Baskys Andrius, Bayazitov Ildar, Fang Liwei, Blaabjerg Morten, Poulsen Frantz Rom, Zimmer Jens
Department of Mental Health, VA Health Care System, Mental Illness Research and Education Clinical Center, Long Beach, University of California at Irvine, 06/116A, 5901 East Seventh Street Long Beach, CA, 90822 Irvine, CA, USA.
Neuropharmacology. 2005;49 Suppl 1:146-56. doi: 10.1016/j.neuropharm.2005.04.029.
Group I metabotropic glutamate receptor (mGluR) agonist DHPG reduced nerve cell death caused by their exposure to NMDA ("neuroprotective effect") and attenuated NMDA receptor-mediated currents [Blaabjerg, M., Baskys, A., Zimmer, J., Vawter, M. P., 2003b. Changes in hippocampal gene expression after neuroprotective activation of group I metabotropic glutamate receptors. Brain Research, Molecular Brain Research 117, 196-205.]. In the present study, we used organotypic hippocampal culture preparation to examine specific phospholipase C (PLC) inhibitor U73122 effects on DHPG-induced neuroprotection, changes in excitatory synaptic transmission associated with the neuroprotective DHPG treatment and a role of group I mGluR ligands in neurogenesis. Results show that short (10 min) DHPG treatment did not result in neuroprotection but significantly depressed field synaptic potentials (fEPSP) in the Schaffer collateral-CA1 pathway. The fEPSP depression was not affected by the PLC inhibitor U73122. In contrast, prolonged (2-h) treatment of cultures with DHPG induced a significant protective effect that was blocked by a PLC inhibitor U73122 but not by its inactive analog U73343. Voltage-clamp measurements of spontaneous miniature excitatory post-synaptic currents (EPSCs) recorded in CA1 neurons from cultures treated with DHPG (10 microM, 2 h) showed a significant reduction of the EPSC amplitude in DHPG-treated but not control (untreated) cultures. This reduction was completely abolished by U73122, suggesting a PLC involvement. Since activation of PLC is thought to be associated with cell proliferation, we investigated whether group I mGluR agonist DHPG or subtype antagonists LY367385 and MPEP have an effect on dentate granule cells expressing immature neuronal marker TOAD-64. DHPG (100 microM, 72 h) slightly but not significantly increased the number of TOAD-64 positive cells. The mGluR1 antagonists LY367385 (10 microM, 72 h) markedly decreased the number of TOAD-64 positive cells and mGluR5 antagonist MPEP (1 microM, 72 h) had no effect. These data suggest that (1) prolonged activation of group I mGluRs reduces nerve cell susceptibility to excitotoxic injury in a PLC-dependent manner; (2) this reduction is associated with a PLC-dependent depression of excitatory synaptic transmission; and (3) mGluR1 activation may facilitate neurogenesis.
I 型代谢型谷氨酸受体（mGluR）激动剂 DHPG 可减少神经细胞因暴露于 NMDA 而导致的死亡（“神经保护作用”），并减弱 NMDA 受体介导的电流[Blaabjerg, M., Baskys, A., Zimmer, J., Vawter, M. P., 2003b. 海马基因表达在 I 型代谢型谷氨酸受体神经保护激活后的变化。《脑研究，分子脑研究》117, 196 - 205。]。在本研究中，我们使用海马脑片培养制备来研究特异性磷脂酶 C（PLC）抑制剂 U73122 对 DHPG 诱导的神经保护作用、与神经保护作用的 DHPG 处理相关的兴奋性突触传递变化以及 I 型 mGluR 配体在神经发生中的作用。结果表明，短时间（10 分钟）的 DHPG 处理并未产生神经保护作用，但显著降低了 Schaffer 侧支 - CA1 通路中的场突触电位（fEPSP）。fEPSP 的降低不受 PLC 抑制剂 U73122 的影响。相反，用 DHPG 对培养物进行长时间（2 小时）处理可诱导显著的保护作用，该作用被 PLC 抑制剂 U73122 阻断，但未被其无活性类似物 U73343 阻断。对用 DHPG（10 μM，2 小时）处理的培养物中 CA1 神经元记录的自发性微小兴奋性突触后电流（EPSC）进行电压钳测量显示，在 DHPG 处理的培养物中 EPSC 幅度显著降低，但在对照（未处理）培养物中未降低。这种降低被 U73122 完全消除，表明有 PLC 参与。由于 PLC 的激活被认为与细胞增殖有关，我们研究了 I 型 mGluR 激动剂 DHPG 或亚型拮抗剂 LY367385 和 MPEP 对表达未成熟神经元标记物 TOAD - 64 的齿状颗粒细胞是否有影响。DHPG（100 μM，72 小时）轻微但不显著地增加了 TOAD - 64 阳性细胞的数量。mGluR1 拮抗剂 LY367385（10 μM，72 小时）显著减少了 TOAD - 64 阳性细胞的数量，而 mGluR5 拮抗剂 MPEP（1 μM，72 小时）则没有作用。这些数据表明：（1）I 型 mGluRs 的长时间激活以 PLC 依赖的方式降低神经细胞对兴奋性毒性损伤的易感性；（2）这种降低与 PLC 依赖的兴奋性突触传递抑制有关；（3）mGluR1 的激活可能促进神经发生。
