The localization of vagal neurons in the terrapin ( Trionyx sinensis) as revealed by the retrograde horseradish peroxidase method

Abstract

After the application of horseradish peroxidase in Nonidet P40 solution to the right cervical vagus in the terrapin, the neurons giving origin to efferent fibers and the transganglionic sensory fibres are labeled. The neurons forming the vagus nerve at the mid-cervical level are located in the dorsal motor nucleus of the vagus nerve (DMX), in the nucleus ambiguus (NA), in an area located ventral to the DMX, and less definitely in the nucleus of the spinal accessory nerve. The DMX and NA neurons are bilaterally distributed with a predominant ipsilateral component. Labeled DMX neurons appear to have a slightly more extensive distribution than those in mammals and their dendrites extend to the nucleus of the tractus solitarius, hypoglossal nucleus (HN), lateral wall and floor of the 4th ventricle and a region dorsomedial to the HN. Some recurrent collaterals of the DMX neurons loop round the medial longitudinal fasciculus to end in a region immediately ventrolateral to the DMX. Transganglionic sensory fibers course with the tractus solitarius and spinal tract of the trigeminal nerve to end in the respective nucleus associated with the tract.