FASTER GASTRIC-EMPTYING OF A LIQUID MEAL IN RATS AFTER HYPOTHALAMIC DORSOMEDIAL NUCLEUS LESION

The effects of dorsomedial hypothalamic (DMH) nucleus lesion on body w eight, plasma glucose levels, and the gastric emptying of a liquid mea l were investigated in male Wistar rats (170-250 g). DMH lesions were produced stereotaxically by delivering a 2.0-mA current for 20 s throu gh nichrome electrodes (0.3-mm tip exposure). In a second set of exper iments, the DMH and the ventromedial hypothalamic (VMH) nucleus were l esioned with a 1.0-mA current for 10 s (0.1-mm tip exposure). The medi al hypothalamus (MH) was also lesioned separately using a nichrome ele ctrode (0.3-mm tip exposure) with a 2.0-mA current for 20 s. Gastric e mptying was measured following the orogastric infusion of a liquid tes t meal consisting of physiological saline (0.9% NaCl, w/v) plus phenol red dye (6 mg/dl) as a marker. Plasma glucose levels were determined after an 18-h fast before the lesion and on the 7th and 15th postopera tive day. Body weight was determined before lesioning and before sacri ficing the rats. The DMH-lesioned rats showed a significantly faster ( P<0.05) gastric emptying (24.7% gastric retention, N = 11) than contro l (33.0% gastric retention, N = 8) and sham-lesioned (33.5% gastric re tention, N = 12) rats, with a transient hypoglycemia on the 7th postop erative day which returned to normal by the 15th postoperative day. In all cases, weight gain was slower among lesioned rats. Additional exp eriments using a smaller current to induce lesions confirmed that DMH- lesioned rats had a faster gastric emptying (25.1% gastric retention, N = 7) than control (33.4% gastric retention, N = 17) and VMH-lesioned (34.6% gastric retention, N = 7) rats. MH lesions resulted in an even slower gastric emptying (43.7% gastric retention, N = 7) than in the latter two groups. We conclude that although DMH lesions reduce weight gain, they do not produce consistent changes in plasma glucose levels . These lesions also promote faster gastric emptying of an inert liqui d meal, thus suggesting a role for the DMH in the regulation of gastri c motility.