Typical histological changes after injections of phosphate-buffered saline (PBS) (c,d), platelet-poor plasma (PPP)-releasate (e,f), or platelet-rich plasma (PRP)-releasate (g,h). On safranin-O-stained sections, a moderate-to-severe degeneration was observed in the PBS (c,d) and PPP (e,f) groups. In the PRP group, the increasing number of chondrocyte-like cells which appeared as large cells encircled with pericellular matrix densely stained with safranin-O were found in the nucleus pulposus (h). The histology of the non-punctured control (L3/4) is shown in (a,b). (b,d,f,h) are magnification images of the area indicated by a square (a,c,e,g), respectively. Scale bars: 1 mm (a,c,e,g) and 5 μm (b,d,f,h). Asterisk indicates osteophyte formation.