| Abstract No.: | C-F3177 |
| Country: | USA |
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| Title: | MANGANESE-ENHANCED MAGNETIC RESONANCE IMAGING ACCURATELY DETECTS THE V1/V2 BORDER IN THE PRIMATE VISUAL CORTEX |
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| Authors/Affiliations: | 1 Nicholas Bock*; 1 Ara Kocharyan; 1 Junjie Liu; 1 Afonso Silva;
1 CMU/LFMI, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA
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| Content: | Objectives: The divalent ion of the metal manganese, Mn2+, is a potent magnetic resonance imaging (MRI) contrast agent that mimics Ca2+ in the central nervous system, entering active neurons through voltage-gated calcium channels where it resides with a long half-life. Previous studies have used manganese-enhanced MRI (MEMRI) to enhance neuroarchitecture and detect neuronal activity in the brains of rodents (Lin et al., Magn. Reson. Med., 38: 378-388, 1997; Yu et al. Proc. Natl. Acad. Sci. U.S.A. 104(29); 12193-12198, 2007). In our lab, we have detected a substantial uptake of Mn2+ in the visual cortex of common marmosets (Callithrix Jacchus) following systemic injections into the tail vein (Bock et. al., Brain Research, 1198; 160-170, 2008). This suggests that MEMRI could be used to detect activity in the visual cortex of non-human primates. The purpose of this work is to more accurately characterize the pattern of Mn2+ uptake in the marmoset visual cortex with high resolution MRI in preparation for future functional studies.
Materials and Methods: Experiments were carried out in two, one year old marmosets weighing about 550 grams following the guidelines of the NINDS, NIH ACUC. The marmosets were injected four times in the lateral tail vein with a 40 mM solution of MnCl2∙4H20 (Sigma Aldrich, St. Louis, MO, USA) prepared in 200 mM bicine buffer to a pH of 7.4. Doses were 30 mg/kg MnCl2∙4H20 (dry drug weight/body weight), spaced 48 hours apart. 24 hours after the final dose, the marmosets were imaged live with a 3D, T1-weighted MP-RAGE sequence producing a 133 micron isotropic resolution over the entire visual cortex. The final images were compared to control images made in the same marmosets before the Mn2+ injections.
Results: Both marmosets showed strong T1-weighted enhancement throughout the visual cortex following the Mn2+ injections. The enhancement was greatest in the V1 region of the visual cortex, and the border between V1 and V2 could be easily identified along its full extent. As well, an enhancement was seen in the rostral portion of the visual cortex that may correspond to the middle temporal area. The pattern appeared similar to that seen with cytochrome oxidase staining (Lyon et al., J. Neurosci., 21(1); 249-261, 2001).
Conclusions: The similarity between the distribution of Mn2+ and cytochrome oxidase in the marmoset visual cortex is intriguing. Whether Mn2+ can be used as a marker of neuronal function (as can cytochrome oxidase) remains to be seen and further experiments are underway. Regardless, MEMRI provides a useful tool for accurately defining the V1/V2 border in vivo in the marmoset, which could serve as a useful landmark for other imaging studies
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