Abstract
Although the predatory stress experimental protocol is considered more psychological than the restraint protocol, it has rarely been used to study the effect of psychological stress on reproduction. Few studies exist on the direct effect of psychological stress to a female on developmental competence of her oocytes, and the direct effect of predatory maternal stress on oocytes has not been reported. In this study, a predatory stress system was first established for mice with cats as predators. Beginning 24 h after injection of equine chorionic gonadotropin, female mice were subjected to predatory stress for 24 h. Evaluation of mouse responses showed that the predatory stress system that we established increased anxiety-like behaviors and plasma cortisol concentrations significantly and continuously while not affecting food and water intake of the mice. In vitro experiments showed that whereas oocyte maturation and Sr2+ activation or fertilization were unaffected by maternal predatory stress, rate of blastocyst formation and number of cells per blastocyst decreased significantly in stressed mice compared to non-stressed controls. In vivo embryo development indicated that both the number of blastocysts recovered per donor mouse and the average number of young per recipient after embryo transfer of blastocysts with similar cell counts were significantly lower in stressed than in unstressed donor mice. It is concluded that the predatory stress system we established was both effective and durative to induce mouse stress responses. Furthermore, predatory stress applied during the oocyte pre-maturation stage significantly impaired oocyte developmental potential while exerting no measurable impact on nuclear maturation, suggesting that cytoplasmic maturation of mouse oocytes was more vulnerable to maternal stress than nuclear maturation.
Highlights
Studies suggest that psychological stress can exert detrimental effects on reproduction in women
The results indicated that the predatory stress system we established evoked dependable stress responses in mice and that maternal predatory psychological stress significantly diminished oocyte developmental potential
To evaluate the stress response of mice to our predatory stress system, mouse anxiety-like behaviors were examined by elevated plus-maze (EPM) tests
Summary
Studies suggest that psychological stress can exert detrimental effects on reproduction in women. Thin women with a poor psychosocial profiles are at increased risk of giving birth to low birth weight and preterm infants when depressed during pregnancy [1], and psychosocial stress during pregnancy is associated with spontaneous preterm birth and low birth weight even after adjustment for maternal demographic and behavioral characteristics [2]. Psychological stress among women undergoing in vitro fertilization (IVF) or gamete intra-fallopian transfer [3] has often been associated with a decrease in number of oocytes retrieved and fertilized, as well as in pregnancy rate, live birth delivery and birth weight [4]. Mice exposed to 5 h of restraint on days 1–3, 4–6, or 1–6 of pregnancy showed increased proportions of abnormal corpora lutea, decreased serum progesterone concentrations, reduced pregnancy rates and lower litter size [9]. Psychological stress applied to ewes for 1 h on days 2 and 3 after conception affected fetal growth and gestation length [14]
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