Abstract
Purpose
To evaluate manganese (Mn^2+^)‐enhanced MRI in a longitudinal study of normal and injured rat visual projections.
Materials and Methods
MRI was performed 24 hours after unilateral intravitreal injection of MnCl~2~ (150 nmol) into adult Fischer rats that were divided into four groups: 1) controls (N = 5), 2) dose‐response (N = 10, 0.2–200 nmol), 3) time‐response with repeated MRI during 24–168 hours post injection (N = 4), and 4) optic nerve crush (ONC) immediately preceding the MnCl~2~ injection (N = 7). Control and ONC animals were reinjected with MnCl~2~ 20 days after the first injection, and MRI was performed 24 hours later.
Results
In the control group, the optic projection was visualized from the retina to the superior colliculus, with indications of transsynaptic transport to the cortex. There was a semilogarithmic relationship between the Mn^2+^ dose and Mn^2+^ enhancement from 4 to 200 nmol, and the enhancement decayed gradually to 0 by 168 hours. No Mn^2+^‐enhanced signal was detected distal to the ON crush site. In the control group, similar enhancement was obtained after the first and second MnCl~2~ injections, while in the ONC group the enhancement proximal to the crush site was reduced 20 days post lesion (20dpl).
Conclusion
Mn^2+^‐enhanced MRI is a viable method for temporospatial visualization of normal and injured ON in the adult rat. The observed reduction in the Mn^2+^ signal proximal to the ONC is probably a result of retrograde damage to the retinal ganglion cells, and not of Mn^2+^ toxicity. J. Magn. Reson. Imaging 2005. © 2005 Wiley‐Liss, Inc.