氯胺酮损害大鼠内嗅皮层mGlu2/3型受体依赖性突触长时程抑制的机理及其防治措施

The mechanism of ketamine induced cognitive dysfunction is unknown, moreover, there is no ideal protection strategy from damage of ketamine. Our previous investigation showed that activation of group II mGluRs (mGluR II) by LY354740 induced robust depression of glutamatergic transmission in the entorhinal cortex (EC). The mGluR II-induced depression was due to a selective reduction of presynaptic release probability without alterations of the quantal size and the number of release sites. The mechanisms underlying mGluR II-mediated suppression of glutamate release included the inhibition of presynaptic release machinery and the depression of presynaptic P/Q-type Ca(2+) channels. Recently, our primary trial showed that LY354740 can reverse the hyper-glutamate state in brain and cognitive dysfunction induced by keatamine, meanwhile, our primary data suggested that mGlu2/3-LTD couldn't be induced in the EC after exposed to ketamine repeatedly. We refer that ketamine can induce NMDA receptor hypofunction and hyper-glutamate state, accordingly impair mGlu2/3-LTD and cognitive function. This investigatation is aimed to determine the effect of pretreatment with LY354740 on the Glu and GABA in the EC via microdialysis.It is also aimed to detect the difference of mGlu2/3 receptor expression and learning and memory ability after pretreatment with LY354740. It is also aimed to test the conclusion via acute brain slice according to the change in vivo, in order to identify the mechanism of cognitive dysfunction induced by ketamine, and identify whether agonist of mGlu2/3 receptor can be used as a new target drug for prevention cognitive dysfunction.

氯胺酮可诱发认知功能障碍，但机制未明，更无理想的防治措施。我们前期研究显示，使用代谢性谷氨酸（mGlu）2/3型受体激动剂LY354740可在大鼠内嗅皮层调控离子型谷氨酸通路，诱导出非NMDA依赖性LTD。近期，预实验显示LY354740可以逆转氯胺酮所诱发的大鼠认知功能障碍及脑内高Glu状态，同时发现大鼠反复予以氯胺酮后,内嗅皮层中不能诱导出mGlu2/3型LTD。我们推论,氯胺酮通过诱发NMDA受体功能低下，高Glu状态导致mGlu2/3受体功能减退，从而损害mGlu2/3型LTD而导致认知功能障碍。本研究通过微透析的方法观测LY354740预先给药对大鼠脑内Glu、GABA等递质的影响；观测内嗅皮层mGlu2/3受体表达及功能、学习记忆行为学的差异；并通过膜片钳检验体内实验的主要结论，以期明确氯胺酮诱发认知障碍的发病机理,明确mGlu2/3型受体激动剂可作为防治措施的新靶点药物。

氯胺酮可诱发认知功能障碍，但机制未明，更无理想的防治措施。我们推测：氯胺酮所诱发的脑内高Glu状态是病因所在及防治目标所在。. 本研究通过水迷宫等测试学习记忆能力的改变，从整体动物行为学的角度证明了 mGlu2/3受体特异性激动剂LY354740可防治氯胺酮导致的认知功能障碍。我们研究还发现，使用mGlu3受体特异性内源性激动剂N-乙酰基-天冬氨酰-谷氨酸（NAAG），也可防治氯胺酮导致的认知功能障碍。相反，通过使用mGlu2/3受体特异性拮抗剂可加重氯胺酮导致的认知功能损伤。. 通过制备脑匀浆及细胞悬液，研究表明mGlu2/3受体特异性激动剂LY354740可防治氯胺酮诱发的高Glu状态。. 通过免疫组化、蛋白免疫印迹等方法，发现使用LY354740可改善氯胺酮慢性暴露所致幼鼠认知功能障碍的机制可能与其减少中枢炎性反应、减少中枢GLU的过度释放，减少tau蛋白、Aβ的表达有关，与内嗅皮层、海马区GCPⅡ的表达有关，与NAAG有关。. 我们通过使用膜片钳研究发现：使用代谢性谷氨酸（mGlu）2/3型受体激动剂LY354740在大鼠内嗅皮层-海马环路可调控离子型谷氨酸通路，并探讨了其中机制：LY354740通过抑制G蛋白－cAMP－PKA途径，并可作用于突触前膜P/Q型Ca通道，从而直接在突触前膜抑制囊泡的释放，抑制谷氨酸释放，从而减少突触间隙谷氨酸浓度，调节谷氨酸平衡。. 本研究明确了氯胺酮诱发认知障碍的发病机理，明确mGlu2/3型受体激动剂可作为防治措施的靶点药物。

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