Estrogen Receptor Immunoreactivity in Late-Gestation Fetal Lambs1

Abstract

Prenatal androgens masculinize postnatal reproductive neuroendocrine function and behavior in sheep. Testosterone treatment of pregnant ewes during midgestation masculinizes sexual behavior and luteinizing hormone secretion in female lambs, presumably in part via aromatization and estrogen receptor (ESR) binding in the brain. We hypothesized that male and female sheep also differ in the number and distribution of ESR-containing neurons. If so, ESR expression should be sensitive to prenatal hormones delivered exogenously or in situ. ESR alpha (ESR1) was compared by immunocytochemistry in male and female lambs at the end of gestation, as well as in fetal females exposed prenatally to testosterone or dihydrotestosterone. ESR1-positive neurons were abundant in the posteromedial bed nucleus of the stria terminalis (BSTpm), medial preoptic area (MPOA), posterior medial amygdaloid nucleus (MeP), amygdalohippocampal area (AHi), ventromedial hypothalamic nuclei (VMH), and arcuate hypothalamic nuclei (ARC). In females, the ARC had the largest number of stained cells (mean 6 SEM, 475.6 6 57.4 cells/0.173 mm 2 ), while staining intensity was greatest in the MPOA (mean 6 SEM gray level, 31.3 6 5.3). The mean 6 SEM integrated gray level (IGL) was high in the ARC (0.63 6 0.13) and in the MPOA (0.51 6 0.08). The mean 6 SEM IGL was low in the MeP (0.31 6 0.10) and in the BSTpm (0.21 6 0.06), while it was intermediate in the AHi (0.36 6 0.10) and in the VMH (0.37 6 0.07). ESR immunostaining was not significantly different in male and female fetal lambs, nor in females fetuses exposed prenatally to androgens (P . 0.05). However, ESR1 staining was significantly increased in the ARC, MPOA, and AHi of adult rams vs. adult ewes. These results suggest that brain ESR immunoreactivity in fetal lambs is unlikely to account for postnatal sex differences in reproductive function. Instead, sex differences in ESR emerge postnatally.

Prenatal Exposure to Androgen Excess Increases LH Pulse Amplitude During Postnatal Life in Male Sheep

“…So it is plausible that some eff ects catalogued as of androgenic origin, may have an estrogenic origin. Moreover, the presence of ERβ (ER2) in fetal male sheep has been described [ 41 ] , which could have a role in masculinization/defeminization of the brain [ 42 ] . However, in this precise type of study, evidence exists that the estradiol receptor mostly involved in gonadotropin secretion is ERα (ER1) and that under prenatal androgenization, most diff erences in the expression of this receptor are being observed postnatally [ 42 ] .…”

“…Moreover, the presence of ERβ (ER2) in fetal male sheep has been described [ 41 ] , which could have a role in masculinization/defeminization of the brain [ 42 ] . However, in this precise type of study, evidence exists that the estradiol receptor mostly involved in gonadotropin secretion is ERα (ER1) and that under prenatal androgenization, most diff erences in the expression of this receptor are being observed postnatally [ 42 ] . In essence, caution must be taken in the interpretation of the mechanisms involved, since evidence exists for a diff erential eff ect upon testicular parameters when males were exposed to T or DHT during gestation [ 43 ] .…”

La conducta sexual del carnero. Revisión

“…The above is demonstrated by treatment pregnant ewes with testosterone during half of the gestation period, which masculinize sexual behavior and secretion of LH in ewe-lambs, presumably in part via aromatization and union of estrogen receptors in the brain (58) .…”

“…Lo anterior lo demuestran tratamientos con testosterona en borregas gestantes durante la mitad de la preñez, mismos que masculinizan la conducta sexual y secreción de la LH en corderas, presumiblemente en parte vía la aromatización y unión de los receptores de estrógeno en el cerebro (58) .…”

Sex Differences in Expression of Oestrogen Receptor α but not Androgen Receptor mRNAs in the Foetal Lamb Brain

“…Additionally, dimorphisms at the level of receptor expression may play a role in determining the degree of brain masculinisation. Previous studies establishing that steroid receptors are expressed in the developing foetal lamb brain used near term foetuses or gross dissections of the diencephalon that may have obscured possible sex differences . The present study used younger foetuses and a more discrete dissection of the medial preoptic area to test for sex differences in the expression levels of ERα and AR mRNA during the window of time that is critical for behavioural masculinisation and oSDN differentiation in the sheep.…”