Howard Hughes Medical Institute, Department of Neurobiology, Harvard Medical School, Boston, United States.
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, United States.
Elife. 2022 Mar 23;11:e76993. doi: 10.7554/eLife.76993.
Back-propagating action potentials (bAPs) regulate synaptic plasticity by evoking voltage-dependent calcium influx throughout dendrites. Attenuation of bAP amplitude in distal dendritic compartments alters plasticity in a location-specific manner by reducing bAP-dependent calcium influx. However, it is not known if neurons exhibit branch-specific variability in bAP-dependent calcium signals, independent of distance-dependent attenuation. Here, we reveal that bAPs fail to evoke calcium influx through voltage-gated calcium channels (VGCCs) in a specific population of dendritic branches in mouse cortical layer 2/3 pyramidal cells, despite evoking substantial VGCC-mediated calcium influx in sister branches. These branches contain VGCCs and successfully propagate bAPs in the absence of synaptic input; nevertheless, they fail to exhibit bAP-evoked calcium influx due to a branch-specific reduction in bAP amplitude. We demonstrate that these branches have more elaborate branch structure compared to sister branches, which causes a local reduction in electrotonic impedance and bAP amplitude. Finally, we show that bAPs still amplify synaptically-mediated calcium influx in these branches because of differences in the voltage-dependence and kinetics of VGCCs and NMDA-type glutamate receptors. Branch-specific compartmentalization of bAP-dependent calcium signals may provide a mechanism for neurons to diversify synaptic tuning across the dendritic tree.
逆行传播动作电位 (bAPs) 通过在整个树突中引发电压依赖性钙内流来调节突触可塑性。远端树突隔室中 bAP 幅度的衰减以位置特异性的方式改变可塑性,方法是减少 bAP 依赖性钙内流。然而,尚不清楚神经元是否表现出与距离依赖性衰减无关的 bAP 依赖性钙信号的分支特异性变异性。在这里,我们揭示了尽管在姐妹分支中引发了大量的电压门控钙通道 (VGCC) 介导的钙内流,但在小鼠皮质 2/3 层锥体神经元的特定树突分支中,bAP 无法通过 VGCC 引发钙内流。这些分支包含 VGCC 并在没有突触输入的情况下成功传播 bAP;然而,由于 bAP 幅度的分支特异性降低,它们未能表现出 bAP 引发的钙内流。我们证明这些分支与姐妹分支相比具有更精细的分支结构,这导致电紧张阻抗和 bAP 幅度的局部降低。最后,我们表明,由于 VGCC 和 NMDA 型谷氨酸受体的电压依赖性和动力学的差异,bAP 仍可放大这些分支中突触介导的钙内流。bAP 依赖性钙信号的分支特异性区室化可能为神经元在整个树突中多样化突触调谐提供了一种机制。