Cheetham Claire E J, Hammond Martin S L, McFarlane Rachael, Finnerty Gerald T
Medical Research Centre for Neurodegeneration Research, King's College London, London SE5 8AF, United Kingdom.
J Neurosci. 2008 Sep 10;28(37):9249-60. doi: 10.1523/JNEUROSCI.2974-08.2008.
Experience-dependent plasticity in adulthood is slower than during development. Previous experience can accelerate adult cortical plasticity. However, the contributions of functional synaptic changes and modifications in neuronal structure to the acceleration of adult cortical plasticity remain unclear. If structural remodeling was important then it should be exhibited by neuronal connections that have altered during plasticity. We trimmed rodents' whiskers to induce experience-dependent plasticity and reconstructed pairs of layer 2/3 (L2/3) pyramidal neurons after electrophysiological recording. We reported recently that local excitatory connections strengthen without a change in synapse number in cortex with retained sensory input (spared) (Cheetham et al., 2007). Here, we show that strengthened connections are rewired. The rewiring involves remodeling of the axonal arbor of excitatory connections with only minor changes in postsynaptic dendritic trees. The axonal remodeling resulted in a greater length of presynaptic axon close to postsynaptic dendrites at existing local excitatory connections in spared cortex. In control cortex, the length of axon close to dendrite in unconnected pairs of L2/3 pyramidal neurons was similar to that in synaptically connected pairs of L2/3 pyramidal neurons. This finding suggests that the probability of forming a synapse and, therefore, establishing a connection, is not driven solely by the length of axon close to dendrite. The axonal remodeling that we describe is not associated with altered synapse number, but instead increases the number of sites where synapses could be formed between synaptically connected neurons with minimal structural changes. This enables rapid and cost-efficient rewiring of local excitatory connections when re-exposed to similarly altered sensory experience in adulthood.
成年期依赖经验的可塑性比发育期间要慢。先前的经验可以加速成年皮质可塑性。然而，功能性突触变化和神经元结构改变对成年皮质可塑性加速的贡献仍不清楚。如果结构重塑很重要，那么它应该在可塑性过程中发生改变的神经元连接中表现出来。我们修剪啮齿动物的胡须以诱导依赖经验的可塑性，并在电生理记录后重建第2/3层（L2/3）锥体神经元对。我们最近报道，在保留感觉输入（ spared ）的皮质中，局部兴奋性连接增强而突触数量没有变化（Cheetham等人，2007年）。在这里，我们表明增强的连接会重新布线。重新布线涉及兴奋性连接轴突分支的重塑，而突触后树突的变化很小。轴突重塑导致在 spared 皮质中现有局部兴奋性连接处，靠近突触后树突的突触前轴突长度增加。在对照皮质中，未连接的L2/3锥体神经元对中靠近树突的轴突长度与突触连接的L2/3锥体神经元对中的轴突长度相似。这一发现表明，形成突触并因此建立连接的可能性并非仅由靠近树突的轴突长度驱动。我们描述的轴突重塑与突触数量的改变无关，而是增加了突触连接的神经元之间在结构变化最小的情况下可能形成突触的位点数量。这使得成年期再次暴露于类似改变的感觉经验时，局部兴奋性连接能够快速且经济高效地重新布线。
