Functional analysis of the glutamate receptor δ2 subunit in the motor learning

在脊椎动物中枢神经系统中，谷氨酸受体（GluR）通道介导了大部分快速兴奋性突触传递。GluRδ2亚基在小脑浦肯野细胞中特异性表达，其消融导致长期抑制（LTD）、运动协调和突触精细的损害。GluRδ2缺陷小鼠接受经典的眨眼条件反射。条件刺激（CS）与非条件刺激（US）在时间上重叠的延迟范式。GluRδ2突变小鼠表现出严重的学习障碍。然而，在无刺激的追踪时间间隔介入CS和US之间的追踪范式中。GluRδ2突变小鼠与野生型小鼠一样成功地学习。因此，小脑LTD在延迟范式中是必不可少的，而在追踪范式中则不是，这表明眨眼条件反射背后的小脑神经基质的改变取决于CS和US的时间重叠。此外，我们将NMDA受体GluRε3亚基基因与Cre重组酶-孕酮受体融合（CrePR）基因联合使用，建立了小脑基因靶向的细胞类型特异性和时间调控系统。我们建立了ECP25转基因小鼠系，在小脑颗粒细胞中选择性强表达CrePR mRNA。我们发现抗孕激素可以诱导ECP25小鼠小脑颗粒细胞中CrePR融合蛋白的重组酶活性。因此，建立的小鼠系将为研究小脑功能的机制提供一个有价值的工具，通过时间调节和颗粒细胞特异性的方式操纵分子。

Glutamate receptor (GluR) channels mediate most of fast excitatory synaptic transmission in the vertebrate central nervous system. The GluRδ2 subunit expressed specifically in cerebellar Purkinje cells, and it's ablation resulted in impairements of long term depression (LTD), motor coordination, and refinement of synapses. GluRδ2 deficient mice received classical eyeblink conditioning. In the delay paradigm in which the conditioned stimuluus (CS) overlapped temporally with unconditioned stimulus (US). GluRδ2 mutant mice exhibited a severe impairment in learning. However, in the trace paradigm in which a stimulus-free trace interval intervened between the CS and US. GluRδ2 mutant mice learned as successfully as wild-type mice. Therefore, cerebellar LTD is essential in the delay paradigm, but not in the trace paradigm, suggesting an alteration of cerebellar neural substrates underlying eyeblink conditioning depending on the temporal overlap of the CS and US. Furthermore, to develop a cell type-specific and temporal regulation system of gene targeting in the cerebellum, we employed the NMDA receptor GluRε3 subunit gene and Cre recombinase-progesterone receptor fusion (CrePR) gene in combination. We established a ECP25 transgenic mouse line that strongly expressed the CrePR mRNA selectively in the granule cells of the cerebellum. We showed that antiprogestins could induce the recombinase activity of CrePR fusion protein of ECP25 mouse in the cerebellar granule cells. Thus, the established mouse line will provide a valuable tool to investigate the mechanism of cerebellar function by manipulating molecules in the temporally regulated and granule cell-specific manner.