Recovery of vision in regeneration of goldfish optic axons: Enhancement of axonal outgrowth by a conditioning lesion

Abstract

Visual recovery in goldfish after lesions of the optic axons was determined by measuring the times required for reappearance of the startle reaction to sudden illumination, the dorsal light reflex, and food localization. The recovery time for the startle reaction (which showed a normal mean value of 14 to 21 days after optic nerve crush in various experiments) was less when the time required for axonal outgrowth was accelerated by means of a prior (“conditioning”) lesion. From the results of these experiments it was deduced that (a) the normal rate of outgrowth of the axons involved in the initial appearance of the startle reaction was 0.5 mm per day; (b) the acceleration of outgrowth resulting from the conditioning lesion was most pronounced when the interval between conditioning and testing lesions was 14 days; and (c) the conditioning lesion effect was already manifest by 2 days after the conditioning lesion. The time for recovery of the dorsal light reflex (with a normal mean value of 20 to 31 days after optic nerve crush) changed somewhat with axonal outgrowth time, but not as markedly as the recovery time for the startle reaction. The recovery time for food localization (with a normal mean of 34 to 42 days after optic nerve crush) showed no systematic change when the time for axonal outgrowth was varied. To explain these results, we postulate that the recovery time is limited by a fixed interval, the “recovery lag”, which is different for each of the three responses examined. It seems likely that the recovery lag in each case reflects a process occurring in the retinal ganglion cells, and that the differences in recovery lag for the three responses indicate that the three retinal ganglion cell populations involved have different recovery characteristics.