IMMEDIATE-EARLY GENE-EXPRESSION IN AXOTOMIZED AND REGENERATING RETINAL GANGLION-CELLS OF THE ADULT-RAT

To determine if axotomy-induced immediate early gene (IEG) expression accompanies regenerative efforts in central nervous system (CNS) neuro ns, immunohistochemistry using antibodies to c-Jun, JunD, JunB, c-Fos, FosB and Krox-24 proteins was used to examine gene expression in iden tified adult rat retinal ganglion cells (RGCs) under two conditions: ( 1) after axotomy alone, and (2) 1 month after replacement of the optic nerve with an autologous peripheral nerve graft to allow axonal regro wth. Strong RGC c-Jun expression was induced 1 day, but not 3 h, after axotomy in most RGCs and was maintained in surviving cells throughout the 3-week study period. Axotomy also induced a limited number of RGC s to express Krox-24, but only transiently. c-Fos expression was also seen in a limited number of control RGCs, however, it was not induced by axotomy. Nucleolar FosB immunoreactivity in axotomized RGCs persist ed 1 day after axotomy, but was subsequently lost. One month after axo tomy and peripheral nerve graft placement, identified RGCs with regrow n axons showed only nuclear c-Jun and nucleolar FosB expression. These findings support a role for IEG expression in the regeneration proces s of CNS neurons.