By using both light and electron microscopic immunocytochemical methods, Met5-Enkephalin-Arg6-Gly7-Leu8 (
MEAGL)-like immunoreactive structures were detected in the pelvic
ganglion of male rats.
Denervation studies were carried out to determine the origin of these immunoreactive fibers and the projection of immunoreactive neurons within the pelvic
ganglion.
MEAGL-like immunoreactivity was found in numerous axon boutons, some small, intensely fluorescent (SIF) cells, and a few principal
ganglion neurons. Most of the immunoreactive nerve fibers formed pericellular plexuses surrounding the
ganglion cells. In addition, there were a few scattered varicose fibers. These fiber plexuses could be classified into two types: type I (approximately 90% of fibers), which consisted of 80-120 small boutons that synapsed on either the dendrites (80% of cases) or somata (20% of cases) of principal neurons; and type II (approximately 10% of fibers), which consisted of 20-40 larger boutons that formed axodendritic synapses exclusively. After transection of the hypogastric and pelvic nerves, virtually all of the pericellular fiber plexuses disappeared, whereas the scattered varicose fibers remained. According to their ultrastructure, these remaining fibers were considered to arise from SIF cells. Following the injection of
Fast Blue into the bladder wall, some of the
MEAGL-like immunoreactive principal neurons were retrogradely labeled. The results of this study indicate that there are two origins for the
MEAGL-like immunoreactive fibers detected in the pelvic
ganglion: most arise from preganglionic neurons in the spinal cord, and a small proportion may originate from intraganglionic
MEAGL-like immunoreactive SIF cells or principal neurons. Some
MEAGL-like immunoreactive principal neurons may project to the urinary bladder.