Nonsaturation of AMPA and NMDA receptors at hippocampal synapses

An important issue in synaptic physiology is the extent to which postsynapt ic receptors are saturated by the neurotransmitter released from a single s ynaptic vesicle. Although the bulk of evidence supports receptor saturation , recent studies have started to reveal that alpha-amino-3-hydroxy-5-methyl -4-isoxazolepropionate (AM PA) and N-methyl-D-aspartate (NMDA) receptors ma y not be saturated by a single vesicle of glutamate, Here, we address this question through a study of putative single synapses, made by hippocampal n eurons in culture, that are identified by FM1-43 staining, An analysis of t he sources of variability in the amplitudes of miniature excitatory postsyn aptic currents at single synapses variability must arise presynaptically, f rom variations in the quantity of agonist released. Thus, glutamate recepto rs at hippocampal synapses are not generally saturated by quantal release.