Disinhibition of GABA Neurons in the Dorsomedial Hypothalmus by Microinjection of BMI Stimulates Cardiovascular and Gastric Motor Function in Rats
Van Bergen, Andrew H.
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The purpose of the present study was to investigate if the blockade of GABA receptors in the dorsomedial hypothalamus (DMB) of rats produces gastrointestinal changes that resemble stress responses. To test this hypothesis, bicuculline methiodide (BMI), a GABA antagonist, was microinjected into the DMH and surrounding hypothalamic nuclei including the para ventricular nucleus (PVN), of anesthetized rats while recording blood pressure, heart rate, tonic intragastric pressure, and pyloric motility. Microinjection ofBMI (30 pmol/30 nl, n=6) into the DMH elicited significant increases in blood pressure, heart rate, and tonic intragastric pressure. The effect of BMI microinjection into the DMH on gastric motor function was diminished by blockade of peripheral cholinergic pathways by systemic administration of atropine methyl bromide (0.51 mg/kg); whereas, the increases in cardiovascular functions were largely unaltered. Microinjection of BMI outside of the DMH, including the PVN, did not appear to alter indices of gastric motor function. The observations provide the first evidence for a role of GABA in the DMH controlling gastric motor activity. Since the gastric excitatory effect of BMI in the DMH was substantially reduced by atropine, it is likely that vagal cholinergic pathways are being activated by the DMH. In conclusion, this study provides new evidence supporting the DMH as a pivotal hypothalamic region in the stress-autonomic pathway, in addition to its known effect on cardiovascular function.