SURVIVAL OF GANGLION-CELLS WHICH FORM THE RETINO-RETINAL PROJECTION DURING OPTIC-NERVE REGENERATION IN THE FROG

During optic nerve regeneration in the frog, axons transiently grow al ong the opposite optic nerve forming a retino-retinal projection. In t he present study, we crushed the left optic nerve in the frog Litoria (Hyla) moorei and later applied horseradish peroxidase (HRP) or diamid ino yellow (DY) to the right optic nerve. In one series, retinae were examined 3 days after application of the tracer. The retino-retinal pr ojection was found to be maximal at 5 weeks, fell significantly by 7 w eeks, and returned to close-to-normal levels by 24 weeks. In a second series, we applied DY at 5 weeks as before but did not sacrifice the f rogs until 7 weeks. Numbers of labeled ganglion cells were not signifi cantly different from those frogs in the first series labeled and exam ined at 5 weeks. We conclude that ganglion cells giving rise to the re tino-retinal projection had not died in appreciable numbers, presumabl y being sustained by collateral axons in the brain.