Olea europaea L. (olive) leaf extract ameliorates learning and memory deficits in streptozotocin-induced diabetic rats

The aim of the present study was to assess olive leaf extract (OLE) effects on learning and memory deficits in a model of diabetes induced by streptozotocin (STZ) in rats. The rats were divided as: (1) control rats, (2) diabetic rats, and (3–6) diabetic rats treated by 100, 200, and 400 mg/kg of OLE or metformin. Using the passive avoidance test (PA), we investigated fear learning and memory behaviors. In cortical and hippocampus tissues, total levels of malondialdehyde (MDA) and thiol were measured along with the activity of catalase (CAT) and superoxide dismutase (SOD). Learning and memory behavior impairment were significantly developed in diabetic rats as shown by the impairment of the PA task compared to the control group (p<0.001). In addition, elevated levels of MDA and reduced overall concentrations of thiol, CAT and SOD activity were obvious in diabetic rats’ cortex and hippocampus tissues (p<0.01–p<0.001). Meanwhile, OLE in a dose-dependent manner, improved memory deficit and cognitive performance that was attributed to a reduction of lipid peroxidation and elevation of total thiol concentration, and CAT and SOD activity levels in the brain tissues (p<0.05–p<0.001).  OLE could be effective in improving cognitive impairment in STZ-induced diabetes by oxidative stress depression.