Effects of intravitreal injection of a Rho-GTPase inhibitor (BA-210), or CNTF combined with an analogue of cAMP, on the dendritic morphology of regenerating retinal ganglion cells

Purpose: In adult rats, intravitreal injections of the Rho-GTPase inhibitor C3 transferase (BA-210), or a cocktail of recombinant ciliary neurotrophic factor (CNTF) and a cyclic AMP analogue (CPTcAMP), increase retinal ganglion cell (RGC) survival and axonal regeneration. Here we examined whether these treatments also affect the dendritic architecture of regrowing RGCs. Methods: In Fischer F344 rats, one optic nerve was cut and an autologous peripheral nerve graft was sutured onto it. Rats then received intravitreal injections (4 mu l) of saline, BA-210 or CNTF + CPTcAMP four and eleven days after the PN graft surgery. After 5 weeks, regenerating RGCs were retrogradely labelled with fluorogold (FG) and in living wholemounts the dendritic trees of FG labelled RGCs were visualised by intracellular injection of 2% Lucifer Yellow. Results: Injection of BA-210 or CNTF + CPTcAMP resulted in significantly more regenerating RGCs with abnormal dendritic morphologies, including abnormally long looping processes. Compared to saline-injected regenerating controls, RGCs in BA-210 injected eyes had significantly smaller dendritic field areas and sparser dendrites, while in CNTF + CPTcAMP injected eyes there was increased branching of more distal dendrites. Conclusions: While both intraocular treatments enhance RGC axonal regrowth, they also induce significant changes in RGC dendritic morphology. It remains to be determined if such changes alter the function of the regenerating neuronal population.