SPARC: Determining the Projections and Expression Profiles of Neurons of the Stomach‐Brain Axis in Rat

Abstract

Effectors in the stomach receive motor innervation from intrinsic (enteric) neurons, nuclei in the brain stem, the spinal cord and other gut regions. Sensory signals are conducted to the brain, spinal cord and sympathetic ganglia. We are analyzing the circuits by selective pathway lesions, orthograde and retrograde tracing, RNAScope and immunohistochemistry. Regions of stomach were denervated by myectomy (removing a region of myenteric ganglia), bilateral vagotomy or sympathectomy, or combined surgeries. Retrogradely transported fluorescent microbeads were injected selectively into the gastric mucosa or muscle layers. Neuronal markers were localized by multi‐labeling immunohistochemistry. When a region of longitudinal muscle and myenteric ganglia was removed, and 7–10 days allowed for fiber degeneration, nerve fibers in the circular muscle and muscularis mucosae were no longer detected. Two major nerve fiber types innervated the muscle, fibers immunoreactive for neuronal NOS and VIP that are deduced to be inhibitory motor neurons and fibers that were labelled by tachykinins and cholinergic markers that are deduced to be excitatory motor neurons. Some inhibitory fibers were also immunoreactive for gastrin releasing peptide (GRP). The muscle was also innervated by sympathetic (tyrosine hydroxylase positive) nerve fibers. The mucosa received a mixed motor and sensory supply from myenteric ganglia, submucosal ganglia, the vagus, and sympathetic pathways. Denervation studies showed that VIP fibers arose from both myenteric ganglia and the nodose ganglia; thus VIP is in subpopulations of motor and of sensory fibers. Some VIP fibers ended in close relation to ghrelin‐containing enteroendocrine cells. There were few sympathetic endings in the mucosa and CGRP fibers were also rare. Arteries in the gastric wall were triply innervated by sympathetic noradrenaline/ NPY fibers, tachykinin fibers and VIP fibers. The origins of the perivascular VIP fibers have yet to be determined. Injection of retrograde tracer into the gastric mucosa labeled large populations of nodose ganglion neurons. Some nodose ganglion neurons were labeled both from the gastric mucosa and from the external muscle. The chemical phenotypes of myenteric and submucosal ganglia are being investigated. VIP‐immunoreactive cell bodies were numerous in submucosal ganglia. We conclude that there is a complex interplay between nerve endings originating in myenteric, submucosal, nodose, sympathetic and spinal ganglia in gastric effector tissues.Support or Funding InformationNIH/SPARC