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Antiseizure Activity of Midazolam in Mice Lacking δ-Subunit Extrasynaptic GABA(A) Receptors.

Abstract
Midazolam is a benzodiazepine anticonvulsant with rapid onset and short duration of action. Midazolam is the current drug of choice for acute seizures and status epilepticus, including those caused by organophosphate nerve agents. The antiseizure activity of midazolam is thought to result from its allosteric potentiation of synaptic GABA(A) receptors in the brain. However, there are indications that benzodiazepines promote neurosteroid synthesis via the 18-kDa cholesterol transporter protein (TSPO). Therefore, we investigated the role of neurosteroids and their extrasynaptic GABA(A) receptor targets in the antiseizure activity of midazolam. Here, we used δ-subunit knockout (DKO) mice bearing a targeted deletion of the extrasynaptic receptors to investigate the contribution of the extrasynaptic receptors to the antiseizure activity of midazolam using the 6-Hz and hippocampus kindling seizure models. In both models, midazolam produced rapid and dose-dependent protection against seizures (ED50, 0.4 mg/kg). Moreover, the antiseizure potency of midazolam was undiminished in DKO mice compared with control mice. Pretreatment with PK11195 [1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide], a TSPO blocker, or finasteride, a 5α-reductase neurosteroid inhibitor, did not affect the antiseizure effect of midazolam. The antiseizure activity of midazolam was significantly reversed by pretreatment with flumazenil, a benzodiazepine antagonist. Plasma and brain levels of the neurosteroid allopregnanolone were not significantly greater in midazolam-treated animals. These studies therefore provide strong evidence that neurosteroids and extrasynaptic GABA(A) receptors are not involved in the antiseizure activity of midazolam, which mainly occurs through synaptic GABA(A) receptors via direct binding to benzodiazepine sites. This study reaffirms midazolam's use for controlling acute seizures and status epilepticus.
AuthorsSandesh D Reddy, Iyan Younus, Bryan L Clossen, Doodipala Samba Reddy
JournalThe Journal of pharmacology and experimental therapeutics (J Pharmacol Exp Ther) Vol. 353 Issue 3 Pg. 517-28 (Jun 2015) ISSN: 1521-0103 [Electronic] United States
PMID25784648 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)
CopyrightCopyright © 2015 by The American Society for Pharmacology and Experimental Therapeutics.
Chemical References
  • Anticonvulsants
  • GABA Modulators
  • Hypnotics and Sedatives
  • Neurotransmitter Agents
  • Receptors, GABA-A
  • Flumazenil
  • Midazolam
Topics
  • Animals
  • Anticonvulsants (pharmacology)
  • Brain Chemistry (drug effects)
  • Female
  • Flumazenil (pharmacology)
  • GABA Modulators (pharmacology)
  • Hippocampus (drug effects, metabolism)
  • Hypnotics and Sedatives (pharmacology)
  • Kindling, Neurologic (drug effects)
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Midazolam (pharmacology)
  • Neurotransmitter Agents (metabolism, pharmacology)
  • Receptors, GABA-A (drug effects, genetics)
  • Seizures (prevention & control)

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