Sex steroids play a major role in sexually dimorphic brain development during not only the perinatal period but also the pubertal period. We previously showed that, in male mice, the estrogen receptor-α (Esr1) and aromatase (Cyp19a1) genes are essential to the sexually dimorphic formation of the anteroventral periventricular nucleus (AVPV) and the principal nucleus of the bed nucleus of the stria terminalis (BNSTp), but the estrogen receptor-β (Esr2) gene is not necessary. We also showed that the androgen receptor (Ar) gene is essential to the sexually dimorphic formation of the BNSTp. These genes are expressed in the AVPV and BNSTp of perinatal mice. However, it remains unknown whether these genes are expressed in the AVPV and BNSTp during puberty, and whether the expression, if any, differs by sex, age, and brain region. Here, we dissected the AVPV and BNSTp from Nissl-stained brain sections of male and female mice on postnatal day (PD) 20 (prepuberty), PD30 (puberty onset in females), PD40 (puberty onset in males), and PD60 (young adult) using a laser microdissection system. We then examined the mRNA levels of Esr1, Esr2, Cyp19a1, and Ar in these brain regions. In the AVPV, Esr1 mRNA levels were greater in females than males during PD20-60. Esr2 and Ar mRNA expressions did not differ between sexes. Ar mRNA levels were higher at PD30 than PD20. Cyp19a1 mRNA was not detected in the AVPV at PD20-60. In the BNSTp, Esr1 and Esr2 mRNA levels were higher in females than in males during PD20-60, although the mRNA levels of Cyp19a1 and Ar did not differ between sexes. Additionally, we revealed that orchiectomy at PD20 induced a failure of normal formation of the male BNSTp and testosterone replacement in the prepubertal period rescued the effect of orchiectomy at PD20. Taken together, it is suggested that pubertal testosterone transported to the AVPV is not converted to estradiol there and does not act via ESR1 and ESR2. By contrast, the formation of the male BNSTp may be affected by testicular testosterone during puberty via AR and/or via ESR1 after conversion to estradiol by CYP19A1.
Abstract Background ESR2, a nuclear estrogen receptor also known as estrogen receptor β, is expressed in the brain and contributes to the actions of estrogen in various physiological phenomena. However, its expression profiles in the brain have long been debated because of difficulties in detecting ESR2-expressing cells. In the present study, we aimed to determine the distribution of ESR2 in rodent brains, as well as its sex and interspecies differences, using immunohistochemical detection with a well-validated anti-ESR2 antibody (PPZ0506). Methods To determine the expression profiles of ESR2 protein in rodent brains, whole brain sections from mice and rats of both sexes were subjected to immunostaining for ESR2. In addition, to evaluate the effects of circulating estrogen on ESR2 expression profiles, ovariectomized female mice and rats were treated with low or high doses of estrogen, and the resulting numbers of ESR2-immunopositive cells were analyzed. Welch’s t-test was used for comparisons between two groups for sex differences, and one-way analysis of variance followed by the Tukey–Kramer test were used for comparisons among multiple groups with different estrogen treatments. Results ESR2-immunopositive cells were observed in several subregions of mouse and rat brains, including the preoptic area, extended amygdala, hypothalamus, mesencephalon, and cerebral cortex. Their distribution profiles exhibited sex and interspecies differences. In addition, low-dose estrogen treatment in ovariectomized female mice and rats tended to increase the numbers of ESR2-immunopositive cells, whereas high-dose estrogen treatment tended to decrease these numbers. Conclusions Immunohistochemistry using the well-validated PPZ0506 antibody revealed a more localized expression of ESR2 protein in rodent brains than has previously been reported. Furthermore, there were marked sex and interspecies differences in its distribution. Our histological analyses also revealed estrogen-dependent changes in ESR2 expression levels in female brains. These findings will be helpful for understanding the ESR2-mediated actions of estrogen in the brain.
Creep-fatigue crack growth behaviours of a Ti-6242 alloy, a low carbon steel, a Type 304 stainless steel and Hastelloy X under reversed loading patterns (C-P, C-C, P-P and saw-tooth of slow-fast type) were investigated in air and vacuum environment in the light of fracture mechanics and fractography. The crack growth rate in each of the materials tested was successfully correlated in terms of the cyclic J integral range ΔJ irrespective of loading patterns. In the region of low growth rate, the crack growth rates of all the materials were about the same for the same value of ΔJ. In the region of high growth rate, on the other hand, the growth rates were somewhat different depending on the creep ductility of material, those with lower ductility giving higher growth rate for the same ΔJ value. Significant difference was not found between the crack growth rates in air and vacuum, and it was consistent with little difference observed between the fracture surface morphologies in these environments. It was confirmed by creep void observation on the cross section of specimens that the difference in fracture morphology between C-C type and C-P type loading was due to the recovery of grain boundary sliding during compression hold in the C-C type loading. An experimental evidence was obtained to suggest that the better correlation in crack growth rate in terms of the separated J integrals-fatigue and creep J integrals, which was reported on a low carbon steel, was possibly related to the specimen geometry rather than the creep-fatigue interaction.
Developmental exposure to environmental chemicals with estrogen-like activity has been known to permanently impair women’s health. In this study, we examined whether tris(2,6-dimethylphenyl) phosphate (TDMPP), an impurity in flame retardant that is not classified as endocrine disruptor at present, impairs sexual differentiation of the brain in mice. Either TDMPP, 17beta-estradiol (E2) as a positive control, or sesame oil as a negative control was administered during late pregnancy and early postnatal period and female reproductive functions of offspring were elucidated. Precocious puberty, irregular estrous cycles, and lowered lordosis response were found in TDMPP-treated group as well as E2-treated group. We also detected masculinization of sexual dimorphic nuclei in the hypothalamus of female mice after TDMPP treatment. Taken together, our empirical evidence suggests that the developmental exposure to TDMPP by using products containing TDMPP might be a potential risk to impair female reproductive functions at later life stages.
The medial preoptic area (MPOA) is a sexually dimorphic region of the brain that regulates social behaviors. The sexually dimorphic nucleus (SDN) of the MPOA has been studied to understand sexual dimorphism, although the anatomy and physiology of the SDN is not fully understood. Here, we characterized SDN neurons that contribute to sexual dimorphism and investigated the mechanisms underlying the emergence of such neurons and their roles in social behaviors. A target-specific neuroanatomical study using transgenic mice expressing Cre recombinase under the control of
