The expression mechanism of long-term potentiation (LTP) remains controversial. Here we combine electrophysiology and Ca(2+) imaging to examine the role of silent synapses in LTP expression. Induction of LTP fails to change p(r) at these synapses but instead mediates an unmasking process that is sensitive to the inhibition of postsynaptic membrane fusion. Once unmasked, however, further potentiation of formerly silent synapses leads to an increase in p(r). The state of the synapse thus determines how LTP is expressed.
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Animals, Animals, Newborn, Calcium Signaling, Electric Stimulation, Excitatory Postsynaptic Potentials, Fluorescent Dyes, Glutamic Acid, Hippocampus, Long-Term Potentiation, Magnesium, Male, Membrane Fusion, Neural Pathways, Optics and Photonics, Organ Culture Techniques, Patch-Clamp Techniques, Rats, Rats, Wistar, Receptors, N-Methyl-D-Aspartate, Synapses, Synaptic Membranes, Synaptic Transmission, Synaptic Vesicles