Vischer H A, Lannoo M J, Heiligenberg W
Neurobiology Unit, Scripps Institution of Oceanography, University of California at San Diego, La Jolla 92093.
J Comp Neurol. 1989 Dec 1;290(1):16-40. doi: 10.1002/cne.902900103.
The nerves of the anterior lateral line system in embryonic and larval stages of the weakly electric gymnotiform fish Eigenmannia were visualized by injection of the fluorescent marker DiI into the primordium of the anterior (ALLN) and posterior (PLLN) lateral line nerves. Examination of developmental series reveals that the nerve fibers that innervate the electrosensory and mechanosensory components of the anterior lateral line system are present before the first mechanoreceptors and electroreceptors have differentiated. This suggests that nerve fibers might induce the formation of lateral line receptors. Whereas the innervation of the mechanoreceptive system is already established at an early stage, the afferent innervation of electroreceptors continues to arborize in the periphery, presumably by following pioneer axon pathways. The earliest recognizable stage of the anterior lateral line nerve ganglion (ALLNG) is evident 2 days after spawning. The ganglion shows two germinal cell masses that develop into the supraorbital-infraorbital and the hyomandibular placodes. The supraorbital-infraorbital placode forms the dorsal part of the ALLNG; the hyomandibular placode forms the ventral part of the ALLNG. Counts of ALLNG cells in embryonic, larval, and adult stages of Eigenmannia show that, at each stage examined, the number of ganglion cells is always significantly larger than the number of mechanoreceptors and electroreceptor units in the periphery. During development, the distribution of ALLNG cell diameters shifts from a unimodal distribution in juveniles to a bimodal distribution in adults, peaking at 8 microns and 18 microns. These results suggest that tuberous electroreceptive organs, which are innervated by the large ALLNG cells, may not be functional prior to day 18. Our results further suggest that the number of ALLNG cells correlates with the rate of induction of lateral line receptors in the periphery.
通过将荧光标记物DiI注入弱电裸背电鳗前侧线神经（ALLN）和后侧线神经（PLLN）的原基，观察了裸背电鳗胚胎期和幼体期前侧线系统的神经。对发育序列的检查表明，在前侧线系统的电感受和机械感受成分的第一批机械感受器和电感受器分化之前，支配它们的神经纤维就已经存在。这表明神经纤维可能诱导侧线感受器的形成。虽然机械感受系统的神经支配在早期就已建立，但电感受器的传入神经支配在周围继续分支，大概是沿着先驱轴突路径进行的。前侧线神经节（ALLNG）最早可识别的阶段在产卵后2天就很明显。神经节显示出两个生发细胞团，它们发育成眶上-眶下板和舌颌板。眶上-眶下板形成ALLNG的背侧部分；舌颌板形成ALLNG的腹侧部分。对裸背电鳗胚胎期、幼体期和成体期ALLNG细胞的计数表明，在每个检查阶段，神经节细胞的数量总是显著多于周围的机械感受器和电感受器单位的数量。在发育过程中，ALLNG细胞直径的分布从幼体的单峰分布转变为成体的双峰分布，峰值分别在8微米和18微米。这些结果表明，由大型ALLNG细胞支配的结节状电感受器官在第18天之前可能没有功能。我们的结果进一步表明，ALLNG细胞的数量与周围侧线感受器的诱导率相关。
