DIFFERENTIAL CONDUCTION BLOCK IN BRANCHES OF A BIFURCATING AXON

被引:132
作者
GROSSMAN, Y [1 ]
PARNAS, I [1 ]
SPIRA, ME [1 ]
机构
[1] HEBREW UNIV JERUSALEM, INST LIFE SCI, NEUROBIOL UNIT, JERUSALEM 91000, ISRAEL
来源
JOURNAL OF PHYSIOLOGY-LONDON | 1979年 / 295卷 / OCT期
关键词
D O I
10.1113/jphysiol.1979.sp012969
中图分类号
Q189 [神经科学];
学科分类号
071006 ;
摘要
Propagation of action potentials at high frequency was studied in a branching axon of the lobster [Panulirus penicillatus] by means of simultaneous intracellular recording before and after the branch point. Although the branching axon studied has a geometrical ratio close to 1 (perfect impedance matching) conduction across the branch point failed at stimulation frequencies above 30 Hz. The block of conduction after high frequency stimulation occurred at the branch point per se. The parent axon and daughter branches continued to conduct action potentials. Conduction block after high frequency stimulation appeard first in the thicker daugher branch and only later in the thin branch. With high frequency stimulation there was a 10-15% reduction in amplitude of the action potential in the parent axon, a corresponding decrease in the rate of rise of the action potential, a 25-30% decrease in conduction velocity, marked increase in threshold and prolongation of the refractory period. The membrane was depolarized by 1-3 mV. Measurements of the membrane current using the patch clamp technique showed a large decrease in the phase inward current associated with the action potential, before the branching point. The small membrane depolarization seen after high frequency stimulation was not the sole cause of the conduction block. Imposed prolonged membrane depolarization (8 mV for 120 s) was insufficient to produce conduction block. In vivo chronic extracellular recordings from the main nerve bundle (which contains the parent axon) and the large daughter branch revealed that the duration and frequency of trains of action potentials along the axons exceeded those used in the isolated nerve experiments and conduction failure in the large daughter branch could be induced in the whole animal by electrical stimulation of the main branch as in the isolated preparation. Possible mechanisms underlying block of conduction after high frequency stimulation in a branching axon are discussed.
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收藏
页码:283 / 305
页数:23
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