Ligand-Gated Ion Channel Subunit Partnerships: GABA<sub>A</sub>Receptor α<sub>6</sub>Subunit Gene Inactivation Inhibits δ Subunit Expression

Jones, Alison; Korpi, Esa R.; McKernan, Ruth M.; Pelz, R.; Nusser, Zoltán; Mäkelä, Riikka; Mellor, Jack R.; Pollard, S; Bahn, Sabine; Stephenson, F. Anne; Randall, Andrew; Sieghart, Werner; Somogyi, Péter; Smith, Andrew J.H.; Wisden, William

doi:10.1523/jneurosci.17-04-01350.1997

Cited by 306 publications

(302 citation statements)

References 60 publications

(72 reference statements)

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“…The results reported here were obtained from cerebellar granule cells, a cell type for which there is strong evidence that receptors containing α6 and δ subunits are extrasynaptic 16,19,36 and are required for tonic GABA current 20,21 . We demonstrate that tonic current is facilitated by low ethanol concentrations and, in addition, identify a variant of α6 (α6-100Q) that renders tonic current carried by α6β3δ GABARs much more sensitive to ethanol.…”

Section: Link Between Tonic Inhibition and Behaviormentioning

confidence: 80%

“…It is possible that Gabra6 −/− mice will show less impairment on the rotarod in a lower range of ethanol doses, but there are reasons to believe that ethanol sensitivity of knockout mice may be complicated. First, the expression of GABAR subunits α1, β2, γ2 and δ is changed markedly in Gabra6 −/− mice 19,36,43 , and other potential ethanol targets such as two-pore domain K + channels 20 show increased function in granule cells, making it difficult to rule out compensatory changes in Gabra6 −/− mice. Second, differences in cerebellum-dependent behavior at moderate ethanol doses may be obscured in the Gabra6 −/− mouse by other more abundant and widely expressed ethanol targets.…”

Section: Gabra6 100q Allele and Behavioral Sensitivity To Ethanolmentioning

confidence: 99%

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Alcohol-induced motor impairment caused by increased extrasynaptic GABAA receptor activity

et al. 2005

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Neuronal mechanisms underlying alcohol intoxication are unclear. We find that alcohol impairs motor coordination by enhancing tonic inhibition mediated by a specific subtype of extrasynaptic GABA A receptor (GABAR), α6β3δ, expressed exclusively in cerebellar granule cells. In recombinant studies, we characterize a naturally occurring single-nucleotide polymorphism that causes a single amino acid change (R100Q) in α6 (encoded in rats by the Gabra6 gene). We show that this change selectively increases alcohol sensitivity of α6β3δ GABARs. Behavioral and electrophysiological comparisons of Gabra6 100R/100R and Gabra6 100Q/100Q rats strongly suggest that alcohol impairs motor coordination by enhancing granule cell tonic inhibition. These findings identify extrasynaptic GABARs as critical targets underlying low-dose alcohol intoxication and demonstrate that subtle changes in tonic inhibition in one class of neurons can alter behavior.Humans have been consuming alcohol for thousands of years, and the use of alcoholic beverages pervades human culture and society and can have substantial health effects 1 . Different mechanisms by which ethanol might depress brain function have been proposed based on ethanol's ability to modulate a wide variety of ion channels 2-4 , neurotransmitter receptors 5-10 and transporters 11 . Among these diverse targets, however, GABARs are arguably the most attractive candidates. This is in part because other classes of known GABAR modulators such as benzodiazepines, barbiturates and certain anesthetics lead to behavioral effects that closely resemble ethanol intoxication. Yet despite strong evidence implicating GABARs in ethanol's action, critical details remain unclear. For instance, although it is known that native GABARs are heteropentamers assembled from 19 possible subunits 12,13 , it has not been possible to link the activity of particular GABAR subunits to changes in behavioral sensitivity to ethanol.Recent studies suggest that specific combinations of GABAR subunits (those containing α4β3δ and α6β3δ) are uniquely sensitive to ethanol, showing dose dependencies that mirror blood alcohol levels associated with intoxication in humans 9,10 . GABARs containing α4 and δ subunits are expressed in many brain regions 14,15 , but α6 is found in only two types of neurons (cerebellar granule cells and granule cells in the cochlear nucleus) and is expressed together with δ only in cerebellar granule cells 14,16,17 . In granule cells α6 and δ combine with β subunits Correspondence should be addressed to M.W. (mwallner@mednet.ucla.edu) or T.S.O. (otist@ucla.edu). 3 These authors contributed equally to this work. COMPETING INTERESTS STATEMENTThe authors declare that they have no competing financial interests. We set out to examine whether such extrasynaptic GABARs containing α6 and δ subunits account for behavioral effects of ethanol at moderately intoxicating doses. To link these particular GABARs to behavioral sensitivity, we first characterized a naturally occurring single-nucleotide polymo...

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Section: Link Between Tonic Inhibition and Behaviormentioning

confidence: 80%

Section: Gabra6 100q Allele and Behavioral Sensitivity To Ethanolmentioning

confidence: 99%

Alcohol-induced motor impairment caused by increased extrasynaptic GABAA receptor activity

et al. 2005

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“…Unexpectedly, this mutation caused the disappearance of the d subunit protein (74). However, since mRNA levels for the d subunit were not affected, this finding suggested that the d subunit protein requires the a6 subunit for assembly in a receptor complex and is degraded rapidly in the absence of this mandatory partner.…”

Section: Effects Of Targeted Subunit Gene Deletion On Cerebellar Gabamentioning

confidence: 90%

Molecular and synaptic organization of GABAA receptors in the cerebellum: Effects of targeted subunit gene deletions

Fritschy

Panzanelli

2006

Cerebellum

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GABA A receptors form heteromeric GABA-gated chloride channels assembled from a large family of subunit genes. In cerebellum, distinct GABA A receptor subtypes, differing in subunit composition, are segregated between cell types and synaptic circuits. The cerebellum therefore represents a useful system to investigate the significance of GABA A receptor heterogeneity. For instance, studies of mice carrying targeted deletion of major GABA A receptor subunit genes revealed the role of a subunit variants for receptor assembly, synaptic targeting, and functional properties. In addition, these studies unraveled mandatory association between certain subunits and demonstrated distinct pharmacology of receptors mediating phasic and tonic inhibition. Although some of these mutants have a profound loss of GABA A receptors, they exhibit only minor impairment of motor function, suggesting activation of compensatory mechanisms to preserve inhibitory networks in the cerebellum. These adaptations include an altered balance between phasic and tonic inhibition, activation of voltageindependent K + conductances, and upregulation of GABA A receptors in interneurons that are not affected directly by the mutation. Deletion of the a1 subunit gene leads to complete loss of GABA A receptors in Purkinje cells. A striking alteration occurs in these mice, whereby presynaptic GABAergic terminals are preserved in the molecular layer but make heterologous synapses with spines, characterized by a glutamatergic-like postsynaptic density. During development of a1 0/0 mice, GABAergic synapses are initially formed but are replaced upon spine maturation. These findings suggest that functional GABA A receptors are required for long-term maintenance of GABAergic synapses in Purkinje cells.

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“…The antibody against α4 subunit (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) has been characterized previously [1,12,32]. The antibodies against the γ2 (1-33) and δ (1-44) subunit of the GABA A receptor have been characterized extensively in the past by immunoprecipitation, Western blot, and immunohistochemistry [11,[19][20][21][22]32]. The antibodies against α1, α4, γ2 and δ were characterized by Western blot.…”

Section: Antibodiesmentioning

confidence: 99%

“…For example, electron microscopic examination of GABAergic synapses in cerebellum and hippocampus reveals aggregates of α1, β2/3, and γ2 subunits at GABAergic synapses [16,19]. Conversely, post-embedding immunogold electron microscopic studies of cerebellar granule cells have demonstrated that α6 and δ subunits are expressed in the extrasynaptic membrane [11,19].…”

Section: Introductionmentioning

confidence: 99%

Distribution of α1, α4, γ2, and δ subunits of GABAA receptors in hippocampal granule cells

2004

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GABA A receptors are pentamers composed of subunits derived from the α, β, γ, δ, θ, ε, and π gene families. α1, α4, γ2, and δ subunits are expressed in the dentate gyrus of the hippocampus, but their subcellular distribution has not been described. Hippocampal sections were double-labeled for the α1, α4, γ2, and δ subunits and GAD65 or gephyrin, and their subcellular distribution on dentate granule cells was studied by means of confocal laser scanning microscopy (CLSM). The synaptic versus extrasynaptic localization of these subunits was inferred by quantitative analysis of the frequency of colocalization of various subunits with synaptic markers in high-resolution images. GAD65 immunoreactive clusters colocalized with 26.24±0.86% of the α1 subunit immunoreactive clusters and 32.35±1.49% of the γ2 subunit clusters. In contrast, only 1.58±0.13% of the α4 subunit immunoreactive clusters and 1.92±0.15% of the δ subunit clusters colocalized with the presynaptic marker GAD65. These findings were confirmed by studying colocalization with immunoreactivity of a postsynaptic marker, gephyrin, which colocalized with 27.61±0.16% of the α1 subunit immunoreactive clusters and 23.45±0.32% of the γ2 subunit immunoreactive clusters. In contrast, only 1.90±0.13% of the α4 subunit immunoreactive clusters and 1.76±0.10% of the δ subunit clusters colocalized with gephyrin. These studies demonstrate that a subset of α1 and γ2 subunit clusters colocalize with synaptic markers in hippocampal dentate granule cells. Furthermore, all four subunits, α1, α4, γ2, and δ, are present in the extrasynaptic locations.

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Ligand-Gated Ion Channel Subunit Partnerships: GABA_AReceptor α₆Subunit Gene Inactivation Inhibits δ Subunit Expression

Cited by 306 publications

References 60 publications

Alcohol-induced motor impairment caused by increased extrasynaptic GABAA receptor activity

Alcohol-induced motor impairment caused by increased extrasynaptic GABAA receptor activity

Molecular and synaptic organization of GABAA receptors in the cerebellum: Effects of targeted subunit gene deletions

Distribution of α1, α4, γ2, and δ subunits of GABAA receptors in hippocampal granule cells

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Ligand-Gated Ion Channel Subunit Partnerships: GABAAReceptor α6Subunit Gene Inactivation Inhibits δ Subunit Expression

Cited by 306 publications

References 60 publications

Alcohol-induced motor impairment caused by increased extrasynaptic GABAA receptor activity

Alcohol-induced motor impairment caused by increased extrasynaptic GABAA receptor activity

Molecular and synaptic organization of GABAA receptors in the cerebellum: Effects of targeted subunit gene deletions

Distribution of α1, α4, γ2, and δ subunits of GABAA receptors in hippocampal granule cells

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Ligand-Gated Ion Channel Subunit Partnerships: GABA_AReceptor α₆Subunit Gene Inactivation Inhibits δ Subunit Expression