Intra-horn insemination in the alpaca Vicugna pacos: Copulatory wounding and deep sperm deposition

Alpacas (Vicugna pacos) are reported to be the rare mammal in which the penis enters the uterus in mating. To date, however, only circumstantial evidence supports this assertion. Using female alpacas culled for meat, we determined that the alpaca penis penetrates to the very tips of the uterine horns, abrading the tract and breaking fine blood vessels. All female alpacas sacrificed one hour or 24 hours after mating showed conspicuous bleeding in the epithelium of some region of their reproductive tract, including the hymen, cervix and the tips of each uterine horn, but typically not in the vagina. Unmated females showed no evidence of conspicuous bleeding. Histological examination of mated females revealed widespread abrasion of the cervical and endometrial epithelium, injuries absent in unmated females. Within one hour of mating, sperm were already present in the oviduct. The male alpaca's cartilaginous penis tip with a hardened urethral process is likely responsible for the copulatory abrasion. The entire female reproductive tract interacts with the penis, functioning like a vagina. Alpacas are induced ovulators, and wounding may hasten delivery of the seminal ovulation-inducing factor beta-NGF into the female's blood stream. There is no evidence of sexual conflict in copulation in alpaca, and thus wounding may also be one of a variety of mechanisms devised by mammals to induce a beneficial, short-term inflammatory response that stimulates blastocyst implantation, the uterine remodeling associated with placental development, and thus the success of early pregnancy.

Perspective: Re-defining “Pheromone” in a Mammalian Context to Encompass Seminal Fluid

The classical view of “pheromone”—an air-borne chemical signal—is challenged by the camelids in which ovulation is triggered by ß-nerve growth factor carried in seminal plasma, effectively extending the pheromone concept to a new medium. We propose further extension of “pheromone” to include a separate class of seminal fluid molecules that acts on the female reproductive tract to enhance the prospect of pregnancy. These molecules include transforming growth factor-ß, 19-OH prostaglandins, various ligands of Toll-like receptor-4 (TLR4), and cyclic ADP ribose hydrolase (CD38). They modulate the immune response to “foreign” male-derived histocompatibility antigens on both sperm and the conceptus, determine pre-implantation embryo development, and then promote implantation by increasing uterine receptivity to the embryo. The relative abundance of these immunological molecules in seminal plasma determines the strength and quality of the immune tolerance that is generated in the female. This phenomenon has profound implications in reproductive biology because it provides a pathway, independent of the fertilizing sperm, by which paternal factors can influence the likelihood of reproductive success, as well as the phenotype and health status of offspring. Moreover, the female actively participates in this exchange—information in seminal fluid is subject to “cryptic female choice,” a process by which females interrogate the reproductive fitness of prospective mates and invest reproductive resources accordingly. These processes participate in driving the evolution of male accessory glands, ensuring optimal female reproductive investment and maximal progeny fitness. An expanded pheromone concept will avoid a constraint in our understanding of mammalian reproductive biology.

Heterologous beta-nerve growth factor (β-NGF) given at the LH surge enhances luteal function in dairy heifers

Genetic selection for high yield milk production has led to a decline in dairy cattle's reproductive performance over the last 40 years. Low progesterone (P4) plasma content following ovulation is associated with suboptimal fertility in dairy cattle. Several pieces of evidence indicate that the protein beta-nerve growth factor (β-NGF) that is present in the male seminal plasma exerts potent ovulatory and luteotrophic effects following systemic administration in camelids but also in other species. In this study, we determine whether systemic administration of purified llama β-NGF given at the induced preovulatory luteinizing hormone (LH) peak improves corpus luteum (CL) function in dairy heifers subjected to an estradiol (E2) / P4 estrus-synchronization protocol. To achieve this, we first determined plasma E2 and LH hormone profiles to establish the timing of the estradiol benzoate (EB)-induced LH peak in estrus-synchronized heifers. Then, we tested whether the administration of β-NGF given at the end of this peak affects the CL and its function by analyzing diameter, vascular area, and P4 output. Our results show that, with the estrus-synchronization protocol applied, plasma LH concentrations peaked (P < 0.01) 40-h and 16-h after removal of the bovine intravaginal device (DIB; containing 1.0 g of P4) plus cloprostenol injection and subsequent EB administration, respectively; after peaking, plasma LH concentrations remained stable for the next 8-h to then return to basal levels. Heifers synchronized with this protocol and receiving a dose of 1 mg of β-NGF at the end of the LH peak (ie, 48-h after DIB removal) did not show significant differences in CL diameter, but these exhibited a greater CL vascular area (P = 0.01) than the observed in vehicle-injected heifers. Furthermore, plasma P4 concentration in β-NGF-treated heifers was higher (P = 0.001) than those quantified in vehicle-injected heifers. These results support the use of β-NGF in estrus-synchronization protocols to improve the early luteal function in dairy heifers.

Current Knowledge on the Multifactorial Regulation of Corpora Lutea Lifespan: The Rabbit Model

Simple Summary

Corpora lutea (CL) are temporary endocrine structures that secrete progesterone, which is essential for maintaining a healthy pregnancy. A variety of regulatory factors come into play in modulating the functional lifespan of CL, with luteotropic and luteolytic effects. Many aspects of luteal phase physiology have been clarified, yet many others have not yet been determined, including the molecular and/or cellular mechanisms that maintain the CL from the beginning of luteolysis during early CL development. This paper summarizes our current knowledge of the endocrine and cellular mechanisms involved in multifactorial CL lifespan regulation, using the pseudopregnant rabbit model.

Abstract

Our research group studied the biological regulatory mechanisms of the corpora lutea (CL), paying particular attention to the pseudopregnant rabbit model, which has the advantage that the relative luteal age following ovulation is induced by the gonadotrophin-releasing hormone (GnRH). CL are temporary endocrine structures that secrete progesterone, which is essential for maintaining a healthy pregnancy. It is now clear that, besides the classical regulatory mechanism exerted by prostaglandin E2 (luteotropic) and prostaglandin F2α (luteolytic), a considerable number of other effectors assist in the regulation of CL. The aim of this paper is to summarize our current knowledge of the multifactorial mechanisms regulating CL lifespan in rabbits. Given the essential role of CL in reproductive success, a deeper understanding of the regulatory mechanisms will provide us with valuable insights on various reproductive issues that hinder fertility in this and other mammalian species, allowing to overcome the challenges for new and more efficient breeding strategies.

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.

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.

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.

Effect of diluent type, cryoprotectant concentration, storage method and freeze/thaw rates on the post-thaw quality and fertility of cryopreserved alpaca spermatozoa

This study compared protocols for cryopreservation of ejaculated, papain-treated alpaca spermatozoa. This included different concentrations of egg yolk (EY; 5, 10 or 15%) and glycerol (2, 5 or 10%), diluent types (SHOTOR, lactose, skim milk or INRA-96™), freeze rates (2, 4 or 8 cm above liquid nitrogen; LN), thaw rates (37 °C for 1 min or 42 °C for 20 sec) and storage vessels (pellets, 0.25 mL straws or 0.5 mL straws). Spermatozoa were assessed pre-freeze and 0, 30, 60 and 90 min post-thaw. Forty-one hembras were inseminated with either fresh, papain-treated or frozen-thawed spermatozoa. Motility was affected by EY concentration (P < 0.001), diluent type (P < 0.001), freeze rate (P = 0.003) and storage vessel (P = 0.001). Viability was affected by EY concentration (P < 0.001), diluent type (P < 0.001), storage vessel (P = 0.002) and thaw rate (P = 0.03). For artificial insemination (AI), semen was diluted 1:3 in a lactose-based diluent, with 5% EY and glycerol. Freezing was in 0.5 mL straws, 2 cm above LN for 4 min then thawing at 37 °C for 1 min. Pregnancy rates of those ovulated (n = 26) were not different (1/5 fresh, 1/4 papain-treated, 0/17 frozen-thawed; P = 0.10). Pregnancy can be achieved after AI with papain-treated spermatozoa. Further work is needed to determine the optimal dose, timing and location for insemination.

Mapping of the Early Intrauterine Morphogenesis in the Alpaca (Vicugna pacos): External Features and Development of the Cephalic Vesicle in Comparison with the Progressive Carnegie Scale

In this study, we characterized the morphological aspects of the early development of the head of the alpaca (Vicugna pacos) and identified the main structures of the central nervous system during the first trimester of pregnancy. The topography and the cytoarchitecture of the fetal brain regions were described by histological analysis of the brain sections. We performed this analysis on alpaca embryos and fetuses presumably aged 20, 30, 45, and 90 days. For the description of the external body structures we considered the shape of the head, the development of the optic primordium, the dorsal curvature of the body, the limb buds, the umbilical cord and relative vessels, and the thickness and transparency of the skin. The prosencephalic, mesencephalic, and the rhomboencephalic vesicles were described by analyzing sagittal sections of the head. The present article provides the first progressive morphological and anatomical description of alpaca brain during early development. A detailed study represents an important basis to further understand the phases of prenatal development in this species, since information about alpaca embryology in incomplete and reproductive failure is a relevant factor. These data are important also for interspecies comparisons and application of reproductive biotechnologies. Anat Rec, 302:1226-1237, 2019. © 2018 Wiley Periodicals, Inc.

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

Female mammals are classified into spontaneous and induced ovulators based on the mechanism eliciting ovulation. Ovulation in spontaneous species (e.g., human, sheep, cattle, horse, pigs, and most rodents) occurs at regular intervals and depends upon the circulating estradiol. However, in induced ovulators (e.g., rabbits, ferrets, cats, and camelids), ovulation is associated with coitus. In the later, various factors have been proposed to trigger ovulation, including auditory, visual, olfactory, and mechanic stimuli. However, other studies have identified a biochemical component in the semen of induced ovulators responsible for the induction of ovulation and named accordingly ovulation-inducing factor (OIF). In camelids, intramuscular or intrauterine administration of seminal plasma (SP) was shown to induce the preovulatory luteinizing hormone (LH) surge followed by ovulation and subsequent formation of corpus luteum. Recently, this OIF has been identified from SP as a neurotrophin, the β subunit of nerve growth factor (β-NGF). β-NGF is well known as promoting neuron survival and growth, but in this case, it appears to induce ovulation through an endocrine mode of action. Indeed, β-NGF may be absorbed through the endometrium to be conveyed, via the blood stream, to the central structures regulating the LH preovulatory surge. In this review, we provide a summary of the most relevant results obtained in the field, and we propose a working hypothesis for the central action of β-NGF based on our recent demonstration of the presence of neurons expressing kisspeptin, a potent stimulator of GnRH/LH, in the camel hypothalamus.

Semen collection methods in alpacas

South American camelids, particularly alpacas, are gaining in popularity outside their native lands. Reproductive biotechnologies, such as artificial insemination or embryo transfer with cryopreserved embryos, are more complicated in these species than many others due to differences in their reproductive physiology compared to the more commonly encountered domestic livestock. This article reviews the methods currently available for obtaining semen or spermatozoa from alpacas and describes some of the problems associated with handling the viscous seminal plasma characteristic of camelids. Possibilities and limitations of reproductive biotechnologies in this species are discussed, and future developments are outlined, especially some new techniques which are currently being developed for use with camel semen and may be transferable to alpacas.