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Microglia cell number, density, and morphology classification at postnatal day 10 in dentate gyrus of female and male C57BL/6J mice

Microglia maintain normal brain function and support the brain’s response to disease and injury. The hippocampus is an area of focus for microglial study due to its central role in many behavioral and cognitive functions. Interestingly, microglia and related cells are distinct in female vs. male rodents, even in early life. Indeed, postnatal day (P)-dependent sex differences in number, density, and morphology of microglia-like cells have been reported in certain hippocampal subregions at specific ages. However, sex differences in hippocampal microglia have not been examined in the P10 mouse hippocampus. In addition, a key subregion of the hippocampus — the dentate gyrus and its hilar region and molecular layer — has not yet been assessed for sex differences in microglia at P10. To address these knowledge gaps, three measures were collected in the dentate gyrus Hilus and Molecular layer in female and male C57BL/6J mice: number of Iba1+ cells (via stereology), density of Iba1+ cells (via stereology), and density of Iba1+ cells (via sampling). We then classified Iba1+ cell morphology to generate a total number of each cell type (percentage of each cell type via sampling multiplied by cell number via stereology). Analysis of total Iba1+ number, Iba1+ cell density, and morphology type shows no difference between female and male mice in either the Molecular layer or the Hilus at P10. This understudied but important postnatal time point — a rodent developmental time point translationally relevant to human term gestation — fills a key knowledge gap. The data presented here from healthy P10 female and male mice will be useful for research on the role of microglia in injury models. Our demonstration of no sex difference in Iba1+ cells in P10 hippocampal dentate gyrus using two different commonly employed methodologies (sampling and stereology) provides a baseline from which to interpret microglia changes seen after injury. HIGHLIGHTS Sex differences in Iba1+ cells were assessed in the dentate gyrus (DG) of P10 mice Iba1+ cells were assessed in microglia-rich DG areas: the Molecular layer and Hilus A stereology approach showed no sex difference in DG Iba1+ number or density A sampling approach showed no sex difference in DG Iba1+ cell morphology In our measures of cell number, density and morphology, there were no sex differences in Iba1+ cells in P10 mice DG