Identification of uterine-related sympathetic neurons in the rat inferior mesenteric ganglion: neurotransmitter content and afferent input.

The rat uterus is innervated by sensory and autonomic nerves. Sensory and sympathetic fibers travel in the hypogastric nerves and are associated with the thoracolumbar spinal cord levels T13-L3. The inferior mesenteric ganglion (IMG) contains the somata of sympathetic postganglionic neurons and some of these may project axons to the uterus. Sensory and parasympathetic fibers travel in the pelvic nerve and are associated with the lumbosacral cord levels L6-S1 and pelvic ganglion (PG). We previously reported data concerning the neurochemical anatomy of the PG with regard to the uterine innervation; the present study was undertaken to characterize the neurochemical anatomy of the IMG with regard to it involvement in uterine innervation. A retrograde axonal tracer was used to verify projections of axons of IMG neurons to the uterus. Immunostaining of cryostat sections of the IMG revealed neurons immunoreactive for neuropeptide Y (NPY) and for tyrosine hydroxylase (TH). Immunostaining for the synaptic terminal protein synapsin I (SYN) revealed numerous fine terminals immediately surrounding the principal neurons and in the interneuronal spaces. Varicosities immunoreactive for calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), enkephalin (ENK), substance P (SP) and galanin (GAL) appear to be associated with principal neurons. Additional varicosities stained for nicotinamide adenine dinucleotide phosphate (reduced)-diaphorase (NADPH-d) and nitric oxide synthase (NOS), thus indicating sites of neuronal nitric oxide synthesis. This study revealed that the IMG contains uterine-related neurons and that some of the retrogradely labeled uterine-related neurons contain NPY, TH or both NPY/TH. In addition, uterine-related neurons received abundant afferent inputs indicated by SYN-immunoreactive (-ir) terminals and some of these varicosities labeled for GAL, CGRP, VIP, ENK, or NADPH-d/NOS.