Chondrocytes of treated Tg197 mice. (a) Chondrocytes of P-NT.II-treated Tg197 mice at 5–8 weeks of age (i.e. 1–4 weeks post-treatment) were similar to those described for normal chondrocytes, with almost intact nucleus (N), basement membrane (arrowhead), and cytoplasmic organelles – vacuoles (v), rough endoplasmic reticulum (r-ER), mitochondria (m); (b) Most chondrocytes of Tg197 mice treated with scrambled P-NT.II at age 8 weeks (i.e. 4 weeks post-treatment) were degenerated, with vacuolated cytoplasm (v), a disrupted Golgi complex (g), pyknotic nuclei (N) with a well-defined, enlarged perinuclear space (arrows), and cytoplasmic projections broken from the cell (arrowhead). N = 4 joints/group; mean percentage of degenerating chondrocytes at age 8 weeks = 20% and 75% of total in (a) and (b), respectively. Bars = 2 μm.