Morphine preconditions Purkinje cells against cell death under in vitro simulated ischemia-reperfusion conditions

Background: Morphine pretreatment via activation of delta(1)-opioid receptors induces cardioprotection. In this study, the authors determined whether morphine preconditioning induces ischemic tolerance in neurons. Methods: Cerebellar brain slices from adult Sprague-Dawley rats were incubated with morphine at 0.1-10 mum in the presence or absence of various antagonists for 30 min. They were then kept in morphine- and antagonist-free buffer for 30 min before they were subjected to simulated ischemia (oxygen-glucose deprivation) for 20 min. After being recovered in oxygenated artificial cerebrospinal fluid for 5 h, they were fixed for morphologic examination to determine the percentage of undamaged Purkinje cells. Results. The survival rate of Purkinje cells was significantly higher in slices preconditioned with morphine (greater than or equal to 0.3 mum) before the oxygen-glucose deprivation (57 +/- 4% at 0.3 mum morphine) than that of the oxygen-glucose deprivation alone (39 3%, P < 0.05). This morphine preconditioning-induced neuroprotection was abolished by naloxone, a non-type-selective opioid receptor antagonist, by naltrindole, a selective delta-opioid receptor antagonist, or by 7-benzylidenenaltrexone, a selective 5,delta(1)-opioid receptor antagonist. However, the effects were not blocked by the mu-, kappa-, or delta(2)-opioid receptor antagonists, beta-fun-altrexamine, nor-binaltorphimine, or naltriben, respectively. Morphine preconditioning-induced neuroprotection was partially blocked by the selective mitochondrial adenosine triphosphate-sensitive potassium channel antagonist, 5-hydroxyde-canoate, or the mitochondrial electron transport inhibitor, myxothiazol. None of the inhibitors used in this study alone affected the simulated ischemia-induced neuronal death. Conclusions: These data suggest that morphine preconditioning is neuroprotective. This neuroprotection may be delta(1)-opioid receptor dependent and may involve mitochondrial adenosmie triphosphate-sensitive potassium channel activation and free radical production. Because morphine is a commonly used analgesic, morphine preconditioning may be explored further for potential clinical use to reduce ischemic brain injury.