Sexual Differentiation Of Brain Research Articles

RAT MODEL FOR POLY-AUTOIMMUNITY

Around 30% of the male PVG rats have very low testosterone levels. Upon immunisation with myelin basic protein in complete Freund’s adjuvant they develop experimental autoimmune encephalomyelitis and adjuvant arthritis. The androgen insensitive syndrome in these rats could be used in studies on poly-autoimmunity as well as in studies on variations in the sexual differentiation of brain and behavior.

Delayed effects of single neonatal subcutaneous exposure of low-dose 17α-ethynylestradiol on reproductive function in female rats

Delayed effects of exposure to small amounts of estrogenic compounds during the critical period of brain sexual differentiation were investigated by subcutaneous treatment of female Sprague-Dawley rats with 0 (vehicle control), 0.08, 0.4, or 2 µg/kg of 17α-ethynylestradiol (EE) on postnatal day (PND) 1. The treatment did not affect growth and development of the treated animals, and the timings of vaginal opening were similar between the EE-treated and control groups. The animals were periodically examined for the estrous cycle from postnatal week (PNW) 8-9 to PNW 32-33. Patterns of the estrous cycle were similar among the groups until PNW 17. None of the control animals showed persistent estrus until PNW 33. The animals treated with 0.4 µg/kg or more EE showed persistent estrus from PNW 20. The alteration was reflected in the number of days judged as proestrus or estrus, and was found to gradually increase in the EE-treated groups. At necropsy on PNW 32-33, ovulation was not confirmed in most EE-treated animals, even on the day of estrus. In addition, sporadic milk accumulations were observed in the mammary gland of the EE-treated animals. Histological evaluation revealed cystic follicle formation in the EE-treated ovaries and also revealed hyperplasia of mammary glands. Furthermore, ovaries from the animals showing persistent estrus lacked corpus luteum, indicating long-term anovulation. These results clearly show that single exposure to EE during the critical period of brain sexual differentiation can exert effects on reproductive functions at a later period in rats.

Sex Steroids and the Control of the Kiss1 System: Developmental Roles and Major Regulatory Actions

Kisspeptins, encoded by the Kiss1 gene, and their canonical receptor, GPR54 (also termed Kiss1R), are unanimously recognised as essential regulators of puberty onset and gonadotrophin secretion. These key reproductive functions stem from the capacity of kisspeptins to stimulate gonadotrophin-releasing hormone (GnRH) secretion in the hypothalamus, where discrete populations of Kiss1 neurones have been identified. In rodents, two major groups of hypothalamic Kiss1 neurones exist: one present in the arcuate nucleus (ARC) and the other located in the anteroventral periventricular area (AVPV/RP3V). In recent years, numerous signals have been identified as putative modulators of the hypothalamic Kiss1 system. Among them, the prominent role of sex steroids as being important regulators of Kiss1 neurones has been documented in different species and developmental stages, such as early brain sex differentiation, puberty, adulthood and senescence. These regulatory actions are (mainly) conducted via oestrogen receptor (ER)α, which is expressed in almost all Kiss1 neurones, and likely involve both classical and nonclassical pathways. The regulatory effects of sex steroids are nucleus-specific. Thus, sex steroids inhibit the expression of Kiss1/kisspeptin at the ARC, as a mechanism to conduct their negative-feedback actions on gonadotrophin secretion. By contrast, oestrogens enhance Kiss1 expression at the AVPV/RP3V in rodents, suggesting the involvement of this population in the positive-feedback actions of oestradiol to generate the preovulatory surge of gonadotrophins. In addition, sex steroids have been shown to act post-transcriptionally, modulating GnRH/gonadotrophin responsiveness to kisspeptin. Finally, sex steroids also regulate the expression of co-transmitters of Kiss1 neurones, such as neurokinin B, whose mRNA content in the ARC fluctuates in parallel to that of Kiss1 in response to changes in the circulating levels of sex steroids, therefore suggesting the contribution of this neuropeptide in the feedback control of gonadotrophin secretion. In sum, compelling experimental evidence obtained in different mammalian (and non-mammalian) species, including primates, demonstrates that sex steroids are essential regulators of hypothalamic Kiss1 neurones, which in turn operate as conduits for their effects on GnRH neurones. The physiological relevance of such regulatory phenomena is thoroughly discussed.

Autism Attenuates Sex Differences in Brain Structure: A Combined Voxel-Based Morphometry and Diffusion Tensor Imaging Study

It has been proposed that autism spectrums condition may represent a form of extreme male brain (EMB), a notion supported by psychometric, behavioral, and endocrine evidence. Yet, limited data are presently available evaluating this hypothesis in terms of neuroanatomy. Here, we investigated sex-related anatomic features in adults with AS, a "pure" form of autism not involving major developmental delay. Males and females with AS and healthy controls (n = 28 and 30, respectively) were recruited. Structural MR imaging was performed to measure overall gray and white matter volume and to assess regional effects by means of VBM. DTI was used to investigate the integrity of the main white matter tracts. Significant interactions were found between sex and diagnosis in total white matter volume, regional gray matter volume in the right parietal operculum, and fractional anisotropy (FA) in the body of the CC, cingulum, and CR. Post hoc comparisons indicated that the typical sexual dimorphism found in controls, whereby males have larger FA and total white matter volume, was absent or attenuated in participants with AS. Our results point to a fundamental role of the factors that underlie sex-specific brain differentiation in the etiology of autism.

MAP7D2 is a brain expressing X-linked maternal imprinted gene in humans

AbstractIncreasing evidence suggests imprinted genes influence mouse and human behaviors and cognitive functions. Unlike autosomal imprinted genes, X-linked imprinted genes are expressed in a sex-dependent manner because of male hemizygosity. Therefore, these genes could directly affect sex-specific brain functions and sex-biased vulnerability to psychiatric disorders such as autism1. Comparing lymphoblastoid cell lines (LCL) and peripheral blood mononuclear cells (PBMC) from healthy adult male and females, we identified MAP7 domain containing 2 (MAP7D2) as the first human X-linked imprinted gene. Both in LCL and PBMC, MAP7D2 expression was significantly suppressed in males by maternal imprinting. In each female LCL clone, MAP7D2 was expressed higher in paternally derived allele and was affected by X-chromosome inactivation. In female PBMC, however, reactivation of maternal MAP7D2 alleles was observed. MAP7D2 was expressed specifically in the brain among human tissues with unique isoforms. These results predict a crucial role of MAP7D2 for human sex-dependent neurobiological traits.

Am I My Brain or My Genitals? A Nature-Culture Controversy in the Hermaphrodite Debate from the mid-1960s to the late 1990s

The groundbreaking and prophetic rhetoric of neuroscience has recently highlighted the fetal brain as the most promising organ for understanding why transsexuals feel "trapped in the wrong body", and for predicting whether children born with "ambiguous" genitalia will grow up to feel like a man or a woman.This article proposes a recent history of the cerebralization of intersexuality and of transsexuality as atypical neurodevelopmental conditions. It examines the ways in which the organizational theory of brain sex differentiation developed in the late 1950s in behavioral neuroendocrinology has gained increased prominence in and through controversies over best practice issues in the case management of intersex newborns, and the etiology of transsexuality.It focuses on the American context and on the leading warrior in this battle: Milton Diamond, now a most prominent figure in professional debates about the clinical management of intersexuality, and the intersex person's best friend. Persons with an intersexed or transsexual condition consider, not their gonads, but their brains, their core sense of self, as the primary determinant of sex. (Diamond and Beh 2005, 6-7, note 1)

Atypical lateralisation in emotional prosody in men with schizotypy

Individuals high in schizotypy have been shown to reveal reduced lateralisation in verbal processing which may be influenced by an impaired left hemisphere performance. However, little is known about schizotypy and right hemisphere functions such as emotional perception. The present study focuses on atypical lateralisation in language and emotional prosody in Impulsive Non-conformity (IMP), a specific aspect of schizotypy. A total of 41 participants (20 females) performed a dichotic listening linguistic and emotional prosody task, which typically shows a right ear advantage (REA) and left ear advantage (LEA), respectively. A median split based on the IMP scale included in the Oxford-Liverpool Inventory of Feelings and Experiences was used to divide the sample into high and low scorers. The results revealed a selective reduction of the LEA in the prosody task in high-IMP males. Females high and low in IMP revealed typical lateralisation in both tasks. The results indicate that high-IMP males are especially prone to atypical lateralisation in emotional prosody, which parallels those findings in male patients with schizophrenia. The results suggest similarities in sex-specific atypical brain organisation between schizotypy and schizophrenia.

DHEA and estradiol levels in brain, gonads, adrenal glands, and plasma of developing male and female European starlings

Traditionally, sexual differentiation of the brain was thought to be driven by gonadal hormones, particularly testosterone (T). However, recent studies in songbirds suggest that other steroids may also be important. For example, dehydroepiandrosterone (DHEA) can be synthesized by the gonads, adrenal glands, and/or brain and locally metabolized into T and 17β-estradiol (E(2)). Here, we examined DHEA and E(2) levels in the brain, peripheral tissues, and plasma of wild European starlings (Sturnus vulgaris). In Study 1, samples were collected from males and females at P0 (day of hatch), P6, and P8. In Study 2, samples were collected at P4. At P0, DHEA levels in the diencephalon were higher in males than females. DHEA levels were generally high in the gonads and adrenals, and they were higher in testes than ovaries at P8. Further, E(2) levels were non-detectable in most brain samples, suggesting that DHEA was not metabolized to E(2) or that locally produced E(2) was rapidly inactivated. At P4, DHEA levels in telencephalic regions were lower in males than females. Taken together, these data suggest that sex differences in peripheral DHEA secretion and neural DHEA metabolism at specific ages during development might play a role in sexual differentiation of the songbird brain.

A NOVEL PEAK OF FUNCTIONAL NEUROSTEROIDOGENESIS AND ESTROGEN SIGNALLING IN THE EARLY BRAIN DEVELOPMENT OF ORANGE-SPOTTED GROUPER EPINEPHELUS COIOIDES

Introduction: Despite neurosteroidogenic enzymes are playing important roles in the regulation of brain development and function, the potential link between brain and gonad by the action of steroid hormones during gondal sex differentiation is still matter of debate in teleosts [1]. In recent years, we focused on the early brain development in response to the synthesis of neurosteroids and receptor activation during gonadal sex differentiation in orangespotted grouper Epinephelus coioides (a mono-female sex development at the juvenile stage) and black porgy Acanthopagrus schlegeli (a mono-male sex development at the juvenile stage) [2,3]. The mechanism of brain sex differentiation and/or brain activation during early ages of female grouper fish is not fully understood yet. Moreover, there is an important lack of information regarding the expression of four key steroidogenic enzymes cyp11a1 (P450scc), hsd3b1, cyp17a1 and cyp19a1b in the early brain development and their potential links with gonadal sex differentiation. Hence, these phenomena support the selection of orange-spotted grouper as a model for neuroendocrine research, principally to understand the molecular mechanism of sex differentiation in female fish. Therefore, in the present study we aimed to test the hypothesis that 1) brain of orange-spotted grouper fish has the capability for de novo steroidogenesis and the production of these neurosteroids may have a correlation to the occurrence of gonadal sex differentiation and 2) we compared the expression of key genes and signalling in the protogynous grouper and protandrous black porgy in order to know whether this expression pattern has gender related event or not during gonadal sex differentiation. Here, we investigated the temporal expression pattern of the genes related to the neurosteroidogenesis and estrogen signaling in different days after hatching ages (dah) in the teleosts brain.

Sex Difference in the Expression of DNA Methyltransferase 3a in the Rat Amygdala During Development

Sexual differentiation of the neonatal rat brain is regulated by dynamic processes occurring at the level of DNA, resulting in sexually dimorphic gene expression. Steroid hormone receptors act partly in the developing brain by recruiting co-activators, thereby increasing the acetylation of histones and gene expression. Recent data indicate that sexual differentiation of the brain may also result, in part, from differences in promoter methylation patterns of some steroid responsive genes. Methylation of DNA is an epigenetic process that can decrease gene expression without altering the original DNA sequence. DNA cytosine-5-methyltransferases (DNMTs) 1 and 3a are two factors that induce methylation. We investigated whether sex differences in the expression of DNMT1 and DNMT3a were apparent in the amygdala, preoptic area and medial basal hypothalamus at different time points during development. We found that females express significantly more DNMT3a mRNA and protein in the amygdala but not within the preoptic area or the medial basal hypothalamus at postnatal day 1. There were no sex differences in DNMT3a mRNA or protein at postnatal day 10. Furthermore, no sex differences were observed in the expression of DNMT1 at either time point. Because most sex differences in the brain are a result of a higher level of gonadal steroid hormone exposure in males at birth, we examined whether dihydrotestosterone or oestradiol exposure would reduce DNMT3a expression in neonatal female rats. We found that both oestradiol and dihydrotestosterone treatment significantly reduced DNMT3a, but not DNMT1, mRNA expression within the developing amygdala. Our results indicate that sex differences in DNMT3a within the developing amygdala are partly a result of steroid exposure. This suggests that steroid hormone exposures may programme lasting differences in amygdala function by altering the expression of the epigenetic factor, DNMT3a.

Progranulin enhances neural progenitor cell proliferation through glycogen synthase kinase 3β phosphorylation

Progranulin (PGRN) is an estrogen-inducible growth factor thought to affect multiple processes in the CNS, including brain sexual differentiation, adult neurogenesis in the hippocampus, and development of neurodegenerative diseases. However, the precise physiological functions of PGRN in individual nerve cells are not fully understood. The aim of the present study was to enhance the understanding of PGRN function in the CNS by investigating the effects of PGRN on neural progenitor cells (NPCs). We found that significant amounts of endogenous PGRN were secreted from isolated NPCs in cultures. To assess the bioactivities of endogenous and exogenous PGRN, we studied NPCs derived from wild-type mice (WT-NPCs) and PGRN-deficient mice (KO-NPCs). We found that proliferation of KO-NPCs was significantly enhanced by PGRN treatment; however, PGRN treatment apparently did not affect proliferation of WT-NPCs perhaps because of the high levels of endogenous PGRN expression. NPC death and asymmetric cellular division of KO-NPCs and WT-NPCs, which results in production of neural stem cells, astrocytes, or oligodendrocytes, were not affected by PGRN treatment. We also investigated the signaling mechanism(s) that mediate PGRN-induced NPC proliferation and found that phosphorylation of serine 9 (S9) of glycogen synthase kinase 3-beta (GSK3β), which was dependent on phosphatidylinositol 3-kinase (PI3K) activity, was induced by PGRN treatment. In addition, a GSK3β-specific inhibitor enhanced NPC proliferation. Taken together, our observations indicate that PGRN enhanced NPC proliferation, at least in part, via inducing GSK3β phosphorylation.

Puberty and Brain Sexual Differentiation: Getting Organized

The adolescent brain undergoes substantial remodeling and is a target of pubertal gonadal steroid hormones. Our work in the Syrian hamster shows that when gonadal hormones are absent during adolescent development, male-typical social behaviors are impaired. In contrast, when present during adolescent development, gonadal hormones program sex-typical adult social behaviors by organizing the adolescent brain. Using rats, we found that during puberty, new cells, including neurons and glia, are added to sexually dimorphic cell groups in the brain. The anteroventral periventricular area (AVPV) is larger in females than in males and is essential for the cyclic production of ovarian hormones. The sexually dimorphic nucleus (SDN) and medial amygdala (ME) are larger in males and functionally linked to male sexual behavior and processing of social sensory stimuli. During puberty, more new cells are added to the male than to the female SDN and ME, whereas more new cells are added to the female than male AVPV. Importantly, prepubertal gonadectomy obliterates these sex differences. Hormone-modulated addition of new cells to hypothalamic and limbic cell groups may be an active mechanism for preserving sexual dimorphisms during remodeling of the adolescent brain or for establishing new functional and behavioral sexual dimorphisms that emerge with adolescent development.

Prenatal PCBs disrupt early neuroendocrine development of the rat hypothalamus

Neonatal exposure to endocrine disrupting chemicals (EDCs) such as polychlorinated biphenyls (PCBs) can interfere with hormone-sensitive developmental processes, including brain sexual differentiation. We hypothesized that disruption of these processes by gestational PCB exposure would be detectable as early as the day after birth (postnatal day (P) 1) through alterations in hypothalamic gene and protein expression. Pregnant Sprague–Dawley rats were injected twice, once each on gestational days 16 and 18, with one of the following: DMSO vehicle; the industrial PCB mixture Aroclor 1221 (A1221); a reconstituted mixture of the three most prevalent congeners found in humans, PCB138, PCB153, and PCB180; or estradiol benzoate (EB). On P1, litter composition, anogenital distance (AGD), and body weight were assessed. Pups were euthanized for immunohistochemistry of estrogen receptor α (ERα) or TUNEL labeling of apoptotic cells or quantitative PCR of 48 selected genes in the preoptic area (POA). We found that treatment with EB or A1221 had a sex-specific effect on developmental apoptosis in the neonatal anteroventral periventricular nucleus (AVPV), a sexually dimorphic hypothalamic region involved in the regulation of reproductive neuroendocrine function. In this region, exposed females had increased numbers of apoptotic nuclei, whereas there was no effect of treatment in males. For ERα, EB treatment increased immunoreactive cell numbers and density in the medial preoptic nucleus (MPN) of both males and females, while A1221 and the PCB mixture had no effect. PCR analysis of gene expression in the POA identified nine genes that were significantly altered by prenatal EDC exposure, in a manner that varied by sex and treatment. These genes included brain-derived neurotrophic factor, GABAB receptors-1 and -2, IGF-1, kisspeptin receptor, NMDA receptor subunits NR2b and NR2c, prodynorphin, and TGFα. Collectively, these results suggest that the disrupted sexual differentiation of the POA by prenatal EDC exposures is already evident as early as the day after birth, effects that may change the trajectory of postnatal development and compromise adult reproductive function.

Effects of environment on brain sexual differentiation:role of steroids and of endocrine disruptors

Several environmental substances (synthetic or natural) are able to impact endocrine function (endocrine disrupting chemicals, EDCs) and, therefore, they may have long-term consequences, especially if exposure occurs during embryonic development. Most of EDCs are agonists or antagonists of androgen or estrogen receptors, therefore they may interfere with brain and behavior sexual differentiation. We present here data collected in our laboratory on two widely used animal models: the mouse and the Japanese quail. In the quail, we investigated the effect of several EDCs [diethylstilbestrol (DES), genistein or ethylene,1,1-dichloro-2,2-bis-p-chlorophenyl (DDE)] administered in eggs on the differentiation of male sexual behavior and of the parvocellular sexually dimorphic vasotocin system. In the mouse we investigated the effects of perinatal exposure to bisphenol A (BPA) or genistein on the sexual differentiation of NO producing system and of the kisspeptin system. We investigated also the organizational effects of these EDCs on sexual, social, and explorative behaviors. Our data suggest that precocious exposure to EDCs through maternal administration (in mice) or in egg deposition (in quail) may permanently alter some sexually dimorphic circuits and influence in a gender-oriented way some behaviors. In particular, the timing of exposure to EDCs is a critical factor, such that the effects of a particular EDC will vary over the lifecycle of the animal as well as across species and phyla. Therefore, exposure to the estrogenic chemicals during embryonic development has consequences beyond impaired function of the reproductive axis. This makes it very challenging to evaluate the short and long-term effects of EDCs. These compounds are therefore, in addition to gonadal steroids and neurosteroids, a third player within the nervous system for its development and differentiation. The evolutionary implications of having them in the normal food supply for certain human populations (i.e. phytoestrogen derivatives from soy), as well as for wild and farm animals should stimulate a wide discussion about their beneficial or adverse role. Acknowledgements. The studies reported here were supported by grants from University of Torino, Regione Piemonte and Fondazione San Paolo (Neuroscience Project)

Environment and brain sexual differentiation

Several environmental substances (synthetic or natural) are able to impact endocrine function (endocrine disrupting chemicals, EDCs) and, therefore, they may have long-term consequences, especially if exposure occurs during embryonic development. Most of EDCs are agonists or antagonists of androgen or estrogen receptors, therefore they may interfere with brain and behavior sexual differentiation. We present here data collected in our laboratory on two widely used animal models: the mouse and the Japanese quail. In the quail, we investigated the effect of several EDCs [diethylstilbestrol (DES), genistein or ethylene,1,1-dichloro-2,2-bis-p-chlorophenyl (DDE)] administered in eggs on the differentiation of male sexual behavior and of the parvocellular sexually dimorphic vasotocin system. In the mouse we investigated the effects of perinatal exposure to bisphenol A (BPA) or genistein on the sexual differentiation of NO producing system and of the kisspeptin system. We investigated also the organizational effects of these EDCs on sexual, social, and explorative behaviors. Our data suggest that precocious exposure to EDCs through maternal administration (in mice) or in egg deposition (in quail) may permanently alter some sexually dimorphic circuits and influence in a gender-oriented way some behaviors. In particular, the timing of exposure to EDCs is a critical factor, such that the effects of a particular EDC will vary over the lifecycle of the animal as well as across species and phyla. Therefore, exposure to the estrogenic chemicals during embryonic development has consequences beyond impaired function of the reproductive axis. This makes it very challenging to evaluate the short and long-term effects of EDCs. These compounds are therefore, in addition to gonadal steroids and neurosteroids, a third player within the nervous system for its development and differentiation. The evolutionary implications of having them in the normal food supply for certain human populations (i.e. phytoestrogen derivatives from soy), as well as for wild and farm animals should stimulate a wide discussion about their beneficial or adverse role. Acknowledgements. The studies reported here were supported by grants from University of Torino, Regione Piemonte and Fondazione San Paolo (Neuroscience Project)

Expression and distribution of aromatas (P450AROM) in selected areas of the developing human brain

Steroids play a crucial role in brain differentiation. In the hypothalamus aromatase (P450AROM), the enzyme responsible for the conversion of testosterone (T) into 17-β estradiol (E2), modulates the mechanisms involved in sexual brain differentiation resulting in differences in specific hypothalamic nuclei between male and female. Recent findings indicate that local E2 synthesis has an impact on other brain areas including the hippocampus, temporal cortex and cerebellum, and may thus influence also cognitive functions. The expression and the distribution of P450AROM has been described throughout ontogenesis and postnatal development of the central nervous system in several mammalian species, including man. Immunohistochemical studies have localized P450AROM in pyramidal neurons, interneurons and astrocytes of human adult temporal cortex. However the cellular distribution of P450AROM has not been thoroughly investigated in fetal/early postnatal human brains. In this study we report the expression, distribution and cellular localization of P450AROM in selected areas (periventricular zones, cortical areas, cerebellum) of some fetal human brains of the second trimester and a few postnatal individuals. In the fetal individuals, P450AROM expression was scarce and limited to groups of cells mostly localized in the neuroepithelium of the subventricular zones, whereas in the neonatal/early postnatal individuals immunoreactive cells were present also in the cortical columns and in the cerebellar Purkinje layer. The enzyme was localized in the cytoplasm and in the fine extensions of the neural cells. Double labeling and confocal analysis using the Glial Fibrillary Acidic Protein (GFAP) indicated that P450AROM was expressed in cortical astrocytes of early postnatal individuals. Our data suggest a possible role for this enzyme in the control of neural development and differentiation since the second trimester of gestation.

Japan Environment and Childrenʼs Study

S-31C2-1 Background/Aims: Ministry of Environment of Japan is planning to launch a nation-wide birth cohort study (Japan Environment and Children's Study; [JECS]) in 2010. The study protocols have been decided by the working group of JECS. Methods: The study structure is composed of a core center, a medical support center, and a dozen of unit centers. Around 10 working hypotheses are proposed to clarify the effects of the exposure to chemical and physical environmental factors on the health and development of children in Japan. Each unit center registers maternity hospitals in its study areas as many as possible, and participants (pregnant women) are recruited at their first visit at the hospitals. Results: Around 100,000 pregnant women will be recruited between 2010 and 2012 for 3 years. Their children are observed from fetus to age 12. In order to evaluate the exposure to environmental factors, we are going to measure heavy metals, POPs, pesticides, and so on in biospecimens from mother and their children besides questionnaires or interviews. The targeted outcomes are physical development (low birth weight, developmental retardation, etc.), congenital anomalies (hypospadias, cryptorchidism, cleft palate, GI obstruction, ventricular septal defect, Down syndrome, etc.), psychoneurodevelopment impairments: autism (learning disorder), ADHD (attention-deficit hyperactivity disorder, etc), immunologic impairments (allergy, atopic dermatitis, asthma, etc), metabolic/endocrinologic impairments (genital hypoplasia, brain sexual differentiation, thyroid dysfunction, impaired glucose tolerance, obesity, etc.). Conclusion: The study results obtained from JECS will be published at an appropriate time.

Endocrine Disruption of Brain Sexual Differentiation by Developmental PCB Exposure

In mammals, sexual differentiation of the hypothalamus occurs during prenatal and early postnatal development due in large part to sex differences in hormones. These early organizational processes are critically important for the attainment and maintenance of adult reproductive functions. We tested the hypothesis that perinatal exposure to polychlorinated biphenyls (PCBs) that disrupt hormonal pathways would perturb reproductive maturation and the sexually dimorphic development of neuroendocrine systems in the preoptic area (POA). Pregnant Sprague-Dawley rats were injected on gestational d 16 and 18 with vehicle (dimethylsulfoxide), Aroclor 1221 (A1221, an estrogenic PCB mix), a reconstituted PCB mixture representing those highest in human body burden (PCBs 138, 153, 180), or estradiol benzoate, an estrogenic control. Male and female pups were monitored for somatic and reproductive development. In adulthood, some rats were perfused and used for immunohistochemistry of estrogen receptor α, kisspeptin, and coexpression of Fos in GnRH neurons. Other rats were used to obtain fresh-frozen POA dissections for use in a PCR-based 48-gene expression array. Pubertal onset was advanced and estrous cyclicity irregular in endocrine-disrupted females. Furthermore, sexual differentiation of female neuroendocrine systems was masculinized/defeminized. Specifically, in the adult female anteroventral periventricular nucleus, estrogen receptor α-cell numbers and kisspeptin fiber density were significantly decreased, as was GnRH-Fos coexpression. PCR analysis identified androgen receptor, IGF-I, N-methyl-d-aspartate receptor subunit NR2b, and TGFβ1 mRNAs as significantly down-regulated in endocrine-disrupted female POAs. These data suggest that developmental PCBs profoundly impair the sexual differentiation of the female hypothalamus.

Gender differences in tryptophan hydroxylase-2 mRNA, serotonin, and 5-hydroxytryptophan levels in the brain of catfish, Clarias gariepinus, during sex differentiation

Tryptophan hydroxylase ( tph) is the key regulator in serotonin (5-HT) biosynthesis that stimulates the release of GnRH and gonadotropins by acting at the level of hypothalamo–hypophyseal axis. In brain, 5-HT is expressed predominantly in preoptic area–hypothalamus (POA–HYP) region in teleosts. Therefore, in the present study we isolated tph2 from catfish brain to evaluate its expression pattern in male and female brains during early development. Tph2 cloned from catfish brain is 2.768 Kb in length which encodes predicted protein of 488 amino acid residues. The characterization of recombinant tph2 was done by transient transfection in CHO cells. Tissue distribution of tph2 revealed ubiquitous expression except ovary. Real time PCR analysis in discrete regions of adult male brain revealed that tph2 mRNA was abundant in the POA–HYP and optic tectum + cerebellum + thalamus (OCT) regions. Differential expression of tph2 was observed at mRNA and protein levels in the POA–HYP and OCT regions of male and female brains during development that further correlate with the 5-hydroxytryptophan (5-HTP) and 5-HT levels measured using HPLC method in these regions of male and female brains. Tph2 immunoreactive neurons were observed in different regions of brain at 50 days post hatch using catfish specific tph2 antibody. Changes in tph2 mRNA expression, 5-HTP, and 5-HT levels in the POA–HYP + OCT region of brains of methyltestosterone and para-chlorophenylalanine treated fishes during development further endorse our results. Based on our results, we propose that the serotonergic system is involved in brain sex differentiation in teleosts.

Developmental Time Course of Estradiol, Testosterone, and Dihydrotestosterone Levels in Discrete Regions of Male and Female Rat Brain

The prevailing view of sexual differentiation of mammalian brain is that androgen synthesized in the fetal and neonatal testis and aromatized centrally during a perinatal sensitive period is the sole source of brain estradiol and the primary determinant of sex differences. Subregions of the diencephalon are among the most sexually dimorphic in the brain, and there are well-established sex differences in the amount of testosterone and estradiol measured in the hypothalamus and preoptic area during the perinatal period. We previously reported unexpectedly high estradiol in the hippocampus and cortex of both male and female newborn rat. This prompted a thorough investigation of the developmental profile of steroids in the rat brain using RIA to quantify the level of estradiol, testosterone, and dihydrotestosterone in discrete subregions of the brain from embryonic d 19 to adulthood. Plasma estradiol levels from individual animals were assessed when sufficient sample was available. A significant sex difference in hypothalamic testosterone prior to birth was consistent with previous findings. Postnatally, there was a distinct pattern of changing steroid concentrations in each brain region, and these were unrelated to circulating steroid. Removal of the gonads and adrenals at birth did not significantly reduce steroids in any brain region assayed 3 d later. Aromatase activity was detectable in all brain areas at birth, and the difference in activity level paralleled the observed regional differences in estradiol content. Based on these findings, we propose that steroidogenesis in the brain, independent of peripherally derived precursors, may play a critical role in mammalian brain development of both sexes, beyond the establishment of sex differences.