Figure 1.

Peripheral origin of repopulating myeloid cells in nonchimeric microglia-depleted parabiotic mice. TK and Act.GFP mice were surgically connected to establish a joined circulatory system. Upon establishment of blood chimerism in both partners (2 wk), icv GCV was administered to the TK partners for 10 d to deplete microglia. Mice were sacrificed 24 d after starting GCV treatment. (a and b) Representative images of GFP-positive cells (middle columns) in microglia-depleted (GCV-treated) TK mice (bottom rows), WT controls (top rows), or non-microglia–depleted aCSF-treated TK controls (middle rows). Shown are cortical (a) or hippocampal (b) brain regions stained for Iba1 (left columns) or GFP (middle columns), as well as merged images (right columns). Bars, 200 µm. (c) Flow cytometric analysis of GFP⁺ cells in blood of parabiotic pairs. (d and e) Stereological quantification of Iba1-positive cells (d; *, P = 0.03; n = 5 per group) and GFP-positive cells (e; *, P = 0.02; n = 5 per group) in brains of mice described in a–c. All data are displayed as mean ± SEM.