Parasympathetic preganglionic neurons in the spinal cord involved in uterine innervation are cholinergic and nitric oxide-containing.

BACKGROUND: The purpose of this study was to elucidate parasympathetic preganglionic neurons in the spinal cord that project axons in pathways to the uterus and to reveal their neurotransmitter phenotype. METHODS: "Uterine-related" neurons were identified by using a combination of retrograde axonal tracers: (1) Fluorogold injected into the ganglia of termination of preganglionic fibers, and (2) a transganglionic axonal tracer (pseudorabies virus) injected into the uterus. Immunohistochemistry was used to reveal virus-labeled neurons and their neurotransmitter marker. RESULTS: Double-labeled (Fluorogold+pseudorabies virus) "uterine" preganglionic neurons were identified in the sacral parasympathetic nucleus of the rat lumbosacral spinal cord. Subpopulations of neurons in the sacral parasympathetic nucleus were shown to be immunoreactive for choline acetyltransferase or nitric oxide synthase. Double-staining immunohistochemistry (for pseudorabies virus+neurotransmitter enzyme) revealed that some of the uterine-related preganglionic neurons were cholinergic and some nitric oxide synthase-containing. CONCLUSIONS: These results demonstrate a subpopulation of preganglionic parasympathetic neurons in the sacral parasympathetic nucleus that are involved in uterine innervation. In addition, both acetylcholine and nitric oxide could be used to modify activity in the postganglionic neurons, which directly innervate the uterus.