氧糖剥夺引起MF-CA3通路突触传递LTD现象及其机制研究

Oxygen / glucose deprivation induces LTD at MF-CA3 synapses

目的 ：观察氧糖剥夺引起的MF-CA3通路突触传递的长时程抑制（long-term depression,LTD）现象,并探讨其分子机制。方法：选择出生后2~3周的Sprague Dawley（SD）乳大鼠,制备海马脑片,通过刺激苔藓纤维,采用膜片钳的方法记录突触后电流。氧糖剥夺15 min后,观察突触传递的变化情况。分别采用犬尿喹啉酸阻断α-氨基羟甲基恶唑丙酸（α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid,AMPA）受体、LY341495阻断代谢型谷氨酸受体﹑BAPTA螯合细胞内钙离子,观察对LTD的可能影响。结果：1氧糖剥夺15 min能引起MF-CA3通路AMPA受体介导的突触电流减弱,产生LTD现象;2若氧糖剥夺过程中运用阻断剂阻断AMPA受体的激活,洗脱后并不影响LTD的产生,而阻断代谢型谷氨酸受体可以使AMPA受体电流的LTD现象消失;3除去外液中的钙离子或用BAPTA螯合细胞内的钙离子均能使LTD现象消失。结论：氧糖剥夺引起MF-CA3通路上AMPA受体介导的突触电流持续减弱,呈现LTD现象。这种LTD现象依赖于代谢型谷氨酸受体的激活及胞内外钙离子浓度升高,但不依赖氧糖剥夺过程中AMPA受体的激活。

Objective：To observe oxygen/glucose deprivation （OGD） induced long-term depression（LTD） during synaptic transmission at mossy fiber to CA3（MF-CA3） synapses and to study the underlying mechanisms. Methods： Sprague Dawley（SD） newborn rats of 2-3 weeks after birth were selected for hippocampal slices. We performed whole-cell patch-clamp recording on CA3 pyramidal neurons and monitored evoked excitatory postsynaptic currents （EPSCs） at MF-CA3 synapses upon mossy fiber stimulation. After 15-min of OGD, we observed the changes of synaptic transmission. We also co-applied blockers of ot-amino-3-hydroxy-5-methyl-4-isoxazole- propionic acid receptors（AMPARs, which blocked by kynurenic acid）, metabotropic glutamate receptors （mGluRs, which blocked by LY341495） or calcium chelator during OGD treatment to examine whether OGD-induced alteration in synaptic transmission requires activation of these receptors or increase of calcium. Results： （1）lS-min OGD induced LTD of AMPA receptor （AMPAR）-mediated synaptic transmission at MF-CA3 synapses. （2）OGD-induced LTD of AMPAR-mediated responses was dependent on activation of mGluRs but not of AMPARs. （3）Removal of Ca2＋ from ACSF during OGD or inclusion of Ca2＋ chelator BAPTA to the patch pipette solution abolished LTD. Conclusion： OGD induces LTD tff AMPAR-mediated synaptic responses at MF-CA3 synapses. This synaptic plasticity requires activation of mGluRs and intracellular Ca2＋ increase without AMPARs.