Perisynaptic Localization of δ Subunit-Containing GABAA Receptors and Their Activation by GABA Spillover in the Mouse Dentate Gyrus

In cerebellar granule cells, δ subunit-containing GABA A receptors are found exclusively at extrasynaptic sites, but their subcellular distribution in other brain areas is poorly understood. We examined the anatomical localization and physiological activation of these receptors in adult mouse dentat...

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Published in:The Journal of neuroscience 2003-11, Vol.23 (33), p.10650-10661
Main Authors: Wei, Weizheng, Zhang, Nianhui, Peng, Zechun, Houser, Carolyn R., Mody, Istvan
Format: Article
Language:English
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Cellular/Molecular
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Summary:In cerebellar granule cells, δ subunit-containing GABA A receptors are found exclusively at extrasynaptic sites, but their subcellular distribution in other brain areas is poorly understood. We examined the anatomical localization and physiological activation of these receptors in adult mouse dentate gyrus granule cells. Immunocytochemistry revealed a high density of δ subunits in the molecular layer and a much lower density in the cell body layer. At the ultrastructural level, immunogold-labeled δ subunits were found at the edge of symmetric synapses on granule cell dendrites. Functional correlates of this perisynaptic localization were obtained by comparing inhibitory responses in δ subunit-deficient (δ-/-) and wild-type (wt) mice. In whole-cell recordings at 22°C, the weighted decay time constants (τ w ) of spontaneous IPSCs (sIPSCs) were significantly longer in wt mice but were similar at 34°C, reflecting the role of temperature-dependent GABA uptake in shaping sIPSC decay. IPSCs evoked by minimal stimulation (eIPSCs) near the somata had similar τ w in δ-/- and wt mice, but eIPSCs elicited from dendritic sites decayed significantly more slowly in wt mice, consistent with a higher density of δ subunit-containing receptors in the molecular layer. The τ w of dendritic eIPSCs of wt mice were shortened by ZnCl 2 (10 μ m ), reflecting the high Zn 2+ sensitivity of δ subunit-containing GABA A receptors, and were prolonged by the GAT-1 GABA transporter inhibitor NO711 (10 μ m ). Our results demonstrate a perisynaptic localization of δ subunit-containing GABA A receptors and indicate that these receptors can be activated by GABA overspill in the molecular layer.
ISSN:0270-6474
1529-2401
DOI:10.1523/JNEUROSCI.23-33-10650.2003