Loss of zolpidem efficacy in the hippocampus of mice with the GABAA receptor γ2 F77I point mutation

doi:10.1111/j.1460-9568.2005.04127.x

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Wiley InterScience

European Journal of Neuroscience

Volume 21 Issue 11, Pages 3002 - 3016

Published Online: 24 Jun 2005

Published on behalf of the Federation of European Neuroscience Societies

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Loss of zolpidem efficacy in the hippocampus of mice with the GABA_A receptor γ2 F77I point mutation

D. W. Cope ^1,*, C. Halbsguth ^1,† , T. Karayannis ¹ , P. Wulff ² , F. Ferraguti ^1,‡ , H. Hoeger ³ , E. Leppä ⁴ , A.-M. Linden ⁴ , A. Oberto ^5,§ , W. Ogris ⁶ , E. R. Korpi ⁴ , W. Sieghart ⁶ , P. Somogyi ¹ , W. Wisden ² and M. Capogna ¹

¹ MRC Anatomical Neuropharmacology Unit, Department of Pharmacology, Oxford University, Mansfield Road, Oxford OX1 3TH, UK
² Department of Clinical Neurobiology, University of Heidelberg, Im Neuenheimer Feld 364, D-69120 Heidelberg, Germany
³ Department of Laboratory Animal Science and Genetics, Medical University Vienna, Brauhausgasse 34, 2325 Himberg, Austria
⁴ Institute of Biomedicine, Pharmacology, Biomedicum Helsinki, University of Helsinki, FIN-00014 Helsinki, Finland
⁵ MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK
⁶ Center for Brain Research, Division of Biochemistry and Molecular Biology, Medical University Vienna, Spitalgasse 4, A-1090 Vienna, Austria

Correspondence to Dr D. Cope, School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3US, UK.
E-mail: copedw@cf.ac.uk

* Present address: School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3US, UK.

† Present address: Dr Kade Pharmazeutische Fabrik GmbH, Opelstrasse 2, D-78467 Konstanz, Germany.

‡ Present address: Department of Pharmacology, University of Innsbruck, Peter-Mayr-Strasse, 1a, A-6020 Innsbruck, Austria.

§ Present address: Department of Pharmacology, and Department of Anatomical, Pharmacological and Forensic Medicine, Via Pietro Giuria, 13, University of Turin, Turin 10125, Italy.

KEYWORDS

benzodiazepine • GABA_A receptor • hippocampus • mIPSC • zolpidem

ABSTRACT

Zolpidem is a hypnotic benzodiazepine site agonist with some γ-aminobutyric acid (GABA)_A receptor subtype selectivity. Here, we have tested the effects of zolpidem on the hippocampus of γ2 subunit (γ2F77I) point mutant mice. Analysis of forebrain GABA_A receptor expression with immunocytochemistry, quantitative [³H]muscimol and [³⁵S] t-butylbicyclophosphorothionate (TBPS) autoradiography, membrane binding with [³H]flunitrazepam and [³H]muscimol, and comparison of miniature inhibitory postsynaptic current (mIPSC) parameters did not reveal any differences between homozygous γ2I77/I77 and γ2F77/F77 mice. However, quantitative immunoblot analysis of γ2I77/I77 hippocampi showed some increased levels of γ2, α1, α4 and δ subunits, suggesting that differences between strains may exist in unassembled subunit levels, but not in assembled receptors. Zolpidem (1 µm) enhanced the decay of mIPSCs in CA1 pyramidal cells of control (C57BL/6J, γ2F77/F77) mice by ∼ 60%, and peak amplitude by ∼ 20% at 33–34 °C in vitro. The actions of zolpidem (100 nm or 1 µm) were substantially reduced in γ2I77/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 µm) on carbachol-induced oscillations in the CA3 area of γ2I77/I77 mice was significantly different compared with controls. Thus, the γ2F77I 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 γ2 subunit.

Received 1 February 2005, revised 22 March 2005, accepted 28 March 2005

DIGITAL OBJECT IDENTIFIER (DOI)

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