Casto J M, Ball G F
Department of Psychology, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Horm Behav. 1996 Dec;30(4):387-406. doi: 10.1006/hbeh.1996.0044.
The vocal control system in many songbird species is a sexually dimorphic neural circuit that mediates learning and production of song. The mechanism by which this system is sexually differentiated has been investigated in only one species, the zebra finch (Taeniopygia guttata). Estradiol may be involved in the sexual differentiation of this system, as female zebra finches treated with estradiol as nestlings develop a male-like song system; however, blocking estradiol action in embryonic and nestling male zebra finches does not demasculinize the song system. Therefore, the role of estradiol in song system development is unclear. The role of estradiol in song system sexual differentiation was assessed in European starlings (Sturnus vulgaris). This species is of potential interest because it is less extreme in the degree of sexual dimorphism of the song system and song behavior than zebra finches. While in the field, starling nestlings were implanted with 500 microg of estradiol at 3 days of age. These birds were brought into the laboratory at Day 11 and hand-reared. In females, estradiol produces significant increases in the volumes of song control regions defined by Nissl stain, as well as by autoradiography for alpha2-adrenergic receptors; however, these estradiol-treated females have song systems that more closely resemble those of control females than control males. Estradiol-treated males exhibit significant hypermasculinization at 210 days of age, but this effect is transient and hypermasculinization is no longer evident at Day 345. The role of estradiol in sexual differentiation of the neural circuit mediating song behavior remains enigmatic.
许多鸣禽物种的发声控制系统是一种介导歌曲学习和产生的两性异形神经回路。仅在斑胸草雀（Taeniopygia guttata）这一物种中研究了该系统两性分化的机制。雌二醇可能参与该系统的两性分化，因为雏鸟期接受雌二醇治疗的雌性斑胸草雀会发育出类似雄性的发声系统；然而，在胚胎期和雏鸟期的雄性斑胸草雀中阻断雌二醇的作用并不会使发声系统去雄性化。因此，雌二醇在发声系统发育中的作用尚不清楚。在欧洲椋鸟（Sturnus vulgaris）中评估了雌二醇在发声系统两性分化中的作用。该物种具有潜在的研究价值，因为其发声系统和鸣叫行为的两性异形程度不如斑胸草雀极端。在野外时，椋鸟雏鸟在3日龄时被植入500微克雌二醇。这些鸟在第11天被带回实验室并人工饲养。在雌性中，雌二醇会使由尼氏染色以及α2 - 肾上腺素能受体放射自显影定义的发声控制区域的体积显著增加；然而，这些接受雌二醇治疗的雌性的发声系统与对照雌性的发声系统比对照雄性的发声系统更相似。接受雌二醇治疗的雄性在210日龄时表现出显著的超雄性化，但这种效应是短暂的，在第345天时超雄性化不再明显。雌二醇在介导鸣叫行为的神经回路两性分化中的作用仍然是个谜。
