Discharge pattern of neurons in the nucleus tractus solitarii (NTS): its cardiac rhythm is modulated by firing rate of the neurons.

In the nucleus tractus solitarii (NTS) neurons discharge in relation to cardiac rhythm. This cardiac rhythm exhibits various patterns designated as CRDPs (cardiac rhythmic discharge patterns). The CRDPs are estimated by post-event-time histograms (PETH) triggered by the R-waves of the ECG. Modulations of CRDPs appear as changes in the number and height of peaks in the PETHs. The amount of basic activity, which is not related to the cardiac cycle, alters CRDP. PETHs constructed during various phases of respiration reveal modulations of CRDPs within the respiratory cycle. As our previous work indicated, the NTS neurons exhibit typical reticular rhythms. In this paper we also found that the basic activity of NTS neurons was often changed by other influences for which no comparable patterns could be observed in other simultaneously acquired signals. When we constructed PETHs according to the activity level of the NTS neurons, i.e., firing level per cardiac cycle, modulations of CRDPs which were even stronger than respiratory or reticular rhythmical modulations became clear. The modulations of CRDPs caused by different origins were found to be present in the same neuron interlaced in time. The possible role played by these modulations of CRDPs in the coordination of different functional systems in the organism is discussed.