ABSTRACT
Objective:To explore the effects of enriched environment combined with melatonin on learning and memory function and DNA oxidative damage in senescence accelerated mouse prone 8 (SAMP8) mice.Methods:Twenty-four 6-month-old SPF healthy male SAMP8 mice were randomly divided into model group, enriched environment group, melatonin group and enriched environment+ melatonin group, with 6 mice in each group. Six homologous SAMR1 mice of the same age were used as the control group. The mice in the enriched environment group and the enriched environment+ melatonin group were fed in the enriched environment. At the same time, the mice in the melatonin group and the enriched environment+ melatonin group were subcutaneously injected with melatonin (8 mg /(kg·d)) once a day for 28 d. The mice in the model group, the control group and the enriched environment group were subcutaneously injected with an equal volume of 0.9% sodium chloride solution once a day for 28 days. Aging score was used to evaluate the aging of mice. Morris water maze and Y maze tests were used to evaluate the learning and memory ability of mice. The cell morphology of hippocampus in mice was observed by hematoxylin-eosin staining, and the level of Aβ 1-42 protein in hippocampus of mice was detected by immunohistochemical staining. The levels of γ-H2A histone family member X(γ-H2AX) and 8-hydroxy-2 deoxyguanosine(8-OHdG) proteins in hippocampus of mice were detected by Western blot and Enzyme-linked immunosorbent assay. SPSS 25.0 statistical software was used to process the data. One-way analysis of variance was used for comparison among multiple groups, and LSD- t test was used for further pairwise comparison. Results:(1)There was a statistical difference in aging scores among the 5 groups of mice after intervention ( F=126.4, P<0.01). After intervention, the aging scores of mice in the enriched environment group, melatonin group, and enriched environment+ melatonin group were lower than that in the model group (all P<0.05), and the score of the enriched environment+ melatonin group was significantly lower than that in the enriched environment group ( P<0.05). (2)The time and group interaction, group main effect and time main effect of the escape latency among the 5 groups of mice were statistically significant ( F=11.2, 799.9, 121.8, all P<0.01). From day 2 to day 4, the escape latencies of mice in the enriched environment group, melatonin group and enriched environment+ melatonin group were significantly lower than that in the model group (all P<0.05). There was a statistically significant difference in the target quadrant residence time and cross-platform times among the 5 groups ( F=70.38, 48.83, both P<0.01). The target quadrant residence time and cross-platform times of mice in the enriched environment group, melatonin group, and enriched environment+ melatonin group were significantly higher than that in the model group (all P<0.05). (3) There were significant differences in the total number of alternations and correct rates among the 5 groups ( F=291.328, 113.482, both P<0.01). The total numbers of alternations and correct rates in melatonin group ((29.46±3.75)times, (53.16±3.47)%) and the enriched environment+ melatonin group((32.57±3.52)times, (58.60±4.13)%)were significantly higher than those in the model group ((18.62±3.96)times, (43.61±3.92) %)(all P<0.05). (4)The results of hematoxylin-eosin staining and immunohistochemistry staining showed that compared with the model group, the cell structure and morphology of the hippocampus of mice in enriched environment group, melatonin group, and enriched environment+ melatonin group were significantly improved, and the expression of Aβ 1-42 was significantly reduced (all P<0.05). (5) There were statistically significant differences in the levels of γ-H2AX and 8-OHdG proteins in the hippocampus of the 5 groups of mice ( F=78.09, 117.20, both P<0.01). The levels of γ-H2AX and 8-OHdG of mice in the enriched environment+ melatonin group ((1.37±0.26), (4.79±0.35)pg/μg) were significantly lower than those in the enriched environment group ((2.83±0.25), (7.23±0.41)pg/μg) and the melatonin group ((2.43±0.22), (6.69±0.28)pg/μg) (all P<0.05). Conclusion:Both enriched environment and melatonin can significantly improve the learning and memory function of SAMP8 mice, and the combined treatment effect is more significant.The mechanism may be related to the reduction of DNA oxidative damage in hippocampus.