CHIASMATIC SPECIFICITY IN THE REGENERATING MAMMALIAN OPTIC-NERVE

The mammalian central nervous system is capable of regenerating; howev er, there is no evidence that the regenerating axons can navigate alon g their normal pathways and reestablish topographically organized proj ections: essential for functional return of vision. Here retinal gangl ion cells in the opossum Monodelphis were birthdated with tritiated th ymidine on the sixth postnatal day (P6), before being lesioned in the temporal retina at P8. Retrograde tracing with horse-radish peroxidase injected into the ipsilateral optic tract at P24 showed that the temp oral crescent had reformed behind the retinal lesion. By comparisons o f cell and thymidine counts from lesioned and control regions of retin a, it was estimated that about 40% of the normal number of ganglion ce lls are able to regenerate into the ipsilateral optic tract following a lesion in the temporal retina at P8. A clear line of decussation (se paration of ipsilateral and contralateral projections) reformed in the lesioned temporal retina and regenerating ganglion cells labeled with DiI were turned at appropriate points on passing through the optic ch iasm. This is evidence of chiasmatic specificity with regard to lesion ed retinal ganglion cells regenerating into the ipsilateral optic trac t. (C) 1997 Academic Press.