Sperk Günther, Schwarzer Christoph, Heilman Jutta, Furtinger Sabine, Reimer Richard J, Edwards Robert H, Nelson Nathan
Department of Pharmacology, University of Innsbruck, Innsbruck, Austria.
Hippocampus. 2003;13(7):806-15. doi: 10.1002/hipo.10133.
Kainic acid-induced seizures cause a marked increase in the expression of glutamate decarboxylase 67 (GAD67) in granule cells of the dentate gyrus. To determine the possible modes of sequestration of newly formed gamma-aminobutyric acid (GABA), we used in situ hybridization and immunocytochemistry to investigate the expression of several proteins related to GABA in dentate granule cells of rats 4 h to 60 days after kainic acid-induced status epilepticus and in controls. GAD67 and GAD65 mRNA levels were increased by up to 300% and 800%, respectively, in the granule cell layer 6-24 h after kainate injection. Subsequently, increased GAD and GABA immunoreactivity was observed in the terminal field of mossy fibers and in presumed dendrites of granule cells. mRNA of both known plasma membrane GABA transporters (GAT-1 and GAT-3) was expressed in granule cells of control rats. GAT-1 mRNA levels increased (by 30%) 9 h after kainate injection but were reduced by about 25% at later intervals. GAT-3 mRNA was reduced (by 35-75%) in granule cells 4 h to 30 days after kainic acid injection. In contrast, no expression of the mRNA or immunoreactivity of the vesicular GABA transporter was detected in granule cells or in mossy fibers, respectively. GABA transaminase mRNA was only faintly expressed in granule cells, and its levels were reduced (by 60-65%) 12 h to 30 days after kainate treatment. The results indicate that GABA can be taken up and synthesized in granule cells. No evidence for the expression of the vesicular GABA transporter (VGAT) in granule cells was obtained. After sustained epileptic seizures, the markedly increased expression of glutamate decarboxylase and the reduced expression of GABA transaminase may result in increased cytoplasmic GABA concentrations in granule cells. It is suggested that, during epileptic seizures, elevated intracellular GABA and sodium concentration could then result in nonvesicular release of GABA from granule cell dendrites. GABA could then act on GABA-A receptors, protecting granule cells from overexcitation.
海人酸诱导的癫痫发作会导致齿状回颗粒细胞中谷氨酸脱羧酶67（GAD67）的表达显著增加。为了确定新形成的γ-氨基丁酸（GABA）的可能隔离模式，我们使用原位杂交和免疫细胞化学方法，研究了海人酸诱导癫痫持续状态后4小时至60天的大鼠齿状颗粒细胞以及对照组中与GABA相关的几种蛋白质的表达。海人酸注射后6 - 24小时，颗粒细胞层中GAD67和GAD65的mRNA水平分别增加了高达300%和800%。随后，在苔藓纤维的终末区域以及颗粒细胞的推测树突中观察到GAD和GABA免疫反应性增加。两种已知的质膜GABA转运体（GAT - 1和GAT - 3）的mRNA在对照大鼠的颗粒细胞中均有表达。海人酸注射后9小时，GAT - 1的mRNA水平增加（30%），但在随后的时间段内降低了约25%。海人酸注射后4小时至30天，颗粒细胞中GAT - 3的mRNA减少（35 - 75%）。相反，在颗粒细胞或苔藓纤维中分别未检测到囊泡GABA转运体的mRNA表达或免疫反应性。GABA转氨酶的mRNA在颗粒细胞中仅微弱表达，其水平在海人酸处理后12小时至30天降低（60 - 65%）。结果表明GABA可在颗粒细胞中摄取和合成。未获得颗粒细胞中囊泡GABA转运体（VGAT）表达的证据。持续癫痫发作后，谷氨酸脱羧酶表达显著增加以及GABA转氨酶表达降低可能导致颗粒细胞胞质中GABA浓度升高。有人提出，在癫痫发作期间，细胞内GABA和钠浓度升高可能会导致GABA从颗粒细胞树突中非囊泡性释放。然后GABA可作用于GABA - A受体，保护颗粒细胞免受过度兴奋。
