A morphologically present but non-functioning synapse is termed a silent synapse. Silent synapses are categorized into “postsynaptically silent synapses,” where AMPA receptors are either absent or non-functional, and “presynaptically silent synapses,” where neurotransmitters cannot be released from nerve terminals. The presence of presynaptically silent synapses remains enigmatic, and their physiological significance is highly intriguing. In this study, we examined the distribution and developmental changes of presynaptically active and silent synapses in individual neurons. Our findings show a gradual increase in the number of excitatory synapses, along with a corresponding decrease in the percentage of presynaptically silent synapses during neuronal development. To pinpoint the distribution of presynaptically active and silent synapses, i.e., their positional information, we employed Sholl analysis. Our results indicate that the distribution of presynaptically silent synapses within a single neuron does not exhibit a distinct pattern during synapse development in different distance from the cell body. However, irrespective of neuronal development, the proportion of presynaptically silent synapses tends to rise as the projection site moves farther from the cell body, suggesting that synapses near the cell body may exhibit higher synaptic transmission efficiency. This study represents the first observation of changes in the distribution of presynaptically active and silent synapses within a single neuron.

中文翻译：

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单培养海马神经元突触前活动和沉默突触的位置分析

形态上存在但无功能的突触被称为沉默突触。沉默突触分为“突触后沉默突触”（其中 AMPA 受体不存在或无功能）和“突触前沉默突触”（其中神经递质无法从神经末梢释放）。突触前沉默突触的存在仍然是个谜，它们的生理意义非常有趣。在这项研究中，我们检查了单个神经元中突触前活跃和沉默突触的分布和发育变化。我们的研究结果表明，在神经元发育过程中，兴奋性突触的数量逐渐增加，而突触前沉默突触的百分比相应减少。为了查明突触前活跃和沉默突触的分布，即它们的位置信息，我们采用了肖尔分析。我们的结果表明，在距细胞体不同距离的突触发育过程中，单个神经元内突触前沉默突触的分布没有表现出明显的模式。然而，无论神经元发育如何，随着投射位点远离细胞体，突触前沉默突触的比例往往会上升，这表明靠近细胞体的突触可能表现出更高的突触传递效率。这项研究首次观察到单个神经元内突触前活跃和沉默突触的分布变化。