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1 Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo 113-0033, Japan
Plastic modifications of synaptic strength are putative mechanisms underlying information processing in the brain, including memory storage, signal integration and filtering. Here we describe a dynamic interplay between short-term and long-term synaptic plasticity. At rat hippocampal CA1 synapses, induction of both long-term potentiation (LTP) and depression (LTD) was accompanied by changes in the profile of short-term plasticity, termed redistribution of synaptic efficacy (RSE). RSE was presynaptically expressed and associated in part with a persistent alteration in hyperpolarization-activated Ih channel activity. Already potentiated synapses were still capable of showing RSE in response to additional LTP-triggering stimulation. Strikingly, RSE took place even after reversal of LTP or LTD, that is, the same synapse can display different levels of short-term plasticity without changing synaptic efficacy for the initial spike in burst presynaptic firing, thereby modulating spike transmission in a firing rate-dependent manner. Thus, the history of long-term synaptic plasticity is registered in the form of short-term plasticity, and RSE extends the information storage capacity of a synapse and adds another dimension of functional complexity to neuronal operations.
(Received 13 March 2005;
accepted after revision 20 April 2005;
first published online 21 April 2005)
Corresponding author Y. Ikegaya: Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. Email: ikegaya{at}tk.air.jp
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