The cover of May 4 issue of Neuron highlighting the work by Dr Duan et al. The cover depicts the conversion of the silent synapse (lower left, blue) into the functional one (upper right, red), induced by high-level neuronal activity (red background and the white spike train). (Cover art by Ye-Fei Li

A group of CAS scientists recently made a research breakthrough in the development of synapse, the key structure of the nervous system that transmits signals from one nerve cell to another. This work was reported as cover story by the May 4th issue of prestigious journal Neuron.

    Headed by Prof. DUAN Shumin from the Institute of Neuroscience under the CAS Shanghai Institutes for Biological Sciences, the research group includes Duan's doctorate students SHEN Wanhua and WU Pei, and co-workers from CAS Graduate University.

    In the nervous system, the neuron, or nerve cell, is the fundamental unit that works by conducting electrical and chemical signals throughout the brain. These signals are transmitted across synapses. Previously, scientists made observations on the silent synapse, which has the synaptic structure but cannot spread the signals. Scientists discovered that, under certain circumstances, the nonfunctional synapses could be converted into functional ones. They believed that the conversion would be the basis for maturation of synapses and the human neurological functions such as learning and memory. This phenomenon sparked great interest among neurologists. According to a classical interpretation, the change is caused by the postsynaptic membrane which has NMDA receptors but lacks the AMPA receptors so that it cannot transmit signals.

    However, Prof. Duan and colleagues have found another scenario in which the silent synapse was found to have AMPA receptors and the reason responsible for its silence lies in the pre-synaptic neuron that cannot release the transmission agent: glutamate acid. Also, the team discovers that the enhancement of the pre-synaptic activity can rapidly transform a "silent synapse" into a functional one. Their further research reveals that the transformation comes from the activation of the small G-protein's signaling molecule, leading to the increased polymerization of skeletal protein at the presynaptic terminals. In this way, the glutamate acid is released and thus the silent synapses can be rapidly converted into functional ones.

    In his comments, Ege T. Kavalali, a renowned neuroscientist from the Center for Basic Neuroscience, the University of Texas Southwestern Medical Center, points out the work "provides a fresh look at these silent synapses and their switching to active ones," and "brings a clear mechanistic insight to this type of off/on switching, which occurs during early synaptic development contributing to the plasticity of synaptic networks." He notes that "a major strength of this study stems from its ability to bring together several disparate earlier observations... in a single coherent model."

    Experts say the work will exert far-reaching influence on the synapse development and its plasticity.