Effect of unilateral enucleation on protein and ribonucleic acid metabolism of avian brain

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The metabolic activity of brain regions at various times after unilateral eye removal has been studied in the chick where the visual pathways are totally crossed over. Protein and ribonucleic acid from cerebral hemispheres and optic lobes were assayed for radioactivity following subcutaneous injection of tritiated leucine or uridine. Cerebral hemispheres and optic lobes contralateral to the extirpated eye showed a reduction of protein and RNA synthetic rate relative to the paired ipsilateral regions. Some of these differential effects were observed in animals as early as 1 hr after enucleation and persisted during the ensuing 17 days. Results were of similar magnitude both in the optic lobes which are directly innervated by the optic nerve and in the cerebral hemispheres which receive little or no direct innervation from the optic tract. The decay rates of protein or ribonucleic acid were unaltered in the paired regions from unilaterally enucleated birds. The results suggest that rapid metabolic alterations subsequent to eye removal are not confined to directly denervated regions. A significant fall in the rate of RNA synthesis is the earliest effect noted; subsequent effects may thus be a reflection of alterations of RNA transcription at the genetic level.