Gahr Manfred
Department of Developmental and Behavioural Neuroscience, Institute of Neuroscience, Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, 1087 De Boelelaan, 1081 HV Amsterdam, The Netherlands.
Ann N Y Acad Sci. 2004 Jun;1016:684-703. doi: 10.1196/annals.1298.025.
The sexual quality of adult song is the result of genetic and epigenetic mechanisms shaping the neural song system throughout life. Genetic brain-intrinsic mechanisms determine the neuron pools that develop into forebrain song control areas independent of gonadal steroid hormones, androgens and estrogens. One fate of these neurons is the potential to express sex steroid receptors, such as androgen and estrogen receptors. Genetic brain-intrinsic mechanisms, too, determine the activity of hypothalamic-pituitary-gonad (HPG) axis, i.e., the working range and responsiveness of HPG axis to produce gonadal hormones. The epigenetic action of gonadal steroid hormones (androgens and estrogens) on determined vocal neurons is required to maintain and increase the pool of determined vocal neurons and to complete the connections of the vocal system, i.e., to make it function motorically. The subsequent influence of environmental information, including both external (socio-sexual and physical) and internal (body physiology) signals, specify the further neural phenotype of vocal areas either through acting on the HPG axis and differential release of gonadal hormones or through non-gonadal hormone systems, both of which have target neurons in the functional vocal system. Despite the clear evidence of hormone dependency of the development of both the adult song phenotype and song system phenotype, their causal relation is complex.
成年鸣唱的性别特征是遗传和表观遗传机制在整个生命过程中塑造神经鸣唱系统的结果。大脑内在的遗传机制决定了神经元群，这些神经元群发育成前脑鸣唱控制区域，独立于性腺类固醇激素、雄激素和雌激素。这些神经元的一个命运是有表达性类固醇受体的潜力，如雄激素和雌激素受体。大脑内在的遗传机制也决定了下丘脑-垂体-性腺（HPG）轴的活性，即HPG轴产生性腺激素的工作范围和反应性。性腺类固醇激素（雄激素和雌激素）对已确定的发声神经元的表观遗传作用，对于维持和增加已确定的发声神经元池以及完成发声系统的连接是必需的，即使其在运动方面发挥功能。随后环境信息的影响，包括外部（社会性别和物理）和内部（身体生理）信号，通过作用于HPG轴和性腺激素的差异释放，或通过非性腺激素系统，进一步确定发声区域的神经表型，这两种系统在功能性发声系统中都有靶神经元。尽管有明确证据表明成年鸣唱表型和鸣唱系统表型的发育依赖于激素，但其因果关系很复杂。
