A behaviorally related developmental switch in nitrergic modulation of locomotor rhythmogenesis in larval Xenopus tadpoles.
A behaviorally related developmental switch in nitrergic modulation of locomotor rhythmogenesis in larval Xenopus tadpoles.
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DOI：
10.1152/jn.00283.2015
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发表时间：
2016-03
影响因子：
2.5
通讯作者：
Sillar KT
中科院分区：
文献类型：
--
作者：
Currie SP;Combes D;Scott NW;Simmers J;Sillar KT
运动控制需要功能上的灵活性来支持动物的全部行为。这种灵活性在一定程度上是由神经调节器赋予的，允许神经网络生成一系列电机输出配置。在刚孵化的非洲爪哇蝌蚪中，在自由游泳行为开始之前，气体调节剂一氧化氮(NO)抑制运动输出，缩短游泳次数，减少游泳周期频率。虽然孵化时蝌蚪的脑干中已经存在大量的氮能神经元，但NO合成酶阳性的神经元随后出现在脊髓中，这表明NO在幼虫发育过程中还有其他未知的作用。在这里，我们首先描述动物从早期的固定生活方式到后来的自由游泳生活方式变化过程中运动行为的表达，然后比较NO在整个蝌蚪发育过程中的作用。我们发现了氮能调节从净抑制到整体兴奋的离散开关，这与自由游泳运动的转变是一致的。此外，我们在分离的老年幼虫的脑干-脊髓标本中显示，NO的兴奋作用表现为自发游泳事件发生的概率增加，就像先前对神经递质多巴胺所发现的那样，但这些影响是在脑干内介导的。此外，尽管NO和多巴胺的作用相似，但这两个调节器是并行作用的，而不是通过调制多巴胺能信号来串联操作的。最后，NO对脑干神经元的激活也导致脊髓中NO的释放，从而有助于NO促进游泳。
Locomotor control requires functional flexibility to support an animal's full behavioral repertoire. This flexibility is partly endowed by neuromodulators, allowing neural networks to generate a range of motor output configurations. In hatchling Xenopus tadpoles, before the onset of free-swimming behavior, the gaseous modulator nitric oxide (NO) inhibits locomotor output, shortening swim episodes and decreasing swim cycle frequency. While populations of nitrergic neurons are already present in the tadpole's brain stem at hatching, neurons positive for the NO-synthetic enzyme, NO synthase, subsequently appear in the spinal cord, suggesting additional as yet unidentified roles for NO during larval development. Here, we first describe the expression of locomotor behavior during the animal's change from an early sessile to a later free-swimming lifestyle and then compare the effects of NO throughout tadpole development. We identify a discrete switch in nitrergic modulation from net inhibition to overall excitation, coincident with the transition to free-swimming locomotion. Additionally, we show in isolated brain stem-spinal cord preparations of older larvae that NO's excitatory effects are manifested as an increase in the probability of spontaneous swim episode occurrence, as found previously for the neurotransmitter dopamine, but that these effects are mediated within the brain stem. Moreover, while the effects of NO and dopamine are similar, the two modulators act in parallel rather than NO operating serially by modulating dopaminergic signaling. Finally, NO's activation of neurons in the brain stem also leads to the release of NO in the spinal cord that subsequently contributes to NO's facilitation of swimming.