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，而突触传递是由钙离子通过电压门控钙通道内流触发的。钙通道和突触前活动区充满递质的囊泡之间的耦合距离是这一过程的速度、可靠性和能量有效性的关键决定因素。紧密的，所谓的纳米域耦合，有利于传输的保真度，而松散的，所谓的微域耦合，与较差的传输特性相关。最初，只有外周神经系统的突触、一个脑干突触和抑制性CNS突触被发现在纳域耦合下工作。另一方面，年轻的兴奋性海马和皮质突触以松散的微域耦合方式工作，这导致了兴奋性皮质突触微域耦合的一般假设。我们小组最近的结果挑战了这一观点的普遍性，表明成人兴奋性平行纤维到小脑皮质浦肯野细胞突触的操作是在纳域耦合的，小脑皮质浦肯野细胞突触可能是大脑中最丰富的突触。我们的实验和之前关于谷氨酸能突触耦合的实验之间一个有趣的区别是实验动物的年龄：其他实验室的实验是在年轻的突触上进行的，而我们分析了更多成年动物的耦合距离。在这一建议中，提出了一种假设，即耦合距离是发展紧缩的基础。对这一观点的支持来自于来自持有的脑干突触的肾盏的公布数据和在本申请中提出的初步观察，然而，这需要更深入的研究。为了得出更普遍的结论，本研究旨在探索青年和成人兴奋性突触的耦合，即大脑和小脑皮质。具体地说，将分析在新皮质第五层锥体神经元之间形成的突触和颗粒细胞和浦肯野细胞之间形成的小脑平行纤维突触之间的耦合。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的机制是至关重要的。由于释放和可塑性是神经元信息处理的核心，这一知识对于理解大脑中突触的成熟和编码是普遍感兴趣的。

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.