In a water maze task, the goal latency and distance of swimming onto the platform of aged rats (24 months old) were slowly shortened by repeated trainings compared with those of young rats (8 weeks old). A significant decrease in choline acetyltransf erase activity in the frontal cortex, parietal cortex and striatum was observed in aged rats. Moreover, the number of neuronal cells in the hippocampal CA1 subfield and dentate gyrus of aged rats was smaller than that of young rats. The atrophy of striatal cells was observed. These results suggest that age-related delay of acquisition is due to the above-mentioned biochemical and histological changes, and that rates of aging in biochemical and morphological parameters are different in the discrete brain areas.
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