FORCED-OSCILLATIONS IN SYMPATHETIC-NERVE DISCHARGE

Periodic electrical stimulation of the medullary raphe or lateral tegmental field in baroreceptor-denervated cats was used to force the central systems responsible for the 10-Hz and 2- to 6-Hz rhythms in postganglionic sympathetic nerve discharge (SND). The 10-Hz rhythm in SND could be entrained either to the frequency of medullary stimulation or to harmonics of the stimulus frequency. The harmonic of the stimulus frequency to which the 10-Hz rhythm was entrained in one postganglionic nerve could be different from that in another nerve. On this basis, we propose that the circuits responsible for the 10-Hz rhythms in SND may be modeled as a system of coupled nonlinear oscillators, each of which either influences one postganglionic nerve or nonuniformly affects different postganglionic nerves. The relatively wide band 2- to 6-Hz component in SND could be forced into a stable oscillatory state by medullary stimulation at frequencies between 3 and 5 Hz. This observation is consistent with the view that the 2- to 6-Hz component reflects the complex behavior of a nonlinear oscillator rather than the output of a physiological noise generator.