Distribution analysis of the two chicken estrogen receptor-alpha isoforms and their transcripts in the hypothalamus and anterior pituitary gland

Withania somnifera inhibits photorefractoriness which triggers neuronal apoptosis in both pre-optic and paraventricular hypothalamic area of Coturnix coturnix japonica: involvement of oxidative stress induced p53 dependent Caspase-3 mediated low immunoreactivity of estrogen receptor alpha

Light has a very important function in the regulation of the normal physiology including the neuroendocrine system, biological rhythms, cognitive behavior, etc. The variation in photoperiod acts as a stressor due to imbalance in endogenous hormones. Estrogen and its receptors ER alpha and beta play a vital role in the control of stress response in birds. The study investigates the estrogenic effects of a well-known medicinal plant Withania somnifera (WS), mediated by estrogen receptor alpha (ERα) in the hypothalamic pre-optic area (POA) and paraventricular nuclei (PVN). Further the study elucidates its anti-oxidants and anti-apoptotic activities in the brain of Japanese quail. To validate this hypothesis, mature male quails were exposed to long day length for 3 months and then transferred to intermediate day length to become photorefractory (PR) while controls were still continued under long daylength. Supplementation of WS root extract in PR quail increases plasma estrogen and lowers corticosterone. Further, in PR quail the variation in light downregulates immunoreactivity of ERα, oxidative stress and antioxidant enzyme activities i.e. superoxide dismutase and catalase in the brain. Neuronal apoptosis was observed in the POA and PVN of PR quail as indicated by the abundant expression of Caspase-3 and p53 which reduces after the administration of WS root extract. The neuronal population also found to decrease in PR although it increased in WS administered quails. Further, the study concluded that change in photoperiod from 3 months exposure of 16L: 8D to 13.5L: 10.5D directly activates neuronal apoptosis via expression of Caspase3 and p53 expression in the brain and increases neuronal and gonadal oxidative stress while WS root extract reverses them via enhanced estrogen and its receptor ERα expression in the hypothalamic pre-optic and PVN area of Japanese quail.

Stress and steroid interaction modulates expression of estrogen receptor alpha in the brain, pituitary, and testes of immature Gallus gallus domesticus

In nature, food availability stimulates hypothalamo-pituitary-gonadal (HPG) axis while its scarcity induces stress, which further stimulates hypothalamo-pituitary-adrenal (HPA) axis producing a detrimental effect on the avian reproductive physiology. The present experiment was designed to examine the interaction of stress like food restriction and estradiol on male reproductive physiology with special emphasis on estrogen receptor alpha (ERα) as these play crucial role in reproduction. To achieve this, 60 day old White Leghorn immature cockrels were taken and divided into four groups (n  =  8 per group). One group was provided with food and water ad libitum. Second group was food restricted (FR) for 9 h/day after 5 days, third and fourth were administered with estradiol benzoate (EB 0.5 mg/100g/day) for 12 days. Fourth group was FR for 9 h/day after 5 days of EB treatment till last day of experiment (EB + FR). Immunofluorescent localization of ERα was principally in the pre-optic area and paraventricular nuclei of hypothalamus and in anterior pituitary gland. ERα expression was highly reduced (from 40 AU to 20 AU) after FR in testis but it increased (50 AU) after EB administration, EB + FR reflects a diminishing pattern in the increment after EB. FR decreased plasma estradiol while EB increased it. Increased plasma corticosterone, hydrogen peroxide, malondialdehyde, and decreased anti-oxidant enzymes in brain and testis of all groups indicate oxidative stress in the HPG axis. The increased ERα after EB and a decrease with FR and EB + FR support their reproductive function. Estrogen and its receptor alpha are responsible for maintaining epithelial morphology but FR along with EB administration modulates the testicular development by significantly decreasing its size (p<.0001) and seminiferous tubules (p<.0001) and no sperm formation via highly reduced expression of ir-ERα in HPG axis. Our findings led us to conclude that stress like FR and estradiol induces testicular regression immature male chickens by modulating ir-ERα expression in the HPG axis thereby resulting in reduction in reproductive physiology.

Effect of estrogen and stress on estrogen receptor 1 in the HPG axis of immature male Gallus gallus domesticus: Involvement of anti-oxidant system

Estrogen plays a key role in the regulation of reproductive behavior and control of the neuroendocrine system in both males and females. However, excessive quantity of exogenous estrogen produces a deleterious effect on the male reproductive system. To elucidate the mechanism by which estrogen modulates its receptor alpha (ESR1) in immature chicken during stress the study has been undertaken. The experiment investigated the physiological changes in the abundance of ESR1 in brain, pituitary and testes of immature male chickens after stress like water restriction. Twenty four immature male chickens were randomly assigned into four groups. The control group was provided with food and water ad libitum, second was water restricted 9 h each day for seven days (WR), third was treated with estradiol benzoate (EB) and fourth group was treated with EB followed by water restriction during last seven days of treatment (EB + WR). EB was administered at a dose of 0.5 mg/100 g/day for 12 days. EB administration as well as WR increases both the H₂O₂ and Malondialdehyde levels indicating oxidative stress in brain as well as in testis. Plasma corticosterone significantly increased in all groups while estradiol significantly decreased after water restriction. ESR1 protein was detected by immuno-fluorescence predominantly in the pre-optic area of the hypothalamus, pituitary and testes after EB administration. EB administration increases ESR1 proteins abundantly in the Sertoli cells, Leydig cells, spermatogonia and spermatids while WR decreases it. The decline in ESR1 proteins after EB administration during stress appears to be mediated by interaction of estrogen with hypothalamo-pituitary-adrenal (HPA) axis. Therefore, the findings substantiate the fact that WR and EB treatment increase the stress and alter the anti-oxidant enzymes via its receptor ESR1 in the brain, pituitary and testis of immature chicks. Moreover, these findings highlight the effect of estradiol in male chicks causing stress which is disrupting the normal physiological feedback mechanism in hormone release and the expression of receptor ESR1 along the hypothalamo-pituitary-gonadal (HPG) axis.

Tamoxifen activates hypothalamic l-dopa synthesis to stimulate ovarian estrogen production in chicken

Estrogen is the primary sex hormone responsible for the development and modulation of the female reproductive system in all vertebrates including avian species. The actions of estrogen are mediated by the estrogen receptor, which could be modulated by the selective estrogen receptor modulator tamoxifen (TAM). In this study, we administered TAM into the actively laying chicken to investigate the ovarian and hypothalamic responses to the estrogen action blockage. The laying was disrupted and the development of the pre-ovulatory hierarchical follicles was arrested. However, the TAM treatment caused an increase of estrogen level in both serum and ovary. Among the main estrogen targeted tissues, the hypothalamus showed specific dopaminergic activation as indicated by gene expression analysis. In the ovary, l-dopa, the precursor of dopamine, could stimulate the estrogen synthesis in undifferentiated follicles but not in the differentiated pre-ovulatory follicles. Thus, we established a feedback loop links ovarian estrogen production with hypothalamic l-dopa synthesis and we propose that the dopamine is involved in estrogen action to regulate the ovarian follicle development and ovulation.

Expression of sex hormone receptors in the brain of male and female newly hatched chicks

Chromosomal sex and steroid hormones play a determining role in brain sexual differentiation during chick embryonic development. Hormone effects on the brain are associated with the expression pattern of their intracellular receptors, which is sexually dimorphic in many species. We determined by Western blot the content of progesterone, estrogen, and androgen receptors (PR-A and PR-B, ERα, and AR, respectively) in the cortex, cerebellum, tectum, and hypothalamus of female and male newly hatched chicks. Males presented a higher content of PR-B in the tectum whereas females exhibited a higher content of PR-A in the hypothalamus. ERα was only detected as a band of 66kDa, and it showed a higher content in the cerebellum and tectum of females as compared to these regions in males. Besides, males exhibited a higher content of AR in the tectum than females. Our study suggests that newly hatched chicks show a sexual dimorphism in the expression of sex hormone receptors in brain regions involved in sexual behavior such as the hypothalamus, and in non-sexual behavior such as the optic tectum and the cerebellum.

Reproduction in hens: is testosterone necessary for the ovulatory process?

Avian reproduction entails complex endocrine interactions at the hypothalamic and ovarian levels. The initiation of the reproductive season is due to the reduction in melatonin and GnIH production as day length increases. The decline in GnIH permits GnRH and gonadotropin secretion starting follicle growth. Follicular steroids stimulate sexual activity and have important roles for the induction of ovulation. Progesterone (P4) is an inductor of the preovulatory surge of LH, while estradiol (E2) acts as a hypothalamic primer to allow P4 receptor development, as well as a stimulator of yolk production. Conversely, the role of testosterone (T) has been more controversial; however, there is now enough evidence, which demonstrates an essential action of T in the ovulatory process. For instance, blockage of endogenous T, by passive or active immunization or by the use of a specific antagonist of T, inhibits ovulation and the preovulatory surges of P4 and LH. This information is supported by the fact that there is a positive correlation between the occurrences of the T preovulatory surge and those of P4 and LH, in which the absence of T caused a lack of P4 and LH increase in almost 90% of the cases. Additionally, it has been observed that T has a paracrine action within the ovary, to promote P4 secretion by granulosa cells from the larger follicles. This has been related with an increased mRNA expression of StAR and P450scc enzymes, which are essential for P4 production, as well as with LH-R mRNA expression in granulosa cells of preovulatory follicles, an effect that should enhance the positive feedback between P4 and LH necessary for ovulation. Lastly, endocrine activity of hierarchical follicles occurs as a result of a complex interaction between the larger follicles (F1-F3) and the smaller follicles (F4-F6), which is necessary to achieve an adequate preovulatory milieu.

Effect of estradiol-17β on follicle-stimulating hormone secretion and egg-laying performance of Japanese quail

The aim of this study was to measure the effect of estradiol-17β (E2) injection on follicle-stimulating hormone (FSH) secretion and egg-laying performance of Japanese quail. Female Japanese quail were housed in cages and fed ad libitum. After a 7-day adaptation period, the birds were randomly assigned to three groups, that is, one control group and two test groups. The birds were weighed, before every injection. The control group was subcutaneously injected with 0.2 ml sesame oil-ethanol mixture, whereas test groups were injected, twice in a week, with 0.2 ml sesame oil-ethanol mixture containing 0.1 or 0.2 mg E2 along the study. One day after the first injection, egg number, egg weight, eggshell strength and food conception were daily recorded. On the last day of the experiment, the birds were injected and 3 h later seven birds from each group were randomly selected for bleeding. Blood samples (2 ml/bird) were collected from the jugular vein for the measurements of serum concentrations of E2, FSH, calcium (Ca) and phosphorus (P). E2 injection did not cause any significant changes in serum FSH concentrations, daily egg laid/bird, food conception/bird, serum concentrations of the Ca and the P. Egg weight was significantly increased in the 0.1 mg E2-injected group as compared with the control and 0.2 mg E2-injected groups. Eggshell strength in the 0.2 mg E2-injected group was significantly high as compared with the control, whereas the difference between the 0.1 mg E2- and 0.2 mg E2-injected groups was not statistically important. These results show that serum FSH concentration was not increased even when slightly suppressed by subcutaneous injection of 0.1 or 0.2 mg E2. Different doses of E2 have different functions. The increase in BWs in the 0.1 mg E2-injected group was a result of the dose effect, which probably increased growth hormone secretion from the pituitary or IGF-1 synthesis from the liver or both. The dose, 0.2 mg E2, was ineffective in increasing the BW, but it significantly increased eggshell strength probably via the increase in Ca and P utilizations.

Oestradiol rapidly inhibits Ca2+ signals in ciliary neurons through classical oestrogen receptors in cytoplasm

Oestrogen plays a key role in a great variety of actions in the nervous system, either through classical or alternative pathways. The classical pathways are initiated after oestrogen binding to the oestrogen receptors ERalpha or ERbeta, which translocate from the cytoplasm to the nucleus and act there as transcription factors. Alternative pathways are initiated at the plasma membrane and cytoplasm, via binding to classical or non-classical ERs. Using isolated ciliary ganglion neurons from the chick embryo and Ca2+ imaging, we demonstrated that a 10-min exposure to 17beta-oestradiol reduces Ca2+ influx through the plasma membrane. This effect was not reproduced by oestradiol conjugated to bovine serum albumin, which does not cross the plasma membrane, indicating that 17beta-oestradiol was acting intracellularly. ERalpha was detected in the cytoplasm by immunostaining and its involvement in the regulation of Ca2+ influx by ICI182,780 inhibition. The phosphatidylinositol-3 kinase (Pi3-kinase) inhibitor wortmannin and the nitric oxide synthase (NOS) inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) both blocked the oestradiol effect. The oestradiol effect was reproduced by 8Br-cGMP and abolished in the presence of the cGMP-dependent protein kinase (PKG) inhibitor KT5823. Our study indicates that 17beta-oestradiol can regulate Ca2+ influx via PI3-kinase, NOS and PKG after activation of cytoplasmic ER.

Ontogeny of estrogen receptor (ER) alpha and its co-localization with pituitary hormones in the pituitary gland of chick embryos

Estrogen is involved in regulating the development and hormone secretion of the anterior pituitary gland following its binding to estrogen receptors (ERs) expressed on pituitary cells. However, the pituitary is comprised of several cell types, and to date, there is no data about the specific cell types expressing ERs in embyonic chick pituitary. We therefore followed, by immunohistochemistry, the ontogeny of the pituitary ER alpha (ERalpha), and the cell types expressing ERalpha throughout chick embryo development. ERalpha immunoreacitivity was restricted to the nuclei of pituitary cells. ERalpha-immunopositive (ERalpha(+)) cells were first detected at embryonic day 6.5 (E6.5), after which ERalpha(+) cells were consistently detected throughout the anterior pituitary gland, although the density of ERalpha(+) cells in the caudal lobe of the pars distalis was higher than that in the cephalic lobe. The proportion of ERalpha(+) cells in the pituitary was about 6% at E8.5; expression increased to 22% by E18.5 of gestation, with no additional change until hatching. Double-labeling of ERalpha and pituitary hormones showed that the dominant cell types expressing ERalpha were gonadotrophs immunopositive for luteinizing hormone (LH); the proportion of ERalpha(+) cells expressing LH increased throughout gestation and reached approximately 57% at hatching. About 2%-6% of thyroid-stimulating-hormone-immunopositive and 1%-2% prolactin-immunopositive cells expressed ERalpha at later stages of embryonic development, but no growth-hormone-positive or adrenocorticotropic-hormone-positive cells expressed ERalpha during the embryonic period. Thus, gonadotrophs are the main cell population expressing ERalpha in the anterior pituitary gland of chick embryo, and ERalpha is involved in regulating the development of the pituitary gland and the maturation of the hormone-secreting function.

Changes in the content of progesterone receptor isoforms and estrogen receptor alpha in the chick brain during embryonic development

Progesterone and estradiol participate in the regulation of several reproductive functions through interaction with intracellular progesterone receptors (PR) and estrogen receptors (ER), respectively. In this work, we determined PR and ER-alpha isoforms content in the brain of chicks of both sexes on days 8 and 13 of embryonic development as well as on the day of hatching by Western blot analysis. PR isoforms protein content increased during embryonic development in both female and male chick brain. The highest PR isoforms content was observed on the day of hatching in both sexes. Interestingly, PR-A content was higher in the brain of chick males than in that of females on day 8 of embryonic development. PR-A/PR-B ratio was higher in the brain of males than in that of females at all ages. We found two ER-alpha isoforms of 66 and 52 kDa; the content of both isoforms was higher in the brain of females than in that of males on days 8 and 13 of embryonic development. An opposite pattern of ER-alpha isoforms content was observed. In males, ER-alpha content increased during embryonic development whereas in the females it decreased during this process. These results indicate that the content of PR and ER-alpha isoforms is related to the degree of brain development in chicks, and suggest that PR and ER-alpha isoforms should exhibit sexual dimorphism in the brain of chicks during embryonic development.

Estrogen receptors in Xenopus: duplicate genes, splice variants, and tissue-specific expression

The estrogenic steroid hormones, acting primarily through the nuclear estrogen receptors ERalpha and ERbeta, regulate sexual differentiation in a wide variety of vertebrates. In the frog Xenopus laevis, estrogen regulates the strength of vocal neuromuscular synapses and contributes to the physiological basis of sexually differentiated songs. To understand the mechanisms by which estrogen produces these effects, we have characterized the ERs of X. laevis and their expression in laryngeal muscle and other tissues. We found a remarkable molecular diversity in the estrogen receptor population within individuals. First, we have identified two distinct ERalpha genes, xlERalpha1 and xlERalpha2, which represent, to our knowledge, the first discovery of retained duplicates of the ERalpha gene in any species. These two genes are highly conserved at the amino acid level but have distinct nucleotide sequences; moreover, ERalpha2 has no N-terminal domain. Cloning of ERalpha and ERbeta in the related species Xenopus tropicalis and phylogenetic analysis indicate that the two xlERalpha loci were generated by a duplication specific to the X. laevis lineage-most likely the genome duplication that led to a doubling of the X. laevis chromosome number about 30 million years ago. The primary ER expressed in X. laevis laryngeal muscle is the novel gene xlERalpha2; ERalpha1 is primarily expressed in liver, forebrain, and oviduct. Alternatively spliced transcripts of both xlERalpha1 and xlERalpha2 are also expressed in a tissue-specific manner. We propose that complementary spatial expression of these two genes and their alternatively spliced transcripts contributes to their conservation over such a long period of time, consistent with the subfunctionalization model for evolution after gene duplication.