Kelley D B
J Neurobiol. 1986 May;17(3):231-48. doi: 10.1002/neu.480170307.
South African clawed frogs use sex-specific vocalizations during courtship. In the male, vocalizations are under the control of gonadal androgen. Though females have moderate levels of circulating androgen, they do not give male-typical mate calls. Both muscles of the vocal organ and neurons of the central nervous system (CNS) vocal pathway are sexually dimorphic and androgen-sensitive. Recent studies suggest that the failure of androgen to masculinize adult females results from a male-specific, androgen-regulated developmental program. At metamorphosis the larynx is sexually monomorphic and feminine in morphology, muscle fiber number and androgen receptor content. During the next six months, under the influence of increasing androgen titers and high receptor levels, myoblasts proliferate in the male and muscle fibers increase at an average rate of 100/day. Females have much lower hormone levels, receptor values decline and they display no net addition of fibers. At metamorphosis, both males and females have approximately 4000 muscle fibers. By adulthood, males have eight times the female fiber number. In the CNS, adult laryngeal motor neurons are more numerous with larger somata and dendritic trees in males than in females. Certain connections of neurons in the vocal pathway are also less robust in females. Unlike the periphery, motor neuron number does not appear to be established by androgen-induced proliferation. Our current hypothesis is that androgen acts at the level of laryngeal muscle to produce more muscle fibers and thus provide more target for motor neurons in the male. This process could regulate cell number by ontogenetic cell death. In the CNS, androgen-target neurons become capable of accumulating hormone shortly before metamorphosis. Androgen receptor in laryngeal motor neurons may permit the dendritic growth characteristic of males by increasing sensitivity to afferent stimuli. Such a process could account for the observed differences in CNS vocal "circuitry" in X. laevis and thus behavioral differences between the sexes.
南非爪蟾在求偶过程中会发出特定性别的叫声。对于雄性而言，叫声受性腺雄激素的控制。虽然雌性体内有中等水平的循环雄激素，但它们不会发出雄性特有的求偶叫声。发声器官的肌肉和中枢神经系统（CNS）发声通路的神经元都具有性别二态性且对雄激素敏感。最近的研究表明，雄激素未能使成年雌性雄性化是由于一种雄性特有的、雄激素调节的发育程序。在变态发育时，喉部在形态、肌纤维数量和雄激素受体含量方面呈现出性别单态且为雌性特征。在接下来的六个月里，在雄激素水平升高和受体水平较高的影响下，雄性的成肌细胞增殖，肌纤维以平均每天100条的速度增加。雌性的激素水平低得多，受体值下降，且它们没有肌纤维的净增加。在变态发育时，雄性和雌性都大约有4000条肌纤维。到成年时，雄性的肌纤维数量是雌性的八倍。在中枢神经系统中，成年喉运动神经元在雄性中比在雌性中数量更多，其胞体和树突更大。发声通路中某些神经元的连接在雌性中也不那么稳固。与外周不同，运动神经元的数量似乎不是由雄激素诱导的增殖所决定的。我们目前的假设是，雄激素作用于喉部肌肉水平，产生更多的肌纤维，从而为雄性的运动神经元提供更多的靶点。这个过程可能通过个体发育过程中的细胞死亡来调节细胞数量。在中枢神经系统中，雄激素靶神经元在变态发育前不久开始能够积累激素。喉运动神经元中的雄激素受体可能通过增加对传入刺激的敏感性，使雄性具有典型的树突生长特征。这样一个过程可以解释在非洲爪蟾中枢神经系统发声“回路”中观察到的差异，进而解释两性之间的行为差异。
