| Introduction and Objective: With the change of medicine mode from simple biomedicine mode to bio-psycho-societal mode, it is important to study the relationship between the stress and health. Stress may cause a series of neuroendocrinal and behavioral changes, including high glucocorticoids (GCs) level and anxiety-like behaviors. The damage of hippocampus was related with lasting high GCs level. The degree of hippocampal damage varied from reversible atrophy of dendrites and neurons to apoptosis or permanent cell loss with the stress intensity and durations. N-acetylaspartate (NAA) is the most abundant acetylated amino acid in brain. Recently, NAA has gained a great interest in the clinical community and is a promising indicator for assessing the neuronal viability. On the base of conflicted animal model, NAA in hippocampus, frontal and hypothalamus, is detected by the HPLC.This study is to explore the relationship between the degrees of stress and behavioral and endorcrinal changes, the weight of different brain regions and the concentration of NAA and hope to search the objective evidences of judgment of psychological stress.Materials and Methods: 63 adult male Sprague-Dawley rats of which the body weight ranged from 180g to 250g were randomly divided into nine groups (n=7 each group): (1) single stress rats (Acute stress group); (2) rats stressed daily for 7 consecutive days (1-week stress group); (3) rats stressed daily for 14 consecutive days (2-week stress group); and (4) rats stressed daily for 28 consecutive days (4-week stress group). And there were four un-stressed control group corresponding to every stress group (Control) and a drug group that was treated with paroxetine (o.p.10mg/kg*d) during the period of stress. The stressed rats were exposed to Vogel conflict test. Behaviors were respectively measured at the beginning and end of conflict stress with the open-field test. Corticosterone was measured by immunoassay using competing with a fixed amount of alkaline phosphatase-labeled corticosterone for sites on a sheep polyclonal antibody. Concentrations of NAA and creatine (Cr) in hippocampus, frontal cortex, and hypothalamus were measured by high performance liquid chromatography coupled with ultraviolet detection. The data were analyzed by one-way analysis of variance (ANOVA), T test with SPSS 11.0 for Windows and Excel 2000. All the value in text and figure was expressed as Mean ±Standard Error ( x±SE). Pearson relation analyzed the relationship of stress intensity andthe behavior, weight, corticosterone and NAA.Results: (1) Behavioral changes. There were no statistic differences in the locomotion between the single stress rats and its control (/=0.599,/t=0.599). There was increased tendency of locomotion in 1-week stress group, as compared to its control (t=\ .233, p=0.249). However, the locomotion of 2-week stress group was significantly larger than its control group ({=2.600, p=0.032). After four weeks stress, interestingly, the rats get more and more active than its control. The difference of locomotion between 4-week stress group and its control become more significant (p=0,0\0). There were no difference between drug group and its control. And changes in the behavior of the rats was positively related with the intensity of stressors (r= 0.768, /K0.01) .(2) Changes in the weight. The body weight of single stress rats had reduced tendency (/=2.305, p=0.06\) as compared to its control. There are significant differences in body weight of the rats between the control and 1-week stress group (/=4.935, p=0.0\). After 2-week stress, the weight of the rats of the control group was much larger than the stress group (r=6.098, p=0.000). The stressed animals weighed less than its control at the end of the 4-week experiment (p=0.000). The weight of drug group decreased (p=0.019) compared with its control but increased by 7.7 %(p=0A24) compared with the simple stress group. And changes in the weight of the rats was negatively related with the intensity of stressors (r=-0.636^7<0.01) .(3) Changes in serum corticosterone level. The level of corticosterone was same to the control (/?=0.884) . The hormone levels of all the stressed rats, including single, 1-week, 2-week, and 4-week stress group, were significantly higher than the control (respectively =0.000, 0.000, 0.000, 0.044). Though corticosterone level for the 4-week stress rats was slightly reduced, it was significantly higher than its control (p=0.002). And the corticosterone level of the 4-week stress rats was lower than single stress rats and the 2-week stress rats (respectively, /?=0.011, p=0.030). There was a negative relationship between the stress intensity and corticosterone level (r= —0.522, p<0.01).(4) The hippocampal weight of 2-week and 4-week stress group was less than the control groups (p<0.01 respectively). And the hippocampal weight of the 4-week stress rats also less than the 4-week control and the drug control (p<0.05, respectively). And the weight of hippocampus was negatively related with the intensity of stressors (r=— 0.393, /K0.01) .(5) The concentration of NAA in hippocampus was less and less with the increasing intensity of stress, and reached to the lowest for two weeks stress. The concentration of NAA in hippocampus of 4-week stress rats had a lifting tendency, but didn't reach to the level of the control. There was no significant difference in hippocampal NAA concentration between the drug group and the control. There was a significant relationship between the concentration of NAA in hippocampus and the stress intensity (r=— 0.398, /KO.Ol) .(6) There was no significant difference in the concentration of NAA in hypothalamus of all groups. The concentration of NAA in the hypothalamus didn't exist significant relationship with the stressful intensity (r=— 0.220, p>0.05) .(7) Compared with the control, the concentration of NAA in the frontal cortex of 2-week and 4-week stress group was reduced (p<0.0l and/?<0.05). The concentration of NAA in the frontal cortex of the drug group was higher than the concentration of 4-week stress group (p <0.01) . The concentration of NAA in the frontal cortex didn't exist significant relationship with the stressful intensity (r= -0.287, /?>0.05) .(8) There were no statistic differences in the concentration of Cr in all the groups.Conclusions: (1) The phenomena of conflict stressed animal, such as increasing anxiety-likely behavior, high corticosterone level and decreasing weight, resembled certain characters of the anxiety. These phenomena would be prevented by the treatment of paroxetine.(2) There were relationship between the behavior, body weight, and corticosterone level and stress intensity. This indicated that the stress response could be described and evaluated by the behavior, body weight, and endorcrine.(3) The conflict model consisted with the symptoms of many anxiety disorders, is predictable in pharmacodynamics, and is on the basis of reasonable theory. And the changes in behavior and endocrine might maintain long time. So the way of conflict stress may be made establishing the psychological stress model and study human stress related disorders.(4) The weight of hippocampus and the concentration of NAA in hippocampus decreased under the conflict stress. All these changes could be prevented by the paroxetine.(5) The intensity of stress had negative relationship with weight and NAA level of hippocampus. These results suggested that stressful responses and brain damage could be evaluated by hippocampal volume and NAA level.
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