Fig. 2.

a Microscopic appearance of intervertebral discs, from top to bottom L1-2, L2-3, L3-4, and L4-5. Microscope magnification 1.25X. The saw cut is on the left margin of the images. The dark lines in the images are drying artifacts not related to disc features. b Immunohistology of key areas: stained with antibodies against collagen type I (low magnification survey and second row), collagen type II (third row), and aggrecan (fourth row). The red boxes indicate the areas of the core nucleus and the inner annulus zone, depicted as containing the enlarged areas below. Survey: 1.25X, details 10× objective magnification (see also scale bar). Positive immunostaining: brown; counterstaining: blue