Axons, but not cell bodies, are activated by electrical stimulation in cortical gray matter II. Evidence from selective inactivation of cell bodies and axon initial segments
Axons, but not cell bodies, are activated by electrical stimulation in cortical gray matter II. Evidence from selective inactivation of cell bodies and axon initial segments
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DOI：
10.1007/s002210050305
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发表时间：
1998-02-01
影响因子：
2
通讯作者：
Bullier, J
中科院分区：
文献类型：
--
作者：
Nowak, LG;Bullier, J
这篇论文的结果表明，细胞外电刺激灰质直接激活轴突，但不能激活细胞体。本文介绍的第二组实验旨在将轴突起始段和胞体与轴突分支对电刺激激活的突触前神经元元素库的贡献分开。为此，N-甲基-D-天冬氨酸(NMDA)离子导入被用来通过去极化阻断诱导细胞体和轴突毗邻部分的选择性失活，而不影响缺乏NMDA受体的轴突分支。NMDA离子导入后，位于离子导入电极附近的神经元不能以不可逆的方式产生动作电位。当在电刺激部位进行NMDA诱导的去极化阻断时，观察到顺向反应的幅度意外增加。几个对照实验表明，电场电位的增加是由于离子导入吸管附近局部环境的变化，从而导致轴突兴奋性增加。在超兴奋期后，尽管刺激部位的细胞体和轴突起始段不能被电刺激激活，但顺行反应的幅度比NMDA诱导的去极化阻断前降低了15%-20%。这一结果表明，轴突起始节段对电刺激激活的神经元元素库的贡献很低。总之，这些实验表明，电刺激皮质灰质后获得的突触后反应几乎完全来自轴突分支的激活。由于新大脑皮层是由局部和远程互惠连接组成的网络，因此必须非常注意对通过电刺激获得的数据的解释。
The results presented in the companion paper showed that extracellular electrical stimulation of the gray matter directly activates axons, but not cell bodies. The second set of experiments presented here was designed to separate the contribution of the axon initial segments and cell bodies from that of the axonal branches to the pool of presynaptic neuronal elements activated by electrical stimulation. For that purpose, N-methyl-D-aspartate (NMDA) iontophoresis was used to induce a selective inactivation of the cell body and of the adjoining portion of the axon by depolarization block, without affecting axonal branches that lack NMDA receptors. After NMDA iontophoresis, the neurons located near the iontophoresis electrode became unable to generate action potentials in an irreversible manner. When the NMDA-induced depolarization block was performed at the site of electrical stimulation, an unexpected increase in the amplitude of the orthodromic responses was observed. Several control experiments suggested that the field potential increase was due to changes of the local environment in the vicinity,of the iontophoresis pipette, which led to an increased excitability of the axons. After the period of superexcitability, the orthodromic responses displayed an amplitude that was 15-20% lower than that observed before the NMDA-induced depolarization block, even though cell bodies and axon initial segment at the site of stimulation could not be activated by electrical stimulation. This result shows a low contribution for axon initial segments to the pool of neuronal elements activated by the electrical stimulation. Altogether, these experiments demonstrate that the postsynaptic responses obtained after electrical stimulation of the cortical gray matter result almost exclusively from the activation of axonal branches. Since the neocortex is organised as a network of local and long-range reciprocal connections, great attention must be paid to the interpretation of data obtained with electrical stimualtion.