Cell Physiology Lab, Department of Physiology, Seoul National University College of Medicine and Neuroscience Research Institute, Seoul National University Medical Research Center, Seoul, Republic of Korea.
Department of Brain and Cognitive Science, Seoul National University, Seoul, Republic of Korea.
Synapse. 2021 Sep;75(9):e22215. doi: 10.1002/syn.22215. Epub 2021 Jul 16.
Although calyx of Held synapses undergo dramatic changes around the hearing onset, previous in vivo studies suggest that the calyx synapses undergo further post-hearing maturation process. While developmental changes over the hearing onset have been extensively studied, this post-hearing maturation process remained relatively little investigated. Because of post-hearing maturation, previous results from studies around hearing onset and studies of post-hearing calyx synapses are somewhat inconsistent. Here, we characterized the post-hearing maturation of calyx synapses with regard to in vitro electrophysiological properties in rats and mice. We found that parameters for residual glutamate in the cleft during a train, EPSC kinetics, and vesicle pool size became close to a full mature level by P14, but they further matured until P16 in the rats. Consistently, the phasic and slow EPSCs evoked by action potential trains at P16 calyx synapses were not different from those at P18 or P25 under physiological extracellular [Ca ] (1.2 mM). In contrast, the parameters for residual current and EPSC kinetics displayed drastic changes until P16 in mice, and slow EPSCs during the train further decreased between P16 and P18, suggesting that maturation of calyx synapses progresses at least up to P16 in rats and P18 in mice.
虽然听敏期前后蜗顶突触发生了显著变化，但先前的活体研究表明，蜗顶突触还经历了进一步的听觉后成熟过程。尽管已广泛研究了听敏期前后的发育变化，但这一听觉后成熟过程仍相对较少被研究。由于听觉后成熟，先前关于听敏期前后的研究结果和听觉后蜗顶突触的研究结果有些不一致。在这里，我们通过在大鼠和小鼠中进行体外电生理特性研究，对蜗顶突触的听觉后成熟进行了描述。我们发现，在 P14 时，在递质释放的串脉冲中，突触小泡内残留谷氨酸的参数、EPSC 动力学和囊泡池大小等参数接近完全成熟水平，但在大鼠中它们会进一步成熟至 P16。一致的是，在 P16 时，动作电位串脉冲诱发的快 EPSC 和慢 EPSC 与 P18 或 P25 时的相似。相比之下，在小鼠中，直到 P16 时，残留电流和 EPSC 动力学的参数才发生急剧变化，并且在 P16 和 P18 之间，慢 EPSC 进一步减少，这表明大鼠的蜗顶突触成熟至少持续到 P16，而在小鼠中则持续到 P18。
