Tobias M L, Kelley D B
Department of Biological Sciences, Columbia University, New York, New York, USA.
J Neurobiol. 1995 Dec;28(4):515-26. doi: 10.1002/neu.480280411.
In Xenopus laevis frogs, sex differences in adult laryngeal synapses contribute to sex differences in vocal behavior. This study explores the development of sex differences in types of neuromuscular synapses and the development and hormone regulation of sex differences in transmitter release. Synapses in the juvenile larynx have characteristics not found in adults: juvenile muscle fibers can produce subthreshold or suprathreshold potentials in response to the same strength of nerve stimulation and can also produce multiple spikes to a single nerve stimulus. Juvenile laryngeal muscle also contains the same synapse types (I, II, and III) as are found in adult laryngeal muscle. The distribution of laryngeal synapse types in juveniles is less sexually dimorphic than the distribution in adults. Analysis of quantal content indicates that laryngeal synapses characteristically release low amounts of transmitter prior to sexual differentiation. Quantal content values from male and female juveniles are similar to values for adult males and are lower than values for adult females. When juveniles are gonadectomized and treated with exogenous estrogen, quantal content values increase significantly, suggesting that this hormone may increase transmitter release at laryngeal synapses during development. Gonadectomy alone does not affect quantal content of laryngeal synapses in either sex. Androgen treatment decreases quantal content in juvenile females but not males; the effect is opposite to and smaller than that of estrogen. Thus, muscle fiber responses to nerve stimulation and transmitter release are not sexually dimorphic in juvenile larynges. Transmitter release is strengthened, or feminized, by the administration of estradiol, an ovarian steroid hormone.
在非洲爪蟾中，成年喉突触的性别差异导致了发声行为的性别差异。本研究探讨了神经肌肉突触类型性别差异的发育过程，以及递质释放性别差异的发育和激素调节。幼体喉部的突触具有一些在成体中未发现的特征：幼体肌纤维对相同强度的神经刺激可产生阈下或阈上电位，并且对单个神经刺激也可产生多个动作电位。幼体喉肌也含有与成体喉肌相同的突触类型（I型、II型和III型）。幼体喉突触类型的分布比成体的性别二态性更小。量子含量分析表明，在性别分化之前，喉突触通常释放少量递质。雄性和雌性幼体的量子含量值与成年雄性的值相似，且低于成年雌性的值。当幼体被性腺切除并用外源性雌激素处理时，量子含量值显著增加，这表明这种激素可能在发育过程中增加喉突触处的递质释放。单独的性腺切除术对两性喉突触的量子含量均无影响。雄激素处理可降低雌性幼体而非雄性幼体的量子含量；其作用与雌激素相反且小于雌激素。因此，幼体喉部肌纤维对神经刺激的反应和递质释放不存在性别二态性。通过给予卵巢甾体激素雌二醇，递质释放会增强或呈现女性化特征。
