Bikson Marom, Inoue Masashi, Akiyama Hiroki, Deans Jackie K, Fox John E, Miyakawa Hiroyoshi, Jefferys John G R
Department of Neurophysiology, University of Birmingham, Egbaston, Birmingham, UK.
J Physiol. 2004 May 15;557(Pt 1):175-90. doi: 10.1113/jphysiol.2003.055772. Epub 2004 Feb 20.
The effects of uniform steady state (DC) extracellular electric fields on neuronal excitability were characterized in rat hippocampal slices using field, intracellular and voltage-sensitive dye recordings. Small electric fields (</40/ mV mm(-1)), applied parallel to the somato-dendritic axis, induced polarization of CA1 pyramidal cells; the relationship between applied field and induced polarization was linear (0.12 +/- 0.05 mV per mV mm(-1) average sensitivity at the soma). The peak amplitude and time constant (15-70 ms) of membrane polarization varied along the axis of neurons with the maximal polarization observed at the tips of basal and apical dendrites. The polarization was biphasic in the mid-apical dendrites; there was a time-dependent shift in the polarity reversal site. DC fields altered the thresholds of action potentials evoked by orthodromic stimulation, and shifted their initiation site along the apical dendrites. Large electric fields could trigger neuronal firing and epileptiform activity, and induce long-term (>1 s) changes in neuronal excitability. Electric fields perpendicular to the apical-dendritic axis did not induce somatic polarization, but did modulate orthodromic responses, indicating an effect on afferents. These results demonstrate that DC fields can modulate neuronal excitability in a time-dependent manner, with no clear threshold, as a result of interactions between neuronal compartments, the non-linear properties of the cell membrane, and effects on afferents.
利用电场、细胞内记录和电压敏感染料记录，在大鼠海马切片中研究了均匀稳态（直流）细胞外电场对神经元兴奋性的影响。平行于胞体 - 树突轴施加小电场（<40 mV/mm(-1)）可诱导CA1锥体细胞极化；施加电场与诱导极化之间的关系呈线性（胞体处平均敏感度为每mV/mm(-1) 0.12±0.05 mV）。膜极化的峰值幅度和时间常数（15 - 70毫秒）沿神经元轴变化，在基底和顶端树突尖端观察到最大极化。在顶端树突中部，极化是双相的；极性反转位点存在时间依赖性偏移。直流电场改变了由顺向刺激诱发的动作电位阈值，并使其起始位点沿顶端树突移动。大电场可触发神经元放电和癫痫样活动，并诱导神经元兴奋性的长期（>1秒）变化。垂直于顶端 - 树突轴的电场不会诱导体细胞极化，但会调节顺向反应，表明对传入神经有影响。这些结果表明，由于神经元区室之间的相互作用、细胞膜的非线性特性以及对传入神经的影响，直流电场可随时间依赖性方式调节神经元兴奋性，且无明确阈值。
