Table 1.

Summary of changes in microglial distribution, morphology, and behavior associated with aging.

Phenotypes
CHANGES IN MICROGLIAL DISTRIBUTION
Increase in microglial numbers/density in neural parenchyma
Decrease in regularity in distribution
Translocation into areas not previously occupied by microglia (e.g., to the outer layers of the retina)
CHANGES IN MICROGLIAL MORPHOLOGY
Decrease in individual microglial ramification (dendritic arbor area, branching, and total process length)
Appearance of morphological changes suggestive of increased activation state (e.g., perinuclear cytoplasmic hypertrophy, retraction of processes)
Sporadic appearance of dystrophic microglia in aged human brains
CHANGES IN MICROGLIAL DYNAMIC BEHAVIOR
Decrease in rate of process movement
Decrease in rate of migration to focal tissue injury