Hypoglossal motoneuron responses to pulmonary and superior laryngeal afferent inputs

In decerebrate, paralyzed cats ventilated with a cycle-triggered pump, the inspiratory discharges of the hypoglossal (whole nerve or single fibers), phrenic, and recurrent laryngeal nerves were compared, and the effects of pulmonary and superior laryngeal afferent inputs were observed. During lung inflations in phase with neural inspiration, hypoglossal and recurrent laryngeal activities differed from phrenic with respect to (a) burst onset times: both preceded the phrenic; (b) overall pattern: phrenic, augmenting; hypoglossal, decrementing; recurrent laryngeal, plateau-like. When inflation was withheld, the phrenic pattern was not markedly changed, but both hypoglossal and recurrent laryngeal became augmenting; the marked increase of hypoglossal activity (both whole nerve and single fiber) indicated strong inhibition by lung afferents. Superior laryngeal electrical stimulation evoked excitation of the contralateral phrenic (latency 4.1 msec) and the ipsilateral whole hypoglossal (latency 5.3 msec), followed by bilateral inhibitions (durations 20-30 msec); most hypoglossal fibers showed only inhibition. We conclude that, although both hypoglossal and phrenic outputs are driven by the inspiratory pattern generator(s), their promotor systems differ with respect to influences from central and peripheral inputs.