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Estradiol alters only GAD67 mRNA levels in ischemic rat brain with no consequent effects on GABA This work was supported by NIH Grants HD21351, AA11415, NS07375, NS33668, NR03521, and NS20020. Dr Murphy was initially supported by an American Heart Association, Mid-Atlantic Affiliate, Postdoctoral Fellowship Award and subsequently by NIH Grant RR00163. An UNCF-Merck Postdoctoral Fellowship supported Dr Searles. Hung-Dong Joh1, Robin V Searles2,4, Michael Selmanoff2,5, Nabil J Alkayed3, Raymond C Koehler1, Patricia D Hurn3 and Stephanie J Murphy3 1. 1 Department of Anesthesiology and Critical Care Medicine, Johns Hopkins Medical Institutions, Baltimore, Maryland, USA 2. 2Department of Physiology, University of Maryland, School of Medicine, Baltimore, Maryland, USA 3. 3Department of Anesthesiology and Perioperative Medicine, Oregon Health and Science University, Portland, Oregon, USA Correspondence: Dr SJ Murphy, Oregon Health and Science University, Anesthesiology and Peri-Operative Medicine, 20000 NW Walker Road, Mail Code: OGI, Beaverton, OR 97006, USA. E-mail: [email protected] 4 Current address: Department of Biology, Morgan State University, Baltimore, MD 21251, USA. 5 Current address: Center for Scientific Review, National Institutes of Health, Bethesda, MD 20892, USA. Received 9 March 2005; Revised 2 June 2005; Accepted 14 July 2005; Published online 10 August 2005. 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 -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 g 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. Endischemic 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.