ACTIVATION OF THE HYPOTHALAMIC DORSOMEDIAL NUCLEUS STIMULATES INTESTINAL MOTILITY IN RATS

Blockade of gamma-aminobutyric acid(A) (GABA(A)) receptors in the dors omedial nucleus of the hypothalamus (DMH) in rats induced cardiovascul ar and behavioral changes resembling those associated with emotional s tress. The purpose of this study was to test the hypothesis that micro injection of the GABA antagonist bicuculline methiodide (BMI) into the DMH of anesthetized rats would produce increases in intestinal motili ty measured manometrically with saline-filled cannulas. Arterial press ure and heart rate were also recorded. Microinjection of BMI (15-30 pm ol/15 nl) into the region of the DMH elicited reproducible and dose-re lated increases in jejunal motility, colonic motility, heart rate, and arterial pressure. Similar microinjection at sites anterior to the DM H into or nearer to the hypothalamic paraventricular nucleus elicited significantly attenuated cardiovascular effects accompanied by either no change in intestinal function or changes that were significantly re duced. Either vagotomy or treatment with atropine methyl bromide (1 mg /kg iv) blocked the increase in jejunal motility and reduced but did n ot abolish the colonic stimulation. Increases in heart rate and arteri al pressure were essentially unaffected by either intervention. The ob servations suggest that disinhibition of neurons in the DMH increases jejunal motility through vagal cholinergic pathways and enhances colon ic motility through vagal and nonvagal cholinergic and noncholinergic pathways.