Impairment of learning and memory and the accessory symptom in aged rats as senile dementia model (2)--Learning and memory]

We attempted to investigate the ability of learning and memory of aged rats. Swimming speed of aged rats in Morris's water maze was slower compared with that of young rats. Therefore, we used goal distance to indicate ability of learning and memory. In training session, distance for both groups decreased with training, but in aged rats it was significantly longer than that in young rats. In retention test 24 d after the training, distance in aged rats was longer than that in young rats, although there was no difference in distance for both groups between acquisition and retention tests. The distance in the working memory tended to increase with aging. There was no difference in time spent within platform phase in probe trial, in percent movement of first trial in habituation test, and in step-through latency in passive avoidance, between young and aged rats. Drinking latency for aged rats in water finding task was significantly longer compared with that in young rats. These findings suggest that learning and memory were impaired by aging in spatial and latent learning tasks. Aged rats could acquire and maintain memory of simple tasks, but in spatial tasks they tended to show decreased ability of retention and working memory.