Loss of zolpidem efficacy in the hippocampus of mice with the GABAA receptor gamma2 F77I point mutation.
Zolpidem is a hypnotic benzodiazepine site agonist with some gamma-aminobutyric acid (GABA)(A) receptor subtype selectivity. Here, we have tested the effects of zolpidem on the hippocampus of gamma2 subunit (gamma2F77I) point mutant mice. Analysis of forebrain GABA(A) receptor expression with immunocytochemistry, quantitative [(3)H]muscimol and [(35)S] t-butylbicyclophosphorothionate (TBPS) autoradiography, membrane binding with [(3)H]flunitrazepam and [(3)H]muscimol, and comparison of miniature inhibitory postsynaptic current (mIPSC) parameters did not reveal any differences between homozygous gamma2I77/I77 and gamma2F77/F77 mice. However, quantitative immunoblot analysis of gamma2I77/I77 hippocampi showed some increased levels of gamma2, alpha1, alpha4 and delta subunits, suggesting that differences between strains may exist in unassembled subunit levels, but not in assembled receptors. Zolpidem (1 microm) enhanced the decay of mIPSCs in CA1 pyramidal cells of control (C57BL/6J, gamma2F77/F77) mice by approximately 60%, and peak amplitude by approximately 20% at 33-34 degrees C in vitro. The actions of zolpidem (100 nm or 1 microm) were substantially reduced in gamma2I77/I77 mice, although residual effects included a 9% increase in decay and 5% decrease in peak amplitude. Similar results were observed in CA1 stratum oriens/alveus interneurons. At network level, the effect of zolpidem (10 microm) on carbachol-induced oscillations in the CA3 area of gamma2I77/I77 mice was significantly different compared with controls. Thus, the gamma2F77I point mutation virtually abolished the actions of zolpidem on GABA(A) receptors in the hippocampus. However, some residual effects of zolpidem may involve receptors that do not contain the gamma2 subunit.
MRC Anatomical Neuropharmacology Unit, Department of Pharmacology, Oxford University, Mansfield Road, Oxford OX1 3TH, UK. copedw@cf.ac.uk
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Cope
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Halbsguth
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Karayannis
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Wulff
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Ferraguti
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Hoeger
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Leppä
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Linden
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A
Oberto
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Ogris
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Korpi
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Sieghart
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Somogyi
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Wisden
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Capogna
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D004351:Drug Resistance / Q000235:genetics*; D005260:Female; D018755:GABA Agonists / Q000494:pharmacology; D006624:Hippocampus / Q000187:drug effects* / Q000378:metabolism; D007395:Interneurons / Q000187:drug effects / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008818:Mice, Neurologic Mutants; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D017354:Point Mutation / Q000187:drug effects* / Q000235:genetics*; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology; D011725:Pyridines / Q000494:pharmacology*; D011869:Radioligand Assay; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000235:genetics*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D000077334:Zolpidem
D018679:Cholinergic Agonists; D018755:GABA Agonists; C546280:Gabrg2 protein, mouse; D011725:Pyridines; D011963:Receptors, GABA-A; D000077334:Zolpidem; D002217:Carbachol