The intervertebral disc phenotype of Caveolin-1 knock-out mice. Typical examples of the intervertebral discs from 3-month-old wild-type (A and C) and Caveolin-1 knock-out (B and D) mice, stained with H&E (A and B) and alcian blue/pricrosirius red (C and D). The pictures on the right are magnifications of the corresponding pictures on the left. The wild-type nucleus pulposus (NP) consisted of centrally located, viable notochordal cells (arrowhead) and a relatively limited amount of chondroid-like intercellular matrix (*), which stains blue in the sections stained with alcian blue/picrosirius red. The NP of the Caveolin-1 KO mice contained apoptotic (arrowheads) and rounded cells, with a smaller amount of cytoplasm lacking the typical vacuolar aspect (arrows), and a relatively large amount of chondroid-like intercellular matrix (*).