Nucleus pulposus inhibits the axonal outgrowth of cultured dorsal root ganglion cells

Although it is well established that nucleus pulposus cells may induce structural and functional changes in adjacent nerve roots when placed epidurally, it is not known whether this is due to direct neurotoxic effects or whether the nerve roots are affected indirectly by reduction of nutrition and inflammatory/immunologic mechanisms. In the present study we assessed the effects of various tissues on cultured dorsal root ganglions from newborn rats. Nucleus pulposus was found to have a toxic effect on the axons by blocking axonal outgrowth, but no similar effects on the nerve cell bodies (extra-ganglionic nerve cell density, nerve cell arborisation) were found as compared to the series with only culture medium. Sterile water for 1 or 24 h (positive controls) induced significant effects by all four criteria, whereas medium without nerve growth factor, fat and frozen nucleus pulposus had no statistically significant effects. The study thus showed that there are direct axonotoxic effects induced by the nucleus pulposus, and since frozen nucleus pulposus did not have any effects, it may be assumed that the mechanisms are related to substances produced by the nucleus pulposus cells. The presented model allows for future studies on the neurotoxic properties of nucleus pulposus cell-derived candidate substances.