Awiszus F
Medizinische Hochschule Hannover, Abteilung Neurophysiologie (OE 4230), D-30623 Hannover, Germany.
Biol Cybern. 1994;70(6):579-83. doi: 10.1007/BF00198811.
Afferent activity in a receptor afferent fiber with several encoding sites is generally believed to represent the activity of the fastest pacemaker that resets all more slowly encoding sites. Alternatively, some impulse mixing as well as some nonlinear summation of receptor current to a single encoder have been considered. In this article the repetitive firing activity of a Hodgkin-Huxley axon consisting of two branches that join into a single stem axon was investigated. The model axon was stimulated by constant-current injection into either the right or the left or both branches. It was found that the model axon generated an (infinite) train of action potentials if the input current was large enough. The discharge frequency found was constant, and on combined stimulation of both branches with different current, the site of impulse initiation was always in the branch receiving the higher input current, excluding a simple impulse mixing. On the other hand, the combined stimulation of both branches evoked repetitive firing with a higher frequency than expected by the pacemaker-resetting hypothesis. Moreover, a stimulus that is subthreshold for repetitive firing if injected into one branch yields repetitive firing when it is injected into both branches, a behavior inconsistent with impulse mixing and pacemaker resetting. On the other hand, current injection into one branch allowed repetitive activity only within a rather limited range of firing frequencies. Using distributed current injection into both branches, however, allowed many more different firing frequencies. Such behavior is inconsistent with both pacemaker resetting and (nonlinear) input current summation. Consequently, the repetitive firing behavior of a branched Hodgkin-Huxley axon with multiple encoding sites appears to be more complex than postulated in the simple hypotheses.
一般认为，具有多个编码位点的感受器传入纤维中的传入活动代表了最快起搏器的活动，该起搏器会重置所有编码速度较慢的位点。另外，也有人考虑过一些冲动混合以及受体电流对单个编码器的一些非线性总和。在本文中，研究了由两个分支合并成单个主干轴突的霍奇金 - 赫胥黎轴突的重复放电活动。通过向右侧或左侧分支或同时向两个分支注入恒定电流来刺激模型轴突。结果发现，如果输入电流足够大，模型轴突会产生（无限）一连串动作电位。所发现的放电频率是恒定的，并且在以不同电流同时刺激两个分支时，冲动起始位点总是在接收较高输入电流的分支中，排除了简单的冲动混合。另一方面，同时刺激两个分支会诱发重复放电，其频率高于起搏器重置假说所预期的频率。此外，如果注入一个分支时对重复放电来说是阈下刺激，那么当注入两个分支时就会产生重复放电，这种行为与冲动混合和起搏器重置不一致。另一方面，向一个分支注入电流仅在相当有限的放电频率范围内允许重复活动。然而，通过向两个分支进行分布式电流注入，可以实现更多不同的放电频率。这种行为与起搏器重置和（非线性）输入电流总和都不一致。因此，具有多个编码位点的分支霍奇金 - 赫胥黎轴突的重复放电行为似乎比简单假说中所假设的更为复杂。
