神经系统对突触可塑性的适应 [复制链接]

在神经元上的突触数目和强度在发育的过程中是变化的，突触连接是活性依赖机制的结果。那么当突触的数目和强度在如此剧烈的改变情况下神经元的活性是怎样保持稳定的呢？新的发现表明神经元上的突触活性会改变来保持神经元活性的稳定。

  Desai et al.研究大鼠在出生后12天到23天之间的视觉皮层。在发育的这个阶段，到皮层神经元上的突触投射会稳定的增加。从这些神经元的记录发现自发的最小兴奋性后突触电流（miniature excitatory postsynaptic currents）的频率稳定的增加，这种电流是当单个的递质量子包自发的释放引起的。当突触的数目和mEPSCs的频率上升时，mEPSCs的大小会下降。

  这些实验的结果也与以前的一些数据相同，兴奋性突触的强度会进行调节来使发放的速度稳定。这种突触活性的缩放比例调控着到达神经元的所有突触的强度，来使神经元的后突触平均活性稳定。

  Desai et al.还发现如果将大鼠置于黑暗环境，mEPSC幅度的减小会停止。这也说明mEPSC幅度的减小是与视皮层发育的活性增加有关的，来与突触活性的增加互补。研究者用注射钠离子通道阻断剂河豚毒素的方法来对大鼠进行单眼去除，他们发现在单眼去除后的不同时期内，从皮层的不同层进行记录，不同的皮层亚层突触活性缩放都不同。第四层，在出生后21到23天进行单眼去除对mEPSC幅度没有影响，而第二和三层，在14和16天之间进行单眼去除对mEPSC没有影响，而在21－23天之间进行去除则抑制了mEPSC幅度的减小。

  突触活性缩放的机制还不清楚，这种现象可能反映了神经系统对于突触可塑性改变的适应性。

文章老了一些（2002）。
http://www.nature.com/neuro/journal/v5/n8/full/nn878.html
Article
Nature Neuroscience 5, 783 - 789 (2002)
Published online: 24 June 2002; Corrected online: 27 June 2002 | doi:10.1038/nn878
Critical periods for experience-dependent synaptic scaling in visual cortex
Niraj S. Desai1, 2, Robert H. Cudmore1, Sacha B. Nelson1 & Gina G. Turrigiano1

1 Department of Biology and Volen National Center for Complex Systems, MS 008, Brandeis University, 415 South Street, Waltham, Massachusetts 02454, USA

2 Current address: The Neuroscience Institute, 10640 John Jay Hopkins Drive, San Diego, California 92121, USA
Correspondence should be addressed to Gina G. Turrigiano turrigiano@brandeis.edu
The mechanisms underlying experience-dependent plasticity and refinement of central circuits are not yet fully understood. A non-Hebbian form of synaptic plasticity, which scales synaptic strengths up or down to stabilize firing rates, has recently been discovered in cultured neuronal networks. Here we demonstrate the existence of a similar mechanism in the intact rodent visual cortex. The frequency of miniature excitatory postsynaptic currents (mEPSCs) in principal neurons increased steeply between post-natal days 12 and 23. There was a concomitant decrease in mEPSC amplitude, which was prevented by rearing rats in complete darkness from 12 days of age. In addition, as little as two days of monocular deprivation scaled up mEPSC amplitude in a layer- and age-dependent manner. These data indicate that mEPSC amplitudes can be globally scaled up or down as a function of development and sensory experience, and suggest that synaptic scaling may be involved in the activity-dependent refinement of cortical connectivity.