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 [Ca²⁺]_o (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.

中文翻译：

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大鼠和小鼠 Held 突触花萼谷氨酸清除和释放动力学的产后成熟

尽管 Held 突触的花萼在听力开始时经历了巨大的变化，但之前的体内研究表明，花萼突触经历了进一步的听力后成熟过程。虽然已经广泛研究了听力开始的发育变化，但这种听力后成熟过程的研究相对较少。由于听力后成熟，先前围绕听力发作的研究和听力后花萼突触的研究结果有些不一致。在这里，我们在大鼠和小鼠的体外电生理特性方面描述了花萼突触的听力后成熟。我们发现，火车期间裂缝中残留谷氨酸的参数、EPSC 动力学和囊泡池大小在 P14 时接近完全成熟水平，但它们在大鼠中进一步成熟到 P16。²⁺ ] _o (1.2 毫米)。相比之下，剩余电流和 EPSC 动力学参数在小鼠 P16 之前显示出剧烈变化，并且在 P16 和 P18 之间火车期间缓慢的 EPSCs 进一步减少，这表明在大鼠和小鼠中，花萼突触的成熟至少进展到 P16 和 P18 .