Gastric mucosal protection and central nervous system.

Several human and experimental data suggest the particular importance of gastric protective processes in maintaining mucosal integrity. Both peripheral and central mechanisms are involved in this process. In the periphery, pre-epithelial mucus-bicarbonate layer, mucus, phospholipids, trefoil peptides, prostaglandins, heat shock proteins, sensory neuropeptides, nitric oxide, and hydrogen sulfide may mediate mucosal protection. In the central nervous system hypothalamus and dorsal vagal complex (DVC) have particular important role in the regulation of centrally-induced gastroprotection. Stimulation of paraventricular nuclei either aggravates or inhibits the mucosal injury depending on the ulcer model. Vagal nerve also has a dual role, its activation can induce mucosal injury (by high dose of thyrotropin- releasing hormone (TRH), electrical stimulation), however, integrity of vagal nerve is necessary for gastroprotection induced either peripherally (by PGE2, prostacyclin, adaptive cytoprotection), or centrally (e.g. by neuropeptides). The centrally induced gastroprotection is likely to be vagal dependent, though vagal independent pathways have also been shown. Endomorphin-1 and endomorphin-2, selective μ-opioid receptor ligands, proved to be highly potent and effective gastroprotective agents in ethanol ulcer model (0.03-3 pmol intracerebroventricularly). Inhibition of the degradation of endomorphins by diprotin A resulted in gastroprotective effect, indicating the potential role of these endogenous opioids in the regulation of gastric mucosal integrity. Endomorphin-2 injected intracerebroventricularly restored the reduced levels of CGRP and somatostatin in gastric mucosa induced by ethanol. In conclusion, neuropeptides expressed in dorsal vagal complex and hypothalamus may have a regulatory role in maintaining gastric mucosal integrity by stimulating the formation of mucosal protective compounds.