Developmental changes in Ca2+ influx release coupling at the active zone of excitatory cortical synapses

中枢神经系统（CNS）的信息处理依赖于快速的化学突触传递，其由通过电压门控钙通道的钙内流触发。在突触前活动区的钙通道和充满递质的囊泡之间的耦合距离是该过程的速度、可靠性和能量功效的关键决定因素。紧密的所谓纳米畴耦合有利于传输的保真度，而松散的所谓微畴耦合与不太有利的传输特性相关联。最初，发现仅外周神经系统的突触、一个脑干突触和抑制性CNS突触在纳米结构域耦合下操作。另一方面，年轻的兴奋性海马和皮质突触在松散的微区耦合下运作，这导致了兴奋性皮质突触微区耦合的一般假设。我们小组最近的研究结果挑战了这种观点的普遍性，表明小脑皮质的成年兴奋性平行纤维与浦肯野细胞突触（可能是大脑中最丰富的突触）在纳米结构域耦合下运作。我们的实验和之前关于突触耦合的实验之间的一个有趣的区别是实验动物的年龄：当其他实验室的实验在年轻的突触上进行时，我们分析了更多成年动物的耦合距离。在这个建议中，假设提出的耦合距离的基础上发展紧缩。支持这一观点的数据来自于已发表的来自Held脑干突触萼的数据和本申请中提出的初步观察结果，然而，这需要更深入的研究。为了得到一个更普遍的结论，它是打算探测耦合在年轻和成年兴奋性突触的大脑和小脑皮质。具体而言，将在新皮层第5层锥体神经元之间形成的突触和颗粒细胞与浦肯野细胞之间形成的小脑平行纤维突触处分析耦合。了解耦合距离及其调节对于正确解释递质释放的有效性和突触可塑性机制至关重要。由于释放和可塑性是神经元信息处理的核心，因此这些知识对于理解突触成熟和大脑中的编码具有普遍意义。

Information processing in the central nervous system (CNS) relies on rapid chemical synaptic transmission, which is triggered by calcium influx through voltage gated calcium channels. The coupling distance between the calcium channels and the transmitter filled vesicles at the presynaptic active zone is a critical determinant of speed, reliability and energy efficacy of this process. A tight, so called nanodomain coupling, favors the fidelity of transmission, while a loose, so called microdomain coupling, is associated with less favorable transmission characteristics. Initially only synapses of the peripheral nervous system, one brain stem synapse, and inhibitory CNS synapses were found to operate at nanodomain coupling. Young excitatory hippocampal and cortical synapses on the other hand operated at loose, microdomain coupling, which led to the general assumption about microdomain coupling at excitatory cortical synapses. Recent results from our group challenged the generality of this view, showing that the adult excitatory parallel fiber to Purkinje cell synapse of the cerebellar cortex, probably the most abundant synapse in the brain, operates at nanodomain coupling. An intriguing difference between our experiments and the preceding experiments on coupling at glutamatergic synapses is the age of the experimental animals: While experiments from the other labs were performed on young synapses, we analyzed the coupling distance in more adult animals. In this proposal, the hypothesis is put forth that the coupling distance underlies a developmental tightening. Support for this idea comes from published data from the Calyx of Held brain stem synapse and preliminary observations presented in this application, which, however, require substantially deeper investigation. In order to arrive at a more general conclusion, it is intended to probe coupling at young and adult excitatory synapses of both, the cerebral and the cerebellar cortex. Specifically, coupling will be analyzed at synapses formed between neocortical layer 5 pyramidal neurons and cerebellar parallel fiber synapses formed between granule cells and Purkinje cells. Knowledge about the coupling distance and its regulation is critical for correctly interpreting the efficacy of transmitter release and mechanisms of synaptic plasticity. Since release and plasticity are at the core of neuronal information processing, this knowledge is of general interest for understanding synapse maturation and coding in the brain.