Comparative molecular neuroanatomy of cloned GABA_Areceptor subunits in the rat CNS

Abstract

gamma-Aminobutyric acidA (GABAA) receptors in the mammalian central nervous system (CNS) are members of a family of ligand-gated ion channels consisting of heterooligomeric glycoprotein complexes in synaptic and extrasynaptic membranes. Although molecular cloning studies have identified 5 subunits (with approximately 40% amino acid homology) and isoforms thereof (approximately 70% homology), namely alpha 1-6, beta 1-4, gamma 1-3, delta, and rho, the subunit composition and stoichiometry of native receptors are not known. The regional distribution and cellular expression of GABAA receptor messenger RNAs (mRNAs) in the rat CNS have now been investigated by in situ hybridization histochemistry with subunit-specific 35S-labelled oligonucleotide probes on adjacent cryostat sections. Whereas alpha 1, beta 2, and gamma 2 transcripts were the most abundant and ubiquitous in the rat brain--correlating with the radioautographic distribution of GABAA receptors revealed by an ionophore ligand--others had a more restricted expression while often being abundant. For example, alpha 2 transcripts were found only in the olfactory bulb, cerebral cortex, caudate putamen, hippocampal formation, and certain lower brain stem nuclei; alpha 3 only in the olfactory bulb and cerebral cortex; alpha 5 in the hippocampal formation; and alpha 6 only in cerebellar granule cells. In addition, beta 1, beta 3, gamma 1, and delta mRNAs were also uniquely expressed in restricted brain regions. Moreover, in the spinal cord, alpha 1-3, beta 2,3, and gamma 2 mRNAs were differently expressed in Rexed layers 2-9, with alpha 2, beta 3, and gamma 2 transcripts most prominent in motoneurons of layer 9. Although differential protein trafficking could lead to the incorporation of some subunits into somatic membranes and others into dendritic membranes, some tentative conclusions as to the probable composition of native proteins in various regions of the CNS may be drawn.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of GABAA receptor subunit mRNAs in hippocampal pyramidal and granular neurons in the kindling model of epileptogenesis: an in situ hybridization study

“…The observed expression patterns in coronal and horizontal sections are in good agreement with the mRNA distributions described by Wisden et al [73] and Persohn et al [54]. Hippocampal GABAergic interneurons, located in stratum oriens, radiatum or moleculare did not express detectable hybridization signals using film detection, indicating that this type of cells did not significantly contribute to the extintion values measured in pyramidal and granular cell layers.…”

“…In the 13 class, the /33 mRNA expression was by far the most abundant subunit followed by /31 and /32. These normalized expression values are in good agreement with the qualitative descriptions of signal intensity presented by Wisden et al [73], Araki and Tohyama [4] and Persohn et al [54]. This analysis showed that all quantified subunits, accounted for at least 10% of the total GABAAR subunit expression within their class with one exception.…”

“…The normalization of the expression levels revealed an expression profile that was in accordance with the relative hybridization signal intensity reported in literature [4,54,73]. All quantified subunits, contributed significantly to the GABAAR subunit expression within their particular class, with the exception of a3 in fascia dentata that accounted for only 3% of the a type subunit mRNA expressed in that area.…”

“…In situ hybridization studies have shown that the distribution of subunit mRNAs displayed a marked regional heterogeneity in the brain suggesting the regionally specific assembly of subunits into various isoforms of the GABAA-receptor [4,54,73]. Furthermore, regional differences in immunoprecipitation patterns, using subunit specific antibodies, supported the concept of structural heterogeneity [10].…”

Normal formation of the postsynaptic elements of GABAergic synapses in the reeler cerebellum

“…In the cerebellum, granule cells express the GABA A receptor α1 and α6 subunit mRNAs and the subunit proteins are targeted to the GABAergic synaptic site in the synaptic glomeruli [28,47,69]. Purkinje cells, on the other hand, express only the α1 subunit but not remaining five α subunits and its protein is trafficked to the dendritic shafts and cell bodies opposite the GABAergic terminals.…”