Experience-dependent plasticity and vision restoration in rats after optic nerve crush

Within the first weeks after brain damage the visual system can spontaneously recover, but it is not known if visual experience plays a role in this process. Therefore, we studied the role of visual experience during recovery by exposing rats to normal, enriched, and impoverished visual conditions. Adult rats, which had learned a six-choice brightness discrimination task, received bilateral partial optic nerve crush (ONC), and were then exposed daily for 34 days to either (1) total darkness, (2) a standard 12-h light:12-h dark cycle, or (3) a 2-h selective visual enrichment. The percentage of correct choices and the maximal performance levels reached were used as recovery end-points. Retinal ganglion cell (RGC) morphology was evaluated following retrograde transport of fluorescent tracer with in vivo confocal neuroimaging (ICON) before and after ONC. Whereas rats kept under normal daylight conditions after ONC recovered their visual functions rather well, rats housed in complete darkness did not recover at all. However, only 2 h of daily exposure to visual enrichment induced significantly enhanced recovery, which was even faster than that seen in rats housed under normal daylight conditions. RGC soma size changes were observed after ONC, but they did not correlate with any measures of behavioral recovery. We conclude that visual experience, even if provided for short daily periods, is a critical factor determining the dynamics of early phases of recovery.