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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.

The specific role of gonadotropin-releasing hormone (GnRH) on brain sexual differentiation remains unclear. To investigate whether gonadotropin and, in turn, testosterone (T) secretion is regulated by GnRH during the critical period for brain differentiation in sheep fetuses, we attempted to selectively suppress pituitary-testicular activation during midgestation with the long-acting GnRH antagonist degarelix. Fetuses received subcutaneous injections of the antagonist or vehicle on day 62 of gestation. After 2 to 3 weeks we examined consequences of the intervention on baseline and GnRH-stimulated plasma luteinizing hormone (LH) and T levels. In addition, we measured the effect of degarelix-treatment on messenger RNA (mRNA) expression for the pituitary gonadotropins and key gonadal steroidogenic enzymes. Baseline and GnRH-stimulated plasma LH levels were significantly suppressed in degarelix-treated male and female fetuses compared to control values. Similarly, T concentrations were suppressed in degarelix-treated males. The percentage of LHβ-immunoreactive cells colocalizing c-fos was significantly reduced by degarelix treatment indicating that pituitary sensitivity was inhibited. Degarelix treatment also led to the significant suppression of mRNA expression coding for the pituitary gonadotropin subunits and for the gonadal enzymes involved in androgen synthesis. These findings demonstrate that pharmacologic inhibition of GnRH early in gestation results in suppression of LH secretion and deficits in the plasma T levels of male lamb fetuses. We conclude that GnRH signaling plays a pivotal role for regulating T exposure during the critical period of sheep gestation when the brain is masculinized. Thus, disturbance to gonadotropin secretion during this phase of gestation could have long-term consequence on adult sexual behaviors and fertility.

Prenatal androgens are largely responsible for growth and differentiation of the genital tract and testis and for organization of the control mechanisms regulating male reproductive physiology and behavior. The aim of the present study was to evaluate the impact of inappropriate exposure to excess testosterone (T) during the first trimester of fetal development on the reproductive function, sexual behavior, and fertility potential of rams. We found that biweekly maternal T propionate (100 mg) treatment administered from Day 30-58 of gestation significantly decreased (P < 0.05) postpubertal scrotal circumference and sperm concentration. Prenatal T exposure did not alter ejaculate volume, sperm motility and morphology or testis morphology. There was, however, a trend for more T-exposed rams than controls to be classified as unsatisfactory potential breeders during breeding soundness examinations. Postnatal serum T concentrations were not affected by prenatal T exposure, nor was the expression of key testicular genes essential for spermatogenesis and steroidogenesis. Basal serum LH did not differ between treatment groups, nor did pituitary responsiveness to GnRH. T-exposed rams, like control males, exhibited vigorous libido and were sexually attracted to estrous females. In summary, these results suggest that exposure to exogenous T during the first trimester of gestation can negatively impact spermatogenesis and compromise the reproductive fitness of rams.

Evidence suggests that the hypothalamic–pituitary–gonadal (HPG) axis is active during the critical period for sexual differentiation of the ovine sexually dimorphic nucleus, which occurs between gestational day (GD) 60 and 90. Two possible neuropeptides that could activate the fetal HPG axis are kisspeptin and neurokinin B (NKB). We used GD85 fetal lambs to determine whether intravenous administration of kisspeptin-10 (KP-10) or senktide (NKB agonist) could elicit luteinizing hormone (LH) release. Immunohistochemistry and fluorescent in situ hybridization (FISH) were employed to localize these peptides in brains of GD60 and GD85 lamb fetuses. In anesthetized fetuses, KP-10 elicited robust release of LH that was accompanied by a delayed rise in serum testosterone in males. Pretreatment with the GnRH receptor antagonist (acyline) abolished the LH response to KP-10, confirming a hypothalamic site of action. In unanesthetized fetuses, senktide, as well as KP-10, elicited LH release. The senktide response of females was greater than that of males, indicating a difference in NKB sensitivity between sexes. Gonadotropin-releasing hormone also induced a greater LH discharge in females than in males, indicating that testosterone negative feedback is mediated through pituitary gonadotrophs. Kisspeptin and NKB immunoreactive cells in the arcuate nucleus were more abundant in females than in males. Greater than 85% of arcuate kisspeptin cells costained for NKB. FISH revealed that the majority of these were kisspeptin/NKB/dynorphin (KNDy) neurons. These results support the hypothesis that kisspeptin–GnRH signaling regulates the reproductive axis of the ovine fetus during the prenatal critical period acting to maintain a stable androgen milieu necessary for brain masculinization.

The sheep is a valuable model to test whether hormone mechanisms that sexually differentiate the brain underlie the expression of sexual partner preferences because as many as 8% of rams prefer same-sex partners. This review presents an overview and update of the experimental evidence that supports this hypothesis. New evidence is presented that demonstrates a critical role for kisspeptin-GnRH signaling for regulating stable fetal testosterone levels necessary for masculinization of brain and behavior. Although these studies provide substantial support for the idea that prenatal hormones program sexual preferences, further experimentation is needed to establish causality.

Prenatal exposure to excess androgen may result in impaired adult fertility in a variety of mammalian species. However, little is known about what feedback mechanisms regulate gonadotropin secretion during early gestation and how they respond to excess T exposure. The objective of this study was to determine the effect of exogenous exposure to T on key genes that regulate gonadotropin and GnRH secretion in fetal male lambs as compared with female cohorts. We found that biweekly maternal testosterone propionate (100 mg) treatment administered from day 30 to day 58 of gestation acutely decreased (P < .05) serum LH concentrations and reduced the expression of gonadotropin subunit mRNA in both sexes and the levels of GnRH receptor mRNA in males. These results are consistent with enhanced negative feedback at the level of the pituitary and were accompanied by reduced mRNA levels for testicular steroidogenic enzymes, suggesting that Leydig cell function was also suppressed. The expression of kisspeptin 1 mRNA, a key regulator of GnRH neurons, was significantly greater (P < .01) in control females than in males and reduced (P < .001) in females by T exposure, indicating that hypothalamic regulation of gonadotropin secretion was also affected by androgen exposure. Although endocrine homeostasis was reestablished 2 weeks after maternal testosterone propionate treatment ceased, additional differences in the gene expression of GnRH, estrogen receptor-β, and kisspeptin receptor (G protein coupled receptor 54) emerged between the treatment cohorts. These changes suggest the normal trajectory of hypothalamic-pituitary axis development was disrupted, which may, in turn, contribute to negative effects on fertility later in life.

Polycystic ovary syndrome is a complex and common disorder in women, and those affected experience an increased burden of cardiovascular disease. It is an intergenerational syndrome, as affected women with high androgen levels during pregnancy “program” fetal development, leading to a similar phenotype in their female offspring. The effect of excess maternal testosterone exposure on fetal cardiomyocyte growth and maturation is unknown. Pregnant ewes received biweekly injections of vehicle (control) or 100 mg testosterone propionate between 30 and 59 days of gestation (early T) or between 60 and 90 days of gestation (late T). Fetuses were delivered at ~135 days of gestation, and their hearts were enzymatically dissociated to measure cardiomyocyte growth (dimensional measurements), maturation (proportion binucleate), and proliferation (nuclear Ki-67 protein). Early T depressed serum insulin-like growth factor 1 and caused intrauterine growth restriction (IUGR; P < 0.0005). Hearts were smaller with early T ( P < 0.001) due to reduced cardiac myocyte maturation ( P < 0.0005) and proliferation ( P = 0.017). Maturation was also lower in male than female fetuses ( P = 0.004) independent of treatment. Late T did not affect cardiac growth. Early excess maternal testosterone exposure depresses circulating insulin-like growth factor 1 near term and causes IUGR in both female and male offspring. These fetuses have small, immature hearts with reduced proliferation, which may reduce cardiac myocyte endowment and predispose to adverse cardiac growth in postnatal life. While excess maternal testosterone exposure leads to polycystic ovary syndrome and cardiovascular disease in female offspring, it may also predispose to complications of IUGR and cardiovascular disease in male offspring. NEW & NOTEWORTHY Using measurements of cardiac myocyte growth and maturation in an ovine model of polycystic ovary syndrome, this study demonstrates that early gestation excess maternal testosterone exposure reduces near-term cardiomyocyte proliferation and maturation in intrauterine growth-restricted female and male fetuses. The effect of testosterone is restricted to exposure during a specific period early in pregnancy, and the effects appear mediated through reduced insulin-like growth factor 1 signaling. Furthermore, male fetuses, regardless of treatment, had fewer mature cardiomyocytes than female fetuses.

In order to maintain the health and wellbeing of all mammals, numerous aspects of physiology are controlled by neuroendocrine mechanisms. These mechanisms ultimately enable communication between neurons 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 essential roles for some of these neuropeptide and steroid hormone mediators in the neuroendocrine regulation of stress-, reproduction-, and behavior- related processes. The present review, accordingly, highlights topics presented in this session, including the role of the neuropeptides corticotropin releasing factor and gonadotropin releasing hormone in stress and reproductive physiology, respectively. Additionally, it details an important role for gonadal sex steroids in the development of behavioral sex preference. Overall, this review suggests that the neuroendocrine regulation of numerous physiological processes cannot occur without the involvement of neuropetides and/or steroid hormones.

Sexual identity and sexual orientation are independent components of a person's sexual identity. These dimensions are most often in harmony with each other and with an individual's genital sex, although not always. The present review discusses the relationship of sexual identity and sexual orientation to prenatal factors that act to shape the development of the brain and the expression of sexual behaviours in animals and humans. One major influence discussed relates to organisational effects that the early hormone environment exerts on both gender identity and sexual orientation. Evidence that gender identity and sexual orientation are masculinised by prenatal exposure to testosterone and feminised in it absence is drawn from basic research in animals, correlations of biometric indices of androgen exposure and studies of clinical conditions associated with disorders in sexual development. There are, however, important exceptions to this theory that have yet to be resolved. Family and twin studies indicate that genes play a role, although no specific candidate genes have been identified. Evidence that relates to the number of older brothers implicates maternal immune responses as a contributing factor for male sexual orientation. It remains speculative how these influences might relate to each other and interact with postnatal socialisation. Nonetheless, despite the many challenges to research in this area, existing empirical evidence makes it clear that there is a significant biological contribution to the development of an individual's sexual identity and sexual orientation.

Dopamine synthesis in the ventral tegmental area (VTA) is necessary for the reinforcement of sexual behavior. The objective of this study determined if sexual stimuli initiates reward, and whether reward is attenuated in sexually inactive rams. Sexually active rams were exposed to urine from estrous (n = 4) or ovariectomized (n = 3) ewes with inactive rams (n = 3) exposed to urine from estrous ewes. Following exposure, rams were exsanguinated and brains perfused. Alternating sections of the VTA were stained for Fos related antigens (FRA), tyrosine hydroxylase, and dopamine beta-hydroxylase activity. Forebrain tissue, mid-sagittal ventral to the anterior corpus callosum, was stained for dopamine D(2) receptors. Concentrations of cortisol was determined prior to and following exposure. Exposure to ovariectomized-ewe urine in sexually active rams did not influence (P = 0.6) FRA expression, but fewer (P < 0.05) neurons were positive for tyrosine hydroxylase in the VTA. Sexually inactive rams had fewer (P < 0.05) FRA and tyrosine hydroxylase positive neurons in the VTA than sexually active rams following exposure to estrous ewe urine. VTA neurons staining positive for dopamine beta-hydroxylase did not differ by sexual activity (P = 0.44) or urine exposure (P = 0.07). Exposure to stimulus did not influence (P = 0.46) numbers of forebrain neurons staining positive for dopamine D2 receptors in sexually active rams, but fewer (P = 0.04) neurons stain positive in inactive rams. Serum concentrations of cortisol did not differ (P ≥ 0.52) among rams prior to or following stimulus. In conclusion sexual inactivity is unlikely due to stress, but may be partially a result of decreased tyrosine hydroxylase and/or the response to dopamine.

The ovine sexually dimorphic nucleus (oSDN) is 2 times larger in rams than in ewes. Sexual differentiation of the oSDN is produced by testosterone exposure during the critical period occurring between gestational day (GD)60 and GD90 (term, 147 d). We tested the hypothesis that testosterone acts through the androgen receptor to control development of the male-typical oSDN. In experiment 1, pregnant ewes received injections of vehicle, androgen receptor antagonist flutamide, or nonaromatizable androgen dihydrotestosterone (DHT) propionate during the critical period. Fetuses were delivered at GD135. Both antagonist and agonist treatments significantly reduced mean oSDN volume in males but had no effects in females. Experiment 2, we analyzed the effect of treatments on the fetal hypothalamic-pituitary-gonadal axis to determine whether compensatory changes in hormone secretion occurred that could explain the effect of DHT. Pregnant ewes were injected with vehicle, flutamide, or DHT propionate from GD60 to GD84, and fetuses were delivered on GD85. Flutamide significantly increased LH and testosterone in males, whereas DHT significantly decreased both hormones. In females, LH was unaffected by flutamide but significantly reduced by DHT exposure. DHT significantly decreased pituitary gonadotropin and hypothalamic kisspeptin mRNA expression in males and females. These results suggest that androgen receptor mediates the effect of testosterone on oSDN masculinization, because this process was blocked by the androgen receptor antagonist flutamide in eugonadal males. In contrast, the reduction of oSDN volume observed after DHT exposure appears to be mediated by a negative feedback mechanism exerted on the hypothalamus to reduce LH and testosterone secretion. The reduced androgen exposure most likely accounted for the decreased oSDN volume. We conclude that, during the critical period, the male reproductive axis in long gestation species, such as sheep, is sufficiently developed to react to perturbations in serum androgens and mitigate disruptions in brain masculinization.

Gonadal steroid hormones play important roles during critical periods of development to organise brain structures that control sexually dimorphic neuroendocrine responses and behaviours. Specific receptors for androgens and oestrogens must be expressed at appropriate times during development to mediate these processes. The present study was performed to test for sex differences in the relative expression of oestrogen receptor (ER)α and androgen receptor (AR) mRNA during the window of time in gestation that is critical for behavioural masculinisation and differentiation of the ovine sexually dimorphic nucleus (oSDN) in the sheep. In addition, we examined whether ERα and AR mRNA expression is localised within the nascent oSDN and could be involved in its development. Using the quantitative real-time polymerase chain reaction, we found that females expressed more ERα mRNA than males in medial preoptic area and medial basal hypothalamus during the mid-gestational critical period for brain sexual differentiation. No sex differences were found for AR mRNA in any tissue examined or for ERα in amygdala and frontal cortex. Using radioactive in situ hybridisation, we found that the distributions of ERα and AR mRNA overlapped with aromatase mRNA, which delineates the boundaries of the developing oSDN and identifies this nucleus as a target for both androgens and oestrogens. These data demonstrate that the transcriptional machinery for synthesising gonadal steroid receptors is functional in the foetal lamb brain during the critical period for sexual differentiation and suggest that possible mechanisms for establishing dimorphisms controlled by gonadal steroids may exist at the level of steroid hormone receptor expression.

Exposure to estrous ewe urine stimulates investigation and mounting activity in sexually active but not sexually inactive rams. It was hypothesized sexual indifference may result from an inability to detect olfactory cues or an interruption of the pathway from detection of the olfactory stimulus to the motor response. Sexually active (n = 4) and inactive (n = 3) rams were exposed to urine from estrous ewes. An additional group of sexually active rams (n = 3) were exposed to urine from ovariectomized ewes. Rams were exsanguinated following 1 h of exposure to stimulus. Neural activity was determined in tissues of interest by the presence of fos and fos-related proteins detected by immunohistochemistry procedures. Sexually active rams exposed to urine from ovariectomized ewes had more (P ≤ 0.05) fos-positive cells in the olfactory bulb, but fewer (P = 0.03) fos-positive cells in the cortical amygdala compared to sexually active rams exposed to urine from estrous ewes. Sexually inactive rams had similar (P ≥ 0.13) numbers of fos positive neurons in the olfactory bulb and medial amygdala but fewer (P ≤ 0.04) in the central amygdala, bed nucleus of the stria terminalis and the medial preoptic area compared to sexually active rams exposed to urine from estrous ewes. Sexual inactivity was not associated with decreased hypothalamic function since fos activity was similar (P ≥ 0.14) among groups in the suprachiasmatic and ventral medial nucleus. Sexual inactivity is not likely due to an impaired ability to detect or process olfactory stimuli by the main olfactory bulb and medial-cortical amygdala. Sexually inactive rams may have reduced attentiveness to sexual stimuli and/or decreased responsiveness of regions in the brain which regulate reproductive behaviors.

In male vertebrates, perinatal exposure to testosterone is both necessary and sufficient to masculinize tonic gonadotropin secretion and copulatory behavior. In contrast, females develop in the absence of high steroid exposure and express cyclic gonadotropin secretion and receptive behaviors. The cellular and molecular processes by which testosterone acts to organize sex specific brain functions are complex and can be modified by social and environmental factors. Studies of humans with clinical syndromes in which fetuses are exposed too much or too little androgen provide support that sex hormones also influence sexual differentiation of the human brain and behavior.

This review highlights the principal effects of steroid hormones at central and peripheral levels in the neuroendocrine axis. The data discussed highlight the principal role of oestrogens and testosterone in hormonal programming in relation to sexual orientation, reproductive and metabolic programming, and the neuroendocrine mechanism involved in the development of polycystic ovary syndrome phenotype. Moreover, consistent with the wide range of processes in which steroid hormones take part, we discuss the protective effects of progesterone on neurodegenerative disease and the signalling mechanism involved in the genesis of oestrogen-induced pituitary prolactinomas. Fil: Zubeldia Brenner, Lautaro. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina Fil: Roselli, C. E.. Oregon Health and Science University Portland; Estados Unidos Fil: Recabarren, S. E.. Universidad de Concepción; Chile Fil: Gonzalez Deniselle, Maria Claudia. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina Fil: Lara, H. E.. Universidad de Chile; Chile

Testosterone exposure during midgestation differentiates neural circuits controlling sex-specific behaviours and patterns of gonadotrophin secretion in male sheep. Testosterone acts through androgen receptors (AR) and/or after aromatisation to oestradiol and binding to oestrogen receptors. The present study assessed the role of AR activation in male sexual differentiation. We compared rams that were exposed to the AR antagonist flutamide (Flu) throughout the critical period (i.e. days 30-90 of gestation) to control rams and ewes that received no prenatal treatments. The external genitalia of all Flu rams were phenotypically female. Testes were positioned s.c. in the inguinal region of the abdomen, exhibited seasonally impaired androgen secretion and were azospermic. Flu rams displayed male-typical precopulatory and mounting behaviours but could not intromit or ejaculate because they lacked a penis. Flu rams exhibited greater mounting behaviour than control rams and, similar to controls, showed sexual partner preferences for oestrous ewes. Neither control, nor Flu rams responded to oestradiol treatments with displays of female-typical receptive behaviour or LH surge responses, whereas all control ewes responded as expected. The ovine sexually dimorphic nucleus in Flu rams was intermediate in volume between control rams and ewes and significantly different from both. These results indicate that prenatal anti-androgen exposure is not able to block male sexual differentiation in sheep and suggest that compensatory mechanisms intervene to maintain sufficient androgen stimulation during development.

The intraneuronal conversion of testosterone to oestradiol constitutes a critical step in the development and sexual differentiation of the brain of many short gestation mammalian species and has been inferred to play a similar role in long gestation sheep. This conversion is catalysed by cytochrome P450 aromatase (CYP19), which is expressed in specific brain structures during foetal development. The present study was undertaken to examine the specific neuroanatomical distribution and relative expression of aromatase mRNA in the developing sheep hypothalamus. The foetal sheep is a highly tractable model system for localising the region-specific expression of aromatase in the brain during prenatal development that can help predict regions where oestrogen acts to shape neural development. Our results, obtained using real time quantitative reverse transcriptase-polymerase chain reaction, revealed that aromatase mRNA was expressed throughout mid to late gestation in the foetal preoptic area and amygdala. In the preoptic area, aromatase expression declined with advancing gestation, whereas, it increased in the amygdala. No sex differences were observed in either brain area. We next investigated the anatomical distribution of aromatase using in situ hybridisation histochemistry and found that the pattern of mRNA expression was largely established by midgestation. High expression was observed in the medial preoptic nucleus, bed nucleus of the stria terminalis and corticomedial amygdala. We also observed substantial expression in the dorsal striatum. These results extend our understanding of the developmental expression of aromatase in the foetal sheep brain and lend support to the view that it plays an essential role in sexual differentiation and maturation of the neuroendocrine, motor and reward control systems.

The sheep offers a unique mammalian model in which to study paradoxical same-sex sexual partner preferences. Variations in sexual partner preferences occur spontaneously with as many as 8% of rams in a population exhibiting a sexual preference for other rams (male-oriented). The current review presents an overview and update of the male-oriented ram model and discusses several theories that have been invoked to explain same sex preferences in this species. Although our understanding of the biological determinants and underlying neural substrates of sexual attraction and mate selection are far from complete, compelling evidence is discussed that supports the idea that neural substrates regulating sexual partner preferences are organized during prenatal development. The challenge for future research will be to construct an integrated picture of how hormones, genes, and experience shape sexual partner preference.

Sheep exposed to testosterone during a critical period from gestational day (GD) 30 to GD 90 develop masculine genitals and an enlarged male-typical ovine sexually dimorphic nucleus of the preoptic area (oSDN). The present study tested the hypothesis that separate critical periods exist for masculinization of these two anatomical end points. Pregnant ewes were treated with testosterone propionate (TP) either from GD 30 to GD 60 (early TP) or GD 60 to GD 90 (late TP). Control (C) pregnant ewes were treated with corn oil. Fetuses were delivered at GD 135 and the volume of the oSDN was measured. Early TP females possessed a penis and a scrotum devoid of testes, whereas late TP and C females had normal female genitals. Neither period of TP exposure grossly affected the genitals of male fetuses. Despite masculinized genitals, the mean volume of the oSDN in early TP females (0.32 ± 0.06 mm3) was not different from C females (0.24 ± 0.02 mm3) but was significantly enlarged in late TP females (0.49 ± 0.04 mm3; P < 0.05 vs. C) when the genitals appeared normal. In contrast, the volume of the oSDN in late TP males (0.51 ± 0.02 mm3) was not different from C males (0.51 ± 0.04 mm3) but was significantly smaller in the early TP males (0.35 ± 0.04 mm3; P < 0.05 vs. C). These results demonstrate that the prenatal critical period for androgen-dependent differentiation of the oSDN occurs later than, and can be separated temporally from, the period for development of masculine genitals.

Domestic pigs have three CYP19 genes encoding functional paralogues of the enzyme aromatase cytochrome P450 (P450arom) that are expressed in the gonads, placenta, and preimplantation blastocyst. All catalyze estrogen synthesis, but the gonadal-type enzyme is unique in also synthesizing a nonaromatizable biopotent testosterone metabolite, 1OH-testosterone (1OH-T). P450arom is expressed in the vertebrate brain, is higher in males than females, but has not been investigated in pigs, to our knowledge. Therefore, these studies defined which of the porcine CYP19 genes was expressed, and at what level, in adult male and female hypothalamus. Regional expression was examined in mature boars, and regulation of P450arom expression in neonatal boars was investigated by inhibition of P450arom with letrozole, which is known to reprogram testicular expression. Pig hypothalami expressed the gonadal form of P450arom (redesignated the "gonadal/hypothalamic" porcine CYP19 gene and paralogue) based on functional analysis confirmed by cloning and sequencing transcripts. Hypothalamic tissue synthesized 1OH-T and was sensitive to the selective P450arom inhibitor etomidate. Levels were 4-fold higher in male than female hypothalami, with expression in the medial preoptic area and lateral borders of the ventromedial hypothalamus of boars. In vivo, letrozole-treated neonates had increased aromatase activity in hypothalami but decreased activity in testes. Therefore, although the same CYP19 gene is expressed in both tissues, expression is regulated differently in the hypothalamus than testis. These investigations, the first such studies in pig brain to our knowledge, demonstrate unusual aspects of P450arom expression and regulation in the hypothalamus, offering promise of gaining better insight into roles of P450arom in reproductive function.

The question of what causes a male animal to seek out and choose a female as opposed to another male mating partner is unresolved and remains an issue of considerable debate. The most developed biologic theory is the perinatal organizational hypothesis, which states that perinatal hormone exposure mediates sexual differentiation of the brain. Numerous animal experiments have assessed the contribution of perinatal testosterone and/or estradiol exposure to the development of a male-typical mate preference, but almost all have used hormonally manipulated animals. In contrast, variations in sexual partner preferences occur spontaneously in domestic rams, with as many as 8% of the population exhibiting a preference for same-sex mating partners (male-oriented rams). Thus, the domestic ram is an excellent experimental model to study possible links between fetal neuroendocrine programming of neural mechanisms and adult sexual partner preferences. In this review, we present an overview of sexual differentiation in relation to sexual partner preferences. We then summarize results that test the relevance of the organizational hypothesis to expression of same-sex sexual partner preferences in rams. Finally, we demonstrate that the sexual differentiation of brain and behavior in sheep does not depend critically on aromatization of testosterone to estradiol.

Aromatization of testosterone to estradiol by neural tissue has classically been associated with the regulation of sexual differentiation, gonadotropin secretion, and copulatory behavior. However, new data indicate that the capacity for aromatization is not restricted to the endocrine brain and demonstrate roles for locally-formed estrogens in neurogenesis and in responses of brain tissue to injury. This manuscript summaries our current understanding of the distribution and regulation of aromatase in the brain and discusses the classical and novel roles it plays. A better understanding of brain aromatization could shed new light on its physiologic and pathologic functions and someday lead to new centrally acting drug therapies.

The ovine sexually dimorphic nucleus (oSDN) is characterized by high levels of aromatase mRNA expression which can be used to delineate its boundaries. The volume of the oSDN is approximately 2 to 3-fold larger in rams that mate with ewes (female-oriented rams) than in rams that mate with other rams (male-oriented rams) and ewes. The sex difference in oSDN volume is present in late gestation fetuses and can be eliminated before birth by exposing genetic females to exogenous testosterone during midgestation, suggesting that early exposure to androgen masculinizes volume of the oSDN. The present study was performed to determine whether differences in oSDN volume are influenced by the adult hormonal environment. Adult rams, behaviorally characterized as female-oriented or male-oriented, and ewes were gonadectomized and treated with subcutaneous implants of testosterone to achieve physiologic concentrations of serum testosterone. Three weeks after implant placement brain tissue was prepared for histological assessment of oSDN volume using in situ hybridization for detection of aromatase mRNA expression. Quantitative analysis revealed that despite similar serum testosterone levels among the groups, the volume of the oSDN was greater in female-oriented rams than in male-oriented rams and ewes (P < 0.05). Differences in oSDN volume were specific and not reflective of differences in preoptic area height or brain size. These results suggest that differences in the size of the oSDN in adult sheep were not influenced by adult exposure to testosterone.

Accumulating evidence in rodents suggests that a prolactin locally synthesized and released within the brain can act together with that taken up from the circulation to modulate neuroendocrine responses. The present study was designed to identify the regional patterns of prolactin expression in the adult and developing sheep brain. Specifically, we tested the hypothesis that prolactin is expressed in regions of the adult and fetal sheep brain that are critical in the development of neuroendocrine homeostatic and behavioral functions. The expression of prolactin protein in sheep brain was demonstrated by Western blot analysis and brain prolactin mRNA was detected and sequenced using RT-PCR. In situ hybridization histochemistry revealed that prolactin mRNA was expressed in the medial preoptic area, periventricular preoptic nucleus, bed nucleus of the stria terminalis, and in the paraventricular nucleus of the hypothalamus, particularly the ventral region. The neuroanatomical distribution of prolactin mRNA was best visualized in the fetus and prolactin-immunoreactive neurons could also be identified in late gestation fetuses. Brain prolactin mRNA was expressed as early as day 60 of gestation and increased as the fetus aged and peaked at day 135 (term = 147 days). Prolactin mRNA expression did not exhibit a sex difference in the preoptic area, but in the amygdala prolactin mRNA was significantly higher in females than in males at day 100 of gestation. We conclude that prolactin expressed in adult and fetal sheep brain could be involved in neurodevelopment and/or modulation of the neuroendocrine stress axis, although it is too early to rule out other possibilities given the diverse actions that have been attributed to prolactin.

The neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide have long been considered as putative regulators of testicular functions. In vitro evidence suggests that VIP could play an important role in testosterone biosynthesis. However, the endogenous role of VIP on testicular functions remained to be demonstrated. In C57BL/6 mice exhibiting a complete disruption of the VIP gene, we first observed here that serum testosterone levels were lower than those of WT littermates. At the age of 4 months, this phenotype was accompanied with a reduction of expression of StAR and 3-β-hydroxysteroid dehydrogenase (3β-HSD) in the testis. In addition, serum levels of FSH but not LH were reduced in young knock-out (KO) males. Testicular anatomy also revealed a higher percentage of degenerated seminiferous tubules in the 4-month-old VIP KO animals when compared with WT. In 15-month-old animals, control males showed typical testicular aging, including a severe degeneration of seminiferous tubules, a dramatic decrease in serum levels of testosterone, and a reduction in StAR and 3β-HSD gene expression. In age-matching VIP KO males, the levels of serum testosterone and steroidogenic enzymes were still very low. Interestingly, in contrast to that observed in young mice, testicular degeneration at 15 months was significantly less severe in VIP KO than WT mice. All together, these results suggest that 1) VIP is an important factor for regulating testosterone biosynthesis and FSH secretion and 2) VIP may influence testicular aging.

The sheep offers a unique model to study male sexual behavior and sexual partner preference. Rams are seasonal breeders and show the greatest libido during short days coincident with the resumption of ovarian cyclicity in the ewe. Threshold concentrations of testosterone are required for the acquisition and display of adult sexual behavior. In addition, estrogens produced from circulating testosterone by cytochrome P450 aromatase in the preoptic area are critical for the maintenance of sexual behaviors in rams. Sex differences in adult reproductive behaviors and hormone responsiveness are the result of permanent organizational effects exerted by testosterone and its metabolites on brain development. Early exposure to ewes enhances ram sexual performance, but cannot prevent some rams from exhibiting male-oriented sexual partner preferences. Neurochemical and neuroanatomical studies suggest that male-oriented ram behavior may be a consequence of individual variations in brain sexual differentiation.

Des travauxin vitro suggerent que le VIP pourrait jouer un role important au niveau de la biosynthese de testosterone. Nous avons demontre que des Souris chez lesquelles le gene codant pour le VIP est supprime montrent des niveaux de testosterone seriques tres reduits compares aux animaux sauvages. Egalement, ces animaux transgeniques presentent une reduction des niveaux de FSH (Follicle-stimulating hormone) a l’âge de quatre mois. L’etude de la structure testiculaire a revele une legere augmentation du pourcentage de tubules degeneres chez les animaux VIP-/-compares aux animaux sauvages. Les animaux chez lesquels le gene codant pour le VIP a ete supprime, a l’âge de quinze mois, ont des niveaux de steroidogenese bas compares aux souris sauvages. De maniere interessante, la degenerescence testiculaire est moins severe chez les animaux VIP-/-comparee a celles des animaux sauvages. L’ensemble de ces resultats suggere que: 1) le VIP est un facteur important pour la regulation de la biosynthese de testosterone et la secretion de FSH et 2) VIP regule le vieillissement testiculaire.

The male-oriented ram is a unique and valuable animal model for the study of hormonal, developmental and genetic contributions to sexual partner preference. Unlike most other mammalian models that are in use currently, variations in sexual attraction occur spontaneously in domestic ram populations. It is estimated that as many as 8-10% of rams exhibit a sexual partner preference for other males, classifying them as male-oriented rams. Studies have failed to identify any compelling social factors that can predict or explain the variations in sexual partner preferences of rams. Nor is there consensus on the endocrine and sensory responsiveness of male-oriented rams to other rams. However, a number of studies have reported differences in brain structure and function between male-oriented and female-oriented rams, suggesting that sexual partner preferences are neurologically hard-wired. Recently, we identified a sexually dimorphic nucleus (oSDN) in the sheep preoptic area-anterior hypothalamus. The oSDN is larger in female-oriented rams than in male-oriented rams and similar in size in male-oriented rams and ewes. In addition, mRNA levels for aromatase in the oSDN were higher in males than in females and were higher in female-oriented rams than in male-oriented rams. These results suggest a relationship between steroid hormones, specifically estrogens and oSDN morphology. In this review, we provide an overview of sexual behavior in rams and discuss the multiple factors that may contribute to the development and adult expression of same-sex partner preferences in rams.

Within the last 20 years, rapid nongenomic actions of steroid hormones have been demonstrated to occur via an interaction with ligand-gated ion channels. For example, the pregnane neurosteroid allopregnanolone (ALLOP) is a potent positive modulator of gamma-aminobutyric acid(A) (GABA(A)) receptors. The physiological significance of fluctuations in endogenous ALLOP levels has been investigated with regard to disease states and the effect of therapeutic agents on ALLOP levels. Because the pharmacological profile of ALLOP is similar to that of ethanol (EtOH), the modulatory effect of pregnane neurosteroids on EtOH dependence and withdrawal will be the focus of this review. Data on the effects of chronic EtOH exposure and withdrawal on pregnane neurosteroid levels, biosynthetic enzymes, and changes in neurosteroid sensitivity will be summarized. Results from genetic animal models indicate that seizure-prone animals have a persistent decrease in endogenous ALLOP levels during EtOH withdrawal in conjunction with tolerance to ALLOP's anticonvulsant effect. Manipulation of endogenous ALLOP levels with finasteride also markedly reduced the severity of chronic EtOH withdrawal. Gene mapping studies provide a hint for an interaction between genes for GABA(A) receptor subunits and the biosynthetic enzyme 5alpha-reductase. Overall, the results are suggestive of a relationship between endogenous pregnane neurosteroid levels and behavioral changes in excitability during EtOH withdrawal, consistent with recent findings in humans. While the findings with ALLOP emphasize the therapeutic potential of neurosteroid treatment during EtOH withdrawal, the gene mapping studies suggest that pregnane neurosteroid biosynthesis may represent a target for therapeutic intervention in the treatment of alcohol dependence.

PC-SPES, a proprietary mixture composed of eight different herbs, is used worldwide as an alternative treatment by prostate cancer patients. It has been suggested that the clinical and in vitro antitumor activity exhibited by PC-SPES may be due to estrogenic activity, which in turn may be mediated by the presence of undeclared prescription drug contaminants. Here, we evaluated the in vivo effects of two different commercial lots of PC-SPES in male and female rats. Our high-pressure liquid chromatography analysis coupled with gas chromatography/mass spectrometry analysis by an independent laboratory suggested that PC-SPES lot 5430125 was contaminated with diethylstilbestrol (DES), whereas lot 5431249 was not. Treatment of male rats with PC-SPES lot 5430125 or DES alone reduced the weight of androgen target organs and decreased circulating levels of sex steroids and luteinizing hormone, whereas lot 5431249 was without effect. In addition, lot 5430125 and DES, but not lot 5431249 increased uterine weight in female rats. These results suggest that the inhibitory effects on androgen targets are mediated through suppression of the hypothalamic-pituitary axis and this suppression is probably due to DES contamination. We assessed the effects of both lots of PC-SPES and DES on hepatic cytochrome P450 expression and activity. Both lots of PC-SPES and DES reduced CYP3A activity and protein levels. Because the response of CYP3A to PC-SPES was not dependent on whether it contained DES, a phytochemical component of PC-SPES is most likely responsible for this effect. Inhibition of CYP3A has important implications for potential herbal-drug interactions.

The aim of the present study was to determine whether the fetal lamb brain has the capacity to aromatize androgens to estrogens during the critical period for sexual differentiation. We also determined whether administration of the aromatase-inhibitor 1,4,6-androstatriene-3,17-dione (ATD) could cross the placenta and inhibit aromatase activity (AA) in fetal brain. Eight pregnant ewes were utilized. On Day 50 of pregnancy, four ewes were given ATD-filled Silastic implants, and the other four ewes received sham surgeries. The fetuses were surgically delivered 2 wk later (Day 64 of gestation). High levels of AA (0.8‐1.4 pmol/ h/mg protein) were present in the hypothalamus and amygdala. Lower levels (0.02‐0.1 pmol/h/mg protein) were measured in brain stem regions, cortex, and olfactory bulbs. The MichaelisMenten dissociation constant (Km) for aromatase in the fetal sheep brain was 3‐4 nM. No significant sex differences in AA were observed in brain. Treatment with ATD produced significant inhibition of AA in most brain areas but did not significantly alter serum profiles of the major sex steroids in maternal and fetal serum. Concentrations of testosterone in serum from the umbilical artery and vein were significantly greater in male than in female fetuses. No other sex differences in serum steroids were observed. These data demonstrate that high levels of AA are found in the fetal sheep hypothalamus and amygdala during the critical period for sexual differentiation. They also demonstrate that AA can be inhibited in the fetal lamb brain by treating the mother with ATD, without harming fetal development. aromatase, behavior, Cyp19, early development, estradiol, neuroendocrinology, sexual differentiation, testosterone

Many of the current procedures for territory management (see Horizon 2020) and marine organism reproductive health assessment are based upon receptor-mediated responses of target genes and are founded on the assumption that these responses accurately reflect exposure of endocrine disrupter that can be linked to different pathological effects. The role of estrogens and their functional mechanism of action in bivalves are therefore far from clear. Building on these observations, the aim of this study, in the frame work of an Italian National Research Project (PRIN 2010 – 2011), was to identify estrogen receptor genes (ER1 and ER2) and to quantify any changes in expression levels using the real-time quantitative PCR technique in response of marine bivalve, Mytilus galloprovincialis at different pollution degree areas. Using gametes obtained by mantle (gonad) tissue of mature bivalves we demonstrated, after sequencing and alignments, the presence of differentially expressed transcripts for ER1 and ER2, quantitative differences in male and female gamete gene expression and an increase in both gametes of ER levels in polluted area. The significance of these findings in terms of the utility of estrogen receptors as biomarkers of reproductive health assessment in bivalve species is discussed.

This study examined systemic testosterone concentrations in rams that were classified according to their sexual behavior and partner preference as either female-oriented (FOR), male-oriented (MOR), or asexual (NOR). For this purpose, we measured testosterone concentrations under three separate conditions: in conscious rams during the nonbreeding season (June) and breeding season (November), and in anesthetized rams during the breeding season. Basal testosterone concentrations in conscious rams were not different among the three groups (P . 0.05) in either season. However, when rams were anesthetized, mean systemic concentrations of testosterone in FORs (mean 6 SEM, 13.9 6 7.4 ng/ml serum) were greater (P , 0.05) than in NORs (0.9 6 0.1 ng/ml), but not in MORs (2.2 6 6.2 ng/ml), whereas testosterone concentrations were not different between MORs and NORs (P . 0.05). Concentrations of testosterone in the spermatic vein of FORs (127 6 66 ng/ml) were greater (P , 0.05) than in MORs (41 6 10 ng/ml) and NORs (19 6 7 ng/ ml). Serum LH concentrations were not different. Cortisol was higher (P , 0.05) in anesthetized MORs (25.1 6 4.2 ng/ml) and NORs (27.2 6 4.4 ng/ml) than in FORs (10.9 6 1.8 ng/ml). These results demonstrate that circulating testosterone concentrations are related to sexual behavior only when rams are bled under anesthesia. Thus, differences in basal androgen concentrations in adulthood cannot be responsible for expression of male-oriented preferences or low libido in sheep. Instead, functional differences must exist between the brains of rams that differ in sexual preference expression.

Testosterone at physiological levels cannot exert negative feedback action on LH secretion in long-term castrated male monkeys. The cellular basis of this refractoriness is unknown. To study it, we compared two groups of male rhesus macaques: one group (group 1, n 5 4) was castrated and immediately treated with testosterone for 30 days; the second group (group 2, n 5 4) was castrated and treated with testosterone for 9 days beginning 21 days after castration. Feedback control of LH by testosterone in group 1 was normal, whereas insensitivity to its action was found in group 2. Using the endpoints of concentrations of aromatase activity (P450AROM messenger RNA [mRNA]) and androgen receptor mRNA in the medial preoptic anterior hypothalamus and in the medial basal hypothalamus, we found that aromatase activity in both of these tissues was significantly lower, P , 0.01, in group 2 compared with group 1 males. P450AROM mRNA and androgen receptor mRNA did not differ, however. Our data suggest that the cellular basis of testosterone insensitivity after long-term castration may reside in the reduced capacity of specific brain areas to aromatize testosterone. Because P450AROM mRNA did not change in group 2 males, we hypothesize that an estrogen-dependent neural deficit, not involving the regulation of the P450AROM mRNA, occurs in long-term castrated monkeys. androgen receptor, estradiol, hypothalamus, Leydig cells, LH, pituitary hormones, steroid hormones, testes, testosterone

We demonstrated previously that testosterone regulates aromatase activity in the anterior/dorsolateral hypothalamus of male rhesus macaques. To determine the level of the androgen effect, we developed a ribonuclease protection assay to study the effects of testosterone or dihydrotestosterone (DHT) on aromatase (P450AROM) mRNA in selected brain areas. Adult male rhesus monkeys were treated with testosterone or DHT. Steroids in serum were quantified by RIA. Fourteen brain regions were analyzed for P450AROM mRNA. Significant elevations of its message over controls (P < 0.05) were found in the medial preoptic area/anterior hypothalamus of both androgen treatment groups and the medial basal hypothalamus of the testosterone-treated males. Other brain areas were not affected by androgen treatment. We conclude that testosterone and DHT regulate P450AROM mRNA in brain regions that mediate reproductive behaviors and gonadotropin release. The P450AROM mRNA of other brain areas is not androgen dependent. Bra...

Because the distribution and hormonal regulation of the androgen receptor (AR) mRNA in brains and pituitaries of adult rhesus monkeys have not been studied, we cloned and sequenced a 329-base pair segment of the 5' coding region of the rhesus AR cDNA. Monkey AR cDNA was 99% identical with the human sequence and 96% homologous with the rat sequence. Using a ribonuclease protection assay, we studied the distribution and regulation of AR mRNA in brains and anterior pituitary glands of three groups of male rhesus monkeys: intact (n = 3), castrated (Cx, n = 4), and Cx treated with testosterone (n = 6). Serum testosterone levels of Cx males treated with testosterone differed significantly (p < 0.05) in the morning but not in the evening hours from those in intact controls. Serum LH concentrations were significantly suppressed (p < 0.05) in both morning and evening serum samples of testosterone-treated males compared to intact controls. We found the highest concentrations of AR mRNA in the medial basal hypothalamus, the bed nucleus of the stria terminalis, the medial preoptic area-anterior hypothalamus, and the lateral dorsomedial hypothalamus. Intermediate amounts were found in the septum and amygdala. Low amounts were found in the hippocampus, cingulate cortex, parietal cortex, and cerebellum. The anterior pituitary gland also contained a large amount of AR mRNA. Surprisingly, neither Cx for 3 wk nor Cx plus testosterone replacement for 3 wk significantly affected AR mRNA in any brain area or in the pituitary gland. The present study demonstrates that the effectiveness of testosterone as a regulator of LH secretion in male monkeys is not related to changes of AR mRNA in the brain or pituitary gland. It appears that AR mRNA in the monkey brain and pituitary gland is not regulated at the transcriptional level by androgen.

Testosterone and estradiol act synergistically to stimulate male sexual behavior. Previous studies demonstrated that testosterone’s actions are mediated genomically. Attempts to show that estradiol acts in a similar fashion have been inconclusive. However, estrogens have been shown to exert short-latency effects by acting directly on neuronal membranes. The present experiment examined whether testosterone or estradiol rapidly facilitates copulatory behaviors in castrated sexually experienced rats. Within 35 min of administration, estradiol stimulated chemoinvestigation and frequency of mounting and reduced mount latency in a dose-dependent manner. In contrast, acute administration of testosterone did not alter sexual activity. These data demonstrate for the first time that estradiol exerts short-latency effects on copulatory behavior, providing indirect evidence that this action is mediated through a nontranscriptional mechanism.

The present experiment was performed to test the hypothesis that gender differences in the capacity for brain estrogen synthesis could constitute a sexually dimorphic mechanism that limits the activational effects of testosterone (T) in females, and enhances them in males. We determined the effects of treatments with equivalent levels of either T or estradiol (E2) on olfactory behavior and mounting in age-matched heterosexually naive gonadectomized male and female rats that were genitally ansthetized with lidocaine paste in order to minimize the contribution of sexually dimorphic somatosensory inputs to the expression of copulatory behavior. We found that T stimulated mounting to a greater extent in males than in females, but had equivalent effects on mount latency and genital investigation in the two sexes. On the other hand, E2 stimulated equivalent levels of mounting in males and females and reduced mount latency to a similar extent in males and females. However, E2 had a pronounced effect on the levels of genital investigation in males but not in females. Serum steroid levels and the levels of nuclear steroid receptor occupation in the brain were not different between males and females, suggesting that the behavioral differences between males and females cannot be attributed to differences in peripheral steroid metabolism or brain uptake. The results obtained corroborate previous studies suggesting that female rats normally undergo considerable male-typical behavioral masculinization during fetal development. However, such male-typical features of normal development in female rats do not extend to the regulation of preoptic aromatase activity or to the capacity of females to display olfactory behaviors in response to adult E2 exposure, functions which are sexually dimorphic even in the rat. The present results support the view that gender differences in the capacity for brain estrogen synthesis contribute to the sexually dimorphic display of T-stimulated male-typical sexual motivation and copulatory behavior in rats.

There are apparently normal male rats that fail to initiate copulation; these animals are called non-copulating (NC) males. Several research groups have demonstrated that conversion of testosterone to oestradiol (aromatisation) in specific brain areas known to be involved in the control of masculine sexual behaviour is fundamental in the control of masculine sexual behaviour. The aim of the present study was to test the hypothesis that the concentration of aromatase activity (AA) in the brain is lower in NC males than in copulating males (C). We quantified AA in several brain nuclei and also evaluated whether NC rats have altered concentrations of testosterone in their plasma. We found that AA was reduced in the medial preoptic nuclei (MPN) of NC male rats vs C males. In addition, NC and C male rats had similar plasma levels of testosterone. These data suggest that reduced levels of AA in the MPN could be a crucial factor associated with lack of male coital behaviour in rats.

The level of aromatase in the preoptic area of rats is transcriptionally regulated through a specific androgen-receptor mediated mechanism and can be used as a measure of central androgenic effect. Therefore, several commonly abused anabolic–androgenic steroids (AAS) were tested for their ability to induce aromatase activity in the preoptic area of castrated rats. In addition, we determined the relative binding affinities of these compounds for the androgen receptor, as well as their ability to bind androgen receptor in vivo following subcutaneous injections. All of the AAS compounds tested significantly stimulated POA aromatase activity above castrate levels. The compounds that produced the greatest stimulation of aromatase activity were those that bound most avidly to the androgen receptor in vitro (i.e., testosterone, dihydrotestosterone and nandrolone). In contrast, the 17α-alkylated compounds that were tested (stanozolol, danazol, methandrostenolone) modestly stimulated aromatase and were weak competitors for the androgen receptor. The subcutaneous injection of AAS compounds increased the concentrations of occupied nuclear androgen receptors in the brain, but the magnitude of effect was not related to their potency for inducing aromatase or their relative binding affinity for the androgen receptor suggesting that androgen receptor occupancy in POA is not correlated with the action of androgen on aromatase. The present results help explain the behavioral effects of AAS compounds in rats.

Recent evidence suggests that two cytochrome P450 aromatase (P450 arom ) mRNA transcripts are present in the rat brain. One of these contains the entire 5'-coding sequence and correlates with the presence of functional enzyme. We designed a new 255-base pair P450 arom probe (AROM255) that recognizes only this full-length P450 arom mRNA. Ribonuclease protection assays verified that the cRNA probe synthesized from this construct recognized a single RNA species in brain tissues that express aromatase activity, but not in the cingulate cortex, an area previously shown to contain only the alternate transcript. Moreover, the P450 arom mRNA content of the preoptic area was significantly lower in castrates than in intact males or testosterone (T)-treated castrates. We employed 33 P-labeled cRNA probes to examine the distribution of P450 arom mRNA by in situ hybridization. High levels of mRNA were detected in the medial preoptic nucleus (MPN), bed nucleus of the stria terminalis (BnST), and medial amygdala (MA). Lower levels were found in the ventromedial hypothalamic nucleus and cortical amygdala. The magnitude of the hybridization signal in the BnST and MPN was greater in males than in females. Treatment with T propionate significantly increased hybridization signal in BnST, MPN, and MA. These results confirm the anatomic distribution of P450 arom mRNA within hypothalamic and limbic nuclei of the adult male rat and demonstrate that steady state concentrations are regionally regulated by T. Moreover, they demonstrate the necessity of using a molecular probe that can distinguish between P450 arom variants in the brain.

The conversion of androgens to estrogens by aromatase cytochrome P450 (P450arom) is an important step in the mechanism of androgen action in the brain. However, the distribution of P450.. mRNA in adult rhesus monkey brains has not been studied because specific probes have not been available. To address this deficit, we cloned and sequenced a 455-basepair segment of the 5' coding region of the rhesus P450arom cDNA. Total RNA was extracted from a rhesus monkey placenta (Day 47 of gestation) and subjected to reverse transcriptase (RT) polymerase chain reaction (PCR) using consensus oligonucleotide primers selected from published human and rat P450am,, DNA sequences. The RT-PCR product was subcloned into a vector and sequenced. The monkey P450,.o cDNA was 97% identical to the human sequence but shared only 86% homology with the rat sequence. We then developed a ribonuclease protection assay using a monkey P450-,,, cDNA and studied the distribution of P450.. mRNA in adult monkey brains. This assay protected two RNA fragments, one 455 nucleotides (nt) in length and the second approximately 300 nt. The relative distribution of P450_,, mRNA (the 455-nt fragment) between brain areas of the adult (n = 3) was high in the bed nucleus of the stria terminalis > medial preoptic/anterior hypothalamus > amygdala; intermediate in the medial basal hypothalamus (infundibular nucleus, median eminence, ventromedial nucleus) > lateral preoptic/anterior hypothalamus; and low in the septum > lateral-dorsalmedial hypothalamus. P450arom mRNA was undetectable in cingulate and parietal cortex, hippocampus, and cerebellum. P450a,,, activity, as measured by the 3 H20 assay, correlated well with the distribution of P450rom mRNA (the 455-nt protected fragment; r = 0.9) in the same tissues. A shorter protected RNA fragment was found in the medial basal hypothalamus, the bed nucleus of the stria terminalis, the amygdala, and the cingulate and parietal cortex but not in the other brain areas investigated. Its presence did not correlate with aromatase activity in brain tissue. This study describes the development of a ribonuclease protection assay using a monkey cDNA produced by RT-PCR and its usefulness for studying the distribution of P450rom mRNA in brains of nonhuman primates.

Brain aromatase plays an important role in the regulation of adult reproductive behavior in male rodents. This report focuses on recent experiments from our laboratory that examined the distribution and regulation of aromatase mRNA in the rat brain. Aromatase mRNA was measured by a highly sensitive ribonuclease protection assay using a 32 P-labeled antisense RNA probe that was complimentary to the 5′ coding region of rat aromatase mRNA. This probe protects two RNA fragments in rat brain tissue: a 430-nt length fragment and a shorter 300-nt fragment. The presence of the 300-nt RNA fragment is not associated with enzyme activity in the rat brain and appears to represent an alternative brain-specific aromatase transcript whose function, if any, is unknown. In contrast, the 430-nt RNA fragment represents mRNA, which is thought to encode functional aromatase enzyme because its levels are correlated with aromatase activity concentrations in preoptic area, hypothalamus, amygdala, and ovary. Aromatase activity and mRNA levels in the preoptic area and hypothalamus decreased by 7 days after castration and were maintained at intact levels by treatment with testosterone and dihyhdrotestosterone, but not with estradiol. In contrast, neither aromatase activity nor mRNA levels in the amygdala are affected by castration or hormone replacement. In addition, sex differences in the regulation of aromatase mRNA were apparent in both the preoptic area and hypothalamus. These results demonstrate that androgens regulate the transcription or stability of aromatase mRNA in specific brain areas. Moreover, they suggest that gender differences in androgen responsiveness play an important role in regulating gene expression in the adult rat brain.

1. The central nervous systems (CNS) of males and females differ in the control mechanisms for the release of gonadotropins from the anterior pituitary gland as well as the capacity to display sex specific behaviors. 2. In guinea pigs and monkeys, these differences are organized through the actions of prenatal androgens secreted by the fetal testes. In both males and females androgen receptors have been identified within the brain during the period in development in which organization of the CNS occurs. Sex differences between the ratio of cytosolic and nuclear androgen receptors are due to the amount of endogenous androgen present in the circulation of the developing fetus. Thus, at least part of the biochemical machinery necessary for androgen action resides in the CNS during the period of sexual differentiation. 3. In addition to the physiological differences that have been observed, morphological differences that are androgen dependent have been found in the medial preoptic nucleus and the bed nucleus of the stria terminalis of the guinea pig. The location of these sex differences in brain morphology coincides roughly with the location of steroid binding neurons. 4. In some species the in situ conversion of testosterone to dihydrotestosterone (DHT) by the 5 alpha-reductases or to estradiol-17 beta by cytochrome P450 aromatase mediates testosterone's action. The gonadotropin surge mechanism of adult guinea pigs exposed to a 5a-reductase inhibitor in utero during the critical period for sexual differentiation was unaffected in either males or females even though the development of the external organs of reproduction of males was feminized by the treatment. Likewise, the gonadotropin surge mechanism of subjects exposed to an aromatase inhibitor in utero during the critical period for sexual differentiation was unaffected by this treatment. 5. The mechanism controlling negative feedback, however, was affected in both males and females. Subjects that were exposed to an aromatase inhibitor while developing in utero could not respond to the negative feedback actions of estrogen on gonadotropin release in adulthood. 6. The surge mechanism for the control of gonadotropin secretion in nonhuman primates is not sexually differentiated as it is in rodents. Castrated male monkeys release surge amounts of LH in response to an estrogen challenge. Both infant and adult dimorphic behaviors of rhesus monkeys are organized by the prenatal actions of androgen.