After-effects of near-threshold stimulation in single human motor axons

被引:40
作者
Bostock, H
Lin, CSY
Howells, J
Trevillion, L
Jankelowitz, S
Burke, D
机构
[1] Inst Neurol, Sobell Dept Neurophysiol, London WC1N 3BG, England
[2] Univ Sydney, Inst Clin Neurosci, Sydney, NSW, Australia
[3] Royal Prince Alfred Hosp, Sydney, NSW, Australia
来源
JOURNAL OF PHYSIOLOGY-LONDON | 2005年 / 564卷 / 03期
关键词
D O I
10.1113/jphysiol.2005.083394
中图分类号
Q189 [神经科学];
学科分类号
071006 ;
摘要
Subthreshold electrical stimuli can generate a long-lasting increase in axonal excitability, superficially resembling the phase of superexcitability that follows a conditioning nerve impulse. This phenomenon of 'subthreshold superexcitability' has been investigated in single motor axons in six healthy human subjects, by tracking the excitability changes produced by conditioning stimuli of different amplitudes and waveforms. Near-threshold 1 ms stimuli caused a mean decrease in threshold at 5 ms of 22.1 +/- 6.0% (mean S.D.) if excitation occurred, or 6.9 +/- 2.6% if excitation did not occur. The subthreshold superexcitability was maximal at an interval of about 5 ins, and fell to zero at 30 ms. It appeared to be made up of two components: a passive component linearly related to conditioning stimulus amplitude, and a non-linear active component. The active component appeared when conditioning stimuli exceeded 60% of threshold, and accounted for a maximal threshold decrease of 2.6 +/- 1.3%. The passive component was directly proportional to stimulus charge, when conditioning stimulus duration was varied between 0.2 and 2 ins, and could be eliminated by using triphasic stimuli with zero net charge. This change in stimulus waveform had little effect on the active component of subthreshold superexcitability or on the 'suprathreshold superexcitability' that followed excitation. It is concluded that subthreshold superexcitability in human motor axons is mainly due to the passive electrotonic effects of the stimulating current, but this is supplemented by an active component (about 12% of suprathreshold superexcitability), due to a local response of voltage-dependent sodium channels.
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收藏
页码:931 / 940
页数:10
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