Ribera A B, Nüsslein-Volhard C
Abteilung III/Genetik, Max-Planck-Institut für Entwicklungsbiologie, Tübingen, Germany D-72076, USA.
J Neurosci. 1998 Nov 15;18(22):9181-91. doi: 10.1523/JNEUROSCI.18-22-09181.1998.
Developmental changes in neuronal connectivity and membrane properties underlie the stage-specific appearance of embryonic behaviors. The behavioral response of embryonic zebrafish to tactile stimulation first appears at 27 hr postfertilization. Because the touch response requires the activation of mechanosensory Rohon-Beard neurons, we have used whole-cell recordings in semi-intact preparations to characterize Rohon-Beard cell electrical membrane properties in several touch-insensitive mutants and then to correlate the development of excitability in these cells with changes in wild-type behavior. Electrophysiological analysis of mechanosensory neurons of touch-insensitive zebrafish mutants indicates that in three mutant lines that have been examined the sodium current amplitudes are reduced, and action potentials either have diminished overshoots or are not generated. In macho mutants the action potential never overshoots, and the sodium current remains small; alligator and steifftier show similar but weaker effects. The effects are specific to sodium channel function; resting membrane potentials are unaffected, and outward currents of normal amplitude are present. Developmental analysis of sodium current expression in mechanosensory neurons of wild-type embryos indicates that, during the transition from a touch-insensitive to a touch-sensitive embryo, action potentials acquire larger overshoots and briefer durations as both sodium and potassium currents increase in amplitude. However, in macho touch-insensitive mutants, developmental changes in action potential overshoot and sodium current are absent despite the normal regulation of action potential duration and potassium current. Thus, the maturation of a voltage-dependent sodium current promotes a behavioral response to touch. A study of these mutants will allow insight into the genes controlling the maturation of the affected sodium current.
神经元连接性和膜特性的发育变化是胚胎行为阶段特异性出现的基础。斑马鱼胚胎对触觉刺激的行为反应最早出现在受精后27小时。由于触觉反应需要机械感觉性罗霍恩-比尔兹神经元的激活，我们使用半完整标本中的全细胞膜片钳记录来表征几种触觉不敏感突变体中罗霍恩-比尔兹细胞的电膜特性，然后将这些细胞兴奋性的发育与野生型行为的变化相关联。对触觉不敏感斑马鱼突变体的机械感觉神经元的电生理分析表明，在所检测的三个突变系中，钠电流幅度降低，动作电位要么超射减弱，要么不产生。在“大男子主义”突变体中，动作电位从不超射，钠电流仍然很小；“短吻鳄”和“硬鳍”表现出类似但较弱的效应。这些效应是钠通道功能特有的；静息膜电位不受影响，且存在正常幅度的外向电流。对野生型胚胎机械感觉神经元中钠电流表达的发育分析表明，在从触觉不敏感胚胎向触觉敏感胚胎转变的过程中，随着钠电流和钾电流幅度的增加，动作电位获得更大的超射和更短的持续时间。然而，在“大男子主义”触觉不敏感突变体中，尽管动作电位持续时间和钾电流受到正常调节，但动作电位超射和钠电流的发育变化却不存在。因此，电压依赖性钠电流的成熟促进了对触觉的行为反应。对这些突变体的研究将有助于深入了解控制受影响钠电流成熟的基因。
