Embryogenesis of the central nervous system of the pond snail <i>Lymnaea stagnalis</i> L.: An ultrastructural study

作     者：Nagy, T Elekes, K 

作者机构：Hungarian Acad Sci Balaton Limnol Res Inst Dept Expt Zool H-8237 Tihany Hungary 

出 版 物：《JOURNAL OF NEUROCYTOLOGY》 (脑细胞生物学杂志)

年 卷 期：2000年第29卷第1期

页      面：43-60页

核心收录：

学科分类：0710[理学-生物学] 1001[医学-基础医学(可授医学、理学学位)] 07[理学] 071003[理学-生理学] 

基　　金：Volkswagen-Foundation Hungarian Scientific Research Fund, OTKA, (23472) 

主　　题：中枢神经系统/细胞学 中枢神经系统/胚胎学 神经节 无脊椎动物/细胞学 神经节 无脊椎动物/胚胎学 椎实螺属/胚胎学 显微镜检查 电子 神经元/超微结构 神经毡/超微结构 突触/超微结构 动物 

摘      要：The ultrastructural characteristics of the developing CNS of the pond snail, Lymnaea stagnalis, were investigated, with special attention paid to three specific stages of embryonic development, representing distinctly different phases of both the body morphogenesis and gangliogenesis. These were the 35% (veliger), the 50-55% (metamorphic), and the 75% (post-metamorphic, adult-like) stages of embryonic development. Also, a brief comparison was done with the CNS of hatchlings (100% of embryonic development). During embryogenesis specialized axo-axonic synapses and elements of the glial system, including the ganglionic (neural) sheath, were rarely observed, whereas the frequent occurrence of unspecialized axo-somatic contacts could be demonstrated. Synapse-like axo-axonic connections could be found first in 75% embryos, showing asymmetric vesicle clustering on the presynaptic side and increased electron density of the apposed membranes. These phenomena may reflect the dominance of modulatory processes in the CNS during embryogenesis, and the absence of the neural sheath may facilitate trophic and/or hormonal influences within the developing ganglia. The gradual increase in the size of ganglia and the diameter of their neuropils was not accompanied by any widening of the cell body layer or increasing diameter of the nerve cell bodies until the very end of embryogenesis. With respect to the ultrastructural organization of the neuropil, and possibly the entire CNS, a determining stage seems to be that of metamorphosis. Two types of neuropil could be observed at this time;the metamorphosing neuropil with an irregular organization of wavy axon profiles, and well-structured neuropil with a regular organization of axon profiles. Ganglia with irregular or regular neuropil occurred simultaneously in the developing CNS.