Non-stationary analysis of synaptic transmission at a central synapse, comparing the quantal sizes used in evoked vs. spontaneous release

grantor: University of TorontoThe postsynaptic response to neurotransmitters released from a single synaptic vesicle is the smallest amount of possible signal transmission in the nervous system, called quantum. Release of synaptic vesicles can occur spontaneously or due to an action potential. One of the assumptions of the quantal hypothesis is that the quanta involved in evoked events are indistinguishable from those occurring spontaneously. We apply variance-mean analysis, desynchronized release in strontium (Sr2+), and unitary quantal release in cadmium (Cd2+) at single axosomatic glutamatergic synapses, to show that the average quantal size underlying evoked excitatory synaptic current (eEPSC) is significantly larger than those involved in spontaneous release (sEPSC). This increase in average size may indicate a preferential selection of certain quanta in evoked release out of all the quanta available. Our data may be important to refine the quantal theory on neurotransmitter release and the current view of synaptic transmission at mammalian central synapses.M.Sc