Magnetic resonance imaging of the visual system in vivo: transsynaptic illumination of V1 and V2 visual cortex.
Brain nuclei directly receiving retinal projections are readily labeled in magnetic resonance images following intraocular injection of manganese (Mn). To assess whether Mn in retinal ganglion cell axons can be transsynaptically delivered to visual cortex, mice that had previously received intraocular Mn injection were anesthetized with isoflurane, and T1-weighted data sets were acquired of the eyes and brain using a 7-T magnetic resonance imaging machine. Image intensity within contralateral brain structures was evaluated by assessing 1) signal-to-noise ratios, 2) mean image intensity, and 3) mean image intensity normalized to facial muscle intensity. Image intensity was increased throughout the visual pathway including within contralateral visual cortex areas V1 and V2L. Mean normalized image intensity was greater by 53% in the ipsilateral optic nerve and by 31% and 28% in the contralateral lateral geniculate nucleus and superior colliculus, respectively (N=5, P<0.02, paired t test). In contralateral visual cortex areas V1 and V2L, image intensity was increased by 7.5% and 6.8%, respectively (P<0.02 for both, paired t test). Power analysis of the different evaluation methods yielded evidence of superior sensitivity using the normalization method. Reconstruction of the visual system based upon threshold analysis allowed simultaneous visualization of all portions of the major retinal projections to the brain. These results support use of high magnetic field MRI imaging and data normalization for in vivo quantitative analysis of the mouse brain visual system including visual cortex.
Lindsey
James D
JD
Sophie and Arthur Brody Optic Nerve Laboratory, Hamilton Glaucoma Center, Department of Ophthalmology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0946, USA. lindsey@eyecenter.ucsd.edu
Scadeng
Miriam
M
Dubowitz
David J
DJ
Crowston
Jonathan G
JG
Weinreb
Robert N
RN
D000818:Animals; D001082:Aqueous Humor; D001931:Brain Mapping / Q000379:methods; D007091:Image Processing, Computer-Assisted; D007267:Injections; D007908:Lens, Crystalline / Q000033:anatomy & histology; D008279:Magnetic Resonance Imaging / Q000379:methods; D008345:Manganese / Q000008:administration & dosage / Q000493:pharmacokinetics; D051379:Mice; D009897:Optic Chiasm / Q000033:anatomy & histology; D009900:Optic Nerve / Q000033:anatomy & histology; D012160:Retina / Q000033:anatomy & histology; D012680:Sensitivity and Specificity; D013569:Synapses / Q000648:ultrastructure*; D014793:Visual Cortex / Q000033:anatomy & histology*; D014795:Visual Pathways / Q000033:anatomy & histology*
D008345:Manganese