35. Visual evoked potentials and MRI in monitoring optic nerve involvement in a relapsing remitting model of EAE

Abstract

Experimental Autoimmune Encephalomyelitis (EAE) is a pre-clinical disease model of Multiple Sclerosis (MS), traditionally induced by injecting Myelin Oligodendrocyte Glycoprotein(MOG). Optic nerve involvement and VEP diagnostic reliability have been already shown in MOG induced EAE rat. In the present study we used spinal cord homogenate (SCH) to induce disease in Dark-Agouti (DA) rats, proposing to show optic nerve involvement and assess VEP usefulness as neurophysiological biomarker also in this model. Nineteen DA rats were used in the experiment: 7 immunized by SCH (EAE) and 12 healthy (H) controls. Flash VEPs from both eyes were recorded with epidural electrodes under sevoflurane volatile anesthesia once a week for 6 weeks (one day before immunization, days 6, 13, 20, 27, 34 post) with measurement P1 latency from N1-P1-N2 complex. Values exceeding 2.5 SD from control mean were considered abnormal. MRI analyses on both Optic Nerves were also performed using a 7 Tesla technology. After the last VEP session, 7 EAE and 3 H animals underwent histological analysis on a transverse section of both optic nerves. P1 latency in EAE group was significantly increased at days 13–20-27 post immunization and was abnormal in 10/14 eyes in EAE rats (p