Assessment of retention and attenuation of motor-learning memory by repeated rotor-rod analyses.

Retention of acquired learning memory is essential for reasonable behavior and crisis avoidance of individuals. Therefore, establishment of a system suitable for analysis of the retention/attenuation of acquired memory is desired. In the present study, mice were conducted on the repeated rotor-rod test, consisting of two series of experiments (Series 1 and 2) of 10 trials each. When rotating speed was 9 rpm, retention time on the rod was gradually increased and reached the maximum value within 10 trials in Series 1. When Series 2 was performed 1 or 3 days after Series 1, retention time of trials 1-3 in Series 2 was not significantly different from that of trials 8-10 in Series 1. On the other hand, retention time of trials 1-3 in Series 2 was significantly declined from that of trials 8-10 in Series 1 when Series 2 was conducted day 7, and returned to the initial level, the same level with trials 1-3 in Series 1, when Series 2 was conducted on days 14 or 30. These results indicate that acquired motor-learning memory is retained for 3 days at least, began to decline by day 7 and returned to the initial level by day 14. In older mice of 10-11 months old, there was a delay in the acquisition of motor learning in Day 0, whereas the retention was not impaired in Day 7. The repeated rotor-rod analyses may useful for research on factors affecting retention/attenuation and acquisition of motor-learning memory and proceed our understanding of motor-learning memory.