Cell proliferation concerns a minority of SON glial cells. BrdU was administrated to osmotically stimulated rats drinking 2% saline during 6 days and the animals were fixed 5 hours after the BrdU administration. A, C, E: Stack confocal images (10 μm-thick) of sections labeled for different glial markers. A: GFAP immunostaining is associated with the cell bodies of SON astrocytes localized to the ventral border of the nucleus and with their elongated processes projecting dorsally throughout the core of the nucleus. C: NG2 immunostaining is associated with small ramified cells dispersed throughout the nucleus. E: IsoB4 labeling is associated both with typical ramified microglial cells dispersed within the nucleus and with some tubular, vessel-like structures. Insets show high magnification of the different labeled cell types. B, D, and F: Merged confocal images of sections double labeled for BrdU and for one the different glial markers. Within the SON, BrdU-labeled nuclei are never associated with GFAP-labeled astrocytes (B) and IsoB4-labeled isolated microglial cells (arrow heads in F), whereas they are associated with some NG2-labeled cells (arrows in D) and with numerous vessel-like structures labeled with the lectin IsoB4 (arrows in F). GFAP: glial fibrillary acidic protein; IsoB4: isolectin B4; NG2: NG2 proteoglycan; OC: optic chiasma. Scale bars: A, C, E = 100 μm; B, D, F = 25 μm; Insets = 25 μm.