Unilateral injury to the adult rat optic nerve causes multiple cellular responses in the contralateral site

This study was undertaken to examine whether unilateral injury to one optic nerve (ON) elicits a response in the microglia, neuroglia and ganglion cells of the retina and ON of the contralateral site as well. Bilateral activation of the transcription factor c-jun could be immunohistochemically detected in the ganglion cell layer 2 days after crush and later. Microglial cells were detected with the activation-specific antibodies MUC 102 and OX-42. They showed an immediate and clear pattern of activation within the contralateral ON and retina, although this response was less pronounced than in the directly lesioned site. Astrocytes and Müller cells showed a typical up-regulation of glial fibrillary acidic protein in the lesioned retina and only focal but virtually no generalized up-regulation in the contralateral eye. Ganglion cells whose axons had been crushed responded with vigorous axonal growth after 2 days in culture, in addition to exhibiting in situ reactions. However, ganglion cells of the contralateral retina responded with a moderate regeneration, too. Growth was less pronounced than in the crushed retina but significantly better than in retinas on untreated animals. The results suggest that unilateral lesion of the optic nerve elicits a defined response in the major cell types of the contralateral retinofugal system. The findings suggest that it is advisable to maintain caution in the use of the contralateral optic nerve and retina as a control in experiments dealing with cellular processes of de- and regeneration.