Center for Integrated Protein Science and Institute of Neuroscience, Technical University Munich, 80802 Munich, Germany.
Proc Natl Acad Sci U S A. 2010 Jul 6;107(27):12323-8. doi: 10.1073/pnas.1001745107. Epub 2010 Jun 21.
The large-conductance voltage- and calcium-activated potassium (BK) channels are ubiquitously expressed in the brain and play an important role in the regulation of neuronal excitation. Previous work has shown that the total deletion of these channels causes an impaired motor behavior, consistent with a cerebellar dysfunction. Cellular analyses showed that a decrease in spike firing rate occurred in at least two types of cerebellar neurons, namely in Purkinje neurons (PNs) and in Golgi cells. To determine the relative role of PNs, we developed a cell-selective mouse mutant, which lacked functional BK channels exclusively in PNs. The behavioral analysis of these mice revealed clear symptoms of ataxia, indicating that the BK channels of PNs are of major importance for normal motor coordination. By using combined two-photon imaging and patch-clamp recordings in these mutant mice, we observed a unique type of synaptic dysfunction in vivo, namely a severe silencing of the climbing fiber-evoked complex spike activity. By performing targeted pharmacological manipulations combined with simultaneous patch-clamp recordings in PNs, we obtained direct evidence that this silencing of climbing fiber activity is due to a malfunction of the tripartite olivo-cerebellar feedback loop, consisting of the inhibitory synaptic connection of PNs to the deep cerebellar nuclei (DCN), followed by a projection of inhibitory DCN afferents to the inferior olive, the origin of climbing fibers. Taken together, our results establish an essential role of BK channels of PNs for both cerebellar motor coordination and feedback regulation in the olivo-cerebellar loop.
大电导电压和钙激活钾 (BK) 通道广泛表达于脑内，在神经元兴奋调节中发挥重要作用。先前的研究表明，这些通道的完全缺失会导致运动行为受损，这与小脑功能障碍一致。细胞分析表明，至少两种类型的小脑神经元（浦肯野细胞和高尔基细胞）的放电频率降低。为了确定浦肯野细胞的相对作用，我们开发了一种细胞选择性的小鼠突变体，该突变体仅在浦肯野细胞中缺乏功能性 BK 通道。这些小鼠的行为分析显示出明显的共济失调症状，表明浦肯野细胞的 BK 通道对于正常运动协调具有重要意义。通过在这些突变小鼠中进行双光子成像和膜片钳记录的组合分析，我们观察到了一种独特的突触功能障碍，即 climbing fiber 诱发的复杂放电活动严重沉默。通过进行靶向药理学操作并结合浦肯野细胞的同时膜片钳记录，我们获得了直接证据，表明 climbing fiber 活动的沉默是由于由浦肯野细胞到小脑深部核团（DCN）的抑制性突触连接组成的三部分橄榄小脑反馈回路的功能障碍，然后是抑制性 DCN 传入纤维投射到 climbing fiber 的起源——橄榄。总之，我们的研究结果确立了浦肯野细胞的 BK 通道对于小脑运动协调和 olivo-cerebellar 回路中的反馈调节都具有重要作用。
