ACTIVATION OF THE HYPOTHALAMIC DORSOMEDIAL NUCLEUS STIMULATES INTESTINAL MOTILITY IN RATS

Blockade of gamma-aminobutyric acid(A) (GABA(A)) receptors in the dorsomedial nucleus of the hypothalamus (DMH) in rats induced cardiovascular and behavioral changes resembling those associated with emotional stress. The purpose of this study was to test the hypothesis that microinjection of the GABA antagonist bicuculline methiodide (BMI) into the DMH of anesthetized rats would produce increases in intestinal motility measured manometrically with saline-filled cannulas. Arterial pressure and heart rate were also recorded. Microinjection of BMI (15-30 pmol/15 nl) into the region of the DMH elicited reproducible and dose-related increases in jejunal motility, colonic motility, heart rate, and arterial pressure. Similar microinjection at sites anterior to the DMH 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 reduced. Either vagotomy or treatment with atropine methyl bromide (1 mg/kg iv) blocked the increase in jejunal motility and reduced but did not abolish the colonic stimulation. Increases in heart rate and arterial pressure were essentially unaffected by either intervention. The observations suggest that disinhibition of neurons in the DMH increases jejunal motility through vagal cholinergic pathways and enhances colonic motility through vagal and nonvagal cholinergic and noncholinergic pathways.