Morphological analysis of vagal input to gastrin releasing peptide and vasoactive intestinal peptide containing neurons in the rat glandular stomach.

Vagal preganglionic efferents to the rat stomach were labeled anterogradely by injecting the fluorescent carbocyanine dye DiA into the dorsal motor nucleus in vivo. Enteric neurons were labeled in toto by intraperitioneal administration of Fluorogold, and neurochemically characterized by simultaneous single- and double-label immunocytochemistry. Single peptide immunocytochemistry revealed that in all three major areas of the stomach, about one-third of all gastrin-releasing peptide immunoreactive (GRP-IR) neurons in the myenteric plexus, received vagal contacts. Because the proportion of GRP-IR neurons was 32% in the fundus, 23% in the corpus, and only 8% in the antrum, the absolute number of vagally contacted GRP-IR neurons per cm2 was also different. Double-label immunocytochemistry revealed colocalization of vasoactive intestinal peptide immunoreactivity (VIP-IR) in 45%, and of enkephalin immunoreactivity (ENK-IR) in about 30%, of the GRP-IR myenteric neurons. A subpopulation of myenteric neurons colocalized GRP-IR and VIP-IR and projects almost exclusively to the gastrin cell-rich basal mucosa of the antrum and the oxyntic mucosa of the corpus. Another subpopulation containing GRP-IR, but not VIP-IR, projects mainly to the myenteric plexus itself and the external muscle layers, particularly the longitudinal muscle. A third group of neurons containing VIP-IR but not GRP-IR projects heavily to the circular muscle layer, the muscularis mucosae, and to other myenteric neurons. Vagal input to these three subpopulations seems not to be selective, in that an equal proportion of about 20 to 30% of each group was vagally contacted. Vagal inputs to these neurochemically and topographically distinct enteric neurons provide the basis for the physiological vagal control of gastrin release, gastric acid secretion, and gastric motility.