Bazzigaluppi Paolo, Isenia Sheena C, Haasdijk Elize D, Elgersma Ype, De Zeeuw Chris I, van der Giessen Ruben S, de Jeu Marcel T G
Department of Neuroscience, Erasmus Medical Center, Rotterdam, Netherlands.
Front Cell Neurosci. 2017 Dec 14;11:397. doi: 10.3389/fncel.2017.00397. eCollection 2017.
The inferior olive (IO) is a nucleus located in the brainstem and it is part of the olivo-cerebellar loop. This circuit plays a fundamental role in generation and acquisition of coherent motor patterns and it relies on synchronous activation of groups of Purkinje cells (PC) in the cerebellar cortex. IO neurons integrate their intrinsic oscillatory activity with excitatory inputs coming from the somatosensory system and inhibitory feedback coming from the cerebellar nuclei. Alongside these chemical synaptic inputs, IO neurons are coupled to one another via connexin 36 (Cx36) containing gap junctions (GJs) that create a functional syncytium between neurons. Communication between olivary neurons is regulated by these GJs and their correct functioning contributes to coherent oscillations in the IO and proper motor learning. Here, we explore the cellular pathways that can regulate the coupling between olivary neurons. We combined electrophysiology and immunohistochemistry (IHC) on mouse acute brain slices to unravel the pathways that regulate olivary coupling. We found that enhancing the activity of the protein kinase A (PKA) pathway and blocking the Ca/calmodulin-dependent protein kinase II (CaMKII) pathway can both down-regulate the size of the coupled network. However, these two kinases follow different mechanisms of action. Our results suggest that activation of the PKA pathway reduces the opening probability of the Cx36 GJs, whereas inhibition of the CaMKII pathway reduces the number of Cx36 GJs. The low densities of Cx36 proteins and electrical synapses in βCaMKII knock-out mice point towards an essential role for this protein kinase in regulating the density of GJs in the IO. Thus, the level of olivary coupling is a dynamic process and regulated by a variety of enzymes modulating GJs expression, docking and activity.
下橄榄核（IO）是位于脑干的一个神经核，是橄榄小脑环路的一部分。该环路在连贯运动模式的产生和习得中起着重要作用，它依赖于小脑皮质中浦肯野细胞（PC）群的同步激活。IO神经元将其内在振荡活动与来自体感系统的兴奋性输入以及来自小脑核的抑制性反馈整合在一起。除了这些化学突触输入外，IO神经元还通过含有缝隙连接（GJ）的连接蛋白36（Cx36）相互耦联，从而在神经元之间形成功能性合胞体。橄榄核神经元之间的通讯受这些GJ调节，其正常功能有助于IO中的连贯振荡和适当的运动学习。在这里，我们探索了可以调节橄榄核神经元之间耦合的细胞途径。我们在小鼠急性脑切片上结合了电生理学和免疫组织化学（IHC），以揭示调节橄榄核耦合的途径。我们发现增强蛋白激酶A（PKA）途径的活性并阻断钙/钙调蛋白依赖性蛋白激酶II（CaMKII）途径，均可下调耦合网络的大小。然而，这两种激酶遵循不同的作用机制。我们的结果表明，PKA途径的激活降低了Cx36 GJ的开放概率，而CaMKII途径的抑制则减少了Cx36 GJ的数量。βCaMKII基因敲除小鼠中Cx36蛋白和电突触的低密度表明该蛋白激酶在调节IO中GJ的密度方面起着重要作用。因此，橄榄核耦合水平是一个动态过程，受多种调节GJ表达、对接和活性的酶调控。
