Prenatal letrozole produces a subpopulation of male rats with same-sex preference and arousal as well as female sexual behavior

Activational and organizational actions of gonadal hormones on the sexual dimorphism of the α6-subunit containing GABAA receptor in Wistar rats with neuropathic pain

Sex differences in pain perception and response to analgesics are well documented, yet the underlying causes remain poorly understood. Here we investigate the sexual dimorphism in the function of α6GABAA receptors in neuropathic pain, focusing on activational and organizational actions of gonadal hormones. Using the nerve ligation model in rats, we found that the positive allosteric modulator, PZ-ll-029 (30 nmol, it), produced a robust antiallodynic effect in females but not in males. Ovariectomy abolished this effect, while a single dose of estradiol (20 μg/kg sc, -24 h), that returned to physiological serum levels, partially restored it, indicating that the activational effect of estradiol is crucial for α6GABAA receptor-mediated antiallodynia in females. Interestingly, adult or neonatal (at postnatal day 3) orchidectomy did not alter the male's insensitivity to PZ-ll-029, even after estradiol treatment. However, neonatal female's virilization (with testosterone propionate 120 μg/rat at postnatal day 3) induced a male-like insensitivity to PZ-ll-029, that was partial when the ovaries were present and complete after adult ovariectomy. These findings reveal that the neonatal organizational effects of testosterone determine the sex-specific insensitivity of α6GABAA receptors to modulate neuropathic pain, while the activational effects of estradiol can partly maintain the female-typical response, despite early androgen exposure. Our results provide new insights into hormonal regulation of pain modulation and suggest that both developmental exposure and adult status should be considered in basic research and preclinical studies investigating sex-based dimorphisms.

Diabetes mellitus and female sexual response: what do animal models tell us?

BACKGROUND

One of the less explored effects of diabetes mellitus (DM) is female sexual dysfunction. Females of different species have been used as models.

AIM

To analyze the information of animal models of DM and female sexual response (FSR).

METHODS

The literature of FSR in models of DM was reviewed.

OUTCOMES

Paradigm- and diabetes-dependent changes have been found in various aspects of the FSR.

RESULTS

Females in a type 1 DM (DM1) model show a decrease in the number of proestrus events, and ovariectomized females treated with sex hormones have been used. In these females, a reduction in lordosis has been reported; in proceptivity, the data are contradictory. These females present a decrease in sexual motivation that was restored after exogenous insulin. In the type 2 DM (DM2) model, females show regular estrous cycles, normal levels of lordosis behavior, and, depending on the paradigm, decreased proceptivity. These females display normal preference for sexually active males or their olfactory cues when having free physical contact; they lose this preference when tested in paradigms where physical interaction is precluded.

CLINICAL TRANSLATION

Preclinical data showing the high deleterious effects of a DM1 model and the less drastic effects under a DM2 model are in accordance with clinical data revealing a much higher prevalence of sexual dysfunction in women with DM1 than DM2.

STRENGTHS AND LIMITATIONS

The main strength is the analysis of the changes in various components of FSR in 2 models of DM. The main limitation is the difficulty in extrapolating the data on FSR from rats to women and that most studies focus on evaluating the impact of severe or chronic-moderate hyperglycemia/hyperinsulinemia on the sexual response, without considering other pathophysiologic alterations generated by DM.

CONCLUSION

Females with severe hyperglycemia have a decrease in FSR, while those with moderate hyperglycemia show much less drastic effects.

Multiparity favors same-sex partner preference in male rats

Same-sex partner preference is present in many mammals, including rodents. Several possible causal factors have been proposed for the establishment of this preference. The Fraternal Birth Order effect refers to the observation that older brothers increase the probability of homosexuality in men, but no experiment has analyzed this possibility. In this study, partner preference (tested in a three compartments box) and female and male sexual behavior (studied in a cylindrical arena) were evaluated in young male rats (3 months) born to multiparous mothers that had 4-6 previous gestations and around 12 months of age. Control groups were young male rats born to primiparous young (4 months) or aged (12 months) mothers. In the partner preference test, the males born to multiparous dams spent less time interacting with the receptive female and more time interacting with the sexually active male, and a 39% exhibited same-sex partner preference. This high percentage seems related to multiparity of their mothers and not to maternal age, because the males born to primiparous aged females (12 months) showed a similar low proportion of same-sex partner preference than the males born to young (4 months) primiparous females (4%). In the sexual behavior tests, no male born of a multiparous dam and with same-sex preference ejaculated and 54% displayed proceptivity and lordosis. Present results suggest that the fraternal birth order effect may occur also in rats.

Neurophysiology of male sexual arousal-Behavioral perspective

In the presented review, we analyzed the physiology of male sexual arousal and its relation to the motivational aspects of this behavior. We highlighted the distinction between these processes based on observable physiological and behavioral parameters. Thus, we proposed the experimentally applicable differentiation between sexual arousal (SA) and sexual motivation (SM). We propose to define sexual arousal as an overall autonomic nervous system response leading to penile erection, triggered selectively by specific sexual cues. These autonomic processes include both spinal and supraspinal neuronal networks, activated by sensory pathways including information from sexual partner and sexual context, as well as external and internal genital organs. To avoid misinterpretation of experimental data, we also propose to precise the term "sexual motivation" as all actions performed by the individual that increase the probability of sexual interactions or increase the probability of exposition to sexual context cues. Neuronal structures such as the amygdala, bed nucleus of stria terminalis, hypothalamus, nucleus raphe, periaqueductal gray, and nucleus paragigantocellularis play crucial roles in controlling the level of arousal and regulating peripheral responses via specific autonomic effectors. On the highest level of CNS, the activity of cortical structures involved in the regulation of the autonomic nervous system, such as the insula and anterior cingulate cortex, can visualize an elevated level of SA in both animal and human brains. From a preclinical perspective, we underlie the usefulness of the non-contact erection test (NCE) procedure in understanding factors influencing sexual arousal, including studies of sexual preference in animal models. Taken together results obtained by different methods, we wanted to focus attention on neurophysiological aspects that are distinctly related to sexual arousal and can be used as an objective parameter, leading to higher translational transparency between basic, preclinical, and clinical studies.

Distribution of estrogen receptors alpha and beta in the brain of male rats with same-sex preference

Two distinct estrogen receptors (ERs) exist, ERα and ERβ. Both receptors participate in sexual differentiation of the rat brain and likely participate in the regulation of adult sexual orientation (i.e. partner preference). This last idea was investigated herein by examining males treated with the aromatase inhibitor, letrozole, administered prenatally (0.56 μg/kg G10-22). This treatment usually provokes same-sex preference in 1-2 males per litter. Vehicle-treated males (with female preference) and females in spontaneous proestrus (with male preference) were included as controls. ERα and ERβ expression was analyzed by immunohistochemistry in brain areas known to control masculine sexual behavior and partner preference, like the medial preoptic area (MPOA), bed nucleus of the stria terminalis (BNST), medial amygdala (MeA) and ventromedial hypothalamic nucleus (VMH), as well as other brain regions suspected to participate in these processes. In addition, serum levels of estradiol were determined in all male groups. Letrozole-treated male rats that preferred sexually experienced males (LPM) showed over-expressed ERα in the hippocampal cornu Ammonis (CA 1, 3, 4) and dentate gyrus. The LPM group showed up-regulated ERβ expression in the CA2 and reticular thalamic nucleus. The levels of estradiol did not differ between the groups. Higher expression of ERs in these males was different than their expression in females, with male sex-preference. This suggests that males with same-sex preference showed a unique brain, this sui generis steroid receptor expression probably participates in the biological underpinnings of sexual preference.

Androgen receptors immunoreactivity in the rat brain of males with same-sex preference

Androgen receptors (AR) are crucial in the control of male sexual behavior and sex preference. AR are particularly concentrated in areas related with the neuroendocrine control of sex preference including the medial amygdala (MeA), the ventromedial nucleus of the hypothalamus (VMH), the bed nucleus of the stria terminalis (BNST), the medial preoptic area (MPOA), the nucleus accumbens (Acb), the suprachiasmatic (SCh) and supraoptic (SO) nuclei, but also seem to be important for the control of reproductive processes in the hippocampus (CA1-CA4 and dentate gyrus, DG). In the present study we analyzed the density of AR in these brain areas of adult male rats with sexual preference (established in a three-compartment box). Same-sex preference was produced in male rats by the prenatal administration of the aromatase inhibitor, letrozole (0.56 μg/kg/ml s.c. G10-22) that usually produces 1-2 animals per litter with same sex preference, while the others retain a female sex preference. We also included a group of proestrus females that had a clear preference for a sexually active male. AR were analyzed by immunocytochemistry using PG21 as primary antibody. We also measured total plasma testosterone concentrations by radioimmunoassay. In males with same sex preference there was a specific AR overexpression in CA3 and CA4 that suggests a feminized pattern because females in proestrus trend to show a higher density of AR in these hippocampal areas. Sex differences in AR density were found in the anterior cingulate cortex (ACg) and frontoparietal cortex (FrPa). Serum levels of testosterone did not differ between groups. Data are discussed based on the role of AR in the hippocampus.

A Protocol for the Non-invasive Method of Ultrasound Separation During the Sociosexual Vocal-Non-contact Model in Rats

Ultrasonic vocalization (USV) is one of the measurable behavioral parameters of sociosexual interactions in rats. To precisely and accurately describe the neurobehavioral properties of USV and the potentially related specific emotional responsiveness of animals, we need to know which animals vocalize and what is their exact behavioral and physiological response. To this end, we modified the non-contact cage [non-contact erection model (NCE)] by adding a modification [vocalization-non-contact erection (VOC-NCE)] that makes it possible to assign emitted ultrasonic signals to a particular animal. Typically, the NCE cage consists of two compartments separated by perforated baffles. A male is placed in one section, and a receptive female is placed in the other section. This makes possible the accurate description of sexual parameters related to the cues controlled by the experimenter. In VOC-NCE, we completely separated the male USV from the female USV by three appropriately perforated baffles and located microphones combined with ultrasonic screening. We recorded emission in both typical bands, the so-called 22- and 50-kHz bands, with various subtypes, thus highlighting the utility of our protocol to investigate the sexual dimorphism of vocalization. Similar to the anticipatory model, we showed that emission can occur without acoustic feedback from concomitants during the VOC-NCE test. Therefore, we propose a relatively simple method for assigning individual vocalization. We discuss its usefulness and limitations in assessing vocal differentiation related to sexual parameters, adaptive changes during conditioning procedures, and further applications.

Retracted: Sexual orientation, neuropsychiatric disorders and the neurotransmitters involved

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor in Chief of Neuroscience and Biobehavioral Reviews after concerns were raised with respect to the phrasing of comparisons drawn between humans and animal models. These comparisons were deemed unsupportable, and thus in the best interests of publication standards the Editor has concluded it is necessary to retract the paper. The authors disagree with the reason for the retraction.

Prolonged use of letrozole causes morphological changes on gonads in Galea spixii

Letrozole is used as a therapeutic agent in reproductive disorders caused by high estrogen levels. Letrozole inhibits cytochrome P450 aromatase and reduces estrogen levels. However, the effects of long-term use on reproductive traits are unknown. The aim of this study was to evaluate the prolonged use of letrozole in the gonads of rodents (Spix's yellow-toothed cavy; Galea spixii). Forty-eight rodents (24 males and 24 females) were randomly divided into the treated and control groups. Letrozole administration started at 15 days of age and continued weekly until 30, 45, 90, and 120 days of age. The body, testis, and ovary weights were analyzed, as well as the morphological progression of spermatogenesis and folliculogenesis. Macroscopically, body weight gain and gonads weight were increased in the letrozole group. Microscopically, the ovaries of treated females showed stratified epithelium and a cellular disorder of the tunica albuginea. In the testes of treated males, the development of seminiferous tubules was delayed and sperm was absent. The collective findings indicate that the prolonged use of letrozole alters secondary sexual characteristics, and causes weight gain, reproductive changes, and male infertility.

Reduced sexual motivation of diabetic female rats: Restoration with insulin

The aim of this study was to evaluate female rat sexual motivation in a model of diabetes mellitus type 1. Severe hyperglycemia was induced in ovariectomized Wistar rats by injecting streptozotocin [STZ, 100 mg/kg, i.p.]. Ten days later, females received estradiol benzoate (10 μg/rat, s.c.) plus progesterone (3 mg/rat, s.c.). A group of STZ-treated animals was administered with insulin (2-4 U) every 12 h for 10 days, which normalized glucose levels. In the partner preference (PP) and sexual incentive motivation (SIM) tests, control females spent more time close to a sexually experienced male (SE) than with a castrated male (CM). STZ-treated females stayed the same amount of time with both stimuli, that is, they lost their sexual preference. We also evaluated the sense of smell using two behavioral tests, one related to sexual odors (SO) and another one to food odors (FO). In the SO test, control females spent more time sniffing the sawdust coming from cages that contained SE males; hyperglycemic females remained the same amount of time sniffing the sawdust of both stimuli: SE and CM. In the FO test, no differences were found between control and STZ-treated groups. Insulin treatment reverted the changes observed in hyperglycemic females in the PP, SIM and SO tests. These data suggest that severe hyperglycemia decreases sexual motivation and that insulin recovers such diminution.

Prenatal EDCs Impair Mate and Odor Preference and Activation of the VMN in Male and Female Rats

Environmental endocrine-disrupting chemicals (EDCs) disrupt hormone-dependent biological processes. We examined how prenatal exposure to EDCs act in a sex-specific manner to disrupt social and olfactory behaviors in adulthood and underlying neurobiological mechanisms. Pregnant rat dams were injected daily from embryonic day 8 to 18 with 1 mg/kg Aroclor 1221 (A1221), 1 mg/kg vinclozolin, or the vehicle (6% DMSO in sesame oil). A1221 is a mixture of polychlorinated biphenyls (weakly estrogenic) while vinclozolin is a fungicide (anti-androgenic). Adult male offspring exposed to A1221 or vinclozolin, and females exposed to A1221, had impaired mate preference behavior when given a choice between 2 opposite-sex rats that differed by hormone status. A similar pattern of impairment was observed in an odor preference test for urine-soaked filter paper from the same rat groups. A habituation/dishabituation test revealed that all rats had normal odor discrimination ability. Because of the importance of the ventrolateral portion of the ventromedial nucleus (VMNvl) in mate choice, expression of the immediate early gene product Fos was measured, along with its co-expression in estrogen receptor alpha (ERα) cells. A1221 females with impaired mate and odor preference behavior also had increased neuronal activation in the VMNvl, although not specific to ERα-expressing neurons. Interestingly, males exposed to EDCs had normal Fos expression in this region, suggesting that other neurons and/or brain regions mediate these effects. The high conservation of hormonal, olfactory, and behavioral traits necessary for reproductive success means that EDC contamination and its ability to alter these traits has widespread effects on wildlife and humans.

Sexual partner preference in animals and humans

Sex differences in brain and behavior of animals including humans result from an interaction between biological and environmental influences. This is also true for the differences between men and women concerning sexual orientation. Sexual differentiation is mediated by three groups of biological mechanisms: early actions of sex steroids, more direct actions of sex-specific genes not mediated by gonadal sex steroids and epigenetic mechanisms. Differential interactions with parents and conspecifics have additionally long-term influences on behavior. This presentation reviews available evidence indicating that these different mechanisms play a significant role in the control of sexual partner preference in animals and humans, in other words the homosexual versus heterosexual orientation. Clinical and epidemiological studies of phenotypically selected populations indicate that early actions of hormones and genetic factors clearly contribute to the determination of sexual orientation. The maternal embryonic environment also modifies the incidence of male homosexuality via immunological mechanisms. The relative contribution of each of these mechanisms remains however to be determined.

Lack of interaction between prenatal stress and prenatal letrozole to induce same-sex preference in male rats

Same-sex partner preference between males has been observed in all species in which this behavior has been studied. Disruption of brain estradiol synthesis during development has been proposed as one of the biological causes underlying this behavior in some mammals. In support of this possibility, perinatal administration of aromatase inhibitors (such as letrozole) to male rat pups, induces around half of them to have same-sex preference and female sexual behavior in adulthood. Another putative factor that modifies sex preference is prenatal stress. Several stress protocols, applied to the pregnant dam, cause some of the adult male progeny to have an increased male preference, a decreased preference for the female, and lordosis behavior. Interestingly, these effects of stress might be mediated by its inhibitory action on brain aromatase. The aim of the present study was to analyze a possible interaction between these two factors in male rats. Pregnant dams were exposed to one of the four treatments across gestation days 10-22 (G10-G22): 1) vehicle-treated non-stressed controls; 2) letrozole (0.56 µg/kg); 3) 30 min immobilization stress); 4) both letrozole and stress combined. The male offspring were tested in adulthood for partner preference in a three-chambered arena, where we also recorded the masculine and feminine sexual behaviors. One week later males were tested for masculine and feminine sexual behavior in cylindrical arenas where they interacted for 30 min with a receptive female and thereafter with a sexually active male for another 30 min. Letrozole, stress and their combination resulted in same-sex preference in 40, 31 and 50% of males, respectively, compared to 5% in the control group. In the sexual behavior tests, prenatal stress reduced the percentage of males displaying intromissions and ejaculation (impaired masculinization), while letrozole mainly increased lordosis (impaired defeminization). The males prenatally submitted to stress and treated with letrozole presented these behavioral features but did not differ from both treatments given independently. The results indicate that the changes induced by stress or the aromatase inhibition produced by letrozole only accounts for a shift in partner preference in around half of the males and that there was no interaction between these two factors.

Establishment of partner preference in male rats: Effect of prenatal letrozole and sexual experience

Repeated testing for masculine sexual behavior influences female sex preference in males. Males perinatally treated with aromatase inhibitors show male preference, but also copulate with the receptive female. Such copulation modifies sex preference most likely because of its rewarding properties. In this study, we intended to equal the incentive value of both stimuli -in the sex preference test- by using receptive females with vaginal occlusion. Vehicle and letrozole-treated (0.56 μg/kg, gestation days 10-21) males were repeatedly tested for sex preference at 40, 55, 70, 85 and 100 days of age. These ages were selected because males of 40 days are unable to copulate, while by 100 days of age almost all males show the complete repertoire of masculine sexual behavior. At 40 days of age, males of all groups fail to show sex preference and none of them was able to copulate. In controls of 100 days of age all males showed female-sex preference and all intromitted the female. A large proportion (44%) of vehicle-treated males that could not copulate the female showed male preference. Twenty to 30% of the prenatally letrozole treated males also had same-sex preference even if they could copulate; and most of them (67%) had a male preference when copulation was precluded. These data support the idea that copulation is crucial for developing a female preference in control animals. The results suggest that brain changes produced by estrogens along early development and stimuli coming from the partner are essential for shaping sex preference.

Effects of prenatal sex hormones on behavioral sexual dimorphism

BACKGROUND

We investigated the association between the hormone environment during the prenatal period using cord blood, and gender-role play behavior in school-aged children.

METHODS

A total of 879 school-aged children (433 boys and 446 girls) in a prospective birth cohort study in Hokkaido were enrolled to analyze the relationship between cord blood level of the sex hormones estradiol (E), testosterone (T), progesterone (P), and dehydroepiandrosterone (DHEA), and the Pre-School Activities Inventory (PSAI) score. The PSAI evaluated sex-typical characteristics, the type of preferred toys and play activities. The PSAI consists of 12 masculine and 12 feminine items, and the composite scores were calculated by subtracting the feminine score from the masculine score. Higher scores indicated male-typical behavior.

RESULTS

Composite and masculine PSAI scores were significantly higher in boys. Meanwhile, the feminine score was significantly lower in boys. Although T and P were significantly higher in boys, E/T was significantly higher in girls. In a multivariate regression model, including covariates of social factors, there was no correlation between any of the hormones and PSAI score in boys. In girls, only P and E/T were positively correlated with the feminine score.

CONCLUSIONS

Prenatal sex hormone exposure may influence the dimorphic brain development and behavior in school-aged girls. Furthermore, the cord blood hormone levels may not fully reflect the hormone environment during the prenatal period.

Sexually Dimorphic Effects of Aromatase on Neurobehavioral Responses

Aromatase is the enzyme responsible for converting testosterone to estradiol. In mammals, aromatase is expressed in the testes, ovaries, brain, and other tissues. While estrogen is traditionally associated with reproduction and sexual behavior in females, our current understanding broadens this perspective to include such biological functions as metabolism and cognition. It is now well-recognized that aromatase plays a vital lifetime role in brain development and neurobehavioral function in both sexes. Thus, ongoing investigations seek to highlight potentially vital sex differences in the role of aromatase, particularly regarding its centrally mediated effects. To characterize the role of aromatase in mediating such functions, effects of aromatase inhibitor (AI) treatments on humans and animal models have been determined. Aromatase knockout (ArKO) mice that systemically lack the enzyme have also been employed. Humans possessing mutations in the gene encoding aromatase, CYP19, have also provided critical insight into how aromatase affects brain function in a possible sex-dependent manner. A better understanding of how AIs, used to treat breast cancer and other clinical conditions, may detrimentally affect neurobehavioral responses will likely promote development of future therapies to combat these effects. Herein, we will provide a critical review of the current knowledge of sex differences in aromatase regulation of various neurobehavioral functions. Although many species have been used to better understand the functions of aromatase, this review focuses on rodent models and humans. Critical gaps in our present understanding of this area will be considered, and important future research directions will be discussed.

Neuropeptide and steroid hormone mediators of neuroendocrine regulation

To maintain the health and well-being of all mammals, numerous aspects of physiology are controlled by neuroendocrine mechanisms. These mechanisms ultimately enable communication between neurones and glands throughout the body and are centrally mediated by neuropeptides and/or steroid hormones. A recent session at the International Workshop in Neuroendocrinology highlighted the essential roles of some of these neuropeptide and steroid hormone mediators in the neuroendocrine regulation of stress-, reproduction- and behaviour-related processes. Accordingly, the present review highlights topics presented in this session, including the role of the neuropeptides corticotrophin-releasing factor and gonadotrophin-releasing hormone in stress and reproductive physiology, respectively. Additionally, it details an important role for gonadal sex steroids in the development of behavioural sex preference.

Male rats with same-sex preference show higher immobility in the forced swim test, but similar effects of fluoxetine and desipramine than males that prefer females

Sex preference in male rats is partly determined by the organizational action of estradiol. Thus, several paradigms have used aromatase inhibitors to manipulate sex preference. We recently showed that a subpopulation of male rats prenatally treated with letrozole (0.56 μg/kg, G10-G22), a non-steroidal third generation aromatase inhibitor, had same-sex preference, female sexual behavior (including lordosis and proceptivity) and penile erections when exposed to other males. These males, in addition, displayed high levels of experimental anxiety in the plus maze test and were insensitive to the anxiogenic-like acute effect of FLX (10 mg/kg). The two main purposes of the present work were: a) to study the behavioral profile of males displaying same-sex preference in the forced swim test (FST), and b) to analyze if the antidepressant-like effect of the subchronic treatment with FLX (10 mg/kg, 3 times) or desipramine (DMI, 10 mg/kg, 3 times) vary according to sex preference. Males treated prenatally with letrozole with same-sex preference showed more immobility and less active behaviors (swimming and climbing) in the FST than males with female preference. Subchronic treatment with FLX and DMI reduced immobility when compared to saline controls, while FLX increased swimming and DMI increased climbing behavior. Treatments were equally effective in males with preference for other males and those that preferred females. These results indicate that an association exists between prenatal letrozole treatment, same-sex preference and immobility in the FST.

Prenatal Exposure to Progesterone Affects Sexual Orientation in Humans

Prenatal sex hormone levels affect physical and behavioral sexual differentiation in animals and humans. Although prenatal hormones are theorized to influence sexual orientation in humans, evidence is sparse. Sexual orientation variables for 34 prenatally progesterone-exposed subjects (17 males and 17 females) were compared to matched controls (M age = 23.2 years). A case-control double-blind design was used drawing on existing data from the US/Denmark Prenatal Development Project. Index cases were exposed to lutocyclin (bioidentical progesterone = C₂₁H₃₀O₂; M _W : 314.46) and no other hormonal preparation. Controls were matched on 14 physical, medical, and socioeconomic variables. A structured interview conducted by a psychologist and self-administered questionnaires were used to collect data on sexual orientation, self-identification, attraction to the same and other sex, and history of sexual behavior with each sex. Compared to the unexposed, fewer exposed males and females identified as heterosexual and more of them reported histories of same-sex sexual behavior, attraction to the same or both sexes, and scored higher on attraction to males. Measures of heterosexual behavior and scores on attraction to females did not differ significantly by exposure. We conclude that, regardless of sex, exposure appeared to be associated with higher rates of bisexuality. Prenatal progesterone may be an underappreciated epigenetic factor in human sexual and psychosexual development and, in light of the current prevalence of progesterone treatment during pregnancy for a variety of pregnancy complications, warrants further investigation. These data on the effects of prenatal exposure to exogenous progesterone also suggest a potential role for natural early perturbations in progesterone levels in the development of sexual orientation.

Prenatal administration of letrozole reduces SDN and SCN volume and cell number independent of partner preference in the male rat

During development, the exposure to testosterone, and its conversion to estradiol by an enzyme complex termed aromatase, appears to be essential in adult male rats for the expression of typical male sexual behavior and female-sex preference. Some hypothalamic areas are the supposed neural bases of sexual preference/orientation; for example, male-oriented rams have a reduced volume of the sexually dimorphic nucleus (oSDN), while in homosexual men this nucleus does not differ from that of heterosexual men. In contrast, homosexual men showed a larger number of vasopressinergic cells in the suprachiasmatic nucleus (SCN). Interestingly, male rats perinatally treated with an aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD), also showed bisexual preference and an increased number of vasopressinergic neurons in the SCN. However, this steroidal aromatase inhibitor has affinity for all three steroid receptors. Recently, we reported that the prenatal administration of the selective aromatase inhibitor, letrozole, produced a subpopulation of males with same-sex preference. The aim of this study was to compare the volume and number of cells of the SDN and SCN (the latter nucleus was immunohistochemically stained for vasopressin) between males treated with letrozole with same-sex preference, males treated with letrozole with female preference and control males with female preference. Results showed that all males prenatally treated with letrozole have a reduced volume and estimated cell number in the SDN and SCN, independent of their partner preference. These results indicate that the changes in these brain areas are not related to sexual preference, but rather to the effects of letrozole. The divergent results may be explained by species differences as well as by the critical windows during which the aromatase inhibitor was administered.

Pentylenetetrazole-induced seizures in developing rats prenatally exposed to valproic acid

BACKGROUND

Epidemiological evidence indicates epilepsy is more common in patients with autism spectrum disorders (ASD) (20-25%) than in the general population. The aim of this project was to analyze seizure susceptibility in developing rats prenatally exposed to valproic acid (VPA) as autism model.

METHODS

Pregnant females were injected with VPA during the twelfth embryonic day. Seizures were induced in fourteen-days-old rat pups using two models of convulsions: pentylenetetrazole (PTZ) and lithium-pilocarpine (Li-Pilo).

RESULTS

Two subgroups with different PTZ-induced seizure susceptibility in rats exposed to VPA were found: a high susceptibility (VPA+) (28/42, seizure severity 5) and a low susceptibility (VPA-) (14/42, seizure severity 2). The VPA+ subgroup exhibited an increased duration of the generalized tonic-clonic seizure (GTCS; 45 ± 2.7 min), a higher number of rats showed several GTCS (14/28) and developed status epilepticus (SE) after PTZ injection (19/27) compared with control animals (36.6 ± 1.9 min; 10/39; 15/39, respectively). No differences in seizure severity, latency or duration of SE induced by Li-Pilo were detected between VPA and control animals.

DISCUSSION

Prenatal VPA modifies the susceptibility to PTZ-induced seizures in developing rats, which may be linked to an alteration in the GABAergic transmission. These findings contribute to a better understanding of the comorbidity between autism and epilepsy.

Fetal safety profile of aromatase inhibitors: Animal data

Aromatase inhibitors (AIs) are a class of drugs that act by blocking the production of estrogens from androgens. The current review concentrates on the prenatal developmental toxicity of AIs in experimental models. Available data indicate that AIs may affect pregnancy at human therapeutic or lower doses. The window of vulnerability to AIs is not limited to organogenesis, but also includes the preimplantation stage and fetal periods. Decreased embryo/fetal survival was the prominent treatment-related effect. Morphological anomalies noted in fetuses exposed to AIs included skeletal anomalies, abnormal head morphology, increased ano-genital distance in female fetuses, and minor urinary tract system anomalies. Placental enlargement was consistently reported in rats and non-human primates after maternal treatment with several AIs. In conclusion, data from basic scientific research suggest that low intensity exposure to AIs applied during a wide gestational window can profoundly affect prenatal development.

The Relationship between the Second-to-Fourth Digit Ratio and Behavioral Sexual Dimorphism in School-Aged Children

Sexually dimorphic brain development and behavior are known to be influenced by sex hormones exposure in prenatal periods. On the other hand, second-to forth digit ratio (2D/4D) has been used as an indirect method to investigate the putative effects of prenatal exposure to androgen. In the present study, we herein investigated the relationship between gender-role play behavior and the second-to-fourth digit ratio (2D/4D), which has been used as an indirect method to investigate the putative effects of prenatal exposure to androgens, in school-aged children. Among 4981 children who became 8 years old by November 2014 and were contactable for this survey by The Hokkaido Study of Environment and Children's Health, 1631 (32.7%), who had data for 2D/4D and Pre-school Activities Inventory (PSAI) as well as data for the survey at baseline, were available for analysis. Parents sent reports of PSAI on the sex-typical characteristics, preferred toys, and play activities of children, and black and white photocopies of the left and right hand palms via mail. PSAI consisted of 12 masculine items and 12 feminine items, and a composite score was created by subtracting the feminine score from the masculine score, with higher scores representing masculine-typical behavior. While composite scores in PSAI were significantly higher in boys than in girls, 2D/4D was significantly lower in boys than in girls. Although the presence or absence of brothers or sisters affected the composite, masculine, and feminine scored of PSAI, a multivariate regression model revealed that 2D/4D negatively correlated with the composite scores of PSAI in boys, whereas no correlation was found in girls. Although 2D/4D negatively correlated with the masculine score in boys and girls, no correlation was observed between 2D/4D and the feminine score. In conclusion, although social factors, such as the existence of brother or sisters, affect dimorphic brain development and behavior in childhood, the present study revealed that the prenatal hormonal environment was an important factor influencing masculine-typical dimorphic brain development and behavior in school-aged children.

Cell-Based High-Throughput Screening for Aromatase Inhibitors in the Tox21 10K Library

Multiple mechanisms exist for endocrine disruption; one nonreceptor-mediated mechanism is via effects on aromatase, an enzyme critical for maintaining the normal in vivo balance of androgens and estrogens. We adapted the AroER tri-screen 96-well assay to 1536-well format to identify potential aromatase inhibitors (AIs) in the U.S. Tox21 10K compound library. In this assay, screening with compound alone identifies estrogen receptor alpha (ERα) agonists, screening in the presence of testosterone (T) identifies AIs and/or ERα antagonists, and screening in the presence of 17β-estradiol (E2) identifies ERα antagonists. Screening the Tox-21 library in the presence of T resulted in finding 302 potential AIs. These compounds, along with 31 known AI actives and inactives, were rescreened using all 3 assay formats. Of the 333 compounds tested, 113 (34%; 63 actives, 50 marginal actives) were considered to be potential AIs independent of cytotoxicity and ER antagonism activity. Structure-activity analysis suggested the presence of both conventional (eg, 1, 2, 4, - triazole class) and novel AI structures. Due to their novel structures, 14 of the 63 potential AI actives, including both drugs and fungicides, were selected for confirmation in the biochemical tritiated water-release aromatase assay. Ten compounds were active in the assay; the remaining 4 were only active in high-throughput screen assay, but with low efficacy. To further characterize these 10 novel AIs, we investigated their binding characteristics. The AroER tri-screen, in high-throughput format, accurately and efficiently identified chemicals in a large and diverse chemical library that selectively interact with aromatase.