Campos Torres A, Vidal P P, de Waele C
Laboratoire de Neurobiologie des Réseaux Sensori-moteurs, ESA 7060, CNRS, Paris VI-Paris VII, France.
Neuroscience. 1999;92(4):1475-90. doi: 10.1016/s0306-4522(99)00078-0.
Following unilateral inner ear lesion, astrocytes undergo hypertrophy in the deafferented vestibular and cochlear nuclei as shown by an increase in the level of glial fibrillary acid. The present study extends our understanding of vestibular and cochlear system plasticity by examining microglial changes in these deafferented nuclei. The microglial reaction was studied 1, 2, 4, 8, 14, 21, 28 and 42 days following the lesion with a monoclonal OX-42 antibody and lectins (Griffonia simplicifolia, B4 isolectin) labelled with horseradish peroxidase or fluorescein. The deafferented nuclei were also examined for apoptotic cells by terminal transferase-mediated nick end labelling of nuclear DNA fragments. In control and sham-operated rats, the distribution of the resting microglial cells was uniform in both the vestibular and cochlear nuclei. In the deafferented vestibular complex, the microglial cells increased in number, became hypertrophied and were distributed in the medial, lateral, superior and inferior vestibular nuclei. Reactive microglial cells were also detected in the ipsilateral cochlear nuclei. Some of the immunostained cells were hypertrophic whereas others presented an ameboid morphology with few short and stout processes. The microglial reaction was confined to the antero- and posteroventral cochlear nuclei. Finally, reactive microglia was also observed in the prepositus hypoglossi ipsilateral to the lesion. The microglial reactions within the prepositus hypoglossi, the vestibular and the cochlear nuclei were detectable as early as one day after the lesion and persisted several weeks in both the vestibular and cochlear nuclei. Apoptotic cells were not detected in the vestibular nuclei at any stage following the lesion. In contrast, terminal deoxynucleotidyl transferase-mediated digoxygenin-11-dUTP nick end labelling-positive cells were first detected in the deafferented cochlear nuclei on the 3rd day following the lesion. They reached an apparent maximum by day 8 and then declined until day 24. Double labelling experiments demonstrate that these cochlear terminal deoxynucleotidyl transferase-mediated digoxygenin-11-dUTP nick end labelling-positive cells were also lectin-positive suggesting that reactive cochlear lectin-positive microglia cells were eliminated by a programmed cell death. Our results establish the two experimental models as reliable tools to understand the role of microglia in adult brain plasticity. The cochlear microglial reaction was probably induced by the degeneration of the acoustic nerve which follows the acoustic ganglion destruction. Interestingly, the same reasoning cannot apply to the vestibular microglial reaction following unilateral labyrinthectomy: the vestibular ganglion was spared and the primary vestibular neurons did not degenerate, at least during the first week following the lesion.
单侧内耳损伤后，星形胶质细胞在去传入神经支配的前庭核和耳蜗核中发生肥大，这可通过胶质纤维酸性蛋白水平的升高得以体现。本研究通过检测这些去传入神经支配核中的小胶质细胞变化，扩展了我们对前庭和耳蜗系统可塑性的认识。在损伤后的第1、2、4、8、14、21、28和42天，使用单克隆OX - 42抗体以及用辣根过氧化物酶或荧光素标记的凝集素（简单型非洲豆蔻凝集素，B4异凝集素）研究小胶质细胞反应。还通过末端转移酶介导的核DNA片段缺口末端标记法检查去传入神经支配核中的凋亡细胞。在对照和假手术大鼠中，静息小胶质细胞在前庭核和耳蜗核中的分布均一。在去传入神经支配后的前庭复合体中，小胶质细胞数量增加、肥大，并分布于内侧、外侧、上和下前庭核。在同侧耳蜗核中也检测到反应性小胶质细胞。一些免疫染色细胞肥大，而另一些呈现阿米巴样形态，具有少量短而粗的突起。小胶质细胞反应局限于前腹侧和后腹侧耳蜗核。最后，在损伤同侧的舌下前置核中也观察到反应性小胶质细胞。舌下前置核、前庭核和耳蜗核内的小胶质细胞反应在损伤后最早1天即可检测到，并在前庭核和耳蜗核中持续数周。在损伤后的任何阶段，前庭核中均未检测到凋亡细胞。相比之下，末端脱氧核苷酸转移酶介导的地高辛 - 11 - dUTP缺口末端标记阳性细胞在损伤后第3天首次在去传入神经支配的耳蜗核中被检测到。它们在第8天达到明显峰值，然后下降直至第24天。双重标记实验表明，这些耳蜗末端脱氧核苷酸转移酶介导的地高辛 - 11 - dUTP缺口末端标记阳性细胞也呈凝集素阳性，提示反应性耳蜗凝集素阳性小胶质细胞通过程序性细胞死亡被清除。我们的结果确立了这两种实验模型作为理解小胶质细胞在成人大脑可塑性中作用的可靠工具。耳蜗小胶质细胞反应可能是由听神经节破坏后听神经的变性所诱导。有趣的是，同样的推理不适用于单侧迷路切除术后的前庭小胶质细胞反应：前庭神经节未受影响，至少在损伤后的第一周内初级前庭神经元未发生变性。
