INTRODUCTION: Degenerative disorders of the spine often result in pain. Interaction between the intervertebral discs and neural structures has been suggested as a possible mechanism behind such pain production. Previous work has demonstrated that both notochordal and chondrocyte like cells from intervertebral discs inhibit neurite outgrowth from DRG:s in vitro. The aim of this study was to analyze the ultrastructure of neurites with and without the presence of intervertebral discs cells in a tissue culture system.
METHODS: Dorsal root ganglia were harvested from newborn rats and cultured on collagen coated Termanox glasses for 48 hours in vitro and studied in three experimental series: 1) 20 000 notochordal cells added, 2) 20 000 chondrocyte like cells added, 3) medium (control). The DRG:s and neurites were then fixed in Karnovsky's fixative and the ultrastructure was evaluated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
RESULTS: Neurite outgrowth from cultured DRG:s was seen as bundles of varying size and complexity. The neurites grew in a close relationship to flattened cells (fibroblasts) and Schwann cells and formed bundles of axons and dendrites with intracellular neurofilaments. Cytoplasmic processes from Schwann cells encircled single axons already after 48 hours in culture. No clear differences in ultrastructure of the neurites were observed between the three experimental series.
DISCUSSION: This is the first description of the ultrastructure of outgrowing neurites from DRG:s in vitro with and without the presence of cells from intervertebral discs in the tissue culture system. Interestingly, Schwann cells seem to play an important role in neurite outgrowth already in the time frame of 48 hours. No obvious morphological changes on neurites or supporting cells were seen after exposure to disc cells. However, the effect of disc cells on neurite outgrowth may be due to soluble factors or cell to cell signalling.