麩胺酸接受體在心血管神經調控的角色

The role of Glutamate receptor on neuronal regulation of cardiovascular function

謝宜璋(Yi-Chang Hsieh)

指導教授 ： 謝瑞香

中原大學/工學院/生物醫學工程研究所/博士(2010年)

https://doi.org/10.6840/CYCU.2010.00004

摘要

之前的研究已經證實，加電刺激在被麻醉烏龜腦室之迷走神經核及運動神經核中，會造成降心跳反應，同時亦有會使血壓下降。目前，我們採以麩胺酸(0.2-20 nl, 50 nM)作為刺激的化學藥劑，作用在烏龜的疑核及運動神經核中，證明會引起降心跳反應。而且降心跳作用在不同的劑量上有不同的反應效果。除此之外，我們分別使用不同劑量之NMDA 接受器的拮抗劑(AP-5, 1-8 nmole)及non-NMDA 接受器的拮抗劑(CNQX, 0.1-0.8 nmole)，在麩胺酸刺激前20分鐘給與微劑量。由數據可知，不同劑量的拮抗劑作用，會引發減緩烏龜腦核因麩胺酸刺激所造成的降心跳反應。由此可知，烏龜腦核中會引發降心跳反應的接受器中，不只有NMDA 接受器，更是包含有non-NMDA 接受器。除了了解腦核接受器的型式外，我們也想利用接受器拮抗劑的特性在熱中風下組織器官受損的修護狀況。於是採用麩胺酸接受器的拮抗劑( kynurenic acid)，靜脈注射在被麻醉後熱中風下的老鼠。將實驗分為兩組，其中一組，實驗動物皆暴露在溫度高於43℃的環境中，持續68 分鐘之久，引發熱中風；並且於熱中風前4個小時分別給與生理食鹽水0.5 ml與kynurenic acid 30 mg/kg。另外一組，則將實驗動物放置於24℃的室溫環境下。分別偵測記錄肛溫、平均動脈壓、心跳速率等生理參數。同時於熱中風後15分鐘進行抽血，檢驗細胞因熱作用所產生的發炎反應分子，以作為細胞凋亡判斷的依據。最後再取下腦、脾臟、腎臟、肺臟及肝臟等器官，進行切片後以HE及特殊螢光染色來計數凋亡細胞數目。在熱中風後，我們亦記錄每隻動物的存活時間。資料顯示，接受生理食鹽水注射的動物其存活時間約為83-95分鐘(n=6)；而以kynurenic acid注射的動物其存活時間約為152-356分鐘(n=6)。而且，以生理食鹽水注射的動物，會有血壓下降的反應產生，並且在其腦中下視丘的細胞有嚴重的凋亡變形；血漿中亦可偵測出大量的發炎反應分子，並在腎臟、脾臟、肝臟及肺臟等細胞上發現大量的凋亡，並引發多重器官損傷。另外，在給與kynurenic acid注射的動物，其細胞凋亡及多重器官衰竭的情況大為改善。所以，我們的結果顯示，麩胺酸接受器的拮抗劑可以有效的降低發炎反應生成因子生成，並可以有效的減緩器官的損傷。

關鍵字

熱中風 ； 多器官損傷 ； 大腦缺血性損傷 ； NMDA接受器 ； 麩胺酸 ； 抑制心跳作用

並列摘要

Our previous results showed that electrical stimulation of the nuclei of the ambiguus or dorsomotor nuclei of the vagus in the brain of spontaneously breathing pond turtles (Cyclemys fiavomarginata), anesthetized with chloralose (4 mg 100 g-1) and urethane (40 mg 100g-1), produced marked slowing or even cessation of the heart rate, and thus resulted in an immediate fall of the blood pressure. The present results further demonstrated that the cardioinhibitory responses could also be elicited by microinjection of monosodium glutamate (0.2-20 nl, 50 nM) into the nuclei of the ambiguus or dorsomotor nuclei of the vagus in turtles. In addition, the glutamate-induced cardioinhibitory responses could be significantly and dose-dependently reduced by treatment with AP-5 (a NMDA receptor antagonist, 1-8 nmole) or CNQX (a non-NMDA receptor antagonist; 0.1-0.8 nmole) 20 minutes before glutamate administration. These results suggest that glutamatergic receptors in the caudal medulla may mediate vagal cardioinhibitory responses in turtles.
To assess whether N-methyl-D-aspartate receptor antagonism with kynurenic acid improves the outcomes of heatstroke in the rat. Anesthetized rats were divided into 2 major groups and given vehicle solution (isotonic saline 0.5 ml per rat) or kynurenic acid (3-30 mg in 0.5 ml isotonic saline per rat) 4 hours before the start of thermal experiments. They were exposed to an ambient temperature of 42.9oC for 68 minutes to induce heatstroke. Another group of rats were exposed to room temperature (24oC) and used as normothermic controls. Their core temperatures, mean arterial pressures, serum levels of systemic inflammatory response molecules, hypothalamic values of apoptolic cells and neuronal damage scores, and serum levels of renal and hepatic dysfunction indicators were determined. Survival time (interval between onset of heat exposure and animals) was 83-95 minutes (n=6) or 152-356 minutes (n=6) for vehicle-treated heatstroke rats or kynurenic acid-treated heatstroke rats, respectively. Vehicle-treated heatstroke rats displayed hypotension, hypothalamic neuronal degeneration and apoptosis, increased serum levels of systemic inflammatory response molecules, and renal and hepatic dysfunction, which could be significantly ameliorated by kynurenic acid preconditioning. Our results suggest that N-methyl-D-aspartate receptor antagonism decreases systemic inflammatory response molecules and multi-organ dysfunction in the experimental heatstroke.

並列關鍵字

hypothalamus ； cytokines ； kynurenic acid ； heatstroke ； CNQX ； AP-5 ； N-methyl-D-aspartate receptor ； bradycardia ； glutamate

參考文獻

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