Abstract
The quantal nature of synaptic transmission has been demonstrated at various types of synapses. Although quantal neurotransmitter release is assumed to underlie the quantal nature of synaptic transmission, it has not been directly examined to date. In this study, we imaged glutamate release at single synapses for quantal analysis by using a fluorescent glutamate probe called EOS. Glutamate release evoked by a single action potential was successfully detected at single synapses in cultured hippocampal neurons. Also, successes of release were distinguishable from failures. The rate of success and the mean amplitude of EOS signals were well fitted with a binomial model, indicating that release events consist of quantal components. Furthermore, the fitting parameters suggest that single synapses typically contain multiple release units. Histogram analysis of glutamate release indicates that release events consist of an integral number of quanta. We conclude that quantal release of glutamate underlies the quantal nature of synaptic transmission at glutamatergic synapses. [J Physiol Sci. 2008;58 Suppl:S122]
