title: Manganese-enhanced MRI of the optic visual pathway and optic nerve injury in adult rats.
abstract: OBJECTIVE
  To evaluate manganese (Mn2+)-enhanced MRI in a longitudinal study of normal and injured rat visual projections.
  
  
  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 (20 dpl).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Circulation and Medical Imaging, NTNU, Norwegian University of Science and Technology, MR Centre, Trondheim, Norway. marte.thuen@medisin.ntnu.no
authors.forename: Marte
authors.initials: M
authors.lastname: Thuen
authors.forename: Trond E
authors.initials: TE
authors.lastname: Singstad
authors.forename: Tina Bugge
authors.initials: TB
authors.lastname: Pedersen
authors.forename: Olav
authors.initials: O
authors.lastname: Haraldseth
authors.forename: Martin
authors.initials: M
authors.lastname: Berry
authors.forename: Axel
authors.initials: A
authors.lastname: Sandvig
authors.forename: Christian
authors.initials: C
authors.lastname: Brekken
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D015636:Magnesium Chloride / Q000494:pharmacology*; D020221:Optic Nerve Injuries / Q000503:physiopathology*; D051381:Rats; D011916:Rats, Inbred F344; D014795:Visual Pathways / Q000187:drug effects / Q000503:physiopathology*
chemical_list: D015636:Magnesium Chloride