Two types of rhythm in the respiratory network output in the isolated ventrolateral medulla in the neonatal rats

Abstract

Effects of substance P and extracellular [K +] o on respiratory motor activity in the ventrolateral medulla in neonatal rat (0–4 days old) brainstem-spinal cord preparation were studied. In addition to fictive eupneic rhythm (8–13 bursts/minute), the respiratory motor output was composed of biphasic bursts which might underlie the sigh pattern in vivo. These bursts had considerably lower frequency (0.15–0.86 bursts/minute) and appeared when inspiratory neurons generated augmented biphasic discharges. The two rhythms were differently affected when the respiratory network excitability was increased by substance P or decreased by lowering external [K +] o, the effects on biphasic burst frequency being considerably greater. The augmented bursts could suppress inspiratory, but not pre-inspiratory neuron discharge, suggesting that pre-inspiratory neurons formed a supplementary rhythmic network which was not directly affected by biphasic burst generation.