Nucleus tractus solitarii respiratory neurons in the chemoreceptor pathway activated by almitrine

In anaesthetized, paralysed and artificially ventilated dogs, activities were recorded from the phrenic nerve and from respiratory units within the nucleus tractus solitarii (NTS). The inspiratory neurons were classified according to their discharge pattern and their response to lung inflation. Two categories of cells with an augmenting discharge pattern were detected: the R alpha inspiratory neurons (18 units) inhibited by lung inflation and the R beta cells (10 units) activated by inflation. Prolonged stimulation of peripheral chemoreceptors by almitrine (50 micrograms/kg i.v.) induced an increase in the firing rate of R alpha and R beta inspiratory neurons. In addition almitrine stimulated R beta cells classified as expiratory-inspiratory units. Two expiratory neurons were found in the NTS and the firing rate of these cells was enhanced by almitrine. It is concluded that the NTS respiratory neurons are strongly involved in the chemoreceptor pathway activated by almitrine.