ABSTRACT
The distribution of serotonin(5-HT), phenylethanolamine-N-methyltransferase (PNMT), substance P(SP) and leu-enkephalin(L-ENK) immunoreactive neurons in the rostral ventrolateral medulla (RVL) of the cat was studied with the immunohistochemical ABC technique, and the projection of 5-HT, SP and L-ENK positive neurons of the RVL into the thoracic cord was preliminarily investigated by a combined fluorescent retrograde transport and immunofluorescence method. The results indicate that 5-HT, PNMT, SP and L-ENK immunoreactive neurons mentioned above were localized primarily in the caudal part of nucleus paragigantocellularis lateralis and the rostral part of nucleus lateralis reticularis. SP positive cell bodies in the reticular formation close ventrolateral to nucleus ambiguus were also found. Some 5-HT, SP and L-ENK positive cells were situated in the area near the pia mater. In the most area of the RVL, 5-HT, PNMT, SP and L-ENK immunoreactive cell bodies had an overlapping distribution. 5-HT or PNMT or L-ENK positive neurons crowded, intertwined each other with their processes in the region at the levels 1.0-3.5mm caudal to trapezoid body, about 3.3mm lateral to the midline and about 0.8mm from the ventral surface of the medulla, and formed a longer or shorter continuous cell column which ran in the rostrocaudal direction. These three columns nearly coincided with each other at the level 1.5-2.5mm caudal to trapezoid body. Part of 5-HT, SP and L-ENK positive neurons in the RVL projected into the thoracic cord. The functional significance of these substances in the RVL was also discussed.