Improvement of melatonin on learning and memory impairment induced by amyloid β-peptide 25-35 in elder rats

AIM: To investigate improvement of melatonin on learning and memory impairment induced by amyloid beta -peptide 25 - 35 (A beta (25-35)) in elder rats. METHODS: Step-down type passive avoidance test, shuttle-box test, and Morris water maze were used together to determine effects of A beta (25-35) and melatonin on teaming and memory. Pathological changes were observed by BE, Congo red, and Ag staining. RESULTS: The elder rats were injected bilaterally A beta (25-35) 20 mug into the hippocampus to induce learning and memory dysfunction. Melatonin administration (0. 1, 1, and 10 mg/kg, ig x 8 d) to the A beta (25-35)-treated rats prolonged the latency, shortened the total stimulating time, and decreased the number of errors in the step-down test. Suttle-box test showed that melatonin improved amnesic rats' performace at the same doses. Melatonin (0. 1, 1, and 10 mg/kg), giving for 10 d, could enhance the spatial resolution of amnesic rats in Morris water maze test. Also in A beta (25-35)-treated group, a decrease in the number of neurons in cortex and hippocampus, a massive glial reaction, and neurophilic phenomenon were detected by HE staining; the positive vascular amyloidosis by Congo red and fibrils by Ag staining were observed. Melatonin (0. 1 and I mg/kg) could inhibit above pathological changes in A beta (25-35) group. CONCLUSION: Melatonin improved the impaired learning and memory induced by A beta (25-35) in elder rats.