Saldanha C J, Schultz J D, London S E, Schlinger B A
Department of Physiological Science, University of California Los Angeles, Los Angeles, CA 90095, USA.
Brain Behav Evol. 2000 Jun;56(1):29-37. doi: 10.1159/000006675.
In oscine passerines, the telencephalon expresses high levels of the estrogen synthetic enzyme aromatase. In contrast, forebrain aromatase is limited to low levels at discrete limbic loci in non-passerines. The function of forebrain aromatase in oscines is unknown, however, estrogen-sensitive elements of the telencephalic song circuit (an oscine characteristic) may be influenced by local aromatization. Very few studies have investigated the neuroendocrine characteristics of sub-oscine passerines. Species of this passerine sub-order are taxonomically similar to oscines, but do not appear to learn how to sing as oscines, and show no evidence of a song circuit. The neural expression of aromatase in these birds is unknown. We asked whether the golden-collared manakin, a sub-oscine, (a) showed evidence of a song circuit, and (b) expressed aromatase in the telencephalon at high levels like the zebra finch (oscine passerine) or at low levels like the quail (non-passerine). Nissl stains and immunocytochemistry for microtubule associated proteins showed no evidence of a song circuit in manakins of either sex, whereas both techniques delineate all song nuclei in the zebra finch. However, biochemical and immunocytochemical measures reveal that in the manakin, several telencephalic loci, including the hippocampus, caudomedial neostriatum, nucleus taeniae, and the lateral neostriatum express aromatase. Assays run in parallel show low to undetectable levels of aromatase in the telencephalon of the quail (nonpasserine) and abundant levels in the zebra finch (oscine passerine), suggesting a dissociation between the presence of a song circuit and forebrain aromatase expression in this sub-oscine. These data suggest that forebrain aromatase may have evolved in sub-oscine songbirds before the evolution of a song circuit and singing behavior in oscines. Alternatively, forebrain aromatase may serve functions distinct from singing behavior.
在鸣禽雀形目鸟类中，端脑表达高水平的雌激素合成酶芳香化酶。相比之下，非雀形目鸟类前脑的芳香化酶仅限于离散边缘位点的低水平表达。然而，鸣禽前脑芳香化酶的功能尚不清楚，端脑鸣唱回路（一种鸣禽特征）的雌激素敏感元件可能会受到局部芳香化作用的影响。很少有研究调查亚鸣禽雀形目鸟类的神经内分泌特征。这个雀形目亚目的物种在分类学上与鸣禽相似，但似乎不会像鸣禽那样学习唱歌，也没有鸣唱回路的证据。这些鸟类中芳香化酶的神经表达情况尚不清楚。我们研究了亚鸣禽金领侏儒鸟是否（a）有鸣唱回路的证据，以及（b）端脑中芳香化酶的表达水平是像斑胸草雀（鸣禽雀形目）那样高，还是像鹌鹑（非雀形目）那样低。尼氏染色和微管相关蛋白的免疫细胞化学检测表明，无论雌雄，侏儒鸟都没有鸣唱回路的证据，而这两种技术都能勾勒出斑胸草雀的所有鸣唱核团。然而，生化和免疫细胞化学检测显示，在侏儒鸟中，包括海马体、尾内侧新纹状体、带状核和外侧新纹状体在内的几个端脑位点表达芳香化酶。同时进行的检测显示，鹌鹑（非雀形目）端脑中的芳香化酶水平低至无法检测，而斑胸草雀（鸣禽雀形目）中的水平丰富，这表明在这种亚鸣禽中，鸣唱回路的存在与前脑芳香化酶表达之间没有关联。这些数据表明，前脑芳香化酶可能在亚鸣禽鸣禽出现鸣唱回路和鸣唱行为之前就已经进化出来了。或者，前脑芳香化酶可能具有与鸣唱行为不同的功能。
