Hyperosmotic stimulus reversibly increases the expression of nestin and vimentin by SON capillary vessels. A-F: Stack confocal images (10 μm-thick) of sections immunostained for nestin (A-C) or vimentin (D-F) in rats normally hydrated (A and D), osmotically stimulated during 6 days (B and E), and rehydrated during 6 days following 6 days of osmotic stimulation (C and E). In all the rats, nestin immunostaining of vessels is more intense in the SON than in the surrounding regions, whereas the number and staining intensity of immunostained SON vessels increases in the osmotically stimulated rats (B vs A), and return to control levels in the rehydrated rats (C). In all the rats, intense vimentin immunostaining is associated with the cell body of astrocytes located along the SON ventral border, and with their elongated processes projecting throughout the nucleus (D-F), whereas vimentin-immunostained vessels are only detected in the SON of the stimulated rat (E). G-L: Merged confocal images of sections double immunostained for EBA and either nestin (G-I) or vimentin (J-L) in rats normally hydrated (G and J), osmotically stimulated during 6 days (H and K), and rehydrated during 6 days following 6 days of osmotic stimulation (I and L). In control (G and I) and rehydrated (I and L) rats, numerous SON vessels are double-immunostained for EBA and nestin (yellow vessels in G and I), whereas in the stimulated rat, number of capillary vessels labeled for nestin appear EBA-negative (red vessels in H). As compared with control (J) and rehydrated (L) rats, the SON of the osmotically stimulated rat contain numerous vessels double immunostained for EBA and vimentin or (yellow vessels in K), or vimentin-positive but EBA-negative (red vessels in K). Control: normally hydrated rat; EBA: endothelial brain antigen; OC: optic chiasma; os 6 days: rat osmotically stimulated during 6 days; reh 6 days: rat rehydrated during 6 days following 6 days of osmotic stimulation. Scale bars: A-C = 100 μm; D-F = 100 μm; G-L= 50 μm.