Images illustrating the histological appearances of in situ zymography (ISZ) and immunohistochemistry (IHC) in moderately degenerate intervertebral discs (IVDs). (a) Photomicrographs taken using the fluorescent microscope. The black rounded areas are regions of matrix degradation. There are none of these areas within the right hand image of a specimen treated with IL-1 receptor antagonist (IL-1Ra). The outlines of cells can just be made out in this image as pale grey ghosts. (b) IHC performed on formalin fixed, paraffin embedded tissue derived from the ISZ experiments. Matrix metalloproteinase (MMP)3 is seen in the cytoplasm of many of the cells in the untreated tissue. It increases (non-significantly) after IL-1 treatment and is markedly reduced following IL-1Ra treatment (right-hand image). In this image the nuclei of the nucleus pulposus (NP) cells can be seen where they have taken up the counterstain, which contrasts with the darker cytoplasmic staining of IHC reaction product for MMP3 in the left and center images.