Different effects of chronic forced swim and restraint stress upon the rat spatial learning and memory

Objective To observe the effect of chronic forced swim or restraint stress on the rat's spatial learning and memory performance.Methods Twenty-four adult male Sprague-Dawley rats were randomly divided into three groups:control group(rats receiving neither stress);chronic forced swim stress (FST) group(rats were forced to swim daily for 20 minutes during 14 days);and chronic restraint stress (CRS) group(rats were loosely restrained daily in a transparent plastic cylinder which made the rats could not move freely for 6 hours during 14 days).1,2 or 3 weeks after the final secession of either stress,the navigation test and probe test of Morris water maze were employed to evaluate the rat's spatial learning and memory ability,respectively.Results (1) 1 and 2 weeks after the final stress secession,the averaged escape latency of FST group in the navigation test was significantly shortened [1week:FST (14.56±2.17)s,(17.93±2.08)s,CONTROL(26.12±5.04)s,(25.22±2.80)s,t=11.21 and 7.25,P＜0.05];meanwhile,the averaged ratio of time spent in the target quadrant for the FST group in the probe test was significantly higher than that of the control group(P＜0.05).3 weeks after the final stress secession,there was no significant difference in the escape latencies and the ratio of time spent in the target quadrant between control and FST group.(2) 1 week after the final stress secession,both the averaged escape latency in the navigation test and the averaged ratio of time spent in the target quadrant for the probe test of CRS group were significantly changed when compared with that of the control group (P＜0.05).While 2 or 3 weeks after the final stress secession,these differences disappeared.Conclusion Chronic forced swim enhanced while the chronic low intensity restrain impaired rat's spatial learning and memory.These effects could not last long since the difference disappeared as the rats withdrew from the stress for a relatively long period.Different patterns of chronic stress gave rise to different reversible influences upon the rat's spatial learning and memory. Key words: Stress ;  Forced swim ;  Chronic restraint ;  Navigation test ;  Probe test ;