Effects Of Antidepressant Paroxetine On The Changes Of Histology And Behavior In Rats Hippocampus Induced By Stress And Their Relationships With CREB-related Signal Cascades

Background and Objective: Stress is the complex response of organism to stimuli from inside and outside environment.It produces positive and negative effects on the individuals and severe or prolonged stress is the precipitative cause of many mental and physical disorders such as recurrent depression, posttraumatic stress disorder (PTSD) and Alzheimer's disease. Hippocampus is the target of stressful hormone and mediates stress response. Studies have indicated that the atrophy and loss of hippocampal CA3 pyramidal neurons induced by stress underlie the pa.thophysiology of mood disorders and associated with the cognitive deficits of many stress-related disorders. Thus, we presume that the impairment of hippocampus play a key role in the pathogenesis of stress-related disorders. cAMP-response-element-binding-protein(CREB ) participates in the modulation of hippocampal neurons survival and long-term memory(LTM), and is regulated by multiple protein kinases of signal pathways. Whether the damages of hippocampal neurons and fimctions induced by stress are involved in CREB-related signal pathways?Whether other brain regions participate in stressful response? Which signal pathways are involved in the modulation of stressful response in different brain field? It is significant to resolve these issues for clarifying the mechanism of stress and the pathogenesis of stress-related disorders. While there are no correlated reports at present Therefore, the present studies investigate the changes of CREB and its related signal cascades cAIvlP ,Ca2+ and Erk/MAPK (extracellular signal-regulated kinase/initcgen-activated protein kinases) of hippocampus and prefrontal cortex in different time course stress which the rats are forced swimming, and explore the effects of these signal systems on the stress-induced impairments of hippocampal histology and learning and memory functions, and on other physical stress response. Our studies provided the first evidence of the association of various signal systems with stress for further elucidate the cellular and molecular mechanism of stress.Materials and Methods: Adult 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), fourteen rats in each group. Except controll group, others were subjected to forced-swimming for one day, one week, two weeks and four weeks respectively, 15 minute per day. The food, water taken by rats and their body weight were measured everyday. Morris water maze (MWM) was applied to measure the spatial learning and memory of rats. Improved Nis;sl stain was used to observe the survival of the pyramidal neurons in hippocampal CA1 and CA3 fields. Western blot was used to quantificationally determine the levels of phosphorylated and total CREB(p-CREB and t-CREB), and phosphorylated and total ERK/MAPK (n- RRK /MAPK and ERK/ MAPK) in hippocampus and prefrontalcortex. The radioactivity of PKA, PKC and CaMKII in hippocampus and prefrontal cortex was quantitated using a liquid scintillation counter.Results :From two weeks following the stress, the food and water taken by rats were significantly lower than that in control group(P<0.05 ) ,and with the prolong of stress, the amount of food and water taken by rats presented less and less. There was no significant difference of body weight gain in group of stress once and control group(i^O.05) .The body weight gains in other stressed groups were all significantly lower than that in control group (P<0.0l) .In 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 (P>0.05 ); The EL of the seventh and eighth trials in group C were significantly lower than that in other four groups (P<0.05) ,there were no significant differences among the other four groups (P>0.05 ) . In the retention test, there were no significant difference of EL between group B and group A, group C and group A, group D and group A respectively (P>0.05 ); while the EL in group E was significantly longer than that in group A (P<0.05) . 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 (PO.05), there were no significant differences between other stressed groups and control group (P>0.05 ) .There were no significant differences of EL in the visible platform test in all groupsThe pyramidal neurons in hippocampal CA1 region in all groups were arranged orderly and densely, the Nissl matters in cytoplasm were visible charly. There were no significant differences of the amount of neurons in all groups CP>0.05) . The pyramidal neurons in hippocampal CA3 region in group A, group B, group C and group D were arranged orderly and theNissl matters in cytoplasm were visible clearly; The pyramidal neurons in hippocampal CA3 region in group E were arranged sparsely and cellular clearance were augmented, the Nissl matters in many cells were lessened or lost, the amount of neurons in CA3 region of this group was significantly less than that of other groups (PO.01) ,there were no significant differences in other four groups (P>0.05 ) .In hippocampus, there were no significant differences of the levels of pCREB and tCREB between group B and group A, and between group C and group A (P>0.05 ); The level of pCREB in group D or group E was significantly lower than that in group A respectively (P<0.05 ) ,while there were no significant differences of the level of tCREB between group D and group A, and between group E and group A (P>0.05 ) . In prefrontal cortex, the level of pCREB in group E was significantly lower than that in group A (P<0.05 ) , there was no significant difference of pCREB between any other stressed group and control group (P>0.05) .There was no significant difference of the level of tCREB between every stressed group and control group respectively (P>0.05) .In hippocampus, the levels of pERK44 and pERK42 in group C, orgroup D ,or group E were significantly lower than that in group Arespectively (P<0.05 or P<0.01) ; there were no significant differences ofthe levels of pERK44 and pERK42 between group B and group A(P>0.05) .There were no significant differences of the levels of ERK44and ERK42 between each stressed group and control group respectively(P>0.05 ) . In prefrontal cortex, the levels of pERK44 and pERK42 andthe levels of ERK44 and ERK42 in each stressed group were allsignificantly lower than that in control group (PO.01) , and the longer thestress lasted, the lower the levels of these four proteins were presented.In hippocampus, there were no significant differences of the activity ofPKA and PKC between group B and group A (P>0.05 ) ; the activity of PKA and PKC in group C were significantly higher than that in group A(PO.01); the activity of PKA and PKC in group D or group E were significantly lower than that in group A respectively (P<0.01) .The activity of CaMKII in each stressed group was significantly lower than that in group A (PO.01) . In prefrontal cortex, the activity of PKA in group C was significantly higher than that in group A (P<0.0\); there was no significant differences of the activity of PKA between every other stressed group and control group respectively (P>0.05) . The activity of PKC in each stressed group was significantly higher than that in control group (PO.01). The activity of CaMKII in group B, group D or group E was significantly lower than that in group A respectively (P<0.01) ; there was no significant differences of the activity of CaMKII between group C and group A (/>>0.05) . Conclusions:1. It was showed that chronic stress could decrease the food and water taken by rats and suppress the body weight gain; acute stress could not affect the body weight gain of rats; acute and short-time repeated stress could not affect the food and water taken by rats.2. Chronic stress could impair the hippocampus-dependent long-term spatial memory of rats; short-time repeated stress could improve hippocampus-dependent shotr-term spatial memory selectively and the ability of spatial exploration of rats.3. Chronic stress could inhibit the survival ability of the pyramidal neurons in hippocampal CA3 region of rats.4. Chronic stress could inhibit CREB phosphorylation in hippocampus and prefrontal cortex of rats, which may be involved in the mechanisms of the impairments of hippocampus-dependent spatial memory and the lossof the pyramidal neurons in hippocampal CA3 region of rats induced by chronic stress.5. Short-time repeated and chronic stress could inhibit the phosphorylation of ERK44 and ERK42 in hippocampus, and suppress the phosphorylation and protein expression of ERK44 and ERK42 in prefrontal cortex of rats, which may be participated in the regulation of the inhibition of CREB phosphorylation in hippocampus and prefrontal cortex of rats ,and may be one of the mechanisms of the impairment of long-term memory induced by chronic stress.6. In hippocampus, short-time repeated stress could increase the activity of PKA and PKC, while chronic stress decrease the activity of them; acute and chronic stress could depress the activity of CaMKII. Chronic stress could inhibit the activity of PKA, PKC and CaMKII in rats' hippocampus, which may be one of the reasons that the level of pCREB was inhibited. The increase of the activity of PKA and PKC caused by short-time repeated stress might be associated with the modulation of the improvement of hippocampus-dependent short-term memory.7. In prefrontal cortex, short-time repeated stress could increase the activity of PKA; acute and chronic stress could improve the activity of PKC while inhibit the activity of CaMKII. It might be the CaMKII which mainly involved in the regulation of the suppression of CREB phosphorylation in prefrontal cortex caused by chronic stress.