Twenty-Five Years of Endocrine Disruption Science: Remembering Theo Colborn

For nearly 30 years, Dr. Theo Colborn (1927–2014) dedicated herself to studying the harmful effects of endocrine-disrupting chemicals on wildlife, humans, and the environment. More recently, she extended this effort to address the health impacts of unconventional oil and gas development. Colborn was a visionary leader who excelled at synthesizing scientific findings across disciplines. Using her unique insights and strong moral convictions, she changed the face of toxicological research, influenced chemical regulatory policy, and educated the public. In 2003, Colborn started a nonprofit organization—The Endocrine Disruption Exchange (TEDX). As we celebrate the 25th anniversary of endocrine disruption science, TEDX continues her legacy of analyzing the extensive body of environmental health research and developing unique educational resources to support public policy and education. Among other tools, TEDX currently uses the systematic review framework developed by the National Toxicology Program at the National Institute of Environmental Health Sciences, to answer research questions of pressing concern. In this article, we pay homage to the tenacious woman and the exemplary contribution she made to the field of environmental health. Recommendations for the future of the field are drawn from her wisdom.

Behavioral Observations of an Infant Squirrel Monkey

The behavioral development and social relations of one infant squirrel monkey were observed in a small caged group of 5 animals. Description is based on 108 hr. of observation over the first 28 wk. of his life. During his first 12 days, the infant either rode on his mother's back or nursed. On the thirteenth day he began to leave her, becoming more independent during the next 5 wk. After 7 wk. he returned to his mother only to nurse or when frightened After Week 21 he was free from bodily contact with his mother at least 95% of the time. The infant first ate monkey chow at 7 wk. of age and regularly are it at 9 wk. Some maternal rejection appeared at 3 wk. and was strong by 16 wk. He still nursed at 28 wk. Incidental interaction among adults was described.

Why public health agencies cannot depend on good laboratory practices as a criterion for selecting data: the case of bisphenol A

BACKGROUND

In their safety evaluations of bisphenol A (BPA), the U.S. Food and Drug Administration (FDA) and a counterpart in Europe, the European Food Safety Authority (EFSA), have given special prominence to two industry-funded studies that adhered to standards defined by Good Laboratory Practices (GLP). These same agencies have given much less weight in risk assessments to a large number of independently replicated non-GLP studies conducted with government funding by the leading experts in various fields of science from around the world.

OBJECTIVES

We reviewed differences between industry-funded GLP studies of BPA conducted by commercial laboratories for regulatory purposes and non-GLP studies conducted in academic and government laboratories to identify hazards and molecular mechanisms mediating adverse effects. We examined the methods and results in the GLP studies that were pivotal in the draft decision of the U.S. FDA declaring BPA safe in relation to findings from studies that were competitive for U.S. National Institutes of Health (NIH) funding, peer-reviewed for publication in leading journals, subject to independent replication, but rejected by the U.S. FDA for regulatory purposes.

DISCUSSION

Although the U.S. FDA and EFSA have deemed two industry-funded GLP studies of BPA to be superior to hundreds of studies funded by the U.S. NIH and NIH counterparts in other countries, the GLP studies on which the agencies based their decisions have serious conceptual and methodologic flaws. In addition, the U.S. FDA and EFSA have mistakenly assumed that GLP yields valid and reliable scientific findings (i.e., "good science"). Their rationale for favoring GLP studies over hundreds of publically funded studies ignores the central factor in determining the reliability and validity of scientific findings, namely, independent replication, and use of the most appropriate and sensitive state-of-the-art assays, neither of which is an expectation of industry-funded GLP research.

CONCLUSIONS

Public health decisions should be based on studies using appropriate protocols with appropriate controls and the most sensitive assays, not GLP. Relevant NIH-funded research using state-of-the-art techniques should play a prominent role in safety evaluations of chemicals.

In vivo effects of bisphenol A in laboratory rodent studies

Concern is mounting regarding the human health and environmental effects of bisphenol A (BPA), a high-production-volume chemical used in synthesis of plastics. We have reviewed the growing literature on effects of low doses of BPA, below 50 mg/(kg day), in laboratory exposures with mammalian model organisms. Many, but not all, effects of BPA are similar to effects seen in response to the model estrogens diethylstilbestrol and ethinylestradiol. For most effects, the potency of BPA is approximately 10-1000-fold less than that of diethylstilbestrol or ethinylestradiol. Based on our review of the literature, a consensus was reached regarding our level of confidence that particular outcomes occur in response to low dose BPA exposure. We are confident that adult exposure to BPA affects the male reproductive tract, and that long lasting, organizational effects in response to developmental exposure to BPA occur in the brain, the male reproductive system, and metabolic processes. We consider it likely, but requiring further confirmation, that adult exposure to BPA affects the brain, the female reproductive system, and the immune system, and that developmental effects occur in the female reproductive system.

Prenatal testosterone exposure permanently masculinizes anogenital distance, nipple development, and reproductive tract morphology in female Sprague-Dawley rats

In mammals, abnormal increases in fetal androgens disrupt normal development of the female phenotype. Due to the recent concern regarding environmental androgen-active chemicals, there is a need to identify sources of fetal androgen variation and sensitive developmental markers for androgenic activity in female rats. Anogenital distances (AGD), nipple retention, reproductive tract, and external genitalia are morphological parameters organized by prenatal androgens and are predictive of altered masculinized/defeminized phenotype in adult female mice and rats. The objectives of this study were to (1) characterize the natural prenatal androgen environment of rats including the magnitude of the intrauterine position (IUP) effect, (2) characterize the permanent effects of prenatal androgen exposure on female rats, and (3) determine the ability of AGD and areolas to predict these permanent androgenic alterations in female rats. Untreated male fetal rats had higher tissue testosterone (T) concentrations than females in the amniotic fluid, reproductive tract, gonad, and fetal body. The intrauterine position (IUP) of male and female fetuses did not affect T concentrations or AGD in male or female rats at gestational day (GD) 22. Female offspring exposed to 0, 1.5, and 2.5 mg/kg/day testosterone propionate (TP) on GDs 14-18 displayed increased AGD at postnatal day (PND) 2 and decreased nipples at PND 13 and as adults. TP-induced changes in neonatal AGD and infant areola number were reliable indicators of permanently altered adult phenotype in female rats. Further, females in the two high-dose groups displayed increased incidences of external genital malformations and the presence of prostatic tissue, not normally found in female rats.

Developmental exposure to environmental estrogens alters anxiety and spatial memory in female mice

Humans and wildlife are exposed to numerous anthropogenic drugs and pollutants. Many of these compounds are hormonally active, and recent evidence suggests that the presence of these endocrine disruptors permanently alters normal development and physiology in a variety of vertebrate species. Here, we report on the effects of developmental exposure to two common estrogenic pollutants, bisphenol A and ethinyl estradiol on sexually dimorphic, non-reproductive behavior. Mice (Mus musculus domesticus) were exposed to environmentally relevant levels of these chemicals (2 and 200 microg/kg/day for bisphenol A and 5 microg/kg/day for ethinyl estradiol) throughout prenatal and early postnatal development. As adults, the animals were observed in a variety of tests measuring sexually dimorphic behaviors including short-term spatial memory (in a radial-arm maze and a Barnes maze) and anxiety (in an elevated-plus maze and a light/dark preference chamber). Developmental exposure to ethinyl estradiol was found to masculinize behavior in all of the assays used. Bisphenol A increased anxious behavior in a dose-dependent fashion but had no effect on spatial memory. These results indicate that non-reproductive, sexually dimorphic behavior is sensitive to endocrine disruption. In addition, these experiments suggest that both humans and wildlife are being exposed to levels of these endocrine disrupting compounds that are sufficient to disrupt the development of the nervous system and that may have permanent consequences on sexually dimorphic behaviors.

Perinatal exposure to endocrine disrupting compounds alters behavior and brain in the female pine vole

Endocrine-disrupting chemicals (EDCs) are synthetic chemicals that arise from sources such as pesticides and have the ability to mimic or inhibit gonadal steroid hormones. The objective of this research was to examine the effects of EDCs on the behaviors associated with monogamy and the expression of related neuropeptide receptors. Pine voles, a novel experimental mammal, were chosen because they display strong monogamous pair bonding. Female pine voles were orally administered estrogenic diethylstilbestrol (DES) and methoxychlor (MXC) or oil control throughout gestation and lactation of pups. Exposed pups were tested as adults. Preference for the mate and maternal behaviors were assessed. While the ability to form partner preferences was intact, DES-exposed females showed increased aggression toward a stranger, while MXC exposed females showed a strong trend toward spending more time alone. Oxytocin (OT) receptor binding in the brain was assessed for possible effects on this behaviorally important neuropeptide signaling system. The cingulate cortex showed a reduction in OT binding in the MXC group. These findings demonstrate that exposure to EDCs during pre- and neonatal development can alter female adult neural phenotype and behavior related to monogamous behavior traits.

The anogenital distance index of mice (Mus musculus domesticus): an analysis

The anogenital distance (AGD) is sexually dimorphic in Mus musculus domesticus, with the male AGD approximately twice as long as that in female mice. Among female mice, the AGD varies as a function of prenatal androgen exposure. The anogenital distance index (AGDI) has been developed to serve as an indicator of prior androgen exposure due to intrauterine position (IUP). Concerns have been raised that the AGDI may not be an appropriate indicator of female IUP in mice. To further refine the AGDI, we have applied some commonly used and suggested transformations to the original data set of female CD-1 mice of known IUP, weaning body mass, and AGD. Our analysis suggests that the residual log transformation and untransformed body mass AGDIs are the most accurate means to predict the IUP of the pup. However, the IUP is only one mechanism by which a fetus may be exposed to hormonal variations in utero. Additional analyses revealed that the AGDI is influenced not only by the IUP of the female fetus but also by the identity of the dam (indicative of maternal influences) and the number of male fetuses found in the particular uterine horn. Therefore, the AGDI is not strictly a predictor of female IUP but of the intrauterine androgen environment in mice.

A Mixture of the “Antiandrogens” Linuron and Butyl Benzyl Phthalate Alters Sexual Differentiation of the Male Rat in a Cumulative Fashion1

Prenatal exposure to environmental chemicals that interfere with the androgen signaling pathway can cause permanent adverse effects on reproductive development in male rats. The objectives of this study were to 1) determine whether a documented antiandrogen butyl benzyl phthalate (BBP) and/or linuron (an androgen receptor antagonist) would decrease fetal testosterone (T) production, 2) describe reproductive developmental effects of linuron and BBP in the male, 3) examine the potential cumulative effects of linuron and BBP, and 4) investigate whether treatment-induced changes to neonatal anogenital distance (AGD) and juvenile areola number were predictive of adult reproductive alterations. Pregnant rats were treated with either corn oil, 75 mg/kg/day of linuron, 500 mg/kg/day of BBP, or a combination of 75 mg/kg/day linuron and 500 mg/kg/day BBP from gestational Day 14 to 18. A cohort of fetuses was removed to assess male testicular T and progesterone production, testicular T concentrations, and whole-body T concentrations. Male offspring from the remaining litters were assessed for AGD and number of areolae and then examined for alterations as young adults. Prenatal exposure to either linuron or BBP or BBP + linuron decreased T production and caused alterations to androgen-organized tissues in a dose-additive manner. Furthermore, treatment-related changes to neonatal AGD and infant areolae significantly correlated with adult AGD, nipple retention, reproductive malformations, and reproductive organ and tissue weights. In general, consideration of the dose-response curves for the antiandrogenic effects suggests that these responses were dose additive rather than synergistic responses. Taken together, these data provide additional evidence of cumulative effects of antiandrogen mixtures on male reproductive development.

Animal Models and Studies of in Utero Endocrine Disruptor Effects

The rate of organ and system development in mammals, including humans, is most rapid during the prenatal period. Perturbations of the endocrine system during this period can have profound effects on later anatomy, physiology, behavior, and the onset of disease. Endocrine-disrupting compounds can cause perturbations during fetal development by mimicking or blocking natural hormones. In experimental studies, compounds that mimic estrogens and those that block androgen action have been shown to have a number of long-term effects. Among these effects are the acceleration of puberty onset, increased incidence of adult cancers such as vaginal and prostate cancers, and alterations in sexually dimorphic anatomy, physiology, and behavior. Laboratory animal models continue to play a crucial role in identifying endocrine disruptors, determining their mode of action, and demonstrating their consequences.

An environmental antiandrogen, vinclozolin, alters the organization of play behavior

During mammalian sexual differentiation, the androgens, testosterone and dihydrotestosterone are critical for the organization of the male phenotype. In rats, play behavior is sexually dimorphic. Administration of exogenous androgens during the perinatal period results in masculine-like play behavior of juveniles. Recently, there has been increasing concern about the potential for environmental endocrine-disrupting chemicals (EDCs) to alter sexual differentiation in mammals. One such EDC is the fungicide and androgen receptor (AR) antagonist, vinclozolin. We tested whether developmental exposure to an EDC could alter androgen-dependent behaviors such as play. To examine this possibility, neonatal male rats were injected from Postnatal Days (PND) 2 to 3 with corn oil, pharmacological antiandrogen flutamide (50 mg/kg/day) or vinclozolin (200 mg/kg/day); whereas neonatal females were treated either with corn oil or testosterone propionate (TP, 250 microg/kg/day). At PNDs 36-37, animals were observed for social play. Behaviors associated with general social activity, such as sniffing and dorsal contact, were unaffected by treatment or sex. However, play behavior in males treated with flutamide or vinclozolin was significantly reduced to near-female levels when compared to control males. Play behavior in females exposed to TP during the neonatal period was significantly increased when compared with control females. Hence, this study suggests that perinatal exposure to vinclozolin, an environmental antiandrogen, can alter androgen-dependent behavior, such as play, in the male rat.

Rickettsia rickettsii infection in the pine vole, Microtus pinetorum: kinetics of infection and quantitation of antioxidant enzyme gene expression by RT-PCR

The pine vole, Microtus pinetorum, was evaluated as a laboratory animal model for infection with Rickettsia rickettsii. Voles demonstrated signs of acute disease, and 45% of infected animals died following intraperitoneal infection with 3 x 10(6) plaque forming units of R. rickettsii. Spleen, liver, kidney, lung, brain, testes and blood were analyzed for rickettsial burden by a quantitative PCR assay. The distribution of rickettsiae in tissues during the course of infection was determined by immunohistochemical staining and pathological changes in tissues were correlated with the clinical severity of infection. Quantitative RT-PCR assays were designed to measure the mRNA levels of the antioxidant enzyme genes for catalase, glutathione peroxidase, glutathione reductase, heme oxygenase, Cu-Zn superoxide dismutase (SOD) and Mn-SOD, and 2 housekeeping genes, actin and glyceraldehyde phosphate dehydrogenase. Tissues from acutely ill animals on days 2 to 6 of infection, convalescent animals, and uninfected control animals were studied. The number of transcripts of each enzyme gene was determined and compared to the degree of rickettsial infection present. These studies demonstrate that the pine vole is a valuable experimental model for studying infection with R. rickettsii. Our results provide the first experimental evidence that R. rickettsii causes alteration(s) of the anti-oxidant system in vivo.

Intrauterine position effects

A review of the literature suggests that individual variability in sex-related traits may be influenced by variations in hormonal exposure during fetal development. In litter-bearing mammals, fetuses develop in utero and may be subjected to differing hormonal environments based upon the sex of neighboring fetuses. Female fetuses developing between two males tend to show masculinized anatomical, physiological and behavioral traits as adults. Female fetuses developing without adjacent males, on the other hand, tend to show more feminized traits as adults. These traits include permanently altered hormone levels, reproductive organs, aggressive behaviors, secondary sex ratios and susceptibility to endocrine disruption. This intrauterine effect is due to the transfer of testosterone from male fetuses to adjacent fetuses. While these effects have been most clearly demonstrated in mice, other rodents and swine also show intrauterine position (IUP) effects. Some of these effects are similar to the influence of prenatal stress on adult phenotypes. A few reports on human twins suggest that variability in some masculine and feminine traits may be due to intrauterine hormonal signals. IUP effects may impact a number of scientific fields of research such as endocrine disruption, toxicology, population biology, animal production and health.

Impaired olfactory behavior in mice deficient in the alpha subunit of G(o)

The ability to respond to chemical signals is essential for the survival and reproduction of most organisms. Olfactory signaling involves odorant receptor-mediated activation of G(olf), a homologue of G(s), on the dendrites of olfactory neurons. Olfactory receptor cells, however, also express Galpha(i2) and Galpha(o) on their axons, with all neurons expressing G(o) and a subset G(i2). Despite their abundance, possible contributions of G(o) and G(i2) to chemoreception remain unexplored. We investigated whether homologous recombinant mice deficient in the alpha subunit of G(o) are able to respond to odorants, whether possible olfactory impairments are dependent on genetic background, and whether formation of glomeruli in their olfactory bulbs is compromised. In an olfactory habituation/dishabituation test, G(o)-/- mice were unresponsive when exposed to odorants. Analysis of variance shows that performance of G(o)+/- mice crossed into the CD-1 background is also diminished in this test compared to their G(o)+/+ counterparts. Following food deprivation, G(o)-/- mice in the 129 Sv-ter/C57BL/6 genetic background were unable to locate a buried food pellet until they were approximately 10 weeks of age after which they performed as well as their litter mate controls. However, CD-1 G(o)-/- mice could locate a buried food pellet even when tested immediately after weaning. Despite their compromised olfactory responsiveness, histological examination did not reveal gross alterations in the olfactory bulbs of G(o)-/- mice. Thus, Galpha(o) is necessary for the expression of olfactory behavior under normal conditions and dependent on genetic background, but is not essential for the formation and maintenance of glomeruli.

Spontaneous mutation in the db gene results in obesity and diabetes in CD-1 outbred mice

Five allelic mutants of the diabetes (db) gene have been previously described in mice and rats causing obesity, infertility, and varying degrees of diabetes. We have identified a new, spontaneous mutation resulting in obesity and diabetes in a colony of CD-1 outbred mice, Mus musculus domesticus. Genetic complementation studies indicated that the new mutation was an allele of the diabetes locus. Sequence analysis of cDNA fragments showed a deletion of one G residue located in exon 12 of the leptin receptor gene. The mutation, Lepr(db-NCSU), results in a frameshift and reduces Lepr transcript levels 10-fold. Mutant mice drank up to four times more water and were up to two times heavier than wild-type mice. Blood glucose and plasma insulin and leptin concentrations were sexually dimorphic among affected mice, suggesting an effect of sex steroids. Mortality of affected males was 100% by 5 mo, whereas affected females survived up to 10 mo of age.

Social influences on intergroup transfer by pine voles (Microtus pinetorum)

Selection to obtain mating opportunities is hypothesized to be a major factor in dispersal. Thus, if individuals move to another group or switch nests to maximize their reproductive opportunities, they should move to groups or sites where they minimize competition for resources or mates and where they can find potential mates. We examined movement of pine voles (Microtus pinetorum) in an orchard habitat. Males dispersed later than females, but the two sexes showed similar patterns of movement with respect to conspecifics. Males and females immigrated to territories that contained some opposite-sex conspecifics; they also immigrated to territories without same-sex conspecifics. The latter suggests that they may avoid competitors and move to territories where an opening exists. When female breeders were removed from a social group, a replacement female arrived and began to breed relatively rapidly. In control groups where breeding females were not removed, no replacement females appeared. These results suggest that pine voles, at least females, may monitor vacancies and immigrate if a vacancy appears.

Behavioural suppression of female pine voles after replacement of the breeding male

Examination of the mechanism of reproductive suppression includes determining which cues are involved and the context in which they occur. We studied groups of pine voles, Microtus pinetorum, that were disrupted by the replacement of the breeding male and compared them with intact family groups. If reproductive suppression is mediated by chemical cues, then soiled bedding should be sufficient to prevent production of litters by daughters. If reproductive suppression involves a behavioural component, we should observe aggressive behaviours or those indicative of dominance interactions directed from the mother towards the daughter or the replacement male. If replacement of the breeding male leads to conflict between the breeding female and her daughter, then more aggression or dominance interactions would be expected in disrupted than in intact families. The presence of the mother decreased reproduction by daughters, but chemical cues alone were not sufficient to prevent the daughter from mating with the replacement male. Rather, this decrease in reproduction seemed to be mediated by behavioural interactions. We propose that the mother's tugging on the daughter may lead to subordination of the daughter. The mother's presence may also alter the behaviour patterns of the male and daughter, which could delay reproductive activation of the daughter, prevent the formation of pair bonds or inhibit sexual behaviour. These behavioural interactions appear to depend on the presence of an unfamiliar male, because tugging, for example, was less frequent in intact family groups. Copyright 1998 The Association for the Study of Animal Behaviour Copyright 1998 The Association for the Study of Animal Behaviour.

Chronic cocaine exposure affects stimulus-induced but not spontaneous behavior of the near-term mouse fetus

Pregnant female mice were injected subcutaneously with a 40-mg/kg dose of cocaine-HCl or physiological saline from day 1 through day 17 of gestation. On day 18 of gestation, dams were surgically prepared to allow the behavior of their fetuses to be observed. Spontaneous motor behavior was unaffected by cocaine exposure. Cocaine exposure potentiated motor responses of the fetuses to ammonia and to control injections of saline into the amniotic sac. Restriction of umbilical blood flow caused a specific stereotyped response in saline-injected fetuses, which is in agreement with studies of other species. This response was markedly potentiated in fetuses exposed to cocaine. The results suggest that the mouse may be a viable model for studies of the neurodevelopmental effects of gestational cocaine exposure and are discussed in relation to current models of the effects of long-term cocaine exposure on brain neurochemistry.

Androgen exposure and reproductive behavior of an induced ovulator, the pine vole (Microtus pinetorum)

The actions of steroid hormones on brain and behavior are classically divided into organizational effects that are permanent and occur early in development and activational effects that are temporary and occur throughout life. Here, we test the hypothesis that in an induced ovulator, testosterone defeminizes only those neural tissues that rely on synergistic interactions of estrogen and progesterone for normal function in adulthood. Female voles, Microtus pinetorum, injected with testosterone (T) or oil neonatally were paired with males for an 8-week period. During the pairing, androgenized and oil-treated females spent a similar amount of time investigating the caudal and rostral regions of the males. Males spent significantly less time investigating the caudal and rostral regions of androgenized females. Androgenized females mounted males, did not exhibit lordosis, and were less likely to be mounted by males. Moreover, none of the 10 androgenized females gave birth, whereas 8 of 9 control females gave birth. Androgenized females were also not capable of being stimulated into reproductive condition by males. Injection of 0.5 microg of estradiol benzoate for 4 consecutive days resulted in reduced uterine hypertrophy in androgenized females. These results support the original organizational-activational hypothesis by showing that neonatal androgenization defeminizes and masculinizes female pine voles.

Chemical cues are necessary but insufficient for reproductive activation of female pine vole (Microtus pinetorum)

Among various arvicoline rodents, reproduction is influenced to varying degrees by social factors, including behavioral or chemical cues. Since previous research suggested that chemosignals from adult males reproductively activate female pine voles (Microtus pine-torum), we sought to determine specifically what types of stimuli promote the activation response. In these experiments, female were exposed to unfamiliar adult males, or to some combination of cues from males, or were housed alone. Using uterine mass as a measure of reproductive activation, we found that females were not activated by exposure either to male urine by itself or to male-soiled bedding by itself, but full contact with a male clearly resulted in heavier uteri. Females whose vomeronasal organs were surgically excised failed to undergo reproductive activation when housed with males. Finally, females allowed physical contact by being housed directly underneath males had heavier uteri than did females whose housing allowed contact only with the chemical cues from males. Among female arvicoline rodents, it appears that there exists a physiological continuum between absolute dependence on both contact and chemical cues from males vs. absolute independence for reproductive activation. The present results place female pine voles closer to the former extreme than to the latter.

Serological evidence for zoonotic hantaviruses in North Carolina rodents

In a survey of seven species of wild rodents (n = 423) collected between October 1993 and March 1994 from the three principal ecological biomes of North Carolina (USA), we found hantavirus antibodies in seven (2%) of 301 Peromyscus spp. Hantavirus antibodies were detected in P. leucopus and P. maniculatus captured from mountain and coastal island biomes. Three mice were positive for Sin Nombre virus, while four others had antibodies to Seoul virus or a related agent. Two mice serologically positive for Sin Nombre virus were collected from inside a private mountain domicile. We conclude that the risk of human exposure to hantaviruses in North Carolina resembles that for most other areas of the continental United States.

The anogenital distance index, a predictor of the intrauterine position effects on reproduction in female house mice

The anogenital distances (AGD) of newborn female house mice vary as a function of prior intrauterine position. Females with long AGDs are more likely to be derived from intrauterine positions adjacent to males (2M) than females not adjacent to males (0M). Females with a male on one side (1M) show intermediate AGDs. Hence the AGD reflects the degree of androgenization experienced by the female in utero and correlates with a number of androgen-dependent anatomical, physiological, and behavioral events in adulthood. This experiment tested the usefulness of AGD measurements of female house mice taken at weaning rather than at birth as an index of prior androgenization. The AGD was normalized for body weight at weaning to yield an anogenital distance index (AGDI). Intrauterine position (IUP) was determined by caesarian section. Pups were marked and reared by foster mothers. Comparison of AGDI showed that 0M females had a significantly lower mean AGDI score than 2M females and 1M females were intermediate. This confirmed that AGDI reflects prior IUP and can be used as an index of prenatal androgenization. While testing for responsiveness to male urine, a stimulus known to accelerate puberty, only females from the 1M and 2M positions differed from controls indicating that 0M females had already attained puberty. Choosing females from unknown IUPs with short-AGDIs, mid-AGDIs, and long AGDIs and treating them with either urine or saline on the nose for the 4 days after weaning yielded much the same response indicating that AGDI can also be used to preselect females for sensitivity to factors influencing puberty. These results demonstrate that some of the variability known to be related to intrauterine position can be predicted by AGDI, a relatively easy measure to acquire at weaning in commonly used laboratory rodents. Such preselection could reduce variability of experimental results in the conduct of studies related to rodent reproduction and may reduce the number of animals needed without loss of predictive ability.

Management, breeding, and reproductive performance of pine voles

Pine voles (Microtus pinetorum) serve as an interesting rodent model for studies of fossorial adaptation and mammalian mating systems. They are unusual among rodents in displaying a cooperative system of breeding. Here we describe the management of a breeding colony of pine voles. This species is relatively easy to maintain in the laboratory, although care must be taken to provide sufficient water in their diet. Details of reproduction, as well as growth and development of the young, are included. Pine voles have a smaller litter size (2.3 +/- 0.9 pups at birth) than do other arvicoline rodents but are still prolific breeders, producing, on average, a litter per month for more than 12 months. These rodents are useful for comparison with other arvicoline rodents, as well as providing an opportunity to investigate the behavior, physiology, and reproduction of an easily managed cooperatively breeding mammal.

Mother's prior intrauterine position affects the sex ratio of her offspring in house mice

Sex ratio alterations related to environmental factors occur in several mammals, but no mechanism has been identified to explain the adjustment. Intrauterine position (IUP) may provide the context in which such alterations occur. Previous studies on house mice and gerbils reveal that the position of a fetus in the uterus in relation to the sex of its neighbors influences its later anatomy, physiology, and behavior. The anogenital distance (AGD) of females located between two males (2M) is longer than that of females not between two males (OM). We have found that the IUP, as determined by cesarean section and by an index of the AGD, correlates with the sex ratio of the litters produced by female mice. The sex ratio of the first litter born to 2M females was 58% males, for 1M females was 51% males and for OM females was 42% males. The effect on sex ratio continues into the second litter. The number of pups produced by mothers of different IUPs in her first two litters did not differ, suggesting that the sex ratio adjustment occurs prior to parturition. These results provide a basis for the natural variability observed in sex ratios of litter-bearing mammals and suggest that one or more intrauterine mechanisms may be responsible for environmentally related sex ratio alterations.

Effect of chronic cocaine on reproduction in female house mice

The effect of chronic cocaine exposure on the reproductive success of juvenile female house mice was studied. We followed two generations of female mice to examine the consequence of cocaine treatment on developmental and reproductive parameters such as weight gain, first estrus, impregnation, fertility, and maternal success. Twenty-two-day-old female mice were given cocaine at a daily total of 40 mg/kg body weight, delivered by two SC injections of 20 mg/kg each, until they were mated and inseminated by experienced males. The treatment attenuated weight gain and delayed puberty in the females but had no discernible effect on their pups. Administration of cocaine to lactating mothers decreased the weaning weight of their pups. Juvenile females previously nursed by mothers receiving cocaine and receiving 40 mg/kg cocaine daily themselves were impregnated at older ages than controls. Nevertheless, once these juveniles reached puberty, they mated successfully and their reproductive parameters did not differ from those of control mice. Thus, chronic cocaine treatment of juvenile female mice slows body growth and development but has little effect on the offspring produced later when they reached adulthood.

Effect of cocaine on the production of puberty-accelerating pheromone by male mice

This study examined whether chronic cocaine exposure could reduce reproductive fitness of adult male mice by interfering with their production of the puberty-accelerating pheromone, an androgen-dependent urinary pheromone that accelerates puberty in juvenile female mice. Administered at a high dose of 60 mg/kg body weight/day, cocaine caused mortality, body weight loss, and suppression of circulating testosterone during the first week of treatment. However, at 40 mg/kg/day, it resulted in little adverse effect on these parameters. Animals showed habituation to repeated cocaine exposure by regaining part of the lost weight and reelevating suppressed testosterone level at later stages of treatment. Urine samples collected from animals receiving 60 mg/kg cocaine daly for 2 weeks lost the puberty-accelerating effect. However, neither a 3-day treatment of the same dose nor a lower dose of 40 mg/kg reduced the effectiveness. The diminished effect of cocaine-treated male mouse urine might reflect lowered testosterone levels with a lag of 10 to 15 days, similar to that of castrated male mouse urine. These results indicate that cocaine has no direct effect on the production of priming pheromone, and its metabolites in the urine did not affect the response of juvenile females to the pheromone.

Cocaine attenuates puberty acceleration in female house mice

The onset of puberty in female house mice is advanced by exposure to a male urinary pheromone. This study tested whether cocaine could modify the juvenile female mouse's response to this pheromone. Puberty acceleration, as measured by uterine weight change, is inhibited by daily SC administration of 30 or 40 mg/kg body weight cocaine HCl between 20 and 26 days of age. Two daily injections of 20 mg/kg cocaine reduced both uterine development and body weight gain. Thus, cocaine may reduce an animals' reproductive fitness by isolating it from its social environment. At higher doses, cocaine can delay body growth, as well as the onset of puberty.

Analysis of puberty-accelerating pheromones

Two experiments were performed to test putative puberty-accelerating pheromones. In the first experiment, 37 weanling female house mice of the ICR strain were exposed to 1 of the following 3 treatments: an airborne mixture of 0.05 M isoamylamine and 0.05 M isobutylamine, fresh male mouse urine, or distilled water, as the control. Neither the amine mixture nor the male urine accelerated first estrus in the mice following airborne exposure to these compounds. In the second experiment, 37 weanling female mice of the same strain were exposed to the same chemicals as in the first experiment by direct contact to the oro-nasal groove. The mixture of isoamylamine and isobutylamine did not accelerate puberty, but direct contact with the male urine accelerated puberty as evidenced by uterine weights.

Puberty acceleration in female mice induced with a partially purified male urine extract: effects on catecholamine release from the olfactory bulbs and hypothalamus

In the present experiment peri-pubertal female mice were treated with a partially purified puberty accelerating urine extract (PAUE). Mice treated with the PAUE showed an advance in the onset of puberty as indicated by significantly increased uterine weights. Treatment with the PAUE did not alter basal or potassium- (K+, 30 mM) stimulated release of catecholamines (dopamine or norepinephrine) from either anterior or posterior superfused olfactory bulb tissue fragments. There was, however, an overall significantly greater amount of basal and K(+)-stimulated release of NE from the posterior vs. the anterior olfactory bulb. Potassium-stimulated-, but not basal, release of catecholamines from the medial basal hypothalamus of PAUE-treated female mice were increased, with dopamine showing a statistically significant difference compared to water-treated females. These data demonstrate that treatment with the PAUE is a very effective means to accelerate the onset of puberty and results in accompanying increases in catecholaminergic activity, in particular dopamine, within the medial basal hypothalamus.

Neuroendocrine responses to social regulation of puberty in the female house mouse

First estrus is advanced in female house mice exposed to an adult male and delayed in those housed in groups. Experiments were conducted to explore possible mechanisms by which the hypothalamus integrates these puberty-regulating social signals. Female mice weaned at 21 days of age were placed in groups of 8 (G8JF), a juvenile female with a juvenile male (JFJM) or juvenile female with an adult male (JFAM). All females were ovariectomized on day 28 and sacrificed on day 29. There was no significant difference between treatments in the postovariectomy rise in LH. Next, female mice were weaned, assigned to G8JF, JFJM or JFAM treatments and ovariectomized on day 22. Females were sacrificed on day 29, 3 h after injection with either 1.0 micrograms of estradiol, or vehicle. Estradiol significantly suppressed LH in all three treatments, with no differences between treatments. Two-way ANOVA (social treatment x estradiol treatment) revealed no differences or interactions in brain catecholamines as a result of estradiol injection. The G8JF treatment significantly increased norepinephrine, (NE), dopamine (DA) and its metabolite 3,4-dihydroxy-phenylacetic acid in the mediobasal hypothalamus (MBH), and the 3-methoxy-4-hydroxy-phenylglycol/NE ratio in the preoptic area (POA). In the final experiments, isolate prepubertal female mice were treated with either water or male urine (MU) on the oronasal groove. Eight days of MU treatment resulted in significant uterine growth, however there were no differences in serum LH, POA or MBH catecholamines or POA and median eminence LHRH. One hour after application of MU, serum LH was significantly elevated, however, there were no differences in accessory olfactory bulb catecholamines. These results suggest that the mechanism by which male and grouped female exposure alters first estrus may not involve changes in sensitivity to estradiol negative feedback. Grouping may delay first estrus through the negative effects of DA on the LHRH system in the MBH. We observed no differences that might help to explain how male exposure causes LH release.

Effect of intrauterine position and social density on age of first reproduction in wild-type female house mice (Mus musculus)

In laboratory strains of mice, reproductive maturation is influenced by both the fetal and the peripubertal social environments experienced by females. Intrauterine position (IUP) for female fetuses is identified by the number of adjacent males; where 0M have zero, 1M have one, and 2M have two male neighbors. We sought to confirm, using wild-type female house mice (Mus musculus), the previous finding in the CF-1 strain of laboratory mouse that males prefer 0M over 2M females as mates. We recorded the age at first reproduction for females of known IUP housed either individually with a male or in a group of 6 females and a male. In neither housing condition were there significant differences in age of first reproduction among females of different IUPs, but 0M females that were group housed had perforate vaginas at an earlier age than other group-housed females. Mean (+/- SE) age at first reproduction was 58.1 (+/- 3.3) for paired and 126.6 (+/- 5.1) for group-housed females. The reproductive suppression observed in the grouped females was probably due to the interaction of inhibitory urinary chemosignals, low body weights, and female dominance hierarchies.

Effects of social stress and intrauterine position on sexual phenotype in wild-type house mice (Mus musculus)

Wild-type house mice were used to test the effect of intrauterine position on anogenital distance (AGD) and to verify whether crowding stress would masculinize female pups, developing at all intrauterine positions, as has been demonstrated in CF-1 mice stressed by restraint, heat, and light. Stress of crowding was documented by comparing aggressive behavior, litter birth weights, and plasma corticosterone levels among females in different densities. AGDs were recorded from pups born to females housed from day 12 to 19 of gestation either individually with their mate (nonstressed) or in one of two group-housed densities. Female pups from nonstressed dams positioned between two males in utero (2M females) had longer AGDs than females positioned between two females (0M females). AGDs of males from nonstressed dams did not differ on the basis of intrauterine position. Group-housed pregnant females in the higher of two densities had female pups with longer AGDs than female pups of other dams. However, variance in female pup AGD was no different among dams in different densities. These results extend to the wild house mouse previous findings in albino mice that intrauterine position influences sexual phenotype. In addition, social stress can induce masculinization of female pups in wild mice as physical stress has been shown to do in albinos. This suggests that intrauterine position effects and their modification by crowding stress can potentially influence the dynamics of wild house mouse populations.

Coordination of social signals and ovarian function during sexual development

Social cues, often in the form of priming pheromones, can retard or enhance the rate of sexual development in a variety of mammals. The complex interactions between the social environment and reproduction have been explored most thoroughly in the house mouse. A urinary pheromone produced by females in a group inhibits sexual development, and a urinary pheromone from adult males accelerates onset of puberty in juvenile females. These priming pheromones apparently are detected by the vomeronasal organ and induce the changes in ovarian function via changes in the hypothalamic-pituitary system. Accelerated onset of puberty is not accompanied by deficits in reproductive performance. Puberty acceleration can have important management implications for domestic farm animals. It already is proving useful for manipulation in rearing swine and in synchronizing seasonal reproductive recrudescence in sheep. In cattle, the results are less clear that signals from the bull can hasten onset of puberty in heifers. The effect may be operable only under certain nutritional or other interacting conditions. Presumably, the postpartum anestrus period in the cow can be shortened by stimulation from the bull, although pheromones have not been implicated in this effect.

The La Parguera, Puerto Rico colony: establishment and early studies

Two islands off the southwest coast of Puerto Rico, La Cueva and Guayacan, were populated with monkeys derived from the Cayo Santiago colony and new imports from India during 1962-1963. This colony became known as the La Parguera Colony due to its proximity to the fishing village of La Parguera. Initial work on the island focused on studies of group formation and dynamics. Later, attention turned to field experiments on the interaction of behavior and hormones in coordinating reproduction and a number of other behavioral studies.

Puberty in pine voles, Microtus pinetorum, and the influence of chemosignals on female reproduction

We investigated the reproductive biology of an induced ovulator, the pine vole (Microtus pinetorum). Male puberty, measured as age at first impregnation, was found to occur as early as 44 days of age. Female puberty measured as age at first conception, was found to occur as early as 32 days of age, considerably earlier than previously reported. Females paired with stud males exhibited a doubling of uterine weight within 12 h, and vaginal sperm were present after 48 h. This indicates that although behavioral responses to males--including mating--require prolonged contact, physiological responses to males occur rapidly. Chemosignals from males slightly increased uterine and ovarian weights of females, but chemosignals from other females did not. Young females paired with stud males for 48 h in the presence of soiled bedding from the female's family had significantly smaller increases in ovarian and uterine weights than similar females paired on clean bedding. Suppression of reproduction in female offspring while they remain with the extended family unit is discussed as a life-history tactic and as a possible mechanism for inbreeding avoidance.

Mouse vomeronasal organ: effects on chemosignal production and maternal behavior

Adult male mice excrete a urinary chemosignal that accelerates puberty in females, whereas group-housed female mice excrete a urinary chemosignal that delays puberty in young females. We found that: (1) the excretion of the puberty-acceleration chemosignal by males persisted in the absence of the vomeronasal organs and (2) the puberty-delay chemosignal was not present in the urine of group-housed females whose vomeronasal organs had been surgically removed (VNX), but was present in the urine of group-housed females subjected to sham surgery (SHAM). These results suggest that in males, vomeronasal chemoreception does not affect the excretion of the puberty-acceleration chemosignal, but that in females, the vomeronasal organ receives chemosignals that influence the excretion of the puberty-delay chemosignal. Additionally, we found no difference between SHAM and VNX females in rates of conception, litter size, pup growth, pup recognition, or maternal behavior, indicating that normal maternal processes are expressed in the absence of an intact accessory olfactory system.

Effect of density, duration of grouping and age of urine stimulus on the puberty delay pheromone in female mice

The ability of urine from female mice to delay puberty in test females was directly related to the density and duration of grouping of females. When females were removed from group housing their urine lost its ability to delay puberty within 10 days. No interactive effects were observed between duration and density of grouping on the onset of pheromone release after grouping or on the persistence of pheromone release after re-isolation. Urine from grouped females lost its ability to delay puberty in test females after 7 days of exposure to air.

The effects of bull urine on puberty and calving date in crossbred beef heifers

The effects of bull urine on the percentage of heifers reaching puberty and on subsequent calving dates were examined with 52 crossbred beef heifers. Heifers were palpated for ovarian condition and classified as prepubertal or pubertal before (Palpation I) and after (Palpation II) eight weekly oronasal treatments with bull urine or water. A larger percentage of urine-treated than water-treated heifers reached puberty during the experimental period (67 vs 32%; P less than .05), supporting the hypothesis that bull urine contains a priming pheromone. Body weight of urine-treated heifers that did not reach puberty by Palpation II was lower than that of water-treated heifers that did not reach puberty (P less than .05), indicating that an association exists between body weight and the response to pheromonal cues in bull urine. There were no treatment differences in pregnancy rate after a 90-d breeding period, and no differences in pregnancy rate between heifers that had reached puberty before the breeding season started and heifers that had not reached puberty. Urine-treated heifers reaching puberty during the experiment calved earlier (P less than .05) in the calving season than did water-treated heifers of the same category. The distribution of these calvings was also different (P less than .01), resulting in a shorter calving season for urine-treated heifers. More heifers that had reached puberty by Palpation II calved in the first 20 d of the calving season that did heifers that had not reached puberty by Palpation II, regardless of treatment group (P = .02). There was a tendency for urine-treated heifers to calve earlier than water-treated heifers, with the exception of urine-treated heifers that had not reached puberty by Palpation II. These data support the hypothesis that there is a priming pheromone in bull urine that can hasten the onset of puberty in beef heifers.

Seasonal influences of births and male sex skin coloration in rhesus monkeys (macaca mulatta) in the southern hemisphere

The annual distribution of births of rhesus monkey in zoos in the southern hemisphere and changes in sex skin coloration in one colony were examined. Most (79%) of the births occurred between October and January and the sex skin reached its greatest development during spring and early summer (i.e. at the time of mating). These results demonstrate a 6-month reversal from the breeding activity of rhesus monkeys in the northern hemisphere.