Ventrolateral medullary respiratory neurons and peripheral chemoreceptor stimulation by almitrine

In anaesthetized, paralysed and artificially ventilated dogs, activities were recorded from the phrenic nerve and from respiratory units within the nucleus ambiguus (nA) and within the nucleus retroambigualis (nRA). The respiratory neurons were classified according to their discharge pattern. Almitrine (50 micrograms/kg i.v.) induced an increase in the firing rate of late peak inspiratory neurons (40 units) and in early burst inspiratory cells (10 units) of the nA. In the nRA, almitrine (50 micrograms/kg i.v.) also stimulated late peak expiratory neurons (17 units) and early burst expiratory cells (9 units). It is concluded that the chemoreceptor pathway is not restricted to the inspiratory neurons of the nTS and that both inspiratory and expiratory neurons of the nA and nRA are involved in the chemoreceptor pathway activated by almitrine.