Effect of delta opioid receptor activation on spatial cognition and neurogenesis in cerebral ischemic rats

This study aimed to investigate whether a selective delta opioid receptor agonist, [D-Ala2, D-Leu5]-Enkephalin (DADLE), regulates neurogenesis in the hippocampus of ischemic rats. Using an intracerebral cannula, rats were subjected to cerebral ischemia using the standard four-vessel occlusion. DADLE (2.5 nmol), DADLE (2.5 nmol) with naltrindole (NAL) (2.5 nmol), or vehicle was administered at the onset of reperfusion. Bromodeoxyuridine (BrdU, 100 mg/kg, intraperitoneal) was used to label newly formed cells from days I to 7 after ischemia. Immunohistochemistry was used to evaluate cell proliferation and apoptosis and differentiation 7 days 28 days, respectively, after ischemia. Morris water maze test was conducted to test spatial learning and memory 23-27 days after ischemia. We found that DADLE treatment improved performance in the Morris water maze test, promoted proliferation and differentiation of newly formed neurons, and inhibited differentiation into astrocytes in a rat model of cerebral ischemia. Furthermore, the protective effects of DADLE were significantly reversed by co-administration of NAL (P < 0.05), a highly potent and selective delta opioid receptor antagonist. Our findings suggest that DADLE promotes spatial cognitive function recovery and regulates neurogenesis after ischemia, which may provide a promising therapeutic strategy for cerebral ischemia. (C) 2016 Elsevier Ireland Ltd. All rights reserved.