Ghrelin对糖尿病大鼠下丘脑弓状核胃牵张敏感神经元放电活动及胃运动的调控

Effects of ghrelin on firing activity of gastric distension-sensitive neurons in hypothalamic arcuatus nucleus and gastric motility in diabetic rats

目的:观察链脲佐菌素(STZ)所致糖尿病(DM)大鼠下丘脑弓状核(Arc)胃牵张(GD)敏感神经元放电活动及胃运动改变,探讨ghrelin对DM大鼠下丘脑Arc GD敏感神经元放电活动和胃运动的影响。方法:采用STZ腹腔注射诱导DM大鼠模型;通过细胞外记录神经元单位放电和在体胃运动方法,观察ghrelin及其受体阻断剂[D-Lys3]-GHRP-6对DM大鼠下丘脑Arc GD敏感神经元自发放电活动和胃运动的影响;应用real-time PCR和荧光免疫组化方法,探讨DM大鼠Arc内ghrelin受体(GHS-R1a)mRNA及其免疫阳性物的表达。结果:在正常大鼠Arc记录到的98个GD敏感神经元中,64.3%为GD兴奋性(GD-E)神经元,35.7%为GD抑制性(GD-I)神经元。在63个GD-E神经元中,Arc微量注射ghrelin可使其中73.0%神经元兴奋,其放电频率与生理盐水组比较显著增加(P<0.05);而在35个GD-I神经元中,Arc微量注射ghrelin可抑制其中60.0%神经元,放电频率显著降低(P<0.01);ghrelin改变GD神经元放电效应可被ghrelin受体阻断剂[D-Lys3]-GHRP-6阻断(P<0.05);在DM大鼠,Arc记录到的66个GD敏感神经元中有56.1%为GD-E神经元,43.9%为GD-I神经元。Arc注射ghrelin可兴奋其中35.1%GD-E神经元,放电频率与生理盐水比较显著增加(P<0.05);而在29个GD-I神经元中,ghrelin可抑制其中21个神经元(72.4%),放电频率显著降低(P<0.01)。与正常大鼠比较,DM大鼠Arc GD敏感神经元中的GD-E和GD-I比例无显著改变(P>0.05),但ghrelin使GD-E神经元兴奋的比率明显降低(P<0.05),放电频率平均增加率也显著下降(P<0.05);但ghrelin使GD-I神经元抑制比率和放电频率平均减少率均无显著改变(P>0.05)。在体胃运动研究结果显示,Arc微量注射ghrelin,可显著促进正常和DM大鼠胃运动,且呈显著量效关系(P<0.05,P<0.01),但ghrelin对正常大鼠的促胃运动作用显著强于其对DM大鼠的作用(P<0.05),[D-Lys3]-GHRP-6可完全阻断ghrelin该作用。Real-time PCR研究结果显示,DM大鼠下丘脑Arc GHS-R1a mRNA表达较正常大鼠明显减少(P<0.05);免疫荧光研究进一步证实DM大鼠下丘脑Arc GHS-R1a免疫阳性物表达较正常大鼠明显减少(P<0.05)。结论:下丘脑Arc ghrelin参与DM大鼠GD敏感神经元自发放电活动,并参与胃运动的调控,该效应可能是通过作用于ghrelin受体而实现的。

AIM： To study the roles of ghrelin in the regulation of gastric distension （GD） -sensitive neurons in the hypothalamic arcuate nucleus （Arc） and gastric motility in diabetes mellitus （DM） rats. METHODS： DM rat model was made by intraperitoneal injection of streptozotocin. The effects of ghrelin and [ D-Lys^3 ] -GHRP-6 on GD-sensitive neu- rons in the Arc of DM rats were observed by recording the extracellular potentials of single neurons, and the gastric motility was also monitored in vivo. The expression of ghrelin receptor, growth hormone secretagogue receptor （GHS-R）, in Arc was studied by real-time PCR and immunofluorescene method. RESULTS ： （ 1 ） Ninety-eight GD-sensitivitv neurons were re-corded in the Arc of normal rats, in which 64.3% were classified as GD-excitatory （GD-E） neurons and 35.7% were GD- inhibitory （GD-I） neurons. Microinjection of ghrelin excited 73.0% of the 63 GD-E neurons and the discharge frequency significantly increased as compared with the neurons treated with saline. Ghrelin inhibited 60.0% of the 35 GD-I neurons and the discharge frequency was significantly reduced （ P 〈 0.01 ）. The effect of ghrelin was blocked by the antagonist of ghrelin [ D-Lys^3 ] -GHRP-6. （2） Sixty-six GD-sensitive neurons were recorded in the Arc of diabetes rats, in which 64.3% were GD-E neurons, and 35.7% were GD-I neurons. Microinjection of ghrelin excited 35.1% of the GD-E neurons and the discharge frequency significantly increased as compared with the neurons treated with saline. Ghrelin inhibited 21 of the 29 GD-I neurons （72.4%） and the discharge frequency was significantly reduced. Compared with normal control group, the ratio of GD-E and GD-I neurons in diabetic rat Are GD-sensitive neurons was not significantly changed. However, the ratio of GD-E neurons treated with ghrelin was significantly decreased, and the average increase rate of discharge frequency was significantly decreased. Ghrelin did not change GD-I neurons rejection ratio and discharge frequency average reduction rate. （3） Microinjection of ghrelin into the Arc significantly promoted gastric motility in normal and DM rats, and a signifi- cant dose-dependent manner was observed. However, the promotion effect of ghrelin on gastric motility in normal rats was stronger than that in DM rats, and the effect was completely blocked by [ D-Lys^3] -GHRP-6. （4） The mRNA expression of GHS-Rla in the hypothalamic Arc of diabetic rats significantly reduced as compared with the normal control rats. The pro- tein level of GHS-Rla in the hypothalamic Arc was also significantly reduced in DM rats. CONCLUSION： Ghrelin regu- lates the activity of GD-sensitive neurons in hippocampus Arc of diabetic rats by the action on ghrelin receptor.