Morphine Preconditions Purkinje Cells against Cell Death under in Vitro Simulated Ischemia-Reperfusion Conditions

Abstract

Background: Morphine pretreatment via activation of δ 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 μM 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 (≥ 0.3 μM) before the oxygen-glucose deprivation (57 ± 4% at 0.3 μM 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 δ-opioid receptor antagonist, or by 7-benzylidenenaltrexone, a selective δ 1-opioid receptor antagonist. However, the effects were not blocked by the μ-, κ-, or δ 2-opioid receptor antagonists, β-funaltrexamine, nor-binaltorphimine, or naltriben, respectively. Morphine preconditioning-induced neuroprotection was partially blocked by the selective mitochondrial adenosine triphosphate-sensitive potassium channel antagonist, 5-hydroxydecanoate, 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 δ 1-opioid receptor dependent and may involve mitochondrial adenosine 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.