Special Reports and ReviewsNeural emergency system in the stomach☆,☆☆
Section snippets
Innervation of the stomach by extrinsic afferent nerve fibers
The extrinsic afferent nerve fibers supplying the stomach arise from two different sources (Figure 1). The spinal sensory neurons originate from cell bodies in the dorsal root ganglia and reach the stomach via the splanchnic and mesenteric nerves,
Vasodilation caused by afferent neuron stimulation
Stimulation of afferent nerve fibers by short-term intragastric administration of capsaicin causes a marked increase in gastric mucosal blood flow (GMBF; Table 2).14, 15, 16, 17, 18 This effect is brought about by dilation of submucosal arterioles, but not venules,17 and depends on the integrity of the extrinsic afferent innervation of the stomach, because pretreatment of rats with a neurotoxic dose of capsaicin prevents the hyperemic response to sensory neuron stimulation.15 Nerve-selective
Enhancement of gastric mucosal vulnerability by sensory neuron ablation
The ability of sensory neurons to strengthen gastric mucosal resistance to damage was first envisaged when Szolcsányi and Barthó56 discovered that capsaicin-induced ablation of afferent neurons aggravated gastric injury caused by pylorus ligation. Subsequent studies have proved that pretreatment of rats with a neurotoxic dose of capsaicin does not cause damage by itself40, 47, 89, 90, 91 but exacerbates mucosal lesion formation caused by injurious factors such as water immersion restraint
Capsaicin-sensitive afferents as neural emergency system
Although capsaicin-sensitive afferent neurons participate in the physiological regulation of gastric functions, their primary role is to operate as a neural emergency system that is called into operation in the face of pending injury to the stomach but is not tonically active (Figure 6). As a result, blood flow to the stomach is greatly augmented, an effect that facilitates
Acknowledgements
The author thanks Dr. Ulrike Holzer-Petsche for drawing the computer graphs.
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Address requests for reprints to: Peter Holzer, Ph.D., Department of Experimental and Clinical Pharmacology, University of Graz, Universitätsplatz 4, A-8010 Graz, Austria. Fax: (43) 316-380-9645.
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Work performed in the author's laboratory was supported by grants 7845, 9473, 9823, and 11834 from the Austrian Science Foundation; grants 4207, 4905, and 6237 from the Austrian National Bank; and by the Franz Lanyar Foundation at the Medical Faculty of the University of Graz.