Quantitative electrophysiological studies of regenerating visuotopic maps in goldfish—II. Delayed recovery of sensitivity to small light flashes

Abstract

The regenerating retinotectal projection of goldfish was mapped with punctate flashes of light produced by red light-emitting diodes. The characteristics of multiunit receptive fields were studied in fish kept at 25°C at different times after unilateral optic nerve crush. From about 20 days, when the first visually-evoked responses to black-on-white stimuli appeared, until about 40 days, no consistent responses to light-emitting diodes could be obtained, although high-contrast, long-duration light-emitting diode stimuli elicited weak off-responding. At around 40 days, responses to light-emitting diodes reappeared as the amplitude of evoked multiunit activity increased sharply. At their emergence, light-emitting diode-sensitive multiunit receptive fields were irregular and only slightly enlarged, but quickly regained normal shape and size. Conformity to a linear and uniform visuotopography recovered more slowly and, in some individuals, incompletely. The results suggest that “on” and “off” optic fiber systems, probably with small terminal arbors, are functionally expressed at a later time in regeneration than the predominantly “off” system manifested earlier. The different time courses of recovery in these systems explain several aspects of the recovery of visual behavior during optic nerve regeneration.