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PubMed2002

Models to study gravitational biology of Mammalian reproduction.

Mammalian reproduction evolved within Earth's 1-g gravitational field. As we move closer to the reality of space habitation, there is growing scientific interest in how different gravitational states influence reproduction in mammals. Habitation of space and extended spaceflight missions require prolonged exposure to decreased gravity (hypogravity, i.e., weightlessness). Lift-off and re-entry of the spacecraft are associated with exposure to increased gravity (hypergravity). Existing data suggest that spaceflight is associated with a constellation of changes in reproductive physiology and function. However, limited spaceflight opportunities and confounding effects of various nongravitational factors associated with spaceflight (i.e., radiation, stress) have led to the development of ground-based models for studying the effects of altered gravity on biological systems. Human bed rest and rodent hindlimb unloading paradigms are used to study exposure to hypogravity. Centrifugation is used to study hypergravity. Here, we review the results of spaceflight and ground-based models of altered gravity on reproductive physiology. Studies utilizing ground-based models that simulate hyper- and hypogravity have produced reproductive results similar to those obtained from spaceflight and are contributing new information on biological responses across the gravity continuum, thereby confirming the appropriateness of these models for studying reproductive responses to altered gravity and the underlying mechanisms of these responses. Together, these unique tools are yielding new insights into the gravitational biology of reproduction in mammals.

Animals↗

PubMed2004

Short day lengths delay reproductive aging.

Caloric restriction and hormone treatment delay reproductive senescence in female mammals, but a natural model of decelerated reproductive aging does not presently exist. In addition to describing such a model, this study shows that an abiotic signal (photoperiod) can induce physiological changes that slow senescence. Relative to animals born in April, rodents born in September delay their first reproductive effort by up to 7 mo, at which age reduced fertility is expected. We tested the hypothesis that the shorter day lengths experienced by late-born Siberian hamsters ameliorate the reproductive decline associated with advancing age. Short-day females (10L:14D) achieved puberty at a much later age than long-day animals (14L:10D) and had twice as many ovarian primordial follicles. At 10 mo of age, 86% of females previously maintained in short day lengths produced litters, compared with 58% of their long day counterparts. Changes in pineal gland production of melatonin appear to mediate the effects of day length on reproductive aging; only 30% of pinealectomized females housed in short days produced litters. Exposure to short days induces substantial decreases in voluntary food intake and body mass, reduced ovarian estradiol secretion, and enhanced production of melatonin. One or more of these changes may account for the protective effect of short day lengths on female reproduction. In delaying reproductive senescence, the decrease in day length after the summer solstice is of presumed adaptive significance for offspring born late in the breeding season that first breed at an advanced chronological age.

Aging↗

PubMed2005

Funding priorities in animal reproduction at the United States Department of Agriculture's Cooperative State Research, Education, and Extension Service.

The National Research Initiative (NRI) Competitive Grants Program is the U.S. Department of Agriculture's major competitive grants program and is administered by the Cooperative State Research, Education, and Extension Service (CSREES). Since its inception in 1991, the NRI has funded competitive grants in the discipline of animal reproduction. Previously, this program provided funding for a broad range of projects encompassing almost every subdiscipline in reproductive biology of farm animals, including aquatic species important to the aquaculture industry. During fiscal year 2004, the NRI Animal Reproduction Program narrowed the focus of funding priorities to the topics of infertility, basic mechanisms regulating fertility, cryopreservation of gametes, reducing the postpartum interval to conception, and sterilization methods or development of monosex populations. In response to a directive to further narrow the focus of funding priorities for fiscal year 2005 and beyond, CSREES conducted a Stakeholder Workshop on Funding Priorities in Animal Reproduction at the 37th Annual Meeting of the Society for the Study of Reproduction in Vancouver, Canada. More than 75 stakeholder scientists from a cross section of federal, public, and private institutions from across the United States participated in the workshop and provided recommendations to CSREES for future NRI-funding priorities in Animal Reproduction. The recommendations provided by stakeholders included continuing efforts to focus funding priorities into fewer high-impact areas relevant to animal agriculture and aquaculture. Recommendations also included movement back toward subdisciplines of animal reproduction that cut across all applicable species. The three funding priorities that consistently emerged as recommendations from the workshop participants were 1) gonadal function and production of gametes, 2) pituitary-hypothalamic function, and 3) embryo and conceptus development, including interaction between the conceptus and uterus. These funding priorities were considered when preparing the fiscal year 2006 NRI Request for Applications.

Animal Husbandry↗

PubMed1984

Environmental and endogenous control of reproductive function in the Great Basin pocket mouse Perognathus parvus.

Pocket mice captured in the field at various times of year were introduced into laboratory experiments to examine the short-term sensitivity of reproductive function to environmental factors, principally day length, and the tendency of the reproductive system to become active spontaneously over longer durations. Spontaneous enlargement and partial activation of the gonads occurred over the course of 4-5 mo in continuous darkness during the hibernation season. Males held for 13 mo in 12L:12D showed patterns of testicular enlargement, but with only partial regression; the degree of endogeneity in the reproductive control system of P. parvus is therefore considerably below that of the pronounced and persistent "endogenous circannual rhythms" shown by certain rodents of the squirrel family. Responses to day length varied seasonally. The partially activated reproductive system of mice that emerged from hibernation in spring was further stimulated by long days (16L:8D); in summer gonadal growth was insensitive to differences in day length, and in autumn the gonads remained undeveloped in short days (8L:16D) but were sensitive to stimulation by long days. This "photoperiodic" response of P. parvus is based on an endogenous circadian rhythm of photosensitivity as proposed by Bünning (1936). We also found that reproductive function of P. parvus is somewhat retarded by low temperature and reduced availability of water. We discuss the general nature of environmental sensitivity of reproductive function and the ways in which the photoperiodic response and spontaneous pattern of winter gonadal development in P. parvus are likely to interact with environmental factors that lead to fine-tuning the final reproductive response.

Animals↗

PubMed1988

Termination of the breeding season in the Suffolk ewe: involvement of an endogenous rhythm of reproduction.

Two studies were performed to determine if the transition into anestrus in the Suffolk ewe results from the lack of a decrease in photoperiod, a signal suggested to be important in maintaining the breeding season, or from an obligatory turn-off that reflects the expression of an endogenous rhythm of reproduction. Shortly after the autumnal equinox, three groups of ovariectomized ewes bearing s.c. Silastic implants of estradiol were placed in different lighting environments. A control group was exposed to normal variations in day length until the winter solstice and held on that day length thereafter. The two experimental groups experienced either a continuously decreasing day length or a continuously increasing duration of elevated melatonin levels during each 24-h period until mid-March. Reproductive activity, assessed by circulating levels of luteinizing hormone (LH), was marginally extended (2-3 wk) in the experimental groups. In a second experiment, two groups of ovary-intact ewes were exposed to photoperiodic treatments shortly after the winter solstice. A control group was held on the winter solstice day length (10L:14D) until the end of the study in mid-March. The experimental group experienced a 3-h photoperiodic reduction to 7L:17D. It remained to determine if that abrupt decrease could maintain reproductive induction. Again, the cessation of reproductive induction was marginally delayed in the experimental group (2-3 wk). This marginal delay in the arrest of reproductive activity seen in both experiments indicates that the lack of decrease in day length around and after the winter solstice may play some role in timing the end of the breeding season. However, our inability to prevent or markedly delay the termination of reproductive activity leads to the conclusion that the primary reason for the transition into anestrus is an obligatory turn-off. This obligatory process may be the expression of an underlying endogenous rhythm of reproduction.

Animals↗

PubMed1991

Characteristics of a genetic polymorphism for reproductive photoresponsiveness in the white-footed mouse (Peromyscus leucopus).

Wild populations of Peromyscus are often composed of individuals that vary greatly in their reproductive response to photoperiod. A population of white-footed mice (P. leucopus) from Michigan (43 degrees N) was subjected to mass selection in the laboratory both for and against reproductive photoresponsiveness for four generations. The first generation of selection yielded one line of mice in which about 80% of the individuals were classified as reproductively photoresponsive (i.e., with undeveloped reproductive tracts when reared in short days, 8L: 16D) and another in which only about 20% were reproductively photoresponsive. Some and perhaps most of this difference was accounted for by changes in degree of responsiveness to photoperiod rather than by alterations in the proportion of discrete responsive vs. unresponsive phenotypes. Alteration of critical day length was not a factor. Three more generations of selection failed to change the proportions noted above significantly. Although the genetic control of reproductive photoresponsiveness is undoubtedly complex, a single variable locus may be responsible for much of the heritable variation present in this population. These results also suggest that natural populations contain genetically determined phenotypes that are intermediate between absolutely photoresponsive and absolutely unresponsive. The factors that might promote maintenance of heterogeneity of reproductive photoresponsiveness in a wild population of rodents are considered.

Animals↗

PubMed1999

D1 and D2 dopamine receptor messenger ribonucleic acid in brain and pituitary during the reproductive cycle of the turkey hen.

The regulation of prolactin secretion during the reproductive cycle of seasonal breeding birds appears to be largely under the stimulatory influence of hypothalamic vasoactive intestinal peptide (VIP). However, the factors influencing VIP secretion, and hence prolactin release, in birds remain largely unexplored. Recent evidence has demonstrated that dopamine and dopamine receptors may affect VIP and prolactin release in birds. The differential expression of dopamine receptors on hypothalamic VIP-releasing neurons may affect the degree of prolactinemia observed during the reproductive cycle of birds. In order to examine this hypothesis, we used reverse transcription-polymerase chain reaction to quantitate the levels of D1 and D2 dopamine receptor subtype mRNAs in the brain of the domestic turkey hen during the reproductive cycle. No significant difference in hypothalamic expression of D1 or D2 dopamine receptor subtypes during the reproductive cycle was observed. However, pronounced differences in D1D and D2 mRNAs were detected in cortex and cerebellum. Interestingly, there was a dramatic increase in pituitary D1D receptor mRNA during the reproductive stages of laying and incubation of eggs, which paralleled the hyperprolactinemic state of the turkey reproductive cycle. In addition, pituitary D2 receptor mRNA steadily increased throughout the reproductive cycle. In light of these observations, a modified hypothesis regarding the effects of dopamine on prolactin secretion is discussed.

Animals↗

PubMed2001

Gonadotropin-releasing hormone content in the brain and pituitary of male and female grass rockfish (Sebastes rastrelliger) in relation to seasonal changes in reproductive status.

The involvement of individual molecular forms of GnRH in the regulation of reproductive cyclicity in a viviparous marine teleost, the grass rockfish (Sebastes rastrelliger), was evaluated by relating the brain and pituitary content of the neuropeptide to reproductive status. The presence of sea bream (sb) GnRH, chicken GnRH-II, and salmon GnRH in the brain was confirmed by their elution pattern on HPLC and RIA. In addition, HPLC elution profiles suggest that there may be a fourth form of GnRH. All forms of GnRH were found in male and female brains in all reproductive conditions. However, only sbGnRH could be detected in appreciable amounts in the pituitary. Of the four forms of GnRH found in the rockfish, only sbGnRH fluctuated during the reproductive cycle and large accumulations were detected in the brains and pituitaries of postspawn females and regressed males. The accumulation of sbGnRH at the end of the reproductive cycle is suggested to reflect a decline in GnRH secretion relative to synthesis. The dominance of sbGnRH in the pituitary and its individual fluctuation in relation to seasonal changes in reproductive status suggests that sbGnRH is an important regulator of gonadotropin-mediated reproductive activity in rockfish.

Animals↗

PubMed2004

The risk of birth defects in children born after assisted reproductive technologies.

PURPOSE OF REVIEW: This review addresses the question of whether there is evidence of an increased risk of birth defects in children born following assisted reproductive technologies compared with spontaneously conceived children. RECENT FINDINGS: Three recent studies added relatively little new information given their modest size (56-472 assisted reproductive technology children). We therefore considered all published papers that compared birth defects in children born following assisted reproductive technologies with those in children born following spontaneous conception. Overall, only six of the 26 relevant papers concluded there was an increased risk of birth defects following assisted reproductive technologies. The interpretation of many studies was based on statistical significance testing alone. When results showed a greater proportion of defects in the assisted reproductive technology group compared with the spontaneous group, but the results were not statistically significant, this was often interpreted as showing no increase in risk, rather than an increase in risk that may have been due to chance. The vast majority of individual studies were too small to have sufficient power to detect, as statistically significant, clinically relevant results. We found that although only eight (30%) of the studies had statistically significant results, 24 (89%) had an odds ratio estimate comparing assisted reproductive technology with spontaneously conceived children of over 1.0; 19 (70%) had an estimate of 1.20 or greater; and 14 (52%) had an estimate of 1.5 or greater. SUMMARY: Current evidence suggests there is an elevated risk of birth defects in children born following assisted reproductive technologies. Whilst others may disagree with our interpretation, one certainly cannot exclude this possibility on the basis of the current evidence.

Congenital Abnormalities↗

PubMed2007

Reproductive choice in men and women living with HIV: evidence from a large representative sample of outpatients attending French hospitals (ANRS-EN12-VESPA Study).

BACKGROUND: In France, the third decade of the HIV epidemic is characterized by a lower age among women who have been recently infected with HIV. This study analysed factors associated with the desire for a child in a sample of heterosexual women and men of reproductive age living with HIV. METHODS: Individuals of reproductive age within the VESPA study were included in the analysis. Desire for a child was analysed according to reproductive potential, cultural aspects and HIV-related health condition (CD4 cell count, plasma HIV load and being on treatment). RESULTS: A total of 555 women and 699 men who self-identified as heterosexual and did not report a medical diagnosis of infertility, were included in the analysis. Among them, 33% of the women and 20% of the men stated that they expected to have children in the future. In multivariate analysis, significant predictors of the desire for a child included factors associated with reproductive potential (younger age, already being a parent, regular relationship), the HIV status of the regular partner and ethnicity (African origin). HIV-related health status did not affect reproductive intentions among men and women. CONCLUSIONS: For both men and women, reproductive potential, ethnicity and partner's HIV status influenced the desire for a child, whereas the person's own clinical condition in relation to HIV had low impact. Reproductive counselling integrated into HIV care should take into account cultural aspects in order to help people living with HIV examine issues of parenthood.

Adolescent↗

PubMed2006

Reproductive health, criminal activity, and abuse among 10- to 15-year-old females enrolled in medicaid.

OBJECTIVE: To quantify the degree of abuse or criminal behavior among young females presenting for reproductive health care services. METHODS: An evaluation was conducted among Alaskan females age 10 through 15 years enrolled in Medicaid. Subjects were identified who had experienced reproductive health outcomes. The Medicaid file was linked to a Child Protective Services database and a Juvenile Justice database to identify episodes of abuse by a caretaker and criminal behavior. RESULTS: Of 21,350 Alaskan females aged 10-15 years enrolled in Medicaid during 1999-2003, 841 (3.9%) presented for reproductive health care, 2,930 (14%) were referred to Child Protective Services and 1,858 (8.7%) were referred to Juvenile Justice for criminal activity. Among the subjects with a reproductive health-related claim, 39% were referred to Child Protective Services while 31% were referred to Juvenile Justice at some point during the study period. Reproductive health care was strongly associated with referral to Child Protective Services (adjusted odds ratio [aOR] 2.9, 95% confidence interval [CI] 2.5-3.4), substantiated sexual abuse (aOR 2.3, 95% CI 1.7-3.2), and referral to Juvenile Justice (aOR 2.9, 95% CI 2.5-3.4). These associations remained regardless of the type of reproductive health care, including contraceptive management. CONCLUSION: Females aged 10-15 years enrolled in Medicaid who present for any type of reproductive health care are at increased risk of abuse by a caretaker and criminal behavior. Clinicians caring for low-income females should consider routine screening for sexual activity and the experience of violence. LEVEL OF EVIDENCE: II-2.

Adolescent↗

PubMed2006

The role of the leptin in reproduction.

PURPOSE OF REVIEW: Since its discovery in 1994, leptin has appeared to be a pleiotrophic hormone, governing energy homeostasis and affecting many tissues in the body. Numerous pieces of evidence have accumulated showing that leptin potentially plays an important role in the control of the reproductive function. RECENT FINDINGS: This review presents the major concepts for the role of leptin in the modulation of reproductive function. As a marker of the nutritional status, leptin affects the hypothalamo-pituitary-gonadal axis, regulating gonadotrophin-releasing hormone and luteinising hormone secretion, and appears to be a permissive factor in the onset of the puberty. This protein and its receptor have been found in the reproductive tissues, indicating that this system could be also implicated in several processes such as embryo development, implantation and pregnancy. Moreover, disorders of the leptin system have been related to some reproductive pathologies such as pre-eclampsia and polycystic ovary syndrome. However, controversy surrounds several aspects of the action of leptin in reproduction that require a deeper investigation of this system. SUMMARY: Results to date suggest that this system could be implicated in important reproductive processes such as embryonic development and implantation. Moreover, understanding the role of leptin might be useful for new treatments in reproductive pathologies.

Embryo Implantation↗

PubMed2006

Nuchal translucency in pregnancies conceived after assisted reproduction technology.

PURPOSE OF REVIEW: Nuchal translucency is one of the important markers in the first trimester during antenatal screening for fetal Down's syndrome. With the observation of alterations in biochemical markers in pregnancies conceived after assisted reproduction, this review presents current information related to the thickness of nuchal translucency in these pregnancies. RECENT FINDINGS: Early small studies did not demonstrate any discrepancy in the thickness of nuchal translucency in fetuses from assisted reproduction and from spontaneous pregnancies, but there has been recent evidence to suggest an increased level of nuchal translucency in singletons from various modes of assisted-reproduction technology. Nuchal translucency in twins following assisted reproduction did not, however, show a similar increase. Although the effect of chorionicity was not specifically addressed, nuchal translucency thickness in twins born after assisted reproduction was reported to be comparable to that in spontaneous singletons. It is possible that singletons and twins after assisted reproduction exhibit different antenatal behavior and pregnancy courses. SUMMARY: Similar to other biochemical markers of fetal Down's syndrome, nuchal translucency is increased in singletons after assisted-reproduction technology. Further studies on twin pregnancies, in particular dichorionic twins, are necessary before conclusive evidence can be drawn for multiple pregnancies.

Down Syndrome↗

PubMed1996

Great tits Parus major trade health for reproduction.

Reproduction and maintenance compete for resources within a single individual. But do individuals invest in reproduction just as much as remains after the requirements of maintenance are covered, or do they sacrifice their health for the sake of still further increase the investment in current reproduction? This question has been found hard to answer because of difficulties of demonstrating that individuals naturally make a reproductive effort of such a magnitude as to inflict health damage. In this paper we present evidence for a trade-off between reproductive effort and health state in great tits, indicated by a positive correlation between total prefledging brood weight and both intensity of Haemoproteus blood parasite infection and heterophile: lymphocyte (H:L) ratio. H:L ratios, which signal stress in birds, were high both among individuals making an intense reproductive effort and among aberrantly behaving individuals, such as females incubating in empty nests and birds which abandoned their broods after blood sampling. Experimental reduction of clutch size resulted in decreased intensity of Haemoproteus parasitemia, providing further evidence that individual great tits accept immunosuppression to increase their reproductive investment.

Animals↗

PubMed2002

State-dependent behaviour in breeding barn swallows (Hirundo rustica): consequences for reproductive effort.

Life-history theory offers an explanation for the intraspecific variation in reproductive effort; increased levels of current reproductive success, for example, may trade off against residual reproductive value. Even where such trade-offs have been demonstrated, however, much variation in effort remains unexplained and the underlying causes are usually obscure. We examined body state, i.e. energy reserves, as a factor, which could moderate reproductive effort. Specifically, overnight heating and cooling treatments were used to adjust dawn energy reserves in female swallows attending their nests without impinging on the opportunities for foraging. Changes in reproductive effort were measured as 'daytime energy expenditure' (doubly labelled water technique) and the 'number of feeding visits' during brood rearing, which both relate positively to current reproductive success. Our experimental treatments and responses were then compared using the common currency of energy. In response to positive and negative state manipulations, female swallows increased and decreased, respectively, their daytime energy expenditure (and number of feeding visits). These responses to experimental manipulation of state provided evidence of a direct link between the energy expenditure, life history and behaviour, which has hitherto proved elusive. They allow that energy supply and expenditure play a regulatory role in reproductive effort, and indicate that units of energy expenditure probably carry fitness costs and benefits, which are context dependent.

Animals↗

PubMed2002

Age- and density-dependent reproductive effort in male red deer.

Reproductive effort in female ungulates originates from gestation and lactation and has been studied extensively; however, no comparable studies of reproductive effort in males (due to fighting for access to mates) have, to our knowledge, previously been reported. Here, we report on weight loss of male red deer during the annual mating season--a direct measure of male reproductive effort (or somatic reproductive costs). The 'terminal investment' hypothesis predicts that reproductive effort should increase with age, given that costs remain stable. We also propose the 'mating strategy-effort' hypothesis, which predicts that reproductive effort peaks in prime-aged males, since they are most often the harem holders. Consistent with the mating strategy-effort hypothesis, relative weight loss during the rutting season peaked at prime age and was lower in younger and senescent males. Weight loss during the rut was relatively smaller as density increased and more so for older males. This is probably primarily due to males (particularly senescent males) starting their rut in poorer condition at high density. The pattern of reproductive effort in males with regard to age and density therefore differs markedly from the pattern reported for females.

Aging↗

PubMed2003

Reproductive strategies in snakes.

Snakes of both sexes display remarkable flexibility and diversity in their reproductive tactics. Many features of reproduction in female snakes (such as reproductive mode and frequency, seasonality and multiple mating) allow flexible maternal control. For example, females can manipulate not only the genotypes of their offspring (through mate choice or enhanced sperm competition) but also the phenotypes of their offspring (through allocation 'decisions', behavioural and physiological thermoregulation, and nest-site selection). Reliance on stored energy ('capital') to fuel breeding results in low frequencies of female reproduction and, in extreme cases, semelparity. A sophisticated vomeronasal system not only allows male snakes to locate reproductive females by following scent trails, but also facilitates pheromonally mediated mate choice by males. Male-male rivalry takes diverse forms, including female mimicry and mate guarding; combat bouts impose strong selection for large body size in males of some species. Intraspecific (geographical) variation and phenotypic plasticity in a wide array of reproductive traits (offspring size and number; reproductive frequency; incidence of multiple mating; male tactics such as mate guarding and combat; mate choice criteria) provide exceptional opportunities for future studies.

Animals↗

PubMed2004

A longitudinal analysis of reproductive skew in male rhesus macaques.

One of the basic tenets of sexual selection is that male reproductive success should be large in polygynous species. Here, we analysed 6 years of molecular genetic data from a semi-free-ranging population of rhesus macaques (Macaca mulatta), using Nonac's B index, to assess the level of male reproductive skew in the study troop. On average, the top sire in each year produced 24% of the infants, while 71% of troop males sired no offspring at all. Consequently, 74% of infants had at least one paternal half-sibling in their own birth cohort. Reproductive success was greatest for high-ranking males, males who spent the whole mating season in the troop and males of 9-11 years of age. Heterozygosity for major histocompatibility complex (MHC) class II gene DQB1 was the strongest single predictor of male reproductive success. A negative relationship suggestive of female mate choice was noted between the B index and the proportion of extragroup paternities. Reproductive skew was not associated with relatedness among potential sires or with female cycle synchrony. We conclude that reproductive skew in male rhesus macaques is best accounted for by the 'limited-control' model, with multiple factors interacting to regulate individual reproductive output.

Animals↗