Media from nucleus pulposus and annulus fibrosus cells cultured under high mechanical strain promote neurite outgrowth of PC12 cells. (A) Conditioned media from static and high mechanical strain (HMS) nucleus pulposus (NP) and annulus fibrosus (AF) cells were incubated with PC12 cells, and neurite outgrowth and viability were observed and compared to vehicle (−NGF) and neural growth factor (NGF)-treated (+NGF) controls. Black arrows in phase images indicate neurites. Scale bar: 200 μm. (B) Quantification of total and multiple neurite outgrowth and viability. Error bars represent SEM three independent experiments were performed. *P < 0.05, **P < 0.01, and #P < 0.05 (all by Student’s t-test) for samples with three or more neurites per cell body. All samples were compared to –NGF controls.