Chiba A, Murphey R K
Department of Biology, State University of New York, Albany 12222.
J Neurobiol. 1991 Mar;22(2):130-42. doi: 10.1002/neu.480220204.
Cercal sensory neurons in the cricket innervate interneurons in the central nervous system (CNS) and provide a model system for studying the formation of central synapses. When axons of the sensory neurons were transected during larval development, the cell bodies and the soma-bearing portion of axons, which are located within the cercus, survived but lost their excitability for 9-10 days. During this period, the sensory neurons grew new axons and reinnervated the terminal abdominal ganglion. Physiological recordings showed that sensory neurons of known identity reestablished monosynaptic contacts with their normal postsynaptic interneuron. Moreover, each synapse exhibited a characteristic strength indistinguishable from the intact synapse in an unoperated cricket. Since this selective connectivity was apparent immediately after the excitability of the axotomized sensory neurons was restored, action potentials in the sensory neurons appear to be unnecessary for normal synaptic regeneration to occur. Consistent with this, the reinnervation process was unaffected even when action potentials in the sensory neurons were blocked by tetrodotoxin (TTX) immediately following axotomy until just before testing. During the normal course of development, the characteristic strength of individual synapses changes systematically, resulting in the developmental rearrangement of these synapses (Chiba et al., 1988). This synaptic rearrangement was also unaffected when action potentials in the sensory neurons were blocked by TTX for the last 30% of larval development. Therefore, in the cricket cercal sensory system, both regeneration of the central synapses following axotomy of the presynaptic sensory neurons and the normal rearrangement of connectivity during larval development appear not to require axonal action potentials.
蟋蟀的尾须感觉神经元支配中枢神经系统（CNS）中的中间神经元，为研究中枢突触的形成提供了一个模型系统。当感觉神经元的轴突在幼虫发育期间被切断时，位于尾须内的细胞体和带有胞体的轴突部分存活下来，但在9 - 10天内失去了兴奋性。在此期间，感觉神经元长出新的轴突并重新支配腹部末端神经节。生理记录表明，已知身份的感觉神经元与其正常的突触后中间神经元重新建立了单突触联系。此外，在未手术的蟋蟀中，每个突触表现出与完整突触难以区分的特征强度。由于这种选择性连接在轴突切断的感觉神经元兴奋性恢复后立即显现，感觉神经元中的动作电位似乎对于正常的突触再生发生并非必要。与此一致的是，即使在轴突切断后立即用河豚毒素（TTX）阻断感觉神经元中的动作电位直至测试前，重新支配过程也未受影响。在正常发育过程中，单个突触的特征强度会系统地变化，导致这些突触的发育重排（千叶等人，1988年）。当在幼虫发育的最后30%期间用TTX阻断感觉神经元中的动作电位时，这种突触重排也未受影响。因此，在蟋蟀尾须感觉系统中，突触前感觉神经元轴突切断后中枢突触的再生以及幼虫发育期间连接性的正常重排似乎都不需要轴突动作电位。
