Nuclear disintegration as a leading step of glutamate excitotoxicity in brain neurons.
Recent studies on ischemic brain disease in vivo and glutamate excitotoxicity in vitro suggest that apoptosis may play a role in excitotoxic neuronal death. To examine the possible involvement of apoptosis in glutamate excitotoxicity, we studied an early process of morphological changes in rat cortical neurons exposed to 1 mM glutamate. Observations under Nomarski optics combined with a digital image processor revealed a rapid change in the nucleus followed by a cellular swelling. The nucleus increased in granularity and swelled in 5 min, then became liquefied in 30 min. The cell body swelled slowly in 15-45 min. These changes could be prevented by treatment of the neuron with MK-801 (dizocilpine maleate), a blocker of N-methyl-D-aspartate (NMDA) receptor-coupled ion channel. However, treatment of the neurons with N(G)-nitro-L-arginine (N-NORG), a nitric oxide synthase inhibitor, had no significant effect. Use of the in situ end-labeling technique for the demonstration of free 3'-hydroxyl ends revealed that DNA fragmentation took place within 1 hr after glutamate exposure. A change in intracellular Ca(2+) concentration was examined with fluo-3 under a confocal laser microscope. Application of 1 mM glutamate induced rapid Ca transients in the nucleus as well as in the cytoplasm. Both of these Ca responses were blocked by MK-801. These results indicate that glutamate excitotoxicity in the brain neuron does not fulfill morphological criteria of apoptosis, but suggest that the nuclear disintegration associated with DNA fragmentation is involved as a leading step in glutamate excitotoxicity.
Ikeda
J
J
Department of Physiological Chemistry, Tokyo Medical and Dental University, Japan.
Terakawa
S
S
Murota
S
S
Morita
I
I
Hirakawa
K
K
D000818:Animals; D001921:Brain / Q000166:cytology / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism; D002467:Cell Nucleus / Q000187:drug effects* / Q000502:physiology*; D053938:DNA Fragmentation; D018698:Glutamic Acid / Q000506:poisoning*; D007425:Intracellular Membranes / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000187:drug effects*; D009994:Osmolar Concentration; D051381:Rats / Q000196:embryology; D013997:Time Factors
D018698:Glutamic Acid; D002118:Calcium