The assembly of uniquely organized sound localization circuits in the brainstem requires precise developmental mechanisms. Glial cells have been shown to shape synaptic connections in the retinogeniculate system during development, but their contributions to specialized auditory synapses have not been identified. Here we investigated the role of microglia in auditory brainstem circuit assembly, focusing on the formation and pruning of the calyx of Held in the medial nucleus of the trapezoid body (MNTB). Microglia were pharmacologically depleted in mice early in development using subcutaneous injections of an inhibitor of colony stimulating factor 1 receptor, which is essential for microglia survival. Brainstems were examined prior to and just after hearing onset, at postnatal days (P) 8 and P13, respectively. We found that at P13 there were significantly more polyinnervated MNTB neurons when microglia were depleted, consistent with a defect in pruning. Expression of glial fibrillary acidic protein (GFAP), a mature astrocyte marker that normally appears in the MNTB late in development, was significantly decreased in microglia-depleted mice at P13, suggesting a delay in astrocyte maturation. Our results demonstrate that monoinnervation of MNTB neurons by the calyx of Held is significantly disrupted or delayed in the absence of microglia. This finding may reflect a direct role for microglia in synaptic pruning. A secondary role for microglia may be in the maturation of astrocytes in MNTB. These findings highlight the significant function of glia in pruning during calyx of Held development.

中文翻译：

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小胶质细胞调节听觉脑干中专门突触的修剪。


脑干中独特组织的声音定位电路的组装需要精确的发育机制。神经胶质细胞已被证明在发育过程中塑造视网膜原化系统中的突触连接，但它们对特殊听觉突触的贡献尚未确定。在这里，我们研究了小胶质细胞在听觉脑干回路组装中的作用，重点关注梯形体内侧核（MNTB）中Held花萼的形成和修剪。通过皮下注射集落刺激因子 1 受体抑制剂，在发育早期的小鼠中，小胶质细胞被药物耗尽，这对于小胶质细胞的生存至关重要。分别在出生后第 8 天 (P) 和第 13 天，在听力出现之前和之后立即检查脑干。我们发现，在 P13，当小胶质细胞耗尽时，多神经支配的 MNTB 神经元明显增多，这与修剪缺陷一致。胶质纤维酸性蛋白（GFAP）是一种成熟星形胶质细胞标记物，通常出现在发育后期的 MNTB 中，但在小胶质细胞耗尽的小鼠中 P13 时表达显着下降，表明星形胶质细胞成熟延迟。我们的结果表明，在没有小胶质细胞的情况下，Held 花萼对 MNTB 神经元的单神经支配被显着破坏或延迟。这一发现可能反映了小胶质细胞在突触修剪中的直接作用。小胶质细胞的第二个作用可能是 MNTB 中星形胶质细胞的成熟。这些发现强调了神经胶质细胞在花萼发育过程中修剪的重要功能。