Persistent Vaginal Estrus Research Articles

Effect of early postnatal exposure to 17α-ethinylestradiol on female rat reproductive physiology

17α-Ethinylestradiol (EE2) is a synthetic compound used as an oral contraceptive in birth control pills. EE2 is a major contaminant in aquatic environments. It is considered an endocrine-disrupting chemical due to its oestrogenic activity. This study investigates the effect of repeated exposure to EE2 at a dose of 1 µg/kg·(body weight)/day on reproductive function and metabolism. Female Sprague–Dawley rats were subcutaneously injected with EE2 at a dose of 1 µg/kg·(body weight)/day from postnatal day 1 until postnatal day 5, which corresponds to a highly sensitive period of neuroendocrine system organisation. The anogenital distance, body weight and blood levels of insulin and glucose of EE2-treated female rats were not different from those of control rats. These results indicate that growth and glucose metabolism were unaffected by treatment. In contrast, vaginal opening occurred significantly earlier in EE2-treated females than in control females. In adulthood, these females present an alteration of their oestrous cyclicity, characterised by persistent vaginal oestrus. Moreover, treated females showed altered uterine and ovarian morphology associated with lower circulating levels of oestradiol and progesterone. These results indicate precocious onset of puberty and dysfunction of the reproductive organs. Therefore, early postnatal exposure to EE2 at a dose of 1 µg/kg·bw/d has delayed adverse effects on reproductive function.

Long-Term Neonatal Estrogen Exposure Causes Irreversible Inhibition of LH Pulses by Suppressing Arcuate Kisspeptin Expression via Estrogen Receptors α and β in Female Rodents.

Exposure to estrogen during the developmental period causes reproductive dysfunction in mammals, because the developing brain is highly sensitive to estrogens. In the present study, we report that long-term exposure to supraphysiological doses of estrogen during the neonatal critical period causes irreversible suppression of Kiss1/kisspeptin expression in the arcuate nucleus (ARC) via estrogen receptor-alpha (ERα) and ERβ, resulting in reproductive dysfunction in female rats. Daily estradiol-benzoate (EB) administration from days 0 to 10 postpartum caused persistent vaginal diestrus in female rats. The female rats showed profound suppression of pulsatile luteinizing hormone (LH) release and ARC Kiss1/kisspeptin expression even after ovariectomy at adulthood. In contrast, female rats treated with a single EB injection at day 5 postpartum exhibited persistent vaginal estrus and showed comparable LH pulses and numbers of ARC Kiss1-expressing cells to vehicle-treated controls after ovariectomy at adulthood. Because the LH secretory response to exogenous kisspeptin was spared in female rats with neonatal long-term estrogen exposure, the LH pulse suppression was most probably due to ARC kisspeptin deficiency. Furthermore, neonatal estrogen might act through both ERα and ERβ, because EB exposure significantly reduced the number of ARC Kiss1-expressing cells in wild-type mice but not in ERα or ERβ knockout mice. Taken together, long-term exposure to supraphysiological doses of estrogen in the developing brain might cause defects in ARC kisspeptin neurons via ERα and ERβ, resulting in inhibition of pulsatile LH release and lack of estrous cyclicity.

Effects of Neonatal Oral Exposure to Ethynylestradiol (EE) on the Puberty of Female Rat.

[Objectives] Perinatal exposure to estrogenic compounds masculinizes the brain in female neonatal rodents and loses cyclic revolution of estrus after puberty. We have shown that oral daily administration with EE to neonatal female rats causes persistent vaginal estrus at a younger age depending on doses of EE. Although the treatment at dose levels up to 2 μg/kg BW did not affect the timing of vaginal opening (VO), it retarded the first ovulation. In order to determine effects of the treatment on the puberty, functional development of the hypothalamus/pituitary/gonadal axis towards puberty was examined by administrating exogenous gonadotropins to EE-treated immature animals. [Materials & Methods] Neonatal pups were obtained by spontaneous delivery from pregnant Sprague-Dawley rats [Crl:CD(SD)IGS]. The day when delivery was confirmed was designated as postnatal day (PND) 0 of the pups. The pups were collected and assigned to treatment groups on PND 1. The pups were identified using tattoos and placed under the same dams at eight pups per dam. If the number of treated pups was less than eight, untreated male pups were included to adjust the litter size to eight. From PND 1 to 5, the pups were given 10 mL/kg BW of corn oil (vehicle) or 2 μg/kg BW of EE orally using intubation tube, and were weaned on PND 21. Around 09:30 of PND 23, both groups of the animals were given 5 IU eCG subcutaneously, and were euthanized under sodium pentobarbital anesthesia on PND 26 to observe ovulation. Some of the animals in the both groups were given 10 IU hCG 56 hours after the eCG injection as an exogenous stimulus for ovulation. Animals treated either with corn oil or EE during the neonatal period were also necropsied on PND 23 or 26 without gonadotropins treatment. At the necropsy, the number of oocytes shed and weights of ovaries and uterus were determined. Ovarian histology was confirmed for representative cases. [Results & Discussion] Single subcutaneous injection of 5 IU eCG on PND 23 failed to induce ovulation in the EE-treated animals, while all of animals in the vehicle-treated animals ovulated by the treatment. Additional ovulatory stimulus of hCG to eCG induced ovulation to 40% of the EE-treated group with smaller number of oocytes shed than that in the vehicle-treated group. Weights of the ovaries and uterus in the EE-treated group were smaller than the vehicle-treated group at any timing of the necropsy. Ovarian histology was tended to show retardation of follicular development in the EE-treated animals. From these results, it is concluded that neonatal oral treatment with 2 μg/kg BW/day of EE could retard puberty exerting its effects probably on both the hypothalamus/pituitary and the ovary. [Acknowledgement] This study was partly supported by a grant-in-aid for research on risk of the origin of chemical compounds from the Minister of Health, Labor and Welfare (H23-Kagaku-Ippan-003).

Exposure of neonatal female rats to p-tert-octylphenol disrupts afternoon surges of luteinizing hormone, follicle-stimulating hormone and prolactin secretion, and interferes with sexual receptive behavior in adulthood.

The present study investigated the effects of exposure of neonatal female rats to p-tert-octylphenol (OP) on estrogen-induced afternoon surges of LH, FSH, and prolactin (PRL) secretion, and on sexual behavior in adulthood. After birth, one group of female Wistar rat pups received s.c. injections of OP (100 mg/kg body weight [BW]; OP group) dissolved in DMSO, while the control group received DMSO only (DMSO group). In order to make a qualitative comparison, a third group was injected with estradiol-17beta (500 microg/kg BW; estradiol group) dissolved in DMSO. Injections were given on Days 1, 3, 5, 7, 9, 11, 13, and 15 of age. The rats from the OP and estradiol groups that were used for subsequent experiments were in persistent vaginal estrus. Spontaneous LH surge measured at Postnatal Days (PND) 78-81 was observed only in the DMSO group on the afternoon of the day of proestrus. At PND 115, randomly selected rats from each of three treatment groups were bilaterally ovariectomized (ovx), and 8 days later, Silastic capsules containing estradiol-17beta were implanted under the skin. Estrogen implants stimulated afternoon surges of LH, FSH, and PRL for two consecutive days in the DMSO group, but not in the OP and estradiol groups. Rats from the OP and DMSO groups underwent ovx at PND 186, and 6 days later they were treated with a combination of estradiol benzoate s.c. (15 microg/kg BW) and progesterone s.c. (2 mg/kg BW) to test the lordosis reflex. In response to this hormone treatment and mounting stimulus delivered by the stud male rats, the OP-treated rats were less receptive compared with control DMSO-treated rats, and thus the lordosis quotient and lordosis rating were significantly (P < 0.05) reduced in the OP group compared with the DMSO group. Analysis of the area of the sexually dimorphic nucleus of the preoptic area of the brain revealed that the area of this nucleus was larger in the OP group than it was in control DMSO rats. We conclude that the exposure of neonatal female rats to higher doses of OP disrupts the cyclic release of LH, FSH, and PRL, and interferes with the display of sexual receptive behavior in adulthood.

Estrous Cyclicity and Behavioral Sensitization in Female Rats Following Repeated Intravenous Cocaine Administration

Repeated intermittent administration of cocaine is well known to produce behavioral sensitization in male animals. The present studies explored whether intact adult female rats maintained normal estrous patterns in response to repeated IV cocaine administration and whether behavioral sensitization occurred with this route of administration. Adult female Sprague–Dawley rats ( N = 48) were surgically implanted with an intravenous access port. Animals received 3.0 mg/kg IV cocaine once/day for 14 days. Daily vaginal lavages indicated that female rats continued to cycle normally throughout the experiment. Estimates of statistical power for detecting alterations in estrous cycle length ranged from 0.61–0.95 for small (0.1) to large (0.4) effect sizes. Moreover, no cocaine-treated animals displayed persistent vaginal estrus or were acyclic and cocaine treatment did not decrease body weight. Immediately after the cocaine injection, animals were placed in IR photocell activity chambers for 60 min. Female rats displayed a significant 75% increase in locomotor activity across the 14-day time course of IV cocaine injections. These data indicate that 3.0 mg/kg of IV cocaine does not interfere with normal estrous cyclicity, and that behavioral sensitization occurs in female rats following repeated daily IV cocaine dosing. Collectively, these data suggest that the IV cocaine-dosing model may be particularly useful in exploring the gender-dependent effects of cocaine using intact female rats.

Disruption of rat estrous cyclicity by the environmental estrogen 4-tert-octylphenol.

4-tert-Octylphenol (OP) is a prevalent environmental pollutant which binds to estrogen receptors and exerts estrogenic actions in vitro. The effects of OP in vivo on mammalian female reproduction are not known. We investigated whether (i) exposure of neonatal rats to OP interfered with the onset of vaginal opening or their ability to have regular estrous cycles as adults and (ii) exposure of adult rats to OP interfered with estrous cyclicity and ovulation. Injection of 1 mg OP in corn oil sc on the day after birth did not affect the day of vaginal opening. However, 9 of 11 OP-treated rats were in persistent vaginal estrus when examined at three months after birth compared with 0 of 9 corn oil-injected controls, which cycled regularly. Ten of eleven neonatal rats injected with 1.7 mg of the estrogenic pesticide methoxychlor also were in persistent estrus at 3 months after birth, and all 10 neonatal rats injected with 1 mg of 2,4,5-trichlorophenol, which is apparently nonestrogenic, cycled regularly. Injection of 20 or 40 mg OP in corn oil vehicle sc three times weekly into previously untreated adult cyclic rats caused persistent estrus in 2 of 6 and 16 of 21 rats, respectively. Injections were continued for three more weeks in 5 of the 16 rats rendered persistent estrus by the 40 mg OP treatment. These rats remained in persistent estrus for the additional 3-week period. The other 11 persistent estrous rats in the 40 mg treatment group started to cycle regularly within 5-7 days after the last injection. Unlike pentobarbital, injection of OP into cyclic rats during the afternoon of proestrus did not block ovulation. These results provide strong evidence that OP acts like estrogen in vivo in both neonatal and adult female rats to exert effects that block reproductive cyclicity.

The oral administration of Polysorbate 80 to the immature female rat does not increase uterine weight

Some xenobiotics display estrogenic activity in in vitro and/or in vivo systems. Previous studies by Gajdova et al. have shown that polysorbate 80 (also known as Tween 80) administered by intraperitoneal injection to neonatal female rats on days 4–7 after birth produced estrogenic effects including earlier vaginal opening, prolongation of the estrus cycle and persistent vaginal estrus [1]. Some of these effects were evident many weeks after cessation of administration of polysorbate 80. The present study has evaluated the estrogenic properties of polysorbate 80 following oral administration, a route of exposure which is more relevant for the consideration of human health hazard. The effects of polysorbate 80 at oral gavage doses of up to 5 g/kg/day for 3 consecutive days on uterine growth of immature female rats, a commonly used in vivo mammalian assay for estrogenic activity, have been determined. Estradiol benzoate administered subcutaneously was used as a positive control and significantly increased uterine weight in this age and strain of female rat (21–23 days, Alpk:APfSD Wistar derived) by up to 4.5-fold above vehicle control values. Polysorbate 80 administered orally to rats had no effect on uterine weight. Thus, intrinsic estrogenic effects of polysorbate 80 reported following its intraperitoneal injection to neonatal 4-day-old female rats are not manifest when it is administered by oral gavage to immature 20- to 22-day-old female rats. This latter route of exposure is of more relevance to human exposure scenarios and these data are, therefore, important in assessing hazard/risk of polysorbate 80 to man.

The pheromonal restoration of cyclic activity in young estrogenized persistent estrus female rats is a vomeronasal effect.

Eight sham-operated (SO) and six vomeronasalectomized (VMNX) young adult female rats were used to demonstrate the participation of the vomeronasal organ (VNO) in the pheromonal restoration of cyclic activity (PRCA). All rats were normal four-day cycling before and after surgery and they received a single subcutaneous injection of 2 mg of estradiol benzoate (EB) to induce an anovulatory persistent vaginal estrus. Fifteen days after EB injection, they were treated by spraying in the nostrils, every 10 min for one hour on only one day, 50 muL of urine from young fertile males. SO rats showed PRCA in the following days, while VMNX did not. These results support the VNO as the receptor of the male urinary pheromone (or pheromones) responsible for PRCA, demonstrating that it is possible to improve the function of aging ovaries acting with an exteroceptive stimulus.

In vivo effects of follicle-stimulating hormone-related synthetic peptides on the mouse estrous cycle.

We have previously shown that a synthetic peptide amide corresponding to residues 34-37 (TRDL) of the human (h) FSH beta-subunit inhibited binding of [125I]hFSH to bovine calf testis membrane receptors and antagonized FSH-stimulated estradiol biosynthesis in primary cultures of rat Sertoli cells. These in vitro effects would have additional significance if they could be confirmed in an in vivo model system. We have obtained several lines of evidence supporting in vivo effects of TRDL on the mouse estrous cycle. 1) A single i.p. injection of 200 microg/g BW TRDL induced persistent vaginal estrus, characterized by the complete absence of epithelial casts in 87% of the mice treated, as determined by vaginal cytology. 2) A synthetic peptide representing a larger receptor-binding domain of the hFSH beta-subunit, hFSHbeta-(33-53), that contains the TRDL sequence had a similar effect, but hFSHbeta-(38-53) lacking the TRDL sequence, did not. 3) A series of unrelated synthetic peptides, tested at a comparable dose (200 microg/g BW), were also without effect, as was a D-amino acid analog of TRDL, TR(D)DL. 4) Serum estradiol levels at proestrus in TRDL-treated mice were significantly lower than those in vehicle-injected control mice. 5) The effect of estrogen on uterine ballooning and weight gain, seen in all vehicle-injected control mice at proestrus, did not occur in 97% of the mice treated with TRDL. 6) The ovaries of TRDL-treated mice taken during persistent vaginal estrus contained a greater number of large hemorrhagic preovulatory follicles and fewer corpora lutea than those in ovaries taken at estrus from vehicle-injected control mice. Taken together, these results indicate disruption of the normal mouse estrous cycle by the TRDL peptide and represent the first demonstration of in vivo effects of gonadotropin-related synthetic peptides on reproductive processes.

Promotion of Endometriosis by 2,3,7,8-Tetrachlorodibenzo-p-dioxin in Rats and Mice: Time–Dose Dependence and Species Comparison

In the disease of endometriosis, endometrial tissue grows outside the uterus, usually in the peritoneal cavity. Rodent models of endometriosis allow a way to reproduce the disease, evaluate effects of chemicals, and study mechanisms. Twenty-one days prior to induction surgery which produces endometriosis, female Sprague–Dawley rats and B6C3F1 mice were pretreated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at 0, 3 or 10 μg TCDD/kg. Animals were treated again at the time of surgery and at 3, 6, and 9 weeks following surgery. Evaluations were made at 3, 6, 9, and 12 weeks postsurgery. TCDD produced a dose-dependent increase in endometriotic site diameter when all time points were pooled within each dose in rats and a dramatic increase in site diameter in mice at 9 and 12 weeks. In rats but not mice, ovarian weight was decreased at 9 and 12 weeks, the occurrence of persistent vaginal estrus was increased at these times, and histological evaluation of the ovaries revealed ovulatory arrest at 12 weeks. In both species, thymic atrophy, indicating immune dysfunction, and hepatomegaly were observed as consequences of TCDD exposure. Body weight was reduced in rats but not in mice. Histological evaluations of endometriotic sites revealed fibrosis in control rats, necrotic and inflammatory changes in the sites from TCDD-treated rats, and predominantly fibrotic changes in sites from TCDD-treated mice. Differences observed between the rat and the mouse with respect to (a) the magnitude of the effect on endometrial site diameter (rats < mice), (b) measured effects on ovarian function (rats > mice) that may be based on the partial antiestrogenicity of TCDD, and (c) evidence that mice and rats differ in their immune response to TCDD suggest that the mechanisms mediating TCDD's action to promote endometriosis are complex and may be different in rats and mice. The mouse may be a better model for future studies necessary to elucidate these mechanisms.

Estrogenic effects of some xenobiotics.

While investigating the estrogenic properties of the pesticide Fosmet administered to neonatal rats we found that a 10% emulsion concentrate of Tween 80 can increase the mean relative weight of the uterus and cause changes in the endometrium that are characteristic of the action of estrogens (Gajdovaet al., 1988). In the rats exposed to Tween 80 we found a significant prolongation of the oestrous cycle and persistent vaginal estrus in adulthood (Vargova et al., 1990). Similar changes after the application of some substances with estrogenic effect were; described by Bulger and Kupfer (1985).

Long-Term Effects on Reproductive Parameters in Female Rats after Translactational Exposure to PCBs

In an integrated series of experiments, we assessed effects of translactational exposure to Aroclor 1254 at three different ages: as young adults (2-4.5 months), as mature adults (5-8 months), and as older adults (8.5-13 months). Developing female rats were exposed postnatally to polychlorinated biphenyls (PCBs) via oral treatment of the dams on Days 1, 3, 5, 7, and 9 of lactation at the following doses: 8 μg/g (PCBI), 32 μg/g (PCBII), and 64 μg/g (PCBIII) in peanut oil. Normal controls (CI) and underfed nutritional controls (CII) received peanut oil. Puberty, both vaginal opening and first estrus, was delayed in PCBII and PCBIII offspring. PCB exposure at all doses had a pronounced and consistent effect on uterine response. In mature PCBII and PCBIII adults, uterine wet weights were reduced at all stages of the estrous cycle and in light-induced persistent vaginal estrus (PVE). PCBI offspring exhibited a decreased uterine weight in proestrus and in light-induced PVE. Exogenous estradiol-17β (0.2 μg) given to ovariectomized offspring was less effective in causing a uterotrophic and vaginal response in all PCB-exposed offspring. Analysis of estrous cycles for 40 days at all ages indicated increases in diestrus. Fertility in young adults and mature adults was affected, with PCBIII young adults exhibiting less success with preimplantation stages, and PCBII and PCBIII mature adults showing an effect at pre- and/or postimplantation stages. As determined by patterns in estrous cycling and rate of development of PVE in 64 days of constant light, exposure to PCBs did not hasten reproductive aging at any of the ages examined. Instead, PCBIII young adults and PCBII and PCBIII older adults exhibited a delay in onset of light-induced PVE. This study demonstrates that translactational exposure to a PCB mixture that has little notable effect on the dams, not only delays puberty in the female offspring, but also several months later results in decreased uterine response, impairment of fertility, and irregular cycle patterns. Reproductive aging, however, is not hastened, and even may be delayed. Many of these effects could be explained, in part, by interference with estrogen.

Delayed effects of neonatal exposure to Tween 80 on female reproductive organs in rats

Neonatal female rats were injected ip (0.1 ml/rat) with Tween 80 in 1, 5 or 10% aqueous solution on days 4–7 after birth. Treatment with Tween 80 accelerated maturation, prolonged the oestrus cycle, and induced persistent vaginal oestrus. The relative weight of the uterus and ovaries was decreased relative to the untreated controls. Squamous cell metaplasia of the epithelial lining of the uterus and cytological changes in the uterus were indicative of chronic oestrogenic stimulation. Ovaries were without corpora lutea, and had degenerative follicles.

Effects of methoxychlor on the reproductive system of the adult female mouse 1. Gross and histologic observations

The purpose of this study is to examine the effects of the pesticide methoxychlor (MXC) on the reproductive system of the adult female mouse. Sexually mature (7- to 8-week) virgin female CD-1 mice were exposed to 1.25, 2.5, or 5.0 mg MXC (50% technical grade) via oral gavage for 5 consecutive days each week for either 2 or 4 weeks. Control groups received either 0.025 mg estradiol-17β (E-17β) or the sesame oil vehicle for the same time period. Vaginal smears were taken daily, and weights were recorded weekly. Twenty-four hours following the final exposure, animals were sacrificed. Ovaries and reproductive tracts were removed and weighed. One ovary from each animal was prepared for light microscopic evaluation. Results revealed a dose dependency of MXC in inducing persistent vaginal estrus (PVE). Ovaries of MXC-exposed and E-17β-exposed animals weighed significantly less than the sesame oil controls. In addition, there was an increase in the number of atretic large follicles in the E-17β group and in those mice treated with the two highes doses of MXC, indicating a potential reduction in the immediate fertility of the animal. Thus, this commonly employed pesticide appears to mimic closely those effects on the female reproductive system induced by estrogens.

Methoxychlor induces estrogen-like alterations of behavior and the reproductive tract in the female rat and hamster: Effects on sex behavior, running wheel activity, and uterine morphology

The current investigation was designed to determine if the pesticide methoxychlor (M) mimicked the effects of estrogen in the brain and on behavior. Running wheel activity (RWA) and sex behaviors were evaluated in this study because the role of estrogen in the regulation of these behaviors has been thoroughly established. M exposure at 400 mg/kg/day (90% pure) induced high levels of acyclic RWA and persistent vaginal estrus in the female rats. Following ovariectomy (ovx), RWA declined precipitously in controls but remained at high levels in M-treated-ovx females. M also produced estrogen-like alterations of the uterine endometrial epithelium, the ovary, and growth after ovx. In another study, ovx female rats were dosed with M at 200 mg/kg/day and then with progesterone (P). P acts as an antiestrogen and specifically suppresses estrogen-induced RWA. P blocks the synthesis of estrogen receptors in the CNS and reproductive tract but does not lower RWA induced by nonestrogenic mechanisms. After 14 days of M administration RWA was increased fourfold over the ovx-oil-treated females. Subsequently, P injections reduced RWA levels far below those seen when the ovx-M-treated rats were injected with oil. The P-induced decline represents a 95% inhibition of the M-induced increase in RWA. Subsequently, M-treated-ovx rats and hamsters were injected with P and tested for their ability to display reproductive behaviors when paired with a stud male. Female sexual behaviors are induced by the administration of estrogen followed by progesterone. In this study the M-treated females displayed reproductive behaviors, in contrast to the oil-treated rats and hamsters. The observation that the high levels of RWA induced by methoxychlor treatment in ovx rats can be suppressed by concurrent progesterone injections demonstrates that the increase in RWA is due to the estrogenic effects of methoxychlor on the CNS. The fact that methoxychlor, followed by P injections, induces behavioral estrus in the rat and hamster extends this estrogenicity to other areas in the CNS.

Female sexual behavior in hypogonadal mice with GnRH-containing brain grafts

Hypogonadal female mice respond to GnRH-containing fetal preoptic area (POA) implants in the third ventricle with vaginal opening and persistent vaginal estrus, ovarian, and uterine development and increased gonadotropin secretion. When these females are mated with normal males, reflex ovulation results in pregnancy. In the present study, POA implants derived from neonatal pups, whether male or female, were also capable of supporting reproductive development in the hypogonadal female mice. Evaluation of female sexual behavior in the mice with grafts showed that these mice responded to normal males with comparable levels of lordosis as are seen in normal female mice on the proestrous days of their cycles.

The distribution of neurotransmitter-specific cells and fibers in the anteroventral periventricular nucleus: Implications for the control of gonadotropin secretion in the rat

The anteroventral periventricular nucleus (AVPv), which lies in the periventricular zone of the preoptic region, is critical for normal phasic gonadotropin secretion since lesions of this nucleus abolish the progesterone-induced surge of luteinizing hormone secretion from the anterior pituitary, block ovulation, and induce persistent vaginal estrus in female rats. However, very little is known about the neurotransmitter-specific pathways associated with this nucleus. In the present study we evaluated the distribution of biochemically specific cells and fibers within the AVPv and adjacent regions by using an indirect immunohistochemical method with antisera to serotonin (5-HT), dopamine β-hydroxylase (DBH), tyrosine hydroxylase (TH), neuropeptide Y (NPY), cholecystokinin-8 (CCK), vasoactive intestinal polypeptide (VIP), substance P (SP), neurotensin (NT), corticotropin-releasing factor (CRF), luteotropin-releasing hormone (LRH), somatostatin (SS), thyrotropin-releasing hormone (TRH), oxytocin (OXY), vasopressin (OXY), adrenocorticotropic hormone (ACTH 1−24), alpha-melanocyte-stimulating hormone (α-MSH), leucine-enkephalin (L-ENK), and calcitonin gene-related peptide (CGRP). Our findings indicate that both cells and fibers containing these putative neurotransmitters are differentially distributed in and around the AVPv in accordance with the cytoarchitectonic organization of this part of the preoptic region. The AVPv itself appears to receive strong inputs from SP-, VAS-, CCK-, and SS-containing pathways, whereas the highest densities of L-ENK-, NT-, 5-HT-, NPY-, and DBH-immunoreactive fibers were found in the cell-sparse zone just lateral to the AVPv. The suprachiasmatic preoptic nucleus (PSCh), a small group of cells located ventral to the AVPv just dorsal to the optic chiasm, contained high densities of α-MSH- and ACTH-immunoreactive fibers, as well as substantial numbers of fibers containing catecholamines or NPY. In contrast, a dense plexus of VAS-stained fibers was distributed fairly evenly throughout the AVPv and PSCh. Numerous L-ENK-immunoreactive cell bodies, and moderate numbers of CCK-, NT-, and CRF-stained cell bodies were found in the AVPv. The PSCh contained many TH-stained cells (presumably dopaminergic), in addition to a moderate number of CCK-containing cell bodies, while a high density of NT- and CRF-stained cells were found in the cell-sparse zone lateral to the AVPv, in addition to several CCK-, SP-, VIP-, and TH-containing cells. These results are consistent with the view that the AVPv may be a nodal point in which a variety of putative neurotransmitter-specific pathways influence the neural control of gonadotropin-release, and perhaps other visceral functions as well.

Vaginal estrus in unmated belding's ground squirrels

Belding's ground squirrels are seasonally breeding rodents that have a single annual mating season (ca. 3 weeks long) which begins shortly after their vernal emergence from a 7-month period of hibernation. In this study, changes in vaginal estrus were assessed among unmated captive females. Following a 7-month period in a coldroom, vaginal lavages were taken daily to monitor changes in estrous condition. Females were in vaginal estrus within 24–48 hr of removal from the coldroom. Rather than exhibiting repeated cycles, adults (⩾ 2 years old) remained in prolonged estrus (typically 3–4 weeks, but 8–10 weeks in some cases), whereas yearlings exhibited similar but shorter and possibly periodic changes in vaginal condition. The difference between the two age classes persisted in a second year of testing, indicating that the preadult status of yearlings (in the first year of testing) did not primarily account for the difference. In another experiment, removal from the coldroom was delayed for 24 days relative to adults removed at a time coincident with emergence from hibernation of free-living females. The “delayed” adults showed persistent vaginal estrus for a shorter total duration, such that both groups reached anestrus at approximately the same time. This implies that the latency to anestrus is not simply a fixed period from the time of removal from the coldroom.

Catecholaminergic-serotonergic balance in the CNS and reproductive cycling in aging rats

Treatment with the serotonin (5-HT) reuptake inhibitor zimelidine, 20 mg/kg/24 hr, SC, for 14 days increased the duration of vaginal cycles in 3 month-old Long Evans hooded rats. It induced persistent vaginal estrus in 12 of 16 ten-month-old animals, and blocked reinitiation of vaginal cycles by L-dopa in 10 of 10 twenty-month-old rats. A single injection of zimelidine at 1400 hr did not alter the vaginal smear pattern of young or middle-aged cycling females or old constant estrus females. Also, a single dose of zimelidine at 1400 hr on the day of vaginal proestrus had no effect on serum LH values in young females. The serotonergic neurotoxin 5,7-dihydroxytryptamine, 4 μg, injected into the ventral and dorsal raphe areas (after desipramine, 25 mg/kg IP) reinitiated vaginal cycling in 8 of 13 twenty-month-old rats. These results suggest that (1) age-dependent changes in serotonin metabolism may contribute to the age-dependent changes in luteinizing hormone secretion which eventually lead to the cessation of ovarian function in the rat and (2) that alterations in serotonin function are an important component of the mechanism by which treatments with catecholamine precursors reinstate ovarian function in the old female rat.

Gonadotropin secretion following intraventricular norepinephrine infusion into neonatally androgenized female rats.

To determine whether norepinephrine (NE) will stimulate gonadotropin secretion in androgenized female rats, we administered NE (0.3 microM in 2 microliter saline; pH 6.0-6.5) into the third ventricle of females which had been treated neonatally with two different doses of testosterone propionate (TP; 10 or 100 micrograms) on day 5 of life. This treatment rendered these animals anovulatory as evidenced by polyfollicular ovaries and a persistent vaginal estrus condition which occurred by 100 days of age. Those females which were determined to be anovulatory were ovariectomized 4 weeks prior to the stereotaxic implantation of an intracerebroventricular (ICV) cannula. Ten to twelve days following cannula placement, animals were primed with either estradiol benzoate (EB; 30 micrograms) or EB and progesterone (P; 5 mg). Two days following steroid priming, NE was infused into the third ventricle at 15.00 h and blood samples were taken via an intra-atrial catheter at 15-min intervals for 2 h before and 2 h after administration. In both TP-treated groups, NE caused rapid and significant (p less than 0.01) elevations in plasma luteinizing hormone (LH) concentrations when animals were primed with EB as compared with control females given acid saline infusions (pH 6.0-6.5). Similar responses to NE were seen after additional priming with P at the same time as EB. Follicle-stimulating hormone (FSH) values did not increase following NE or saline infusion to any of the groups.(ABSTRACT TRUNCATED AT 250 WORDS)