Brenowitz Eliot A
Department of Psychology, Virginia Merrill Bloedel Hearing Research Center, University of Washington, Seattle, WA 98195-1525, USA.
Ann N Y Acad Sci. 2004 Jun;1016:560-85. doi: 10.1196/annals.1298.006.
There is extensive plasticity of the song behavior of birds and the neuroendocrine circuit that regulates this behavior in adulthood. One of the most pronounced examples of plasticity, found in every species of seasonally breeding bird examined, is the occurrence of large seasonal changes in the size of song control nuclei and in their cellular attributes. This seasonal plasticity of the song circuits is primarily regulated by changes in the secretion and metabolism of gonadal testosterone (T). Both androgenic and estrogenic sex steroids contribute to seasonal growth of the song system. These steroids act directly on the forebrain song nucleus HVC, which then stimulates growth of its efferent target nuclei transsynaptically. Seasonal growth and regression of the song circuits occur rapidly and sequentially following changes in circulating T and its metabolites. As the neural song circuits change across seasons, there are changes in different aspects of song behavior, including the structural stereotypy of songs, their duration, and the rate of production. The burden of evidence supports a model in which changes in song behavior are a consequence rather than a cause of the changes in the song circuits of the brain. Seasonal plasticity of the song system may have evolved as an adaptation to reduce the energetic demands imposed by these regions of the brain outside the breeding season, when the use of song for mate attraction and territorial defense is reduced or absent. The synaptic plasticity that accompanies seasonal changes in the song system may have acted as a preadaptation that enabled the evolution of adult song learning in some species of birds.
鸟类的鸣叫行为及其在成年期调节这种行为的神经内分泌回路具有广泛的可塑性。在每一种被研究的季节性繁殖鸟类中都发现了可塑性最显著的例子之一，即鸣叫控制核团的大小及其细胞属性会发生巨大的季节性变化。鸣叫回路的这种季节性可塑性主要受性腺睾酮（T）分泌和代谢变化的调节。雄激素和雌激素性类固醇都有助于鸣叫系统的季节性生长。这些类固醇直接作用于前脑鸣叫核团HVC，然后通过跨突触刺激其传出靶核的生长。随着循环中的T及其代谢产物的变化，鸣叫回路的季节性生长和退化迅速且依次发生。随着神经鸣叫回路随季节变化，鸣叫行为的不同方面也会发生变化，包括鸣叫的结构刻板性、时长和产生速率。证据支持这样一种模型，即鸣叫行为的变化是大脑鸣叫回路变化的结果而非原因。鸣叫系统的季节性可塑性可能是作为一种适应进化而来的，以减少在繁殖季节之外大脑这些区域所施加的能量需求，此时用于吸引配偶和保卫领地的鸣叫减少或不存在。鸣叫系统中伴随季节性变化的突触可塑性可能起到了一种预适应的作用，使得某些鸟类物种能够进化出成年期鸣叫学习能力。
