Ringstedt T, Copray S, Walro J, Kucera J
Laboratory of Molecular Neurobiology, Department of Neuroscience, Karolinska Institute, Stockholm, Sweden.
Brain Res Dev Brain Res. 1998 Dec 7;111(2):295-300. doi: 10.1016/s0165-3806(98)00146-1.
Fusimotor neurons, group Ia afferents and muscle spindles are absent in mutant mice lacking the gene for neurotrophin-3 (NT3). To partition the effect of Ia afferent or spindle absence from that of NT3 deprivation on fusimotor neuron development, we examined the fusimotor system in a mutant mouse (NesPIXpNT3) that lacks Ia afferents and spindles, but has normal or elevated tissue levels of NT3 during embryogenesis. Fusimotor fibers were absent in lumbar ventral spinal roots, and limb muscles were devoid of Ia afferents and spindles in adult NesPIXpNT3 mice. In contrast, no deficiency in motoneuron numbers was observed in the trigeminal nucleus which contains cell bodies of motor axons innervating muscles of mastication. Spindles and Ia afferents were also present in the masticatory muscles. Thus, the development and/or survival of fusimotor neurons correlates with the presence of Ia afferents and/or spindles, and not with the amount of NT3 in the spinal cord or muscle.
缺乏神经营养因子-3（NT3）基因的突变小鼠中不存在肌梭运动神经元、Ia类传入神经和肌梭。为了区分Ia类传入神经或肌梭缺失对肌梭运动神经元发育的影响与NT3缺乏的影响，我们研究了一种突变小鼠（NesPIXpNT3）的肌梭运动系统，该小鼠缺乏Ia类传入神经和肌梭，但在胚胎发育过程中NT3的组织水平正常或升高。成年NesPIXpNT3小鼠的腰段腹侧脊髓神经根中没有肌梭运动纤维，肢体肌肉中没有Ia类传入神经和肌梭。相比之下，在支配咀嚼肌的运动轴突细胞体所在的三叉神经核中，未观察到运动神经元数量的减少。咀嚼肌中也存在肌梭和Ia类传入神经。因此，肌梭运动神经元的发育和/或存活与Ia类传入神经和/或肌梭的存在相关，而与脊髓或肌肉中NT3的含量无关。
