The hypothalamus and vagally mediated gastric relaxation.

Experiments, with recording of gastric volume, were performed in chloralosed cats. Topical hypothalamic stimulations produced vagally mediated increases in volume by two mechanisms. One type of response, due to central inhibition of vagal excitatory tone was induced from the defence area and eliminated by atropine or vagotomy. The other type of response, far less commonly encountered, remained after atropine and spinal cord section, but was abolished by vagotomy. The latter type was not induced from any well defined hypothalamic region, and had a high stimulation threshold. While sham feeding in conscious cats with esophagostomy and gastrostomy induced prompt, marked and longlasting gastric volume increases in connection with swallowing, such responses were not evoked as "anticipatory" reaction to food intake;The relaxations could be prevented by vagotomy but not by guanethidine nor atropine. It is concluded that the vagally mediated relaxation in connection with sham feeding occurs mainly from activation of mechanoreceptors and that the hypothalamic control over the vagal relaxatory fibres is probably minor.