Neuroendocrine regulation of sexually dimorphic brain structure and associated sexual behavior in male rats is genetically controlled

Sex and stress steroids in adolescence: Gonadal regulation of the hypothalamic-pituitary-adrenal axis in the rat

This review provides an overview of the current understanding of the role of the hypothalamic-pituitary-gonadal (HPG) axis in regulating the hypothalamic-pituitary-adrenal (HPA) axis response to stressors. HPA function is influenced by both organizational (programming) and activational effects of gonadal hormones. Typically, in adult rats, estradiol increases and androgens decrease the HPA response to stressors, thereby contributing to sex differences in HPA function, and sensitivity of the HPA axis to gonadal steroids is in part determined by exposure to these hormones in early development. Although developmental differences in HPA function are well characterized, the extent to which gonadal steroids contribute to age differences in HPA function is not well understood. Deficits in the understanding of the relationships between the HPA and HPG axes are greatest for the adolescent period of development. The critical outstanding questions are, when do gonadal hormones begin to regulate HPA function in adolescence, and what mechanisms precipitate change in sensitivity of the HPA axis to the HPG axis at this stage of life.

Low oral doses of bisphenol A increase volume of the sexually dimorphic nucleus of the preoptic area in male, but not female, rats at postnatal day 21

Perinatal treatment with relatively high doses of bisphenol A (BPA) appears to have little effect on volume of the rodent sexually dimorphic nucleus of the preoptic area (SDN-POA). However, doses more relevant to human exposures have not been examined. Here, effects of pre- and post-natal treatment with low BPA doses on SDN-POA volume of postnatal day (PND) 21 Sprague-Dawley rats were evaluated. Pregnant rats were orally gavaged with vehicle, 2.5 or 25.0 μg/kg BPA, or 5.0 or 10.0 μg/kg ethinyl estradiol (EE₂) on gestational days 6-21. Beginning on the day after birth, offspring were orally treated with the same dose their dam had received. On PND 21, offspring (n=10-15/sex/group; 1/sex/litter) were perfused and volume evaluation was conducted blind to treatment. SDN-POA outline was delineated using calbindin D28K immunoreactivity. Pairwise comparisons of the significant treatment by sex interaction indicated that neither BPA dose affected female volume. However, females treated with 5.0 or 10.0 μg/kg EE₂ exhibited volumes that were larger than same-sex controls, respectively (p<0.001). Males treated with either BPA dose or 10.0 μg/kg/day EE₂ had larger volumes than same-sex controls (p<0.006). These data indicate that BPA can have sex-specific effects on SDN-POA volume and that these effects manifest as larger volumes in males. Sensitivity of the methodology as well as the treatment paradigm was confirmed by the expected EE₂-induced increase in female volume. These treatment effects might lead to organizational changes within sexually dimorphic neuroendocrine pathways which, if persistent, could theoretically alter adult reproductive physiology and socio-sexual behavior in rats.

Changes of pituitary and penile structure in male adult rats following castration and high-fat diet

AIM

To investigate the influence of low androgen levels and high-fat diet on the structure of pituitary and penis in male rats.

METHODS

Ten-week-old adult male Sprague-Dawley rats were randomly divided into 2 groups, one fed a high-fat diet the other fed a normal diet; each group consisted of 3 subgroups: controls, castrated rats (with low androgen), and castrated rats given undecanoate replenishment. After 11 weeks, the structure of pituitary and penis were observed under light microscopy. Immunohistochemistry was used to assess the expression of FSH in pituitary and cyclooxygenase-2 (COX-2) in corpora cavernosa penis.

RESULTS

The structures of pituitary and penis in castrated rats were injured, and were more damaged in castration together with high-fat diet. Immunohistochemistry showed FSH expression in castrated rats pituitary while castrated rats on a high-fat diet had less positive staining than those on a normal diet. Vascular structure of corpora cavernosa penis, showed a strongly positive COX-2 expression in high-fat diet rats.

CONCLUSIONS

Castration and high-fat diet could induce structural damages of pituitary and penis in male rats. Replacement with testosterone could partially restore the impaired structure. The positive expression of COX-2 implied inflammatory pathway existence on vascular structure of penis in high-fat diet and low-androgen male rats.

The multiple roles of estrogens and the enzyme aromatase

Aromatase is the enzyme that catalyzes the last step of estrogen biosynthesis. It is expressed in many tissues such as the gonads, brain and adipose tissue. The regulation of the level and activity of aromatase determines the levels of estrogens that have endocrine, paracrine and autocrine effects on tissues. Estrogens play many roles in the body, regulating reproduction, metabolism and behavior. In the brain, cell survival and the activity of neurons are affected by estrogens and hence aromatase.

Ginsenoside Rg1 improves male copulatory behavior via nitric oxide/cyclic guanosine monophosphate pathway

INTRODUCTION

Ginsenoside Rg1 is the purified ingredient from ginseng, there has been little research on the effect of Rg1 on male copulatory behavior and its mechanism of action.

AIM

The purpose of this study was to investigate the effect of ginsenoside Rg1 on copulatory behavior of male mice and the mechanism of its action.

METHODS

Male mice were treated with Rg1 intraperitoneally; three elements of copulatory behavior (mounting, intromission, pelvic thrusting) were assessed. After final treatment and behavior determination, nitric oxide (NO) concentration were determined by spectrophotometry method. Plasma testosterone, cyclic guanosine monophosphate (cGMP) in corpus cavernosum both in vivo and in vitro were measured by radioimmunoassay. Rabbit corpus cavernosum segments were incubated with Rg1 (0.05, 0.5 and 5 microM) in the presence of exogenous NO donor sodium nitroprusside (SNP) (10 microM), and the cGMP level was measured. The half maximal inhibitory concentration (IC50) of Rg1 for phosphodiesterase type 5 (PDE5) inhibitors was determined by measuring the conversion of cGMP to 5'-mononucleotides. Sildenafil was set as a positive control. MAIN COME OUT MEASURES: Mounting and intromission frequency, pelvic thrusts, serum testosterone, NO level, cGMP accumulation, IC50 for PDE5.

RESULTS

Rg1 (10 mg/kg) significantly increased mounting and pelvic thrusting frequency and numbers of intromission of male mice from d16 to d20. Rg1 increased serum testosterone concentration, enhanced NO release, and cGMP accumulation in corpus cavernosum both in vivo and in vitro. The IC50 of sildenafil and Rg1 for PDE5 were 4.24 +/- 0.78 and 12.47 +/- 2.31 nmol/L.

CONCLUSIONS

Ginsenoside Rg1 improved copulatory behavior of male mice and this may attribute to its actions at both testosterone level and signal transduction pathway in corpus cavernosum. NO/cGMP pathway appeared to play a key role in mediating the effect of Rg1 on male sexual function. These experimental data provide evidence that Rg1 could be a promising new drug for erectile dysfunction and low libido.

Stereological sex difference during development of the magnocelluar subdivision of the medial preoptic nucleus (MPN mag)

In Syrian hamsters, reproductive behaviors are initiated in the presence of appropriate hormonal and chemosensory cues. These cues are detected and integrated within a highly conserved pathway that converges on a small nuclear group in the lateral aspect of the medial preoptic area, the magnocellular subdivision of the medial preoptic nucleus (MPN mag). The MPN mag plays a critical role in the regulation of male mating behavior--bilateral ablation of the MPN mag eliminates copulation. The MPN mag is sexually differentiated in both neuron number and density, but not in overall volume or volume of individual neurons. The current study used unbiased stereological methods to determine when the MPN mag becomes sexually differentiated. Our data indicate that the MPN mag becomes sexually dimorphic in volume and cell number after the critical period when steroid treatment induces male sexual behavior.

Gender role behavior in children with XY karyotype and disorders of sex development

Children exhibit gender-typical preferences in play, toys, activities and interests, and playmates. Several studies suggest that high concentrations of pre- and postnatal androgens contribute to male-typical behavior development, whereas female-typical behavior develops in the absence of high androgens levels. This study aims to explore the consequences of hypoandrogenization on gender-typical behavior in children who have an XY karyotype and disorder of sex development (DSD). Participants included 33 children (ages 2-12 years) with an XY karyotype and DSD; 21 reared as girls and 12 reared as boys. Children's preferred activities and interests and playmate preferences were assessed with parent report questionnaires, a structured free-play task, and choice of a toy to keep as a gift. Participant's responses were compared to those of children recruited in a pre-school and elementary school survey (N=166). In this study, the degree of hypoandrogenization as indicated by genital stage and diagnosis showed a significant relationship to nearly all of the gender-related behaviors assessed, supporting the hypothesis that masculinization of gender role behavior is a function of prenatal androgen exposure. Despite the fact that children with partial androgen effects reared as girls showed increased "boyish" behaviors, they did not show increased signs of gender identity confusion or instability on a group level. We conclude that androgen exposure plays a decisive role in the development of gender-typical behavior in children with XY karyotype and DSD conditions.

The control of sexual differentiation of the reproductive system and brain

This review summarizes current knowledge of the genetic and hormonal control of sexual differentiation of the reproductive system, brain and brain function. While the chromosomal regulation of sexual differentiation has been understood for over 60 years, the genes involved and their actions on the reproductive system and brain are still under investigation. In 1990, the predicted testicular determining factor was shown to be theSRYgene. However, this discovery has not been followed up by elucidation of the actions of SRY, which may either stimulate a cascade of downstream genes, or inhibit a suppressor gene. The number of other genes known to be involved in sexual differentiation is increasing and the way in which they may interact is discussed. The hormonal control of sexual differentiation is well-established in rodents, in which prenatal androgens masculinize the reproductive tract and perinatal oestradiol (derived from testosterone) masculinizes the brain. In humans, genetic mutations have revealed that it is probably prenatal testosterone that masculinizes both the reproductive system and the brain. Sexual differentiation of brain structures and the way in which steroids induce this differentiation, is an active research area. The multiplicity of steroid actions, which may be specific to individual cell types, demonstrates how a single hormonal regulator, e.g. oestradiol, can exert different and even opposite actions at different sites. This complexity is enhanced by the involvement of neurotransmitters as mediators of steroid hormone actions. In view of current environmental concerns, a brief summary of the effects of endocrine disruptors on sexual differentiation is presented.

Intrauterine proximity to male fetuses affects the morphology of the sexually dimorphic nucleus of the preoptic area in the adult rat brain

Previous studies on polytocous rodents have revealed that the fetal intrauterine position influences its later anatomy, physiology, reproductive performance and behavior. To investigate whether the position of a fetus in the uterus modifies the development of the brain, we examined whether the structure of the sexually dimorphic nucleus of the preoptic area (SDN-POA) of rat brains accorded to their intrauterine positions. Brain sections of adult rats gestated between two male fetuses (2M) and between two female fetuses (2F) in the uterus were analysed for their immunoreactivity to calbindin-D28k, which is a marker of the SDN-POA. The SDN-POA volume of the 2M adult males was greater than that of the 2F adult males, whereas the SDN-POA volume of the 2M and 2F adult females showed no significant difference. This result indicated that contiguous male fetuses have a masculinizing effect on the SDN-POA volume of the male. To further examine whether the increment of SDN-POA volume in adulthood was due to exposure to elevated steroid hormones during fetal life, concentrations of testosterone and 17beta-estradiol in the brain were measured with 2M and 2F fetuses during gestation, respectively. On gestation day 21, the concentrations of testosterone and 17beta-estradiol in the brain were significantly higher in the 2M male rats as compared with the 2F male rats. The results suggested that there was a relationship between the fetal intrauterine position, hormone transfer from adjacent fetuses and the SDN-POA volume in adult rat brains.

"Any decision is better than none" decision-making about sex of rearing for siblings with 17beta-hydroxysteroid-dehydrogenase-3 deficiency

Children with 17beta-hydroxysteroid-dehydrogenase-3 (17beta-HSD-3) deficiency have a defect of testosterone biosynthesis with subsequent diminished virilization in XY individuals. Some are raised as girls and some as boys. There were two purposes of this case report: First, it analyzed the process of decision-making in a family with a pair of siblings with identical mutations leading to 17beta-HSD-3 deficiency whose parents chose to raise one child as a boy and one as a girl. This analysis was based on narrative interviews with the parents. Second, we assessed the gender role behavior and gender identity in the children to examine if the psychosexual development of these children correspond with the sex of rearing their parents chose. When participating in the study, the children were 7 (boy) and 5 (girl) years old. Parents described a difficult process of decision-making and voiced concerns about lack of appropriate and understandable information, and anticipated decision regret. However, they did not feel that the decision to "normalize" the external genitalia should have been deferred. Both children appeared to show age-typical gender-related behavior and did not show any signs of physical or mental distress.

Effects of experimental hyperandrogenemia on the female rat reproductive axis: suppression of progesterone-receptor messenger RNA expression in the brain and blockade of luteinizing hormone surges

BACKGROUND

Preovulatory gonadotropin-releasing hormone and luteinizing hormone (LH) surges depend on activation of estrogen-inducible progesterone receptors (PRs) in the hypothalamus. Although testosterone treatment can suppress LH secretion under some circumstances, how androgens affect the release of preovulatory hormone surges, and the cellular mechanisms by which androgens exert any such effects, remains unknown.

OBJECTIVE

This study examined the hypothesis that testosterone can block the release of estrogen-induced gonadotropin surges via attenuation of estrogen's ability to induce PRs in the preoptic area (POA)-hypothalamus.

METHODS

In experiment 1, proestrus rats were implanted with capsules filled with crystalline testosterone or empty control capsules. Four days later, animals were bled via atrial catheters at 30-minute intervals from noon to 9:00 pm. In experiment 2, proestrus rats received testosterone-filled or empty control capsules, and 3 days later were ovariectomized (OVX) and injected with estradiol benzoate (EB) 30 mug SC or sesame oil vehicle. The next day, blood samples were obtained from the rats. In experiment 3, proestrus rats similarly implanted with testosterone-filled or empty control capsules, OVX, and injected with EB or vehicle were sacrificed, and POA-hypothalamic tissue was collected for quantitative reverse transcription-polymerase chain reaction analysis of PR messenger RNA.

RESULTS

In experiment 1, radioimmunoassay of serum revealed that testosterone completely blocked release of LH surges that were fully evident in the control group. In experiment 2, LH radioimmunoassay revealed that high-physiologic testosterone exposure completely abolished the release of EB-induced LH surges. In experiment 3, although EB treatment was found to induce an increase in PR expression in control animals, no such induction of PR expression was observed in the testosterone-treated rats.

CONCLUSIONS

Our findings are consistent with the hypothesis that hyperandrogenic interference in the release of preovulatory LH surges is mediated by the suppressive effects of androgens on PR expression in POA-hypothalamic tissue. These findings may have important implications in the understanding of reproductive dysregulation in female hyperandrogenic syndromes, including polycystic ovary syndrome.

EVALUATION OF GENERAL BEHAVIOR, MEMORY, LEARNING PERFORMANCE, AND BRAIN SEXUAL DIFFERENTIATION IN F1 OFFSPRING MALES OF RATS TREATED WITH FLUTAMIDE DURING LATE GESTATION

Flutamide is a drug with antiandrogen effects that are mediated through androgen receptors (ARs). In this study, flutamide was subcutaneously administered to female rats (3, 10 or 30 mg/kg/day) on gestation Days 16-21 to evaluate effects on memory and learning performance in F1 offspring. Brain sexual differentiation was also evaluated by measuring the volume of the sexual dimorphic nucleus of the preoptic area (SDN-POA) and analyzing levels of androgen receptor (AR) mRNA expression in the prostate, hypothalamus and hippocampus. In F1 offspring exposed in utero to flutamide, evaluation of motor activity, learning performance and spatial perception showed that flutamide tended to exert a dose-dependent increase on the motor activity in F1 males, but no significant differences were identified in the other measurements. Prominent changes in development of the SDN-POA were apparent in males after maturation. Doses of > or =3 mg/kg/day resulted in significantly decreased length and volume of the SDN-POA compared to controls. These differences tended to become more marked at higher doses. Volumes of the SDN-POA did not differ significantly between F1 males and females exposed to flutamide at 30 mg/kg/day. AR mRNA was assayed using the dot-blotting method in F1 animals. In flutamide dose groups, AR mRNA expression tended to be increased in the prostate gland and decreased in the hippocampus. These results might suggest that exposure to flutamide in utero might affect controlling AR expression on a hormonal signal transduction system mediated by testosterone. However, these changes were not clearly correlated to learning performance in male offspring other than motor activity.

Morphological effects of estrogen on cholinergic neurons in vitro involves activation of extracellular signal-regulated kinases

In the present study, we examined the ability of estrogen to enhance cholinergic neurite arborization in vitro and identified the signal transduction cascade associated with this effect. Basal forebrain primordia collected from rat pups on postnatal day 1 were cultured for 2 weeks and then treated with 5 nm 17beta-estradiol for 24 hr. Cholinergic neurons were identified immunocytochemically with an antibody against the vesicular acetylcholine transporter and digitally photographed. Morphological analysis indicated that female cultures respond to estrogen treatment with an increase in total neurite length per neuron (4.5-fold over untreated controls) and in total branch segment number per neuron (2.3-fold over controls). In contrast, there was no change in total neurite length per neuron in male cultures, and we also observed a decrease in total branch segment number per neuron (0.5-fold below controls). Detailed histograms indicated that estrogen increases primary and secondary branch length and number and also increases terminal neuritic branches to the seventh order in female cultures. In a second set of experiments, we investigated the signal transduction cascade involved in this response, and found that an upstream extracellular signal-regulated kinase (ERK) inhibitor blocked the ability of estrogen to enhance outgrowth in female cultures. Our study provides strong evidence in support of the fact that the ERK pathway is required for estrogen-induced structural plasticity in the cholinergic system of female rats. Understanding the intracellular processes that underlie the response of cholinergic neurons to estrogen provides a necessary step in elucidating how cholinergic neurons can be particularly susceptible to degeneration in postmenopausal women.

Adult gonadal hormones selectively regulate sexually dimorphic quantitative traits observed in experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) and multiple sclerosis (MS) are characterized by strong sexual dimorphisms, many of which may be due to genetically controlled sex hormone effects on the immune system, the central nervous system (CNS), or both. In the present study we used 487 gonadectomized and 376 intact age-matched F(2) mice generated through crosses of B10.S/SgMcdJ and SJL/J mice to assess the role of adult gonadal hormones in regulating clinical and histopathological quantitative traits (QT) associated with EAE in the context of genetic heterogeneity. We found that gonadectomy resulted in different effects, depending on the QT and the sex of the mouse. Ovariectomized mice on average had lower cumulative clinical disease scores, shorter duration of clinical signs, and increased peak disease scores. This trend was accompanied by a significant increase in the incidence of acute, progressive EAE which is more frequently seen in intact and orchiectomized males. Although spinal cord (SC) inflammation was the better predictor of clinical signs of EAE in both sexes, ovariectomized females had considerable reductions in nearly all histopathological QT in both the brain and SC. Orchiectomy resulted in modestly significant increases in disease severity and peak score and earlier onset of clinical signs. With the exception of SC demyelination and lesion scores, orchiectomy had no effect on histopathological QT. Importantly, gonadectomy reduced but did not completely abolish any of the sexually dimorphic clinical QT seen in intact mice. It did however, lead to a significant sexual dimorphism in incidence and severity not seen in intact mice. For histopathological QT, no sexual dimorphism was detected for brain lesions in either intact or gonadectomized mice. In contrast, SC histopathological QT exhibited significant sexual dimorphisms, which were impacted by gonadectomy. The results from this study indicate that within the context of genetic heterogeneity, circulating gonadal hormones influence both clinical and histopathological QT in this model of MS, but they do not solely account for the sexual dimorphisms seen in these traits. Thus, additional mechanisms must play a role in regulating gender differences in autoimmune disease of the CNS.

Estrogens and phytoestrogens: brain plasticity of sexually dimorphic brain volumes

Sexually dimorphic brain volumes (sexually dimorphic nucleus of the preoptic area (SDN-POA) and anteroventral periventricular (AVPV) nucleus) are influenced by estrogens. Phytoestrogens, derived from plants (especially soy products), are molecules structurally and functionally similar to estradiol. The purpose of this study was to examine: the consumption of phytoestrogen (using a phytoestrogen-rich (Phyto-600) versus a phytoestrogen-free (Phyto-free)) diets from conception to adulthood (or changing the diets during adulthood) and characterizing (a) circulating plasma phytoestrogen levels, (b) testosterone levels in males, (c) sexually dimorphic brain volumes (i.e. the SDN-POA and AVPV) and (d) the presence of apoptotic cells in these brain structures in Long-Evans rats. Phyto-600 fed animals displayed total serum phytoestrogens levels 37-fold higher compared to Phyto-free values. Circulating testosterone levels were not significantly altered by the diets. Female SDN-POA volumes were not altered by the diets. Whereas, males fed a Phyto-free diet displayed decreased SDN-POA volumes compared to male Phyto-600 values. Females fed the Phyto-600 diet displayed larger AVPV volumes compared to males on the same diet or females on the Phyto-free diet. Males fed the Phyto-free diet had the largest AVPV values compared to Phyto-600 fed males. When the SDN-POA region was examined in lifelong Phyto-free fed males, apoptotic cells were present versus males fed the Phyto-600 diet and in the AVPV region the opposite results were obtained. In summary, consumption of dietary phytoestrogens (estrogen mimics) can alter hormone-sensitive hypothalamic brain volumes in rodents during adulthood.

Sexual experience interacts with steroid exposure to shape the partner preferences of rats

A three-phase experiment manipulated sexual experience and hormone exposure (perinatally and in adulthood) in female rats housed individually from weaning so as to limit peripubertal social and sexual experience. Noncontact partner preference for a male or estrous female rat was measured both before and after sexual experience, first while rats were under the influence of circulating testosterone propionate (TP) and later after priming them with ovarian hormones (estradiol benzoate and progesterone; EB & P). When implanted with TP capsules and tested while sexually naive, all groups of female rats preferred females to males without differing statistically. However, following three sexual experience sessions with estrous females, differences emerged between the masculinized and control groups in the magnitude of their female-directed preference, with masculinized females demonstrating a significantly greater preference for estrous females. Sexual experience with male rats under EB & P did not result in a significant shift in preference in any group. Histological assessment indicated that the volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) was increased by exposure to TP postnatally, and SDN-POA volume correlated positively with partner preference scores but only when rats were both sexually experienced and exposed to circulating TP in adulthood. These results suggest that sexual experience interacts with steroid exposure to shape partner preference.

Neonatal sex steroids affect ventilatory responses to aspartic acid and NMDA receptor subunit 1 in rats

We hypothesized that administration of estradiol benzoate to males and testosterone propionate to female neonatal rat pups alters sex-specific ventilatory responses to aspartic acid with correspondent changes in N-methyl-D-aspartate receptor subunit 1 (NR1) expression determined by Western blot in specific brain regions. One-day-old rat pups received estradiol benzoate, testosterone propionate, or vehicle and were studied at weanling and adulthood. Different groups had distinct patterns of changes in tidal volume and frequency of breathing after aspartic acid administration. NR1 expression in hypothalamus was altered by age, sex, and treatment. Medullary and pontine NR1 expression correlated with baseline ventilation and magnitude of the ventilatory response to aspartic acid in some groups. Thus 1) tidal volume and breathing frequency patterns in response to aspartic acid are gender, age, and treatment dependent; 2) sex, age, and exogenous steroid hormones affect NR1 expression primarily in the hypothalamus; and 3) there is correlation between NR1 expression in pons and medulla with ventilatory parameters.