Central distribution of efferent and afferent components of the cervical branches of the vagus nerve. A HRP study in the cat.

Abstract

Central distribution of efferent and afferent components of the cervical branches of the vagus nerve in the cat was studied by applying horseradish peroxidase (HRP) to the superior laryngeal nerve (SLN), pharyngeal branch (PhB), recurrent laryngeal nerve (RLN) or middle portion of the cervical trunk of the vagus nerve (CTV). After applying HRP to the SLN, PhB or RLN, labeled neurons were mainly seen ipsilaterally in the ambiguus nuclear complex (Amb) at levels of the rostral, middle, or caudal portions of the Amb, respectively. After application of HRP to the CTV, labeled neurons were distributed ipsilaterally throughout the Amb. Neurons in the lateral reticular formation medial to the spinal trigeminal nucleus were also labeled ipsilaterally with HRP from the SLN or CTV; these neurons appeared to be the caudal extension of the inferior salivatory nucleus. Neurons within the dorsal motor nucleus of the vagus nerve (DMV) were labeled ipsilaterally only after HRP application to the CTV. The axons of neurons in the rostral Amb and the lateral reticular formation, labeled retrogradely from the SLN or CTV, ran dorsomedially to form a genu in the dorsomedial tegmental region near the floor of the fourth ventricle, and then turned and left ventrolaterally from the medulla oblongata. On the other hand, axons of neurons in the caudal two-thirds of the Amb, labeled retrogradely from the PhB, RLN or CTV, ran dorsomedially to a region ventral to the DMV, where they turned ventrolaterally to form loops before leaving the brainstem. A few axons of neurons in the rostralmost regions of the DMV were also found to form a genu near the floor of the fourth ventricle before running ventrolaterally to leave the brianstem. Axon terminals in the solitary nucleus (Sn) were transganglionically labeled most densely in the medial and interstitial subnuclei from the SLN, in the medial and dorsolateral subnuclei from the RLN, and in the medial and gelatinous subnuclei from the CTV. Application of HRP to the SLN also revealed labeling of axon terminals in the principal sensory and spinal trigeminal nuclei, the medial cuneate nucleus and the dorsal horn of the C1 and C2 cord segments.