Largo C, Cuevas P, Somjen G G, Martín del Río R, Herreras O
Departamento de Investigación, Hospital Ramón y Cajal, Madrid, Spain.
J Neurosci. 1996 Feb 1;16(3):1219-29. doi: 10.1523/JNEUROSCI.16-03-01219.1996.
The supporting role of glial cells in maintaining neurons and in ion homeostasis has been studied in situ by perfusing the gliotoxin fluorocitrate (FC) through a microdialysis fiber in the CA1 area of urethane-anesthetized rats. Extracellular direct current potential, extracellular potassium concentration ([K+]o) and amino acid levels, extracellular pH (pHo), and evoked field activity were studied. Histology verified the swelling of glial cells after 4 hr of FC treatment. Massive neuron damage was evident after 8 hr. FC dialysis caused the rapid decrease of glutamine, pHo became progressively more acid, and [K+]o moderately elevated. Orthodromic transmission was variably blocked within 30 min to 4 hr. After 4 hr, spreading depression (SD) waves that originated from the neocortex invaded hippocampal CA1, [K+]o increased to higher levels, pHo became very acid, and there were steep increases in taurine, glutamate, and GABA levels. Simultaneously, the antidromic population spike (a-PS) became depressed and eventually disappeared. When a shorter dialysis probe that spared cortex was used to sample CA1, no SD was seen, a-PS was not abolished, and ion homeostasis was altered less markedly. Repeated SD provoked in hippocampus in the absence of FC caused only mild depression of a-PS. Dialysis of high-K+ solution in healthy neocortex or hippocampus caused only slight elevation of [K+]o at distances of 200-400 microns from the dialysis membrane. After treatment with FC, similar high-K+ dialysis raised [K+]o much more. We conclude the following: (1) recurrent SD waves injure neurons if and only if glial function has failed; (2) neurons can regulate [K+]o, albeit imperfectly; (3) glia is required for the normal fine tuning of [K+]o and particularly for the recovery of pathologically elevated [K+]o; and (4) glia are required for the regulation of pHo. The similarities between glial poisoning by FC and the reported changes in the penumbra of ischemic infarcts suggest that the extension of neuron loss into the penumbral region might depend on failure of glial protection.
通过在氨基甲酸乙酯麻醉大鼠的CA1区经微透析纤维灌注胶质毒素氟柠檬酸（FC），对神经胶质细胞在维持神经元及离子稳态方面的支持作用进行了原位研究。研究了细胞外直流电位、细胞外钾离子浓度（[K⁺]o）和氨基酸水平、细胞外pH值（pHo）以及诱发场活动。组织学检查证实FC处理4小时后神经胶质细胞肿胀。8小时后出现明显的大量神经元损伤。FC透析导致谷氨酰胺迅速减少，pHo逐渐变得更酸，[K⁺]o适度升高。在30分钟至4小时内，顺向传播可变地受阻。4小时后，源自新皮层的扩散性抑制（SD）波侵入海马CA1区，[K⁺]o升高至更高水平，pHo变得非常酸，牛磺酸、谷氨酸和γ-氨基丁酸水平急剧上升。同时，逆向群体峰电位（a-PS）变得压低并最终消失。当使用较短的、未损伤皮层的透析探针采样CA1区时，未观察到SD，a-PS未被消除，离子稳态改变不太明显。在无FC情况下，海马中反复诱发的SD仅导致a-PS轻度压低。在健康的新皮层或海马中透析高钾溶液，在距透析膜200 - 400微米处仅导致[K⁺]o轻微升高。用FC处理后，类似的高钾透析使[K⁺]o升高得更多。我们得出以下结论：（1）反复的SD波仅在神经胶质细胞功能失效时才会损伤神经元；（2）神经元能够调节[K⁺]o，尽管并不完美；（3）神经胶质细胞对于[K⁺]o的正常精细调节尤其是对于病理性升高的[K⁺]o的恢复是必需的；（4）神经胶质细胞对于pHo的调节是必需的。FC导致的神经胶质细胞中毒与缺血性梗死半暗带中报道的变化之间的相似性表明，神经元丢失扩展至半暗带区域可能取决于神经胶质细胞保护功能的失效。
