SYNCHRONIZATION OF CARDIAC-RELATED DISCHARGES OF SYMPATHETIC-NERVES WITH INPUTS FROM WIDELY SEPARATED SPINAL SEGMENTS

We used phase spectral analysis to study the relationships between the cardiac-related discharges of pairs of postganglionic sympathetic ner ves in urethan-anesthetized or decerebrate cats. Phase angle when conv erted to a time interval should equal the difference in conduction tim es from the brain to the nerves (i.e., transportation lag) if their ca rdiac-related discharges have a common central source. Transportation lag was estimated as the difference in the onset latencies of activati on of the nerves by electrical stimulation of the medulla or cervical spinal cord. The phase angle for the cardiac-related discharges of two nerves was not always equivalent in time to the transportation lag. F or example, in some cases the cardiac-related discharges of the renal nerve were coincident with or led those of the inferior cardiac nerve. In contrast, the electrically evoked responses of the renal nerve lag ged those of the inferior cardiac nerve by greater than or equal to 32 ms. These observations are consistent with a model of multiple and dy namically coupled brain stem generators of the cardiac-related rhythm, each controlling a different sympathetic nerve or exerting nonuniform influences on different portions of the spinal sympathetic outflow.