Reflex effects evoked by stimulation of hypoglossal afferent fibers.

In pentobarbitone-anesthetized cats, electrical stimulation of the central ends of the main trunks of transected hypoglossal nerves evoked vascular (pressor or depressor) reactions, mydriasis, slow and deep breathing, and reflex activation of laryngeal and facial muscles. Stimulation of the central end of the transected ramus descendens hypoglossi also provoked reflex contraction of cricothyroideus. These reflexes may be elicited also after intracranial section of hypoglossal nerve roots, but not after intracranial section of ipsilateral vagal roots. The above reflexes were abolished by acute section of the ipsilateral hypoglossonodosal branch, but they may be reproduced by electrical stimulation of the central end of this anastomotic branch between hypoglossal nerve and nodose ganglion. Stimulation of the central end of one transected hypoglossus evoked reflex efferent discharges in contralateral hypoglossus and contraction of contralateral tongue muscles. Stimulation of the central end of one transected hypoglossal end-branch inhibited efferent discharges in another end-branch. The crossed hypoglossohypoglossal reflex and the ipsilateral reflex inhibition were abolished by section of the hypoglossonodosal branch or vagal roots at the stimulated side. We conclude that reflexes evoked by stimulation of peripheral hypoglossal nerve in cats are mediated by afferent fibers directed to the nodose ganglion and entering the brain stem via vagal roots.