Memantine restores long term potentiation impaired by tonic N-methyl-D-aspartate (NMDA) receptor activation following reduction of Mg2+ in hippocampal slices.
This study compared the ability of memantine and (+)MK-801 to counteract deficits in the induction of long term potentiation (LTP) following reduction of Mg2+ in hippocampal slices--a model of increased synaptic noise due to tonic N-methyl-D-aspartate (NMDA) receptor activation. Decreasing Mg2+ from 1 mM to 10 microM for 60 min enhanced baseline field excitatory post-synaptic potential (fEPSP) slopes (87.2 +/- 10.6% above control) and impaired LTP (-4.1 +/- 9.8% compared to pre-tetanic levels). Long pre-incubations with memantine (1 microM), a concentration achieved in the CSF of dementia patients, almost fully restored the induction of LTP (to 43.4 +/- 8.4%) without changing the enhancement of baseline fEPSP slopes (84.1 +/- 11.6%). Memantine (10 microM) fully restored the induction of LTP (61.5 +/- 5.3%) and also decreased the enhancement of baseline fEPSP slopes (30.1 +/- 4.9%). In contrast, although (+)MK-801 (0.01, 0.1 and 1 microM) caused a concentration-dependent reduction in the low Mg2+ -induced enhancement of baseline fEPSP slopes, it was not able to restore the induction of LTP (3.0 +/- 9.8%, 16.3 +/- 5.7% and 4.8 +/- 6.7% respectively). These data indicate that memantine could produce symptomatological improvement in learning under conditions of tonic NMDA receptor activation such as those occurring in chronic neurodegenerative diseases whereas (+)MK-801 is likely to have only negative effects.
Frankiewicz
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Department of Pharmacology, Merz and Co., Frankfurt am Main, Germany.
Parsons
C G
CG
D000818:Animals; D016291:Dizocilpine Maleate / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects* / Q000378:metabolism; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D008559:Memantine / Q000494:pharmacology*; D010084:Oxidation-Reduction; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors*
D018691:Excitatory Amino Acid Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D016291:Dizocilpine Maleate; D008274:Magnesium; D008559:Memantine