Search

Female rats show a gonadotrophin-releasing hormone (GnRH)/luteinising hormone (LH) surge in the presence of a preovulatory level of oestrogen, whereas males do not because of brain defeminisation during the developmental period by perinatal oestrogen converted from androgen. The present study aimed to identify the site(s) of oestrogen action and the critical period for defeminising the mechanism regulating the GnRH/LH surge. Animals given perinatal treatments, such as steroidal manipulations, brain local implantation of oestradiol (E(2) ) or administration of an NMDA antagonist, were examined for their ability to show an E(2) -induced LH surge at adulthood. Lordosis behaviour was examined to compare the mechanisms defeminising the GnRH/LH surge and sexual behaviour. A single s.c. oestradiol-benzoate administration on either the day before birth (E21), the day of birth (D0) or day 5 (D5) postpartum completely abolished the E(2) -induced LH surge at adulthood in female rats, although the same treatment did not inhibit lordosis. Perinatal castration on E21 or D0 partially rescued the E2-induced LH surge in genetically male rats, whereas castration from E21 to D5 totally rescued lordosis. Neonatal E(2) implantation in the anterior hypothalamus including the anteroventral periventricular nucleus (AVPV)/preoptic area (POA) abolished the E(2) -induced LH surge in female rats, whereas E(2) implantation in the mid and posterior hypothalamic regions had no inhibitory effect on the LH surge. Lordosis was not affected by neonatal E(2) implantation in any hypothalamic regions. In male rats, neonatal NMDA antagonist treatment rescued lordosis but not the LH surge. Taken together, these results suggest that an anterior hypothalamic region such as the AVPV/POA region is a perinatal site of oestrogen action where the GnRH/LH regulating system is defeminised to abolish the oestrogen-induced surge. The mechanism for defeminisation of the GnRH/LH surge system might be different from that of sexual behaviour, in terms of the site(s) of oestrogen action and critical period, as well as the neurotransmitter system involved.

The brain mechanism regulating gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) release is sexually differentiated in rodents. Kisspeptin neurons in the anteroventral periventricular nucleus (AVPV) have been suggested to be sexually dimorphic and involved in the GnRH/LH surge generation. The present study aimed to determine the significance of neonatal testicular androgen to defeminize AVPV kisspeptin expression and the GnRH/LH surge-generating system. To this end, we tested whether neonatal castration feminizes AVPV kisspeptin neurons and the LH surge-generating system in male rats and whether neonatal estradiol benzoate (EB) treatment suppresses the kisspeptin expression and the LH surge in female rats. Immunohistochemistry, in situ hybridization, and quantitative real-time RT-PCR were performed to investigate kisspeptin and Kiss1 mRNA expressions. Male rats were castrated immediately after birth, and females were treated with EB on postnatal Day 5. Neonatal castration caused an increase in AVPV kisspeptin expression at peptide and mRNA levels in the genetically male rats, and the animals showed surge-like LH release in the presence of the preovulatory level of estradiol (E2) at adulthood. On the other hand, neonatal EB treatment decreased the number of AVPV kisspeptin neurons and caused an absence of E2-induced LH surge in female rats. Semiquantitative RT-PCR analysis showed that neonatal steroidal manipulation affects Kiss1 expression but does not significantly affect gene expressions of neuropeptides (neurotensin and galanin) and enzymes or transporter for neurotransmitters (gamma-aminobutyric acid, glutamate, and dopamine) in the AVPV, suggesting that the manipulation specifically affects Kiss1 expressions. Taken together, our present results provide physiological evidence that neonatal testicular androgen causes the reduction of AVPV kisspeptin expression and failure of LH surge in genetically male rats. Thus, it is plausible that perinatal testicular androgen causes defeminization of the AVPV kisspeptin system, resulting in the loss of the surge system in male rats.

Galanin-like peptide (GALP), a ligand for three types of galanin receptor, is reported to have a role in regulating luteinising hormone (LH) release in male rodents and primates, but its role in LH release in female rodents remains controversial. The present study was conducted to test whether GALP has a stimulatory role in regulating LH secretion in female rats. The effect of i.c.v. infusion of GALP (5 nmol) on pulsatile LH release was investigated in Wistar-Imamichi strain female rats, or lean and obese Zucker rats. In oestradiol-17beta (oestradiol)-primed ovariectomised (OVX) Wistar-Imamichi female rats, i.c.v. infusion of GALP caused a gradual increase in LH release for the first 1.5 h after the infusion followed by an increased LH pulse frequency during the next 1.5 h, resulting in a significant increase in the mean LH concentrations and baseline levels of LH pulses throughout the sampling period and in the frequency of LH pulses at the last half of the period compared to vehicle-treated controls. The stimulatory effect of GALP was oestrogen-dependent because the same GALP treatment did not affect LH release in OVX rats in the absence of oestradiol. In lean Zucker rats, LH pulses were found in oestradiol-primed OVX individuals and central GALP infusion increased mean LH concentrations in the last half of the period. By contrast, few LH pulses were found in oestradiol-primed OVX obese Zucker rats reportedly with lower hypothalamic GALP expression. Central GALP infusion caused an apparent but transient increase in LH release, resulting in the significant increase in all pulse parameters of LH pulses compared to vehicle-treated controls in the first half of the sampling period. These results suggest that hypothalamic GALP is likely involved in stimulating GnRH/LH release, and that the stimulatory effect of GALP on LH release is oestrogen-dependent in female rats.

Sexual dimorphism of the behaviors or physiological functions in mammals is mainly due to the sex difference of the brain. A number of studies have suggested that the brain is masculinized or defeminized by estradiol converted from testicular androgens in perinatal period in rodents. However, the mechanisms of estrogen action resulting in masculinization/defeminization of the brain have not been clarified yet. The large-scale analysis with microarray in the present study is an attempt to obtain the candidate gene(s) mediating the perinatal estrogen effect causing the brain sexual differentiation. Female mice were injected with estradiol benzoate (EB) or vehicle on the day of birth, and the hypothalamus was collected at either 1, 3, 6, 12, or 24 h after the EB injection. More than one hundred genes down-regulated by the EB treatment in a biphasic manner peaked at 3 h and 12-24 h after the EB treatment, while forty to seventy genes were constantly up-regulated after it. Twelve genes, including Ptgds, Hcrt, Tmed2, Klc1, and Nedd4, whose mRNA expressions were down-regulated by the neonatal EB treatment, were chosen for further examination by semiquantitative RT-PCR in the hypothalamus of perinatal intact male and female mice. We selected the genes based on the known profiles of their potential roles in brain development. mRNA expression levels of Ptgds, Hcrt, Tmed2, and Nedd4 were significantly lower in male mice than females at the day of birth, suggesting that the genes are down-regulated by estrogen converted from testicular androgen in perinatal male mice. Some genes, such as Ptgds encoding prostaglandin D2 production enzyme and Hcrt encording orexin, have been reported to have a role in neuroprotection. Thus, Ptgds and Hcrt could be possible candidate genes, which may mediate the effect of perinatal estrogen responsible for brain sexual differentiation.

The brain mechanism regulating gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) release is sexually differentiated in rodents. Kisspeptin neurons in the anteroventral periventricular nucleus (AVPV) have been suggested to be sexually dimorphic and involved in the GnRH/LH surge generation. The present study aimed to determine the significance of neonatal testicular androgen to defeminize AVPV kisspeptin expression and the GnRH/LH surge-generating system. To this end, we tested whether neonatal castration feminizes AVPV kisspeptin neurons and the LH surge-generating system in male rats and whether neonatal estradiol benzoate (EB) treatment suppresses the kisspeptin expression and the LH surge in female rats. Immunohistochemistry, in situ hybridization, and quantitative real-time RT-PCR were performed to investigate kisspeptin and Kiss1 mRNA expressions. Male rats were castrated immediately after birth, and females were treated with EB on postnatal Day 5. Neonatal castration caused an increase in AVPV kisspeptin expression at peptide and mRNA levels in the genetically male rats, and the animals showed surge-like LH release in the presence of the preovulatory level of estradiol (E2) at adulthood. On the other hand, neonatal EB treatment decreased the number of AVPV kisspeptin neurons and caused an absence of E2-induced LH surge in female rats. Semiquantitative RT-PCR analysis showed that neonatal steroidal manipulation affects Kiss1 expression but does not significantly affect gene expressions of neuropeptides (neurotensin and galanin) and enzymes or transporter for neurotransmitters (gamma-aminobutyric acid, glutamate, and dopamine) in the AVPV, suggesting that the manipulation specifically affects Kiss1 expressions. Taken together, our present results provide physiological evidence that neonatal testicular androgen causes the reduction of AVPV kisspeptin expression and failure of LH surge in genetically male rats. Thus, it is plausible that perinatal testicular androgen causes defeminization of the AVPV kisspeptin system, resulting in the loss of the surge system in male rats.