Journal of Neuroscience, Vol 8, 4745-4754, Copyright © 1988 by Society for Neuroscience
Neuroprotective effects of MK-801 in vivo: selectivity and evidence for delayed degeneration mediated by NMDA receptor activation
AC Foster, R Gill and GN Woodruff
Merck Sharp and Dohme Research Laboratories, Neuroscience Research Centre, Harlow, Essex, United Kingdom.
The ability of the noncompetitive N-methyl-D-aspartate (NMDA) receptor
antagonist MK-801 to prevent neuronal degeneration in the rat striatum and
hippocampus caused by intracerebral injection of excitotoxins has been
examined. Excitotoxic damage was assessed after 7 d, using histological and
biochemical [choline acetyltransferase (ChAT) glutamate decarboxylase
(GAD)] measurements. Systemically administered MK-801 was found to protect
against neurodegeneration caused by NMDA (200 nmol) and the naturally
occurring NMDA receptor agonist quinolinate (120-600 nmol) but not against
that induced by kainate (5 nmol) or
alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA; 50 nmol),
indicating a selectivity for NMDA receptor-mediated neuronal loss.
Neurotoxicity caused by NMDA (200 nmol) or quinolinate (200 nmol) was
prevented by MK-801 (1-10 mg/kg, i.p.) administered in a single dose after
excitotoxin injection. In the striatum, significant protection of
cholinergic neurons (assessed by ChAT measurements) was observed when
MK-801 was given up to 5 hr after injection of NMDA or quinolinate, whereas
protection of GABAergic neurons (assessed by GAD measurements) was obtained
up to 2 hr. The results suggest that GABAergic neurons degenerate more
rapidly than cholinergic neurons. The competitive NMDA receptor antagonist
3-[(+/-)-2-carboxypiperazin-4-yl]- propyl-1-phosphonate (100 mg/kg, i.p.)
gave partial protection of striatal neurons when administered 1 hr after
quinolinate injection. In the rat hippocampus, administration of 10 mg/kg
MK-801 i.p. 1 hr after quinolinate injection caused almost complete
protection of pyramidal and granule neurons, whereas the degeneration of
CA3/CA4 pyramidal neurons caused by kainate injection was unaffected. These
observations indicate that neurons in rat striatum and hippocampus do not
die as an immediate consequence of exposure to high concentrations of NMDA
agonists but that a delayed process is involved that requires NMDA receptor
activation. In this respect, intracerebral injections of NMDA agonists may
mimic the pathological changes that are thought to occur in the brain
following periods of cerebral ischemia, where delayed neuronal degeneration
occurs.