Effect of mild hypothermia and hyperthermia on excitatory amino acid-induced brain damage

过量的谷氨酸对神经元是致命的，谷氨酸兴奋毒性的概念已经被广泛接受。本研究旨在探讨亚低温和高温对谷氨酸兴奋性毒性的影响。在低温(32℃)、常温(37℃)和高温(40℃)大鼠中，用0.5M谷氨酸溶液通过微透析探头灌流，造成谷氨酸诱导的皮质损伤。1)谷氨酸灌流7d后，通过图像分析对病变体积进行定量。亚低温可缩小损伤体积，亚高温可扩大损伤体积。2)用抗GFAP(星形胶质细胞)和ED1(巨噬细胞)的单抗研究正常和低温动物谷氨酸灌流后0、1、3和5天的组织学变化。TUNEL法检测细胞凋亡率。亚低温可延缓巨噬细胞的增殖和凋亡。3)为了观察亚低温对谷氨酸诱导的NO合成的影响，在常温条件下观察NO终产物的变化。两种一氧化氮合酶抑制剂(L-NAME，7-NI)也抑制谷氨酸诱导的NO合成。4)我们还利用含有~&lt；14&gt；C标记蔗糖的谷氨酸灌流溶液的放射自显影，研究了温度对外源性物质在细胞外空间扩散的影响。随着脑温的升高，~(14)C扩散的体积增大。这些结果证明，脑温度的微小变化改变了谷氨酸的毒性，低温神经保护作用是通过抑制谷氨酸诱导的NO合成来实现的。结果还表明，亚低温和高温分别发挥保护作用和有害作用的机制之一是细胞外间隙谷氨酸扩散的改变。

Excessive glutamate is lethal to neurons, and the concept of glutamate excitotoxicity has become widely accepted. The purpose of this study was to examine the effects of mild hypothermia and hyperthermia on glutamate excitotoxicity. Glutamate-induced cortical lesions were produced in hypothermic (32℃), normothermic (37℃) and hyperthermic (40℃) rats by perfusion of a 0.5 M glutamate solution via a microdialysis probe. 1) The volume of the lesion 7 days after glutamate perfusion was quantified histologically by image analysis of the lesion. The volume of damage was reduced by mild hypothermia and enlarged by mild hyperthermia. 2) Histological changes in normo- and hypothermic animals were studied using monoclonal antibodies against GFAP (for astrocytes) and ED1 (for macrophages) 0, 1, 3 and 5 days after glutamate perfusion. TUNEL staining was used for evaluation of apoptosis. Mild hypothermia delays macrophage proliferation and apoptosis. 3) In order to examine the effects of mild hypothermia on glutamate-induced NO synthesis, the NO end-products which was observed under the normothermic condition. Both of two No synthase inhibitors (L-NAME, 7-NI) also inhibited the glutamate-induced NO synthesis. 4) We also examined the effect of temperature on the diffusion of exogenously delivered material in the extracellular space using autoradiography of the perfused glutamate solution containing ^<14>C-labeled sucrose. The volume of ^<14>C diffusion also increased as brain temperature increased. These results provide evidence that small variations of brain temperature modify glutamate exicitotoxicity, and that hypothermic neuroprotection is exerted by inhibition of the glutamate-induced NO synthesis. The results also suggest that the change in glutamate diffusion in the extracellular space is one mechanism by which mild hypothermia and hyperthermia exert their protective and harmful effects respectively.