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.
Stabel
J
J
Institut für Neurophysiologie, Zentrum Physiologie und Pathophysiologie, Universität zu Köln, Cologne, F.R.G.
Wisskirchen
T
T
Heinemann
U
U
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