Science2014-06-11 12:38 PM

什么神经元在控制你向后退? Neuronal Control of Drosophila Walking Direction

论文摘要 

果蝇向后挪动躲开一小块潮湿的香蕉的情景可能会让人感到奇怪,但果蝇是可以这样做的;如今科学家们已经发现,仅需2个神经元就能控制这一向后退的能力。这一发现可能会阐释其它有腿的动物是如何在向后及向前运动中做出选择的。把一只脚放在另一只脚之后的能力并不局限于人类。人类也能向后行走,且这种行动并非仅仅是向前行走的反转(在向后行走时,髋部肌肉实际上有着不同的运动),而涉及这一过程的神经回路还没有被很好地了解。科学家们知道,大脑扮演着一个指挥的作用,它会对载有神经的运动系统发出信号,而该运动系统接着会选择性地激活相关的肌肉。但现在,通过在果蝇中的研究,他们揭示了有关的特定神经系统回路。

Salil Bidaye及其同事以创建大约3500个果蝇世系作为开始,每个果蝇世系具有一个不同的神经系统表达模式,旨在确认被激活时能改变果蝇行走方向的神经元组合。在这些果蝇世系中,他们发现了一个被称作“月行者”的世系,在该世系中,向后行走行为最为明显。他们将该世系放入一个特殊的腔室并在其中将激活的神经元沉寂;这种做法阻止了果蝇的向后行走行为——即使是当这样做会是有帮助的时候果蝇也不会向后行走,如当其到达某条路的尽头的时候。

研究人员在另外的实验中发现,在该月行者果蝇中的7个独特地被激活的神经元中,只需要激活它们中的一对神经元——其中之一在脑中,另一个则沿着果蝇的腹部——就足以让果蝇向后行走。通过应用精确的遗传学工具来确定哪个神经元在做什么,他们发现,激活脑中的一个神经元足以诱发反向的运动;激活第2个神经元则不会出现反向运动。研究人员发现的那一个神经元主要通过抑制向前的运动而帮助了总体的退行过程。这些发现让人们第一次得窥果蝇及可能还有其它有腿的动物是如何控制其行走方向的。一篇《观点栏目》文章提出了更多的见解。

Abstract 

Most land animals normally walk forward but switch to backward walking upon sensing an obstacle or danger in the path ahead. A change in walking direction is likely to be triggered by descending “command” neurons from the brain that act upon local motor circuits to alter the timing of leg muscle activation. Here we identify descending neurons for backward walking in Drosophila—the MDN neurons. MDN activity is required for flies to walk backward when they encounter an impassable barrier and is sufficient to trigger backward walking under conditions in which flies would otherwise walk forward. We also identify ascending neurons, MAN, that promote persistent backward walking, possibly by inhibiting forward walking. These findings provide an initial glimpse into the circuits and logic that control walking direction in Drosophila.

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