Study on the regulatory mechanisms of transmitter release from presynaptic nerve boutons in CNS

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It was reported that some mammalian CNS neurons co-release GABA and Gly, and that a single unitary IPSC consists of GABA and Gly (Joneas et al.) Furthermore, IPSCs observed in the postsynaptic neurons were due to GABA, Gly, or combined action of GABA and Gly. They suggested that the dual nature of unitary IPSC and subset of mIPSCs are due to GABA and Gly co-released from a single spinal interneuron. Similar co-transmission of GABA and Gly to motoneurons was found in mIPSCs by O'brien et al., who also suggested that GABA and Gly are co-localized in the same presynaptic vesicle and are co-released from the nerve ending. We investigated, therefore, whether or not GABA and Gly are co-released from the same synaptic vesicle by use of 'synaptic bouton' preparation of rat spinal neurons and 'a single bouton focal stimulation' technique, which we recently developed. When spontaneous miniature postsynaptic currents were recorded from 'synaptic bouton' preparation, GABA, Gly, and mixed mIPSCs were constantly recorded at 2mM [Ca^<2+>]_o. Interestingly, the co-release of GABA and Gly was always observed ever at a relatively lower or higher external Ca concentration external Ca (0.3-7mM, respectively). When focal stimulation (0.2Hz) were applied in co-released synapse of a single bouton, three different pattern of release including GABA, Gly, or the mixed co-release of these transmitters were observed, indicating that GABA , Gly and GABA and Gty combination are separately stored in individual vesicles and are co-released.