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The Journal of Neuroscience, May 1, 2002, 22(9):3795-3805

Stress-Induced Deoxycorticosterone-Derived Neurosteroids Modulate GABA_A Receptor Function and Seizure Susceptibility

Doodipala S. Reddy and Michael A. Rogawski

Epilepsy Research Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892

Stress affects seizure susceptibility in animals and humans, but the underlying mechanisms are obscure. Here, we provide evidence that GABA_A receptor-modulating neurosteroids derived from deoxycorticosterone (DOC) play a role in stress-related changes in seizure control. DOC, an adrenal steroid whose synthesis is enhanced during stress, undergoes sequential metabolic reduction by 5-reductase and 3-hydroxysteroid oxidoreductase to form 5-dihydrodeoxycorticosterone (DHDOC) and allotetrahydrodeoxycorticosterone (THDOC), a GABA_A receptor-modulating neurosteroid with anticonvulsant properties. Acute swim stress in rats significantly elevated plasma THDOC concentrations and raised the pentylenetetrazol (PTZ) seizure threshold. Small systemic doses of DOC produced comparable increases in THDOC and PTZ seizure threshold. Pretreatment with finasteride, a 5-reductase inhibitor that blocks the conversion of DOC to DHDOC, reversed the antiseizure effects of stress. DOC also elevated plasma THDOC levels and protected mice against PTZ, methyl-6,7-dimethoxy-4-ethyl--carboline-3-carboxylate, picrotoxin, and amygdala-kindled seizures in mice (ED₅₀ values, 84-97 mg/kg). Finasteride reversed the antiseizure activity of DOC (ED₅₀, 7.2 mg/kg); partial antagonism was also obtained with indomethacin (100 mg/kg), an inhibitor of 3-hydroxysteroid oxidoreductase. Finasteride had no effect on seizure protection by DHDOC and THDOC, whereas indomethacin partially reversed DHDOC but not THDOC. DHDOC, like THDOC, potentiated GABA-activated Cl currents in cultured hippocampal neurons (1 µM) and directly activated GABA_A receptor currents (1 µM), compatible with a role for DHDOC in the antiseizure activity of DOC. DOC is a mediator of the physiological effects of acute stress that could contribute to stress-induced changes in seizure susceptibility through its conversion to neurosteroids with modulatory actions on GABA_A receptors including THDOC and possibly also DHDOC.

Key words: stress; seizure; pentylenetetrazol; kindling; neurosteroid; deoxycorticosterone; 5-dihydrodeoxycorticosterone; 5,3tetrahydrodeoxycorticosterone (3,21-dihydroxy-5-pregnan-20-one); finasteride; indomethacin; GABA_A receptor

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Copyright © 2002 Society for Neuroscience  0270-6474/02/2293795-11$05.00/0

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