[Experiment-time affects the cognitive behavior in aged Sprague-Dawley rats].

In order to investigate if the experiment-time affects cognitive performance in aged rats in different learning and memory behavioral tests, the aged Sprague-Dawley (SD) rats were divided into two groups randomly and subjected to open field test, Morris water maze test and social discrimination test. The experiment of one group was conducted in 8:00 - 11:00 AM (AM group), and the other group in 15:00 - 18:00 PM (PM group). PM group exhibited higher locomotor activity than AM group in the open field test. Compared with AM group rats, PM group rats had significantly shorter swimming distance and escape latency to find the platform in Morris water maze training session, but no significant difference in the swimming velocity was observed between the two groups. And in probe-test, PM group spent more time in target quadrant than AM group. These results revealed that PM group showed better spatial learning and memory abilities than AM group. However, there was no significant difference between the two groups in social investigation index in social discrimination test. These results show that experiment-time may affect cognitive performance in Morris water maze but not in social discrimination task in aged rats. And the results indicate that experiment-time affects cognitive performance of aged rats selectively in different learning and memory behavioral tasks.