Microstructural changes in locus coeruleus-cortical projections in aged bonnet macaques are independent of myelin loss

Motivation: Little is understood about the effects of normal aging on the locus coeruleus and whether quantitative MRI maps are sensitive enough to detect changes. Goal(s): To understand which MRI maps show sensitivity to LC changes in high resolution ex vivo imaging. Approach: We utilized aged and adult female bonnet macaque specimens. Whole brains underwent an extensive ex vivo protocol to generate comprehensive and complimentary sets of quantitative maps. Results: We found subtle changes in restriction based metrics with age in the LC nucleus itself and alterations in diffusivity metrics but not volume changes or changes in measures of myelin content in LC projections. Impact: Our study reports subtle changes in the LC and its projections and highlights the benefit of combining multiple quantitative MRI maps. This suggests that incorporating advanced diffusion maps to understand microstructural changes in clinical applications could be beneficial.