Presynaptic action potential spikes control neurotransmitter release and thus interneuronal communication. However, the properties and the dynamics of presynaptic spikes in the neocortex remain enigmatic because boutons in the neocortex are small and direct patch-clamp recordings have not been performed. Here we report direct recordings from boutons of neocortical pyramidal neurons and interneurons. Our data reveal rapid and large presynaptic action potentials in layer 5 neurons and fast-spiking interneurons reliably propagating into axon collaterals. For in-depth analyses we validate boutons of mature cultured neurons as models for excitatory neocortical boutons, demonstrating that the presynaptic spike amplitude was unaffected by potassium channels, homeostatic long-term plasticity, and high-frequency firing. In contrast to the stable amplitude, presynaptic spikes profoundly broadened for example during high-frequency firing in layer 5 pyramidal neurons but not in fast-spiking interneurons. Thus, our data demonstrate large presynaptic spikes and fundamental differences between excitatory and inhibitory boutons in the neocortex.

中文翻译：

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大而稳定的尖峰表现出兴奋性和抑制性新皮层钮扣的差异加宽

突触前动作电位尖峰控制神经递质的释放，从而控制神经元间的通讯。但是，新皮层中突触前尖峰的性质和动力学仍然是令人迷惑的，因为新皮层中的钮扣很小，并且未进行直接膜片钳记录。在这里，我们报告从新皮质锥体神经元和中间神经元的boutons直接记录。我们的数据揭示了在第5层神经元和快速突触的中间神经元中迅速而又大的突触前动作电位可靠地传播到轴突侧支中。为了进行深入分析，我们将成熟的培养神经元钮扣作为兴奋性新皮层钮扣的模型，表明突触前突波波幅不受钾通道，稳态长期可塑性和高频发射的影响。与稳定的幅度相比，突触前突增明显增加，例如在第5层锥体神经元的高频发射期间，而在快速突触的中间神经元中则没有。因此，我们的数据显示出新皮层中突触前突突和兴奋性和抑制性按钮之间的根本差异。