Polycystic ovary syndrome: brain-derived neurotrophic factor (BDNF) plasma and follicular fluid levels

Follicular fluid exosomes inhibit BDNF expression and promote the secretion of chemokines in granulosa cells by delivering miR-10b-5p

Ovulation is an inflammatory response. Before ovulation, follicle cells release chemokines to recruit immune cells and promote ovulation. The objective of this study was to investigate whether follicular fluid exosomes promote chemokine secretion by granulosa cells (GCs). Porcine follicular fluid exosomes and follicular GCs were isolated in vitro. GCs were treated with follicular fluid exosomes in vitro and the differential gene expression profiles of the exosome-treated and control groups were obtained by transcriptome sequencing. The results showed that, when compared to the controls, the expression of the chemokines CCL2 and CXCL8 was significantly increased, whereas the expression of brain-derived neurotrophic factor (BDNF) was significantly decreased. The miRNA expression profiles in follicular fluid exosomes were obtained by microRNA sequencing. The results showed that exosomes carried many microRNAs, and that miR-10b-5p carried by exosomes could promote the secretion of CCL2 and CXCL8 by targeting BDNF. In conclusion, the present study demonstrates that exosomes promote the secretion of CCL2 and CXCL8 by granulosa cells through the miR-10b-5p/BDNF axis to promote ovulation.

Updates in diagnosing polycystic ovary syndrome-related infertility

INTRODUCTION

Polycystic ovary syndrome (PCOS) is a condition that affects approximately 13% of reproductive age women and is characterized by androgen excess, menstrual irregularity and altered ovarian morphology. PCOS presents a complex etiology and pathophysiology, which still requires a detailed investigation of biochemical signatures to identify the molecules and mechanisms that govern it.

AREAS COVERED

This narrative review summarizes the main molecular alterations found in the ovarian follicular fluid, endometrium and placenta of women with PCOS, and the genotypes potentially associated with the outcome of infertility treatments in PCOS.

EXPERT OPINION

PCOS is associated with multiple alterations in growth factors, sex steroid hormones, reactive oxygen species, proinflammatory cytokines and adipokines, which contribute to follicle arrest/ anovulation or suboptimal corpus luteum function, and ultimately to menstrual irregularity and hyperandrogenic symptoms. A panel of PCOS biomarkers should include, besides ovarian products, markers of adipose tissue function, insulin resistance, vascular health, and low-grade chronic inflammation. The effects of ovarian stimulation drugs on infertile women with PCOS are likely to be modified by genetic factors, but the available evidence is heterogeneous; therefore, future studies should evaluate standard treatments and pre-specified outcomes of interest to provide more conclusive answers.

Moderate Aerobic Exercise Regulates Follicular Dysfunction by Initiating Brain-Derived Neurotrophic Factor (BDNF)-Mediated Anti-Apoptotic Signaling Pathways in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a common endocrine disorder among women. Moderate aerobic exercise intervention is considered an initial treatment strategy for managing PCOS. Brain-derived neurotrophic factor (BDNF) is an important molecular mediator and a beneficial response to exercise. We aimed to investigate the expression pattern and underlying molecular mechanisms of this neurotrophic factor during follicle development in ovarian tissues. The PCOS model was established by subcutaneous injection of 60 mg/kg dehydroepiandrosterone (DHEA) into the neck of Sprague Dawley rats for 35 consecutive days. PCOS rats then received aerobic exercise for 8 weeks. Body/ovarian weight and peripheral serum hormone levels were observed. Immunohistochemistry combined with Western blot analysis and fluorescence quantitative polymerase chain reaction were used to detect the changes in BDNF-TrkB/p75NTR pathway, apoptosis, and inflammatory factors. We show that moderate aerobic exercise not only reverses the PCOS phenotype but also activates the BDNF-TrkB pathway and initiates downstream targets. p-TrkB upregulates and phosphorylates phosphatidylinositol 3-kinase (PI3K) and protein kinase B (Akt) to inhibit apoptosis. In addition, aerobic exercise therapy reduces the high expression of p75NTR in the ovarian tissue of PCOS rats and initiates the anti-apoptotic effect from the downstream pathway of NF-κB/JNK. Our in vitro results state that treatment with BDNF ameliorated dihydrotestosterone (DHT)-induced granulosa cells (GCs) apoptosis by provoking p-TrkB activation and upregulating the PI3K/AKT pathway. The present study suggests that moderate aerobic exercise regulates follicular dysfunction in PCOS-like rats. One possible mechanism is to initiate the BDNF-mediated anti-apoptotic signaling pathway.

Intrinsic innervation of the ovary and its variations in the rat senescence process

Ovarian functions decrease with perimenopause. The ovary has extrinsic innervation, but the neural influence on ovarian functions and dysfunction is not well-studied. The present study aimed to biochemically and morphometrically characterize the intrinsic neurons in ovaries from young adult, middle-aged, and senescent Long Evans CII-ZV rats (3, 12, and 15 months old, respectively). Ovaries were extracted from four rats of each age group (n = 12 total), cryopreserved, and processed for immunofluorescence studies with the primary NeuN/β-tubulin and NeuN/tyrosine hydroxylase (TH) antibodies. The soma area and number of intrinsic neurons in the ovarian stroma, surrounding follicles, corpus luteum, or cyst were evaluated. The intrinsic neurons were grouped in cluster-like shapes in ovarian structures. In senescent rats, the intrinsic neurons were mainly localized in the ovarian stroma and around the cysts. The number of neurons was lower in senescent rats than in young adult rats (p < 0.05), but the soma size was larger than in young adult rats. Immunoreactivity to TH indicated the presence of noradrenergic neurons in the ovary with the same characteristics as NeuN/β-tubulin, which indicates that they are part of the same neuronal group. Taken together, the findings indicate that the intrinsic neurons may be related to the loss of ovarian functions associated with aging.

Current Treatments and New Possible Complementary Therapies for Epithelial Ovarian Cancer

Epithelial ovarian cancer (EOC) is one of the deadliest gynaecological malignancies. The late diagnosis is frequent due to the absence of specific symptomatology and the molecular complexity of the disease, which includes a high angiogenesis potential. The first-line treatment is based on optimal debulking surgery following chemotherapy with platinum/gemcitabine and taxane compounds. During the last years, anti-angiogenic therapy and poly adenosine diphosphate-ribose polymerases (PARP)-inhibitors were introduced in therapeutic schemes. Several studies have shown that these drugs increase the progression-free survival and overall survival of patients with ovarian cancer, but the identification of patients who have the greatest benefits is still under investigation. In the present review, we discuss about the molecular characteristics of the disease, the recent evidence of approved treatments and the new possible complementary approaches, focusing on drug repurposing, non-coding RNAs, and nanomedicine as a new method for drug delivery.

Brain-derived neurotrophic factor (BDNF) expression and function in the mammalian reproductive Tract

BACKGROUND

Neurotrophins of the nerve growth factor family are soluble polypeptides that are best known for their role in nerve growth, survival and differentiation in the central nervous system. A growing body of literature shows that neurotrophins and their receptors are also expressed throughout the reproductive tract.

OBJECTIVE AND RATIONALE

Neurotrophins are key regulatory proteins in reproductive physiology during development and throughout adult life. Of the neurotrophins, the literature describing the expression and function of brain-derived neurotrophic factor (BDNF) and its high-affinity receptor, neurotrophin receptor kinase-2 (NTRK2), has been expanding rapidly. We therefore conducted a systematic inductive qualitative review of the literature to better define the role of the BDNF in the reproductive tract. We postulate that BDNF and NTRK2 are central regulatory proteins throughout the reproductive system.

SEARCH METHODS

An electronic search of Medline (PubMed) and Web of Science for articles relating to BDNF and the reproductive system was carried out between January 2018 and February 2019.

OUTCOMES

In the ovary, BDNF expression and levels have been linked with follicle organisation during ovarian development, follicle recruitment and growth and oocyte maturation. In the endometrium, BDNF is involved in cell proliferation and neurogenesis. In contrast, literature describing the role of BDNF in other reproductive tissues is sparse and BDNF-NTRK2 signalling in the male reproductive tract has been largely overlooked. Whilst estradiol appears to be the primary regulator of BDNF expression, we also identified reports describing binding sites for glucocorticoid and myocyte enhancer factor-2, a calcium-response element through activation of an N-methyl-D-aspartate (NMDA) receptor, and aryl hydrocarbon receptor nuclear transporter protein-4 (ARNT) response elements in promoter regions of the BDNF gene. Expression is also regulated by multiple microRNAs and post-translational processing of precursor proteins and intracellular shuttling. BDNF-NTRK2 signalling is modulated through tissue specific receptor expression of either the full-length or truncated NTRK2 receptor; however, the functional importance remains to be elucidated. Dysregulation of BDNF expression and circulating concentrations have been implicated in several reproductive disorders including premature ovarian failure, endometriosis, pre-eclampsia, intra-uterine growth restriction (IUGR) and several reproductive cancers.

WIDER IMPLICATIONS

We conclude that BDNF and its receptors are key regulatory proteins central to gonadal development, ovarian regulation and uterine physiology, as well as embryo and placenta development. Furthermore, dysregulation of BDNF-NTRK2 in reproductive diseases suggests their potential role as candidate clinical markers of disease and potential therapeutic targets.

Factors affecting stability of plasma brain-derived neurotrophic factor

Circulating concentrations of brain-derived neurotrophic factor (BDNF) have been linked to cancer, neuropsychiatric, diabetes, and gynecological disorders. However, factors influencing plasma storage and subsequent BDNF quantification are incompletely understood. Therefore, the anticoagulant used in plasma separator tubes, storage-time, storage-temperature, and repeated freeze–thaw cycles on circulating BDNF concentrations was evaluated. Peripheral blood samples were collected from healthy women (n = 14) and men (n = 10) recruited prospectively from McMaster University (August 2014). Blood was collected from the cubital vein into plasma separator tubes containing five different anticoagulant systems [K2EDTA, Li-Hep, Li-Hep (gel), Na-Hep, Na-Hep (glass)], and placed on ice for transport to the lab for centrifugation. Plasma samples (n = 16) collected in K2EDTA tubes from women recruited to a previous study (April 2011 to December 2012) were used to determine the effect of multiple freeze–thaw cycles. Plasma BDNF was quantified using a commercially available ELISA kit. Plasma concentrations of BDNF were significantly affected by the type of plasma separator tube, storage-time, and number of freeze–thaw cycles. Storage temperature (− 20 vs. − 80 °C) did not significantly affect the quantity of BDNF measured as mean BDNF concentrations generally fell within our calculated acceptable change limit up to 6 months in the freezer. Our results suggest that for quantification of circulating BDNF blood collected in K2EDTA tubes and plasma stored up to 6 months at either − 20 or − 80 °C produces reproducible results that fall within an acceptable range. However, plasma samples stored beyond 6 months and repeated freeze–thaw cycles should be avoided.

Effects of Temperamental Characteristics on Depression-Anxiety Levels and the Quality of Life in Infertile Women

Objective

It is known that the risk of anxiety disorders and depression in infertile women increases and their quality of life deteriorates. Temperamental characteristics are considered as predictors of mood disorders. The aim of this study was to investigate temperamental characteristics in infertile women and their effects on depression and anxiety levels, and the quality of life, and to reveal the differences and level of relationship compared to healthy women.

Method

Fourty-four female patients with primary infertility and 30 healthy female controls were included in this study. Temperamental characteristics of the participants were assessed with Temperament Evaluation of Memphis, Pisa, Paris and San Diego-Autoquestionnaire version (TEMPS-A). Depression and anxiety severity were evaluated with Beck Depression Inventory (BDI), and Beck Anxiety Inventory (BAI). To evaluate the quality of life, Short Form 36 (SF-36) health survey questionnaire was also applied.

Results

Hyperthymic temperament scores were higher in infertile women than the control group (p=0.001). BDI scores were positively correlated with depressive and cyclothymic temperament scores, and BAI scores were positively correlated with depressive and anxious temperament scores. A negative correlation was found between hyperthymic temperament and BAI and BDI scores. Hyperthymic temperament scores were positively correlated with both physical and mental subdimension scores of the quality of life scale.

Conclusion

In this study, hyperthymic temperament in infertile women was shown to be protective against anxiety and depression and it also improves the quality of life. Additional studies are needed to clarify the relationship between hyperthymic temperament and ovarian hormones or other biological parameters.

Molecular mechanisms underlying altered neurobehavioural development of female offspring of mothers with polycystic ovary syndrome: FOS-mediated regulation of neurotrophins in placenta

BACKGROUND

This study explored the mechanisms underlying altered neurobehavioural development of female offspring born to mothers with polycystic ovary syndrome (PCOS).

METHODS

In total, 20 women with PCOS and 32 healthy women who underwent caesarean deliveries with a single female foetus were recruited. Infants were assessed with Dubowitz scoring. Swan71 cell line with stable FOS overexpression was used to verify the regulatory effects of FOS on brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) expression. Learning and memory in female first-generation (F1) and second-generation (F2) offspring in a rat model of PCOS was tested using the Morris water maze at puberty and adulthood. Transcriptome analysis of pubertal hippocampi and hypothalami of female F1 offspring was conducted.

FINDINGS

Total score and behaviour subscales of Dubowitz scoring were significantly lower in female infants of women with PCOS. FOS and NGF protein levels were downregulated in placental villi of the PCOS group. FOS played a key role in BDNF inhibition and enhancing NGF in Swan71 cells. PCOS female F1 rats exhibited lower target crossing times during puberty when compared to controls. Transcriptome analysis revealed significant changes in hippocampal and hypothalamic neuronal pathways in female F1 rats at puberty.

INTERPRETATION

FOS regulation of neurotrophins in the placenta negatively affects neurobehavioural development of female offspring of PCOS mothers.

FUNDING

This study was funded by the National Key R&D Program of China (2018YFC1004900 to F.Q. and F.W.) and the National Natural Science Foundation of China (81874480 to F.Q.; 81873837 to F.W.).

Neurotrophins and glial cell line-derived neurotrophic factor in the ovary: physiological and pathophysiological implications

BACKGROUND

Neurotrophins [nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4)] and glial cell line-derived neurotrophic factor (GDNF) are soluble polypeptide growth factors that are widely recognized for their roles in promoting cell growth, survival and differentiation in several classes of neurons. Outside the nervous system, neurotrophin (NT) and GDNF signaling events have substantial roles in various non-neural tissues, including the ovary.

OBJECTIVE AND RATIONALE

The molecular mechanisms that promote and regulate follicular development and oocyte maturation have been extensively investigated. However, most information has been obtained from animal models. Even though the fundamental process is highly similar across species, the paracrine regulation of ovarian function in humans remains poorly characterized. Therefore, this review aims to summarize the expression and functional roles of NTs and GDNF in human ovarian biology and disorders, and to describe and propose the development of novel strategies for diagnosing, treating and preventing related abnormalities.

SEARCH METHODS

Relevant literature in the English language from 1990 to 2018 describing the role of NTs and GDNF in mammalian ovarian biology and phenotypes was comprehensively selected using PubMed, MEDLINE and Google Scholar.

OUTCOMES

Studies have shown that the neurotrophins NGF, BDNF, NT-3 and NT-4 as well as GDNF and their functional receptors are expressed in the human ovary. Recently, gathered experimental data suggest putative roles for NT and GDNF signaling in the direct control of ovarian function, including follicle assembly, activation of the primordial follicles, follicular growth and development, oocyte maturation, steroidogenesis, ovulation and corpus luteum formation. Additionally, crosstalk occurs between these ovarian regulators and the endocrine signaling system. Dysregulation of the NT system may negatively affect ovarian function, leading to reproductive pathology (decreased ovarian reserve, polycystic ovary syndrome and endometriosis), female infertility and even epithelial ovarian cancers.

WIDER IMPLICATIONS

A comprehensive understanding of the expression, actions and underlying molecular mechanisms of the NT/GDNF system in the human ovary is essential for novel approaches to therapeutic and diagnostic interventions in ovarian diseases and to develop more safe, effective methods of inducing ovulation in ART in the treatment of female infertility.

Chaiyu-Dixian Formula Exerts Protective Effects on Ovarian Follicular Abnormal Development in Chronic Unpredictable Mild Stress (CUMS) Rat Model

Background

Chronic stress has been known to impair the female reproductive function, but the mechanism remains to be further investigated. Chaiyu-Dixian Formula (CYDXF) has been reported to regulate human endocrine disorders clinically. However, whether this formula can affect chronic stress-induced ovarian follicular development is not clear.

Aim of the study

To examine effects of CYDXF on follicular development and explore possible mech anisms in a chronic unpredictable mild stress (CUMS) model.

Materials and Methods

Adult female rats were randomly divided into 5 groups control group, CUMS group (saline treatment), CUMS+Estradiol (E₂) (0.1 mg/kg) group, CUMS+CYDXF (2.73 g/kg) group, and CUMS+CYDXF (5.46 g/kg) group. Body weights and behavioral tests were documented. Serum hormone levels were determined by enzyme-linked immunosorbent assay (ELISA). Western blotting was used to detect the protein levels in the PI3K/Akt pathway and brain-derived neurotrophic factor (BDNF). The follicles were analyzed and classified according to their morphological characterization.

Results

CYDXF relieved depression-like behaviors and ameliorated the abnormality in rat estrous cycle within the rat model of CUMS. Moreover, CYDXF could regulate endocrine disorders, increase the proportion of antral follicles as well as decrease the proportion of follicular atresia, which suggested that CYDXF could alleviate abnormal follicular development and improve overall ovarian function. Furthermore, CYDXF also activated the BDNF-mediated PI3K/Akt signaling pathway.

Conclusions

CYDXF (at dose of both 2.73 and 5.46 g/kg) attenuated chronic stress-induced abnormal ovarian follicular development by relieving depression-like behaviors and improving ovarian function through partly the regulation of the BDNF-mediated PI3K/Akt pathway.

Reducing luteinizing hormone levels after ovariectomy improves spatial memory: Possible role of brain-derived neurotrophic factor

Alzheimer's disease and other forms of cognitive decline are significantly more prevalent in post-menopausal women. Decreased estrogen levels, due to menopause or ovariectomy, may contribute to memory impairments and neurodegeneration. Another result of decreased estrogen levels is elevated luteinizing hormone (LH). Elevated LH after menopause/ovariectomy has been shown to impair cognition in both human and animal studies. Lowering LH levels rescues spatial memory in ovariectomized (ovx) rodents, yet the mechanisms of these effects are still unclear. Estrogens appear to exert some of their effects on memory by increasing levels of brain-derived neurotrophic factor (BDNF) in the hippocampus. In these studies, we explored whether lowering LH may act by increasing BDNF. Ovx rats were treated with Antide, a gonadotropin releasing hormone receptor antagonist that lowers LH levels, or with estradiol. Both Antide and estradiol treatment enhanced spatial memory in ovx females. Both were found to be ineffective when a BDNF receptor antagonist was administered. Immunohistochemical analysis revealed that both Antide and estradiol increased BDNF expression in the hippocampus. Dendritic spine density on pyramidal cells in CA1 was unchanged by any treatment. These results provide evidence for a relationship between LH and BDNF in the hippocampus and demonstrate that estrogen-increasing and LH-lowering treatments may both require BDNF signaling in order to improve spatial memory.

Prenatal Androgenization Induces Anxiety-Like Behavior in Female Rats, Associated with Reduction of Inhibitory Interneurons and Increased BDNF in Hippocampus and Cortex

Anxiety is one of the most frequent psychiatric disorders. Despite the fact that most studies describe an anxiolytic effect of testosterone, hyperandrogenemia in mothers is assumed to be related to an increased risk of mood disorders in their offspring. An increasing body of scientific evidence suggests that an altered expression of interneuronal markers of the hippocampus may be the cause of anxiety. The aim of this study was to examine the influence of maternal hyperandrogenemia on behavioral parameters of anxiety-like behavior, neuropeptide Y (NPY) and parvalbumin (PV) expression in the hippocampus, and the level of the brain-derived neurotrophic factor (BDNF) in the hippocampus and cerebral cortex. Pregnant female Wistar albino rats were treated with testosterone undecanoate on the 20th day of gestation. Anxiety-like behavior in adult female offspring was evaluated by the elevated plus maze test and the open field. The number of PV and NPY immunoreactive cells in the hippocampus was determined immunohistochemically. The level of BDNF expression in the hippocampus and cerebral cortex was analyzed with the Western blot test. Prenatal hyperandrogenization increased anxiety-like behavior in female offspring and decreased expression of NPY+ and PV+ in the CA1 region of the hippocampus as compared to the control group. BDNF expression in the hippocampus and cerebral cortex of prenatally androgenized female offspring was significantly increased in comparison with the controls. Prenatal hyperandrogenization may be the cause of anxiety-like behavior in female offspring. Decrease in NPY and PV expression in the hippocampus may explain the possible mechanism of hyperandrogenization induced anxiety.

Serum brain-derived neurotrophic factor (BDNF) is not regulated by testosterone in transmen

Brain morphology significantly differs between the sexes. It has been shown before that some of these differences are attributable to the sex-specific hormonal milieu. Brain-derived neurotrophic factor (BDNF) is involved in myriads of neuroplastic processes and shows a sexual dimorphism. Transsexual persons may serve as a model to study sex steroid-mediated effects on brain plasticity. We have recently demonstrated that serum levels of BDNF are reduced in transwomen following 12 months of cross-sex hormone treatment. We now wanted to look at the effects of testosterone treatment on BDNF in transmen. In contrast to our initial hypothesis, BDNF levels did not significantly change, despite dramatic changes in the sex-hormonal milieu. Our data indicate that testosterone does not seem to play a major role in the regulation of BDNF in females.

Effects of brain-derived neurotrophic factor on oocyte maturation and embryonic development in a rat model of polycystic ovary syndrome

Brain-derived neurotrophic factor (BDNF) is expressed extensively in the mammalian female reproductive system and has been implicated in the development of follicles and oocytes. However, BDNF expression patterns in the ovary and its effects on oocyte maturation and embryonic development in polycystic ovary syndrome (PCOS) have not been established. In the present study, we established a PCOS model by treating the rats with insulin and human chorionic gonadotropin (hCG). Rats treated with insulin + hCG had heavier bodyweight and ovarian weight, higher circulating concentrations of luteinising hormone (LH) and testosterone (T), and greater homeostatic model assessment of insulin resistance (HOMA-IR) values compared with control rats (P < 0.05). BDNF and its receptor tyrosine kinase type B (TrkB) were located in cyst walls, granulosa and theca cells, and BDNF protein levels were lower in ovaries of insulin + hCG-treated rats (P < 0.05). The rate of oocyte maturation and formation of blastocysts and morulae was greatest in rats treated with 5 ng mL–1 BDNF (P < 0.05) compared to other BDNF groups (1 and 10 ng mL–1) and the control. The control rats were also PCOS rats and were treated without BDNF. There were no significant differences in the rate of germinal vesicle breakdown (GVBD) and fertilisation among the various treatment groups (1, 5 and 10 ng mL–1) and the control group (P > 0.05). The results indicate that in vitro treatment with an appropriate concentration of BDNF not only promotes oocyte maturation, but also rescues embryonic development in rats treated with insulin + hCG as a model of PCOS.

Chronic unpredictable stress decreases expression of brain-derived neurotrophic factor (BDNF) in mouse ovaries: relationship to oocytes developmental potential

Background

Brain-derived neurotropic factor (BDNF) was originally described in the nervous system but has been shown to be expressed in ovary tissues recently, acting as a paracrine/autocrine regulator required for developments of follicles and oocytes. Although it is generally accepted that chronic stress impairs female reproduction and decreases the expression of BDNF in limbic structures of central nervous system, which contributes to mood disorder. However, it is not known whether chronic stress affects oocytes developments, nor whether it affects expression of BDNF in ovary.

Methods

Mice were randomly assigned into control group, stressed group, BDNF-treated group and BDNF-treated stressed group. The chronic unpredictable mild stress model was used to produce psychosocial stress in mice, and the model was verified by open field test and hypothalamic-pituitary-adrenal (HPA) axis activity. The methods of immunohistochemistry and western blotting were used to detect BDNF protein level and distribution. The number of retrieved oocytes, oocyte maturation, embryo cleavage and the rates of blastocyst formation after parthenogenetic activation were evaluated.

Results

Chronic unpredictable stress decreased the BDNF expression in antral follicles, but didn’t affect the BDNF expression in primordial, primary and secondary follicles. Chronic unpredictable stress also decreased the number of retrieved oocytes and the rate of blastocyst formation, which was rescued by exogenous BDNF treatment.

Conclusion

BDNF in mouse ovaries may be related to the decreased number of retrieved oocytes and impaired oocytes developmental potential induced by chronic unpredictable stress.