Laboratory of Ion Channel Pathophysiology,
Laboratory for Motor Learning Control, RIKEN Brain Science Institute, Wako 351-0198, Japan.
J Neurosci. 2018 Jul 4;38(27):6130-6144. doi: 10.1523/JNEUROSCI.3238-17.2018. Epub 2018 Jun 1.
Perineuronal nets (PNNs), composed mainly of chondroitin sulfate proteoglycans, are the extracellular matrix that surrounds cell bodies, proximal dendrites, and axon initial segments of adult CNS neurons. PNNs are known to regulate neuronal plasticity, although their physiological roles in cerebellar functions have yet to be elucidated. Here, we investigated the contribution of PNNs to GABAergic transmission from cerebellar Purkinje cells (PCs) to large glutamatergic neurons in the deep cerebellar nuclei (DCN) in male mice by recording IPSCs from cerebellar slices, in which PNNs were depleted with chondroitinase ABC (ChABC). We found that PNN depletion increased the amplitude of evoked IPSCs and enhanced the paired-pulse depression. ChABC treatment also facilitated spontaneous IPSCs and increased the miniature IPSC frequency without changing not only the amplitude but also the density of PC terminals, suggesting that PNN depletion enhances presynaptic GABA release. We also demonstrated that the enhanced GABAergic transmission facilitated rebound firing in large glutamatergic DCN neurons, which is expected to result in the efficient induction of synaptic plasticity at synapses onto DCN neurons. Furthermore, we tested whether PNN depletion affects cerebellar motor learning. Mice having received the enzyme into the interpositus nuclei, which are responsible for delay eyeblink conditioning, exhibited the conditioned response at a significantly higher rate than control mice. Therefore, our results suggest that PNNs of the DCN suppress GABAergic transmission between PCs and large glutamatergic DCN neurons and restrict synaptic plasticity associated with motor learning in the adult cerebellum. Perineuronal nets (PNNs) are one of the extracellular matrices of adult CNS neurons and implicated in regulating various brain functions. Here we found that enzymatic PNN depletion in the mouse deep cerebellar nuclei (DCN) reduced the paired-pulse ratio of IPSCs and increased the miniature IPSC frequency without changing the amplitude, suggesting that PNN depletion enhances GABA release from the presynaptic Purkinje cell (PC) terminals. Mice having received the enzyme in the interpositus nuclei exhibited a higher conditioned response rate in delay eyeblink conditioning than control mice. These results suggest that PNNs regulate presynaptic functions of PC terminals in the DCN and functional plasticity of synapses on DCN neurons, which influences the flexibility of adult cerebellar functions.
周围神经毡网络（PNNs）主要由软骨素硫酸盐蛋白聚糖组成，是围绕成年中枢神经系统神经元胞体、近端树突和轴突起始段的细胞外基质。已知 PNNs 调节神经元可塑性，尽管它们在小脑功能中的生理作用尚未阐明。在这里，我们通过记录小脑切片中的 IPSC，研究了 PNNs 对小脑浦肯野细胞（PCs）向深部小脑核（DCN）中大型谷氨酸神经元 GABA 能传递的贡献，在小脑切片中用软骨素酶 ABC（ChABC）耗尽 PNNs。我们发现，PNN 耗竭增加了诱发 IPSC 的幅度，并增强了成对脉冲抑制。ChABC 处理还促进了自发性 IPSC，并增加了微小 IPSC 的频率，而不仅改变了 PC 末梢的幅度，而且改变了 PC 末梢的密度，表明 PNN 耗竭增强了 GABA 能释放的突触前。我们还证明，增强的 GABA 能传递促进了大型谷氨酸 DCN 神经元中的反弹发射，这有望导致 DCN 神经元上突触的有效诱导突触可塑性。此外，我们测试了 PNN 耗竭是否影响小脑运动学习。将酶注入负责延迟眨眼条件反射的中间核的小鼠表现出明显高于对照小鼠的条件反射率。因此，我们的结果表明，DCN 的 PNN 抑制了 PCs 和大型谷氨酸 DCN 神经元之间的 GABA 能传递，并限制了成年小脑与运动学习相关的突触可塑性。周围神经毡网络（PNNs）是成年中枢神经系统神经元的细胞外基质之一，与调节各种脑功能有关。在这里，我们发现，在小鼠深部小脑核（DCN）中，酶促 PNN 耗竭降低了 IPSC 的成对脉冲比，并增加了微小 IPSC 的频率，而不改变幅度，表明 PNN 耗竭增强了来自突触前浦肯野细胞（PC）末梢的 GABA 释放。在中间核中接受酶的小鼠在延迟眨眼条件反射中的条件反射率高于对照小鼠。这些结果表明，PNNs 调节 DCN 中 PC 末梢的突触前功能和 DCN 神经元上突触的功能可塑性，这影响了成年小脑功能的灵活性。
