Central distribution of afferent and efferent components of the glossopharyngeal nerve: an HRP study in the cat.

Central distribution of efferent and afferent components of the glossopharyngeal (IX) nerve in the cat was studied by applying horseradish peroxidase (HRP) to the lesser petrosal nerve (LPN), carotid sinus nerve (CSN) or cervical trunk (CT) distal to the branching point of the CSN. After applying HRP to the LPN or CT, HRP-labeled neurons were distributed ipsilaterally in the lateral regions of the reticular formation from the caudalmost levels of the facial nerve genu to the rostral levels of the solitary nucleus. HRP-labeled axons of these neurons ran dorsomedially and then medially along the ventral borders of the medial vestibular nucleus and the facial nerve genu, to form a small genu rostrally at the regions medial to the facial genu and caudally at the medial tip of the medial vestibular nucleus. Subsequently, the labeled axons coursed ventrolaterally to exit from the brain stem with other IX nerve components. After HRP application to the CT, labeled neurons were also seen ipsilaterally within the rostral most levels of the nucleus ambiguous, and labeled fibers were traced ipsilaterally to the medial and interstitial subnuclei of the solarity nucleus, dorsolateral portions of the spinal trigeminal nucleus at the caudalmost levels of the alaminar parts, and ventrolateral regions of the medial cuneate nucleus. Afferent components of the CSN ended ipsilaterally in the medial subnucleus, and bilaterally in the commissural subnucleus of the solitary nucleus; within the medial subnucleus, the CSN terminals located more dorsolaterally than the CT terminals. No efferent components were found in the CSN.