Spontaneous Neurotransmission as a Driver of Calcium Signaling
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Spontaneous neurotransmission is a stochastic mode of neurotransmitter release that is not coupled to action potential arrival at the presynapse. Recent evidence has shed light upon the presynaptic and vesicular fusion machinery that makes this mode of release unique to action potential driven, or evoked release, yet the postsynaptic reception of these differing signals has yet to be probed in detail. Here, I illustrate that evoked and spontaneous release modes coexist within the same synapses, yet the neurotransmitter released falls upon separate subsets of postsynaptic receptors. As a consequence of this phenomenon, in glutamatergic hippocampal synapses the NMDA receptors activated by spontaneous release are able to drive large calcium transients that maintain synaptic homeostasis and suppress local protein synthesis.