González-Martínez Tatiana, Germanà Germana P, Monjil Diego F, Silos-Santiago Inmaculada, de Carlos Félix, Germanà Giovanni, Cobo Juan, Vega José A
Departamento de Morfología y Biología Celular, Facultad de Medicina, C/ Julián Clavería, s/n, 33006 Oviedo, Spain.
Brain Res. 2004 Mar 26;1002(1-2):120-8. doi: 10.1016/j.brainres.2004.01.003.
The TrkB-expressing sensory neurons seem to be involved in touch and other discriminative sensibilities. Thus, several slowly and rapidly adapting cutaneous mechanoreceptors, as well as muscle spindles, are reduced or absent in the territory of the trigeminal nerve in functionally TrkB-deficient mice. Whether this also occurs in the cutaneous or muscular territories of dorsal root ganglia has not been analyzed. Here we used immunohistochemistry and transmission-electron microscopy to analyze the impact of a mutation in the gene coding for TrkB on Meissner and Pacinian corpuscles, and muscle spindles. The animals were studied at the post-natal days 15 and 25, because at this time all the mechanoreceptors examined are fully developed. Typical Meissner's corpuscles, displaying S-100 protein immunoreactivity, were found in the digital pads of wild-type and TrkB+/- mice whereas they were absent in the TrkB-/- animals. Regarding Pacinian corpuscles, the mutation in the trkB gene does not alter either the immunohistochemical or the ultrastructural characteristics. Finally, in muscle spindles the arrangement of the intrafusal muscle fibers and nerve fibers was unchanged in the mutated animals. Nevertheless, about 10% of muscle spindles showed increased number of the intrafusal cells (between 6 and 12) and were supplied by more than one large myelinic nerve fiber. The present results strongly suggest that TrkB-expressing sensory neurons in dorsal root ganglia, like those of the trigeminal ganglion, are responsible for the development and maintenance of several rapidly adapting cutaneous mechanoreceptors, i.e. Meissner's corpuscles.
表达TrkB的感觉神经元似乎参与触觉和其他辨别性感觉。因此，在功能上缺乏TrkB的小鼠三叉神经区域，几种慢适应和快适应皮肤机械感受器以及肌梭数量减少或缺失。在背根神经节的皮肤或肌肉区域是否也会出现这种情况尚未进行分析。在这里，我们使用免疫组织化学和透射电子显微镜来分析TrkB编码基因突变对迈斯纳小体、环层小体和肌梭的影响。在出生后第15天和第25天对动物进行研究，因为此时所有检查的机械感受器都已完全发育。在野生型和TrkB+/-小鼠的趾垫中发现了显示S-100蛋白免疫反应性的典型迈斯纳小体，而在TrkB-/-动物中则没有。关于环层小体，trkB基因突变既不改变免疫组织化学特征也不改变超微结构特征。最后，在肌梭中，突变动物的梭内肌纤维和神经纤维的排列没有变化。然而，约10%的肌梭显示梭内细胞数量增加（6至12个之间），并由不止一条大型有髓神经纤维支配。目前的结果强烈表明，背根神经节中表达TrkB的感觉神经元，与三叉神经节中的神经元一样，负责几种快适应皮肤机械感受器即迈斯纳小体的发育和维持。
