Neuronal activity with cardiac rhythm in the nucleus of the solitary tract in cats and dogs. II. Activity modulation in relation to the respiratory cycle.

In anaesthetized, spontaneously breathing cats and dogs extracellular recordings were made of the spontaneous activities of 28 single neurones with cardiac rhythm. Histological exmaination confirmed that the neurones were situated in the mediodorsal portion of the nucleus of the solitary tract. The neurones, which had already been analysed in respect to their pulse-rhythmical pattern27, were investigated by means of inspiration triggered histograms. The neurones could be grouped according to the respiratory modulations of their activities. Increased activities occurred during (a) the rise of the respiratory blood pressure wave, (b) the respiratory rest period, and (c) the inspiration. Three neurones did not exhibit respiratory modulation. The respiratory modulations of groups a and b were most probably caused by changing inputs from cardiovascular receptors in the course of respiration. It could be shown by adequate stimulation and elimination of the vagus nerves that the neurones of group c were influenced by lung inflation receptors as well as by cardiovascular receptors.