Representative sagittal sections of BrdU-labeled RMS of three separate BXD RI lines. All mice received a single pulse of BrdU for one hour. BrdU immunohistochemistry revealed inter-strain differences in BrdU + cell numbers from BXD 39 having high numbers of BrdU + cells in the RMS to BXD 55 having low numbers of BrdU + cells in RMS. Whereas BXD 77 have intermediate numbers of BrdU + cells in the RMS. Arrows mark the beginning and end of the RMS.LV, lateral ventricle; scale bar: 200 μm.