Sexual behavior in ewes and other domestic ruminants

Hair from sexually active bucks strongly activates olfactory sensory inputs but fails to trigger early first ovulation in prepubescent does

Early exposure of does to sexually active bucks triggers early puberty onset correlating with neuroendocrine changes. However, the sensory pathways that are stimulated by the male are still unknown. Here, we assessed whether responses to olfactory stimuli are modulated by social experience (exposure to males or not) and/or endocrine status (prepubescent or pubescent). We used a calcium imaging approach on goat sensory cells from the main olfactory epithelium (MOE) and the vomeronasal organ (VNO). For both cell types, we observed robust responses to active male hair in females under three physiological conditions: prepubescent females isolated from males (ISOL PrePub), pubescent females exposed to males (INT Pub) and isolated females (ISOL Pub). Response analysis showed overall greater proportion of responses to buck hair in ISOL PrePub. We hypothesized that females would be more responsive to active buck hair during the prepubertal period, with numerous responses perhaps originating from immature neurons. We also observed a greater proportion of mature olfactory neurons in the MOE and VNO of INT Pub females suggesting that male exposure can induce plastic changes on olfactory cell function and organization. To determine whether stimulation by male odor can advance puberty, we exposed prepubescent does to active buck hair (ODOR). In both ODOR and females isolated from males (ISOL) groups, puberty was reached one month after females exposed to intact bucks (INT), suggesting that olfactory stimulation is not sufficient to trigger puberty.

The effect of human menopausal gonadotropin and equine chorionic gonadotropin on the reproductive performance of treated ewes with short-term progesterone injections and sponge during the non-breeding season

This study investigated the effect of human menopausal gonadotropin (hMG) on reproductive efficiency of synchronized ewes with the sponge and progesterone (P4) injection-based protocols. In study 1, anoestrous ewes (n = 120) were used. Sixty ewes were treated with sponge (S) for 12 days. The injection of eCG (SeCG group, n = 30) or hMG (ShMG, n = 30) was given at the time of sponge removal. Thirty ewes received IM injection of P4, three times every 48 h and the injection of hMG was given 24 h after the third P4 injection (3PhMG group, n = 30), and 30 ewes were used as control group. Pregnancy was diagnosed on day 50 after the release of ram. In study 2, 60 ewes were randomly divided into two equal groups. In the treated group with antibiotics (n = 30), before inserting, the sponges were impregnated with the antibiotic penicillin G sodium (5,000,000 IU) and in the control group (n = 30), there was no added antibiotics. Before inserting and after removing sponges, a vaginal cytology sample was taken with a sterile cotton swab. The number of neutrophils in each sample was counted and analysed. The rate of oestrus and total pregnancy was greater in SeCG (96.7, 93.3%), ShMG (82.8, 93.1%) and 3PhMG (67.9, 89.3%) groups compared with the control group (13.8, 41.4%) (p < .05). No significant difference was found in single, twin and total lambing and pregnancy rates after injection of eCG and hMG during the non-breeding season (p > .05). A higher percentage of control ewes had the vaginal smear with neutrophils more than 50% (96.7% vs. 76.7%; p < .05). In conclusion, a single dose of hMG can induce fertile oestrus in synchronized ewes with P4 administered by either injection or intravaginally. Purulent discharge and percentage of neutrophils were significantly reduced in the synchronized ewes by the impregnated sponges with the antibiotic penicillin.

Social Stress during the Estrus or Luteal Phase in Sheep

In mammals, progesterone and estrogens affect the stress response. The study aimed to compare the physiological and behavioral responses to the social isolation of ewes during the estrus or luteal phase. Estrous and diestrous ewes (n = 10 and 8 respectively) were individually isolated in a novel place for 10 min. Ewes' behavior was recorded during the test. Cortisol, blood proteins and glucose concentrations, and the skin surface temperature were determined before and after the test. Cortisol increased immediately after the test ended (P = 0.02). Serum total protein (P = 0.02), globulin (P < 0.0001), and plasma glucose (P = 0.006) concentrations were greater in estrus than in the luteal phase. The abdominal skin surface temperature was greater during estrus than during the luteal phase (P = 0.02). Ewes in estrus spent more time standing up immobile than ewes in the luteal phase (P = 0.05). In conclusion, the physiological and behavioral responses changed according to the phase of the estrous cycle. These results highlight the need for future studies focusing on how reproductive status influences the stress response to different management practices in sheep.

Male-induced early puberty correlates with the maturation of arcuate nucleus kisspeptin neurons in does

In goats, early exposure of spring-born females to sexually active bucks induces an early puberty onset assessed by the first ovulation. This effect is found when females are continuously exposed well before the male breeding season starting in September. The first aim of this study was to evaluate whether a shortened exposure of females to males could also lead to early puberty. We assessed the onset of puberty in Alpine does isolated from bucks (ISOL), exposed to wethers (CAS), exposed to intact bucks from the end of June (INT1), or mid-August (INT2). Intact bucks became sexually active in mid-September. At the beginning of October, 100% of INT1 and 90% of INT2 exposed does ovulated, in contrast to the ISOL (0%) and CAS (20%) groups. This demonstrated that contact with males that become sexually active is the main factor prompting precocious puberty in females. Furthermore, a reduced male exposure during a short window before the breeding season is sufficient to induce this phenomenon. The second aim was to investigate the neuroendocrine changes induced by male exposure. We found a significant increase in kisspeptin immunoreactivity (fiber density and number of cell bodies) in the caudal part of the arcuate nucleus of INT1 and INT2 exposed females. Thus, our results suggest that sensory stimuli from sexually active bucks (e.g., chemosignals) may trigger an early maturation of the ARC kisspeptin neuronal network leading to gonadotropin-releasing hormone secretion and first ovulation.

Physiological Action of Progesterone in the Nonhuman Primate Oviduct

Therapies that target progesterone action hold potential as contraceptives and in managing gynecological disorders. Recent literature reviews describe the role of steroid hormones in regulating the mammalian oviduct and document that estrogen is required to stimulate epithelial differentiation into a fully functional ciliated and secretory state. However, these reviews do not specifically address progesterone action in nonhuman primates (NHPs). Primates differ from most other mammals in that estrogen levels are >50 pg/mL during the entire menstrual cycle, except for a brief decline immediately preceding menstruation. Progesterone secreted in the luteal phase suppresses oviductal ciliation and secretion; at the end of the menstrual cycle, the drop in progesterone triggers renewed estrogen-driven tubal cell proliferation ciliation secretory activity. Thus, progesterone, not estrogen, drives fallopian tube cycles. Specific receptors mediate these actions of progesterone, and synthetic progesterone receptor modulators (PRMs) disrupt the normal cyclic regulation of the tube, significantly altering steroid receptor expression, cilia abundance, cilia beat frequency, and the tubal secretory milieu. Addressing the role of progesterone in the NHP oviduct is a critical step in advancing PRMs as pharmaceutical therapies.

The Effect of P4 + eCG Estrus Induction Protocol during the Deep and the Transition Anestrous Period on the Reproductive Performance of Crossbred Dairy Goats

Simple Summary

The effect of an ultra-short progesterone (P4) plus equine chorionic gonadotropin (eCG) based estrus induction protocol during deep seasonal anestrous, or the reproductive transition period upon reproductive performance in an arid environment (26° N) was assessed. Results confirm a multidimensional response of goats regarding the effectiveness of P4 + eCG estrus induction protocols, mainly modulated by a specific time within the anestrous season (June) or even by specific management or a particular environment at herd level (herd 1 in this study), although, it is quite remarkably non–dependent on the animal’s body weight or body condition score.

Abstract

Seasonal reproduction restricts the offering of goat commodities across the year. Therefore, it is crucial to improve diverse strategies to induce the reproductive response in goats during the anestrus stage. The effectiveness of a short P4 + eCG-based estrus induction protocol during both the deep anestrous (March) or the reproductive transition period (June) upon the reproductive performance of crossbred dairy goats was assessed. Adult, anestrous, 24–30-month- old dairy crossbred (Saanen–Alpine–Nubian × Criollo) goats (n = 123) from two commercial herds and 10 sexually active goat bucks were used. Before the trials, the anestrous status of goats was confirmed. Then, goats were randomly allocated into two different experiments. In Exp. 1, we tested the effect of different doses (D) of intramuscular progesterone (P4; 10 or 20 mg + eCG (100 UI)) and type of breeding (TB), natural mating (NM), or artificial insemination (AI), on two commercial goat herds (H1 & H2), in March (deep anestrous). In Exp. 2, we evaluated the effect of D (P4; 10 or 20 mg + 100 UI eCG) in goats subjected to NM, and either during deep anestrous (March; M) or transitional anestrous (June; J), in two commercial herds. After breeding, conception and pregnancy were diagnosed with ultrasound scanning. The response variables were estrus induction (EI; %), estrus latency (EL; h), ovulation (OVP; %), ovulation rate (OR; units), fertility (FERT; %), and pregnancy (PREG; %). No differences (p > 0.05) in live weight (LW) and body condition score (BCS) occurred between herds in both trials. In Exp. 1, EI, EL, OVP, OR, FERT, and PREG were affected (p < 0.05) by the H–TB–D interaction, whereas in H1 + P4–20 combination had the highest (p < 0.05) EI, EL, and OVP values. Irrespective of TB, H1 had the largest (p < 0.05) OR, independently of TB or D. Also, the lowest (p < 0.05) OVP occurred in the AI + P4–10 group, while the AI had the lowest (p < 0.05) FERT, irrespective of D. FERT and PREG were two-fold higher (p < 0.05) in NM compared with AI. In Exp. 2, EI, EL, OVP, OR, FERT, and PREG were affected (p < 0.05) by the H–M–D interaction. In general, H2 + P4–10 had the lowest (p < 0.05) reproductive outcomes in March, whereas H1 had the largest (p < 0.05) values in either month. No differences (p > 0.05) between P4 doses occurred for EI, OVP, OR, FERT, and PREG. Yet, the largest (p < 0.05) EL occurred with P4–20 in June. No correlations (p > 0.05) occurred between LW and all the reproductive variables. BCS was positively correlated (p < 0.05) with EI (0.34), OVP (0.44), OR (0.58), and PREG (0.20). Also, positive correlations (p < 0.05) occurred between EI with EL (0.83), OVP (0.80), OR (0.64), and PREG (0.56); EL with OVP (0.58), OR (0.44), and PREG (0.42); OVP with OR (0.79) and PREG (0.70), as well as OR and PREG (0.63). Results of these studies confirm a multidimensional response regarding the effectiveness of P4 + eCG for estrus induction in goats mainly modulated by a specific time within the anestrous season, or even by specific management or a particular environment at the herd level (H1), although quite remarkably independent of the animal’s LW or BCS at herd level. Moreover, the best reproductive outcomes occurred with NM in June. The most reproductive variables were similar using either 10 or 20 mg P4 + 100 IU eCG, giving the possibility to lessen the scale in the use of exogenous hormones while obtaining acceptable out of season reproductive response.

Understanding the trade-off between the environment and fertility in cows and ewes

The environment contributes to production diseases that in turn badly affect cow performance, fertility and culling. Oestrus intensity is lower in lame cows, and in all cows 26% potential oestrus events are not expressed (to avoid getting pregnant). To understand these trade-offs, we need to know how animals react to their environment and how the environment influences hypothalamus-pituitary-adrenal axis (HPA) interactions with the hypothalamus-pituitary-ovarian axis (HPO). Neurotransmitters control secretion of GnRH into hypophyseal portal blood. GnRH/LH pulse amplitude and frequency drive oestradiol production, culminating in oestrus behaviour and a precisely-timed GnRH/LH surge, all of which are disrupted by poor environments. Responses to peripheral neuronal agents give clues about mechanisms, but do these drugs alter perception of stimuli, or suppress consequent responses? In vitro studies confirm some neuronal interactions between the HPA and HPO; and immuno-histochemistry clarifies the location and sequence of inter-neurone activity within the brain. In both species, exogenous corticoids, ACTH and/or CRH act at the pituitary (reduce LH release by GnRH), and hypothalamus (lower GnRH pulse frequency and delay surge release). This requires inter-neurones as GnRH cells do not have receptors for HPA compounds. There are two (simultaneous, therefore fail-safe?) pathways for CRH suppression of GnRH release via CRH-Receptors: one being the regulation of kisspeptin/dynorphin and other cell types in the hypothalamus, and the other being the direct contact between CRH and GnRH cell terminals in the median eminence. When we domesticate animals, we must provide the best possible environment otherwise animals trade-off with lower production, less intense oestrus behaviour, and impaired fertility. Avoiding life-time peri-parturient problems by managing persistent lactations in cows may be a worthy trade-off on both welfare and economic terms – better than the camouflage use of drugs/hormones/feed additives/intricate technologies? In the long term, getting animals and environment in a more harmonious balance is the ultimate strategy.

Reproductive performance of goats treated with free gonadorelin or nanoconjugated gonadorelin at estrus

The reproductive performance of goats that received a GnRH analog (gonadorelin) fabricated with or without chitosan-sodium tripolyphosphate (TPP) nanoparticles on the day of estrus (day 0) was evaluated. The chitosan-TPP polymer was conjugated with gonadorelin using an ionic gelation method. Thirty-three multiparous Zaraiebi goats were synchronized for estrus with 2 intramuscular (im) injections of 125 μg prostaglandin F_2α 14 d apart. Goats showing signs of estrus were divided equally into 3 experimental groups and received a single im injection of 1 mL physiological saline (placebo; control), 50 μg/mL gonadorelin (GnRH), or 12.5 μg (quarter of GnRH dose)/mL chitosan-TPP-conjugated gonadorelin nanoparticles (NGnRH). Each goat underwent ultrasound imaging of their ovaries at day 0 and at day 10 after mating, and pregnancy was diagnosed 28 and 45 d after mating. The concentrations of estradiol (E₂) and progesterone (P₄) were determined at day 0 and at days 7, 14, 21, and 42 after mating. NGnRH size, polydispersity, and zeta potential were 93.91 nm, 0.302, and 11.6 mV, respectively. Chitosan-TPP nanoparticles showed 91.2% entrapment efficiency for GnRH. No differences in estrus rate, interval to estrus, or ovarian structure at day 0 were observed among the experimental groups, but the GnRH and NGnRH treatments significantly decreased the duration of estrus compared with the control. At day 10 after mating, both GnRH and NGnRH increased (P = 0.011) the number of corpora lutea compared with the control. Treatment with GnRH increased (P = 0.023) serum E₂ concentrations from day 7 to 42 after mating compared with NGnRH and control treatments. The highest (P = 0.043) serum P₄ concentration was observed in the GnRH group, followed by the NGnRH and control groups. The increase in serum P₄ concentration started earlier a on day 7 in the GnRH group but later on day 14 in the NGnRH group. Compared with the control, GnRH resulted in a higher (P = 0.041) P₄-to-E₂ ratio, followed by NGnRH. Both gonadorelin treatments significantly increased the twinning rate, the number of embryos at days 28 and 42, and prolificacy and decreased pregnancy losses compared with the control. In conclusion, the administration of GnRH at the time of estrus improved the prolificacy of goats by increasing both the ovulation rate and the number of embryos. In addition, the nanoformulation developed in this study allowed a 75% reduction in the conventional dose of gonadorelin without affecting the fertility and prolificacy of goats, indicating the bioavailability of the reduced GnRH dose after conjugation with developed nanoformula.

Sexually active bucks are a critical social cue that activates the gonadotrope axis and early puberty onset in does

In rodents, early exposure to adult male is well known to induce an early puberty in females (Vandenbergh effect). This phenomenon has been less studied in other mammals. In goats, despite our extensive knowledge about the "male-effect" phenomenon in adults (i.e. ovulation induced by the introduction of the male during the anestrous), there are few data on the consequences of an early exposure of females to males. Here, we evaluated the puberty onset of young alpine goats when raised since weaning with intact bucks (INT), with castrated bucks (CAS) or isolated from bucks (ISOL). The INT group had the first ovulation 1.5 month before the two other groups. Despite the earlier puberty the INT group of females had normal and regular ovarian cycles. Morphological study of the genital tract showed that at 6 months, uterus of INT goats was 40% heavier than CAS and ISOL goats. Moreover, INT females had a myometrium significantly thicker and INT was the only group having corpora lutea. In our study, INT females were pubescent in the month following the entry of bucks into the breeding season, suggesting that only sexually active bucks provide the signal responsible for puberty acceleration. By removing direct contact with the bucks, we showed that somatosensory interactions were dispensable for an early puberty induction. Finally, no difference in the GnRH network (fiber density and number of synaptic appositions) can be detected between pubescent and non-pubescent females, suggesting that the male stimulations triggering puberty onset act probably on upstream neuronal networks, potentially on kisspeptin neurons.

Preclinical and Translational Studies in Small Ruminants (Sheep and Goat) as Models for Osteoporosis Research

PURPOSE OF THE REVIEW

This review summarizes research on the use of sheep and goats as large animal models of human osteoporosis for preclinical and translational studies.

RECENT FINDINGS

The most frequent osteoporotic sheep model used is the ovariectomized sheep with 12 months post-operatively or more and the combined treatment of ovariectomized sheep associated to calcium/vitamin D-deficient diet and glucocorticoid applications for 6 months, but other methods are also described, like pinealectomy or hypothalamic-pituitary disconnection in ovariectomized sheep. The goat model for osteoporosis research has been used in a very limited number of studies in osteoporosis research relative to sheep. These osteoporotic small ruminant models are applied for biomaterial research, bone augmentation, efficacy of implant fixation, fragility fracture-healing process improvement, or bone-defect repair studies in the osteopenic or osteoporotic bone. Sheep are a recognized large animal model for preclinical and translational studies in osteoporosis research and the goat to a lesser extent. Recently, the pathophysiological mechanism underlying induction of osteoporosis in glucocorticoid-treated ovariectomized aged sheep was clarified, being similar to what occurs in postmenopausal women with glucocorticoid-induced osteoporosis. It was also concluded that the receptor activator of NF-κB ligand was stimulated in the late progressive phase of the osteoporosis induced by steroids in sheep. The knowledge of the pathophysiological mechanisms at the cellular and molecular levels of the induction of osteoporosis in small ruminants, if identical to humans, will allow in the future, the use of these animal models with greater confidence in the preclinical and translational studies for osteoporosis research.

Effects of Trifolium alexandrinum phytoestrogens on oestrous behaviour, ovarian activity and reproductive performance of ewes during the non-breeding season

Phytoestrogens are classified as naturally occurring endocrine disrupting chemicals that may affect reproductive performance of farm animals. To investigate the effects of Berseem clover phytoestrogens on reproductive performance of seasonal anoestrus ewes, twenty four late pregnant Rahmani ewes were fed either Berseem clover or maize silage (n = 12/treatment). Treatment started 2 months prepartum and continued until oestrous induction (week 8 postpartum), using the CIDR-eCG based protocol, and early pregnancy. Throughout the 2-8 weeks postpartum, oestrous rate and ovarian activity were not affected by treatment. After oestrous induction, ewes in both groups expressed comparable oestrous rates; however feeding Berseem clover extended (P < 0.05) interval to oestrus (57.00 compared with 42.54 h) and shortened (P < 0.05) oestrous duration (20.0 compared with 34.90 h). Feeding Berseem clover did not affect follicular activity except the number of medium follicles, which was less (P < 0.05) on day of oestrus (Day 0). Feeding maize silage increased (P < 0.05) the total number of follicles and number of small and medium follicles the day before oestrus (Day -1). On Day 0, the greater total number of follicles was due to the greater (P < 0.05) number of medium follicles that was associated with less number of small follicles. Although, the number and diameter of corpora lutea (CLs) were not affected by treatment, serum P₄ concentration was greater (P < 0.05) for ewes fed maize silage than for those fed Berseem clover. Fecundity and litter size tended to be greater (about 35%; P = 0.132 and 0.085, respectively) in the maize silage fed ewes. In conclusion, feeding Berseem clover throughout seasonal anoestrus disrupted aspects of behavioural oestrus and there was less luteal P₄ synthesis and fecundity of ewes.

KNDy neurone activation prior to the LH surge of the ewe is disrupted by LPS

In the ewe, steroid hormones act on the hypothalamic arcuate nucleus (ARC) to initiate the GnRH/LH surge. Within the ARC, steroid signal transduction may be mediated by estrogen receptive dopamine-, β-endorphin- or neuropeptide Y (NPY)-expressing cells, as well as those co-localising kisspeptin, neurokinin B (NKB) and dynorphin (termed KNDy). We investigated the time during the follicular phase when these cells become activated (i.e., co-localise c-Fos) relative to the timing of the LH surge onset and may therefore be involved in the surge generating mechanism. Furthermore, we aimed to elucidate whether these activation patterns are altered after lipopolysaccharide (LPS) administration, which is known to inhibit the LH surge. Follicular phases of ewes were synchronised by progesterone withdrawal and blood samples were collected every 2 h. Hypothalamic tissue was retrieved at various times during the follicular phase with or without the administration of LPS (100 ng/kg). The percentage of activated dopamine cells decreased before the onset of sexual behaviour, whereas activation of β-endorphin decreased and NPY activation tended to increase during the LH surge. These patterns were not disturbed by LPS administration. Maximal co-expression of c-Fos in dynorphin immunoreactive neurons was observed earlier during the follicular phase, compared to kisspeptin and NKB, which were maximally activated during the surge. This indicates a distinct role for ARC dynorphin in the LH surge generation mechanism. Acute LPS decreased the percentage of activated dynorphin and kisspeptin immunoreactive cells. Thus, in the ovary-intact ewe, KNDy neurones are activated prior to the LH surge onset and this pattern is inhibited by the administration of LPS.

Infection and pubertal timing: a systematic review

The decline in age of pubertal timing has serious public health implications ranging from psychosocial adjustment problems to a possible increase in reproductive cancers. One biologically plausible explanation for the decline is a decrease in exposures to infections. To systematically review studies that assess the role of infection in pubertal timing, Medline, Web of Science and EMBASE were systematically searched and retrieved studies were reviewed for eligibility. Eligible studies examined the association between infections, including microbial exposures, and physical pubertal characteristics (breast, genitalia and pubic hair development) or age at menarche. We excluded studies that were published in a language other than English, focused on precocious puberty, were case studies, and/or included youth with autoimmune diseases. We report on study design, population characteristics, measurement of infection and puberty and the main effects of infection on pubertal development. Based on our search terms we identified 1372 unique articles, of which only 15 human and five animal studies met our eligibility criteria. Not all studies examined all outcomes. Infection was associated with later breast development (4/4 human studies), with less consistent evidence for genitalia and pubic hair development. Seven studies assessed age at menarche with inconsistent findings (three supporting later, four no association). We conclude that a small but consistent literature supports that infection is associated with later breast development; the evidence for other pubertal events and age at menarche is less clear. Where fewer childhood infections coincide with the rise in incidence of hormone-related cancers.

Impact of psychosocial stress on gonadotrophins and sexual behaviour in females: role for cortisol?

This review focuses on the importance of cortisol in mediating the inhibitory effects of psychosocial stress on reproduction in females. In particular, we have summarized our research in sheep where we have systematically established whether cortisol is both sufficient and necessary to suppress reproductive hormone secretion and inhibit sexual behaviour. Our findings are put into context with previous work and are used to develop important concepts as well as to identify productive further lines of investigation. It is clear that cortisol is necessary to inhibit some, but not all, aspects of reproduction in female sheep. These actions vary with reproductive state, and there are important interactions with gonadal steroids. The impact of cortisol on the tonic secretion of gonadotrophin-releasing hormone and luteinizing hormone has been investigated extensively, but less is known about the surge secretion of these hormones and their effects on sexual behaviour. Furthermore, there are separate effects of cortisol in the brain (hypothalamus) and at the anterior pituitary, illustrating that there are different mechanisms of action. Thus, although cortisol is important in mediating some of the effects of stress on reproduction, we need to look beyond cortisol and investigate some of the other mechanisms and mediators that relay the effects of stress on reproduction. In this regard, we propose that a group of neurons in the hypothalamus that co-synthesize kisspeptin, neurokinin B and dynorphin, termed KNDy cells, play important roles in mediating the effects of cortisol on reproduction. This hypothesis needs to be rigorously tested.

The effect of cooling management on blood flow to the dominant follicle and estrous cycle length at heat stress

The use of ultrasound imaging for the examination of reproductive organs has contributed substantially to the fertility management of dairy cows around the world. This method has many advantages such as noninvasiveness and immediate availability of information. Adding Doppler index to the ultrasound imaging examination, improved the estimation of blood volume and flow rate to the ovaries in general and to the dominant follicle in particular. The aim of this study was to examine changes in the blood flow to the dominant follicle and compare them to the follicular development throughout the cycle. We further set out to examine the effects of different types of cooling management during the summer on the changes in blood flow to the dominant follicle. For this purpose, 24 Israeli-Holstein dairy cows, under heat stress, were randomly assigned one of two groups: one was exposed to five cooling sessions per day (5CS) and the other to eight cooling sessions per day (8CS). Blood flow to the dominant follicle was measured daily using Doppler index throughout the estrous cycle. No differences in the preovulatory dominant follicle diameter were detected between the two cooling management regimens during the cycle. However, the length of the first follicular wave was significantly longer, whereas the second follicular wave was nonsignificantly shorter in the 5CS group as compared to the 8CS group. In addition, no difference in blood flow was found during the first 18 days of the cycle between the two groups. However, from Day 20 until ovulation a higher rate of blood flow was measured in the ovaries of cows cooled 8 times per day as compared to the 5CS group. No differences in progesterone levels were noted. Finally, the estrous cycle length was shorter in the 8CS group as compared to the 5CS group. Our data suggest that blood flow to the dominant follicle and estrous cycle length is affected by heat stress. Using the appropriate cooling management during heat stress can enhance the blood flow to the ovary and may contribute to improved fertility in dairy cows.

Sexually active bucks are efficient to stimulate female ovulatory activity during the anestrous season also under temperate latitudes

Goats are seasonal breeders and photoperiod is the main cue controlling the onset and offset of the breeding season. Nevertheless introducing a sexually active buck in a group of females during anestrous can stimulate their reproductive function and induce ovulation. This "male-effect" is very efficient under subtropical latitudes, when using sexually active males previously stimulated by a photoperiodic treatment. However, there is less evidence of its feasibility under temperate latitudes where the more important variation in day length could be responsible for a stronger inhibition of female sexual activity. The aim of this study was therefore to determine whether intense sexual activity can be induced in alpine bucks during the non-breeding season by a long-day treatment under temperate latitude and if these males could be used to produce an efficient male-effect. Bucks (n=21) were divided in two groups, one submitted to a photoperiodic treatment from November 1st to January 15th and then switched to natural photoperiod, while the other group remained entirely under the natural photoperiod. The ones submitted to this light treatment exhibit higher testicular volume and testosterone level 6 weeks after the end of the treatment. At the end of March, bucks were used to stimulate anestrous does (n=41) continuously for 15 days. We showed that (a) light treatment was efficient to induce an increase of sexual activity in bucks and (b) that the introduction of stimulated bucks among females induced a significantly higher proportion of ovulation in anestrous does than control bucks (86% vs 5%). Our results indicate that under temperate latitudes induction of ovulation in females during the anestrous season is feasible using bucks treated with long-days during winter.

Ovarian and hormonal responses to single or continuous peripheral administration of senktide, a neurokinin 3 receptor agonist, during the follicular phase in goats

The present study aimed to investigate the effects of single or continuous administration of a neurokinin 3 receptor agonist, senktide, on hormonal and follicular dynamics in follicular phase goats. Goats were injected with PGF2α in the luteal phase and treated with an intravaginal progesterone device for 10 d. At 12 h after the cessation of progesterone treatment, the goats received a single intravenous injection of senktide (200 nmol, n = 4) or vehicle (n = 4), or continuous intravenous infusion of senktide (20 nmol/min, n = 6) or vehicle (n = 6) for 6 h. Blood sampling and ovarian ultrasonography were performed during the experiment. A single injection of senktide did not influence the number of luteinizing hormone (LH) pulses and mean LH concentration. On the other hand, continuous injection of senktide caused a sustained increase in LH secretion, and mean LH concentration in samples collected at 10-min intervals for 6 h after the start of infusion was higher than that of vehicle-treated goats (2.8 ± 1.3 vs 1.0 ± 0.6 ng/mL, P < 0.01). In 4 of 6 goats, LH concentrations reached their peaks during the 6-h senktide infusion, and ovulation was observed at 48 h after the start of infusion without estrous behavior. The remaining 2 senktide-treated goats and all vehicle-treated goats showed estrus and ovulated at 72 or 96 h after treatment. These results suggest that continuous infusion of senktide in follicular phase goats can cause a sustained increase in LH and advance the time of ovulation.

Activation of cells containing estrogen receptor alpha or somatostatin in the medial preoptic area, arcuate nucleus, and ventromedial nucleus of intact ewes during the follicular phase, and alteration after lipopolysaccharide

Cells in the medial preoptic area (mPOA), arcuate nucleus (ARC), and ventromedial nucleus (VMN) that possess estrogen receptor alpha (ER alpha) mediate estradiol feedback to regulate endocrine and behavioral events during the estrous cycle. A percentage of ER alpha cells located in the ARC and VMN express somatostatin (SST) and are activated in response to estradiol. The aims of the present study were to investigate the location of c-Fos, a marker for activation, in cells containing ER alpha or SST at various times during the follicular phase and to determine whether lipopolysaccharide (LPS) administration, which leads to disruption of the luteinizing hormone (LH) surge, is accompanied by altered ER alpha and/or SST activation patterns. Follicular phases were synchronized with progesterone vaginal pessaries, and control animals were killed at 0, 16, 31, and 40 h (n = 4-6/group) after progesterone withdrawal (PW [time 0]). At 28 h, other animals received LPS (100 ng/kg) and were subsequently killed at 31 h or 40 h (n = 5/group). Hypothalamic sections were immunostained for c-Fos and ER alpha or SST. LH surges occurred only in control ewes with onset at 36.7 ± 1.3 h after PW; these animals had a marked increase in the percentage of ER alpha cells that colocalized c-Fos (%ER alpha/c-Fos) in the ARC and mPOA from 31 h after PW and throughout the LH surge. In the VMN, %ER alpha/c-Fos was higher in animals that expressed sexual behavior than in those that did not. SST cell activation in the ARC and VMN was greater during the LH surge than in other stages in the follicular phase. At 31 or 40 h after PW (i.e., 3 or 12 h after treatment, respectively), LPS decreased %ER alpha/c-Fos in the ARC and the mPOA, but there was no change in the VMN compared to that in controls. The %SST/c-Fos increased in the VMN at 31 h after PW (i.e., 3 h after LPS) with no change in the ARC compared to controls. These results indicate that there is a distinct temporal pattern of ER alpha cell activation in the hypothalamus during the follicular phase, which begins in the ARC and mPOA at least 6-7 h before the LH surge onset and extends to the VMN after the onset of sexual behavior and LH surge. Furthermore, during the surge, some of these ER alpha-activated cells may be SST-secreting cells. This pattern is markedly altered by LPS administered during the late follicular phase, indicating that the disruptive effects of this stressor are mediated by suppressing ER alpha cell activation at the level of the mPOA and ARC and enhancing SST cell activation in the VMN, leading to the attenuation of the LH surge.

Progesterone improves the maturation of male-induced preovulatory follicles in anoestrous ewes

The first ovulation induced by male effect in sheep during seasonal anoestrus usually results in the development of a short cycle that can be avoided by progesterone priming before ram introduction. In elucidating the involvement of the hypothalamic–pituitary–gonadal axis in the occurrence of short cycles, the effects of progesterone and the time of anoestrus on the development of male-induced preovulatory follicles were investigated in anoestrous ewes using morphological, endocrine and molecular approaches. Ewes were primed with progesterone for 2 (CIDR2) or 12 days (CIDR12) and untreated ewes used as controls during early (April) and late (June) anoestrus. The duration of follicular growth and the lifespan of the male-induced preovulatory follicles were prolonged by ∼1.6 days in CIDR12 ewes compared with the controls. These changes were accompanied by a delay in the preovulatory LH and FSH surges and ovulation. Intra-follicular oestradiol concentration and mRNA levels ofLHCGRandSTARin the granulosa and theca cells of the preovulatory follicles were higher in CIDR12 ewes than the control ewes. The expression of mRNA levels ofCYP11A1andCYP17A1also increased in theca cells of CIDR12 ewes. CIDR2 ewes gave intermediate results. Moreover, ewes ovulated earlier in June than in April, without changes in the duration of follicular growth, but these effects were unrelated to the lifespan of corpus luteum. Our results give the first evidence supporting the positive effect of progesterone priming on the completion of growth and maturation of preovulatory follicles induced by male effect in seasonal anoestrous ewes, thereby preventing short cycles.

Central genomic regulation of the expression of oestrous behaviour in dairy cows: a review

The expression of oestrous behaviour in Holstein Friesian dairy cows has progressively decreased over the past 50 years. Reduced oestrus expression is one of the factors contributing to the current suboptimal reproductive efficiency in dairy farming. Variation between and within cows in the expression of oestrous behaviour is associated with variation in peripheral blood oestradiol concentrations during oestrus. In addition, there is evidence for a priming role of progesterone for the full display of oestrous behaviour. A higher rate of metabolic clearance of ovarian steroids could be one of the factors leading to lower peripheral blood concentrations of oestradiol and progesterone in high-producing dairy cows. Oestradiol acts on the brain by genomic, non-genomic and growth factor-dependent mechanisms. A firm base of understanding of the ovarian steroid-driven central genomic regulation of female sexual behaviour has been obtained from studies on rodents. These studies have resulted in the definition of five modules of oestradiol-activated genes in the brain, referred to as the GAPPS modules. In a recent series of studies, gene expression in the anterior pituitary and four brain areas (amygdala, hippocampus, dorsal hypothalamus and ventral hypothalamus) in oestrous and luteal phase cows, respectively, has been measured, and the relation with oestrous behaviour of these cows was analysed. These studies identified a number of genes of which the expression was associated with the intensity of oestrous behaviour. These genes could be grouped according to the GAPPS modules, suggesting close similarity of the regulation of oestrous behaviour in cows and female sexual behaviour in rodents. A better understanding of the central genomic regulation of the expression of oestrous behaviour in dairy cows may in due time contribute to improved (genomic) selection strategies for appropriate oestrus expression in high-producing dairy cows.

Sexually-dimorphic expression of tyrosine hydroxylase immunoreactivity in the brain of a vocal teleost fish (Porichthys notatus)

Vocal communication has emerged as a powerful model for the study of neural mechanisms of social behavior. Modulatory neurochemicals postulated to play a central role in social behavior, related to motivation, arousal, incentive and reward, include the catecholamines, particularly dopamine and noradrenaline. Many questions remain regarding the functional mechanisms by which these modulators interact with sensory and motor systems. Here, we begin to address these questions in a model system for vocal and social behavior, the plainfin midshipman fish (Porichthys notatus). We mapped the distribution of immunoreactivity for the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH) in the midshipman brain. The general pattern of TH(+) cell groups in midshipman appears to be highly conserved with other teleost fish, with a few exceptions, including the apparent absence of pretectal catecholamine cells. Many components of the midshipman vocal and auditory systems were innervated by TH(+) fibers and terminals, including portions of the subpallial area ventralis, the preoptic complex, and the anterior hypothalamus, the midbrain periaqueductal gray and torus semicircularis, several hindbrain auditory nuclei, and parts of the hindbrain vocal pattern generator. These areas thus represent potential sites for catecholamine modulation of vocal and/or auditory behavior. To begin to test functionally whether catecholamines modulate vocal social behaviors, we hypothesized that male and female midshipman, which are sexually dimorphic in both their vocal-motor repertoires and in their responses to hearing conspecific vocalizations, should exhibit sexually dimorphic expression of TH immunoreactivity in their vocal and/or auditory systems. We used quantitative immunohistochemical techniques to test this hypothesis across a number of brain areas. We found significantly higher levels of TH expression in male midshipman relative to females in the TH cell population in the paraventricular organ of the diencephalon and in the TH-innervated torus semicircularis, the main teleost midbrain auditory structure. The torus semicircularis has been implicated in sexually dimorphic behavioral responses to conspecific vocalizations. Our data thus support the general idea that catecholamines modulate vocal and auditory processing in midshipman, and the specific hypothesis that they shape sexually dimorphic auditory responses in the auditory midbrain.

Developmental programming: postnatal steroids complete prenatal steroid actions to differentially organize the GnRH surge mechanism and reproductive behavior in female sheep

In female sheep, estradiol (E2) stimulates the preovulatory GnRH/LH surge and receptive behavior, whereas progesterone blocks these effects. Prenatal exposure to testosterone disrupts both the positive feedback action of E2 and sexual behavior although the mechanisms remain unknown. The current study tested the hypothesis that both prenatal and postnatal steroids are required to organize the surge and sex differences in reproductive behavior. Our approach was to characterize the LH surge and mating behavior in prenatally untreated (Control) and testosterone-treated (T) female sheep subsequently exposed to one of three postnatal steroid manipulations: endogenous E2, excess E2 from a chronic implant, or no E2 due to neonatal ovariectomy (OVX). All females were then perfused at the time of the expected surge and brains processed for estrogen receptor and Fos immunoreactivity. None of the T females exposed postnatally to E2 exhibited an E2-induced LH surge, but a surge was produced in five of six T/OVX and all Control females. No surges were produced when progesterone was administered concomitantly with E2. All Control females were mounted by males, but significantly fewer T females were mounted by a male, including the T/OVX females that exhibited LH surges. The percentage of estrogen receptor neurons containing Fos was significantly influenced in a brain region-, developmental stage-, and steroid-specific fashion by testosterone and E2 treatments. These findings support the hypothesis that the feedback controls of the GnRH surge are sensitive to programming by prenatal and postnatal steroids in a precocial species.

Estrous behavior in dairy cows: identification of underlying mechanisms and gene functions

Selection in dairy cattle for a higher milk yield has coincided with declined fertility. One of the factors is reduced expression of estrous behavior. Changes in systems that regulate the estrous behavior could be manifested by altered gene expression. This literature review describes the current knowledge on mechanisms and genes involved in the regulation of estrous behavior. The endocrinological regulation of the estrous cycle in dairy cows is well described. Estradiol (E2) is assumed to be the key regulator that synchronizes endocrine and behavioral events. Other pivotal hormones are, for example, progesterone, gonadotropin releasing hormone and insulin-like growth factor-1. Interactions between the latter and E2 may play a role in the unfavorable effects of milk yield-related metabolic stress on fertility in high milk-producing dairy cows. However, a clear understanding of how endocrine mechanisms are tied to estrous behavior in cows is only starting to emerge. Recent studies on gene expression and signaling pathways in rodents and other animals contribute to our understanding of genes and mechanisms involved in estrous behavior. Studies in rodents, for example, show that estrogen-induced gene expression in specific brain areas such as the hypothalamus play an important role. Through these estrogen-induced gene expressions, E2 alters the functioning of neuronal networks that underlie estrous behavior, by affecting dendritic connections between cells, receptor populations and neurotransmitter releases. To improve the understanding of complex biological networks, like estrus regulation, and to deal with the increasing amount of genomic information that becomes available, mathematical models can be helpful. Systems biology combines physiological and genomic data with mathematical modeling. Possible applications of systems biology approaches in the field of female fertility and estrous behavior are discussed.

Follicular dynamics, interval to ovulation and fertility after AI in short-term progesterone and PGF2α oestrous synchronization protocol in sheep

The study was aimed to assess the influence that short-term progesterone treatments have on follicular dynamics, oestrus and ovulation in sheep. The treatment was tested thereafter in a field trial to assess its fertility after AI with fresh semen. In a first experiment, 12 ewes without CL were grouped to receive a new (n = 6) or used CIDR (n = 6) for 7 days and blood samples were obtained to follow plasma progesterone profiles. In a second experiment, 39 cycling ewes were synchronized by a 7-day P4+PGF2α protocol using a new (n = 20) or a 7-day used CIDR (n = 19). Half of both groups received 400 IU eCG and half remained untreated as controls. Ultrasound ovarian examination and oestrous detection were used to compare follicular dynamics, oestrus and ovulation in both groups. In a third experiment, 288 ewes in 3 farms were synchronized by the short-term P4+PGF2α+eCG protocol and ewes were AI with fresh semen 24 h after oestrous detection. Lambing performance was used to test the fertility of the treatment. In Experiment 1, ewes with new inserts presented higher P4 concentration than ewes with used inserts throughout the sampling period (p < 0.05) and exhibited a P4 peak at days 1-2 of the treatment that was not observed in ewes with used inserts. In Experiment 2, ewes treated with new and used inserts show similar ovarian and behavioral traits (p > 0.10). However, ewes treated with eCG show shorter interval to oestrus (p = 0.004) and tend to have larger mature CL (p = 0.06). In Experiment 3, oestrous presentation and lambing performance after AI with fresh semen was considered normal compared to published results. Results suggest that the oestrous synchronization protocol based on P4+PGF2α allows little control of follicular dynamics without compromising fertility after AI with fresh semen provided that eCG is added at the end of the treatment.

Progesterone signaling mechanisms in brain and behavior

Steroid hormone, progesterone, modulates neuroendocrine functions in the central nervous system resulting in alterations in physiology and behavior. These neuronal effects are mediated primarily by intracellular progestin receptors (PRs) in the steroid-sensitive neurons, resulting in transcription-dependent genomic actions (classical mechanism). In addition to progesterone, intracellular PRs can also be activated in a "ligand-independent" manner by neurotransmitters, peptide growth factors, cyclic nucleotides, and neurosteroids. Recent studies indicate that rapid, non-classical progesterone actions involving cytoplasmic kinase signaling and/or extranuclear PRs can result in both transcription-independent and transcription-dependent actions. Cross-talk between extranuclear and classical intracellular signaling pathways promotes progesterone-dependent behavior in mammals. This review focuses on the mechanisms by which progesterone-initiated signaling mechanisms converge with PRs in the brain to modulate reproductive behavior in female rodents.

Effect of summer heat environment on body temperature, estrous cycles and blood antioxidant levels in Japanese Black cow

This study investigated the effect of summer heat environment on estrous cycles and blood antioxidant levels in Japanese Black cows. A total of 13 non-lactating Japanese Black cows (summer: 9, winter: 4) were examined. Body temperature was measured rectally and intravaginally using a thermometer and data logger, respectively. Estrous behavior was monitored using a radiotelemetric pedometer that recorded walking activity. Rectal temperatures were higher during summer than winter (P<0.001). There was an acute increase in vaginal temperature at the onset of estrus during winter but such an increase was not observed during summer. Walking activity during estrus decreased dramatically in the summer compared to the winter. Duration of estrous cycle was longer in summer (23.4 days, P<0.05) than winter (21.5 days), and the subsequent rise in progesterone concentrations following estrus tended to be delayed in summer. The level of thiobarbituric acid reactive substances (TBARS) in peripheral blood cells was higher during summer (P<0.05), while the levels of superoixde dismutase (SOD), glutathione peroxidase (GPx) and glutathione were lower (P<0.05). These results indicate that high ambient temperature during summer increases both body temperature and oxidative stress, and also reduces signs of estrus in Japanese Black cows.

Acute and chronic stress-like levels of cortisol inhibit the oestradiol stimulus to induce sexual receptivity but have no effect on sexual attractivity or proceptivity in female sheep

Stress-like levels of cortisol inhibit sexual receptivity in ewes but the mechanism of this action is not understood. One possibility is that cortisol interferes with the actions of oestradiol to induce sexual receptivity. We tested this hypothesis in 2 experiments with ovariectomised ewes that were artificially induced into oestrus by 12 days of i.m. injections of progesterone followed by an i.m. injection of oestradiol benzoate (ODB) 48 h later. In Experiment 1, ewes were randomly allocated to the following groups: saline infusion+25 μg ODB, saline infusion+50 μg ODB, cortisol infusion+25 μg ODB or cortisol infusion+50 μg ODB (n=5 per group). Saline or cortisol was infused i.v. for 40 h beginning at the ODB injection. In Experiment 2, ewes were infused with saline or cortisol (n=5 per group) for 5h beginning 1h before ODB injection. In both experiments, ewe sexual behaviour (attractivity, proceptivity and receptivity) was quantified every 6h. Blood samples were also collected. The cortisol infusion yielded plasma concentrations of cortisol similar to those seen during psychosocial stress. In both experiments, cortisol suppressed receptivity index (number of immobilisations by ewe/courtship displays by ram) and the number of times ewes were mounted but had no effect on attractivity or proceptivity, irrespective of the dose of ODB (Experiment 1). Cortisol also suppressed LH pulse amplitude. These results suggest that both an acute (5h) and chronic (40 h) infusion of cortisol inhibit oestradiol-induced sexual receptivity in ewes and that increasing the dose of ODB does not overcome the inhibitory effects of cortisol.

Breed and experience effect on the sexual behaviors of Damascus and Egyptian-Nubian goat bucks

This study compares the sexual behaviors of bucks from two pure breeds of goats, Damascus and Egyptian-Nubian (Zaraibi), and assesses their relationships with the pregnancy and kidding rates of their inseminated does. Twenty-three bucks (12 Damascus and 11 Egyptian-Nubian bucks) were used in this study. These bucks were either in their first season of service (N =12, with an average age of 1.51 years) or had been previously used in service for several seasons (N = 11, with an average age of 3.34 years). Buck service behaviors toward estrous does were continuously recorded for 30 minutes from the moment of appearance of the doe. Egyptian-Nubian bucks were highly sexually active with estrous does in comparison with Damascus bucks. They required less time to mount and ejaculate for the first (P < 0.04) and second times (P < 0.0002) and tended to sniff, nudge and vocalize more frequently than Damascus bucks. In addition, Egyptian-Nubian bucks had more ejaculations and a higher mating efficiency (27.48% vs. 10.21%, P < 0.001), and their inseminated does had a higher pregnancy rate and larger litter sizes. Regarding the effect of experience, the data revealed a limited influence. No significant differences in sexual behavior were recorded between younger and older bucks. Conversely, pregnancy, kidding rates, and litter size were not influenced by the total number of ejaculations. From these results, it can be concluded that there were sexual behavior differences as a function of breed between Damascus and Egyptian-Nubian bucks and that experience had little impact in this study.

Effects of gonadotropin-releasing hormone immunization on reproductive function and behavior in captive female Rocky Mountain elk (Cervus elaphus nelsoni)

Fertility control is a potential method for managing overabundant wildlife populations; however, current technology is limited by duration of treatment efficacy and unacceptable side effects. The objective of this study was to determine the efficacy of a single immunization with gonadotropin-releasing hormone (GnRH) vaccine to suppress reproductive function in pregnant female elk and to evaluate potential behavioral and pathological side effects of treatment. Eighteen captive adult female elk were randomly allocated to one of two experimental groups. Ten females were administered a conjugated and adjuvanted GnRH vaccine intramuscularly, and eight elk received an adjuvant sham vaccine without conjugated GnRH. We compared success of existing pregnancy, neonatal survival, subsequent fertility, reproductive behavior rates, and side effects of treatment between January 2006 and January 2010. The GnRH vaccination did not affect existing pregnancy or calf survival during the year that it was applied; however, it reduced the proportion of pregnant females for 3 yr. Male precopulatory behavior rates exhibited toward GnRH-vaccinated females tended to be greater than those directed at sham-vaccinated females during the second half of the breeding season, when GnRH vaccinates continued to be proceptive. Strong immune and inflammatory responses, including robust GnRH antibody concentrations in GnRH vaccinates, and sterile pyogranulomatous injection site abscesses in both groups, were consistent with vaccination. In conclusion, this GnRH vaccine resulted in prolonged, albeit reversible, impairment of fertility, and is associated with extended reproductive behaviors and partial suppression of hypothalamic-pituitary-gonadal axis function in captive female elk.

Evidence for cell proliferation in the sheep brain and its down-regulation by parturition and interactions with the young

Production of new neurons continues throughout life in the subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampus and is influenced by both endocrine and social factors. In sheep parturition is associated with the establishment of a selective bond with the young based on an olfactory learning. The possibility exists that endocrine changes at parturition together with interactions with the young modulate cell proliferation in the neurogenic zones. In the present study, we first investigated the existence of cell proliferation in sheep. Newly born cells labeled by the cell proliferation marker 5-bromo-2'-deoxyuridine (BrdU) were found in the SVZ, the main olfactory bulb (MOB) and the DG and completely co-localized with Ki-67, another mitotic marker. Forty to 50% of the BrdU-labeled cells contained GFAP suggestive of the presence of neural stem cells. Secondly, parturition with or without interactions with the lamb for 2 days, down-regulated the number of BrdU-labeled cells in the 3 proliferation sites in comparison to no pregnancy. An additional control provided evidence that this effect is specific to early postpartum period: estrus with interactions with males did not affect cell proliferation. Our results provide the first characterization of neural cell proliferation in the SVZ, the DG and unexpectedly in the MOB of adult sheep. We hypothesize that the down-regulation of cell proliferation observed in the early postpartum period could facilitate the olfactory perceptual and memory demands associated with maternal behavior by favouring the survival and integration of neurons born earlier.

Activation of progestin receptors in female reproductive behavior: Interactions with neurotransmitters

The steroid hormone, progesterone (P), modulates neuroendocrine functions in the central nervous system resulting in alterations in physiology and reproductive behavior in female mammals. A wide body of evidence indicates that these neural effects of P are predominantly mediated via their intracellular progestin receptors (PRs) functioning as "ligand-dependent" transcription factors in the steroid-sensitive neurons regulating genes and genomic networks. In addition to P, intracellular PRs can be activated by neurotransmitters, growth factors and cyclic nucleotides in a ligand-independent manner via crosstalk and convergence of pathways. Furthermore, recent studies indicate that rapid signaling events associated with membrane PRs and/or extra-nuclear, cytoplasmic PRs converge with classical PR activated pathways in neuroendocrine regulation of female reproductive behavior. The molecular mechanisms, by which multiple signaling pathways converge on PRs to modulate PR-dependent female reproductive behavior, are discussed in this review.

The inhibition of female rabbit sexual behavior by progesterone: progesterone receptor-dependent and-independent effects

In the pregnant domestic rabbit, scent marking ("chinning") and sexual behavior are inhibited by ovarian-derived progesterone (P). In order to distinguish behavioral effects of P that are PR-dependent from those mediated by its ring A reduced metabolites, we administered P, P+RU486 (PR antagonist), chlormadinone acetate (CA, synthetic progestin that does not form ring A reduced metabolites), or vehicle to ovariectomized (ovx) estradiol-benzoate (EB)-treated female rabbits, via sc injection, on experimental day 0. Chinning was quantified daily, and mating tests were done on days -1, 1, 3, 5, and 7. On day 1, chinning was significantly decreased, and the latency to be mounted by the male was significantly increased (indicating decreased sexual attractivity of the female) in P-treated females. The effect of P on chinning, but not its effect on sexual attractivity, was completely blocked by RU486 and replicated by CA. Although CA had no effect on attractivity on day 1, it decreased both sexual receptivity and attractivity on day 3. In a preference test in which the male could interact with either an ovx EB-treated female or an ovx female that had received one of the above hormone treatments 24 h earlier, P decreased sexual attractivity and increased aggression. The effect of P on aggression, but not its effect on attractivity, was blocked by RU486 and replicated by CA. These results indicate that both PR-dependent and PR-independent mechanisms decrease sexual attractivity, whereas PR activation is necessary for the inhibition of chinning and sexual receptivity, and for the stimulation of aggression.

Review of nonprimate, large animal models for osteoporosis research

Large animal models are required for preclinical prevention and intervention studies related to osteoporosis research. The challenging aspect of this requirement is that no single animal model exactly mimics the progression of this human-specific chronic condition. There are pros and cons associated with the skeletal, hormonal, and metabolic conditions of each species that influence their relevance and applicability to human physiology. Of all larger mammalian species, nonhuman primates (NHPs) are preeminent in terms of replicating important aspects of human physiology. However, NHPs are very expensive, putting them out of reach of the vast majority of researchers. Practical, cost-effective alternatives to NHPs are sought after among ungulate (porcine, caprine, and ovine) and canine species that are the focus of this review. The overriding caveat to using large lower-order species is to take the time in advance to understand and appreciate the limitations and strengths of each animal model. Under these circumstances, experiments can be strategically designed to optimize the potential of an animal to develop the cardinal features of postmenopausal bone loss and/or yield information of relevance to treatment.

Psychosocial stress suppresses attractivity, proceptivity and pulsatile LH secretion in the ewe

Various stressors suppress pulsatile secretion of luteinizing hormone (LH) in ewes and cortisol has been shown to be a mediator of this effect under various conditions. In contrast, little is known about the impact of stress and cortisol on sexual behavior in the ewe. Therefore, we tested the hypothesis that both psychosocial stress and stress-like levels of cortisol will reduce the level of attractivity, proceptivity and receptivity in addition to suppressing LH secretion in the ewe. In Experiment 1, a layered stress paradigm of psychosocial stress was used, consisting of isolation for 4 h with the addition of restraint, blindfold and noise of a barking dog (predator stress) at hourly intervals. This stress paradigm reduced LH pulse amplitude in ovariectomized ewes. In Experiment 2, ovariectomized ewes were artificially induced into estrus with progesterone and estradiol benzoate treatment and the layered stress paradigm was applied. LH was measured and sexual behavior was assessed using T-mazes and mating tests. Stress reduced pulsatile LH secretion, and also reduced attractivity and proceptivity of ewes but had no effect on receptivity. In Experiment 3, ewes artificially induced into estrus were infused with cortisol for 30 h. Cortisol elevated circulating plasma concentrations of cortisol, delayed the onset of estrus and resulted in increased circling behavior of ewes (i.e. moderate avoidance) during estrus and increased investigation and courtship from rams. There was no effect of cortisol on attractivity, proceptivity or receptivity during estrus. We conclude that psychosocial stress inhibits LH secretion, the ability of ewes to attract rams (attractivity) and the motivation of ewes to seek rams and initiate mating (proceptivity), but cortisol is unlikely to be the principal mediator of these effects.