Lithium compartmentation in brain by 7Li MRS: effect of total lithium concentration

• Published in: NMR in biomedicine Vol. 26; no. 9; pp. 1152 - 1157
• Main Authors: Komoroski, Richard A., Lindquist, Diana M., Pearce, John M.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.09.2013; Wiley Subscription Services, Inc
• Subjects: Animals; biexponential relaxation; bipolar disorder; Brain - cytology; Brain - metabolism; Lithium - analysis; Lithium - metabolism; Magnetic Resonance Spectroscopy; Male; Protons; rat brain; Rats; Rats, Sprague-Dawley; spin-spin relaxation time; transverse relaxation time; rat brain; transverse relaxation time; bipolar disorder; biexponential relaxation; spin-spin relaxation time
• ISSN: 0952-3480; 1099-1492
• DOI: 10.1002/nbm.2929

In previous work at 4.7 T, the individual components of biexponential 7Li transverse (T2) spin relaxation in rat brain in vivo were tentatively identified with intra‐ and extracellular Li. The goal in this work was to estimate Li's compartmental distribution as a function of total Li concentration in brain from the biexponential decays. Here a localized, biexponential 7Li T2 MR spin‐relaxation study with isotopically enriched 7LiCl is reported in rat brain in vivo at 7 T. Additionally, a simple linear interpolation using the biexponential T2 values to estimate intracellular Li from individual monoexponential T2 decays was assessed. Intracellular T2 was 14.8 ± 4.3 ms and extracellular T2 was 295 ± 61 ms. The fraction of intracellular brain Li ranged from 37.3 to 64.8% (mean 54.5 ± 6.7%) and did not correlate with total Li concentration. The estimated intracellular Li concentration ranged from 47 to 80% (mean 68.3 ± 8.5%) of the total brain Li concentration and was highly correlated with it. The monoexponential estimates of the intracellular‐Li fractions and derived concentrations averaged about 15% higher than the corresponding biexponential estimates. This work supports the previous conclusion that a large fraction of Li in the brain is within the intracellular compartment. Copyright © 2013 John Wiley & Sons, Ltd. A localized, biexponential 7Li T2 MR spin‐relaxation study with isotopically enriched 7LiCl is reported in rat brain in vivo at 7 T. The goal was to estimate Li's compartmental distribution as a function of total Li concentration in brain. The estimated intracellular Li concentration was 47–80% of the total brain Li concentration and was highly correlated with it. This work supports the previous conclusion that a substantial fraction of Li enters the cell in vivo in brain.