Key role of estrogen receptor β in the organization of brain and behavior of the Japanese quail

Abstract

Estrogens play a key role in the sexual differentiation of the brain and behavior. While early estrogen actions exert masculinizing effects on the brain of male rodents, a diametrically opposite effect is observed in birds where estrogens demasculinize the brain of females. Yet, the two vertebrate classes express similar sex differences in the brain and behavior. Although ERα is thought to play a major role in these processes in rodents, the role of ERβ is still controversial. In birds, the identity of the estrogen receptor(s) underlying the demasculinization of the female brain remains unclear. The aim of the present study was thus to determine in Japanese quail the effects of specific agonists of ERα (propylpyrazole triol, PPT) and ERβ (diarylpropionitrile, DPN) administered at the beginning of the sensitive period (embryonic day 7, E7) on the sexual differentiation of male sexual behavior and on the density of vasotocin-immunoreactive (VT-ir) fibers, a known marker of the organizational action of estrogens on the quail brain. We demonstrate that estradiol benzoate and the ERβ agonist (DPN) demasculinize male sexual behavior and decrease the density of VT-ir fibers in the medial preoptic nucleus and the bed nucleus of the stria terminalis, while PPT has no effect on these measures. These results clearly indicate that ERβ, but not ERα, is involved in the estrogen-induced sexual differentiation of brain and sexual behavior in quail.

Keywords: DPN; Estrogen receptor α; Estrogen receptor β; PPT; Sexual differentiation; Vasotocin.

Figure 1:

Specificity of the immunostaining against vasotocin. Vasotocin immunoreactive fibers in the medial preoptic nucleus (POM), bed nucleus of the stria terminalis (BST) and lateral septum (LS) in control conditions (left column) and following pre-adsorption with 10μg of vasotocin per ml of primary antibody (right column). Magnification bar, 200μm.

Figure 2.

Body weight (A) and cloacal gland area (B) in adult male (M) and female (F) quail treated in ovo with estradiol benzoate (EB), the ERα agonist PPT, the ERβ agonist DPN or their vehicle (CTL) and chronically treated with testosterone in adulthood. ** = p< 0.01 vs. CTL males (Tukey post-hoc test following significant one way ANOVA).

Figure 3.

Percentage of adult male (M) and female (F) quail that displayed at least one mount attempt (A) or one cloacal contact movement (B) after being treated in ovo with estradiol benzoate (EB), the ERα agonist PPT, the ERβ agonist DPN or their vehicle (CTL) and chronically treated with testosterone in adulthood. *** p<0.001 by Fisher’s exact probability test when compared to CTL- or PPT-treated males.

Figure 4.

Effect of an in ovo injection at embryonic day 7 with estradiol benzoate (EB), the ERα agonist PPT, the ERβ agonist DPN or their vehicle (CTL) in male (M) quail on the expression of adult male sexual behavior. The figure shows the frequencies (A-B) and latencies (C-D) to display mount attempts (MA; A,C) and cloacal contact movements (CCM; B,D) during the seven tests. Data for control females (F) are also shown. Data for each test were analyzed by Kruskal-Wallis ANOVA followed when significant by Dunn’s post hoc tests, whose results are indicated by letters in the graphs. a and b represent significant differences (p<0.05) between the CTL M or the PPT M groups and the EB M, DPN M and CTL F groups, c corresponds to differences between the PPT M and the EB M groups.

Figure 5.

Percentage of area covered by vasotocin-immunoreactive fibers in the medial preoptic nucleus (POM), the bed nucleus of the stria terminalis (BST) and the lateral septal nucleus (LS) of adult male (M) and female (F) quail treated in ovo with estradiol benzoate (EB), the ERα agonist PPT, the ERβ agonist DPN or their vehicle (CTL) and chronically treated with testosterone in adulthood. Data for each nucleus were analyzed by Kruskal-Wallis ANOVA followed when significant by Dunn’s post hoc tests whose results are indicated by letters in the graphs. a = p<0.05 vs. CTL M, PPT M, CTL F; b = p<0.05 vs. CTL M and PPT M; c = p<0.05 vs. all groups.

Figure 6.

Representative photomicrographs illustrating the effects of the embryonic treatments on the density of vasotocin-immunoreactive fibers in the medial preoptic nucleus (POM), the bed nucleus of the stria terminalis (BST) and the lateral septum (LS). Abbreviations: V3, third ventricle; CA, anterior commisure; FPL, lateral forebrain bundle; LV, lateral ventricle; CTL F, control females; CTL M, control males; DPN, ERβ agonist; EB, estradiol benzoate; PPT, ERα agonist. Scale bar represents 100 μm.