Figure 3. The density and morphology of microglia within cognitive regions of the brain are significantly affected by sex and age.

At embryonic day 17 (Prenatal; first column from left), males (top row of representative coronal sections) and females (bottom row) have a similar number of microglia within the hippocampus (HP), cortex (CX), and the amygdala (AMY.) At birth (Postnatal day 0), females (bottom series of representative coronal sections) have slightly more microglia than males (top series of representative coronal sections) within the CA3 region of HP and AMY, though not within the CX. As the brain develops and microglia continue to enter the brain, this sex difference reverses. By Postnatal day 4, males have significantly more microglia within the CX, all subregions of the HP, and AMY than females. Beginning around adolescence (postnatal day 30) and into adulthood (postnatal day 60) the sex difference reverses again. At this age, microglia generally appear within all brain regions in a ramified state, represented by thin, long processes. However, at postnatal day 30 and 60, females have a significantly greater population of microglia with thicker, longer processes than males in all three regions, suggestive of a differential function between the sexes at this age. One representative light micrograph is displayed below each diagram, which schematize cell density. Scale bars (in the first column from left): dotted line = 100 µm (for representative pictures at 4× for all ages), solid line = 50 µm (for inset pictures at 20× for all ages). One schematized coronal section is equivalent to 10 sections analyzed for cell counts and morphology at all ages. 1 cell shown above at postnatal day 0 and postnatal day 4 represents approximately 10 counted cells. 1 cell shown above at postnatal day 30 – 60 represents approximately 200 counted cells.