生物谷：一直以来，科学家认为大脑神经轴突（axon）的作用只是用来在脑细胞间传递信号。美国科学家近日研究发现，神经轴突的作用不仅仅限于传递信号，在适当的刺激下，它还可以加强或减弱信号的作用。该发现有望为精神分裂症等精神病患者带来福音。相关论文在线发表于8月19日的《自然—神经学》上。
该项研究由加州大学欧文分校听觉研究中心的神经生物学副教授Raju Metherate领导完成。起初，他和研究小组想确定的是，烟碱（nicotine）改变了在大脑池体（cell body）中处理的信息，但是，一系列的实验失败使他们将研究重点转向了神经轴突。研究小组检测了小鼠大脑中与听觉有关的区域，该区域的脑细胞通过神经轴突与大脑皮层相连。他们用烟碱刺激神经轴突，以确定它怎样影响信号在脑细胞和大脑皮层之间的传递。结果发现，如果不使用烟碱，脑细胞发出的信号大约有35％到达了大脑皮层；如果使用烟碱，这一数字则大约为70％。
Metherate表示，迄今为止，科学家一直认为在大脑皮层中，信号仅仅只在池体中进行加工处理。此次的研究表明，神经轴突也是一个处理信息的地方。他说：“我们过去以为神经轴突就像广播电线一样，用来传输信号。但是现在发现，如果你刺激神经轴突，信号就会发生改变，就像广播调频一样。”他认为，烟碱的作用可能在于激活了神经轴突上的相关蛋白。而此次的发现可以说是一种关于大脑工作方式的全新理念。
此次研究具有重要的实践意义。比如精神分裂等精神病一直被认为是由于大脑不同部位交流紊乱造成的，此次研究将有助于为这些患者提供有效治疗手段。（科学网 梅进/编译）
原始出处:
Published online: 19 August 2007; | doi:10.1038/nn1956
Nicotinic control of axon excitability regulates thalamocortical transmission
Hideki Kawai, Ronit Lazar & Raju Metherate
Department of Neurobiology and Behavior and Center for Hearing Research, University of California, Irvine, 2205 McGaugh Hall, Irvine, California 92697-4550, USA.
Correspondence should be addressed to Raju Metherate rmethera@uci.edu
The thalamocortical pathway, a bundle of myelinated axons that arises from thalamic relay neurons, carries sensory information to the neocortex. Because axon excitation is an obligatory step in the relay of information from the thalamus to the cortex, it represents a potential point of control. We now show that, in adult mice, the activation of nicotinic acetylcholine receptors (nAChRs) in the initial portion of the auditory thalamocortical pathway modulates thalamocortical transmission of information by regulating axon excitability. Exogenous nicotine enhanced the probability and synchrony of evoked action potential discharges along thalamocortical axons in vitro, but had little effect on synaptic release mechanisms. In vivo, the blockade of nAChRs in the thalamocortical pathway reduced sound-evoked cortical responses, especially those evoked by sounds near the acoustic threshold. These data indicate that endogenous acetylcholine activates nAChRs in the thalamocortical pathway to lower the threshold for thalamocortical transmission and to increase the magnitude of sensory-evoked cortical responses. Our results show that a neurotransmitter can modulate sensory processing by regulating conduction along myelinated thalamocortical axons.
