Electron microscopy analysis of neurites extending from dorsal root ganglia in vitro following exposure to intervertebral disc cells

Nucleus pulposus cells from the intervertebral disc have been shown to have inhibiting effects on neurite outgrowth in vitro. The nucleus pulposus consists of at least 2 cell populations, notochordal cells and chondrocyte-like cells. The aim of this study was to analyze the morphology of the neurites, from rat dorsal root ganglia (DRG) in a culture system, after exposure of these 2 cell populations. DRG from perinatal rats was harvested and placed in culture dishes for 24 h. Nucleus pulposus cells from donor rats were separated into 2 populations and applied to the DRG and neurite culture for a further 24 h and compared to control cultures exposed to culture medium without cells. The DRG and neurites were thereafter prepared for scanning or transmission electron microscopy (SEM/TEM). Descriptive SEM and TEM analyses and calculations of the neurite diameter were performed. The visual appearance after SEM and TEM preparation was similar in the three different culture conditions. However, there was a statistically significant reduction of the neurite diameter for the cultures exposed to notochordal cells compared to the cultures exposed to medium and chondrocyte-like cells (TEM preparation). Prominent and frequent pathologic abnormalities in peripheral nerve diseases have been observed with changes in axonal caliber. This study may suggest that a preserved small amount of notochordal cells, as seen in human adults, may play a role in clinical situations where nerve tissue is exposed to disc material, i.e. in disc herniation or degeneration.