Phrenic, vagal and hypoglossal activities in rat: pre-inspiratory, inspiratory, expiratory components.

During eupnea in an in situ perfused preparation of the rat, inspiratory activities of the hypoglossal and vagal nerves commence before the phrenic; the vagus also discharges in expiration. The hypoglossal discharge has a prominent "pre-inspiratory" component. Power spectral analysis indicated that peak frequencies of oscillations in phrenic, hypoglossal and vagal inspiratory and expiratory activities were the same during eupnea. "Pre-inspiratory" hypoglossal activity had significantly lower peak frequencies. In gasping, "pre-inspiratory" hypoglossal activity ceased and all neural activities became purely inspiratory. High frequency oscillations of phrenic and vagal activities during gasping were shifted upward, compared to those in eupnea, whereas that of the hypoglossal was unaltered. In gasping, the temporal patterns of activities of the phrenic, hypoglossal and vagal nerves, and the level of coherence between these activities implies a restricted and shared set of pre-motor neurons. During eupnea, the activity patterns in the phrenic, hypoglossal and vagal nerves seem to originate from different sets of pre-motor neurons.