Locus coeruleus mediates cold stress-induced polycystic ovary in rats

Rodent models in polycystic ovarian syndrome: Dissecting reproductive and metabolic phenotypes for therapeutic advancements

The most prevalent reason for female infertility is polycystic ovarian syndrome (PCOS) exhibiting two of three phenotypes including biochemical or clinical hyperandrogenism, anovulation and polycystic ovaries. Insulin resistance and obesity are common in PCOS-afflicted women. Androgens are thought to be the primary cause of PCOS causing symptoms including anovulation, follicles that resemble cysts, higher levels of the luteinizing hormone (LH), increased adiposity, and insulin resistance. However, due to the heterogeneity of PCOS, it is challenging to establish a single model that accurately mimics all the reproductive and metabolic phenotypes seen in PCOS patients. In this review, we aimed to investigate rodent models of PCOS and related phenotypes with or without direct hormonal treatments and to determine the underlying mechanisms to comprehend PCOS better. We summarized rodent models of PCOS that includes direct and indirect hormone intervention and discussed the aetiology of PCOS and related phenotypes produced in rodent models. We presented combined insights on multiple rodent models of PCOS and compared their reproductive and/or metabolic phenotypes. Our review indicates that there are various models for studying PCOS and one should select a model most suitable for their purpose. This review will be helpful for consideration of rodent models for PCOS which are not conventionally used to determine mechanisms at the molecular/cellular levels encouraging development of novel treatments and control methods for PCOS.

The role of the autonomic nervous system in polycystic ovary syndrome

This article reviewed the relationship between the autonomic nervous system and the development of polycystic ovary syndrome (PCOS). PCOS is the most common reproductive endocrine disorder among women of reproductive age. Its primary characteristics include persistent anovulation, hyperandrogenism, and polycystic ovarian morphology, often accompanied by disturbances in glucose and lipid metabolism. The body's functions are regulated by the autonomic nervous system, which consists mainly of the sympathetic and parasympathetic nervous systems. The autonomic nervous system helps maintain homeostasis in the body. Research indicates that ovarian function in mammals is under autonomic neural control. The ovaries receive central nervous system information through the ovarian plexus nerves and the superior ovarian nerves. Neurotransmitters mediate neural function, with acetylcholine and norepinephrine being the predominant autonomic neurotransmitters. They influence the secretion of ovarian steroids and follicular development. In animal experiments, estrogen, androgens, and stress-induced rat models have been used to explore the relationship between PCOS and the autonomic nervous system. Results have shown that the activation of the autonomic nervous system contributes to the development of PCOS in rat. In clinical practice, assessments of autonomic nervous system function in PCOS patients have been gradually employed. These assessments include heart rate variability testing, measurement of muscle sympathetic nerve activity, skin sympathetic response testing, and post-exercise heart rate recovery evaluation. PCOS patients exhibit autonomic nervous system dysfunction, characterized by increased sympathetic nervous system activity and decreased vagal nerve activity. Abnormal metabolic indicators in PCOS women can also impact autonomic nervous system activity. Clinical studies have shown that various effective methods for managing PCOS regulate patients' autonomic nervous system activity during the treatment process. This suggests that improving autonomic nervous system activity may be an effective approach in treating PCOS.

Multi-Organ Increase in Norepinephrine Levels after Central Leptin Administration and Diet-Induced Obesity

Autonomic innervation is important to regulate homeostasis in every organ of the body. The sympathetic nervous system controls several organs associated with metabolism and reproduction, including adipose tissue, the liver, and the ovaries. The sympathetic nervous system is controlled within the central nervous system by neurons located in the hypothalamus, which in turn are regulated by hormones like leptin. Leptin action in the hypothalamus leads to increased sympathetic activity in the adipose tissue. In this short report, we propose that leptin action in the brain also controls the sympathetic innervation of other organs like the liver and the ovary. We performed two experiments: We performed an intracerebroventricular (ICV) injection of leptin and measured norepinephrine levels in several organs, and we used a validated model of overnutrition and obesity to evaluate whether an increase in leptin levels coexists with high levels of norepinephrine in the liver and ovaries. Norepinephrine was measured by ELISA in adipose tissue and by HPLC-EC in other tissues. Leptin was measured by ELISA. We found that the ICV injection of leptin increases norepinephrine levels in several organs, including the liver and ovaries. Also, we found that diet-induced obesity leads to an increase in leptin levels while inducing an increase in norepinephrine levels in the liver and ovaries. Finally, since hyperactivity of the sympathetic nervous system is observed both in non-alcoholic fatty liver disease and polycystic ovary syndrome, we think that an increase in norepinephrine levels induced by hyperleptinemia could be involved in the pathogenesis of both diseases.

Allostasis in Neuroendocrine Systems Controlling Reproduction

Allostasis provides a supporting role to the homeostatic control of biological variables in mammalian species. While the concept of homeostasis is related to the control of variables within a set point or range that are essential to life, allostasis refers to systems that facilitate adaptation to challenges that the organism faces and the new requirements for survival. Essential for such adaptation is the role played by the brain in eliciting neural and neuroendocrine responses. Reproductive function is fundamental for the survival of species but is costly in energetic terms and requires a synchrony with an ever-changing environment. Thus, in many species reproductive function is blocked or delayed over immediate challenges. This review will cover the physiological systems and neuroendocrine pathways that supply allostatic control over reproductive neuroendocrine systems. Light, hypoxia, temperature, nutrition, psychosocial, and immune mediators influence the neuroendocrine control of reproductive functions through pathways that are confluent at the paraventricular nucleus; however, understanding of the integrative responses to these stimuli has not been clarified. Likely, the ultimate consequence of these allostatic mechanisms is the modification of kisspeptin and gonadotropin-releasing hormone neuronal activity, thus compromising reproduction function in the short term, while preserving species survivability.

Effects of chronic exposure to cold stress on ovarian functions in prepubertal rats

Ovarian functions are modulated by the hypothalamus-pituitary-ovary axis and neural signals. Stress modifies the activity of the sympathetic nervous system. In adult female rats, cold stress results in higher noradrenergic and steroidogenic activity of the ovary, anovulation and the presence of ovarian cysts; however, it is unknown whether this response occurs in prepubertal rats. The purpose of this study was to analyse the effects of cold stress initiated in the prepubertal stage of female rats on ovarian function. Female rats 24 days old were exposed to three, five or eight weeks of cold stress. Autopsies were performed at the end of each stress period. The parameters analysed were the number of ova shed by ovulating animals; the number of ovulating animals; the serum concentrations of progesterone, testosterone, and oestradiol; and the ovarian concentrations of norepinephrine and 3-methoxy-4-hydroxyphenyl-glycol. Our results show that chronic cold stress applied to prepubertal rats did not modify the number of ovulating animals, the total number of ova shed, or progesterone and testosterone concentrations in any of the periods analysed. Oestradiol concentration was lower in the animals exposed to five or eight weeks of stress. The ovarian norepinephrine concentration was higher in the animals exposed to three weeks of stress and was lower at eight weeks of stress. No changes in ovarian morphology were observed. Our data suggest that the changes in noradrenergic activity resulting from chronic cold stress experienced in the prepubertal stage do not modify ovarian architecture or affect the ovulatory response in adulthood.

Exposure of the Gestating Mother to Sympathetic Stress Modifies the Cardiovascular Function of the Progeny in Male Rats

BACKGROUND

Sympathetic stress stimulates norepinephrine (NE) release from sympathetic nerves. During pregnancy, it modifies the fetal environment, increases NE to the fetus through the placental NE transporter, and affects adult physiological functions. Gestating rats were exposed to stress, and then the heart function and sensitivity to in vivo adrenergic stimulation were studied in male progeny.

METHODS

Pregnant Sprague-Dawley rats were exposed to cold stress (4 °C/3 h/day); rats' male progeny were euthanized at 20 and 60 days old, and their hearts were used to determine the β-adrenergic receptor (βAR) (radioligand binding) and NE concentration. The in vivo arterial pressure response to isoproterenol (ISO, 1 mg/kg weight/day/10 days) was monitored in real time (microchip in the descending aorta).

RESULTS

Stressed male progeny presented no differences in ventricular weight, the cardiac NE was lower, and high corticosterone plasma levels were recorded at 20 and 60 days old. The relative abundance of β1 adrenergic receptors decreased by 36% and 45%, respectively (p < 0.01), determined by Western blot analysis without changes in β2 adrenergic receptors. A decrease in the ratio between β1/β2 receptors was found. Displacement of ³H-dihydroalprenolol (DHA) from a membrane fraction with propranolol (β antagonist), atenolol (β1 antagonist), or zinterol (β2 agonist) shows decreased affinity but no changes in the β-adrenergic receptor number. In vivo exposure to ISO to induce a β-adrenergic overload provoked death in 50% of stressed males by day 3 of ISO treatment.

CONCLUSION

These data suggest permanent changes to the heart's adrenergic response after rat progeny were stressed in the uterus.

Bovine models for human ovarian diseases

During early embryonic development, late fetal growth, puberty, adult reproductive years, and advanced aging, bovine and human ovaries closely share molecular pathways and hormonal signaling mechanisms. Other similarities between these species include the size of ovaries, length of gestation, ovarian follicular and luteal dynamics, and pathophysiology of ovarian diseases. As an economically important agriculture species, cattle are a foundational species in fertility research with decades of groundwork using physiologic, genetic, and therapeutic experimental techniques. Many technologies used in modern reproductive medicine, such as ovulation induction using hormonal therapy, were first used in cows before human trials. Human ovarian diseases with naturally occurring bovine correlates include premature ovary insufficiency (POI), polycystic ovarian syndrome (PCOS), and sex-cord stromal tumors (SCSTs). This article presents an overview of bovine ovary research related to causes of infertility, ovarian diseases, diagnostics, and therapeutics, emphasizing where the bovine model can offer advantages over other lab animals for translational applications.

Gestational Sympathetic Stress Programs the Fertility of Offspring: A Rat Multi-Generation Study

The exposure to sympathetic stress during the entire period of gestation (4 °C/3 h/day) strongly affects the postnatal reproductive performance of the first generation of female offspring and their fertility capacity. The aim of this work was to determine whether this exposure to sympathetic stress affects the reproductive capacity of the next three generations of female offspring as adults. Adult female Sprague–Dawley rats were mated with males of proven fertility. We studied the reproductive capacity of the second, third, and fourth generations of female offspring (the percentage of pregnancy and the number and weight of female offspring). The estrus cycle activity of the progenies was studied, and a morphological analysis of the ovaries was carried out to study the follicular population. The second generation had a lower number of pups per litter and a 20% decrease in fertile capacity. The estrus cycle activity of the third generation decreased even more, and they had a 50% decrease in their fertile capacity, and their ovaries presented polycystic morphology. The fourth generation however, recovered their reproductive capacity but not the amount of newborns pups. Most probably, the chronic intrauterine exposure to the sympathetic stress programs the female gonads to be stressed in a stressful environment; since the fourth generation was the first born with no direct exposure to stress during development, it opens studies on intrauterine factors affecting early follicular development.

Is Chlamydia to Blame for Koala Reproductive Cysts?

A significant threat to koala populations is infection from Chlamydia, which results in disease and death. Wild koalas with Chlamydia infections are admitted to wildlife hospitals and treated with antibiotics; however, up to 50% of koalas that present to wildlife hospitals do not survive. A major contributor to high mortality is the development of reproductive cysts, resulting in female infertility and euthanasia. However, the diagnosis of reproductive disease is limited to ultrasound with no further investigations. This communication highlights reports of histological and microbiological findings, the accuracy of ultrasound to necropsy reports and other possible causes for reproductive cyst development previously reported in other hosts. Our conclusions identify a significant knowledge gap in the aetiology of koala reproductive cysts and highlight the urgent need for future investigations.

Oxidized high-density lipoprotein enhances endocrine disorders and ovarian damage in rats

Previous findings have highlighted the association between oxidized high‐density lipoprotein (ox‐HDL) and polycystic ovary syndrome (PCOS) development; however, the underlying mechanism remains unclear. Under such context, the present study aimed to investigate the mechanism underlying the involvement of ox‐HDL in PCOS in relation to the p65/micro‐RNA‐34a (miR‐34a)/FOS axis. PCOS rat models were established with the injection of dehydroepiandrosterone (6 mg/100 g body weight). Both PCOS‐modelled rats and granulosa cells (GCs) were received treatment with ox‐HDL in order to identify its role in PCOS. Next, apoptosis and viability of GCs were detected with the application of TdT‐mediated dUTP Nick‐End Labeling and flow cytometry and Cell counting kit‐8, respectively. A series of assays were performed to determine the interaction among ox‐HDL, p65, miR‐34a, FOS and nuclear factor‐κB (NF‐κB). The results revealed high expression of ox‐HDL in PCOS, and enhanced endocrine disorders and ovarian damage in rats. ox‐HDL promoted apoptosis of GCs and decreased its viability. ox‐HDL activated NF‐κB pathway and induced p65 phosphorylation to promote miR‐34a expression. miR‐34a targeted and inhibited FOS expression. In conclusion, our findings suggested that ox‐HDL promoted the activation of p65 and transcription of miR‐34a, which stimulated apoptosis of GCs and inhibited expression of FOS, resulting in the overall acceleration of PCOS development.

Recent updates on animal models for understanding the etiopathogenesis of polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS) is the primary cause of female infertility affecting several women worldwide. Changes in hormonal functions such as hyperandrogenism are considered a significant factor in developing PCOS in women. In addition, many molecular pathways are involved in the pathogenesis of PCOS in women. To have better insights about PCOS, it is data from clinical studies carried on women suffering from PCOS should be collected. However, this approach has several implications, including ethical considerations, cost involved and availability of subject. Moreover, during the early drug development process, it is always advisable to use non-human models mimicking human physiology as they are less expensive, readily available, have a shorter gestation period and less risk involved. Many animal models have been reported that resemble the PCOS pathways in human subjects. However, the models developed on rats and mice are more preferred over other rodent/non-rodent models due to their closer resemblance with human PCOS development mechanism. The most extensively reported PCOS models for rats and mice include those induced by using testosterone, letrozole and estradiol valerate. As the pathophysiology of PCOS is complex, none of the explored models completely surrogates the PCOS related conditions occurring in women. Hence, there is a need to develop an animal model that can resemble the pathophysiology of PCOS in women. The review focuses on various animal models explored to understand the pathophysiology of PCOS. The article also highlights some environmental and food-related models that have been used to induce PCOS.

Animal Models in Polycystic Ovarian Syndrome

The pathogenesis of polycystic ovarian syndrome (PCOS) in women is poorly understood. With its varied endocrine and metabolic effects, it is unlikely a single genetic mutation or biological insult is the cause of the disease. Animals have been the proposed model for further studying the pathogenesis of PCOS and many modalities can be used to induce PCOS-like phenotypes in animals, most often with rodents. While there is not yet an animal model that perfectly recapitulates the classic PCOS phenotype in human women, many models allow for a better understanding of the complex disease process as well as possible treatments.

Animal Models for Human Polycystic Ovary Syndrome (PCOS) Focused on the Use of Indirect Hormonal Perturbations: A Review of the Literature

Hormonal disturbances, such as hyperandrogenism, are considered important for developing polycystic ovary syndrome (PCOS) in humans. Accordingly, directly hormone-regulated animal models are widely used for studying PCOS, as they replicate several key PCOS features. However, the pathogenesis and treatment of PCOS are still unclear. In this review, we aimed to investigate animal PCOS models and PCOS-like phenotypes in animal experiments without direct hormonal interventions and determine the underlying mechanisms for a better understanding of PCOS. We summarized animal PCOS models that used indirect hormonal interventions and suggested or discussed pathogenesis of PCOS-like features in animals and PCOS-like phenotypes generated in other animals. We presented integrated physiological insights and shared cellular pathways underlying the pathogenesis of PCOS in reviewed animal models. Our review indicates that the hormonal and metabolic changes could be due to molecular dysregulations, such as upregulated PI3K-Akt and extracellular signal-regulated kinase (ERK) signalling, that potentially cause PCOS-like phenotypes in the animal models. This review will be helpful for considering alternative animal PCOS models to determine the cellular/molecular mechanisms underlying PCOS symptoms. The efforts to determine the specific cellular mechanisms of PCOS will contribute to novel treatments and control methods for this complex syndrome.

Chronic predator stress in female mice reduces primordial follicle numbers: implications for the role of ghrelin

Chronic stress is a known suppressor of female reproductive function. However, attempts to isolate single causal links between stress and reproductive dysfunction have not yet been successful due to their multi-faceted aetiologies. The gut-derived hormone ghrelin regulates stress and reproductive function and may therefore be pivotal in the neuroendocrine integration of the hypothalamic-pituitary-adrenal (HPA) and -gonadal (HPG) axes. Here, we hypothesised that chronic stress disrupts ovarian follicle maturation and that this effect is mediated by a stress-induced increase in acyl ghrelin and activation of the growth hormone secretatogue receptor (GHSR). We gave C57BL/6J female mice 30 min daily chronic predator stress for 4 weeks, or no stress, and gave them daily GHSR antagonist (d-Lys3-GHRP-6) or saline. Exposure to chronic predator stress reduced circulating corticosterone, elevated acyl ghrelin levels and led to significantly depleted primordial follicle numbers. GHSR antagonism stress-dependently altered the expression of genes regulating ovarian responsiveness to gonadotropins and was able to attenuate the stress-induced depletion of primordial follicles. These findings suggest that chronic stress-induced elevations of acyl ghrelin may be detrimental for ovarian follicle maturation.

Effect of Superior Ovarian Nerve and Plexus Nerve Sympathetic Denervation on Ovarian-Derived Infertility Provoked by Estradiol Exposure to Rats

Sympathetic innervation of the ovary in rodents occurs via two routes: the superior ovarian nerve (SON), which runs along the ovarian ligament, and the plexus nerve (PN), which is mainly associated with the vasculature. SON and ovarian norepinephrine (NE) levels play a major role in regulating ovarian cystic health. Although it was previously described that the polycystic ovarian phenotype (PCO) is causally related to hyperstimulation of the sympathetic nerves of the ovary, much less is known, however, regarding the role of PN in ovarian physiology. We studied the role of SON and PN in relation to the maintenance of the PCO phenotype induced in the rat by exposure to estradiol valerate (EV). EV exposure at 24 days old (juvenile exposure) increases NE in the ovary for up to 90 days after EV injection. SON or PN denervation (SONX and PNX) decreased NE. SONXreversed the acyclic condition from 30 days after surgery (p < 0.05), but PNXdid not. SONX was more effective than PNX to downregulate the increased number of cysts induced by EV, with the presence of the corpora lutea (CL, signifying ovulation) in the SONX group. Seventy percent of SONX rats presented with pregnancy at 60 days post-EV (6 of the 7 sperm-positive rats were pregnant); however, SONX rats had a reduced number (half) of pups compared with vehicle-treated rats and 60% more pups than EV rats. These data suggest that the SON plays a predominant role in follicular development, ovulation and pregnancy during ovarian diseases.

Impact of Cold Exposure on the Reproductive Function in Female Rats

Female reproductive system diseases caused by exposure to a cold environment are widely considered as important human health challenges. Although the projection of female reproduction in cold temperature has been studied, a holistic view on the probable effects of cold exposure on the functions of the female reproductive system has not been achieved. Our aim was to evaluate the effects of cold exposure to the functions of the ovary and uterus in female rats. For this purpose, female rats were randomly grouped as follows: (1) the cold group was exposed to -10°C, 4 h per day for 2 weeks, and (2) the normal temperature (23 ± 1°C) group was used as control. Alterations were observed in different parameters, including body weight gain, organ coefficients, estrus cycle, and pathology of the cold-exposed female rats. Similarly, the serum reproductive hormones and mRNA expression were evaluated. Cold exposure induced estrus cycle irregularity and some alterations in the morphology of the ovary. Cold exposure impairs the function of the ovary probably by changing the level of serum LH and increasing LHR expression. Cold exposure induced a significant reduction of uterine epithelium height. Cold exposure causes alterations in the morphology of the uterus probably because of the effect of progesterone, the increase in the PR level, and the decrease in the ER level.

Role of RFRP-3 in the development of cold stress-induced polycystic ovary phenotype in rats

RFamide-related peptide (RFRP-3) is a regulator of GnRH secretion from the brain, but it can also act in human ovary to influence steroidogenesis. We aimed to study the putative local role of RFRP-3 in the ovary and its potential participation in the development of a polycystic ovary phenotype induced by chronic sympathetic stress (cold stress). We used adult Sprague–Dawley rats divided into control and stressed groups. In both groups, we studied the effect of intraovarian exposure to RFRP-3 on follicular development and plasma ovarian steroid concentrations. We also tested the effect of RFRP-3 on ovarian steroid production in vitro. Chronic in vivo intraovarian exposure to RFRP-3 decreased basal testosterone concentrations and cold stress-induced progesterone production by the ovary. In vitro, RFRP-3 decreased hCG-induced ovarian progesterone and testosterone secretion. Immunohistochemistry and mRNA expression analysis showed a decrease in Rfrp and expression of its receptor in the ovary of stressed rats, a result which is in line with the increased testosterone levels found in stressed rats. In vivo application of RFRP-3 recovered the low levels of secondary and healthy antral follicles found in stressed rats. Taken together, our data indicate a previously unknown response of hypothalamic and ovarian RFRP-3 to chronic cold stress, influencing ovarian steroidogenesis and follicular dynamics. Thus, it is likely that RFRP-3 modulation in the ovary is a key component of development of the polycystic ovary phenotype.

Pharmacological sympathetic denervation prevents the development of polycystic ovarian syndrome in rats injected with estradiol valerate

BACKGROUND

The injection of estradiol valerate in female rats induces polycystic ovary syndrome, which is characterized by polycystic ovaries, anovulation, and hyperandrogenism. These characteristics have been associated with an increase in the ovarian concentration of norepinephrine, which occurs before establishing the polycystic ovary syndrome. The bilateral section of the superior ovarian nerve restores ovarian functions in animals with polycystic ovary syndrome. The superior ovarian nerve provides norepinephrine and vasoactive intestinal peptide to the ovary. An increase in the activity of both neurotransmitters has been associated with the development of polycystic ovary syndrome. The purpose of the present study was analyzed the participation of the noradrenergic nervous system in the development of polycystic ovary syndrome using guanethidine as a pharmacological tool that destroys peripheral noradrenergic nerve fibers.

METHODS

Fourteen-day old female rats of the CIIZ-V strain were injected with estradiol valerate or vehicle solution. Rats were randomly allotted to one of three guanethidine treatment groups for denervation: 1) guanethidine treatment at age 7 to 27-days, 2) guanethidine treatment at age 14 to 34- days, and 3) guanethidine treatment at age 70 to 90- days. All animals were sacrificed when presenting vaginal oestrus at age 90 to 94-days. The parameters analyzed were the number of ova shed by ovulating animals, the ovulation rate (i.e., the numbers of ovulating animals/the numbers of used animals), the serum concentration of progesterone, testosterone, oestradiol and the immunoreactivity for tyrosine hydroxylase enzyme. All data were analyzed statistically. A p-value of less than 0.05 was considered significant.

RESULTS

Our results show that the elimination of noradrenergic fibers before the establishment of polycystic ovary syndrome prevents two characteristics of the syndrome, blocking of ovulation and hyperandrogenism. We also found that in animals that have already developed polycystic ovary syndrome, sympathetic denervation restores ovulatory capacity, but it was not as efficient in reducing hyperandrogenism.

CONCLUSION

The results of the present study suggest that the noradrenergic fibers play a stimulant role in the establishment of polycystic ovary syndrome.

High-Frequency Electrical Modulation of the Superior Ovarian Nerve as a Treatment of Polycystic Ovary Syndrome in the Rat

The polycystic ovary syndrome (PCOS) is the most prevalent ovarian pathology in women, with excessive sympathetic activity in the superior ovarian nerve (SON) playing an important role in inducing the PCOS symptoms in the rats and humans. Our previous studies have shown that surgical transection of the SON can reverse the disease progression, prompting us to explore the effect of the kilohertz frequency alternating current (KHFAC) modulation as a method of reversible non-surgical suppression of the nerve activity in the rodent model of PCOS. 56 animals were randomly allocated to three groups: the Control group (n = 18), the PCOS group (n = 15), and the PCOS + KHFAC group (n = 23). The physiological, anatomical, and biochemical parameters of ovarian function were evaluated during the progression of the experimentally-induced PCOS and during long-term KHFAC modulation applied for 2-3 weeks. The KHFAC modulation has been able to reverse the pathological changes in assessed PCOS parameters, namely the irregular or absent estrous cycling, formation of ovarian cysts, reduction in the number of corpora lutea, and ovarian norepinephrine concentration. The fertility capacity was similar in the PCOS and the PCOS + KHFAC groups, indicating the safety of KHFAC modulation approach. In summary, these results suggest that the KHFAC modulation approach of suppressing the SON activity could become a useful treatment modality for PCOS and potentially other pathological ovarian conditions.

Linking Stress and Infertility: A Novel Role for Ghrelin

Infertility affects a remarkable one in four couples in developing countries. Psychological stress is a ubiquitous facet of life, and although stress affects us all at some point, prolonged or unmanageable stress may become harmful for some individuals, negatively impacting on their health, including fertility. For instance, women who struggle to conceive are twice as likely to suffer from emotional distress than fertile women. Assisted reproductive technology treatments place an additional physical, emotional, and financial burden of stress, particularly on women, who are often exposed to invasive techniques associated with treatment. Stress-reduction interventions can reduce negative affect and in some cases to improve in vitro fertilization outcomes. Although it has been well-established that stress negatively affects fertility in animal models, human research remains inconsistent due to individual differences and methodological flaws. Attempts to isolate single causal links between stress and infertility have not yet been successful due to their multifaceted etiologies. In this review, we will discuss the current literature in the field of stress-induced reproductive dysfunction based on animal and human models, and introduce a recently unexplored link between stress and infertility, the gut-derived hormone, ghrelin. We also present evidence from recent seminal studies demonstrating that ghrelin has a principal role in the stress response and reward processing, as well as in regulating reproductive function, and that these roles are tightly interlinked. Collectively, these data support the hypothesis that stress may negatively impact upon fertility at least in part by stimulating a dysregulation in ghrelin signaling.

Xiao-Yao-San, a Chinese Medicine Formula, Ameliorates Chronic Unpredictable Mild Stress Induced Polycystic Ovary in Rat

Chronic stress induces endocrine disturbance, which contributes to the development of polycystic ovary syndrome (PCOS), a condition that remains a challenge for clinicians to cope with. The present study investigated the effect of Xiao-Yao-San (XYS), a traditional Chinese medicine formula used for treatment of gynecological disease, on the chronic stress-induced polycystic ovary and its underlying mechanism. Female Sprague-Dwaley rats underwent a 3 weeks chronic unpredictable mild stress (CUMS) procedure to establish the PCOS model, followed by 4 weeks treatment with XYS (0.505 g/kg or 1.01 g/kg) by gavage. Granulosa cells were exposed to noradrenaline (1 mM) in vitro for 24 h, followed by incubation with or without XYS-treated rat serum for 24 h. Post-treatment with XYS ameliorated CUMS-induced irregular estrous cycles and follicles development abnormalities, decrease of estradiol and progesterone level as well as increase of luteinizing hormone in serum, reduced cystic follicles formation and the apoptosis and autophagy of granulosa cells, attenuated the increase in dopamine beta hydroxylase and c-fos level in locus coeruleus, the noradrenaline level in serum and ovarian tissue, and the expression of beta 2 adrenergic receptor in ovarian tissue. Besides, XYS alleviated the reduction of phosphorylation of ribosomal protein S6 kinase polypeptide I and protein kinase B, as well as the increase of microtubule-associated protein light chain 3-I to microtubule-associated protein light chain 3-II conversion both in vivo and in vitro. This study demonstrated XYS as a potential strategy for CUMS induced polycystic ovary, and suggested that the beneficial role of XYS was correlated with the regulation of the sympathetic nerve activity.

Animal models of hyperandrogenism and ovarian morphology changes as features of polycystic ovary syndrome: a systematic review

Polycystic ovary syndrome (PCOS) is a common endocrine disorder, affecting 9-18% of women in reproductive age that causes hyperandrogenism and infertility due to dysfunctional follicular maturation and anovulation. The etiology of PCOS is still poorly known, and information from experimental animal models may help improve current understanding of the mechanisms of PCOS initiation and development. Therefore, we conducted a systematic review of currently available methods for simulation of PCOS in experimental models, focusing on two main endocrine traits: ovarian morphology changes and circulating levels of sex hormones and gonadotropins.We searched the MEDLINE database for articles in English or Spanish published until October 2016. Of 933 studies identified, 39 were included in the systematic review. One study compared interventions with androgens versus estrogens, 18 used androgen-induced stimulation, 9 used estrogens or drugs with estrogen action, including endocrine disruptors, to induce PCOS-like models, and 12 used miscellaneous interventions. Broad differences were found among the studies concerning hormonal interventions, animal species, and developmental stage at the time of the experiments, and most models resulted in ovarian morphology changes, mainly increases in the number of cystic and antral follicles and decreases in the corpus luteum. Hyperandrogenism was produced by using androgens and other drugs as the stimulatory agent. However, studies using drugs with estrogenic effect did not observe changes in circulating androgens.In conclusion, medium- or long-term testosterone administration in the pre- and postnatal periods performed best for induction of a PCOS-like phenotype, in rhesus macaque and rat models respectively. In rats, postnatal exposure to androgens results in reprogramming of the hypothalamic-pituitary-ovarian-axis. Thus, comparisons between different intervention models may be useful to define the timing of reproductive PCOS phenotypes in experimental animal models.

Gestational stress, placental norepinephrine transporter and offspring fertility

Chronic cold stress produces adrenergic overload that can affect fetal development. The placental norepinephrine transporter (NET) clears norepinephrine (NE) from both maternal circulation and the fetus during gestation. If this system fails, NE clearance can be reduced, leading to high fetal exposure to NE. The main aim of this study was to determine the changes in NET expression during gestation and their relationship with the functional capacity of NET to transport NE under stressful conditions. Additionally, this study correlated these findings with the reproductive capacity of 2nd-generation progeny. Pregnant rats were subjected to chronic cold stress at 4°C for 3 h each day throughout their pregnancies. We found that exposure of pregnant rats to sympathetic stress caused the following effects: increased NE and corticosterone levels throughout pregnancy, decreased capacity of the placenta to clear NE from the fetus to the mother's circulation, altered NET protein levels depending on the sex of the fetus and increased placental and body weights of pups. For the first time, we also described the disrupted fertility of progeny as adults. Increased NE plasma levels during pregnancy under sympathetic stress conditions correlated with decreased NET functionality that provoked changes in the development of progeny and their fertility in adulthood.

Participation of the extrinsic cholinergic innervation in the action of nitric oxide on the ovarian steroidogenesis in the first proestrous in rats

An ex-vivo Coeliac Ganglion-Superior Ovarian Nerve-Ovary (CG-SON-O) system and an ovary without peripheral neural influence from virgin rats in the first proestrous were used to test whether ovarian extrinsic innervation and nitric oxide (NO) affects steroidogenesis in the ovary. The CG and the ovary were placed in separate buffered-compartments, connected by the SON. Stimulation of the CG was achieved by 10(-6)M acetylcholine (Ach). The ovary without peripheral neural influence was placed alone in a buffered-compartment. To test a possible role of NO in the ovarian response to peripheral neural influence, 100μM sodium nitroprusside (SNP, an NO donor) and 100μM N(G)-nitro-l-arginine methyl ester (l-NAME, an inhibitor of NO synthase) were added to the ovarian compartment separately. In the CG-SON-O system, SNP into the ovarian compartment increased the concentration of NO, reduced the release of progesterone and increased the release of estradiol (E2), increasing the mRNAs related to their synthesis enzyme. The addition of l-NAME to the ovarian compartment caused an opposite effect. In the ovary alone, NO manifested an antisteroidogenic effect on both hormones. These results show that the ovarian extrinsic innervation maintains a direct relationship between NO and E2, both needed at high levels during the follicular phase, allowing the continuity of the estrous cycle.

In vivo blockade of acetylcholinesterase increases intraovarian acetylcholine and enhances follicular development and fertility in the rat

Growth and differentiation of ovarian follicles are regulated by systemic and local factors, which may include acetylcholine (ACh). Granulosa cells (GCs) of growing follicles and luteal cells produce ACh and in cultured GCs it exerts trophic actions via muscarinic receptors. However, such actions were not studied in vivo. After having established that rat ovarian GCs and luteal cells express the ACh-metabolizing enzyme ACh esterase (AChE), we examined the consequences of local application of an AChE inhibitor, huperzine A (HupA), by osmotic minipump delivery into the ovarian bursa of hemiovariectomized rats. Saline was used in the control group. Local delivery of HupA for 4 weeks increased ovarian ACh content. Estrus cyclicity was not changed indicating a locally restricted range of HupA action. The number of primordial and primary follicles was unaffected, but small secondary follicles significantly increased in the HupA group. Furthermore, a significant increase in the number of corpora lutea suggested increased ovulatory events. In support, as shown upon mating, HupA-treated females had significantly increased implantation sites and more pups. Thus the data are in support of a trophic role of ACh in follicular development and ovulation and point to an important role of ACh in female fertility.

Reproductive alterations in hyperinsulinemic but normoandrogenic MSG obese female rats

Obesity and metabolic syndrome are the common causes of reproductive and fertility disorders in women. In particular, polycystic ovary syndrome, which is clinically characterized by hyperandrogenism, oligo/anovulation, and polycystic ovarian morphology, has been increasingly associated with metabolic disorders. However, given the broad interplay between metabolic and reproductive functions, this remains a field of intense research. In this study, we investigated the effect of monosodium l-glutamate (MSG)-induced obesity on reproductive biology of female rats. Newborn female rats were subcutaneously injected with MSG (4g/kg/day) or equiosmolar saline (CTR) each 2 days up to postnatal day (pnd) 10. On pnd 60, estrous cycle was evaluated using vaginal smears twice a day for 15 days, which showed MSG rats to be oligocyclic. Thereafter, animals were killed on estrous phase for blood and tissue collection. MSG rats had increased body mass, accumulation of retroperitoneal and visceral fat pads, and visceral adipocyte hypertrophy compared with CTR rats. MSG rats were also dyslipidemic and hyperinsulinemic but were normoglycemic and normoandrogenic. Ovarian morphology analysis showed that MSG rats had a two-fold decrease in oocyte count but a six-fold increase on ovarian follicular cysts, along with a higher number of total primordial and atretic follicles. Moreover, MSG rats had a four-fold increase in anti-Müllerian hormone immunohistochemical staining on antral follicles. Taken together, data presented here characterize MSG obesity as a unique model to study the metabolic pathways underlying reproductive disorders in the absence of overactivated hypothalamic-pituitary-gonadal axis.

Noradrenaline modulates the presence of gonadotropin-releasing hormone in ovary. The importance of its interrelation on the ovarian steroidogenesis and apoptosis on dioestrus II in rat

The aim of this work was to investigate if noradrenaline (NA), added in the coeliac ganglion -superior ovarian nerve- ovary system (CG-SON-O) and in ovary incubation, modifies the release of ovarian progesterone (P4), gonadotropin-releasing hormone (GnRH) and oestradiol (E2), and the expression of 3β-HSD and 20α-HSD and proapoptotic bax and antiapoptotic bcl-2 on dioestrus II in the rat. The CG-SON-O system and the ovary were removed and placed in one cuvette containing Krebs-Ringer solution (control groups), and NA was added to the ganglion compartment in the ex vivo system and in the ovary compartment in the ovary incubation (experimental groups). P4, GnRH and E2 were measured by RIA, and gene expression was measured by RT-PCR. In the ex-vivo system, the release of ovarian P4 and GnRH and the expression of 3β-HSD and bax decreased; E2 and bcl-2 increased, and the bax/bcl-2 ratio decreased. However, in the ovary incubation, P4, GnRH, the expression of 3β-HSD and bax increased; E2, the expression of 20α-HSD and bcl-2 decreased while the bax/bcl-2 ratio increased, thus favoring apoptosis. The peripheral nervous system protected the ovary from the apoptotic mechanisms while in the ovary incubation the effect was reverted. Our results indicate that NA regulates ovarian steroidogenesis and apoptosis by modulating GnRH release from the coeliac ganglion and ovary, being NA a possible generator of a GnRH-gonadotropins axis in the ovary. This work is expected to contribute with new evidence of the clinical importance of catecholamines and GnRH in therapy and prevention of ovarian pathologies.

Preimplantation genetic diagnosis (PGD) influences adrenal development and response to cold stress in resulting mice

Preimplantation genetic diagnosis (PGD) has gained widespread application in clinical medicine and hence the health of PGD offspring needs to be systematically assessed. Given the critical role of the stress response in growth and health, assessments of the development and function of the stress system might help to clarify the health outcomes of PGD. In this study, we constructed a PGD-conceived mouse model and used naturally conceived mice as controls; we used this model to evaluate the potential effect of PGD procedures on the stress system of the offspring. Serum and tissues of stress organs, namely the hypothalamus, locus coeruleus and adrenal gland, were collected from 5-week-old mice in the basal state or after cold stress. The serum levels of stress-related hormones and the structural and functional indices of the stress organs were then examined. In the basal state, ultrastructural abnormalities and low expression of genes involved in steroid hormone synthesis were found in the adrenals of the PGD mice, which had low corticosterone and high epinephrine levels compared with those of control mice. After acute cold stress, the PGD mice continued to show structural and glucocorticoid secretion abnormalities resulting in a late response to the environmental change. Thus, our study indicates that PGD manipulations affect adrenal development, result in structural and functional abnormalities of the adrenals in the offspring and influence their reactivity and adaptability to cold stress.

Unilateral or bilateral vagotomy induces ovulation in both ovaries of rats with polycystic ovarian syndrome

BACKGROUND

Injecting estradiol valerate (EV) to pre-pubertal or adult female rat results in effects similar to those observed in women with polycystic ovarian syndrome (PCOS). One of the mechanisms involved in PCOS development is the hyperactivity of the sympathetic nervous system. In EV-induced PCOS rats, the unilateral sectioning of the superior ovarian nerve (SON) restores ovulation of the innervated ovary. This suggests that, in addition to the sympathetic innervation, other neural mechanisms are involved in the development/maintenance of PCOS. The aims of present study were analyze if the vagus nerve is one of the neural pathways participating in PCOS development.

METHODS

Ten-day old rats were injected with EV dissolved in corn oil. At 24-days of age sham-surgery, unilateral, or bilateral sectioning of the vagus nerve (vagotomy) was performed on these rats. The animals were sacrificed at 90-92 days of age, when they presented vaginal estrous preceded by a pro-estrus smear.

RESULTS

In EV-induced PCOS rats, unilateral or bilateral vagotomy restored ovulation in both ovaries. Follicle-stimulating hormone (FSH) levels in PCOS rats with unilateral or bilateral vagotomy were lower than in control rats.

CONCLUSIONS

This result suggests that in EV-induced PCOS rats the vagus nerve is a neural pathway participating in maintaining PCOS. The vagus nerve innervates the ovaries directly and indirectly through its synapsis in the celiac-superior-mesenteric ganglion, where the somas of neurons originating in the SON are located. Then, it is possible that vagotomy effects in EV-induced PCOS rats may be explained as a lack of communication between the central nervous system and the ovaries.

Transitory activation of the central and ovarian norepinephrine systems during cold stress-induced polycystic ovary in rats

Cold stress-induced ovarian sympathetic activation is associated with the development of ovarian cysts in rats. Although we have hypothesised that polycystic ovary (PCO) features induced by cold stress, as prevented by lesion of the noradrenergic nucleus locus coeruleus (LC), were a result of the increased activity of the ovarian norepinephrine (NE) system, this was not evident after 8 weeks of stress. In the present study, we investigated the temporal changes in LC and ovarian NE activities and steroid secretion in rats exposed to single (SS) or repeated (RS) cold stress. SS and 4 week (4W)-RS but not 8 week (8W)-RS increased c-Fos expression in the LC and ovarian NE release. Plasma oestradiol, testosterone and progesterone levels tended to increase in 4W-RS and were elevated in 8W-RS rats, which displayed PCO morphology. β-adrenergic receptor agonist increased steroid hormone release from the ovary of unstressed (US) but not from 8W-RS rats. To determine whether increased activity of noradrenergic system during the initial 4 weeks of RS would be sufficient to promote PCO, rats were exposed to 4 weeks of cold stress and kept in ambient temperature for the next 4 weeks (4W-RS/4W-US). Accordingly, PCO morphology, increased steroid secretion and decreased ovulation rate were found in 4W-RS/4W-US rats, strengthening the hypothesis that the initial increase in NE release triggers the development of PCO. The correlated activity of LC neurones and ovarian noradrenergic terminals and the induction of PCO in 4W-RS/4W-US rats provide functional evidence for a major role of NE in disrupting follicular development and causing the long-lasting endocrine abnormalities found in stress-induced PCO.

Evidence for a celiac ganglion-ovarian kisspeptin neural network in the rat: intraovarian anti-kisspeptin delays vaginal opening and alters estrous cyclicity

Kisspeptin and its receptor GPR54 have been described as key hypothalamic components in the regulation of GnRH secretion. Kisspeptin is also present in several regions of the central nervous system and the peripheral organs and has recently been identified in the superior ganglion. Herein, we tested the possibility that ovarian kisspeptin is regulated by the sympathetic nervous system and participates locally in the regulation of ovarian function. Both ovarian and celiac ganglion kisspeptin mRNA levels increase during development, whereas kisspeptin peptide levels and plasma levels decrease during development. In the celiac ganglion, kisspeptin colocalized with tyrosine hydroxylase, indicating potential kisspeptin synthesis and transport within the sympathetic neurons. A continuous (64 h) cold stress induced marked changes within the kisspeptin neural system along the celiac ganglion-ovary axis. In vitro incubation with the β-adrenergic agonist isoproterenol increased ovarian kisspeptin mRNA and peptide levels, and this increase was inhibited by treatment with the β-antagonist propranolol. Sectioning the superior ovarian nerve altered the feedback information within the kisspeptin celiac ganglion-ovary axis. In vivo administration of a kisspeptin antagonist to the left ovarian bursa of 22- to 50-d-old unilaterally ovariectomized rats delayed the vaginal opening, decreased the percentage of estrous cyclicity, and decreased plasma, ovarian, and celiac ganglion kisspeptin concentrations but did not modify the LH plasma levels. These results indicate that the intraovarian kisspeptin system may be regulated by sympathetic nerve activity and that the peptide, either from a neural or ovarian origin, is required for proper coordinated ovarian function.

Hormonal programming across the lifespan

Hormones influence countless biological processes across an animal's lifespan. Many hormone-mediated events occur within developmental sensitive periods, during which hormones have the potential to cause permanent tissue-specific alterations in anatomy and physiology. There are numerous selective critical periods in development with different targets being affected during different periods. This review outlines the proceedings of the Hormonal Programming in Development session at the US-South American Workshop in Neuroendocrinology in August 2011. Here we discuss how gonadal steroid hormones impact various biological processes within the brain and gonads during early development and describe the changes that take place in the aging female ovary. At the cellular level, hormonal targets in the brain include neurons, glia, or vasculature. On a genomic/epigenomic level, transcription factor signaling and epigenetic changes alter the expression of critical hormone receptor genes across development and following ischemic brain insult. In addition, organizational hormone exposure alters epigenetic processes in specific brain nuclei and may be an important mediator of sexual differentiation of the neonatal brain. Brain targets of hormonal programming, such as the paraventricular nucleus of the hypothalamus, may be critical in influencing the development of peripheral targets, such as the ovary. Exposure to excess hormones can cause abnormalities in the ovary during development leading to polycystic ovarian syndrome (PCOS). Exposure to excess androgens during fetal development also has a profound effect on the development of the male reproductive system. In addition, increased activity of the sympathetic nerve and stress during early life have been linked to PCOS symptomology in adulthood. Finally, we describe how age-related decreases in fertility are linked to high levels of nerve growth factor (NGF), which enhances sympathetic nerve activity and alters ovarian function.

Vagus nerve stimulation enhances perforant path-CA3 synaptic transmission via the activation of β-adrenergic receptors and the locus coeruleus

Vagus nerve stimulation (VNS) is an approved treatment for epilepsy and depression and has cognition-enhancing effects in patients with Alzheimer's disease. The hippocampus is widely recognized to be related to epilepsy, depression, and Alzheimer's disease. One possible mechanism of VNS involves its effect on the hippocampus; i.e. it increases the release of noradrenaline in the hippocampus. However, the effect of VNS on synaptic transmission in the hippocampus is unknown. To determine whether VNS modulates neurotransmission in the hippocampus, we examined the effects of VNS on perforant path (PP)-CA3 synaptic transmission electrophysiologically in anaesthetized rats. VNS induces a persistent enhancement of PP-CA3 field excitatory post-synaptic potentials (fEPSPs). Arc, an immediate early gene, was used to identify active brain regions after VNS. The locus coeruleus (LC), which contains the perikarya of noradrenergic projections, harboured more Arc-positive cells, as measured by in-situ hybridization, after 10-min VNS. In addition, electrical lesions of LC neurons or intraventricular administration of the β-adrenergic receptor antagonist timolol prevented the enhancement of PP-CA3 responses by VNS. In conclusion, the protracted increase in PP-CA3 synaptic transmission that is induced by VNS entails activation of the LC and β-adrenergic receptors. Our novel findings suggest that information from the periphery modulates synaptic transmission in the CA3 region of the hippocampus.

Sympathetic nerve activity in normal and cystic follicles from isolated bovine ovary: local effect of beta-adrenergic stimulation on steroid secretion

Cystic ovarian disease (COD) is an important cause of abnormal estrous behavior and infertility in dairy cows. COD is mainly observed in high-yielding dairy cows during the first months post-partum, a period of high stress. We have previously reported that, in lower mammals, stress induces a cystic condition similar to the polycystic ovary syndrome in humans and that stress is a definitive component in the human pathology. To know if COD in cows is also associated with high sympathetic activity, we studied isolated small antral (5 mm), preovulatory (10 mm) and cystic follicles (25 mm). Cystic follicles which present an area 600 fold greater compared with preovulatory follicles has only 10 times less concentration of NE as compared with small antral and preovulatory follicles but they had 10 times more NE in follicular fluid, suggesting a high efflux of neurotransmitter from the cyst wall. This suggestion was reinforced by the high basal release of recently taken-up 3H-NE found in cystic follicles. While lower levels of beta-adrenergic receptor were found in cystic follicles, there was a heightened response to the beta-adrenergic agonist isoproterenol and to hCG, as measured by testosterone secretion. There was however an unexpected capacity of the ovary in vitro to produce cortisol and to secrete it in response to hCG but not to isoproterenol. These data suggest that, during COD, the bovine ovary is under high sympathetic nerve activity that in addition to an increased response to hCG in cortisol secretion could participate in COD development.

Neonatal programming by immunological challenge: effects on ovarian function in the adult rat

Neonatal exposure to an immunological challenge (lipopolysaccharide, LPS) increases the activity of hypothalamo-pituitary-adrenal axis and sensitises the GNRH pulse generator to the inhibitory influence of stress in adult rats. We investigated the effects of neonatal exposure to LPS on various reproductive parameters during puberty and into adulthood in female rats. LPS (50 μg/kg, i.p.) or saline was administered on postnatal days 3 and 5. Vaginal opening was recorded, and oestrous cyclicity was monitored immediately post puberty and again at 8-9 weeks of age. At 10 weeks of age, the ovaries were removed and the number of follicles was counted, together with the thickness of the theca interna of the largest antral follicles. Ovarian sympathetic nerve activity was assessed immunohistochemically by measurement of the levels of ovarian low-affinity receptor of nerve growth factor (p75NGFR). In rats exposed to LPS in early life, there was a significant delay in puberty and disruption of oestrous cyclicity immediately post puberty, which persisted into adulthood. The follicle reserve was decreased, the thickness of the theca interna increased and the expression profile of ovarian p75NGFR increased in the neonatal LPS-treated animals. These data suggest that exposure to LPS during early neonatal life can have long-term dysfunctional effects on the female reproductive system, which might involve, at least in part, increased ovarian sympathetic nerve activity.

Cold-induced glutamate release in vivo from the magnocellular region of the paraventricular nucleus is involved in ovarian sympathetic activation

We previously reported that centrally-induced sympathetic activation in response to cold stress is associated with a polycystic ovarian condition in rats, and thyrotrophin-releasing hormone (TRH) released locally from the magnocellular region of the paraventricular nucleus (PVN) appears to be involved in this activation. Because TRH neurones express NMDA glutamate receptors, in the present study, we investigated the role of glutamate in the increased release of TRH from magnocellular neurones induced by cold stress and its relationship to ovarian neurotransmission. Animals with a push-pull cannula stereotaxically implanted into the magnocellular portion of the PVN were exposed to cold stress (4 degrees C for 64 h) and subjected to intracerebral perfusion. Perfusate fractions were obtained and analysed by high-performance liquid chromatography to measure glutamate and GABA levels. Glutamate, but not GABA, release increased significantly in animals perfused under cold exposure. In vivo administration of glutamate to the PVN increased TRH release. Injection of MK-801 into the magnocellular portion of the PVN reduced ovarian noradrenaline turnover and led to an increase in catecholamine concentration from the adrenal glands and celiac ganglia. Taken together, the results obtained in the present study strongly suggest that glutamate release from the magnocellular PVN is sensitive to cold stress and that glutamate acts through the NMDA receptor to mediate cold-induced TRH release. This in turn triggers hypothalamic-ovarian pathway activation, which might be responsible for the polycystic condition induced by cold stress and other ovarian pathologies characterised by increased sympathetic discharge.

Kisspeptin regulates prolactin release through hypothalamic dopaminergic neurons

Prolactin (PRL) is tonically inhibited by dopamine (DA) released from neurons in the arcuate and periventricular nuclei. Kisspeptin plays a pivotal role in LH regulation. In rodents, kisspeptin neurons are found mostly in the anteroventral periventricular and arcuate nuclei, but the physiology of arcuate kisspeptin neurons is not completely understood. We investigated the role of kisspeptin in the control of hypothalamic DA and pituitary PRL secretion in adult rats. Intracerebroventricular kisspeptin-10 (Kp-10) elicited PRL release in a dose-dependent manner in estradiol (E2)-treated ovariectomized rats (OVX+E2), whereas no effect was found in oil-treated ovariectomized rats (OVX). Kp-10 increased PRL release in males and proestrous but not diestrous females. Associated with the increase in PRL release, intracerebroventricular Kp-10 reduced Fos-related antigen expression in tyrosine hydroxylase-immunoreactive (ir) neurons of arcuate and periventricular nuclei in OVX+E2 rats, with no effect in OVX rats. Kp-10 also decreased 3,4-dihydroxyphenylacetic acid concentration and 3,4-dihydroxyphenylacetic acid-DA ratio in the median eminence but not striatum in OVX+E2 rats. Double-label immunofluorescence combined with confocal microscopy revealed kisspeptin-ir fibers in close apposition to and in contact with tyrosine hydroxylase-ir perikarya in the arcuate. In addition, Kp-10 was not found to alter PRL release from anterior pituitary cell cultures regardless of E2 treatment. We provide herein evidence that kisspeptin regulates PRL release through inhibition of hypothalamic dopaminergic neurons, and that this mechanism is E2 dependent in females. These findings suggest a new role for central kisspeptin with possible implications for reproductive physiology.

Superior ovarian nerve (SON) transection leads to stunted follicular maturation: a histomorphologic and morphometric analysis in the rat model

Histomorphologic and morphometric effects of peripubertal superior ovarian nerve (SON) transection were evaluated during adult life in rats. Twenty Sprague-Dawley rats were randomly divided into two groups: the SON-transected (SON-t) group (n = 10) and the sham-operated control group (n = 10). Total follicle development was not influenced; however, follicular maturation was seriously stunted by the procedure, as evidenced by significantly thinner theca interna and follicular wall.

Ovarian-steroid modulation of locus coeruleus activity in female rats: involvement in luteinising hormone regulation

The noradrenergic nucleus locus coeruleus (LC) has been reported to regulate luteinising hormone (LH) secretion in female rats. Both oestrogen and progestin receptors have been demonstrated in LC neurones, suggesting that these cells are possibly responsive to variations in circulating levels of ovarian steroids. We therefore evaluated changes in the activity of LC neurones during the oestrous cycle and after ovarian-steroid treatment in ovariectomised (OVX) rats, as determined by immunoreactivity to Fos-related antigens (FRA), which comprises all of the known members of the Fos family. Effects of ovarian steroids on the firing rate of LC neurones were also determined in a slice preparation. The number of FRA/tyrosine hydroxylase (TH)-immunoreactive (ir) neurones in the LC increased from 14.00-16.00 h on pro-oestrus, coinciding with the onset of the LH surge and rise in plasma progesterone. FRA immunoreactivity was unaltered during dioestrus. Oestradiol-treated OVX rats (OVX+E) displayed marked reduction in FRA/TH-ir neurones in LC compared to oil-treated OVX rats. Accordingly, oestradiol superfusion significantly reduced the spontaneous firing rate of LC neurones in slices from OVX rats. Compared to OVX+E, oestradiol-treated rats injected with progesterone at 08.00 h (OVX+EP) exhibited higher number of FRA/TH-ir neurones in the LC at 10.00 h and 16.00 h, and great amplification of the LH surge. Bath application of progesterone significantly increased the spontaneous firing rate of OVX+E LC neurones. Our data suggest that ovarian steroids may physiologically modulate the activity of LC neurones in females, with possible implications for LH secretion. Moreover, oestradiol and progesterone appear to exert opposite and complementary effects (i.e. whereas oestradiol inhibits, progesterone, after oestradiol priming, stimulates LC activity).

Chronic-intermittent cold stress in rats induces selective ovarian insulin resistance

In rat ovary chronic cold stress increases sympathetic nerve activity, modifies follicular development, and initiates a polycystic condition. To see whether there is a relationship between the previously described changes in follicular development and metabolic changes similar to those in women with polycystic ovary, we have studied the effect of chronic cold stress (4 degrees C for 3 h/day, Monday to Friday, for 4 wk) on insulin sensitivity and the effect of insulin on sympathetic ovarian activity. Although cold-stressed rats ate more than the controls, they did not gain more weight. Insulin sensitivity, determined by hyperinsulinemic-euglycemic clamp, was significantly increased in the stressed animals. Insulin in vitro increased the basal release of norepinephrine from the ovaries of control rats but not from those of stressed rats, suggesting a local neural resistance to insulin in stressed rats. The levels of mRNA and protein for IRS1 and SLC2A4 (also known as GLUT4), molecules involved in insulin signaling, decreased significantly in the ovaries but not in the muscle of stressed rats. This decrease was preferentially located in theca-interstitial cells compared with granulosa cells, indicating that theca cells (the only cells directly innervated by sympathetic nerves) are responsible for the ovarian insulin resistance found in stressed rats. These findings suggest that ovarian insulin resistance produced by chronic stress could be in part responsible for the development of the polycystic condition induced by stress.

Catecholamine uptake, storage, and regulated release by ovarian granulosa cells

Catecholamines present in the mammalian ovary are involved in many normal aspects of ovarian functions, including initial follicle growth, steroidogenesis, and pathological states such as polycystic ovary syndrome. Sympathetic nerve fibers are the largest source of norepinephrine (NE), but not the only one. Surgical denervation of the rat ovary reduces, but does not eliminate, the ovarian content of NE. The aim of this work was to explore which intraovarian cells may participate in the ovarian NE homeostasis and the mechanisms involved. It was found that denervated rat ovaries can take up NE and cocaine considerably, decreased its uptake, suggesting involvement of catecholamine transporters. Granulosa cells of rat ovarian follicles present dopamine transporter and NE transporter. Their functionality was confirmed in isolated rat granulosa cells while cocaine blocked the uptake of NE. Furthermore, the presence of the vesicular monoamine transporter 2, together with the exocytotic protein (synaptosome-associated protein of 25 kDa) in granulosa cells, implies catecholamine storage and regulated release. Regulated calcium-dependent release of NE was shown after depolarization by potassium, implying all neuron-like cellular machinery in granulosa cells. These results in rats may be of relevance for the human ovary because dopamine transporter, NE transporter, vesicular monoamine transporter 2, and synaptosome-associated protein of 25-kDa protein and mRNA are found in human ovarian follicles and/or isolated granulosa cells. Thus, ovarian nonneuronal granulosa cells, after taking up catecholamines, can serve as an intraovarian catecholamine-storing compartment, releasing them in a regulated way. This suggests a more complex involvement of catecholamines in ovarian functions as is currently being recognized.

Ventilation and phrenic output following high cervical spinal hemisection in male vs. female rats

Female sex hormones influence the neural control of breathing and may impact neurologic recovery from spinal cord injury. We hypothesized that respiratory recovery after C2 spinal hemisection (C2HS) differs between males and females and is blunted by prior ovariectomy (OVX) in females. Inspiratory tidal volume (VT), frequency (fR), and ventilation (VE) were quantified during quiet breathing (baseline) and 7% CO2 challenge before and after C2HS in unanesthetized adult rats via plethysmography. Baseline breathing was similarly altered in all rats (reduced VT, elevated fR) but during hypercapnia females had relatively higher VT (i.e. compared to pre-injury) than male or OVX rats (p<0.05). Phrenic neurograms recorded in anesthetized rats indicated that normalized burst amplitude recorded ipsilateral to C2HS (i.e. the crossed phrenic phenomenon) is greater in females during respiratory challenge (p<0.05 vs. male and OVX). We conclude that sex differences in recovery of VT and phrenic output are present at 2 weeks post-C2HS. These differences are consistent with the hypothesis that ovarian sex hormones influence respiratory recovery after cervical spinal cord injury.