Estradiol alters only GAD67 mRNA levels in ischemic rat brain with no consequent effects on GABA.
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.
Joh
Hung-Dong
HD
Department of Anesthesiology and Critical Care Medicine, Johns Hopkins Medical Institutions, Baltimore, Maryland, USA.
Searles
Robin V
RV
Selmanoff
Michael
M
Alkayed
Nabil J
NJ
Koehler
Raymond C
RC
Hurn
Patricia D
PD
Murphy
Stephanie J
SJ
D000818:Animals; D001923:Brain Chemistry; D002545:Brain Ischemia / Q000378:metabolism*; D002540:Cerebral Cortex / Q000737:chemistry; D003342:Corpus Striatum / Q000737:chemistry; D004958:Estradiol / Q000172:deficiency / Q000494:pharmacology*; D005260:Female; D005968:Glutamate Decarboxylase / Q000187:drug effects / Q000235:genetics*; D020244:Infarction, Middle Cerebral Artery; D007527:Isoenzymes / Q000187:drug effects / Q000235:genetics*; D010052:Ovariectomy; D012333:RNA, Messenger / Q000032:analysis / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D005680:gamma-Aminobutyric Acid / Q000187:drug effects*
D007527:Isoenzymes; D012333:RNA, Messenger; D004958:Estradiol; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1