新发现挑战神经元通讯经典学说.doc

Conventional Wisdom of How Neurons Operate Challenged: Axons Can Work in Reverse 新发现挑战神经元通讯经典学说译者：DocofsoulScienceDaily (Feb. 19, 2011) Neurons are complicated, but the basic functional conceptis that synapses transmit electrical signals to the dendrites and cell body (input), and axons carry signals away (output). In one of many surprise findings, Northwestern University scientists have discovered that axons can operate in reverse: they can send signals to the cell body, too.每日科学2011年2月19日报道神经元很复杂，但传统理论认为神经元的基本工作原理是：突触将电信号传递给树突与细胞体（输入），轴突则携带信号离开（输出）。但在众多的令人惊讶的发现中，美国西北大学的科学家们发现了轴突也可以反向运作：向细胞体发送信号。Computer-generated image representing connections between neurons. (Credit: iStockphoto/Guido Vrola) 电脑制作的代表神经元之间连接的图像（图片来源：iStockphoto/Guido Vrola)It also turns out axons can talk to each other. Before sending signals in reverse, axons can perform their own neural computations without any involvement from the cell body or dendrites. This is contrary to typical neuronal communication where an axon of one neuron is in contact with another neurons dendrite or cell body, not its axon. And, unlike the computations performed in dendrites, the computations occurring in axons are thousands of times slower, potentially creating a means for neurons to compute fast things in dendrites and slow things in axons.并且，轴突之间也可以互相对话。在反向发送信号前，轴突本身可进行神经计算而无需细胞体与树突的参与。这种现象显然与经典的神经元通讯理论相悖。因为在经典理论中，一个神经元的轴突应该与另一个神经元的树突或细胞体进行交流，而不是与其轴突相联系。同时，与树突上执行的计算不同，轴突上所出现的计算，其速度慢了几千倍，由此可能建立了一种运作方式：当神经元需要快速计算时，任务就交给树突来完成，慢速运算则由轴突处理。A deeper understanding of how a normal neuron works is critical to scientists who study neurological diseases, such as epilepsy, autism, Alzheimers disease and schizophrenia.对于正常神经元的工作原理的更深层次的理解对于研究神经系统疾病（诸如癫痫、自闭症与精神分裂症）的科学家而言至关重要。The findings are published in the February issue of the journal Nature Neuroscience.本发现已发表于二月份的Nature Neuroscience（自然神经科学）杂志。We have discovered a number of things fundamental to how neurons work that are contrary to the information you find in neuroscience textbooks, said Nelson Spruston, senior author of the paper and professor of neurobiology and physiology in the Weinberg College of Arts and Sciences. Signals can travel from the end of the axon toward the cell body, when it typically is the other way around. We were amazed to see this.论文通讯作者、温伯格艺术与科学学院神经生物学与生理学教授Nelson Spruston说：“我们已经发现了很多与神经科学教科书记载的内容截然不同的有关神经元基本工作原理的信息。信号可以从轴突的末端向细胞体运动，而通常情况下并非如此。我们对此感到非常惊讶。”He and his colleagues first discovered individual nerve cells can fire off signals even in the absence of electrical stimulations in the cell body or dendrites. Its not always stimulus in, immediate action potential out. (Action potentials are the fundamental electrical signaling elements used by neurons; they are very brief changes in the membrane voltage of the neuron.)他与同事首次发现单个神经细胞甚至在细胞体与树突内没有电刺激时也能够发送信号。并非总是“刺激输入、即时动作电位输出”（动作电位是神经元所用的基本的电信号单位；是神经元膜电压的极为短暂的变化）。Similar to our working memory when we memorize a telephone number for later use, the nerve cell can store and integrate stimuli over a long period of time, from tens of seconds to minutes. (Thats a very long time for neurons.) Then, when the neuron reaches a threshold, it fires off a long series of signals, or action potentials, even in the absence of stimuli. The researchers call this persistent firing, and it all seems to be happening in the axon.与记住电话号码以备后用时的记忆活动相似，神经元能够在一段很长的时间内（从数十秒到几分钟，这对神经元来说已经很长了）存贮与整合刺激。然后，当神经元到达一个域值时，它会发送一串长系列信号或动作电位，即使刺激并不存在的情形下也是如此。研究者将此称之为持续开火，并且所有这些看起来都发生于轴突内。Spruston and his team stimulated a neuron for one to two minutes, providing a stimulus every 10 seconds. The neuron fired during this time but, when the stimulation was stopped, the neuron continued to fire for a minute.Spruston及其研究小组刺激一个神经元一到两分钟（每10秒提供一次刺激）。在此期间神经元发送信号，但是，当刺激停止后，神经元继续发送信号达一分钟之久。Its very unusual to think that a neuron could fire continually without stimuli, Spruston said. This is something new - that a neuron can integrate information over a long time period, longer than the typical operational speed of neurons, which is milliseconds to a second.Spruston 说：“想一下：一个神经元在没有刺激的情形下能够持续发送信号，真的不同寻常。这太新颖了一个神经元能够在一段很长的时间内整合信息，其时间长度超过了神经元的典型运作速度（数毫秒到一秒种）”This unique neuronal functionmight be relevant to normal process, such as memory, but it also could be relevant to disease. The persistent firing of these inhibitory neurons might counteract hyperactive states in the brain, such as preventing the runaway excitation that happens during epileptic seizures.这一特殊的神经元功能可能与诸如记忆等正常过程有关，但也可能与疾病有关。这些抑制性神经元持续发送信号的行为可能旨在弥消大脑的过度活跃状态，比如说防止癫痫抽搐期间的失控的大脑激发态。Spruston credits the discovery of the persistent firing in normal individual neurons to the astute observation of Mark Sheffield, a graduate student in his lab. Sheffield is first author of the paper.Spruston将正常个体神经元持续发送信号的发现归功于Mark Sheffield的观察。Mark Sheffield是他的实验室的研究生，本论文的第一作者。The researchers think that others have seen this persistent firing behavior in neurons but dismissed it as something wrong with the signal recording. When Sheffield saw the firing in the neurons he was studying, he waited until it stopped. Then he stimulated the neuron over a period of time, stopped the stimulation and then watched as the neuron fired later.研究者认为其他人也已经观察到这种持续发送信号的现象，只是把这种现象看成信号记录错误而失之交臂。当Mark Sheffield看到他正在研究的神经元在发送信号时，他耐心在一旁等待直到信号停止。接着他在一段时间内刺激该神经元、停止刺激后，然后又观察神经元稍后又开始发送信号的情况。This cellular memory is a novelty, Spruston said. The neuron is responding to the history of what happened to it in the minute or so before.Spruston 说：“这种细胞记忆确实风格独特。该神经元正在对一分钟左右前所经历过的历史作出响应。”Spruston and Sheffield found that the cellular memory is stored in the axon and the action potential is generated farther down the axon than they would have expected. Instead of being near the cell body it occurs toward the end of the axon.Spruston 与Sheffield发现这种细胞记忆存贮于轴突中，并且轴突产生的动作电位比他们预期的更远：并非在靠近细胞体的部位产生，而是在接近轴突的末端出现。Their studies of individual neurons (from the hippocampus and neocortex of mice) led to experiments with multiple neurons, which resulted in perhaps the biggest surprise of all. The researchers found that one axon can talk to another. They stimulated one neuron, and detected the persistent firing in the other unstimulated neuron. No dendrites or cell bodies were involved in this communication.他们的有关个体神经元（来自小鼠的海马体与新皮层）的研究导致多种多样神经元实验的随即跟进。这些实验产生了可能是最令人惊奇的结果。研究者发现一个轴突可与另一个轴突交谈；刺激一个神经元，又在另一个未受刺激的神经元中探测到了持续的信号发送行为。而这种通讯并未有树突或细胞体的参与。The axons are t