Optical analysis of neural activities in the trigeminal nucleus of the rat embryo

我们使用多点光学记录技术研究了大鼠三叉神经核复合体的功能组织及其发育动力学。取E12-E16大鼠胚胎，解剖脑干标本，分别刺激神经(V_1~V_3)的三支。从E13开始检测突触前纤维的动作电位活动。谷氨酸介导的突触后反应从胚胎15开始明显观察到。在E14时，诱发信号通常只由动作电位相关的快成分组成。但去除胞外的镁离子后，出现明显的APV敏感的慢成分。这些结果表明，NMDA(N-甲基-D-天冬氨酸)受体介导的突触后功能早在E14就已经潜伏地产生了。三叉神经三支反应区均有一定的功能体位组织，其中眼(V1)神经区位于内侧，下颌(V3)神经区位于外侧。三叉神经核复合体的中心随着发育而尾移，三叉神经核复合体中神经元/突触功能的活性最强，提示~TdR的功能结构。三叉神经核复合体在胚胎发育过程中不是固定的，而是动态变化的。在电子显微镜研究中，我们没有观察到功能数据和形态信息之间的明显相关性：就我们在EL 6准备中所观察的情况而言，我们无法识别DiI标记的三叉神经末梢和三叉神经核复合体中的神经元之间的典型突触结构。这一结果表明，三叉神经核复合体的突触后功能早于常规突触的形态结构出现。

We examined the functional organization of the rat trigeminal nuclear complex and its developmental dynamics, using a multiple-site optical recording technique. Brainstem preparations were dissected from E12-E16 rat embryos, and stimulation was applied individually to the three branches of the tngerninal nerve (V_1-V_3). The action potential activity of presynaptic fibers was detected from E13. The glutamate-mediated postsynaptic response was observed significantly from E15. At E14, the evoked signals usually consisted of only the action potential-related fast component. However, when extracellular Mg^<2+> removed, significant APV-sensitive slow component appeared. These results suggest that postsynaptic function mediated by NMDA (N-methyl-D-aspartate) receptors is latently generated as early as E14. The response area of the three branches of the trigemmal nerve showed some functional somatotopic organization, with the ophthalmic (V_1) nerve area located medially and the mandibular (V_3) nerve area laterally. The center of the trigeminal nuclear complex, in which the activity of neurons/synaptic function was greatest, shifted caudally with development, suggesting that the functional architecture of ~the. trigeminal nuclear complex is not fixed, but changes dynamically, during embryogenesis. In an electron microscopic study, we could not observe clear correlations between functional data and morphological information: as far as we surveyed in El 6 preparations, we could not identify typical synaptic structures between the DiI-labeled trigemmal nerve terminals and the neurons in the trigeminal nuclear complex. The result implies that postsynaptic function in the trigeminal nuclear complex is generated well before the appearance of the morphological structure of conventional synapses.