Central connections of the IXth and Xth cranial nerves in the clearnose skate, Raja eglanteria

Abstract

The anterograde and retrograde transport of horseradish peroxidase was utilized to identify the motor nuclei and sensory connections of the IXth and Xth cranial nerves in the clearnose skate, Raja eglanteria. The majority of VIIth, IXth, and Xth nerve motoneurons form an ipsilateral dorsal visceromotor column, extending from the level of the posterior lateral line nerve root to the 3rd–4th ventral spinal roots. Within this column, the motor nucleus of IX (IXm) occurs rostral to vagal motoneurons (dorsal motor nucleus of X, Xmd). Vagal motoneurons are also located ventrolaterally in a ventral motor nucleus (Xmv), which extends from the level of the middle vagal rootlets to the 5th–6th ventral spinal roots. IXth and Xth nerve afferents terminate predominantly in the ipsilateral visceral sensory column (vS). Many vagal but few glossopharyngeal afferents form a solitary tract. A distinct nucleus of the solitary tract could not be identified; rather fibers terminate among cells scattered in the tract, adjacent vS, and nucleus of the commissura infima, where some vagal fibers decussate. Vagal and glossopharyngeal somatic sensory fibers were not found.