Effect of the Camelid's Seminal Plasma Ovulation-Inducing Factor/β-NGF: A Kisspeptin Target Hypothesis

Semen promotes oocyte development in Sebastesschlegelii elucidating ovarian development dynamics in live-bearing fish

In some vertebrates and invertebrates, semen release factors affecting female physiology and behavior. Here, we report that semen delivered to females is potentially beneficial for promoting oocyte development in a viviparous teleost, Sebastes schlegelii. 88% of mated ovaries develop normally and give birth to larval fish, whereas 61% of non-mated ovaries are arrested in the previtellogenic stage. Semen's significant role (p < 0.0001) in promoting oocyte development may involve remodeling follicular cells and regulating the expression of the extracellular matrix, which facilitates cell communication. Furthermore, the ovarian response to semen may influence the brain, affecting hormone release, follicular cell development and steroid production, and crucial for oocyte growth. This mechanism, which could potentially delay maternal investment in offspring until male genetic input occurs to avoid energy wastage, has not been previously described in teleosts. These findings enhance our understanding of ovarian development in viviparous fish, with broader implications for reproductive biology.

Hypothalamic-pituitary-gonadal axis response to photoperiod changes in female guanacos (Lama guanicoe)

The guanaco, a wild South American camelid, is renowned for its remarkable resilience to extreme conditions. Despite this, little is known about how reproductive hormones in female camelids are influenced during their seasonal breeding period, which occurs during long photoperiod. To explore this, the study investigated the response of the hypothalamic-pituitary-gonadal axis in female guanacos during short days (10L:14D; July) and long days (16L:8D; December) in the Mediterranean ecosystem (33°38'28″S, 70°34'27″W). Blood samples from 14 adult animals were collected, and measurements of melatonin, 17β-estradiol, FSH, and LH concentrations were taken. The results showed that melatonin concentration was lower (P < 0.05) during long days than short days, whereas 17β-estradiol, FSH, and LH concentrations were higher (P < 0.05) during long days compared to short days. Furthermore, the study detected the expression of the melatonin receptor 1A and kisspeptin in the hypothalamus and pituitary, suggesting that the pineal gland of female guanacos is sensitive to seasonal changes in day length. These findings also indicate a seasonal variation in the concentration of reproductive hormones, likely linked to the distinct modulation of the hypothalamic-pituitary-gonadal axis of female guanacos during short and long days.

Neuroendocrine control of gonadotropin-releasing hormone: Pulsatile and surge modes of secretion

The concept that different systems control episodic and surge secretion of gonadotropin-releasing hormone (GnRH) was well established by the time that GnRH was identified and formed the framework for studies of the physiological roles of GnRH, and later kisspeptin. Here, we focus on recent studies identifying the neural mechanisms underlying these two modes of secretion, with an emphasis on their core components. There is now compelling data that kisspeptin neurons in the arcuate nucleus that also contain neurokinin B (NKB) and dynorphin (i.e., KNDy cells) and their projections to GnRH dendrons constitute the GnRH pulse generator in mice and rats. There is also strong evidence for a similar role for KNDy neurons in sheep and goats, and weaker data in monkeys and humans. However, whether KNDy neurons act on GnRH dendrons and/or GnRH soma and dendrites that are found in the mediobasal hypothalamus (MBH) of these species remains unclear. The core components of the GnRH/luteinising hormone surge consist of an endocrine signal that initiates the process and a neural trigger that drives GnRH secretion during the surge. In all spontaneous ovulators, the core endocrine signal is a rise in estradiol secretion from the maturing follicle(s), with the site of estrogen positive feedback being the rostral periventricular kisspeptin neurons in rodents and neurons in the MBH of sheep and primates. There is considerable species variations in the neural trigger, with three major classes. First, in reflex ovulators, this trigger is initiated by coitus and carried to the hypothalamus by neural or vascular pathways. Second, in rodents, there is a time of day signal that originates in the suprachiasmatic nucleus and activates rostral periventricular kisspeptin neurons and GnRH soma and dendrites. Finally, in sheep nitric oxide-producing neurons in the ventromedial nucleus, KNDy neurons and rostral kisspeptin neurons all appear to participate in driving GnRH release during the surge.

Assessment of Biostimulation Methods Based on Chemical Communication in Female Doe Reproduction

Biostimulation is an animal management practice that helps improve reproductive parameters by modulating animal sensory systems. Chemical signals, mostly known as pheromones, have a great potential in this regard. This study was conducted to determine the influence of short-term female rabbit exposure to different conditions, mainly pheromone-mediated, on reproductive parameters of inseminated does. Groups of 60 females/each were exposed to (1) female urine, (2) male urine, (3) seminal plasma and (4) female-female (F-F) separated, just before artificial insemination, and compared to a 'golden method' female-female interaction. The following reproductive parameters were analyzed for each group: receptivity (vulvar color), fertility (kindling rate), prolificacy and number of born alive and dead kits/litter. Our results showed that the biostimulation methods employed in this experiment did not significantly improve any of the analyzed parameters. However, female doe exposure to urine, especially to male urine, showed no significant higher fertility values (95.4%) when compared to the rest of the experimental conditions (on average 92.4%). Female-female interaction before artificial insemination, which is a common practice in rabbit farms, showed similar results as not establishing social interaction (F-F separated), which suggests that F-F interaction could be replaced by F-F separated, therefore avoiding unnecessary animal management and time cost. On the other hand, fertility ranges were lower for animals with a pale vulvar color whereas no differences were noticed among the other three colors which measure receptivity (pink, red, purple), thus suggesting that these three colors could be grouped together. Future studies should aim at determining potential chemical cues/pheromones released through bodily secretions that influence reproduction in rabbits, therefore contributing to animal welfare and to a natural image of animal production.

Physiology and modulation factors of ovulation in rabbit reproduction management

Rabbit is an induced ovulatory species, so ovulation takes place after mating. Traditionally, exogenous and synthetic hormonal factors (administered by intramuscular and intravaginal route) such as GnRH and analogues, or different physical procedures (i.e. stimulation by intravaginal cannula) have been used to induce ovulation in females when artificial insemination is applied in rabbit farms. Restriction and public rejection of the use of hormones is leading to the study of the seminal plasma components with potential action on ovulation induction. The aim of the present review is to collect and summarise the strategies used in recent years to trigger ovulation and improve rabbit fertility management with respect to more animal-friendly manipulation methods. Furthermore, special attention has been paid to the use of a semen component (as endogen molecule) such as beta nerve growth factor (β-NGF) in male and female rabbit reproductive physiology. This neurotrophin and its receptors (TrKA and p75NTR) are abundantly distributed in both male and female rabbit reproductive tracts, and it seems to have an important physiological role in sperm maturation and behaviour (velocity, apoptosis and capacitation), as well as a modulatory factor of ovulation. Endogen β-NGF is diluted in the seminal doses with the extenders; hence it could be considered an innovative and alternative strategy to avoid the current exogenous (by intramuscular route) and stressful hormonal treatments used in ovulation induction. Their addition in seminal dose could be more physiological and improve animal welfare in rabbit farms.

Male-derived copulatory plugs enhance implantation success in female Mus musculus

Among a wide diversity of sexually reproducing species, male ejaculates coagulate to form what has been termed a copulatory plug. A number of functions have been attributed to copulatory plugs, including the inhibition of female remating and the promotion of ejaculate movement. Here we demonstrate that copulatory plugs also influence the likelihood of implantation, which occurs roughly 4 days after copulation in mice. Using a bead transfer method to control for differences in ejaculate retention and fertilization rates, we show that implantation rates significantly drop among females mated to genetically engineered males incapable of forming plugs (because they lack functional transglutaminase 4, the main enzyme responsible for its formation). Surprisingly, this result does not correlate with differences in circulating progesterone levels among females, an important hormone involved in implantation. We discuss three models that connect male-derived copulatory plugs to implantation success, including the hypothesis that plugs contribute to a threshold amount of stimulation required for females to become receptive to implantation.

Distribution of GnRH and Kisspeptin Immunoreactivity in the Female Llama Hypothalamus

Llamas are induced non-reflex ovulators, which ovulate in response to the hormonal stimulus of the male protein beta-nerve growth factor (β-NGF) that is present in the seminal plasma; this response is dependent on the preovulatory gonadotrophin-releasing hormone (GnRH) release from the hypothalamus. GnRH neurones are vital for reproduction, as these provide the input that controls the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland. However, in spontaneous ovulators, the activity of GnRH cells is regulated by kisspeptin neurones that relay the oestrogen signal arising from the periphery. Here, we investigated the organisation of GnRH and kisspeptin systems in the hypothalamus of receptive adult female llamas. We found that GnRH cells exhibiting different shapes were distributed throughout the ventral forebrain and some of these were located in proximity to blood vessels; sections of the mediobasal hypothalamus (MBH) displayed the highest number of cells. GnRH fibres were observed in both the organum vasculosum laminae terminalis (OVLT) and median eminence (ME). We also detected abundant kisspeptin fibres in the MBH and ME; kisspeptin cells were found in the arcuate nucleus (ARC), but not in rostral areas of the hypothalamus. Quantitative analysis of GnRH and kisspeptin fibres in the ME revealed a higher innervation density of kisspeptin than of GnRH fibres. The physiological significance of the anatomical findings reported here for the ovulatory mechanism in llamas is still to be determined.

New Insights Into the Role of β-NGF/TrKA System in the Endometrium of Alpacas During Early Pregnancy

One striking reproductive feature in South American camelids is that more than 90% of gestations are established in the left uterine horn (LUH). This phenomenon could be related to a differential vascular irrigation of the LUH. An increase of vascularization in llama endometrium was observed after systemic administration of Beta Nerve Growth Factor (β-NGF), a neurotrophin present in the uterus and placenta of various mammals that is involved in pregnancy development. We hypothesized that the β-NGF signaling pathway is related to embryo implantation in the LUH in camelids. The aim of this study was to characterize the spatial expression of β-NGF and its high-affinity receptor, TrKA, between LUH and right uterine horn (RUH) of non-pregnant (NP) and early pregnant alpacas (15 and 30 days of gestation, 15 and 30P, respectively). In addition, β-NGF, TrKA, and Vascular Endothelium Growth Factor A (VEGFA) temporal gene expression patterns and counting of blood vessels were evaluated among groups. The β-NGF and TrKA were localized in the luminal, glandular, and vascular epithelium of the alpaca uterus and in the embryonic membranes of the 30-days-old conceptus. β-NGF and TrKA immunosignal were stronger in 15P females than that of NP and 30P. In addition, TrKA signal was higher in the LUH luminal epithelium of NP and 15P alpacas than that of NP-RUH and 15P-RUH. β-NGF mRNA relative abundance was higher in the 30P-RUH than that of NP-RUH; whereas TrKA mRNA abundance only differed between 15P-RUH and NP-LUH. VEGFA mRNA relative abundance was higher in NP females compared to the LUH of 15P and 30P alpacas, and lower to their right counterparts. The number of vessels per field was higher in 15P than that of 30P. A positive correlation was observed between the number of vessels per field and β-NGF immunosignal in 15P-LUH. In contrast, the area occupied by vessels was higher in 30P alpacas than of NP and 15P females. The changes of β-NGF/TrKA expression pattern in the peri-implantation endometria between LUH and RUH and their localization in the extraembryonic membranes support the implication of the neurotrophin during implantation and pregnancy development in South American Camelids.

Nerve Growth Factor (NGF) and Animal Reproduction

Stimuli that lead to the release of gonadotropin-releasing hormone (GnRH) and pituitary gonadotropins and, consequently, ovulation in mammals fall into two broad categories. In the first, high plasma oestrogen concentrations induce the events that trigger ovulation, a characteristic of spontaneous ovulators. In the second, nerve stimuli occurring during mating reach the hypothalamus and trigger the release of GnRH and ovulation with a neuroendocrine reflex that characterizes induced ovulators.In this review, we will give an overview of the distribution of NGF and its expression in the different tissues of the male accessory sex glands, the main sites of NGF production. Next, we will highlight the role of NGF in sperm function and its potential cryopreserving role in artificial insemination techniques. Finally, we will evaluate the functions of NGF in ovulation, particularly in induced ovulators. Overall, the information obtained so far indicates that NGF is widely distributed in organs that regulate the reproductive activity, in both males and females. In spontaneous ovulators, NGF exerts mainly a luteotrophic action, while, in induced ovulators it is the main ovulation-inducing factor. A better understanding of the role of NGF in reproduction would be of great interest, since it could help finding innovative therapeutic aids to improve mammalian fertility.

Semen Handling in South American Camelids: State of the Art

Reproductive biotechnologies such as artificial insemination could be very useful for South American camelids, allowing widespread use of semen from breeding males with desirable genetics. However, artificial insemination is not widely employed in these species and is considered to have low overall efficiency. This is due in part to incomplete knowledge about the physiology of conception in these species, and also to challenges presented by semen collection and handling. Several recent reviews have centered on female camelid reproduction; therefore, in this review, the focus is on semen handling. Various semen collection methods are presented. Different methods of reducing seminal viscosity are compared, such as needling, enzyme treatment, and colloid centrifugation. Use of enzymes remains controversial because of widely differing results among research groups. Colloid centrifugation, particularly single layer centrifugation, has proved to be successful in facilitating development of sperm handling techniques in dromedary camels, and has also been used with llama semen. Therefore, protocols for colloid centrifugation of alpaca semen could be developed in the future.

Physiological effects on rabbit sperm and reproductive response to recombinant rabbit beta nerve growth factor administered by intravaginal route in rabbit does

Beta nerve growth factor (β-NGF) is present in the seminal plasma of some species, including rabbits, acting as an ovulation-inducing factor in camelids. Traditionally, GnRH analogues are used to induce ovulation by intramuscular route when artificial insemination (AI) is performed in rabbit does. A specific rabbit recombinant β-NGF (rrβ-NGF) produced in our laboratory was tested as an alternative method to conventional treatment with GnRH analogues to induce ovulation. In the present work, different concentrations (0, 20, 100 ng/mL and 1, 20 and 100 μg/mL) of rrβ-NGF were added to diluted semen to assess its effect on sperm traits (viability and motility parameters). rrβ-NG was used also, incorporated to the AI dose, to evaluate ovulation response (LH and progesterone plasma concentrations, ovulation rate (OR) and embryo implantation at Day 7) after intravaginal administration. A negative control group stimulated with an empty catheter, and a positive control group inseminated and intramuscularly treated as usual with GnRH were also set up. Results showed that seminal quality was influenced by rrβ-NGF depending on the concentration added, being the highest concentrations tested deleterious for semen. Whereas the highest OR was found in the positive control group (100%), concentrations of 20 ng/mL, 1 μg/mL and 20 μg/mL of rrβ-NGF triggered intermediate OR (30, 60 and 42.9%, respectively), and 100 ng/mL and 100 μg/mL had the lowest OR (20 and 14.3%, respectively). Although LH peak was not observed in the first 2 h after AI in the ovulated females from rrβ-NGF groups, plasma progesterone significantly increased at Day 7, except in those females treated with 20 and 100 μg/mL. Also, 98.4% of ovulated females were pregnant on Day 7. In conclusion, rrβ-NGF added to diluted semen affects seminal quality and provokes ovulation, the development of functional CL and conception by intravaginal route in rabbit does, depending on the concentration added.

Neurotrophins and glial cell line-derived neurotrophic factor in the ovary: physiological and pathophysiological implications

BACKGROUND

Neurotrophins [nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4)] and glial cell line-derived neurotrophic factor (GDNF) are soluble polypeptide growth factors that are widely recognized for their roles in promoting cell growth, survival and differentiation in several classes of neurons. Outside the nervous system, neurotrophin (NT) and GDNF signaling events have substantial roles in various non-neural tissues, including the ovary.

OBJECTIVE AND RATIONALE

The molecular mechanisms that promote and regulate follicular development and oocyte maturation have been extensively investigated. However, most information has been obtained from animal models. Even though the fundamental process is highly similar across species, the paracrine regulation of ovarian function in humans remains poorly characterized. Therefore, this review aims to summarize the expression and functional roles of NTs and GDNF in human ovarian biology and disorders, and to describe and propose the development of novel strategies for diagnosing, treating and preventing related abnormalities.

SEARCH METHODS

Relevant literature in the English language from 1990 to 2018 describing the role of NTs and GDNF in mammalian ovarian biology and phenotypes was comprehensively selected using PubMed, MEDLINE and Google Scholar.

OUTCOMES

Studies have shown that the neurotrophins NGF, BDNF, NT-3 and NT-4 as well as GDNF and their functional receptors are expressed in the human ovary. Recently, gathered experimental data suggest putative roles for NT and GDNF signaling in the direct control of ovarian function, including follicle assembly, activation of the primordial follicles, follicular growth and development, oocyte maturation, steroidogenesis, ovulation and corpus luteum formation. Additionally, crosstalk occurs between these ovarian regulators and the endocrine signaling system. Dysregulation of the NT system may negatively affect ovarian function, leading to reproductive pathology (decreased ovarian reserve, polycystic ovary syndrome and endometriosis), female infertility and even epithelial ovarian cancers.

WIDER IMPLICATIONS

A comprehensive understanding of the expression, actions and underlying molecular mechanisms of the NT/GDNF system in the human ovary is essential for novel approaches to therapeutic and diagnostic interventions in ovarian diseases and to develop more safe, effective methods of inducing ovulation in ART in the treatment of female infertility.

Administration of nerve growth factor-β to heifers with a pre-ovulatory follicle enhanced luteal formation and function and promoted LH release

The objective of this study was to determine the effects of bovine nerve growth factor-β (NGF) on pre-ovulatory follicle vascular area, LH release, ovulation, and luteal function when administered systemically to heifers. Post-pubertal Holstein heifers (n = 12) received an intravaginal progesterone-releasing device (CIDR) and GnRH agonist (100 μg IM). The CIDR was removed 5 d later, and heifers were given dinoprost (25 mg IM) at CIDR removal and 24 h later, followed by a second dose of GnRH agonist 48 h later. Heifers were randomly assigned to treatments using a cross-over design. For example, heifers assigned to NGF (250 μg reconstituted in 12 mL PBS IM) in replicate 1 were assigned to control (12 mL PBS IM) in replicate 2. Transrectal ultrasonography was performed before treatment and repeated every 4 h up to 32 h to determine the pre-ovulatory follicle diameter, vascular area, and ovulation. Serum samples were obtained to assess LH concentrations during the periovulatory period and every 2 d post-ovulation for measuring progesterone concentrations. A subset of heifers had luteal biopsies performed on days 9 (n = 6 per treatment) and 14 (n = 6 per treatment) post-ovulation to count luteal cell numbers and measure relative mRNA abundance for steroidogenic and angiogenic enzymes and LH receptor. Treatment with NGF increased pre-ovulatory follicle diameter (P = 0.02) and serum LH concentrations (P = 0.03) but did not affect time to ovulation (P = 0.42). Heifers treated with NGF had increased serum progesterone concentrations in the subsequent luteal phase (P = 0.03), but no change in vascular area of the follicle (P = 0.16) or CL (P = 0.20). Heifers treated with NGF had a greater number of small luteal cells (P < 0.01) and a tendency for increased LH receptor (LHR) mRNA abundance in the CL (P = 0.10). There was also increased steroidogenic acute regulatory protein (STAR; P = 0.05) and a tendency for increased cytochrome P450 family 11 (CYP11A1; P = 0.10) mRNA abundance in the CL of NGF-treated heifers. There was decreased prostaglandin E₂ synthase (PGES; P = 0.03) and its receptor (PGER; P = 0.05) mRNA abundance and a tendency for decreased cytochrome P450 family 17 subfamily A member 1 (CYP17A1; P = 0.08) and hydroxysteroid 17-beta dehydrogenase (HSD17B; P = 0.06) mRNA abundance in the CL of NGF-treated heifers. Administration of NGF improved CL function in heifers potentially as a result of increased LH release.

Insights into nerve growth factor-β role in bovine reproduction - Review

Nerve growth factor-β (NGF), initially recognized as a neurotrophin involved in regulating neuronal survival and differentiation, was also later revealed as a ubiquitous seminal plasma protein in mammals. In South American camelids, NGF was initially named ovulation-inducing factor and a dose-dependent luteotropic effect was also reported in llamas. Although NGF was present in the seminal plasma of bulls, the first studies only indicated a potential role on regulation of sperm physiology. The breakthrough discovery of NGF ability to induce ovulation in camelids led to a series of studies investigating the potential functions of NGF within the female reproductive system. In the bovine, a potential luteotropic effect of NGF was perceived as potential tool to overcome the current issues with early embryonic losses attributed at least in part to luteal insufficiency and failed maternal recognition of pregnancy. The aims of this review are to discuss recent advancements in the understanding of the biological roles of NGF in the bovine species. The insights of recent studies with NGF administered in cattle include enhancement of steroidogenesis, luteal formation, and function through increased release of LH, and downstream effect of increased expression of interferon-stimulated genes. In addition, a positive association with sire conception rates; the determination that is produced in the ampulla and vesicular glands of bulls and that is secreted into the sperm-rich fraction of the ejaculate; and the absence of improved post-thaw sperm motility, viability, acrosome integrity, or chromatin stability in ejaculated or epididymal derived sperm supplemented with purified NGF is also discussed.

Ovulation mechanism in South American Camelids: The active role of β-NGF as the chemical signal eliciting ovulation in llamas and alpacas

The ovulation-inducing effect of seminal plasma was first suggested in Bactrian camels over 30 years ago, initiating a long search to identify the 'ovulation-inducing factor' (OIF) present in camelids semen. During the last decade, primarily in llamas and alpacas, this molecule has been intensively studied characterizing its biological and chemical properties and ultimately identifying it as β-Nerve Growth Factor (β-NGF). The high concentration of OIF/β-NGF in seminal plasma of llamas and alpacas, and the striking effects of seminal fluid on ovarian function strongly support the notion of an endocrine mode of action. Also, have challenged the dogma of mating induced ovulation in camelid species, questioning the classical definition of reflex ovulators, which at the light of new evidence should be revised and updated. On the other hand, the presence of OIF/β-NGF and its ovulatory effect in camelids confirm the notion that seminal plasma is not only a transport and survival medium for sperm but also, a signaling agent targeting female tissues after insemination, generating relevant physiological and reproductive consequences. The presence of this molecule, conserved among induced as well as spontaneous ovulating species, clearly suggests that the potential impacts of this reproductive feature extend beyond the camelid species and may have broad implications in mammalian fertility. The aim of the present review is to provide a brief summary of all research efforts undertaken to isolate and identify the ovulation inducing factor present in the seminal plasma of camelids. Also to give an update of the current understanding of the mechanism of action of seminal β-NGF, at central and ovarian level; finally suggesting possible brain targets for this molecule.

Role of nerve growth factor in the reproductive physiology of female rabbits: A review

Rabbit does are reflex ovulators such that coitus is needed to release GnRH and elicit the LH surge that triggers the ovulation of mature oocytes. However, the mechanisms eliciting ovulation in this species remain unclear. One of the most promising recently discovered candidates with a role in female reproductive physiology is nerve growth factor beta (β-NGF). This neurotrophin and its high-affinity receptor TrkA and low affinity receptor p75, is present in all compartments of the ovary, oviduct and uterus suggesting a physiologic role in ovarian folliculogenesis, steroidogenesis, ovulation, luteogenesis and embryo development. Besides, evidence exists that β-NGF found in seminal plasma could exert a modulatory role in the female hypothalamus-pituitary-ovarian axis contributing to the adrenergic and cholinergic neuronal stimulus of GnRH neurons in an endocrine manner during natural mating. Probably, the paracrine and local roles of the neurotrophin in steroidogenesis and ovulation reinforce the neuroendocrine pathway that leads to ovulation. This review updates knowledge of the role of β-NGF in rabbit reproduction, including its possible contribution to the mechanisms of action that induce ovulation, and discusses perspectives for the future applications of this neurotrophin on rabbit farms.

New insights on a NGF-mediated pathway to induce ovulation in rabbits (Oryctolagus cuniculus)

To investigate the ovulatory mechanisms triggered by raw semen (RS) in rabbits, we examined the expression of nerve growth factor (NGF)-a supposed ovulation-inducing factor (OIF)-and cognate receptors in anterior pituitary, ovary, and cervix as well as plasma NGF and luteinizing hormone (LH) concentrations. Six does/group were sham-inseminated with sterile saline (PBS), naturally mated (NM), inseminated with RS alone or after lumbar anesthesia (ARS), or treatment with COX inhibitors (CIRS). Immunohistochemistry revealed positive signals for NGF and receptors in all tissues. RT-PCR confirmed the presence of the target transcripts in the same tissues, except NTRK1 in the cervix. Circulating NGF concentrations rose 3- to 6-fold (P < 0.01) 15 min after semen deposition into the genital tract of NM, RS, and ARS rabbits and remained sustained thereafter. Circulating NGF was 4-fold lower (P < 0.01) in CIRS than in RS does indicating that NGF is mainly synthesized by the uterus. A concomitant rise of LH and NGF concentrations was found in 83.3%, 50.0%, and 16.7% of NM, RS, and CIRS does, respectively, but not in ARS (despite high NGF circulating levels). Seminal plasma NGF concentration was 151.9 ± 9.25 μg/mL. The ovulatory responses were 0%, 83.3%, 66.7%, 16.7%, and 0% in PBS, NM, RS, ARS, and CIRS groups, respectively. Present data confirm that, although RS may induce ovulation via endocrine mechanisms through binding to NGF receptors in the ovary, a novel OIF-mediated neural mechanism facilitates ovulation in rabbits.

The relationship between gonadotropin releasing hormone and ovulation inducing factor/nerve growth factor receptors in the hypothalamus of the llama

BACKGROUND

A molecule identical to nerve growth factor, with ovulation-inducing properties has been discovered in the seminal plasma of South American camelids (ovulation-inducing factor/nerve growth factor; OIF/NGF). We hypothesize that the ovulatory effect of OIF/NGF is initiated at the level of the hypothalamus, presumably by GnRH neurons. The objective of the present study was to determine the structural relationship between GnRH neurons and neurons expressing high- and low-affinity receptors for NGF (i.e., TrkA and p75, respectively) in the hypothalamus.

METHODS

Mature llamas (n = 4) were euthanized and their hypothalamic tissue was fixed, sectioned, and processed for immunohistochemistry on free-floating sections. Ten equidistant sections per brain were double stained for immunofluorescence detection of TrkA and GnRH, or p75 and GnRH.

RESULTS

Cells immunoreactive to TrkA were detected in most hypothalamic areas, but the majority of cells were detected in the diagonal band of Broca (part of the ventral forebrain) and the supraoptic nuclei and periventricular area. The number of cells immunoreactive to p75 was highest in the diagonal band of Broca and lateral preoptic areas and least in more caudal areas of the hypothalamus (p < 0.05) in a pattern similar to that of TrkA. A low proportion of GnRH neurons were immunoreactive to TrkA (2.5% of total GnRH cells), and no co-localization between GnRH and p75 was detected. GnRH neuron fibers were detected only occasionally in proximity to TrkA immunopositive neurons.

CONCLUSIONS

Results do not support the hypothesis that the effect of OIF/NGF is driven by a direct interaction with GnRH neurons, but rather provide rationale for the hypothesis that interneurons exist in the hypothalamus that mediate OIF/NGF-induced ovulation.

PRELIMINARY EVALUATION OF SEMINAL PLASMA PROTEINS AND IMMUNOREACTIVITY OF NERVE GROWTH FACTOR AS INDICATIVE OF AN OVULATION INDUCING FACTOR IN ODONTOCETES

In the seminal plasma of terrestrial mammalian species known as induced (e.g., camels) and spontaneous (e.g., cattle) ovulators, an ovulation-inducing factor (OIF) with a protein structure similar to beta-nerve growth factor (β-NGF) has been identified. Detection of an OIF/NGF in the seminal plasma of cetaceans would have both basic and applied implications in reproductive biology and conservation management programs. A preliminary evaluation was conducted to characterize the distribution and abundance of seminal plasma proteins in aquarium-based belugas and a Pacific white-sided and bottlenose dolphin. Initially, SDS-PAGE was used with 50 μg of total protein for separation; thereafter, Western immunoblot was used with anti-NGF. In addition to odontocete seminal plasma, a purified fraction of llama seminal plasma (100 ng protein) and an extract of mouse brain (20 μg total protein) were included as positive controls for NGF. Within the two belugas, visual inspection of the protein bands indicated similar distribution and intensity. However, among the belugas and Pacific white-sided and bottlenose dolphins there was more diversity than similarity in the distribution and abundance of seminal plasma proteins. While immunoreactivity of NGF was distinctly evident in the llama and mouse positive controls, there was no visual reactivity in any of the odontocete samples. These preliminary results provide novel information indicating more homogeneity within and heterogeneity among seminal plasma proteins of ondentocetes. Although NGF was not immunologically detected, future studies are required to address the apparent limitations of immuno-detection of NGF, especially if the post-translational form of β-NGF is in low abundance in the seminal plasma of belugas and Pacific white-sided and bottlenose dolphins.