The control of locomotor frequency by excitation and inhibition.
The control of locomotor frequency by excitation and inhibition.
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DOI：
10.1523/jneurosci.6289-11.2012
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发表时间：
2012-05-02
期刊：
影响因子：
--
通讯作者：
Moult PR
中科院分区：
文献类型：
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作者：
Li WC;Moult PR
每种类型的神经节律都有自己的工作频率范围。然而，不同频率的节律背后的神经机制却知之甚少。我们使用一种简单的水生脊椎动物，两天大的非洲爪哇蝌蚪，来研究脑干和脊髓回路是如何产生不同速度的游泳节奏的。我们首先确定了基本的运动输出模式不会随着游泳频率的变化而改变。分析了参与游泳运动的不同类型节律神经元的放电可靠性。结果表明，假想游泳减慢时，部分抑制性中间神经元的放电可靠性下降。我们最近证实，运动前兴奋性中间神经元(DINS)在游泳道中有节奏的驱动活动中起关键作用。DINS的电压钳记录显示，高频游泳与较强的背景兴奋和时相抑制相关，但与时相兴奋无关。已经提出了两种平行的蝌蚪游泳维持机制：抑制后反弹放电和依赖NMDAR的DINS起搏放电。本研究中DINS的反弹试验表明，更大的背景去极化和时相抑制导致更快的反弹激发。先前有研究表明，在NMDA存在的情况下，更高的去极化可以加速DIN起搏。实验结果表明，游泳过程中增强DIN背景兴奋可加快虚拟游泳频率，而在不改变背景兴奋的情况下减弱相抑制可减慢游泳节奏。我们得出结论，强烈的背景刺激和相抑制都能促进蝌蚪游得更快。
Every type of neural rhythm has its own operational range of frequency. Neuronal mechanisms underlying rhythms at different frequencies, however, are poorly understood. We use a simple aquatic vertebrate, the two day old Xenopus tadpole, to investigate how the brainstem and spinal circuits generate swimming rhythms of different speeds. We first determined that the basic motor output pattern was not altered with varying swimming frequencies. The firing reliability of different types of rhythmic neuron involved in swimming was then analysed. The results showed that there was a drop in the firing reliability in some inhibitory interneurons when fictive swimming slowed. We have recently established that premotor excitatory interneurons (descending interneurons; dINs) are critical in rhythmically driving activity in the swimming circuit. Voltage-clamp recordings from dINs showed higher frequency swimming correlated with stronger background excitation and phasic inhibition, but did not correlate with phasic excitation. Two parallel mechanisms have been proposed for tadpole swimming maintenance: post-inhibition rebound firing and NMDA receptor (NMDAR) dependent pace-maker firing in dINs. Rebound tests in dINs in this study showed that greater background depolarization and phasic inhibition led to faster rebound firing. Higher depolarization was previously shown to accelerate dIN pace-maker firing in the presence of NMDA. Here we show that enhancing dIN background excitation during swimming speeds up fictive swimming frequency whilst weakening phasic inhibition without changing background excitation slows down swimming rhythms. We conclude that both strong background excitation and phasic inhibition can promote faster tadpole swimming.