Behavioral tests of compression of retinotectal projection after partial tectal ablation in goldfish

Abstract

The course of functional recovery of vision during the compression of the retinotectal projection that follows hemitectal ablations was mapped by behavioral methods in goldfish ( Carassius auratus). Differential suppression of respiration to red or green stimuli was used as a behavioral measure. Results show that vision was restored throughout the temporal half-field, originally blinded by tectal lesion, within 84 to 112 days of surgery. The scotoma diminished in an orderly fashion, starting from the central edge and progressing caudalward. Color discriminability was concomitant with visual recovery. The return of color vision indicates prespecification of retinal and tectal cells for color and selective reconnection of neurons according to their specificities. Functional topographic reorganization of the retinotectal projection implies that locus-specific affinities between retinal and tectal neurons, which may play a prominent role in the direction of nerve growth and formation of synapses under more normal circumstances, are not permanently fixed even in mature goldfish and may yield to compensatory developmental pressures created by the size disparity.