Elsevier

Neuroscience

Volume 80, Issue 4, 11 August 1997, Pages 987-1000
Neuroscience

GABAA receptor subunits in the rat hippocampus I: Immunocytochemical distribution of 13 subunits

https://doi.org/10.1016/S0306-4522(97)00146-2Get rights and content

Abstract

The GABAA receptor is a ligand-operated chloride channel. It has a pentameric structure. In mammalian brain different subunits are recruited from four gene subfamilies. Using immunocytochemistry, we investigated the distribution of the 13 GABAA receptor subunits in the hippocampus of the rat. GABAA receptor subunits were heterogeneously distributed within different hippocampal subfields. High concentrations of α1-, α2-, α4-, β3-, γ2- and δ-immunoreactivities were observed within the molecular layer of the dentate gyrus, representing the dendritic area of the granule cells. In the hippocampus proper, the predominant GABAA receptor subunits were α1, α2, α5, β3 and γ2 that were located throughout the strata radiatum and oriens of CA1 to CA3. Immunocytochemical staining was there less prominent for α4-, β1-, β2-, γ3- and δ- subunits. In the hippocampus proper, the β1 subunit was preferentially located in CA2. The α4- and δ-subunits were somewhat more abundant in CA1 than in CA3. Numerous local circuit neurons in the hippocampus proper and the hilus of the dentate gyrus contained α1-, β2-, γ2- and/or δ-subunits. α3 and γ1 were present only in minute amounts and no α6-IR was detected in the hippocampal formation.

The distribution of the GABAA receptor subunits indicates the existence of heterogenously constituted GABAA receptor complexes within various hippocampal subfields, which may exert different physiological or pharmacological properties upon stimulation by GABA or its agonists.

Section snippets

Animals and tissue preparation

Male Sprague–Dawley rats (250–350 g, Forschungsinstitut für Versuchstierzucht, Himberg, Austria) were injected with a lethal dose of thiopental (150 mg/kg, i.p., Sanabo, Austria) and perfused immediately through the ascending aorta with 50 ml ice-cold phosphate-buffered saline (PBS; 50 mM phosphate buffer, pH 7.4 in 0.9% NaCl) followed by 200 ml chilled 4% paraformaldehyde in PBS. The brains were removed from the skulls and divided by coronal cuts into three parts. They were postfixed in the same

Antibodies

In the present experiments the antibodies appeared highly specific, revealing staining patterns characteristic for each subunit in different brain areas (data not shown). Notably, subunits which were less prominently expressed in the hippocampus were detected at considerable concentrations in other brain regions: e.g., α3 in the cortex, striatum and tuberculum olfactorium, α6 in granule cells of the cerebellum, β1 in the cerebral cortex, tuberculum olfactorium and cerebellum, γ1 in the ventral

Discussion

The present data provide a detailed survey of the immunocytochemical distribution of 13 GABAA receptor subunits in the hippocampal formation in the rat.

Conclusion

A heterogeneous distribution of GABAA receptor subunits has been found within the hippocampus. The predominant subunits within the molecular layer of the dentate gyrus are α1, α2, α4, β1, β3, γ2 and δ. Within the dendritic areas of the hippocampus proper the α1-, α2-, α5-, β3- and the γ2- subunits predominate. GABAA receptors within local circuit neurons of the hippocampus consist mainly of α1, β2, and of either γ2- or δ-subunits (or both γ2 and δ). These data imply heterogeneously constituted

Acknowledgements

We would like to thank C. Wanzenböck and E. Kirchmair for technical assistance and C. Trawöger for preparing the photographs. We also thank Dr U. Berresheim for critically reading the manuscript. The work was supported by grants from the Austrian Science Foundation (to G.S. and W.S.), the Jubiläumsfoolns of the Austrian National Bank (to G.S.) and of the Japanese Foundation for Aging and Health (to K.T.). For information concerning antibodies contact Dr W. Sieghart. We would like to dedicate

References (50)

  • C Schwarzer et al.

    GABAA -Receptors in the rat hippocampus II: altered subunit distribution in kainic acid-induced temporal lobe epilepsy

    Neuroscience

    (1997)
  • G Sperk et al.

    Functional changes in neuropeptide Y and somatostatin containing neurons induced by limbic seizures in the rat

    Neuroscience

    (1992)
  • K Tsunashima et al.

    GABAA receptor subunits in the rat hippocampus III: altered expression of their mRNAs in kainic acid-induced epilepsy

    Neuroscience

    (1997)
  • W Wisden et al.

    Cloning, pharmacological characteristics and expression pattern of the rat GABAA receptor α4 subunit

    Fedn Eur. biochem. Socs Lett.

    (1991)
  • J Zezula et al.

    Separation of α1-, α2- and α3-subunits of the GABAA benzodiazepine receptor complex by immunoaffinity chromatography

    Brain Res.

    (1991)
  • J Zezula et al.

    Isolation of type I and type II GABAA-benzodiazepine receptors by immunoaffinity chromatography

    Fedn Eur. biochem. Socs Lett.

    (1991)
  • F Zimprich et al.

    Immunohistochemical localization of the α1-, α2- und α3-subunit of the GABAA receptor in the rat brain

    Neurosci. Lett.

    (1991)
  • T.V.P Bliss et al.

    A synaptic model of memory: long-term potentiation in the hippocampus

    Nature

    (1993)
  • M.S Buckwalter et al.

    Localization of the human chromosome 5q genes GABRA-1, GABRA-2, II-4, II-5 and Irf-1 on mouse chromosome 11

    Mamm. Genome

    (1992)
  • E.H Buhl et al.

    Diverse sources of hippocampal unitary inhibitory postsynaptic potentials and the number of synaptic release sites

    Nature

    (1994)
  • S.R Cobb et al.

    Synchronization of neuronal activity in hippocampus by individual GABAergic interneurons

    Nature

    (1995)
  • A Draghun et al.

    Functional and molecular distinction between recombinant rat GABAA receptor subtypes by Zn2+

    Neuron

    (1990)
  • M Escalpez et al.

    Subpopulations of GABA neurons in the dentate gyrus express high levels of the α1-subunit of the GABAA receptor

    Hippocampus

    (1996)
  • J.M Fritschy et al.

    Five subtypes of type A γ-aminobutyric acid receptors identified in neurons by double and triple immunofluorescence staining with subunit-specific antibodies

    Proc. natn. Acad. Sci. U.S.A.

    (1992)
  • J.M Fritschy et al.

    GABAA -receptor heterogeneity in the adult rat brain: differential regional and cellular distribution of seven major subunits

    J. comp. Neurol.

    (1995)
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