Neuronal activity with cardiac rhythm in the nucleus of the solitary tract in cats and dogs. I. Different discharge patterns related to the cardiac cycle.

In anaesthetized, spontaneously breathing cats and dogs, extracellular recordings were made of the spontaneous activities of 28 single neurones with cardiac rhythm. It was confirmed by histological examination that the neurones were situated in the mediodorsal portion of the nucleus of the solitary tract. Different discharge patterns in relation to the heart cycle were demonstrated using R-deflection triggered histograms. Most of the neurones discharged with systolic bursts. In the cat, about half the neurones showed two to three activity peaks in the histograms which could occur at any time of the heart cycle. The height of the various peaks sometimes changed in different ways in the course of the respiratory cycle. It can be concluded that different cardiovascular afferents converge to single neurones. In some neurones it could be shown by elimination of the vagus nerves that the pulse-rhythmical discharge pattern was induced mainly by vagal inputs, mainly by glossopharyngeal inputs or by inputs from both nerves. Two-thirds of the neurones discharging with systolic bursts could be enhanced by increasing the arterial blood pressure. In some of these neurones a proportionality between the number of impulses per heart cycle and the mean arterial blood pressure was found.