Comparative Study on the Estimation of Estrous Cycle in Mice by Visual and Vaginal Lavage Method

Overestimation of sex differences in psychostimulant activity via comparisons of males and females from different behavioral groups

Background

There are inconsistencies in the observation of sex differences in baseline activity and psychostimulant activity. To address this, we have developed the MISSING (Mapping Intrinsic Sex Similarities as an Integral quality of Normalized Groups) model. MISSING model proposes that sex similarities are observed when we compare similar behavioral groups of males and females, with sex differences occurring when we compare distinct groups of sexes, but this model has not been tested.

Methods

To test this model, we identified within-sex groups of Sprague Dawley rats (male n = 22, female n = 23) by conducted normal mixtures clustering of baseline activity, cocaine activity (as distance traveled in cm over 90 min) and cocaine activity normalized-to-baseline activity (NBA) of all subjects. We employed 2-way ANOVA to determine the impact of within-sex heterogeneity on sex differences. We compared our cluster-based method to current median-split approaches.

Results

Our new cluster-based method revealed three distinct clusters, each consisting of both males and females. We determined there were no sex differences in any of the variables when males and females from the same clusters were compared. The within-sex clusters for females were not defined by estrous phase. Median split analysis was ineffective in accurately identifying within-sex groups.

Conclusions

Our results validate the MISSING model: there are no sex differences in psychostimulant activity except when we compare males and females from different behavioral groups. This has significant implications for how we proceed with research towards understanding the mechanism governing sex differences in psychostimulant activity.

Activity of isoflavone in managing polycystic ovary syndrome symptoms (Review)

Polycystic ovary syndrome (PCOS), a hormonal and metabolic disorder manifested in women of reproductive age, is still being treated using drugs with side effects. As an alternative to these drugs, isoflavone, also identified as phytoestrogen, has anti-PCOS activity. Isoflavone can help relieve PCOS symptoms by lowering the level of testosterone, which causes hyperandrogenism, thereby normalizing the menstrual cycle and restoring normal ovarian morphology. Furthermore, isoflavone influences the improvement of the metabolic profile, which changes because of PCOS, as well as the reduction of inflammatory markers and oxidative stress. However, both significant and non-significant results have been generated on the activity of isoflavones in PCOS. The present review aims to discuss the existing literature on the effect of isoflavone on PCOS symptoms based on in vivo and clinical trial studies.

Engagement of basal amygdala-nucleus accumbens glutamate neurons in the processing of rewarding or aversive social stimuli

Basal amygdala (BA) neurons projecting to nucleus accumbens (NAc) core/shell are primarily glutamatergic and are integral to the circuitry of emotional processing. Several recent mouse studies have addressed whether neurons in this population(s) respond to reward, aversion or both emotional valences. The focus has been on processing of physical emotional stimuli, and here, we extend this to salient social stimuli. In male mice, an iterative study was conducted into engagement of BA-NAc neurons in response to estrous female (social reward, SR) and/or aggressive-dominant male (social aversion, SA). In BL/6J mice, SR and SA activated c-Fos expression in a high and similar number/density of BA-NAc neurons in the anteroposterior intermediate BA (int-BA), whereas activation was predominantly by SA in posterior (post-)BA. In Fos-TRAP2 mice, compared with SR-SR or SA-SA controls, exposure to successive presentation of SR-SA or SA-SR, followed by assessment of tdTomato reporter and/or c-Fos expression, demonstrated that many int-BA-NAc neurons were activated by only one of SR and SA; these SR/SA monovalent neurons were similar in number and present in both magnocellular and parvocellular int-BA subregions. In freely moving BL/6J mice exposed to SR, bulk GCaMP6 fibre photometry provided confirmatory in vivo evidence for engagement of int-BA-NAc neurons during social and sexual interactions. Therefore, populations of BA-NAc glutamate neurons are engaged by salient rewarding and aversive social stimuli in a topographic and valence-specific manner; this novel evidence is important to the overall understanding of the roles of this pathway in the circuitry of socio-emotional processing.

Mmp2 Deficiency Leads to Defective Parturition and High Dystocia Rates in Mice

Parturition is the final and essential step for mammalian reproduction. While the uterus is quiescent during pregnancy, fundamental changes arise in the myometrial contractility, inducing fetal expulsion. Extracellular matrix (ECM) remodeling is fundamental for these events. The gelatinases subgroup of matrix metalloproteinases (MMPs), MMP2 and MMP9, participate in uterine ECM remodeling throughout pregnancy and parturition. However, their loss-of-function effect is unknown. Here, we determined the result of eliminating Mmp2 and/or Mmp9 on parturition in vivo, using single- and double-knockout (dKO) mice. The dystocia rates were measured in each genotype, and uterine tissue was collected from nulliparous synchronized females at the ages of 2, 4, 9 and 12 months. Very high percentages of dystocia (40-55%) were found in the Mmp2-/- and dKO females, contrary to the Mmp9-/- and wild-type females. The histological analysis of the uterus and cervix revealed that Mmp2-/- tissues undergo marked structural alterations, including highly enlarged myometrial, endometrial and luminal cavity. Increased collagen deposition was also demonstrated, suggesting a mechanism of extensive fibrosis in the Mmp2-/- myometrium, which may result in dystocia. Overall, this study describes a new role for MMP2 in myometrium remodeling during mammalian parturition process, highlighting a novel cause for dystocia due to a loss in MMP2 activity in the uterine tissue.

Re-evaluation of mouse models of endometriosis for pathological and immunological research

Endometriosis is an estrogen-dependent gynecological disease with chronic pelvic inflammation. In order to study the pathophysiology of endometriosis and examine the therapeutic effects of new pharmaceuticals for endometriosis treatment, different animal models had been developed in the last two decades, especially mouse models. However, no study evaluated the effects of various modeling approaches on pathology and immunology in endometriosis. This study aimed to compare endometriotic lesion development and immune profiles under different methods of establishing endometriosis models in mice, including estrus synchronization (ovariectomy with estrogen supplement versus male urine-soaked transfer bedding), endometrium preparations (whole uterus including endometrium and myometrium fragments versus solely endometrium fragments), and surgical transplantation (subcutaneous transplantation versus intraperitoneal injection). Our results showed that lesion growth under estrus synchronization by ovariectomy with estrogen supplement had a higher success rate and more proliferative endometrium, apart from higher body weight gain. Immune responses in peripheral blood were similar in the whole uterus and solely endometrium fragments and in intraperitoneal injection and subcutaneous transplantation, but a more innate immune response in the peritoneal microenvironment was found in solely endometrium fragments and intraperitoneal injection than counterparts. In conclusion, different endometriosis modeling methods result in different pathological and immunological features. Ovariectomy with estrogen supplement, solely endometrium fragments, and intraperitoneal injection are more suitable for both pathological and immunological studies of endometriosis in mice, which are important for mechanistic studies and immunotherapy development.

Long Term Oral Administration of Oregano Essence Effectively Relieves Polycystic Ovarian Rats through Endocrine and Inflammatory Balance

Polycystic ovarian syndrome (PCOS) is alarmingly rising and sustainable therapy/prevention is needed. Here, we evaluated the therapeutic effects of oregano or Origanum vulgare (O. vulgare) essence (OE) on the PCOS rat model system. Vaginal smears monitored the estrous cycle of 40 virgin adult rats, and they received 2 mg estradiol valerate (EV)/0.2 ml corn oil intramuscularly to induce PCOS. At 60 days post-EV injection, all rats were evaluated for follicular development/cysts. The EV-induced PCOS rats were orally administered 250 and 500 mg/kgBW/day of OE for 30 days. OE was also further assessed for its predominant components along with hormonal, histological, and inflammatory-related gene expressions in the ovaries. The main components of the OE were predominantly pulegone (36.3), L-menthone (31.3%), far less piperitone (7.8%), isopiperitone (6.4%), isomenthol (3.6%), humulene epoxide II (2.2%), α-pinene (1.7%), and thymol (1.5%). Hormonal, histological, and inflammatory-related gene expression results showed >4-fold and 1.5-fold increase in FSH and progesterone; ∼50%, 85%, 45%, 55%, and 30% decreased in LH, estradiol, estrogen, testosterone, and AMH; and dose-dependently decreased in mRNA expression of IL-6, IL-1α, NF-kB, TNF-α, and IL-1β by 25–65%, 55–75%, 15–40%, 30–55%, and 35–55%, respectively, and thus decreased the severity of PCOS, boosted endocrine balance, restored functional follicles and corpus luteum, and thus ovulation in PCOS rats. Overall, in the disrupted PCOS rats, OE oral treatment effectively relieved estradiol-induced PCOS rats via: (1) its endocrine balancing on GnRH, FSH, and LH and (2) its anti-inflammatory and antioxidant properties on ovary caused by OE's useful compounds like pulegone, thymol, and L-menthone. Though many aspects of the effects remain to be tested, such an underlying mechanistic reproductive regulatory effect observed in OE-administered rats further proves its sensible pharmaceutical applications in reproductive medicine and more specifically, PCOS.

Network Pharmacology-Based Prediction and Verification of the Potential Mechanisms of He's Yangchao Formula against Diminished Ovarian Reserve

Background

He's Yangchao formula (HSYC) has been clinically proven to be effective in treating diminished ovarian reserve (DOR). However, the underlying molecular mechanisms of HSYC in DOR are unclear.

Objective

This study aims to predict the underlying mechanisms of He's Yangchao formula (HSYC) against DOR through network pharmacology strategies and verify in vivo.

Methods

Systematic network pharmacology was used to speculate the bioactive components, potential targets, and the underlying mechanism of HSYC in the treatment of DOR. Then, the CTX-induced DOR mouse model was established to verify the effect of HSYC against DOR and the possible molecular mechanisms as predicted in the network pharmacology approach.

Results

A total of 44 active components and 423 potential targets were obtained in HSYC. In addition, 91 targets of DOR were also screened. The identified hub genes were AKT1, ESR1, IL6, and P53. Further molecular docking showed that the four hub targets were well-bound with their corresponding compounds. In vivo experiments showed that HSYC could promote the recovery of the estrous cycle and increase the number of primordial, growing follicles and corpora lutea. Besides, The results of qRT-PCR showed HSYC could regulate the expression of AKT1, ESR1, P53, and IL6 in DOR mice.

Conclusion

It was demonstrated that HSYC could increase ovarian reserves, and AKT1, ESR1, IL6, and P53 may play an essential role in this effect, which provided a new reference for the current lack of active interventions of DOR.

Influence of ethanolic extract of avocado (Persea americana Mill.) seed flour on the estrous cycle, the serum concentrations of reproductive hormones, and the activities of oxidative stress markers in female cavies (Cavia porcellus L.)

OBJECTIVE

The purpose of this study was to determine the effects of the ethanolic extract of avocado seed flour on the estrous cycle characteristics, the concentrations of reproductive hormones [luteinizing hormone (LH) and estradiol], and the activities of some tissues (ovarian and uterine) that are markers of oxidative stress in female guinea pigs (Cavia porcellus).

MATERIALS AND METHODS

Twenty-four female cavies with normal estrous cycles and equivalent body weights (464.25 and 71.88 gm) were randomly assigned to four groups, each with six females. The control group received 1 ml of distilled water orally, whereas the EE100, EE200, and EE400 groups received 100, 200, and 400 mg/kg bw of ethanolic extract of Persea americana seed, respectively. Following that, three consecutive estrous cycles were observed using vaginal smears. After the trial, the females were slaughtered, and blood and organs were gathered for study.

RESULTS

The mean duration of the estrus phase is considerably (p < 0.05) longer in group EE100 animals than in control animals. LH concentrations were substantially (p < 0.05) higher in females in group EE200 than in controls. Total cholesterol levels typically dropped in females in the extract groups, but only significantly (p < 0.05) in those in group EE100 compared to the control group. Serum estradiol levels increased considerably (p < 0.05) in treated females compared to controls. Catalase activity rose considerably (p < 0.05) in the ovaries of group EE400 when compared to the control. Superoxide dismutase activity rose considerably (p < 0.05) in the uterus of female cavies given the extract compared to the control.

CONCLUSION

Avocado seed ethanolic extract prolongs the estrus phase, increases estradiol and LH levels, and protects the uterus from oxidative stress in female cavies.

Insular cortex dopamine 1 and 2 receptors in methamphetamine conditioned place preference and aversion: Age and sex differences

Rodent studies have proposed that adolescent susceptibility to substance use is at least partly due to adolescents experiencing reduced aversive effects of drugs compared to adults. We thus investigated methamphetamine (meth) conditioned place preference/aversion (CPP/CPA) in adolescent and adult mice in both sexes using a high dose of meth (3 mg/kg) or saline as controls. Mice tagged with green-fluorescent protein (GFP) at Drd1a or Drd2 were used so that dopamine receptor 1 (D1) and 2 (D2) expression within the insular cortex (insula) could be quantified. There are sex differences in how the density of D1+ and D2+ cells in the insula changes across adolescence that may be related to drug-seeking behaviors. Immunohistochemistry followed by stereology were used to quantify the density of cells with c-Fos and/or GFP in the insula. Unexpectedly, mice showed huge variability in behaviors including CPA, CPP, or no preference or aversion. Females were less likely to show CPP compared to males, but no age differences in behavior were observed. Conditioning with meth increased the number of D2 + cells co-labelled with c-Fos in adults but not in adolescents. D1:D2 ratio also sex- and age-dependently changed due to meth compared to saline. These findings suggest that reduced aversion to meth is unlikely an explanation for adolescent vulnerability to meth use. Sex- and age-specific expressions of insula D1 and D2 are changed by meth injections, which has implications for subsequent meth use.

The Stage of the Estrus Cycle Is Critical for Interpretation of Female Mouse Social Interaction Behavior

Female animals in biomedical research have traditionally been excluded from research studies due to the perceived added complexity caused by the estrus cycle. However, given the importance of sex differences in a variety of neurological disorders, testing female mice is critical to identifying sex-linked effects in diseases. To determine the susceptibility of simple behaviors to hormonal fluctuations in the estrus cycle, we studied the effects of sex and the estrus cycle on a variety of behavioral tasks commonly used in mouse phenotyping laboratories. Male and female C57BL/6J mice were tested in a small battery of short duration tests and, immediately on completion of each test, females were classified using cytology of vaginal lavages as sexually-receptive (proestrus and estrus) or non-receptive (NR; metestrus and diestrus). We showed that there was a significant difference in 3-chamber social interaction (SI) between female mice at different stages of their estrus cycle, with sexually-receptive mice showing no preferential interest in a novel female mouse compared with an empty chamber. NR female mice showed the same level of preference for a novel female mouse as male mice did for a novel male mouse. No differences between or within sexes were found for tests of anxiety elevated plus maze (EPM; Hole board), working memory [Novel object recognition (NOR)], and motor learning (repeated tests on rotarod). We conclude that the stage of the estrus cycle may impact SI between same-sex conspecifics, and does not impact performance in the elevated plus-maze, hole board, NOR, and rotarod.

Staging of the estrous cycle and induction of estrus in experimental rodents: an update

Background

Determination of the phases of the estrous cycle and induction of estrus (heat) in experimental animals remains useful, especially in reproductive function research.

Main body of the abstract

This review provides a detailed description and discusses extensively the variations observed in different phases of the estrous cycle in laboratory animals using rats and mice as examples. It also illustrates how these phases can be determined and how to induce estrus ‘heat’ when required. The phases of the estrous cycle can be determined using various methods such as visual assessment, vaginal smear/cytology, histology of female reproductive organs (vagina, uterus and ovaries), vaginal wall impedance assessment and determination of urine biochemical parameters. Female animals can be artificially brought to estrus phase ‘heat’ to make them receptive to male counterparts.

Conclusion

Determination of the length and phases of the estrous cycle and induction of estrus are useful in teaching and research and evaluating the effects of drugs/chemicals on the reproductive functions.

Simple Recommendations for Improving Efficiency in Generating Genome-Edited Mice

The generation of transgenic model organisms (primarily mice) is an integral part of modern fundamental and applied research. Simple techniques based on the biology of these laboratory rodents can often increase efficiency when generating genome-edited mouse strains. In this study, we share our three years of experience in the optimization of mouse genome editing based on microinjection of CRISPR/Cas9 components into ca. 10,000 zygotes. We tested a number of techniques meant to improve efficiency in generating knockout mice, such as optimization of the superovulation method and choosing the optimal mouse strains to be used as zygote donors and foster mothers. The presented results might be useful to laboratories aiming to quickly and efficiently create new mouse strains with tailored genome editing.

The effects of myricitrin and vitamin E against reproductive changes induced by D-galactose as an aging model in female mice: An experimental study

Background

Aging is accompanied by decreasing general function in the cells and tissues. D-galactose (D-gal) induces aging and plays a role in the pathogenesis of it. Myricitrin is a plant-derived antioxidant.

Objective

The present study was performed to evaluate the effects of myricitrin on antioxidant defense, sex hormone levels, uterus, and ovarian histology in D-gal-induced aging female mouse model.

Materials and Methods

In this experimental study, 72 female adult NMRI mice, weighing 30-35 gr, 3-4 months old, were randomly divided into six groups (n = 12/each): (I) Control (vehicle; normal saline), (II) D-gal at 500 mg/kg/d for 45 days, (III-V) D-gal + myricitrin-treated groups (these groups received myricitrin at 5, 10, and 20 mg/kg/d, and (VI) D-gal + 100 mg/kg/d vitamin E orally for the last 28 days. The antioxidant indices were done on the basis of colorimetric method, and sex hormone levels were measured by using enzyme-linked immunosorbent assay kits. Histological assessment of the uterus and ovaries were also evaluated.

Results

D-gal impaired the estrous cycle, also degenerative changes occur in the ovarian follicles and damage to the uterus and ovarian tissue occurs. In D-gal group, the level of sex hormones (p = 0.03) and the total antioxidant capacity (p = 0.002) decreased, while the level of malondialdehyde and gonadotropins increased (p = 0.03). Myricitrin at lower doses and vitamin E ameliorated the D-gal effects.

Conclusion

These findings suggest that myricitrin at low doses can effectively prevent D-gal-induced oxidation and aging in mice. The effect of myricitrin was equivalent and sometimes better than vitamin E.

Sex Differences and Estrous Influences on Oxytocin Control of Food Intake

Central oxytocin potently reduces food intake and is being pursued as a clinical treatment for obesity. While sexually dimorphic effects have been described for the effects of oxytocin on several behavioral outcomes, the role of sex in central oxytocin modulation of feeding behavior is poorly understood. Here we investigated the effects of sex, estrous cycle stage, and female sex hormones (estrogen, progesterone) on central oxytocin-mediated reduction of food intake in rats. Results show that while intracerebroventricular (ICV) oxytocin potently reduces chow intake in both male and female rats, these effects were more pronounced in males than in females. We next examined whether estrous cycle stage affects oxytocin's food intake-reducing effects in females. Results show that ICV oxytocin administration significantly reduces food intake during all estrous cycle stages except proestrous, suggesting that female sex hormones may modulate the feeding effects of oxytocin. Indeed, additional results reveal that estrogen, but not progesterone replacement, in ovariectomized rats abolishes oxytocin-mediated reductions in chow intake. Lastly, oxytocin receptor mRNA (Oxtr) quantification (via quantitative PCR) and anatomical localization (via fluorescent in situ hybridization) in previously established sites of action for oxytocin control of food intake revealed comparable Oxtr expression between male and female rats, suggesting that observed sex and estrous differences may be based on variations in ligand availability and/or binding. Overall, these data show that estrogen reduces the effectiveness of central oxytocin to inhibit food intake, suggesting that sex hormones and estrous cycle should be considered in clinical investigations of oxytocin for obesity treatment.

Fenugreek seeds estrogenic activity in ovariectomized female rats

The estrogenic activities of fenugreek seeds (Trigonella foenum-graecum L.), widely used in traditional pharmacopoeia, are reflected in the uterus of ovariectomized female rats, with a slight increase in dry and wet weight, a thickening of the stroma and the uterine epithelium and the development of the endometrial glands. In the vagina, the estrogenic action is shown through an increase in the epidermal cell number and a tendency to keratinization, leading to vaginal opening.

Furthermore, this estrogenic potential of fenugreek seeds is confirmed by the over-expression of progesterone receptors in the uterine tissues supporting possible interactions between phytoestrogens and estrogen receptors.

Therefore, Fenugreek seeds may be capable of promoting the development of reproductive tissues of immature ovariectomized rats, and its estrogenic activity may take its action by holding phystoestrogens that interact with estrogen binding sites and activate the same estradiol-mediated cell signaling pathways.

Thus, our results give added scientific support to the popular use of Fenugreek seeds as an alternative for several health problems such as fertility and menopause related disorders.

Modulation of the lung inflammatory response to ozone by the estrous cycle

Emerging evidence suggests that sex differences exist in the control of lung innate immunity; however, the specific roles of sex hormones in the inflammatory response, and the mechanisms involved are unclear. Here, we investigated whether fluctuations in circulating hormone levels occurring in the mouse estrous cycle could affect the inflammatory response to air pollution exposure. For this, we exposed female mice (C57BL/6J, 8 weeks old) at different phases of the estrous cycle to 2 ppm of ozone or filtered air (FA) for 3 h. Following exposure, we collected lung tissue and bronchoalveolar lavage fluid (BAL), and performed lung function measurements to evaluate inflammatory responses and respiratory mechanics. We found a differential inflammatory response to ozone in females exposed in the luteal phase (metestrus, diestrus) versus the follicular phase (proestrus, estrus). Females exposed to ozone in the follicular phase had significantly higher expression of inflammatory genes, including Ccl2, Cxcl2, Ccl20, and Il6, compared to females exposed in the luteal phase (P < 0.05), and displayed differential activation of regulatory pathways. Exposure to ozone in the follicular phase also resulted in higher BAL neutrophilia, lipocalin levels, and airway resistance than exposure in the luteal phase (P < 0.05). Together, these results show that the effects of ozone exposure in the female lung are affected by the estrous cycle phase, and potentially hormonal status. Future studies investigating air pollution effects and inflammation in women should consider the menstrual cycle phase and/or circulating hormone levels.