Neuroprotective role of delta-opioid receptors in cortical neurons.
We recently demonstrated that delta-opioid receptor (DOR) activation protects cortical neurons against glutamate-induced injury. Because glutamate is a mediator of hypoxic injury in neurons, we hypothesized that DOR is involved in neuroprotection during O2 deprivation and that its activation/inhibition may alter neuronal susceptibility to hypoxic stress. In this work, we tested the effect of opioid receptor activation and inhibition on cultured cortical neurons in hypoxia (1% O2). Cell injury was assessed by lactate dehydrogenase release, morphology-based quantification, and live/dead staining. Our results show that 1) immature neurons (days 4 and 6) were not significantly injured by hypoxia until 72 h of exposure, whereas day 8 neurons were injured after only 24-h hypoxia; 2) DOR inhibition (naltrindole) caused neuronal injury in both day 4 and day 8 normoxic cultures and further augmented hypoxic injury in these neurons; 3) DOR activation ([D-Ala2,D-Leu5]enkephalin) reduced neuronal injury in day 8 cultures after 24 h of normoxic or hypoxic exposure and attenuated naltrindole-induced injury with prolonged exposure; and 4) mu- or kappa-opioid receptor inhibition (beta-funaltrexamine or nor-binaltorphimine) had little effect on neurons in either normoxic or hypoxic conditions. Collectively, these data suggest that DOR plays a crucial role in neuroprotection in normoxic and hypoxic environments.
Zhang
Junhui
J
Department of Pediatrics, Yale University, New Haven, Connecticut 06520, USA.
Gibney
Geoffrey Thomas
GT
Zhao
Peng
P
Xia
Ying
Y
D000818:Animals; D002452:Cell Count; D002454:Cell Differentiation / Q000502:physiology; D015687:Cell Hypoxia / Q000502:physiology*; D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D016308:Enkephalin, Leucine-2-Alanine / Q000494:pharmacology; D002534:Hypoxia, Brain / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017465:Receptors, Opioid, delta / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017473:Receptors, Opioid, kappa / Q000037:antagonists & inhibitors; D013997:Time Factors
D009292:Narcotic Antagonists; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D009271:Naltrexone; D016308:Enkephalin, Leucine-2-Alanine; D007770:L-Lactate Dehydrogenase; C055382:naltrindole