Roberts Todd F, Wild J Martin, Kubke M Fabiana, Mooney Richard
Department of Neurobiology, Duke University Medical Center, Durham North Carolina 27710, USA.
J Comp Neurol. 2007 May 1;502(1):157-69. doi: 10.1002/cne.21310.
Sex differences in behavioral repertoires are often reflected in the underlying electrophysiological and morphological properties of motor neurons. Male zebra finches produce long, spectrally complex, learned songs and short calls, whereas female finches only produce short, innate, and spectrally simple calls. In both sexes, vocalizations are produced by using syringeal muscles controlled by motoneurons within the tracheosyringeal part of the hypoglossal motor nucleus (XIIts). We asked whether the sexually dimorphic vocal repertoire of adult zebra finches is paralleled by structural and functional differences in syringeal motoneurons. By using immunohistochemical and intracellular staining methods, we describe sex differences in the morphology of XIIts and its surrounding neuropil (suprahypoglossal region; SH). Although the overall number of XIIts neurons and the proportions of somata/neuropil were not sexually dimorphic, the volumes of both XIIts and SH were larger in males, in part because male XIIts neurons had larger somata. In contrast, female XIIts motoneurons had a more complex dendritic structure than did male neurons, suggesting that the larger volume of the male XIIts is due in part to increased numbers of afferents. Intracellular recordings in brain slices revealed that the intrinsic electrophysiological properties of female XIIts neurons were similar to published values for male XIIts motoneurons. We also show that female neurons received glycinergic inputs from the brainstem respiratory premotor column, similar to those described in males. These findings indicate that male and female zebra finches produce their disparate vocal repertoires using physiologically similar motoneurons. Thus, sites upstream of the motoneuron pool may be the major determinants of sexually dimorphic vocal behaviors in this species.
行为模式中的性别差异通常反映在运动神经元潜在的电生理和形态学特性上。雄性斑胸草雀会发出长而频谱复杂的习得歌声和短叫声，而雌性草雀只发出短的、天生的且频谱简单的叫声。在两性中，发声都是通过使用由舌下运动核气管鸣管部分（XIIts）内的运动神经元控制的鸣管肌肉来实现的。我们询问成年斑胸草雀的性别二态性发声模式是否与鸣管运动神经元的结构和功能差异相对应。通过使用免疫组织化学和细胞内染色方法，我们描述了XIIts及其周围神经毡（舌下上区域；SH）形态上的性别差异。尽管XIIts神经元的总数以及胞体/神经毡的比例没有性别二态性，但雄性的XIIts和SH的体积都更大，部分原因是雄性XIIts神经元的胞体更大。相比之下，雌性XIIts运动神经元的树突结构比雄性神经元更复杂，这表明雄性XIIts体积较大部分是由于传入神经元数量增加。脑片内的细胞内记录显示，雌性XIIts神经元的内在电生理特性与已发表的雄性XIIts运动神经元的值相似。我们还表明，雌性神经元从脑干呼吸运动前柱接受甘氨酸能输入，这与雄性中描述的情况类似。这些发现表明，雄性和雌性斑胸草雀使用生理上相似的运动神经元产生不同的发声模式。因此，运动神经元池上游的部位可能是该物种性别二态性发声行为的主要决定因素。
