Research on acquisition of ischemic-tolerance-like phenomenon intermediated by opioid receptors

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In this study, we examined the role of opioid receptors in ischemic-tolerance-like phenomenon by short period of forebrain ischemia. In male gerbils used bilateral common carotid afrter-occlusion model. Animals were divided into six groups : 5 min ischemia and 7 days reperfusion (Isch group), 2 min ischemia and 3 days reperfusion followed by 5 min ischemia and 7 days reperfusion (PC group), naloxone 3 mg/kg iv. followed by the sam condition as PC group (NX1 group), naloxone 0.03 mg/kg iv. followed by the same condition of PC group (NX2 group), and control group. After reperfusion after 5 min ischemia, all gerbils were perfused with formaldehyde, and the brain samples were evaluated for neuronal damage in the hippocampus with HE-staining. In control group, the CA1-2 region of hippocampus showed no damage. In Isch group, they were severely damaged revealing vacuolation and pyknosis of neurons. However, the neuronal injury in hippocampus was significantly better in PC group compared to the other groups. In NX1 and NX2 groups, the CA1-2 regions were again worse than control group, and the neurons in hippocampus were also worse in M group. These findings suggest that the involvement of opioid receptors, possibly other than ?-receptors in the phenomenon of ischemic tolerance.