Bedi S S, Salim A, Chen S, Glanzman D L
Department of Physiological Science, UCLA, Los Angeles, California 90095-1568, USA.
J Neurophysiol. 1998 Mar;79(3):1371-83. doi: 10.1152/jn.1998.79.3.1371.
Crushing nerves, which contain the axons of central sensory neurons, in Aplysia causes the neurons to become hyperexcitable and to sprout new processes. Previous experiments that examined the effects of axonal injury on Aplysia sensory neurons have been performed in the intact animal or in the semi-intact CNS of Aplysia. It therefore has been unclear to what extent the long-term neuronal consequences of injury are due to intrinsic or extrinsic cellular signals. To determine whether injury-induced changes in Aplysia sensory neurons are due to intrinsic or extrinsic signals, we have developed an in vitro model of axonal injury. Isolated central sensory neurons grown for 2 days in cell culture were axotomized. Approximately 24 h after axotomy, sensory neurons exhibited a greater excitability-reflected, in part, as a significant reduction in spike accommodation-and greater neuritic outgrowth than did control (unaxotomized) neurons. Rp diastereoisomer of the cyclic adenosine 3',5'-monophosphorothiate (Rp-cAMPS), an inhibitor of protein kinase A, blocked both the reduction in accommodation and increased neuritic outgrowth induced by axotomy. Rp-cAMPS also blocked similar, albeit smaller, alterations observed in control sensory neurons during the 24-h period of our experiments. These results indicate that axonal injury elevates cAMP levels within Aplysia sensory neurons, and that this elevation is directly responsible, in part, for the previously described long-term electrophysiological and morphological changes induced in Aplysia sensory neurons by nerve crush. In addition, the results indicate that control sensory neurons in culture are also undergoing injury-related electrophysiological and structural changes, probably due to cellular processes triggered when the neurons are axotomized during cell culturing. Finally, the results provide support for the idea that the cellular processes activated within Aplysia sensory neurons by injury, and those activated during long-term behavioral sensitization, overlap significantly.
在海兔中挤压包含中枢感觉神经元轴突的神经，会使这些神经元变得过度兴奋并长出新的突起。之前研究轴突损伤对海兔感觉神经元影响的实验是在完整动物或海兔的半完整中枢神经系统中进行的。因此，损伤导致的神经元长期后果在多大程度上归因于内在或外在细胞信号尚不清楚。为了确定海兔感觉神经元中损伤诱导的变化是由于内在还是外在信号，我们建立了一个轴突损伤的体外模型。在细胞培养中生长2天的分离中枢感觉神经元被切断轴突。轴突切断后约24小时，感觉神经元表现出更高的兴奋性——部分表现为动作电位适应的显著降低——并且与对照（未切断轴突的）神经元相比，有更多的神经突生长。环腺苷3',5'-单磷酸硫代磷酸酯（Rp-cAMPS）的Rp非对映异构体，一种蛋白激酶A的抑制剂，阻断了轴突切断诱导的动作电位适应降低和神经突生长增加。Rp-cAMPS也阻断了在我们实验的24小时期间在对照感觉神经元中观察到的类似但较小的变化。这些结果表明轴突损伤会提高海兔感觉神经元内的cAMP水平，并且这种升高部分直接导致了之前描述的神经挤压在海兔感觉神经元中诱导的长期电生理和形态学变化。此外，结果表明培养中的对照感觉神经元也在经历与损伤相关的电生理和结构变化，这可能是由于在细胞培养过程中神经元轴突切断时触发的细胞过程。最后，这些结果支持了这样一种观点，即损伤在海兔感觉神经元内激活的细胞过程与长期行为敏感化期间激活的细胞过程有显著重叠。
