Mel Bartlett W, Schiller Jackie
Department of Biomedical Engineering and Neuroscience Graduate Program, University of Southern California, Los Angeles, CA 90089, USA.
Sci STKE. 2004 Sep 7;2004(250):PE44. doi: 10.1126/stke.2502004pe44.
In the intact brain, neurons are constantly subjected to both excitatory and inhibitory inputs to their dendritic trees. Although it is accepted that the overall response of a neuron--its train of output spikes--depends on the balance of excitation and inhibition, we continue to lack specific knowledge of the rules that govern how excitatory and inhibitory inputs interact in space and time within the confines of individual neurons. In a recent paper, Liu starts by providing evidence that the relative locations and numbers of excitatory and inhibitory synapses are tightly regulated in cultured neurons from the hippocampus. This is consistent with findings in other labs that suggest neurons work hard, and in a variety of different ways, to maintain their inputs in proper balance and their outputs within appropriate ranges. On this backdrop, Liu's most important finding of a functional nature is that inhibition appears to act quite locally; that is, an inhibitory synapse effectively opposes an excitatory synapse only when it is very close by within the same dendritic branch (Fig. 1). This finding provides further support for the view--anticipated by neural theorists more than 20 years ago--that the brain's principal neurons contain a potentially large number of separate computational subunits.
在完整的大脑中，神经元的树突不断受到兴奋性和抑制性输入的影响。虽然人们公认神经元的整体反应——其输出尖峰序列——取决于兴奋和抑制的平衡，但我们仍然缺乏关于兴奋性和抑制性输入如何在单个神经元范围内在空间和时间上相互作用的具体规则的知识。在最近的一篇论文中，刘首先提供证据表明，在来自海马体的培养神经元中，兴奋性和抑制性突触的相对位置和数量受到严格调控。这与其他实验室的研究结果一致，这些研究结果表明，神经元会以各种不同方式努力维持其输入的适当平衡，并将其输出保持在适当范围内。在此背景下，刘在功能方面最重要的发现是抑制作用似乎相当局部；也就是说，只有当抑制性突触与同一树突分支内的兴奋性突触非常接近时，它才会有效地对抗兴奋性突触（图1）。这一发现为20多年前神经理论家所预期的观点提供了进一步支持，即大脑的主要神经元包含大量潜在的独立计算亚单元。
