Blockade of gabaa receptors in the dorsal vagal complex inhibits intestinal motility in hats

Many studies have shown that vagal motor function is important in the regulation of intestinal motility. Although GABAergic inhibitory neurotransmission within the dorsal vagal complex (DVC) modulates autonomie function, there is little information about the tonic influence of GABAA receptor activation within the DVC on intestinal motility. Our aim was to test the hypothesis that microinjection of the GABAA antagonist bicuculline methiodide (BMI) into the DVC alters intestinal motility. Rats were anesthetized and mean arterial pressure (MAP) and heart rate (HR) monitored. Jejunal and colonie motility were measured manometrically and motility indices were calculated manually. BMI (O.SrnM) was administered into the DVC bilaterally through stereotaxically placed micropipettes. The injection sites were confirmed histologically using Aldan Blue. BMI microinjected into the DVC produced a 76.3% inhibition of spontaneous jejunal motility and a 51.7% inhibition of colonie motility. HR decreased by 27.6% and MAP decreased by 23.3%. In a subset of rats (n-4) bilateral cervical vagotomy attenuated the BMI-induced inhibition of spontaneous jejunal and colonie motility. Our observations suggest that within the DVM there is tonic GABAergic regulation of the small intestine and colon by GABAA receptors. Furthermore, BMI-induced inhibition of motility involves either 1) disinhibition of vagal inhibitory fibers or 2) disinhibition of vagal excitatory fibers.