Department of Biology & Neuroscience Program, Hope College, Holland, MI 49423, USA.
Gen Comp Endocrinol. 2010 Mar 1;166(1):66-71. doi: 10.1016/j.ygcen.2009.08.001. Epub 2009 Aug 15.
In songbirds, neurons that regulate learned song behavior undergo extensive seasonal plasticity in their number and size in relation to the bird's reproductive status. Seasonal plasticity of these brain regions is primarily regulated by changes in circulating concentrations of testosterone. Androgen receptors are present in all of the major song nuclei, but it is unknown whether levels of androgen receptor mRNA in the telencephalic song regions HVC, the robust nucleus of the arcopallium, and the lateral magnocellular nucleus of the anterior nidopallium change as a function of season in white-crowned sparrows. To determine whether seasonal changes in levels of androgen receptor mRNA are specific to the song control system, we also measured levels of androgen receptor mRNA in a limbic nucleus, the lateral division of the bed nucleus of the stria terminalis (the lateral division of the bed nucleus of the stria terminalis). We found that levels of androgen receptor mRNA were higher in HVC and the lateral division of the bed nucleus of the stria terminalis of birds in the breeding condition compared with the nonbreeding condition; however, we observed no seasonal differences in levels of androgen receptor mRNA in either the robust nucleus of the arcopallium or the lateral magnocellular nucleus of the anterior nidopallium. These results are consistent with previous observations that seasonal plasticity of the song nuclei results from testosterone acting directly on HVC, which then exerts transsynaptic trophic effects on its efferent targets. The seasonal change in the expression of androgen receptor in HVC may be one component of the cellular mechanisms underlying androgenic effects on seasonal plasticity of the song control nuclei.
在鸣禽中，与鸟类繁殖状态相关的调节习得鸣唱行为的神经元在数量和大小上经历了广泛的季节性变化。这些脑区的季节性变化主要受循环睾丸激素浓度变化的调节。雄激素受体存在于所有主要的鸣唱核中，但尚不清楚在白头翁的 Telencephalic 鸣唱区 HVC、arcopallium 的粗壮核和前 nidopallium 的外侧大细胞核中，雄激素受体 mRNA 的水平是否会随着季节的变化而变化。为了确定雄激素受体 mRNA 水平的季节性变化是否是特定于鸣唱控制系统的，我们还测量了边缘核、终纹床核的外侧部（终纹床核的外侧部）中的雄激素受体 mRNA 水平。我们发现，繁殖期鸟类的 HVC 和终纹床核的外侧部中的雄激素受体 mRNA 水平高于非繁殖期；然而，我们在 arcopallium 的粗壮核或前 nidopallium 的外侧大细胞核中均未观察到雄激素受体 mRNA 水平的季节性差异。这些结果与先前的观察结果一致，即鸣唱核的季节性变化是由睾丸激素直接作用于 HVC 引起的，HVC 然后对其传出靶标发挥突触前营养作用。HVC 中雄激素受体表达的季节性变化可能是雄激素对鸣唱控制核季节性可塑性的细胞机制的一个组成部分。
