Saldanha C J, Schlinger B A
Department of Physiological Science, University of California, Los Angeles 90095-1527, USA.
Gen Comp Endocrinol. 1997 Mar;105(3):390-401. doi: 10.1006/gcen.1996.6841.
Estrogens exert profound effects on vertebrate physiology and behavior. In most vertebrates, including birds, estrogens derived from ovarian tissue circulate at high levels during discrete periods of reproductive activity, and estrogen levels in males are low. In some songbirds (Passeriformes) plasma estrogens are high in both males and females. In the zebra finch, aromatase (estrogen-synthetase) is expressed abundantly in several regions of the male and female telencephalon and contributes to peripheral estrogen titers. To determine if this pattern of neural aromatase and estrogen synthesis is found in other songbirds, we have examined the patterns of estrogen synthesis in various tissues of another songbird, the common North American cowbird (Molothrus ater). Radiolabeled aromatizable androgenic substrate was injected in vivo or provided in vitro to telencephalic and gonadal tissue from adult male and female cowbirds. Estrogenic products were assayed in blood from the carotid artery and jugular vein, and in the telencephalon, ovary, and testes. Additionally, the presence of aromatase mRNA was studied in the brain using in situ hybridization. Radiolabeled androgenic substrate, injected in vivo, was readily converted to estrogens with higher amounts in the jugular compared to carotid blood, suggesting that the brain contains relatively high levels of aromatase. Further, radiolabeled androgens, provided in vitro to telencephalic, ovarian, and testicular tissue, resulted in the formation of radiolabeled estrogens. Aromatase mRNA is distributed widely in several areas of the cowbird telencephalon including the hippocampus, caudomedial neostriatum (including Field L), and nucleus taeniae. This pattern of neural aromatase expression resembles what we found previously in the zebra finch. Telencephalic aromatase may be characteristic of passerine songbirds and may function to provide local estrogenic cues to estrogen-sensitive neural loci, and/or contribute to peripheral estrogen titers in male and female songbirds.
雌激素对脊椎动物的生理和行为有着深远影响。在大多数脊椎动物中，包括鸟类，卵巢组织产生的雌激素在生殖活动的特定时期会大量循环，而雄性体内的雌激素水平较低。在一些鸣禽（雀形目）中，雄性和雌性的血浆雌激素水平都很高。在斑胸草雀中，芳香化酶（雌激素合成酶）在雄性和雌性端脑的多个区域大量表达，并影响外周雌激素水平。为了确定这种神经芳香化酶和雌激素合成模式是否也存在于其他鸣禽中，我们研究了另一种鸣禽——北美褐头牛鹂（Molothrus ater）不同组织中的雌激素合成模式。将放射性标记的可芳香化雄激素底物注射到成年雄性和雌性褐头牛鹂的体内，或提供给其端脑和性腺组织进行体外实验。对颈动脉和颈静脉血液、端脑、卵巢和睾丸中的雌激素产物进行了检测。此外，还使用原位杂交技术研究了脑中芳香化酶mRNA的存在情况。体内注射的放射性标记雄激素底物很容易转化为雌激素，颈静脉血液中的雌激素含量高于颈动脉血液，这表明脑中含有相对较高水平的芳香化酶。此外，体外提供给端脑、卵巢和睾丸组织的放射性标记雄激素会导致放射性标记雌激素的形成。芳香化酶mRNA广泛分布于褐头牛鹂端脑的多个区域，包括海马体、尾内侧新纹状体（包括L区）和带状核。这种神经芳香化酶表达模式与我们之前在斑胸草雀中发现的相似。端脑芳香化酶可能是雀形目鸣禽的特征，其作用可能是为雌激素敏感的神经位点提供局部雌激素信号，和/或影响雄性和雌性鸣禽的外周雌激素水平。
