Restoration of visual function following optic nerve regeneration in bluegill (Lepomis macrochirus) × pumpkinseed (Lepomis gibbosus) hybrid sunfish

Abstract

Simple (dorsal light reflex) and complex (predator-prey interactions) visually mediated behaviors were used concurrently with morphological examination to assess restoration of visual function following optic nerve crush in bluegill (Lepomis macrochirus) × pumpkinseed (Lepomis gibbosus) hybrid sunfish. Regenerating optic nerve axons projected into thestratum opticum-stratum fibrosum et griseum superficialeby week 2, thestratum griseum centraleby week 4, andstratum album centraleby week 6. Initial projections into the laminae were diffuse and less stratified compared to controls. By week 12, the projection pattern of regenerating nerve fibers closely resembled the innervation of normal tecta. Visual improvements were correlated with increasing projections into the tectum. The dorsal light reflex improved from a 45° vertical deviation following nerve crush to 4.5° by week 16. Initial predator-prey interactions were exclusively mediated by the control eye. As regeneration progressed, there was a gradual expansion of the visual field. The reaction distance and attack angles within the visual field of the experimental eye were initially less than controls, however, these differences disappeared by week 10. Improvements in visual function were closely correlated with an increase of regenerating ganglion cell axons into the optic tectum indicating sufficient synaptogenesis to mediate both simple and complex visual behavior.