Differential relationships among discharges of postganglionic sympathetic nerves.

The relationships among the simultaneously recorded discharges of as many as four postganglionic sympathetic nerves were studied with coherence and phase spectral analyses in baroreceptor-denervated cats. Discharges were recorded from the inferior cardiac (CN), vertebral (VN), and renal (RN) nerves. Most of the power in sympathetic nerve discharge was less than 6 Hz, and the discharges of any two nerves coherred over a frequency band generally between 0 and 15 Hz. Peak coherence occurred between 2 and 6 Hz in most cases. Our most important observations are as follows. 1) Coherence values were significantly higher in chloralose-anesthetized than in unanesthetized decerebrate cats. 2) Coherence values were higher for near ipsilateral nerves (e.g., CN and VN) than for widely separated ipsilateral nerves (e.g., CN and RN). 3) Coherence values for most pairs were higher when the nerves were located on the same side (ipsilateral nerves) rather than on opposite sides (contralateral nerves) of the body. 4) Coherence values were higher for some functionally complementary nerves (e.g., CN and RN) than for noncomplementary nerves (e.g., VN and RN). These results support the hypothesis that the central circuits responsible for the basal discharges of different postganglionic sympathetic nerves are selectively coupled.