Rapid hypoxia preconditioning protects cortical neurons from glutamate toxicity through delta-opioid receptor.
OBJECTIVE
Hypoxia preconditioning (HPC), rapid or delayed, has been reported to induce neuroprotection against subsequent severe stress. Because delta-opioid receptor (DOR) plays an important role in delayed HPC-induced neuroprotection against severe hypoxic injury, we asked whether DOR is also involved in the rapid HPC-induced neuroprotection.


METHODS
Cultured rat cortical neurons at culture days 8 to 9 were exposed to a short-term hypoxia (1% O2 for 30 minutes) to induce HPC followed by 30-minute normoxia before exposing to glutamate toxicity (100 micromol/L; 4 hours). Neuronal viability was assessed by lactate dehydrogenase leakage and morphological assessment. Protein and mRNA levels of DOR were detected by receptor binding and RT-PCR, respectively. Naltrindole was used to block DOR. Developmental changes in NMDA receptor expression was measured by Western blots.


RESULTS
HPC significantly reduced the glutamate-induced neuronal injury. Receptor binding showed that HPC increased DADLE (a DOR ligand) binding density in the cultured cortical neurons by >90% over control level (P<0.05), although RT-PCR did not detect any appreciable change in DOR mRNA. DOR inhibition with naltrindole had no effect on neuronal injury and completely abolished the HPC-induced neuroprotection. In contrast to HPC-induced increase in DADLE binding density, prolonged hypoxia caused severe neuronal injury with a significant decrease in DADLE binding density and DOR mRNA level.


CONCLUSIONS
DOR is involved in neuroprotection induced by rapid HPC in cortical neurons.
Zhang
Junhui
J
Department of Pediatrics, Yale University School of Medicine, New Haven, CT 06520, USA.
Qian
Hong
H
Zhao
Peng
P
Hong
Soon-Sun
SS
Xia
Ying
Y
D000818:Animals; D002478:Cells, Cultured; D016922:Cellular Senescence; D002540:Cerebral Cortex / Q000187:drug effects* / Q000378:metabolism; D016308:Enkephalin, Leucine-2-Alanine / Q000378:metabolism; D018698:Glutamic Acid / Q000506:poisoning*; D000860:Hypoxia / Q000503:physiopathology*; D019194:Ischemic Preconditioning; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D016202:N-Methylaspartate / Q000378:metabolism; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017465:Receptors, Opioid, delta / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D015854:Up-Regulation
D009292:Narcotic Antagonists; D012333:RNA, Messenger; D017465:Receptors, Opioid, delta; D018698:Glutamic Acid; D009271:Naltrexone; D016308:Enkephalin, Leucine-2-Alanine; D016202:N-Methylaspartate; D007770:L-Lactate Dehydrogenase; C055382:naltrindole