Differentiation of primary and secondary degeneration in the visual pathway using in vivo Mn-enhanced MRI

Abstract

This study explores the capability of high-resolution Mn-enhanced MRI (MEMRI) for in vivo, longitudinal evaluation of primary and secondary degeneration along the retinocollicular projections after partial transection of right superior optic nerve in rats. At 1 week and 6 weeks after partial optic nerve injury, a consistent T1W hypointensity by about 28% was observed in the left lateral superior colliculus (SC) relative to the contralateral hemisphere, reflective of primary loss of topological connections and Mn2+ transport in the retinocollicular projections. The left medial SC had a reduced T1W signal intensity by 11% compared to the right medial SC at Week 1. Such reduction further increased to 16% at Week 6, indicative of secondary loss of retinal ganglion cells and axons projecting through the uninjured, inferior optic nerve. The results of this study demonstrated the feasibility of in vivo, high-resolution MEMRI for assessing the primary and secondary degeneration topologically and longitudinally along the visual pathway. Future MEMRI studies are envisioned that measure the secondary changes in topological connections in various neurodegenerative diseases and injuries and upon therapeutic interventions in longitudinal studies.