Abstract
Previous research demonstrates that microglia are activated by both chronic and acute stress, and that the type, intensity, and duration of the stressor may lead to variable alterations in morphology and markers of inflammation. To examine microglia differences in the brains of mice living in an ethologically relevant environment, 12 adult male CD1 mice were group housed for 21 days in an enriched enclosure measuring 150 × 150 × 80 cm. Mice were observed and social interactions were recorded for a minimum of two hours each day during the dark cycle. Hierarchy status was determined by analyzing the relative proportion of aggression given and received by each animal. Paraformaldehyde-fixed frozen brain tissue from the three most dominant and three most subordinate mice from seven cohorts was cryosectioned (50 microns), immunolabeled with Iba-1 antibody and stained with either fluorescence or DAB-peroxidase, and photographed using a 40X objective. Eight stress-responsive brain regions were analyzed, namely, CA1, medial amygdala, nucleus accumbens core and shell, ventral striatum, medial prefrontal cortex, ventral tegmental area, and substantia nigra. To assess differences in each brain region we considered cell number, size, and overall morphological state score on a scale of 1–4, with 1 being ramified and 4 being amoeboid. This study serves to characterize regional differences in microglia number and morphology with consideration to individual dominance ranking within a naturalistic environment.
Published Version
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