Kainic acid injection into medullary raphe produces gastric lesions through the vagal system in rats

Abstract

There is little evidence of a role of nuclei in the brain stem, other than the dorsal motor nucleus of the vagus nerve in the medulla oblongata, in terms of central mechanisms for gastric ulcer formation. Recent reports suggest that the medullary raphe nuclei may be involved in the central regulation of gastric functions such as gastric acid secretion and motility. In the present study, we examined whether neurons in the nucleus raphe obscurus (NRO) played a significant role in the formation of gastric ulcers with the use of Sprague-Dawley rats. First, we determined whether excitation of the medullary raphe resulted in the development of gastric lesions. Chemical stimulation of neurons in the NRO by kainic acid produced gastric erosions within 4 h in 24-h fasted rats. Saline tested under the same conditions did not modify the integrity of the gastric mucosa. It was also demonstrated that kainic acid injection outside the raphe obscurus boundaries failed to develop gastric lesions. Next, we examined the effects of the vagal system on the gastric lesion formation induced by stimulation of the raphe nucleus. Bilateral gastric branch vagotomies completely prevented the development of the raphe nucleus-provoked gastric mucosal damage. All these results suggest, for the first time, that excitation of neurons in the medullary raphe obscurus induces gastric ulceration through vagal stimulation.