Visual functional and histopathological correlation in experimental autoimmune optic neuritis

To elucidate the correlation between visual threshold of optokinetic tracking (OKT), visual evoked potential (VEP), and histopathology at different time points after induction of experimental autoimmune optic neuritis (EAON). EAON was induced in C57BL/6 mice by subcutaneous immunization with an emulsified mixture of myelin oligodendrocyte glycoprotein (MOG)(35-55) peptide. OKT and VEP were measured on days 7, 14, 21, 28, and 42 postimmunization. After VEP measurements, the mice were killed and their eyes were enucleated for histopathological studies. Immunohistochemical staining was performed using cell-specific markers for characterization of cells in the optic nerve: CD3 (T cells), Iba-1 (microglia), MBP (myelin basic protein), and neurofilament (axons). Functionally, OKT threshold decreased as early as day 7, and VEP latency was significantly prolonged on day 21. Axon degeneration was observed as early as day 14. Activated microglia infiltration was also observed on day 14, before T cell infiltration, which peaked on day 21. Demyelination, confirmed by MBP staining, was observed on day 21. Microglial infiltration in the optic nerve coincided with decline in OKT threshold and preceded VEP latency prolongation, while VEP latency prolongation coincided with T cell infiltration and demyelination of the optic nerve. These findings may contribute to understanding of the pathophysiology of optic neuritis and future development of more effective therapeutic strategy for refractory optic neuritis.