グルタミン酸シナプス伝達の可視化解析
詳細
At individual glutamatergic synapses, the amount of released glutamate per action potential determines the synaptic strength. However, the direct measurement of synaptically released glutamate has not been done. To measure glutamate release at single synapses, we developed a novel fluorescent glutamate probe called EOS (Glutamate Optical Sensor). Electrically evoked glutamate release was successfully detected at synapses in cultured hippocampal neurons. We found that released glutamate varied in amount among synapses. Also, we found that changes in release probability by manipulating extracellular calcium concentration were associated with changes in the amount of released glutamate at individual synapses. These findings suggest that single synapses contain several release sites. In the presence of tetrodotoxin, we detected spontaneous glutamate release which was stochastic and variable in amplitude. Further, the frequency of spontaneous release was increased upon application of high concentrations of sucrose. These properties were similar to those of miniature EPSC. Surprisingly, spontaneous glutamate release often occurred at non-synaptic sites. Moreover, the amount of spontaneously released glutamate had a tendency to be larger than evoked one. In summary, we evaluated the functional release properties of each individual synapses by using EOS. [J Physiol Sci. 2007;57 Suppl:S155]
