Sexual behaviour of neonatally castrated rats injected during infancy with oestrogen and dihydrotestosterone

Brain-derived estrogen and neural function

Although classically known as an endocrine signal produced by the ovary, 17β-estradiol (E₂) is also a neurosteroid produced in neurons and astrocytes in the brain of many different species. In this review, we provide a comprehensive overview of the localization, regulation, sex differences, and physiological/pathological roles of brain-derived E₂ (BDE₂). Much of what we know regarding the functional roles of BDE₂ has come from studies using specific inhibitors of the E₂ synthesis enzyme, aromatase, as well as the recent development of conditional forebrain neuron-specific and astrocyte-specific aromatase knockout mouse models. The evidence from these studies support a critical role for neuron-derived E₂ (NDE₂) in the regulation of synaptic plasticity, memory, socio-sexual behavior, sexual differentiation, reproduction, injury-induced reactive gliosis, and neuroprotection. Furthermore, we review evidence that astrocyte-derived E₂ (ADE₂) is induced following brain injury/ischemia, and plays a key role in reactive gliosis, neuroprotection, and cognitive preservation. Finally, we conclude by discussing the key controversies and challenges in this area, as well as potential future directions for the field.

The effects of neonatal cryoanaesthesia-induced hypothermia on adult emotional behaviour and stress markers in C57BL/6 mice

Since the early 1930s, deep hypothermia (cryoanaesthesia) has been a useful anaesthetic in several types of surgery on neonatal rodents. Especially against the background of modern techniques in systems neuroscience, the method enjoys again increasing popularity. However, little is known about its effects on the subsequent adult behavioural and physiological profile. To systematically investigate the effects of neonatal cryoanaesthesia on adult basal and emotional behaviour as well as on physiological development, 59 C57BL/6 mouse pups were randomly assigned to one of three treatment groups: Pups of the first group were exposed to the hypothermia treatment (H) on postnatal day 3, while pups of the other two groups served as controls: These pups either remained in the home cage without any intervention (C), or were separated from the mother for 15 min (MS) to differentiate between effects of neonatal isolation alone versus hypothermia that inevitably goes along with neonatal isolation. Subsequent behavioural analyses were conducted during adulthood (P 84-P 130), including tests for exploratory, anxiety-like and depression-like behaviour. At the age of about 145 days mice were decapitated to record BDNF levels in the hippocampus and serum corticosterone. Altogether, H mice were found to display slightly increased anxiety levels on the O-Maze, but did not differ from the control animals in any other behavioural test. Subtle alterations in anxiety-like behaviour, however, were not accompanied by physiological changes in serum corticosterone and hippocampal BDNF levels, arguing against an overall long-lasting effect of neonatal hypothermia on the emotional profile of adult mice.

The effect of brief neonatal cryoanesthesia on physical development and adult cognitive function in mice

Deep hypothermia (cryoanesthesia) is often used as general anesthesia during surgery in neonatal rodents. Neonatal cryoanesthesia has been used recently to generate somatic brain transgenic (SBT) mouse models via intracerebral ventricular injection of rAAV vectors into both non-transgenic mice and numerous transgenic mouse models. Since, the evaluation of cognition is one of the main experimental endpoints in many of these studies, we examined the consequences of brief neonatal cryoanesthesia on the physical development and mnemonic function of adult mice. Two groups of 129FVBF1 pups from reciprocal breeding crosses underwent cryoanesthesia for 6 min (Cryo6) or 12 min (Cryo12), respectively, within the first hours (<12h) of postnatal life. A group of pups separated from the nest and kept in ambient temperature of 33 °C for 6 min served as a control. Our results revealed that lowering the temperature of pups to ~8 °C (Cryo6) or ~5 °C (Cryo12) did not affect their body weight at pre-weaning stage and in the adulthood. The evaluation of cognitive function in adult mice revealed strong and comparable to control spatial reference, and context and tone fear memories of neonatally cryoanesthetized mice. Also, the experimental and control groups had comparable brain weight at the end of the study. Our results demonstrate that neonatal cryoanesthesia, lasting up to 12 min, has no adverse effects on the body weight of mice during development, and on their cognition in the adulthood.

Developmental exposure to Passiflora incarnata induces behavioural alterations in the male progeny

Passiflora incarnata is marketed in many countries as a phytomedicine and is prescribed mainly as a sedative and anxiolytic. Even though the directions of most marketed phytomedicines recommend them to be used under medical supervision, reproductive and developmental studies are sparse and not mandatory for regulatory purposes. To evaluate the reproductive and developmental toxicity of P. incarnata, Wistar female rats were gavaged with 30 or 300 mg kg–1 of this herb from gestational Day (GD) 0 to postnatal Day (PND) 21. P. incarnata treatment did not influence dams’ bodyweight or food intake or their reproductive performance (post-implantation loss, litter size, litter weight). There was also no influence on the physical development of pups (bodyweight gain, day of vaginal opening or preputial separation) or their behaviour in the open-field at PND 22, 35 and 75. Sexual behaviour was disrupted in adult male pups exposed to 300 mg kg–1 of P. incarnata; in this group, only 3 out of 11 pups were sexually competent. This behavioural disruption was not accompanied by alterations in plasma testosterone levels, reproductive-related organs and glands weights or sperm count. It is hypothesised that aromatase inhibition may be involved in the observed effect.

Of mice and rats: key species variations in the sexual differentiation of brain and behavior

Mice and rats are important mammalian models in biomedical research. In contrast to other biomedical fields, work on sexual differentiation of brain and behavior has traditionally utilized comparative animal models. As mice are gaining in popularity, it is essential to acknowledge the differences between these two rodents. Here we review neural and behavioral sexual dimorphisms in rats and mice, which highlight species differences and experimental gaps in the literature, that are needed for direct species comparisons. Moving forward, investigators must answer fundamental questions about their chosen organism, and attend to both species and strain differences as they select the optimal animal models for their research questions.

Caveolin proteins and estrogen signaling in the brain

Best described outside the nervous system, caveolins are structural proteins that form caveolae, functional microdomains at the plasma membrane that cluster related signaling molecules. Caveolin-associated proteins include G protein-coupled receptors and G proteins, receptor tyrosine kinases, as well as protein kinases, ion channels and various other signaling enzymes. Not surprisingly, a wide array of biological disorders are thought to be rooted in caveolin dysfunction. In addition, caveolins traffic and cluster estrogen receptors to caveolae. Interactions between the estrogen receptors ERalpha and ERbeta with caveolins appear critical in many non-neuronal cell types, e.g., disruption of normal function may underlie many forms of breast cancer. Recent findings suggest caveolins may also play an essential role in membrane estrogen receptor function in the nervous system. Not only are they expressed in neurons and glia, but different caveolin isoforms also appear necessary to generate distinct functional signaling complexes. With membrane estrogen receptors responsible for the efficient activation of a multitude of intracellular signaling pathways, which in turn influence a wide variety of nervous system functions, caveolin proteins are poised to act as the central coordinators of these processes.

Steroid-induced sexual differentiation of the developing brain: multiple pathways, one goal

Hormone exposure, including testosterone and its metabolite estradiol, induces a myriad of effects during a critical period of brain development that are necessary for brain sexual differentiation. Nuclear volume, neuronal morphology, and astrocyte complexity are examples of the wide range of effects by which testosterone and estradiol can induce permanent changes in the function of neurons for the purpose of reproduction in adulthood. This review will examine the multitude of mechanisms by which steroid hormones induce these permanent changes in brain structure and function. Elucidating how steroids alter brain development sheds light on how individual variation in neuronal phenotype is established during a critical period.

Glutamate AMPA/kainate receptors, not GABA(A) receptors, mediate estradiol-induced sex differences in the hypothalamus

Sex differences in brain morphology underlie physiological and behavioral differences between males and females. During the critical perinatal period for sexual differentiation in the rat, gonadal steroids act in a regionally specific manner to alter neuronal morphology. Using Golgi-Cox impregnation, we examined several parameters of neuronal morphology in postnatal day 2 (PN2) rats. We found that in the ventromedial nucleus of the hypothalamus (VMN) and in areas just dorsal and just lateral to the VMN that there was a sex difference in total dendritic spine number (males greater) that was abolished by treating female neonates with exogenous testosterone. Dendritic branching was similarly sexually differentiated and hormonally modulated in the VMN and dorsal to the VMN. We then used spinophilin, a protein that positively correlates with the amount of dendritic spines, to investigate the mechanisms underlying these sex differences. Estradiol, which mediates most aspects of masculinization and is the aromatized product of testosterone, increased spinophilin levels in female PN2 rats to that of males. Muscimol, an agonist at GABA(A) receptors, did not affect spinophilin protein levels in either male or female neonates. Kainic acid, an agonist at glutamatergic AMPA/kainate receptors, mimicked the effect of estradiol in females. Antagonizing AMPA/kainate receptors with NBQX prevented the estradiol-induced increase in spinophilin in females but did not affect spinophilin level in males.

Exploration of prostanoid receptor subtype regulating estradiol and prostaglandin E2 induction of spinophilin in developing preoptic area neurons

The prostaglandin E2 (PGE2) mediates estradiol-induced masculinization of sexual behavior in the rat during a perinatal sensitive period. PGE2 induces formation of dendritic spines on preoptic area (POA) neurons and this synaptic pattern change is associated with the ability to express male sexual behavior as an adult. Whether PGE2 is released from astrocytes or neurons in the developing POA is unknown. To further understanding of how PGE2 induces dendritic spine formation at the cellular level, we have explored the PGE2 receptor subtype mediating this response. There are four receptors for PGE2, EP1, EP2, EP3 and EP4, each having unique but interacting signal transduction profiles. Treatment of newborn female rats with the EP receptor agonists iloprost, butaprost and sulprostone indicated that stimulation of both the EP2 and EP3 receptors significantly increased spinophilin, a protein whose levels positively correlate to the presence of dendritic spines and masculinization of the POA. Use of antisense oligonucleotides against the mRNA for each receptor reveals that either EP2 or EP3 receptor knockdown reduces spinophilin in PGE2- or estradiol-treated females, whereas reducing EP1 or EP4 receptor levels by the same means has a smaller but also significant effect. A developmental profile of EP receptor expression indicates EP1 in particular is elevated for the first few days of life, corresponding to the critical period for masculinization, whereas mRNA levels for the other three receptors remain relatively constant.

Steroid receptor control of reproductive behavior

Steroid hormone receptors in the brain were thought to be only activated by steroid hormones. Once steroid binds to the receptor, it would act on DNA to regulate gene transcription. Recent data indicate that steroid receptor action is more complex. Steroid receptor activity in the brain is under the control of co-regulatory proteins, such as coactivators. It is the expression of these additional proteins that modulate the activity of steroid receptors. Furthermore, steroid receptors are not only activated by steroid, but can also be activated by neurotransmitters in the absence of steroid. For example, progestin receptors in rodent brain are sensitive to progesterone and to social cues in the environment. This review discusses these emerging mechanisms for steroid receptor control in developing and adult brain.

Nuclear receptor coactivator function in reproductive physiology and behavior

Gonadal steroid hormones act throughout the body to elicit changes in gene expression that result in profound effects on reproductive physiology and behavior. Steroid hormones exert many of these effects by binding to their respective intracellular receptors, which are members of a nuclear receptor superfamily of transcriptional activators. A variety of in vitro studies indicate that nuclear receptor coactivators are required for efficient transcriptional activity of steroid receptors. Many of these coactivators are found in a variety of steroid hormone-responsive reproductive tissues, including the reproductive tract, mammary gland, and brain. While many nuclear receptor coactivators have been investigated in vitro, we are only now beginning to understand their function in reproductive physiology and behavior. In this review, we discuss the general mechanisms of action of nuclear receptor coactivators in steroid-dependent gene transcription. We then review some recent and exciting findings on the function of nuclear receptor coactivators in steroid-dependent brain development and reproductive physiology and behavior.

Reproductive changes in male rats treated perinatally with an aromatase inhibitor

The effects of maternal exposure to aromatase inhibitor during the perinatal period of sexual brain differentiation were studied. The fertility was assessed in adult, male rat offspring of aromatase inhibitor-treated dams. The following results were obtained: (1) Sexual maturation, body weight, and wet weights of testis, pituitary, seminal vesicle, ventral prostate, and levatori ani muscle were unchanged at adult life. (2) Fifty percent of the animals were able to mate with normal females, which became pregnant but exhibited an increased number of preimplantation loss. (3) There was a decrease in the number of spermatozoa found in the testes and in the daily sperm production. (4) Of those, 25% of the male rats treated with aromatase inhibitor did not present male sexual behavior, showing female behavior when pretreated with estrogen. These results indicate that perinatal exposure to aromatase inhibitor during the critical period of male brain sexual differentiation has a long-term effect on the reproductive physiology and behavior of male rats.

Steroid receptor coactivator-1 (SRC-1) mediates the development of sex-specific brain morphology and behavior

Steroid hormone action during brain development exerts profound effects on reproductive physiology and behavior that last into adulthood. A variety of in vitro studies indicate that steroid receptors require nuclear receptor coactivators for efficient transcriptional activity. To determine the functional significance of the nuclear receptor coactivator SRC-1 in developing brain, we investigated the consequence of reducing SRC-1 protein during sexual differentiation of the brain. We report that reducing SRC-1 protein interferes with the defeminizing actions of estrogen in neonatal rat brain. Our data indicate that SRC-1 protein expression is critically involved in the hormone-dependent development of normal male reproductive behavior and brain morphology.

Neonatal androgen affects copulatory behavior in the female musk shrew

The role of neonatal testosterone in the development of copulatory behavior was examined in an insectivore, the musk shrew (Suncus murinus). Female musk shrews were treated with testosterone propionate (TP) for the first 5 days of life and then tested in adulthood for either female or male-like copulatory behavior. Early TP had a masculinizing effect; neonatally treated animals mounted a stimulus female more frequently, and with shorter latencies, in response to adult testosterone treatment than did control females. Neonatally androgenized females also showed deficits in female sexual behavior; few received ejaculations from stud males. This difference was likely caused by increased aggression exhibited by the neonatally TP-treated females toward males. In turn, female aggression decreased efficiency of male partners' intromission attempts. Early TP treatments also caused structural abnormalities in the ovaries, but did not effect their capacity to ovulate in response to either gonadotropin-releasing hormone or human chorionic gonadotropin injection. In sum, exposure to TP during development augmented display of male-like behavior in females and had subtle deleterious effects on expression of feminine behavior.

Sex and the developing brain: suppression of neuronal estrogen sensitivity by developmental androgen exposure

The developmental effects of androgen play a central role in sexual differentiation of the mammalian central nervous system. The cellular mechanisms responsible for mediating these effects remain incompletely understood. A considerable amount of evidence has accumulated indicating that one of the earliest detectable events in the mechanism of sexual differentiation is a selective and permanent reduction in estrogen receptor concentrations in specific regions of the brain. Using quantitative autoradiographic methods, it has been possible to precisely map the regional distribution of estrogen receptors in the brains of male and female rats, as well as to study the development of sexual dimorphisms in receptor distribution. Despite previous data suggesting that the left and right sides of the brain may be differentially responsive to early androgen exposure, there is no significant right-left asymmetry in estrogen receptor distribution, in either sex. Significant sex differences in receptor density are, however, observed in several regions of the preoptic area, the bed nucleus of the stria terminalis and the ventromedial nucleus of the hypothalamus, particularly in its most rostral and caudal aspects. In the periventricular preoptic area of the female, highest estrogen receptor density occurs in the anteroventral periventricular region: binding in this region is reduced by approximately 50% in the male, as compared to the female. These data are consistent with the hypothesis that androgen-induced defeminization of feminine behavioral and neuroendocrine responses to estrogen may involve selective reductions in the estrogen sensitivity of critical components of the neural circuitry regulating these responses, mediated in part through a reduction in estrogen receptor biosynthesis.

Neural aromatization and the control of sexual behavior

Neural aromatization of androgens to estrogens is known to be a critical step in the development and adult expression of male sexual behavior in a variety of species. The medial preoptic area (mPOA) is an important site of aromatization necessary for the expression of copulatory behavior in males. The neuroendocrine regulation of female sexual behavior in the musk shrew, an evolutionary "primitive" insectivore, shares several similarities with the regulation of male sexual behavior in many other species. We review the evidence that neural aromatization in the mPOA triggers female sexual behavior in the musk shrew, and speculate on the presence of a similar pathway in other mammalian species.

Estrogen receptor mRNA levels in the preoptic area of neonatal rats are responsive to hormone manipulation

Testosterone, after conversion to estrogen, masculinizes the developing preoptic area (POA) of rats, via binding to intracellular estrogen receptors located within the POA. Our previous studies have shown what seems to be a paradox, in that the levels of estrogen receptor mRNA are lower in males than in females. In the present study, we examined the effects of hormone manipulations on estrogen receptor (ER) mRNA levels in the preoptic area of neonatal male and female rats to test the hypothesis that gonadal steroid hormones regulate ER mRNA during the perinatal period. The relative amount of steady state ER mRNA was assessed in the preoptic area of postnatal day 4 animals using in situ hybridization and film autoradiography. Hybridization density was approximately 2-fold higher in females compared with hybridization density in males. Depletion of testosterone by bilateral removal of the testes on the day of birth increased the level of ER mRNA in males to that observed in females. Treatment of females with the synthetic estrogen, diethylstilbestrol (1 microgram per day, in pellet form), reduced ER mRNA levels to a level comparable to that in intact males. The non-aromatizable androgen, dihydrotestosterone (50 micrograms per day, in pellet form), had no effect on ER mRNA in females. These results suggest that estrogen, derived from the local aromatization of circulating testosterone, down-regulates ER mRNA in the neonatal male preoptic area. Down-regulation of ER mRNA may be an important estrogen-regulated event in the process of sexual differentiation of the preoptic area.

Neuronal aromatase expression in preoptic, strial, and amygdaloid regions during late prenatal and early postnatal development in the rat

Brain aromatase has been considered to be an important clue in elucidating the actions of androgen on brain sexual differentiation. Using highly specific anti-P450arom antiserum, the regional and subcellular distributions were immunohistochemically evaluated in the preoptic, strial, and amygdaloid regions of developing rat brains. Aromatase-immunoreactive (AROM-I) neurons were classified into three groups. The first, in which immunostaining occurs only during certain pre- or neonatal days (E16-P2), included the anterior medial preoptic nucleus, the periventricular preoptic nucleus, neurons associated with the strial part of the preoptic area, and the rostral portion of the medial preoptic nucleus. The second is a striking AROM-I cell group in the "medial preopticoamygdaloid neuronal arc," which extends from the medial preoptic nucleus to the principal nucleus of the bed nucleus of the stria terminalis and the posterodorsal part of the medial amygdaloid nucleus. The AROM-I neurons appeared by E16, reaching a peak in staining intensity between E18 and P2 and diminishing after the perinatal stage. After P14, a third group of AROM-I neurons emerged in the lateral septal nucleus, the oval nucleus of the bed nucleus of the stria terminalis, and the central amygdaloid nucleus. The second group was thought to be the major aromatization center in developing rat brains, while the center might partly shift to the third group of neurons after the late infantile stage. The distribution and developmental patterns were basically similar in males and females, suggesting that the neonatally prominent aromatase is not induced by male-specific androgen surges occurring around birth. On immunoelectron microscopy, subneuronal aromatase was predominantly localized on the nuclear membrane and endoplasmic reticulum, which appeared to be appropriate for the efficient conversion of androgen into estrogen just prior to binding to the nuclear receptors.

Role of perinatal estrogens in sexual differentiation of the inhibition of lordosis by exogenous cholecystokinin

Microinjections of sulphated cholecystokinin octapeptide (sCCK-8) into the ventromedial nucleus of the hypothalamus inhibit lordosis behavior in receptive female rats. This effect of sCCK-8 seems to differentiate under the control of gonadal steroids shortly after birth. Neonatally castrated males and normal females show similar responses, while androgenized females are less sensitive to sCCK-8. The current study investigated estrogen's role on the differentiation of the response to sCCK-8. On the day of birth male rat pups were castrated, given sham surgeries, or implanted with the antiestrogen tamoxifen or the aromatase inhibitor androst-1, 4, 6-triene-3, 17-dione (ATD). Females were implanted with testosterone propionate or tamoxifen, or given sham surgeries. Implants were removed 10 days later. As adults, rats were tested for female sexual behavior after microinjections of sCCK-8 into the ventromedial nucleus of the hypothalamus. Neonatally castrated males, ATD-treated males, and control females showed profound inhibition of lordosis behavior after sCCK-8. These results suggest that elimination of estrogen postnatally prevents defeminization of the reproductive circuitry that responds to sCCK-8.

Brain sites projecting to the spinal nucleus of the bulbocavernosus

Motoneurons of the spinal nucleus of the bulbocavernosus (SNB) occupy a distinct dorsomedial position in the ventral horn of lumbar segments 5 and 6 and innervate sexually dimorphic striated muscles of the rat perineum, including the bulbocavernosus and levator ani. To begin the study of brain influences upon SNB function, we used retrograde tracers to identify brain regions that project to the area of SNB motoneurons. Our findings provide strong evidence that lateral vestibular and several reticular nuclei innervate the SNB. Additional possible afferents include the superior and medial vestibular nuclei, raphe nucleus, red nucleus, interstitial nucleus of the medial longitudinal fasciculus, and paraventricular nucleus.

Role of postnatal androgens in sexual differentiation of the lordosis-inhibiting effect of central injections of cholecystokinin

The neuropeptide cholecystokinin (CCK) inhibits lordosis behavior when infused into the ventromedial nucleus of the hypothalamus (VMN) of female rats and has no effect when infused into the VMN of male rats. To test whether this sex difference develops under the control of perinatal steroids, male rats were castrated or given sham surgeries within 3 h of birth and female rats were injected with either 0 or 100 micrograms testosterone propionate on postnatal day 5. As adults, these rats were castrated as necessary, implanted with unilateral cannulae directed at the VMN, and tested for their ability to display female sexual behavior and to respond to CCK. Neonatal castration of males prevented defeminization of this response. When treated with 5 micrograms estradiol benzoate (EB), neonatally castrated males showed both lordosis behavior and a profound inhibition of that behavior after infusions of CCK. Neonatally castrated males did not display lordosis behavior when treated with 2 micrograms EB. Control males showed no lordosis behavior and, therefore, no response to CCK. Both doses of EB induced lordosis behavior in neonatally androgenized females. Significantly, these neonatally androgenized females were less responsive to CCK's inhibition of lordosis and were also anovulatory. These results imply that androgens alter the development of CCK responsive circuits as well as defeminize cyclic gonadotropin release. Levels of 125I-sCCK-8 binding in the VMN were correlated closely with an individual's ability to respond to sCCK-8. In summary, the inhibition of female sexual behavior caused by exogenously administered CCK in normal adult female rats appears to be controlled at least partially by levels of CCK receptors in the VMN and to differentiate under the control of perinatally present testosterone.

A comparison of the effects of three androgens on sexual differentiation in female hamsters

The effectiveness of the synthetic androgen 17 beta-hydroxy-17 alpha-methyl-estra-4,9,11-triene-3-one (R 1881), 5 alpha-dihydrotestosterone (DHT), and testosterone to suppress the development of lordotic behavior in female hamsters were compared. Selection of these three androgens was based upon their ability to identify the active agent in defeminization. While all three hormones bind with high affinity to CNS androgen receptors, R 1881 differs from DHT because it is presumably not metabolized into less potent androgens and differs from testosterone because it is presumably not metabolized into estrogen. At birth, female hamsters were given either a single injection of 100 micrograms of hormone, five daily injections of 100 micrograms of hormone, or implanted with Silicone elastomer capsules containing hormone. Controls consisted of hamsters receiving oil injections or cholesterol implants. As adults, the hamsters wee gonadectomized, injected with estradiol benzoate and progesterone and then tested for lordosis. A single injection of androgen at birth was ineffective in suppressing lordosis duration in female hamsters. Multiple injections and implants of R 1881 or testosterone inhibited the development of female sexual behavior. R 1881 administered as five daily injections or implanted for seven days caused a similar partial reduction in lordosis duration. Testosterone was more effective in inhibiting receptivity when given as implants rather than injection. No differences were observed between females receiving testosterone implants at birth and males. DHT had no appreciable effect upon the development of behavior regardless of the route of administration or the length of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Role for prenatal estrogen in the development of masculine sexual behavior in the male ferret

Previous studies have shown that neonatal exposure to testosterone is essential for coital masculinization in male ferrets. In the present experiments, masculine sexual behavior was diminished in male ferrets by prenatal exposure to drugs which inhibited estrogenic stimulation of the brain. Similarly timed prenatal treatments with testosterone failed to masculinize the behavior of female offspring. We hypothesize that prenatal exposure of the male ferret to estrogen, derived from the neural aromatization of circulating androgen, may sensitize the developing brain to the subsequent masculinizing action of testosterone shortly after birth.

Estrogens before birth and development of sex-related reproductive traits in the female guinea pig

Influences of estrogens on the differentiation of psychosexual traits in the female guinea pig were studied. Pregnant animals were injected intramuscularly with either 1, 2, or 3.3 micrograms estradiol benzoate (EB) or with 1 or 3 micrograms diethylstilbestrol dipropionate (DESDP). Injections were started on the 29th day of pregnancy, given daily for 6 days, and continued every other day until parturition. Female offspring were evaluated for onset of puberty, ovarian function, and lordosis and mounting behavior in adulthood. Prenatal treatment with 3 micrograms DESDP caused delayed puberty, impaired ovarian function, reduced responsiveness of lordosis to EB and P in adulthood (defeminization), augmented mounting in the absence of hormones (masculinization), and reduced responsiveness of mounting to exogenous EB and P in adulthood (defeminization). Prenatal treatment with 1 microgram DESDP produced similar but less pronounced effects. Prenatal treatment with 3.3 micrograms EB also caused a delay in puberty. However, responsiveness of lordosis to EB and P in adulthood was enhanced by treatment with either 1 or 3.3 micrograms EB prenatally. Further, neither mounting in the absence of hormones nor mounting in response to EB and P in adulthood were affected in any measurable way by any prenatal treatment with EB. These results show that estrogens can have masculinizing and defeminizing effects on sexually dimorphic reproductive traits in guinea pigs. The failure of EB to duplicate or parallel the effects of DESDP is not completely understood at this time, but it may indicate that less of the active substance reaches the target tissues following maternal and placental metabolism of EB than of DESDP.

Masculinization of the female rat spinal cord following a single neonatal injection of testosterone propionate but not estradiol benzoate

We previously reported that a motor nucleus of the rat spinal cord, the spinal nucleus of the bulbocavernosus (SNB), has more and larger neurons in males than females. The SNB is significantly masculinized in adult female rats receiving 1 mg of testosterone propionate (TP) on the second day of life, compared to that of their oil treated sisters. This masculinization consists of more neurons in the region of the SNB. These results are consistent with the hypothesis that the action of androgens during the early perinatal period is responsible for the sexually dimorphic development of the SNB. Neonatal TP caused no detected masculinization, i.e. enlargement of the size of individual neurons in this region in females. Male rats given TP on day 2 had significantly smaller testes and smaller SNB somas in adulthood than oil treated males. In female rats given 100 micrograms of estradiol benzoate (EB) on day 2, the SNB was not masculinized in either number of size when observed in adulthood. The lack of a masculinizing effect of EB suggests that the aromatization of testosterone to estradiol is not sufficient for this dimorphic development.

Sexual differentiation of the central nervous system

Sexual differentiation of reproductive and behavior patterns is largely effected by hormones produced by the gonads. In many higher vertebrates, an integral part of this process is the induction of permanent and essentially irreversible sex differences in central nervous function, in response to gonadal hormones secreted early in development.

Differentiation of coital behavior in mammals: a comparative analysis

The evidence reviewed suggests that in all mammalian species the adult male's ability to display masculine coital behavior depends in part on exposure of the developing brain to testicular testosterone or its metabolites. In many mammals, particularly rodents, ruminants, and some carnivores, perinatal exposure to androgen also causes behavioral defeminization, i.e., reduced capacity to display typically feminine coital behavior in response to gonadal hormones in adulthood. The data reviewed suggest that no such process occurs in certain other mammalian species, including ferret, rhesus monkey, marmoset, and man. Testicular androgen may cause behavioral defeminization only in those species in which expression of feminine sexual behavior normally depends on the neural action of progesterone, acting synergistically with estradiol; new data support this claim in the ferret. The possible contribution of estrogenic and 5 alpha-reduced androgenic metabolites of testosterone to the occurrence of behavioral masculinization and defeminization is considered in those mammalian species for which data are available.