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Mechanisms of D-aspartate release under ischemic conditions in mouse hippocampal slices
1Tampere Brain Research Center, University of Tampere Medical School, Finland. blpisa@uta.fi
Abstract:
The release of preloaded D-[3H]aspartate, an unmetabolizable analogue of L-glutamate, was studied in superfused hippocampal slices from 7-day-old and 3-month-old (adult) mice under various cell-damaging conditions, including hypoxia, hypoglycemia, ischemia, oxidative stress and the presence of free radicals and metabolic poisons. The release was generally markedly enhanced in most of the above conditions, the responses being greater in adults than in developing mice. The presence of dinitrophenol had the most pronounced effect at both ages, followed by NaCN- and free-radical-containing media and ischemia. Hypoxia did not affect release in the immature hippocampus. Under most conditions K+ stimulation (50 mM) was still able markedly to enhance D-aspartate release. This potentiation under cell-damaging conditions in both adult and developing hippocampus signifies that increased L-glutamate release contributes to excitotoxicity and subsequent cell death. The mechanisms of ischemia-induced release of D-aspartate were analyzed in the adult hippocampus using ion channel inhibitors and modified superfusion media. The induced release proved to be partly Ca(2+)-dependent and partly Ca(2+)-independent. The results obtained with Na+ omission and homo- and heteroexchange with D-aspartate and L-glutamate demonstrated that a part of the release in normoxia and ischemia is mediated by the reversal of Na(+)-dependent glutamate transporters. The Na+ channel blockers amiloride and riluzole reduced the ischemia-induced release, also indicating the involvement of Na+ channels. In addition to this, the enhanced release of D-aspartate may comprise a swelling-induced component through chloride channels.
Insights
Cell damage significantly increases glutamate release in mouse hippocampus, particularly in adults. This enhanced release contributes to excitotoxicity and neuronal death, highlighting potential therapeutic targets.
Area of Science:
- Neuroscience
- Neurobiology
- Cellular Biology
Background:
- L-glutamate is a key excitatory neurotransmitter in the brain.
- Excitotoxicity, mediated by excessive glutamate, contributes to neuronal damage.
- Understanding glutamate release mechanisms under stress is crucial for neuroprotection.
Purpose of the Study:
- To investigate the release of D-aspartate, an L-glutamate analog, from hippocampal slices under various cell-damaging conditions.
- To compare release patterns between developing and adult mice.
- To elucidate the mechanisms underlying ischemia-induced D-aspartate release.
Main Methods:
- Superfusion of hippocampal slices from mice of different ages.
- Exposure to various cell-damaging conditions: hypoxia, hypoglycemia, ischemia, oxidative stress, metabolic poisons.
- Use of ion channel inhibitors and modified superfusion media to study release mechanisms.
Main Results:
- D-aspartate release was markedly enhanced under most cell-damaging conditions, with greater responses in adults.
- Dinitrophenol, NaCN, free radicals, and ischemia showed pronounced effects.
- Ischemia-induced release was partly Ca(2+)-dependent and Ca(2+)-independent, involving reversed glutamate transporters and Na+ channels.
Conclusions:
- Enhanced L-glutamate release under cell-damaging conditions contributes to excitotoxicity and neuronal death.
- Mechanisms include reversed Na(+)-dependent glutamate transporters, Na+ channels, and potentially swelling-induced chloride channel activity.
- Age-dependent differences in release suggest developmental changes in neuroprotective mechanisms.