Effects Of Enriched Environment On The Myelinated Fibers And Oligodendorcytes In Middle-aged Female Rat Brain

Objective: To investigate the effects of enriched environment on the spatial learning ability of middle-aged female rats and then investigate the effects of short-term enriched environment on the age-related changes of the corpus callosum (CC) and the age-related changes of the myelinated fibers in the corpus callosum by means of unbiased stereologlcal methods.Methods:24 female SD rats (14 months old) were divided randomly into two groups: 12 rats lived in an enriched environment (EE) and 12 control rats were reared in standard environment (SE). The rats were housed for 4 months under either EE or SE. The spatial memory of aged rats was examined with Morris water maze for five consecutive days. The time latency was record. After the behavioral tests, five rats of each group were selected randomly for stereological study. The brains were cut into 1mm-thick serial sections, and the volume of corpus callosum was calculated according to Cavalieri's principle. Four brain slices were sampled according to systematic random sampling fashions. Four tissue blocks were sampled randomly from the sampled brain slices and embedded for electronic microscopy following isector process. From each section, four visional fields were photographed randomly at a magnification of 6 000×. The total volume of myelinated nerve fibers and the total volume of myelin sheath, the total myelinated fiber length and mean diameter of the myelinated fibers in the corpus callosum were quantitatively investigated using stereological methods.Results: Compared with SE group, the time latency of hidden-platform test was shortened significantly in EE group (p = 0.001). There was no significant difference of mean myelinated fiber diameter between EE group and SE group (p = 0.069). When compared to SE rats, the total volume of corpus callosum was significantly increased by 34.5% (p = 0.017). Compared to SE rats, the total volumes of the myelinated nerve fibers and the total volume of the myelin sheaths in the corpus callosum were significantly increased by 60.8% (p = 0.007) and 57.7% (p = 0.008), respectively. Compared to SE rats, the total myelinated fiber length in CC of EE rats was significantly increased by 82.5% (p = 0.016). In contrast, the mean diameter of the myelinated fibers in the CC of EE rats was significantly decreased by 9.3% (p = 0.045) when compared to that of SE rats. The the enrichment-induced changes of the myelinated nerve fibers in the CC of EE rats were mainly due to the marked increases of the myelinated nerve fibers with diameter less than 1μm, especially the fibers with diameter of 0.4 0.6μmConclusion: The increase of the myelinated fibers in enriched rat corpus callosum might provide one of the structural bases for the enrichment-induced improvement of the spatial memory. The present study provided, to the best of our knowledge, the first evidence of environmental enrichment-induced increases of the corpus callosum volume and the myelinated fibers in the corpus callosum of aged rats. Objective: To investigate the effects of enriched environment on the spatial learning ability of middle-aged female rats and then investigate the effects of short-term enriched environment on the age-related changes of mature oligodendrocytes in the corpus callosum by means of unbiased stereological methods.Methods: The enriched environment protocol and behavioral tests were the same as in part one. After the behavioral tests, five rats of each group were selected randomly for stereological study. The brains were cut into 2 mm-thick serial slabs. The slabs of the randomly selected hemisphere were embedded in paraffin. Serial coronal sections with thickness of 14μm were cut with a sliding microtome. One section was systematically sampled every 30th section. On average, 13 15 sections were sampling per rat. CNPase was used to mark the mature oligodendrocytes. The nuclei were satined by haematoxylin. The optical disector was used to count the number of positive cells in the corpus callosum of each section. Then, the total number of CNPase positive cells in each rat corpus callosum was calculated. Results: For hidden-platform test, the mean latency of EE group from day 1 to 4 was significantly shortened when compared to SE group (p = 0.002), and there was no significant change for visible-platform test between them ( p = 0.371). When compared to SE group, the total number of CNPase⁺ cells was significantly increased by 343.6% (p < 0.001).Conclusion: The increase of the CNPase⁺ cells in enriched rat corpus callosum might provide one of the structural bases for the enrichment-related improvement of the myelinated nerve fibers. Objective: To investigate the effects of enriched environment on the spatial learning ability of middle-aged female rats and then investigate the effects of short-term enriched environment on the age-related changes of mature oligodendrocytes in the hippocampus by means of unbiased stereological methods.Methods: The enriched environment protocol, material and behavioral tests were the same as in part one. One section was systematically sampled every 10th section. On average, 15 20 sections were sampling per rat. The number of positive cells in the whole hippocampus, hippocampal CA₁ and DG of each section was counted. Then, the total number of CNPase positive cells in each rat hippocampus was calculated.Results: The results of Morris water maze tests were the same as in part two. When compared to SE group, the total number of CNPase⁺ cells was significantly increased by 113% (p = 0.008), 127% (p = 0.005) and 127% (p = 0.006) in the whole hippocampus, CA₁ and DG, respectively.Conclusion: The increase of the CNPase⁺ cells in enriched rat whole hippocampus and subdivisions in hippocampus might provide one of the structural bases for the enrichment-induced improvement of the myelinated nerve fibers in hippocampus.