Immunocytochemical localization of neurophysin and oxytocin in ovine corpora lutea

Exposure to either Bisphenol A or S Represents a Risk for Crucial Behaviors for Pup Survival, Such as Spontaneous Maternal Behavior in Mice

INTRODUCTION

Maternal behavior depends on a multitude of factors, including environmental ones, such as Endocrine Disrupting Chemicals (EDCs), which are increasingly attracting attention. Bisphenol A (BPA), an EDC present in plastic, is known to exert negative effects on maternal behavior. Bisphenol S (BPS), a BPA substitute, seems to share some endocrine disrupting properties. In this study, we focused on the analysis of the effects of low-dose (i.e., 4 µg/kg body weight/day, EFSA TDI for BPA) BPA or BPS exposure throughout pregnancy and lactation in mice.

METHODS

We administered adult C57BL/6 J females orally BPA, BPS, or vehicle from mating to offspring weaning. We assessed the number of pups at birth, the sex ratio, and the percentage of dead pups in each litter, and during the first postnatal week, we observed spontaneous maternal behavior. At the weaning of the pups, we sacrificed the dams and analyzed the oxytocin system, known to be involved in the control of maternal care, in the hypothalamic magnocellular nuclei.

RESULTS

At birth, pups from BPA-treated dams tended to have a lower male-to-female ratio compared to controls, while the opposite was observed among BPS-treated dams' litters. During the first postnatal week, offspring mortality impacted differentially in the BPA and BPS litters, with more female dead pups among the BPA litters, while more male dead pups in the BPS litters, sharpening the difference in the sex ratio. BPA- and BPS-treated dams spent significantly less time in pup-related behaviors than controls. Oxytocin immunoreactivity in the paraventricular and supraoptic nuclei was increased only in the BPA-treated dams.

DISCUSSION/CONCLUSIONS

Alterations in maternal care, along with the treatment itself, may affect, later in life, the offspring's physiology and behavior. Exposure to BPs during sensitive developmental periods represents a risk for both dams and offspring, even at low environmentally relevant doses, through the functional alteration of neural circuits controlling fundamental behaviors for pup survival, such as maternal behaviors.

Effects of chronic exposure to bisphenol A in adult female mice on social behavior, vasopressin system, and estrogen membrane receptor (GPER1)

Bisphenol A (BPA), an organic synthetic compound found in some plastics and epoxy resins, is classified as an endocrine disrupting chemical. Exposure to BPA is especially dangerous if it occurs during specific "critical periods" of life, when organisms are more sensitive to hormonal changes (i.e., intrauterine, perinatal, juvenile or puberty periods). In this study, we focused on the effects of chronic exposure to BPA in adult female mice starting during pregnancy. Three months old C57BL/6J females were orally exposed to BPA or to vehicle (corn oil). The treatment (4 µg/kg body weight/day) started the day 0 of pregnancy and continued throughout pregnancy, lactation, and lasted for a total of 20 weeks. BPA-treated dams did not show differences in body weight or food intake, but they showed an altered estrous cycle compared to the controls. In order to evidence alterations in social and sociosexual behaviors, we performed the Three-Chamber test for sociability, and analyzed two hypothalamic circuits (well-known targets of endocrine disruption) particularly involved in the control of social behavior: the vasopressin and the oxytocin systems. The test revealed some alterations in the displaying of social behavior: BPA-treated dams have higher locomotor activity compared to the control dams, probably a signal of high level of anxiety. In addition, BPA-treated dams spent more time interacting with no-tester females than with no-tester males. In brain sections, we observed a decrease of vasopressin immunoreactivity (only in the paraventricular and suprachiasmatic nuclei) of BPA-treated females, while we did not find any alteration of the oxytocin system. In parallel, we have also observed, in the same hypothalamic nuclei, a significant reduction of the membrane estrogen receptor GPER1 expression.

Influences of oxytocin on the synthesis of prostaglandins by uterus from rats in different stages of the estrous cycle

We explored the oxytocin-prostaglandin interactions during the rat estrous cycle. The experiments were done with uterine preparations isolated from rats in different stages of the sex cycle incubated 'in vitro' with oxytocin (O) (50 mU/ml). We found that the effect of O on prostaglandin (PG) synthesis was associated to the sex hormones, and varied during the estrous cycle. Indeed, during the estrogenic influence (i.e. at proestrus and estrus) O diminished the synthesis of PGE2 and with the highest estradiol concentration (i.e. during estrus) the hormone also augmented the synthesis of PGF2 alpha. During metestrus, no changes in PG synthesis after treatment were found. Likewise, during diestrus, when progesterone levels fall, O enhanced PGF2 alpha uterine synthesis. In this study an inhibitory action of O on the uterine production of 6-keto-PGF1 alpha at proestrus was also seen. The present results indicate that when estrogen concentration increases (during estrus) 6-keto-PGF1 alpha synthesis also increases. In summary, we have observed that sex hormones exert a modulating action on the influences of O on uterine PGs synthesis.

Immunohistochemical evidence for the presence of oxytocin in the opossum corpus luteum

Corpora lutea from opossums late in pregnancy were examined by immunohistochemistry for the presence of oxytocin. Oxytocin-immunoreactivity was observed in all corpora lutea examined but not elsewhere in ovarian tissue. The immunoreactive staining observed was confined primarily to the perinuclear cytoplasm of reactive luteal cells. Not all luteal cells showed oxytocin-immunoreactivity. The immunohistochemical localization of oxytocin in the pregnant opossum corpus luteum demonstrates for the first time this peptide in a metatherian ovary. Its presence in this primitive species suggests that oxytocin has a fundamental role in the physiology of the mammalian ovary.

Immunocytochemical localization of oxytocin in corpora lutea and luteinized cysts from anoestrous ewes stimulated with gonadotrophin-releasing hormone

Anoestrous Romney Marsh ewes with or without progesterone pretreatment were injected with multiple low-doses of gonadotrophin-releasing hormone followed by a single, larger bolus. Blood samples were taken at twelve-hourly intervals for progesterone radioimmunoassay. Ewes were slaughtered on day 3 or 5 after the bolus injection, and the ovaries were collected for histology and immunocytochemical examination for oxytocin-immunoreactivity. The corpora lutea of all ewes killed on day 3 had similar weights and morphology. The ovaries of those ewes which were not pretreated with progesterone also contained some luteinized cysts. Ewes slaughtered on day 5 were separated into 2 groups according to plasma progesterone profiles, which were either rising ('normal'), or falling after a transitory rise ('abnormal'). Those ewes pretreated with progesterone all had a 'normal' progesterone profile whereas, of 14 ewes not pretreated with progesterone, 6 were 'normal' and 8 'abnormal'. Corpora lutea were significantly lighter in the 'abnormal' group and the ovaries of most of these ewes also contained luteinized cysts. All corpora lutea and luteinized cysts showed staining for oxytocin-immunoreactivity although the staining intensity was variable. In corpora lutea from 'normal' ewes oxytocin was restricted to large luteal cells. In addition tissues from 'abnormal' ewes also contained many cells with an atypical elongated shape which stained for oxytocin-immunoreactivity. These results show that progesterone pretreatment is needed for both normal morphological and endocrine development of corpora lutea in anoestrous ewes stimulated with gonadotrophin-releasing hormone.

The involvement of oxytocin in ovulation and in the outputs of cyclo-oxygenase and 5-lipoxygenase products from isolated rat ovaries

The effects on ovulation of a specific anti-oxytocin rabbit serum (anti-OT) (50.0 microliters) given by intrabursal injection into the right ovaries of etherized adult female rats at proestrus, were explored by counting the number of ovulated ova present within the right oviducts. Left ovaries were not treated and served as control ovaries. Control rats were treated with male normal rabbit serum (NRS) (50.0 microliters) given by intrabursal injections into the right ovaries of animals at proestrus. Ovulation was induced by injection of human chorionic gonadotrophin (hCG). Anti-OT administered into the right ovarian bursae of proestrous rat ovaries evoked a significant 51% inhibition of ovulation in comparison with that observed in control non-injected left ovaries (p less than 0.01). Also, when the ovulation of right ovaries injected with anti-OT was compared with that of left ovaries injected with NRS, the number of ovulated ova in the right side was significantly smaller (30%) than on the contralateral side (p less than 0.02). However, in rats pre-treated with hCG the intrabursal injection of oxytocin (OT) (50.0 mU/ml) into right and left ovaries failed to alter the number of ovulated ova compared with that of rats receiving intrabursal injections of saline. The basal control and the OT-evoked synthesis and release of endogenous prostaglandin E2 (PGE2) and PGF2 alpha were explored in ovaries isolated from prepuberal rats injected with pregnant mare's serum gonadotrophin (PMSG), two days prior to sacrifice. OT augmented the basal release of PGF2 alpha but did not influence that of PGE2. Moreover, the conversion of exogenous 14C-arachidonic acid (14C-AA) into different prostanoids and into 5-HETE, in the presence and in the absence of added OT (50.0 mU/ml), was studied in rat ovaries isolated in proestrus. The challenge with OT augmented the basal synthesis and release of PGF2 alpha and of 5-HETE from 14C-AA, but failed to influence the formation of products generated via the cyclo-oxygenase pathway, namely 6-keto-PGF1 alpha, PGE2 and thromboxane B2 (TXB2). Therefore, the present results suggest that ovarian OT may play a role in the ovulatory process, via generation of PGF2 alpha to enhance contractions of ovarian smooth muscle and of 5-HETE to promote follicular collagenolysis.

Immunocytochemical localization of oxytocin and neurophysin in human corpora lutea

Corpora lutea, corpora albicantia, and ovarian stroma from normal human premenopausal ovaries were examined for the presence of oxytocin and neurophysin by using highly specific antisera and peroxidase-antiperoxidase light-microscopic immunohistochemistry. Oxytocin and neurophysin immunoreactivity was found in some but not all cells of the corpora lutea obtained on days 19 to 24 of the menstrual cycle. Stromal tissue and corpora albicantia did not give a positive reaction for either of these peptides, and negative results were also obtained with corpora lutea of mid- and term-pregnancy and preovulatory follicles. Specificity of the immunohistochemical reaction was confirmed by immunoabsorption tests. The specific localization of immunoreactive oxytocin and neurophysin in corpora lutea of the human menstrual cycle directly demonstrates the presence of oxytocin- and neurophysin-positive cells within the human corpus luteum.