Iba1+ cell density and morphology classification at postnatal day 10 in four hippocampal subregions of female and male C57BL/6J mice

Abstract

Microglia, the resident immune cells of the brain, support normal brain function and the brains response to disease and injury. The hippocampal dentate gyrus (DG) is an area of 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 have been reported in certain hippocampal subregions at specific ages. However, sex differences in the DG have not yet been assessed at P10, a rodent developmental time point translationally relevant to human term gestation. To address this knowledge gap, Iba1+ cells in the DG (which are enriched in the Hilus and Molecular Layer) in female and male C57BL/6J mice were analyzed for their number (via stereology) and density (via stereology and via sampling). Next, Iba1+ cells were classified into published morphology categories. Finally, the percent of Iba1+ cells in each morphology category was multiplied by total cell number to generate a total number of Iba1+ cells in each morphological category. Results show no sex difference in Iba1+ cell number, density, or morphology in the P10 Hilus or Molecular Layer. The lack of sex difference in Iba1+ cells in P10 DG using commonly-employed methodologies (sampling, stereology, morphology classification) provides a baseline from which to interpret microglia changes seen after injury. HIGHLIGHTSO_LISex differences in Iba1+ cells were assessed in the dentate gyrus (DG) of P10 mice C_LIO_LIIba1+ cells were assessed in DG microglia-rich subregions: Hilus and Molecular Layer C_LIO_LIBoth stereology and sampling approaches were used to quantify Iba1+ cells C_LIO_LINo sex difference found in Iba1+ cell number, density, or morphology in P10 mice DG C_LI