Nowacek Ari S, Sengelaub Dale R
Department of Psychological and Brain Sciences, Indiana University, Bloomington, 47405, USA.
J Neurobiol. 2006 Aug;66(9):962-76. doi: 10.1002/neu.20274.
The lumbar spinal cord of rats contains the sexually dimorphic, steroid-sensitive spinal nucleus of the bulbocavernosus (SNB). In males, the growth of SNB dendrites is steroid-dependent: dendrites fail to grow after castration, but grow in castrates treated with androgens or estrogens. Blocking estradiol synthesis or estrogen receptors in gonadally intact males attenuates SNB dendritic growth, suggesting that estrogens are required and must be able to act at their receptors to support normal masculine dendritic growth. However, SNB motoneurons do not accumulate estrogens, suggesting that estrogens act indirectly to support SNB dendritic growth. In this experiment, we examined whether local estrogen action in the neuromuscular periphery was involved in the postnatal development of SNB motoneurons. Motoneuron morphology was assessed in gonadally intact and castrated males. Gonadally intact males were left untreated or given either blank or tamoxifen implants sutured to the target musculature, or tamoxifen interscapular implants. Castrated males were left untreated or were given estradiol by muscle or interscapular implants or systemic injection during the period of SNB dendritic growth. At postnatal day 28, when SNB dendritic length is normally maximal, SNB motoneurons were retrogradely labeled with cholera toxin-HRP and reconstructed in three dimensions. While interscapular tamoxifen implants were ineffective, blocking estrogen receptors at the target musculature resulted in attenuation of SNB dendritic growth. In contrast, while interscapular implants of estradiol were ineffective, local treatment with estradiol at the target musculature in castrated males resulted in masculinization of dendritic growth. Thus, estrogens may act by an indirect action in the neuromuscular periphery to support SNB dendritic growth.
大鼠的腰脊髓包含具有性别二态性、对类固醇敏感的球海绵体肌脊髓核（SNB）。在雄性大鼠中，SNB树突的生长依赖于类固醇：去势后树突无法生长，但在接受雄激素或雌激素治疗的去势大鼠中树突会生长。在性腺完整的雄性大鼠中阻断雌二醇合成或雌激素受体可减弱SNB树突的生长，这表明雌激素是必需的，且必须能够作用于其受体以支持正常的雄性树突生长。然而，SNB运动神经元不会积累雌激素，这表明雌激素通过间接作用来支持SNB树突的生长。在本实验中，我们研究了神经肌肉外周局部雌激素作用是否参与SNB运动神经元的出生后发育。评估了性腺完整和去势雄性大鼠的运动神经元形态。性腺完整的雄性大鼠不进行处理，或在目标肌肉组织缝合空白或他莫昔芬植入物，或进行肩胛间他莫昔芬植入。去势雄性大鼠不进行处理，或在SNB树突生长期间通过肌肉或肩胛间植入或全身注射给予雌二醇。在出生后第28天，当SNB树突长度通常达到最大值时，用霍乱毒素 - HRP对SNB运动神经元进行逆行标记并进行三维重建。虽然肩胛间他莫昔芬植入无效，但在目标肌肉组织阻断雌激素受体导致SNB树突生长减弱。相反，虽然肩胛间雌二醇植入无效，但在去势雄性大鼠的目标肌肉组织局部给予雌二醇导致树突生长男性化。因此，雌激素可能通过在神经肌肉外周的间接作用来支持SNB树突的生长。
