Figure 3.

Little variation of microglial density in cortical gray and white matter. A, Distribution of microglial density in the cortical gray and white matter at individual sites per clade (top), average across all samples (middle), and average per clade (bottom). Values are given in Table 4. Average microglial densities in gray matter cortical sites differ significantly across clades at the p < 0.01 level, except between Artiodactyla and Afrotheria (Wilcoxon, p = 0.1877; not significant), Afrotheria and Marsupialia (p = 0.0442), and Artiodactyla and Marsupialia (p = 0.7454), and in the white matter, between Artiodactyla and Carnivora (p = 0.8260). Differences in microglial cell density between white and gray matter are significant (Wilcoxon p < 0.01) in all clades (see Table 4), except Afrotheria (p = 0.2835) and Marsupialia (p = 0.0151). B, Relationship between structure mass and number of microglial cells across cortical sites and mammalian species. C, Function plotted applies to all species and gray and white matter together with exponent (0.905 ± 0.008, p < 0.0001, r² = 0.878). B′, B′′, This same relationship for gray (B′) and white (B′′) matter sites separately. Spearman correlations, p values, and other fit values in each clade and species are listed in Table 4. C, Relationship between the density of microglial cells and the number of microglial cells across cortical sites and mammalian species. C′, C′′, This same relationship for gray (C′) and white (C′′) matter sites separately. Spearman correlation ρ and p values are given in Table 4. D, Relationship between microglial density and neuronal cell density across cortical gray matter sites and mammalian species. Spearman coefficients and p values as well as exponents and p values for each clade and species are listed in Table 4. E, Relationship between microglial density and non-neuronal density across cortical white matter sites and mammalian species. Spearman coefficients and p values as well as exponents and p values for each clade and species are listed in Table 4. B, B′, B′′, C, C′, C′′, D, E, Each data point represents the values found per cortical site examined for each species colored by clade as in the key. Filled circles represent cortical gray matter sites of the Cx, including the hippocampus (GM). *White matter sites (WM). A, *Significance.