Site of action potential initiation in layer 5 pyramidal neurons
Site of action potential initiation in layer 5 pyramidal neurons
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DOI：
10.1523/jneurosci.4812-05.2006
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发表时间：
2006-02-08
影响因子：
5.3
通讯作者：
Stuart, GJ
中科院分区：
文献类型：
--
作者：
Palmer, LM;Stuart, GJ
了解神经元如何整合突触输入的基础是了解该信息在神经元内的何处转换为输出信号（动作电位）。尽管人们早就知道动作电位的启动发生在神经元轴突内，但精确的位置仍然难以捉摸。在这里，我们使用电压敏感染料提供了直接证据，表明皮质第 5 层锥体神经元的动作电位起始位点与轴突小丘的 35 μm 相似。这是在各种条件下、轴突抑制后以及不同发育阶段的动作电位产生过程中的情况。一旦启动，动作电位就会以跳跃的方式沿着轴突传播。局部应用低钠溶液和 TTX 的实验以及轴突长度对动作电位特性影响的研究提供了证据，表明轴突的初始 40 μm 对于动作电位的产生至关重要。为了从形态学上识别动作电位起始位点与轴突髓鞘形成之间的关系，我们标记了向轴突近端区域提供过程的少突胶质细胞。这些实验表明，轴突起始段的长度约为40μm，Ranvier第一节距轴突小丘的长度约为90μm。针对朗飞的第一个节点的实验表明它不参与动作电位的启动。总之，这些结果表明，在第 5 层锥体神经元中，动作电位是在轴突初始段的远端区域产生的。
Fundamental to an understanding of how neurons integrate synaptic input is the knowledge of where within a neuron this information is converted into an output signal, the action potential. Although it has been known for some time that action potential initiation occurs within the axon of neurons, the precise location has remained elusive. Here, we provide direct evidence using voltage-sensitive dyes that the site of action potential initiation in cortical layer 5 pyramidal neurons is similar to 35 mu m from the axon hillock. This was the case during action potential generation under a variety of conditions, after axonal inhibition, and at different stages of development. Once initiated action potentials propagated down the axon in a saltatory manner. Experiments using local application of low-sodium solution and TTX, as well as an investigation of the influence of axonal length on action potential properties, provided evidence that the initial 40 mu m of the axon is essential for action potential generation. To morphologically identify the relationship between the site of action potential initiation and axonal myelination, we labeled oligodendrocytes supplying processes to the proximal region of the axon. These experiments indicated that the axon initial segment was similar to 40 mu m in length, and the first node of Ranvier was similar to 90 mu m from the axon hillock. Experiments targeting the first node of Ranvier suggested it was not involved in action potential initiation. In conclusion, these results indicate that, in layer 5 pyramidal neurons, action potentials are generated in the distal region of the axon initial segment.