Bonthius D J, Lothman E W, Steward O
Department of Neuroscience, University of Virginia Health Sciences Center, Charlottesville 22908, USA.
Brain Res. 1995 Mar 20;674(2):314-28. doi: 10.1016/0006-8993(95)00035-o.
While spreading depression has been shown to be a powerful stimulus in upregulating glial fibrillary acidic protein (GFAP) mRNA expression, the specific physiological signal underlying the upregulation is unknown. During spreading depression, extracellular ionic concentrations are altered markedly. The present study evaluates the role of these changes in extracellular ionic concentrations as potential signals influencing GFAP mRNA expression. Gel foam pledgets saturated with artificial cerebrospinal fluid (CSF) solutions in which [Na+], [Ca2+], [K+] and [H+] were altered one at a time to match concentrations seen in spreading depression were applied to exposed parietal cortex for one hour. Dot and in situ hybridization techniques were used to evaluate GFAP mRNA levels. We found that CSF containing 60 mM KCl produced a dramatic upregulation of GFAP mRNA levels throughout the cerebral cortex of the ipsilateral hemisphere without causing detectable tissue damage. The pattern and time course of the change were similar to those following application of 3 M KCl. Alteration of other ionic species did not affect GFAP mRNA levels. However, the upregulation of GFAP mRNA was not likely due directly to the increased [K+], but rather to the spreading depression that the elevated [K+] induced. This was demonstrated by the finding that the upregulation in GFAP mRNA induced by the potassium exposure was totally blocked by prior administration of MK-801, an NMDA antagonist that blocks spreading depression. These results demonstrate that an upregulation in GFAP mRNA can occur in the absence of degeneration debris and that the initiating events can be related to physiological changes, but that changes in extracellular ionic concentrations are not the likely molecular signals underlying the upregulation.
虽然扩散性抑制已被证明是上调胶质纤维酸性蛋白（GFAP）mRNA表达的有力刺激因素，但上调背后的具体生理信号尚不清楚。在扩散性抑制过程中，细胞外离子浓度会发生显著变化。本研究评估了这些细胞外离子浓度变化作为影响GFAP mRNA表达的潜在信号的作用。将浸有人工脑脊液（CSF）溶液的明胶海绵小块应用于暴露的顶叶皮质1小时，其中[Na⁺]、[Ca²⁺]、[K⁺]和[H⁺]一次改变一种，以匹配扩散性抑制中所见的浓度。采用斑点杂交和原位杂交技术评估GFAP mRNA水平。我们发现，含有60 mM KCl的CSF在同侧半球的整个大脑皮质中导致GFAP mRNA水平显著上调，且未造成可检测到的组织损伤。变化的模式和时间进程与应用3 M KCl后相似。其他离子种类的改变不影响GFAP mRNA水平。然而，GFAP mRNA的上调不太可能直接归因于[K⁺]的增加，而是归因于升高的[K⁺]诱导的扩散性抑制。这一点通过以下发现得到证明：钾暴露诱导的GFAP mRNA上调被预先给予的MK - 801（一种阻断扩散性抑制的NMDA拮抗剂）完全阻断。这些结果表明，在没有变性碎片的情况下，GFAP mRNA也可以发生上调，且起始事件可能与生理变化有关，但细胞外离子浓度的变化不太可能是上调背后的分子信号。
