Morphological Study On The Medullary Visceral Zone In The Rat

A total of 105 adult Sprague-Dawley (SD) rats of either sex were used in the present study which was consisted of the following 4 parts:1. CytoarchitectureThe medullary visceral zone (MVZ) in the rat were defined as a neuron band zone from the dorsomedial part to the ventrolateral part in the coronal section of the middle and caudal medulla oblongata (from the level of 1.0mm caudal to the obex, to the level of 0.8mm rostral to the obex) with a width of 0.6mm-1.3mm, being described in levels of the pyramidal decussation(PY), area postrema(AP), obex and 0.8mm rostral to the obex. The names of nuclei within the MVZ were chiefly referred to Paxinos and Watson , Kalia et al.In the Nissl stained coronal sections, gracile nucleus (Gr),cuneate nucleus (Cu), 4th ventricle (4V),medial vestibular nucleus (MVe), and spinal trigeminal nucleus(nSpV) were dorsal and lateral to the MVZ, hypoglossal nucleus (nXII), ventral part of medullary reticular nuclei (MdV) , gigantocellular reticular nucleus(Gi) and lateral paragigantocellular nucleus (LPGi) were ventral and medial to the MVZ. The MVZ was divided into three regions—dorsomedial region (DMR),intermediate region (IMR) and ventrolateral region (VLR).The DMR, with width of about 0.6mm,includes the nucleus tractus solitarii (nTS), dorsal motor nucleus of the vagus nerve (dmnX) and area postrema (AP). The ambiguus nucleus (nA) , lateral reticular nucleus (LRt, including the maganocellular, parvocellular and subtrigeminal subnuclei) and ventrolateral reticular nucleus (nVL) were in the VLR with a width of 1.3mm. The dorsal part of medullary reticular field (MdD) and parvocellular reticular nucleus (PCRt) were in the IMR. Most of the neurons in the IMR were small in size (diameter 10-16μm) , fusiform and spherical in shape with their long axis arranged in dorsomedial-ventrolateral direction.In the Golgi silver stained sections, the neurons in the MVZ were different in size, shape and length of their dendrites (with a few or numerous spines on them) , but type I and II neurons could be classified according to the process lengths and limits of spread. Type I neurons were chracteratized by the extension of their dendrites or axons within the MVZ. Most of them were small in size, fushform and spnerical in shape and short in length of most of their dendrites or axons. A few of type I neurons spread their dendrites or axons throughout every part (DMR,IMR,VLR) of the MVZ. Whearas type II neurons were mainly medium and large in size ,with the spreading of their dendrites or axons beyond the limits of the MVZ. With the extension of dendrites or...