The Effects Of Enriched Environment On Age-Related Changes Of Hippocampus

PART ONESIDE DIFFERENCES OF THE AGED-RELATED CHANGES IN THE WHITE MATTER AND MYELINATED NERVE FIBERS IN THE WHITE MATTER OF FEMALE RATSObjective: To investigate if there were side differences of the white matter and the myelinated fibers in the white matter of female rats and if there were side differences in the age-related changes of the white matter and the myelinated fibers in the white matter of female rats using new stereological methods.Methods: Five young (6-month), five middle-aged (18-month) and five old-aged (28-month) female Long-Evans rats were used. The white matter volume, the total volume, total length and mean diameter of the myelinated fibers in the white matter of young, middle-aged and aged female rats were quantitatively investigated using electron microscopic technique and stereological methods.Results: There were no side differences of the white matter volume, the total volume, total length and mean diameter of the myelinated fibers in the white matter of young, middle-aged and aged female rats. When compared to young and middle-aged female rats, the total length of the myelinated fibers in the white matter of the left hemisphere in aged female rats was decreased significantly, but the total length of the myelinated fibers in the white matter of the right hemisphere in aged female rats was non-significantly decreased by 34.5% and 42.8%, respectively.Conclusiton: Our data indicated that there were no significant side differences in the white matter and the myelinated fibers in the white matter of young, middle-aged and aged female rats. However, we demonstrated that the aged-related changes of the myelinated fibers of white matter in left hemisphere and right hemisphere were significantly different. The results obtained in the present study will provide biological basis for the understanding of the asymmetry of cerebral functions. PART TWOTHE EFFECTS OF SHORT-TERM ENRICHED ENVIRONMENT ON THE HIPPOCAMPUS AND THE MYELINATED FIBERS IN THE HIPPOCAMPUS OF AGED FEMALE RATSObjective: To investigate the effects of short-term enriched environment on the hippocampus and the myelinated fibers in the hippocampus of aged female rats.Methods: Twenty 24-month female SD rats were randomly divided into ten enriched environment (EE) rats and ten standard environment (SE) rats. EE group were reared in enriched environment and SE group were reared in standard environment for 4 months. Then, the spatial learning capacity of EE rats and SE rats was assessed using Morris Water Maze. After the Morris Water Maze was done, 5 rats were randomly chosen from each group. The hippocampus and the myelinated fibers in the hippocampus of EE rats and SE rats were quantitatively investigated with transmission electron microscope and stereological techniques.Results: No significant differences were found in the spatial learning capacity between EE group and SE group. There were no significant differences in the the hippocampal volume, the total length and total volume of the myelinated fibers in the hippocampus between EE rats and SE rats. Conclusiton: Short-term enriched environment has no significant effects on the hippocampus and the myelinated fibers in the hippocampus of 24-month female rats. The present study has established 3-dimensional stereological techniques for quantitatively investigating the myelinated nerve fibers in hippocampus. Meanwhile, the current results provide scientific basis for how to further investigate if enriched environment can delay the age-related changes of hippocampus.PART THREEEFFECTS OF THE ENRICHED ENVIRONMENT ON THE NEURON NUMBER AND SYNAPTOPHYSI-POSITIVE BOUTON NUMBER IN MIDDLE-AGED HIPPOCAMPUSObjective: To investigate the effects of enriched environment on the spatial learning ability of middle-aged rats and old-aged rats, and then for the first time use the new stereological methods to investigate the effects of enriched environment on the age-related changes of the neuron number and the synaptophysin-positive bouton number. Methods: Twenty-four 14 month female rats were randomly divided into enriched environment (EE) group (12) and standard environment (SE) group (12). Rats were housed in enriched environment and standard environment for 4 months. Spatial memory was examined with Morris water maze tasks for five consecutive days. Time latency was recorded. After the behavioral tests, five rats of each group were randomly sampled for stereological study. One of the two hemispheres was sampled randomly, then embedded in paraffin blocks. Serial coronal sections with thickness of 14μm were cut. The sections were uniformly and randomly sampled from the consecutive sections through hippocampus according to the principles of systematic, uniform and random sampling. One series of sections were stained for Nissl substance for the quantification of neuron number, and another series of sections were stained for the quantification of synaptophysin-positive bouton number.Results: Enrichment has a significant effect on spatial memory. There was no significant increase of neurons in the CA1 and dentate gyrus of enriched environment group, but the number of the synaptophysin-positive boutons in CA1, CA1 stratum radiatum, the inner molecular layer and outer molecular layer of dentate gyrus was significantly increased by 78.8%, 90.8%, 50.3%, 106.0% in enriched environment group, respectively, when compared to standard environment group.Conclusion: The spatial memory of middle-aged female rats was significantly improved by the exposure to short-term enriched environment, and the number of synaptophysin-positive boutons in the hippocampus was increased significantly. The changes of the the number of synaptophysin-positive boutons in the hippocampus induced by enriched environment might provide one of the important structural bases for the enriched environment-induced improvement of the spatial learning ability of aged rats.