Wisden W, Cope D, Klausberger T, Hauer B, Sinkkonen S T, Tretter V, Lujan R, Jones A, Korpi E R, Mody I, Sieghart W, Somogyi P
Department of Clinical Neurobiology, University of Heidelberg, Im Neuenheimer Feld 364, Germany.
Neuropharmacology. 2002 Sep;43(4):530-49. doi: 10.1016/s0028-3908(02)00151-x.
We generated transgenic (Thy1alpha6) mice in which the GABA(A) receptor alpha6 subunit, whose expression is usually confined to granule cells of cerebellum and cochlear nuclei, is ectopically expressed under the control of the pan-neuronal Thy-1.2 promoter. Strong Thy1alpha6 subunit expression occurs, for example, in deep cerebellar nuclei, layer V iscocortical and hippocampal pyramidal cells and dentate granule cells. Ligand binding and protein biochemistry show that most forebrain alpha6 subunits assemble as alpha6betagamma2-type receptors, and some as alpha1alpha6betagamma2 and alpha3alpha6betagamma2 receptors. Electron microscopic immunogold labeling shows that most Thy1-derived alpha6 immunoreactivity is in the extrasynaptic plasma membrane of dendrites and spines in both layer V isocortical and CA1pyramidal cells. Synaptic immunolabeling is rare. Consistent with the alpha6 subunits' extrasynaptic localization, Thy1alpha6 CA1 pyramidal neurons have a five-fold increased tonic GABA(A) receptor-mediated current compared with wild-type cells; however, the spontaneous IPSC frequency and the mIPSC amplitude in Thy1alpha6 mice decrease 37 and 30%, respectively compared with wild-type. Our results strengthen the idea that GABA(A) receptors containing alpha6 subunits can function as extrasynaptic receptors responsible for tonic inhibition and further suggest that a homeostatic mechanism might operate, whereby increased tonic inhibition causes a compensatory decrease in synaptic GABA(A) receptor responses.
我们构建了转基因（Thy1α6）小鼠，其中γ-氨基丁酸A（GABA(A)）受体α6亚基通常仅在小脑颗粒细胞和耳蜗核中表达，在此转基因小鼠中，该亚基在泛神经元Thy-1.2启动子的控制下异位表达。例如，在小脑深部核团、V层视皮质和海马锥体细胞以及齿状颗粒细胞中会出现强烈的Thy1α6亚基表达。配体结合和蛋白质生化分析表明，大多数前脑α6亚基组装成α6βγ2型受体，还有一些组装成α1α6βγ2和α3α6βγ2受体。电子显微镜免疫金标记显示，在V层视皮质和CA1锥体细胞中，大多数源自Thy1的α6免疫反应性位于树突和棘突的突触外质膜上。突触免疫标记很少见。与α6亚基的突触外定位一致，与野生型细胞相比，Thy1α6 CA1锥体细胞中，GABA(A)受体介导的张力性电流增加了五倍；然而，与野生型相比，Thy1α6小鼠的自发性抑制性突触后电流（sIPSC）频率和微小抑制性突触后电流（mIPSC）幅度分别降低了37%和30%。我们的结果强化了这样一种观点，即含有α6亚基的GABA(A)受体可作为负责张力性抑制的突触外受体发挥作用，并进一步表明可能存在一种稳态机制，即张力性抑制增加会导致突触GABA(A)受体反应的代偿性降低。
