Functional consequences of GABAA receptor α4 subunit deletion on synaptic and extrasynaptic currents in mouse dentate granule cells
Functional consequences of GABAA receptor α4 subunit deletion on synaptic and extrasynaptic currents in mouse dentate granule cells
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DOI：
10.1111/j.1530-0277.2007.00564.x
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发表时间：
2008-01-01
影响因子：
3.2
通讯作者：
Spigelman, Igor
中科院分区：
文献类型：
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作者：
Liang, Jing;Suryanarayanan, Asha;Spigelman, Igor
背景：含α4亚单位的γ-氨基丁酸受体(GABA(A)Rs)主要在齿状回(DG)和丘脑的突触外部位高表达，并被认为参与了对加博沙多和乙醇(EtoH)增强敏感的紧张性抑制。与野生型(WT)对照相比，全球α4亚单位基因敲除(KO)小鼠的紧张性电流显著减少，对加博沙多的共济失调、镇静和止痛作用不敏感。阿尔法4KO小鼠对戊四氮诱导的癫痫发作也明显更敏感。然而，在其他基线行为和乙醇对这些行为的影响方面，阿尔法4KO小鼠和WT小鼠之间没有观察到差异。为了研究GABA(A)R在功能和药理上的变化，并寻找乙醇行为缺乏差异的原因，我们研究了急性应用乙醇对α4 KO和WT对照组小鼠DG细胞GABA(A)R电流的影响，并辅之以Western印迹检测。方法：采用免疫印迹和全细胞贴片记录方法，研究了α4亚单位缺失的后果。结果：乙醇(10~100 mM)、αxone(3 MU M)、而Ro15-4513(0.3 mU M)在α4 KO小鼠体内则明显减弱。与WT小鼠相比，α4 KO小鼠的微小抑制性突触后电流(MIPSCs)动力学明显减慢。在α4KO小鼠中，α-单抗对小鼠骨髓间充质干细胞的增强作用显著降低。Ro15-4513对WT或KO小鼠的mIPSCs无影响。然而，Alpha4KO小鼠的mIPSCs对乙醇的敏感性明显高于WT小鼠。结论：α4亚基的整体缺失导致脑区和细胞内γ2亚基的代偿性增加，进而改变突触和突触外GABA(A)R电流的药理敏感性。我们的数据还表明，虽然加博沙多、α-黄体酮和乙醇对紧张性抑制电流的增强作用减弱，对加博沙多和α-黄体酮的行为敏感性可能降低，但突触GABA(A)R亚单位的代偿性变化可能阻止对乙醇的行为敏感性的类似降低。
Background: The alpha 4 subunit-containing gamma-aminobutyric acid (A) receptors (GABA(A)Rs) are highly expressed primarily at extrasynaptic sites in the dentate gyrus (DG) and thalamus and are suspected to contribute to tonic inhibition that is sensitive to potentiation by gaboxadol and ethanol (EtOH). Global alpha 4 subunit knockout (KO) mice exhibit greatly reduced tonic currents and insensitivity to ataxic, sedative and analgesic effects of gaboxadol compared to wild type (WT) controls. The alpha 4 KO mice were also significantly more sensitive to pentylenetetrazol-induced seizures. However, no differences were observed between alpha 4 KO and WT mice in other baseline behaviors or in the effects of EtOH on these behaviors. To examine possible functional and pharmacological GABA(A)R alterations, and search for causes for the lack of differences in EtOH behaviors we studied the effects of acute EtOH application on GABA(A)R-currents of DG cells from alpha 4 KO and WT control mice complemented by Western blot measurements.Methods: We studied the consequences of alpha 4 subunit deletion using Western immunoblotting and whole cell patch recordings from DG cells in brain slices from alpha 4 KO and WT mice.Results: The magnitude of tonic current and its potentiation by EtOH (10 to 100 mM), alphaxalone (3 mu M), and Ro15-4513 (0.3 mu M) was greatly attenuated in alpha 4 KO mice. The kinetics of miniature inhibitory postsynaptic currents (mIPSCs) in alpha 4 KO mice were significantly slower compared to WT mice. Potentiation of mIPSCs by alphaxalone was greatly reduced in alpha 4 KO mice. Ro15-4513 had no effect on mIPSCs from WT or KO mice. However, mIPSCs of alpha 4 KO mice were significantly more sensitive to EtOH than those from WT mice. The gamma 2 subunit protein levels were selectively increased in hippocampus and thalamus, but not cortex of alpha 4 KO mice.Conclusions: These data suggest that the global loss of alpha 4 subunits leads to region- and cell location-specific compensatory increases in gamma 2 subunits, which in turn alter the pharmacological sensitivity of synaptic and extrasynaptic GABA(A)R-currents. Our data also suggests that while enhancement of tonic inhibitory currents by gaboxadol, alphaxalone, and EtOH are reduced, and behavioral sensitivity to gaboxadol and alphaxalone may be reduced, compensatory changes in synaptic GABA(A)R subunits may prevent similar reductions in behavioral sensitivity to EtOH.