Monsma S A, Booker R
Section of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853, USA.
J Comp Neurol. 1996 Mar 25;367(1):21-35. doi: 10.1002/(SICI)1096-9861(19960325)367:1<21::AID-CNE3>3.0.CO;2-L.
We have examined factors affecting neuronal proliferation and cell death during development of the adult outer optic ganglia in the moth Manduca sexta. The role of retinal afferents was addressed by optic nerve section on the first day of pupation, when the retina is only partially formed. Deafferentation by optic nerve section resulted in increased levels of cell death in the medulla cortex but did not affect medulla precursor proliferation. Conversely, division of lamina ganglion mother cells ceased following deafferentation, whereas cell death in the lamina cortex did not increase significantly. Implantation of isolated outer optic anlage into host animals demonstrated that medulla precursor proliferation was independent of centripetal inputs and retinal afferents. The role of developmental hormones in regulating outer optic ganglia development was also investigated. Many events in medulla and lamina development are correlated with changes in the titers of the ecdysteroids, and these events could be prevented by application of a juvenile hormone mimic (JHM). Application of JHM early in the fifth (final) larval instar terminated medulla precursor proliferation and prevented the initiation of lamina precursor proliferation, but application late in the fifth instar (after the commitment peak of ecdysteroids) had little effect on proliferation. Application of JHM on the third or fourth day of pupal life prolonged precursor proliferation and delayed degeneration of the outer optic anlage. Precocious application of 20-hydroxyecdysone on the first day of pupal life accelerated outer optic anlage degeneration but did not cause premature termination of proliferation.
我们研究了影响烟草天蛾成虫外视神经节发育过程中神经元增殖和细胞死亡的因素。在化蛹第一天，当视网膜仅部分形成时，通过切断视神经来探讨视网膜传入神经的作用。切断视神经导致髓质皮质中的细胞死亡水平增加，但不影响髓质前体细胞的增殖。相反，切断传入神经后，板层神经节母细胞的分裂停止，而板层皮质中的细胞死亡并未显著增加。将分离的外视神经原基植入宿主动物表明，髓质前体细胞的增殖独立于向心输入和视网膜传入神经。我们还研究了发育激素在调节外视神经节发育中的作用。髓质和板层发育中的许多事件与蜕皮甾体滴度的变化相关，并且这些事件可以通过应用保幼激素类似物（JHM）来预防。在第五（最后）龄幼虫早期应用JHM可终止髓质前体细胞的增殖并阻止板层前体细胞增殖的启动，但在第五龄后期（蜕皮甾体的峰值期之后）应用对增殖几乎没有影响。在化蛹后的第三天或第四天应用JHM可延长前体细胞的增殖并延迟外视神经原基的退化。在化蛹第一天过早应用20-羟基蜕皮酮可加速外视神经原基的退化，但不会导致增殖过早终止。
