Fields R D, Nelson P G
Laboratory of Developmental Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.
J Neurobiol. 1994 Mar;25(3):281-93. doi: 10.1002/neu.480250308.
The relevant parameters of calcium fluxes mediating activation of immediate-early genes and the collapse of growth cones in mouse DRG neurons in response to action potentials delivered in different temporal patterns were measured in a multicompartment cell culture preparation using digital fluorescence videomicroscopy. Growth cone collapse was produced by trains of action potentials causing a large rise in [Ca2+]i, but after chronic exposure to patterned stimulation growth cones regenerated and became insensitive to the stimulus-induced increase in [Ca2+]i. Calcium reached similar peak concentrations, but the [Ca2+]i increased more slowly than in naive growth cones (time constant of 6.0 s versus 1.4 s in naive growth cones). Semiquantitative PCR measurements of gene expression showed that pulsed stimulation delivered at 1-min intervals for 30 min induced expression of c-fos, but the same total number of action potentials delivered at 2-min intervals failed to induce c-fos expression, even though this stimulus induces a larger peak [Ca2+]i than the effective stimulus pattern. The experiments suggest that the kinetics of calcium fluxes produced by different patterns of stimulation, and changes in the kinetics of calcium flux in neurons under different states of activation, are critical in determining the effects of action potentials on growth cone motility or expression of IE genes during development of neuronal circuits. We propose that differences in kinetics of individual reactions in the stimulus-response pathway may lead to resonance of activation in the neuron, such that certain processes will be selectively activated by particular temporal patterns of stimulation.
利用数字荧光视频显微镜，在多隔室细胞培养制剂中测量了介导小鼠背根神经节神经元中即刻早期基因激活和生长锥塌陷的钙通量的相关参数，这些参数是针对以不同时间模式传递的动作电位而言的。动作电位序列导致细胞内钙离子浓度（[Ca2+]i）大幅升高，从而引起生长锥塌陷，但在长期暴露于模式化刺激后，生长锥再生并对刺激诱导的[Ca2+]i升高变得不敏感。钙离子达到相似的峰值浓度，但[Ca2+]i升高的速度比未受刺激的生长锥慢（时间常数分别为6.0秒和未受刺激生长锥的1.4秒）。基因表达的半定量PCR测量结果表明，以1分钟间隔施加30分钟的脉冲刺激可诱导c-fos表达，但以2分钟间隔施加相同总数的动作电位却未能诱导c-fos表达，尽管这种刺激诱导的[Ca2+]i峰值比有效刺激模式更大。这些实验表明，不同刺激模式产生的钙通量动力学，以及处于不同激活状态的神经元中钙通量动力学的变化，对于确定动作电位在神经回路发育过程中对生长锥运动性或即刻早期基因表达的影响至关重要。我们提出，刺激-反应途径中各个反应的动力学差异可能导致神经元激活的共振，从而使某些过程将被特定的时间刺激模式选择性激活。
