Developmental Tightening of Cerebellar Cortical Synaptic Influx-Release Coupling
Developmental Tightening of Cerebellar Cortical Synaptic Influx-Release Coupling
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DOI：
10.1523/jneurosci.2900-14.2015
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发表时间：
2015-02-04
影响因子：
5.3
通讯作者：
Schmidt, Hartmut
中科院分区：
文献类型：
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作者：
Baur, David;Bornschein, Grit;Schmidt, Hartmut
Ca2+通道与突触前活跃区（AZ）囊状递质释放传感器之间的紧密耦合对于高保真突触传递至关重要。据推测，从松散耦合到紧密耦合的传递模式的转换是中枢神经系统突触成熟的一个常见步骤。然而，这一假设从未在皮质突触上得到验证。我们在一个具有代表性的小皮层突触上解决了这一假设：连接小鼠小脑皮层平行纤维和浦肯野神经元的突触。我们发现缓慢的Ca2+螯合剂EGTA对未成熟突触的释放影响明显强于成熟突触，而快速螯合剂BAPTA在两组中同样有效。用多概率波动分析对脉冲比率和定量释放概率（p(r)）的分析显示，未成熟突触的易化性增加伴随着pr的降低。定量高分辨率免疫电镜评估的Cav2.1 Ca2+通道免疫反应性分散在未成熟扣上，但仅限于成熟扣上的推定AZs。突触前Ca2+信号用双光子显微镜量化，发现成熟阶段之间相似。调整后的模型拟合EGTA剂量-反应曲线以及Ca2+通道阻滞剂Cd2+的差异效应表明，与成熟末端相比，未成熟末端的偶联更松散，同质性更低。这些结果表明，在单个AZ皮质突触中，流入-释放偶联的发育收紧与功能相关，并证实了发育收紧偶联是哺乳动物大脑中普遍存在的现象。
Tight coupling between Ca2+ channels and the sensor for vesicular transmitter release at the presynaptic active zone (AZ) is crucial for high-fidelity synaptic transmission. It has been hypothesized that a switch from a loosely coupled to a tightly coupled transmission mode is a common step in the maturation of CNS synapses. However, this hypothesis has never been tested at cortical synapses. We addressed this hypothesis at a representative small cortical synapse: the synapse connecting mouse cerebellar cortical parallel fibers to Purkinje neurons. We found that the slow Ca2+ chelator EGTA affected release significantly stronger at immature than at mature synapses, while the fast chelator BAPTA was similarly effective in both groups. Analysis of paired-pulse ratios and quantification of release probability (p(r)) with multiple-probability fluctuation analysis revealed increased facilitation at immature synapses accompanied by reduced pr. Cav2.1 Ca2+ channel immunoreactivity, assessed by quantitative high-resolution immuno-electron microscopy, was scattered over immature boutons but confined to putative AZs at mature boutons. Presynaptic Ca2+ signals were quantified with two-photon microscopy and found to be similar between maturation stages. Models adjusted to fit EGTA dose-response curves as well as differential effects of the Ca2+ channel blocker Cd2+ indicate looser and less homogenous coupling at immature terminals compared with mature ones. These results demonstrate functionally relevant developmental tightening of influx-release coupling at a single AZ cortical synapse and corroborate developmental tightening of coupling as a prevalent phenomenon in the mammalian brain.