Postganglionic sympathetic nerve discharges can contain both central and pulse-related oscillations simultaneously in rabbits.

We examined whether modulation of sympathetic nerve discharges (SND) by changes in carotid sinus pressure (CSP) is influenced by the pattern of the rhythm of central sympathetic neurons and whether the rhythm of the sympathetic nerve derived from central sympathetic neurons and that from the inputs from baroreceptors can coexist in postganglionic renal SND. In alpha-chloralose-anesthetized rabbits with aortic denervation and vagotomy, firing of central sympathetic neurons was at first left spontaneous and then driven artificially at 3 Hz by peroneal nerve stimulation. Under these conditions, renal SND were recorded and compared while CSP was altered at low frequencies. When central sympathetic neurons were firing spontaneously and low frequency oscillation was applied to CSP, two kinds of oscillation were noted in SND; first oscillation at the same frequency as that of central sympathetic neurons, and second oscillation of CSP changes. Power spectra of SND also showed two peaks at these two oscillations. When central sympathetic neurons regularly discharged at 3 Hz by electrical stimulation and CSP was kept constant, the power spectra of SND had a discrete single peak at 3 Hz. When a regular oscillation was applied to CSP at 1 Hz, the amplitude of central sympathetic outflow at 3 Hz was modulated at 1 Hz without disturbance of the frequency of the central 3 Hz rhythm. In other words, two apparently different rhythms coexisted in SND. In the power spectra, two discrete peaks were noted at the frequency of CSP changes and at the central sympathetic oscillation. When SND were averaged by CSP-triggered summation during spontaneous or artificial 3 Hz central firing, it was revealed that the shape of these two averaged SND were completely same in spite of obviously different central firing patterns. Nadir of SND occurred about 400 ms after the peak of CSP during changes in CSP at several frequencies in these two conditions. Thus, these results indicated two points; (1) CSP changes modulate the amplitude of SND in the same manner irrespective of the frequency or pattern of discharge of central sympathetic neurons; (2) both of frequency components of SND induced by oscillatory changes in central sympathetic neurons and oscillatory inhibitory input from baroreceptors can coexist even if their frequencies were different.