Manganese-enhanced MRI of the optic visual pathway and optic nerve injury in adult rats

• Published in: Journal of magnetic resonance imaging Vol. 22; no. 4; pp. 492 - 500
• Main Authors: Thuen, Marte, Singstad, Trond E., Pedersen, Tina Bugge, Haraldseth, Olav, Berry, Martin, Sandvig, Axel, Brekken, Christian
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01-10-2005
• Subjects: Animals; Dose-Response Relationship, Drug; Female; Magnesium Chloride - pharmacology; manganese; Mn2+-enhanced MRI; optic nerve; optic nerve crush; Optic Nerve Injuries - physiopathology; Rats; Rats, Inbred F344; visual pathway; Visual Pathways - drug effects; Visual Pathways - physiopathology
• ISSN: 1053-1807; 1522-2586
• DOI: 10.1002/jmri.20400

Purpose
To evaluate manganese (Mn2+)‐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 MnCl2 (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 MnCl2 injection (N = 7). Control and ONC animals were reinjected with MnCl2 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 Mn2+ dose and Mn2+ enhancement from 4 to 200 nmol, and the enhancement decayed gradually to 0 by 168 hours. No Mn2+‐enhanced signal was detected distal to the ON crush site. In the control group, similar enhancement was obtained after the first and second MnCl2 injections, while in the ONC group the enhancement proximal to the crush site was reduced 20 days post lesion (20dpl).
Conclusion
Mn2+‐enhanced MRI is a viable method for temporospatial visualization of normal and injured ON in the adult rat. The observed reduction in the Mn2+ signal proximal to the ONC is probably a result of retrograde damage to the retinal ganglion cells, and not of Mn2+ toxicity. J. Magn. Reson. Imaging 2005. © 2005 Wiley‐Liss, Inc.