Abstract
It has become a consensus that the AMPA type glutamate receptor (AMPA-R) is transported to the synapse by LTP induction, thereby contributing to the enhanced synaptic transmission. However, AMPA-R itself does not exist by itself. It binds with many other synaptic proteins which support the AMPA-R both from inside and outside of the synapse through direct or indirect interaction. Then, when AMPA-R is transported to the synapse, other proteins should be transported as well. To test this, we chose several representative postsynaptic proteins and investigated their transport after LTP induction. They were fused with GFP and coexpressed RFP, as a volume filler, in hippocampal CA1 pyramidal neurons. Upon LTP induction with two-photon-uncaging of glutamate on the single dendritic spine, these proteins showed different kinetics of delivery. While some proteins are immediately transported to the synapse, others were significantly slower. We then tested whether these slow proteins are moving at all by using FRAP assay. As opposed to our expectation, FRAP assay indicates that those molecules are constantly undergoing turnover between dendritic spine and shaft. Our results indicate that a synapse that has undergone synaptic plasticity is different in the composition compared with naive synapes. This may explain phenomenon known as metaplasticity, where a prior plasticity induction changes the properties synapse to further induction of synaptic plasticity. [J Physiol Sci. 2008;58 Suppl:S6]
