Excitatory synapses in the mammalian brain exhibit diverse functional properties in transmission and plasticity. Directly visualizing the structural correlates of such functional heterogeneity is often hindered by the diffraction-limited resolution of conventional optical imaging techniques. Here, we used super-resolution stochastic optical reconstruction microscopy (STORM) to resolve structurally distinct excitatory synapses formed on dendritic shafts and spines. The majority of these shaft synapses contained N-methyl-d-aspartate receptors (NMDARs) but not α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), suggesting that they were functionally silent. During development, as more spine synapses formed with increasing sizes and expression of AMPARs and NMDARs, shaft synapses exhibited moderate reduction in density with largely unchanged sizes and receptor expression. Furthermore, upon glycine stimulation to induce chemical long-term potentiation (cLTP), the previously silent shaft synapses became functional shaft synapses by recruiting more AMPARs than did spine synapses. Thus, silent shaft synapse may represent a synaptic state in developing neurons with enhanced capacity of activity-dependent potentiation.

哺乳动物大脑中的兴奋性突触在传递和可塑性方面表现出多种功能特性。传统光学成像技术的衍射极限分辨率常常阻碍直接可视化这种功能异质性的结构相关性。在这里，我们使用超分辨率随机光学重建显微镜（STORM）来解析树突轴和树棘上形成的结构不同的兴奋性突触。这些轴突触中的大多数含有N-甲基-d-天冬氨酸受体（NMDAR），但不含有α-氨基-3-羟基-5-甲基-4-异恶唑丙酸受体（AMPAR），这表明它们在功能上是沉默的。在发育过程中，随着 AMPAR 和 NMDAR 的大小和表达增加，形成更多的棘突触，轴突触的密度适度降低，而大小和受体表达基本不变。此外，在甘氨酸刺激诱导化学长时程增强（cLTP）后，先前沉默的轴突触通过募集比棘突触更多的 AMPAR 而成为功能性轴突触。因此，沉默轴突触可能代表发育中神经元的突触状态，具有增强的活动依赖性增强能力。