Joh Hung-Dong, Searles Robin V, Selmanoff Michael, Alkayed Nabil J, Koehler Raymond C, Hurn Patricia D, Murphy Stephanie J
Department of Anesthesiology and Critical Care Medicine, Johns Hopkins Medical Institutions, Baltimore, Maryland, USA.
J Cereb Blood Flow Metab. 2006 Apr;26(4):518-26. doi: 10.1038/sj.jcbfm.9600211.
The present study tested the hypothesis that estradiol reduces tissue infarction after middle cerebral artery occlusion (MCAO) in estradiol-deficient females by augmenting glutamic acid decarboxylase (GAD) expression and thus activity, leading to increases in gamma-amino-butyric acid (GABA) tissue levels. Glutamic acid decarboxylase is the principal enzyme for GABA synthesis and has two isoforms, GAD65 and GAD67, which differ in size and cellular distribution. Rats were ovariectomized 7 to 8 days before receiving no hormone, placebo, or 25 microg estradiol via subcutaneous implant 7 to 10 days before harvesting tissue in either ischemic cohorts after 2 h of MCAO (end-ischemia) or in nonischemic cohorts. Selected cortical and striatal regions were microdissected from harvested brains. GAD65/67 mRNA levels were determined by microlysate ribonuclease protection assay. End-ischemic GABA concentrations were determined by HPLC. Steroid treatment selectively decreased ischemic cortical GAD67 mRNA levels. In most brain regions evaluated, regional GABA concentrations increased with ischemia regardless of treatment. Estradiol blocked MCAO-induced increases in GABA concentration only in dorsomedial cortex. These data suggest that estradiol repletion in ischemic rat brain selectively decreases GAD67 mRNA levels but does not alter steady-state GABA concentrations. It may be that estradiol under ischemic conditions is attenuating GABA metabolism rather than enhancing synthesis or is augmenting other aspects of GABAergic transmission such as GABA transporters and receptors.
在雌激素缺乏的雌性大鼠中，雌二醇通过增强谷氨酸脱羧酶（GAD）的表达及活性，进而增加γ-氨基丁酸（GABA）的组织水平，来减少大脑中动脉闭塞（MCAO）后的组织梗死。谷氨酸脱羧酶是GABA合成的主要酶，有两种同工型，即GAD65和GAD67，它们在大小和细胞分布上有所不同。在MCAO 2小时后（缺血末期）的缺血组或非缺血组大鼠在收获组织前7至10天，通过皮下植入接受无激素、安慰剂或25微克雌二醇处理，这些大鼠在7至8天前已进行卵巢切除术。从收获的大脑中显微解剖出选定的皮质和纹状体区域。通过微量裂解物核糖核酸酶保护试验测定GAD65/67 mRNA水平。通过高效液相色谱法测定缺血末期的GABA浓度。类固醇治疗选择性地降低了缺血皮质GAD67 mRNA水平。在评估的大多数脑区，无论治疗如何，区域GABA浓度均随缺血而增加。雌二醇仅在背内侧皮质阻断了MCAO诱导的GABA浓度升高。这些数据表明，缺血大鼠脑中补充雌二醇可选择性降低GAD67 mRNA水平，但不会改变稳态GABA浓度。可能是缺血条件下的雌二醇减弱了GABA代谢，而非增强其合成，或者是增强了GABA能传递的其他方面，如GABA转运体和受体。
