Effects Of Acute And Chronic Restraint Stress On The Reproduction Of The Virgin Female Mice And The Behavior Of The Offspring

In recent years, with the development of society, the pace of life accelerating, people are faced more and more pressure(stress), the main psychological stressors include life, career and the family, and has detrimental effects on human health. And women in social life are often several, who is also the role of all in one, ont only work well, but also take care of family, so career women than other groups are more vulnerable than other people to stressors.Women are more susceptible than men to stress-related mental illness and twice as likely to experience depression. While the impact of maternal stress during pregnancy on physiology and behaviour of the offspring has been well documented, up to date very few studies have explored the effect of psychological stress on virgin females, so we conducted a series of experiments to study the effects of psychological stress on the reproduction of the virgin female and the behavior of the offspring. In this study, KunMing mice of 8 weeks old were used , acute(24h) and chronic(8h/d, 60days) restraint stress were used as psychological stress model, to investigate the effects of acute psychological stress on the development of oocytes and chronic psychological stress on the physiological index(body weight and the estrous cycle), the reproduction performance of the virgin female mice (gestation stage, litter size, the offspring bodyweight) and the offspring's behavior(anxiety and the spatial learning memory ability).The results are summarized as follows:1. Intact mice were exposed to restraint for 24 h starting from the onset of proestrus, and the acute restraint stress had no effect on the maturation and activation, but significantly reduceed fertilization and blastocyst development were unaffected by restraint.2. Stimulated mice were exposed to restraint for 24 h starting from 24 h after eCG injection,and the maturation,activation/fertilization were uneffected by acute restratint stress ,but blastocyst development were significantly reduced.3. Unstimulated and stimulated mice were injected with cortisol of different dosages at the onset of proestrus and 24 h after eCG injection, respectively. In both the unstimulated and stimulated mice, while oocyte maturation and fertilization were unaffected, rates for blastocyst formation and cell number per blastocyst decreased significantly when the cortisol dosage increased to 50 mg/kg body weight .4. Oocyte maturation, activation and morula/blastocyst development were unaffected until the cortisol concentration increased to 50μg/ml medium .5. While injection of cortisol (6.78±0.57 and 7.76±0.0 ng/ml) had no effect, restraint decreased the FSH level significantly at late proestrus (4.64±0.19 ng/ml) and estrus (6.19±0.34 ng/ml) in comparison with that of control mice.6. Chronic restraint stress significantly affected body weight gain of virgin female mice, once stress has ended, restrained mice failed to return to the body weight of control animals.7. The number of rats cycling was significantly disrupted in the stressed group compared with controls, but the estrous cycle gradually recovered at the latter stage of the stress, at last 90% of stressed mice recovered the normal cycling.8. Chronic restraint stress had no effect on the duration of the gestational period of virgin mice,but significantly reduced the littter size of the first-born, the litter size of the second-born returned to the control level.9. Chronic restraint stress lowered the birthweight of offspring, but had no effect on the average weight per pup from PN2 to PN28.10. The sex ratio(number of males/total number of young rats per litter) was different between the chronic restraint stressed group and the control, the ratio of stressed offspring varied from 27% to 80%, however the controls only varied from 40% to 70%, and the coefficient variation significantly higher in the stressed group than the control(35.56% vs21%).11. The offspring of maternal stressed mice spent more time in the open arms, and the ratio of open arm entries/ to the total arm entrie significantly increased in the EPM.The locomotor activity (estimated by the total number of entries into the open and the closed arms)and overall activity level(defined by total distance traveled)was not different between the chronic restraint stressed offspring and the controls. 12. Spatial learning was assessed using the Morris water maze for five consecutives days.All groups of animals were able to learn the task through consecutive trials and days of testing. However, the stressed male offspring performanced much better than every other groups in the first two days.13. In our study, chronic restraint stress significantly reduced offspring's anxiety, in order to investigate whether this low anxiety trait can stable inheritated to next generation and the inheritance pattern, we conducted a series of experiment using direct cross and reciprocal cross model.The results suggested that, for the male F2 generation, no matter direct cross or reciprocal cross ,the anxiety behavior consistent with the behavior of the mother's, that is maternally inheritance (cytoplasmic inheritance).But when it referred to female F2 generation, there was some difference between different cross pattern, and not totally consistent with the maternal behavior. The reasons for these differences may be due to the estrous cycle which we hadn't monitor before the EPM experiment.Some research found that Changes in plasma corticosterone are associated with estrous cycle stage in rodents such that peak adrenocorticotrophic hormone (ACTH) and corticosterone levels are highest in the proestrus. In addition, the stress responsiveness of the female HPA varies with the estrous cycle, with increased corticosterone release in response to stress occuring at proestrus.Our above results demonstrated that:1)Acute restraint stress applied to both gonadotropin-stimulated and intact females during oocyte growth and maturation impaired oocyte developmental potential; 2) Injection of cortisol also decreased oocyte developmental potential in both stimulated and intact mice; 3) Cortisol damages the oocyte directly on the ovary, restraint stress impairs oocyte competence by actions on both the hypothalamic-pituitary-gonadal and the hypothalamic-pituitary-adrenal axis. 4)Chronic psychological stress significantly reduced body weight gain and disrupted the estrous cycle of the virgin female mice; 5)Chronic psychological stressed mice need more time to recover their reproduction performance(about 6 weeks from gestation to weaning of the offspring). 6)Chronic psychological stress affected the birth weight and the sex ration of the offspring, but had no effect on the average body weight from PN2 to PN28. 7)Chronic psychological stress significantly reduced the offspring's anxiety behavior, increased their risk-taking behavior. 8)Chronic psychological stress had no effect on the spatial learning and memory in the Morris Water Maze of female offspring, but it significantly increased the performance of male offspring in the first two days. 9)Chronic psychological stress affected the offspring behavior through epigenetic mechanisms, and this low anxiety behavior can inheritated to next generation throuh cytoplasmic inheritance.