Abstract
The retinal ganglion cells (RGCs) in mammals cannot regrow their axons and become apoptotic after optic nerve lesion. In contrast, fish optic nerve can spontaneously regenerate and finally their visual function can also restore even after axotomy. We determined a correct time schedule of goldfish optic nerve regeneration process using morphological and behavioral parameters. The process was divided into four periods 1) preparation period (0-6 days), ii) axonal elongation and synaptic formation period (1-6 weeks), iii) synaptic reinforcement and refinement period (1.5-4 months) and iv) recovery of visual function period (4-6 months). For screening of interest molecules at early stage, retinal cDNA library was prepared from axotomized goldfish retinas 5 days previously. We obtained several cDNA clones with differential hybridization of normal and injured retinas. Among of them, purpurin and IGF-I mRNAs rapidly increased in goldfish retina 1 or 2 days after axotomy, whereas Na,K-ATPase and transglutaminase (TG) mRNAs increased in the RGCs 10-20 days after axotomy. We conclude that the former involves in the preparation of optic nerve regeneration and the latter involves in the axonal elongation. Actually, IGF-I and TG identified from goldfish regenerating retinas could induce a striking neurite outgrowth from adult rat retina in culture. Thus the fish visual system offers a useful clue for searching for reliable and effective molecules of mammalian CNS regeneration. [J Physiol Sci. 2007;57 Suppl:S29]
