The selective effects of different period swimming stresses on the hippocampus-dependent spatial learning and memory and the damage of hippocampal neurons of rats

ObjectiveTo explore the different effects of different period-stresses on the hippocampus-dependent spatial learning and memory, and on the hippocampal neurons of rats. MethodsAdult male Sprague Dawley (SD) rats were used as experimental subjects. They were divided into five groups: control group(A), group of stress once(B), group of stress for one week(C), group of stress for two weeks(D)and group of stress for four weeks(E), twelve rats in each group. Forced-swimming was used as stress model. Morris water maze (MWM) was applied to measure the spatial learning and memory of rats. Improved Nissl stain was used to observe the survival of the pyramidal neurons in hippocampal CA1 and CA3 fields. ResultsIn the hiding platform test of MWM, there were no significant differences of the escape latency(EL)of former six and later four trials in all groups(P0.05).The EL of the seventh and eighth trials in group C(9.80±2.84 and 9.78±4.64 respectively) were significantly lower than that in other four groups(48.08±16.95 and 42.65±19.22,40.54±14.23 and 29.44±14.36,45.64±17.61 and 45.28±15.07,41.59±16.07 and 37.77±13.14 respectively)(P0.05).In the retention test, there were no significant difference of EL between group B(37.86±24.82,20.22±13.83,18.95±14.77 respectively )and group A(34.61±10.97,18.46±6.12,17.54±6.20 respectively), group C(19.26±15.74,13.51±6.15,11.16±6.70 respectively )and group A, group D and group A respectively (P0.05);while the EL in group E was significantly longer than that in group A(P0.05). In the probe test, the times through the position of the hiding platform within 60s in group C was significantly more than that in group A(P0.05),there were no significant differences between other stressed groups and control group(P0.05). There were no significant differences of the amount of neurons in all groups(P0.05). The amount of neurons in CA3 region of group E was significantly less than that of other groups(P0.01). ConclusionsDifferent period-stresses could selectively affect the hippocampus-dependent spatial learning and memory of rats, and chronic stress could damage the survival of the pyramidal neurons in hippocampal CA3 region selectively.