Download Estradiol alters only GAD67 mRNA levels in ischemic rat brain with

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.