LONG-LASTING DECREASES OF AMPA RESPONSES FOLLOWING POSTSYNAPTIC ACTIVITY IN SINGLE HIPPOCAMPAL-NEURONS

Direct postsynaptic depolarization and firing of single CA1 neurons ca used decreased responses to iontophoresed alpha-amino-3-hydroxy-5-meth yl-4-isoxazole propionic acid (AMPA). Since there was no associated ch ange in the excitatory postsynaptic potential (EPSP) evoked by electri cal stimulation in the same band of stratum radiatum, we infer that th e decreased AMPA response was mediated predominantly by extrasynaptic receptors. The decreased AMPA response developed within 10-30 min afte r conditioning, a time course similar to the delayed increase in AMPA responses associated with long-term potentiation (LTP) [Davies et al. (1989), Nature, 338:500-503; Sergueeva et al. (1993), Neuropharmacolog y, 32:933-935]. Our observations suggest the existence of mirror-image processes that may regulate AMPA receptors and possibly synaptic effi cacy. (C) 1997 Wiley-Liss, Inc.