title: Changes in the state of the excitatory synaptic system in the hippocampus on prolonged exposure to excitatory amino acids and antagonists.
abstract: Prolonged exposure of hippocampal slices to L-glutamate was found to produce a biphasic effect on excitatory synaptic transmission from Schaffer collateral-commissural fibers to CA1 pyramidal neurons: an early blockade of postsynaptic responses was followed by a progressive recovery. Antagonists of N-methyl-D-aspartate (NMDA) receptors, which had no effect on the initial responses, blocked the responses which reappeared during continued exposure to L-glutamate. Furthermore, when NMDA antagonists were maintained in the presence of glutamate, excitatory transmission was again restored and the new responses were now insensitive both to 'NMDA' and 'non-NMDA' antagonists. Once elicited, the changes in synaptic transmission appear to be 'memorized' by the slice for at least tens of minutes. These phenomena suggest that the well-known plasticity of the hippocampal synapses may involve a sequence of distinct 'states', and that transitions between these states can be induced by certain pharmacological stimuli.
mesh_terms: D015763:2-Amino-5-phosphonovalerate; D015074:2-Aminoadipic Acid / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology*; D004151:Dipeptides / Q000494:pharmacology; D005260:Female; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D011247:Pregnancy; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects*; D014633:Valine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D004151:Dipeptides; D005971:Glutamates; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter; C028929:gamma-glutamylglycine; D015074:2-Aminoadipic Acid; D001224:Aspartic Acid; D018698:Glutamic Acid; D015763:2-Amino-5-phosphonovalerate; D014633:Valine