Single synapse evaluation of the postsynaptic NMDA receptors targeted by evoked and spontaneous neurotransmission

Recent studies indicate that within individual synapses spontaneous and evoked release processes are segregated and regulated independently. In the hippocampus, earlier electrophysiological recordings suggested that spontaneous and evoked glutamate release can activate separate groups of postsynaptic NMDA receptors with limited overlap. However, it is still unclear how this separation of NMDA receptors is distributed across individual synapses. In a previous paper (Reese and Kavalali, 2015) we showed that NMDA receptor mediated spontaneous transmission signals to the postsynaptic protein translation machinery through Ca²⁺- induced Ca2+ release. Here, we show that in rat hippocampal neurons although spontaneous and evoked glutamate release driven NMDA receptor mediated Ca2+ transients often occur at the same synapse, these two signals do not show significant correlation or cross talk.