Recovery of visual evoked potentials after regeneration of cut retinal ganglion cell axons within the ascending visual pathway in adult rats.

Abstract

PURPOSE: Following optic nerve damage, retinal ganglion cells (RGCs) fail to regenerate their axons and soon undergo apoptosis. However, many RGCs survive axotomy and regenerate lengthy axons after a lens injury (LI). If the cut optic nerve is re-sutured, RGC axons grow into the distal part of the optic nerve and reach their natural targets within the thalamus and midbrain. In this study, we check time-dependence and extent of restoration of flash visual evoked potentials (FVEPs) to examine the functional relevance of the regenerated retinogeniculate pathway. METHODS: The optic nerve in adult rats was cut and re-sutured. The lens was injured transsclerally using a pointed glass capillary. FVEPs were measured starting at the time point of surgery, and then repeatedly up to an age of several months. RESULTS: Detectable FVEPs appeared approximately ten weeks after the surgery, and their amplitudes increased during the next months to reach eventually 15-40% of their values before surgery. CONCLUSIONS: Partial restoration of FVEPs indicates that some regenerating RGC axons have "bridged" the distance between the eye and the central targets forming a functional re-connection of the corresponding RGC with thalamic target neurones to elicit recordable activation of the visual cortex.