Laminar profiles of N-methyl-D-aspartate- and quisqualate-induced [Na+]o changes in rat hippocampus.
Since plastic changes in neuronal tissue are often associated with changes in responses to excitatory amino acids (EAA), a method is required which permits mapping of functional EAA receptor sites. In this study the measurement of extracellular sodium concentration changes [( Na+]o) induced by iontophoretic application of N-methyl-D-aspartate (NMDA) and quisqualate (Quis) is used as a tool to estimate the density of functional NMDA- and Quis-receptor sites in area CA1 and dentate gyrus of rat hippocampus. Largest decreases of [Na+]o induced by NMDA were found in basal and apical dendritic fields of area CA1 and in stratum moleculare of dentate gyrus at a distance of 50-100 microns from stratum granulare. Peak decreases in [Na+]o induced by Quis occurred at similar positions. Bath application of tetrodotoxin (TTX) suppressed that part of the extracellular Na+ loss mediated by Na+ fluxes through voltage activated Na+ channels. However, the laminar profiles of Quis- and NMDA-induced [Na+]o changes were not affected by TTX. Thus, EAA induced decreases in [Na+]o can be used to detect changes in receptor density and in receptor functionality of hippocampus which had undergone plastic changes.
Institut für Neurophysiologie, Zentrum Physiologie und Pathophysiologie, Universität zu Köln, Cologne, F.R.G.
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Wisskirchen
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Heinemann
D000818:Animals; D004558:Electric Stimulation; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D066298:In Vitro Techniques; D007478:Iontophoresis; D008564:Membrane Potentials / Q000187:drug effects; D016202:N-Methylaspartate / Q000494:pharmacology*; D011712:Pyramidal Tracts / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D016318:Quisqualic Acid / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology
D013779:Tetrodotoxin; D016202:N-Methylaspartate; D016318:Quisqualic Acid; D012964:Sodium