Watson J T, Robertson J, Sachdev U, Kelley D B
Department of Biological Sciences, Sherman Fairchild Center for the Life Sciences, Columbia University, New York, New York 10027.
J Neurobiol. 1993 Dec;24(12):1615-25. doi: 10.1002/neu.480241206.
In Xenopus laevis, the sexual differentiation of the neuromuscular system responsible for courtship song is controlled by testicular androgen secretion. To explore the sensitivity of this system to androgenic stimulation, male and female frogs were gonadectomized and given testis transplants at seven different developmental stages between the end of metamorphosis and adulthood, grown to sexual maturity, and the laryngeal muscle fibers and motor axons were counted. Muscle fiber and axon numbers in males were not affected by the testicular transplant at any stage. In females, testicular transplants at all developmental stages increased muscle fiber numbers in adulthood. Values attained were, however, significantly less than those of adult intact or testis-transplanted males. Testis transplantation increased laryngeal axon numbers in females to levels equivalent to those of intact males; this effect was obtained at every stage of postmetamorphic development including adulthood. To further explore androgen regulation in adults, males and females were gonadectomized and implanted with silicone tubes containing testosterone propionate for 1.5-3 years and laryngeal muscle fibers and axon numbers compared to those of gonadectomized or sham-operated adult controls. Neither treatment with exogenous androgen nor gonadectomy had any effect on laryngeal muscle fiber or axon number in either males or females; values did not differ from those of sham-operated controls. We conclude that testicular secretions can induce laryngeal muscle fiber and axon addition in females throughout postmetamorphic life. This degree of plasticity, exhibited after the period when adult values are normally attained, stands in contrast to the effects of administration of synthetic androgen and suggests that the degree of plasticity in adult females may be underestimated if exogenous hormones rather than testicular transplants are provided.
在非洲爪蟾中，负责求偶鸣叫的神经肌肉系统的性别分化受睾丸雄激素分泌的控制。为了探究该系统对雄激素刺激的敏感性，在变态末期至成年期之间的七个不同发育阶段，对雄性和雌性青蛙进行性腺切除并进行睾丸移植，待其发育至性成熟后，对喉肌纤维和运动轴突进行计数。在任何阶段，睾丸移植均未影响雄性的肌纤维和轴突数量。在雌性中，所有发育阶段进行睾丸移植均增加了成年期的肌纤维数量。然而，所达到的值显著低于成年未处理或睾丸移植雄性的值。睾丸移植使雌性的喉轴突数量增加至与完整雄性相当的水平；在变态后发育的每个阶段（包括成年期）均获得此效果。为了进一步探究成年期的雄激素调节，对雄性和雌性进行性腺切除并植入含有丙酸睾酮的硅胶管1.5 - 3年，然后将喉肌纤维和轴突数量与性腺切除或假手术成年对照进行比较。外源性雄激素处理和性腺切除对雄性或雌性的喉肌纤维或轴突数量均无任何影响；其值与假手术对照无差异。我们得出结论，睾丸分泌物可在变态后整个生命过程中诱导雌性喉肌纤维和轴突增加。这种在通常达到成年值之后表现出的可塑性程度，与合成雄激素给药的效果形成对比，表明如果提供外源性激素而非睾丸移植，成年雌性的可塑性程度可能被低估。
