Spatial Learning Paradigm Can Increase Post-Stress Total Time of REM Sleep in Immobilized Rats

Stress contributes to sleep-wake behavior in all animals. It seems that factors such as learning and memory processes can improve sleep disorders. Therefore, the present study was conducted to determine the effects of stress and learning (spatial memory) on total post-stress rapid-eye-movement (REM), non-rapid-eye-movement (NREM) and waking time in rats.

Adult rats (n=21) were divided into 3 groups; group 1 received only immobilization stress; group 2 was subjected only to the learning process (Barnes maze); and group 3 underwent both the stress and learning conditions. For each rat, sleep signals were recorded for 2 hours for 3 consecutive days. After recording of sleep or awakening signals, animal subjected to immobilization stress for 2 hours in each day. Then, post-stress and post-learning signals were recorded for another 2 hours.

Immobilization stress resulted in significant decrease in total REM sleep time. However, total time of NREM increased following stress. Performing the learning task resulted in a significant increase in post-learning REM time (P<0.05). Moreover, total NREM time did not change markedly following the learning process. Interestingly, the learning process significantly (P<0.05) decreased total time of awakening when compared with pre-learning condition. However, learning process could increase REM sleep significantly (P<0.05) after the stress condition has been administered. 

Our data suggested that immobilization stress could not prevent REM sleep after a learning process has been administered. However, the completion of a learning process increased post-stress REM time. It seems that learning helps to prevent the inhibitory effects of stress on REM sleep.