Effects of environmental enrichment on learning and memory ability, and the expression of brain-derived neurotrophic factor and synaptophysin in hippocampus of neonatal rats with hypoxic-ischemic brain damage

Objective To explore the effects of environmental enrichment (EE)on learning and memory ability and the expression of brain-derived neurotrophic factor (BDNF) and synaptophysin in hippocampus of neonatal rats with hypoxic-ischemic brain damage(HIBD). Methods Forty Wistar neonatal male rats aged 7 days were randomly divided into EE intervention for 6 hours(6 h EE) group (n=10), EE intervention for 12 hours (12 h EE) group (n=10), model group (n=10) and sham group (n=10). The first 3 groups were performed with HIBD.The 6 h EE and 12 h EE group received EE stimuli for 6 h and 12 h respectively, once a day for 14 days.Learning and memory of the rats were tested by using Morris water maze.The expression levels of BDNF and synaptophysin in hippocampus were determined with Western blot. Results The escape latency of all groups gradually reduced with the increase of training days, but there was no significant difference in the escape latency among the 4 groups(F=0.237, P>0.05). The rats in the 6 h EE group, 12 h EE group and model group spent less time in the target quadrant and showed a significant reduction of BDNF and synaptophysin(6 h EE group: 0.529±0.038, 0.889±0.027; 12 h EE group: 0.660±0.034, 1.114±0.037; model group: 0.225±0.015, 0.672±0.057)in the hippocampus compared with the sham group(0.803±0.026, 1.347±0.092)(all P<0.01). In the 6 h EE group and 12 h EE group, the rats significantly increased the time spent in target quadrant and aggrandized the expression of BDNF and synaptophysin in hippocampus compared with the model group. Moreover, the 12 h EE group had a better performance than the 6 h EE group in the space exploration and the expression of BDNF and synaptophysin. Conclusion EE is helpful for improving learning and memory ability in neonatal rats with HIBD, which may be associated with up-regulating the expression of BDNF and synaptophysin in hippocampus. Key words: Environmental enrichment; Hypoxic-ischemic brain damage; Learning and memory; Brain-derived neurotrophic factor; Synaptophysin; Rat