White matter lipid alterations during aging in the rhesus monkey brain.

The brain of higher organisms, such as nonhuman primates, is particularly rich in lipids, with a gray to white matter ratio of approximately 40 to 60%. White matter primarily consists of lipids, and during normal aging, it undergoes significant degeneration due to myelin pathology, which includes structural abnormalities, like sheath splitting, and local inflammation. Cognitive decline in normal aging, without neurodegenerative diseases, is strongly linked to myelin pathology.

Immune proteins C1q and CD47 may contribute to aberrant microglia-mediated synapse loss in the aging monkey brain that is associated with cognitive impairment.

Cognitive impairment in learning, memory, and executive function occurs in normal aging even in the absence of Alzheimer's disease (AD). While neurons do not degenerate in humans or monkeys free of AD, there are structural changes including synapse loss and dendritic atrophy, especially in the dorsolateral prefrontal cortex (dlPFC), and these correlate with cognitive age-related impairment. Developmental studies revealed activity-dependent neuronal properties that lead to synapse remodeling by microglia.

Potential trade-off between olfactory and visual discrimination learning in common marmosets (Callithrix jacchus): Implications for the assessment of age-related cognitive decline.

Olfactory dysfunction has been identified as an early biomarker for dementia risk but has rarely been assessed in nonhuman primate models of human aging. To better characterize common marmosets as such models, we assessed olfactory discrimination performance in a sample of 10 animals (5 females), aged 2.5-8.