Tymianski M, Sattler R, Zabramski J M, Spetzler R F
The Toronto Hospital Research Institute, and Division of Neurosurgery, The Toronto Hospital, University of Toronto, Ontario, Canada.
J Cereb Blood Flow Metab. 1998 Aug;18(8):848-67. doi: 10.1097/00004647-199808000-00005.
Although profound hypothermia has been used for decades to protect the human brain from hypoxic or ischemic insults, little is known about the underlying mechanism. We therefore report the first characterization of the effects of moderate (30 degrees C) and profound hypothermia (12 degrees to 20 degrees C) on excitotoxicity in cultured cortical neurons exposed to excitatory amino acids (EAA; glutamate, N-methyl-D-aspartate [NMDA], AMPA, or kainate) at different temperatures (12 degrees to 37 degrees C). Cooling neurons to 30 degrees C and 20 degrees C was neuroprotective, but cooling to 12 degrees C was toxic. The extent of protection depended on the temperature, the EAA receptor agonist employed, and the duration of the EAA challenge. Neurons challenged briefly (5 minutes) with all EAA were protected, as were neurons challenged for 60 minutes with NMDA, AMPA, or kainate. The protective effects of hypothermia (20 degrees and 30 degrees C) persisted after rewarming to 37 degrees C, but rewarming from 12 degrees C was deleterious. Surprisingly, however, prolonged (60 minutes) exposures to glutamate unmasked a temperature-insensitive component of glutamate neurotoxicity that was not seen with the other, synthetic EAA; this component was still mediated via NMDA receptors, not by ionotropic or metabotropic non-NMDA receptors. The temperature-insensitivity of glutamate toxicity was not explained by effects of hypothermia on EAA-evoked [Ca2+]i increases measured using high- and low-affinity Ca2+ indicators, nor by effects on mitochondrial production of reactive oxygen species. This first characterization of excitotoxicity at profoundly hypothermic temperatures reveals a previously unnoticed feature of glutamate neurotoxicity unseen with the other EAA, and also suggests that hypothermia protects the brain at the level of neurons by blocking, rather than slowing, excitotoxicity.
尽管深度低温已被用于保护人类大脑免受缺氧或缺血性损伤数十年，但对其潜在机制却知之甚少。因此，我们首次描述了中度低温（30摄氏度）和深度低温（12至20摄氏度）对在不同温度（12至37摄氏度）下暴露于兴奋性氨基酸（EAA；谷氨酸、N-甲基-D-天冬氨酸[NMDA]、α-氨基-3-羟基-5-甲基-4-异恶唑丙酸[AMPA]或海人藻酸）的培养皮层神经元兴奋性毒性的影响。将神经元冷却至30摄氏度和20摄氏度具有神经保护作用，但冷却至12摄氏度则具有毒性。保护程度取决于温度、所使用的EAA受体激动剂以及EAA刺激的持续时间。所有EAA短暂刺激（5分钟）的神经元均受到保护，用NMDA、AMPA或海人藻酸刺激60分钟的神经元也受到保护。低温（20摄氏度和30摄氏度）的保护作用在复温至37摄氏度后仍然存在，但从12摄氏度复温则有害。然而，令人惊讶的是，长时间（60分钟）暴露于谷氨酸会揭示出一种对温度不敏感的谷氨酸神经毒性成分，而在其他合成EAA中未观察到这种成分；该成分仍通过NMDA受体介导，而非离子型或代谢型非NMDA受体。谷氨酸毒性的温度不敏感性无法通过低温对使用高亲和力和低亲和力Ca2+指示剂测量的EAA诱发的[Ca2+]i增加的影响来解释，也无法通过对线粒体活性氧产生的影响来解释。在深度低温温度下对兴奋性毒性的这一首次描述揭示了谷氨酸神经毒性一个以前未被注意到的特征，而在其他EAA中未观察到这一特征，并且还表明低温通过阻断而非减缓兴奋性毒性在神经元水平上保护大脑。
