Post-stimulus facilitatory and inhibitory effects on respiration induced by chemical and electrical stimulation of thin-fiber muscular afferents in dogs.

In anesthetized, vagotomized, paralyzed, and artificially ventilated dogs, respiratory responses to both electrical stimulation of the muscle nerve and chemical stimulation of muscular (polymodal) receptors by means of intra-arterial injection of NaCl solution were studied by recording phrenic nervous discharges. During the period of stimulation both types of stimulation caused intensity-dependent facilitation of neural respiratory outputs. After cessation of stimulation, facilitation persisted for a long time (more than 5 min) with a lower intensity stimulation; however, suppression was observed with a higher intensity stimulation. The present results suggest that afferent inputs from the muscular polymodal receptors activate long-acting central mechanisms for enhancement or suppression of respiration.