Pneumotaxic mechanisms influence phrenic, hypoglossal, and trigeminal activities

The influence of the pneumotaxic center on activities of the phrenic, hypoglossal, and trigeminal nerves was investigated in decerebrate, vagotomized, paralyzed, and ventilated cats. Stimulation of the pneumotaxic region caused a premature termination of activity of the phrenic nerve. Currents required for terminating this activity decreased during inspiration. Inspiratory hypoglossal and trigeminal activities were terminated concomitant with phrenic activity. The expiratory duration following stimulus-induced cessation of inspiration was directly related to inspiratory duration. During expiration, trigeminal activity was greatly augmented; a hypoglossal burst was also recorded in some trials. Stimulations in expiration elicited premature onsets of phrenic, hypoglossal, and trigeminal activities. The currents required declined during expiration. The durations of neural inspiration and expiration and peak phrenic and hypoglossal activities which followed stimulus-induced terminations of expiration approximated prestimulation values. Phasic trigeminal and expiratory hypoglossal activities were greatly augmented. Currents required for terminating either inspiratory or expiratory phases were augmented in hypercapnia. The data support pneumotaxic mechanisms as producing global onsets or terminations of inspiratory activity. Respiratory motoneurons of the brain stem and spinal cord differ in their sensitivities to efferent influences from the pneumotaxic center.