Department of Neurophysiology, Graduate School of Medicine, The University of Tokyo Tokyo, Japan.
Front Neural Circuits. 2013 Aug 20;7:130. doi: 10.3389/fncir.2013.00130. eCollection 2013.
Cerebellar cortex has an elaborate rostrocaudal organization comprised of numerous microzones. Purkinje cells (PCs) in the same microzone show synchronous activity of complex spikes (CSs) evoked by excitatory inputs from climbing fibers (CFs) that arise from neurons in the inferior olive (IO). The synchronous CS activity is considered to depend on electrical coupling among IO neurons and anatomical organization of the olivo-cerebellar projection. To determine how the CF-PC wiring contributes to the formation of microzone, we examined the synchronous CS activities between neighboring PCs in the glutamate receptor δ2 knockout (GluD2 KO) mouse in which exuberant surplus CFs make ectopic innervations onto distal dendrites of PCs. We performed in vivo two-photon calcium imaging for PC populations to detect CF inputs. Neighboring PCs in GluD2 KO mice showed higher synchrony of calcium transients than those in wild-type (control) mice. Moreover, the synchrony in GluD2 KO mice hardly declined with mediolateral separation between PCs up to ~200 μm, which was in marked contrast to the falloff of the synchrony in control mice. The enhanced synchrony was only partially affected by the blockade of gap junctional coupling. On the other hand, transverse CF collaterals in GluD2 KO mice extended beyond the border of microzone and formed locally clustered ectopic synapses onto dendrites of neighboring PCs. Furthermore, PCs in GluD2 KO mice exhibited clustered firing (Cf), the characteristic CF response that was not found in PCs of wild-type mice. Importantly, Cf was often associated with localized calcium transients in distal dendrites of PCs, which are likely to contribute to the enhanced synchrony of calcium signals in GluD2 KO mice. Thus, our results indicate that CF signals in GluD2 KO mice propagate across multiple microzones, and that proper formation of longitudinal olivo-cerebellar projection is essential for the spatiotemporal organization of CS activity in the cerebellum.
小脑皮层具有精细的前后组织，由多个微区组成。同一微区中的浦肯野细胞（PCs）在由橄榄下核（IO）神经元产生的兴奋性输入引起的复杂 spikes（CSs）的同步活动中表现出同步活动。这种同步 CS 活动被认为依赖于 IO 神经元之间的电耦合和橄榄小脑投射的解剖组织。为了确定 CF-PC 连接如何有助于微区的形成，我们检查了谷氨酸受体 δ2 敲除（GluD2 KO）小鼠中相邻 PCs 之间的同步 CS 活动，其中过多的 CF 产生异位神经支配到 PCs 的远端树突。我们对 PC 群体进行了体内双光子钙成像以检测 CF 输入。GluD2 KO 小鼠中的相邻 PCs 表现出比野生型（对照）小鼠更高的钙瞬变同步性。此外，GluD2 KO 小鼠中的同步性几乎没有随着 PCs 之间的中侧分离而下降，直到~200μm，这与对照小鼠中的同步性下降形成鲜明对比。增强的同步性仅部分受到缝隙连接偶联阻断的影响。另一方面，GluD2 KO 小鼠中的横断 CF 侧支延伸超出微区的边界，并在相邻 PCs 的树突上形成局部簇状异位突触。此外，GluD2 KO 小鼠中的 PCs 表现出簇状放电（Cf），这是在野生型小鼠的 PCs 中未发现的 CF 反应。重要的是，Cf 通常与 PCs 远端树突中的局部钙瞬变相关，这可能有助于增强 GluD2 KO 小鼠中钙信号的同步性。因此，我们的结果表明，GluD2 KO 小鼠中的 CF 信号在多个微区中传播，适当形成纵向橄榄小脑投射对于小脑 CS 活动的时空组织是必不可少的。
