Flores Carmen E, Nikonenko Irina, Mendez Pablo, Fritschy Jean-Marc, Tyagarajan Shiva K, Muller Dominique
Département des Neurosciences Fondamentales, Faculté de Médecine, Centre Médical Universitaire, Université de Genève, 1211 Geneve 4, Switzerland; and.
Institute of Pharmacology and Toxicology, University of Zürich, 8057 Zurich, Switzerland.
Proc Natl Acad Sci U S A. 2015 Jan 6;112(1):E65-72. doi: 10.1073/pnas.1411170112. Epub 2014 Dec 22.
Maintaining a proper balance between excitation and inhibition is essential for the functioning of neuronal networks. However, little is known about the mechanisms through which excitatory activity can affect inhibitory synapse plasticity. Here we used tagged gephyrin, one of the main scaffolding proteins of the postsynaptic density at GABAergic synapses, to monitor the activity-dependent adaptation of perisomatic inhibitory synapses over prolonged periods of time in hippocampal slice cultures. We find that learning-related activity patterns known to induce N-methyl-D-aspartate (NMDA) receptor-dependent long-term potentiation and transient optogenetic activation of single neurons induce within hours a robust increase in the formation and size of gephyrin-tagged clusters at inhibitory synapses identified by correlated confocal electron microscopy. This inhibitory morphological plasticity was associated with an increase in spontaneous inhibitory activity but did not require activation of GABAA receptors. Importantly, this activity-dependent inhibitory plasticity was prevented by pharmacological blockade of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), it was associated with an increased phosphorylation of gephyrin on a site targeted by CaMKII, and could be prevented or mimicked by gephyrin phospho-mutants for this site. These results reveal a homeostatic mechanism through which activity regulates the dynamics and function of perisomatic inhibitory synapses, and they identify a CaMKII-dependent phosphorylation site on gephyrin as critically important for this process.
维持兴奋与抑制之间的适当平衡对于神经网络的功能至关重要。然而，关于兴奋性活动影响抑制性突触可塑性的机制，我们所知甚少。在此，我们利用标记的桥连蛋白（Gephyrin），它是γ-氨基丁酸（GABA）能突触后致密区的主要支架蛋白之一，来监测海马脑片培养物中胞体周围抑制性突触在长时间内的活动依赖性适应性变化。我们发现，已知能诱导N-甲基-D-天冬氨酸（NMDA）受体依赖性长时程增强的学习相关活动模式以及单个神经元的短暂光遗传学激活，在数小时内会导致通过相关共聚焦电子显微镜鉴定的抑制性突触处桥连蛋白标记簇的形成和大小显著增加。这种抑制性形态可塑性与自发抑制性活动的增加相关，但不需要GABAA受体的激活。重要的是，这种活动依赖性抑制可塑性可通过钙/钙调蛋白依赖性蛋白激酶II（CaMKII）的药理学阻断来防止，它与桥连蛋白在CaMKII靶向位点的磷酸化增加相关，并且可被该位点的桥连蛋白磷酸化突变体阻止或模拟。这些结果揭示了一种稳态机制，通过该机制活动调节胞体周围抑制性突触的动力学和功能，并且它们确定了桥连蛋白上一个CaMKII依赖性磷酸化位点对该过程至关重要。
