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GABA A ‐receptor heterogeneity in the adult rat brain: Differential regional and cellular distribution of seven major subunits
Author(s) -
Fritschy JeanMarc,
Mohler Hanns
Publication year - 1995
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.903590111
Subject(s) - biology , protein subunit , colocalization , receptor , allosteric regulation , gabaa receptor , gabaa rho receptor , g alpha subunit , cys loop receptors , microbiology and biotechnology , alpha (finance) , gamma subunit , beta (programming language) , neuroscience , biochemistry , gene , nicotinic agonist , nicotinic acetylcholine receptor , medicine , construct validity , nursing , computer science , patient satisfaction , programming language
Abstract GABA A ‐receptors display an extensive structural heterogeneity based on the differential assembly of a family of at least 15 subunits (α1–6, β1–3, γ1–3, θ, ρl–2) into distinct heteromeric receptor complexes. The subunit composition of receptor subtypes is expected to determine their physiological properties andipharmacological profiles, thereby contributing to flexibility in signal transduction and allosteric modulation. In heterologous expression systems, functional receptors require a combination of α‐, β‐, and γ‐subunit variants, the γ2‐subunit being essential to convey a classical benzodiazepine site to the receptor. The subunit composition and stoichiometry of native GABA A ‐receptor subtypes remain unknown. The aim of this study was to identify immunohistochemically the main subunit combinations expressed in the adult rat brain and to allocate them to identified neurons. The regional and cellular distribution of seven major subunits (α1, α2, α3, α5, β2,3, γ2, δ) was visualized by immunoperoxidase staining with subunit‐specific antibodies (the β2‐ and β3‐subunits were covisualized with the monoclonal antibody bd‐17). Putative receptor subtypes were identified on the basis of colocalization of subunits within individual neurons, as analyzed by confocal laser microscopy in double‐ and triple‐immunofluoreseence staining expeximents. The results reveal an extraordinary heterogeneity in the distribution of GABA A ‐receptor subunits, as evidenced by abrupt changes in immunoreactivity along well‐defined cytoarchitectonic boundaries and by pronounced differences in the cellular distribution of subunits among various types of neurons. Thus, functionally and morphologically diverse neurons were characterized by a distinct GABA A ‐receptor subunit repertoire. The pultiple staining experiments identified 12 subunit combinations in defined neurons. The most prevalent combination was the triplet α1/β2,3/γ2, detected in numerous cell types throughout the brain. An additional subunit (α2, α3, or δ) sometimes was associated with this triplet, pointing to the existence of receptors containing four subunits. The triplets α2/β2,3/γ2, α3/β2,3/γ2, and α5/β2,3/γ2 were also identified in discrete cell populations. The prevalence of these seven combinations suggest that they represent major GABAA‐receptor subtypes. Five combinations also apparently lacked the β2,3‐subunits, including one devoid of γ2‐subunit (α1/α2/γ2, α2/γ2, α3/γ2, α2/α3/γ2, α2/α5/δ). These combinations were selectively associated with small neuron populations, thereby representing minor GABA A receptor subtypes. These results provide the basis for a functional analysis of GABA A ‐receptor subtypes of known subunit composition and may open the way for unproved therapeutic approaches based on the development of subtype‐selective drugs. © 1995 Wiley‐Liss, Inc.