are firing and suggest that the number of pregan glionic neurons which activate the cardiac fibers naturally was larges t in the T3 segment. The periodicity of the Tc and Tb rhythms of the s ynchronized discharges is, however, constant between the various prega nglionic inputs.