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Journal Article

Differences in magnesium and calcium effects on N−methyl−D−aspartate− and quisqualate−induced decreases in extracellular sodium concentration in rat hippocampal slices

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http://pubman.mpdl.mpg.de/cone/persons/resource/persons93955

Köhr,  Georg
Department of Molecular Neurobiology, Max Planck Institute for Medical Research, Max Planck Society;
Directly responsible to the Managing Director, Max Planck Institute for Medical Research, Max Planck Society;
Georg Köhr Group, Max Planck Institute for Medical Research, Max Planck Society;

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Citation

Köhr, G., & Heinemann, U. (1988). Differences in magnesium and calcium effects on N−methyl−D−aspartate− and quisqualate−induced decreases in extracellular sodium concentration in rat hippocampal slices. Experimental Brain Research, 71(2), 425-430. doi:10.1007/BF00247502.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0019-AE2B-2
Abstract
Decreases in extracellular sodium concentration ([Na+]o) and associated slow negative field potentials (fps) were monitored with double barreled sodium sensitive/reference microelectrodes in area CA1 of rat hippocampal slices during iontophoretic application of the glutamate receptor agonists N−methyl−D−aspartate (NMDA) and quisqualate (quis). The effects of lowering [Ca2+]o on these signals were compared to those of lowering [Mg2+]o. Both NMDA− and quis−induced decreases in [Na+]o of up to 60 mM and in the fp's of up to 8 inV. Decreasing [Mg2+]o enhanced NMDA−induced signals, whereas quis−induced signals were unaffected. Lowering [Ca>]o also enhanced NMDA signals, although somewhat less than lowering [Mg2+]o. This effect was still present, even when voltage dependent Na+ currents were blocked by 10 −7 tetrodotoxin. Interestingly, quis−induced signals could be enhanced in a low Ca 2+ medium as well, but only when high quis concentrations were used. The results suggest that, during the sorts of large decreases of [Ca2+]oobserved during seizure activity, activation of NMDA receptors is facilitated