Olfactory ensheathing cells promote neurite extension from embryonic olfactory receptor cells in vitro

The role of ensheathing cells, a macroglial cell type with a unique presenc e in the olfactory system, in the outgrowth of olfactory receptor cell neur ites was explored in vitro. Glial cell cultures harvested from both the olf actory bulb nerve layer and the hippocampus were established and immunocyto chemically characterized. The expression of the p75 low-affinity nerve grow th factor receptor by ensheathing cells was used to distinguish them from o ther macroglial subpopulations. Results indicated that ensheathing cell cul tures were approximately 80% pure. Olfactory receptor cells were cocultured with ensheathing or hippocampal glial cells or were seeded on laminin or p oly-L-lysine as controls. Olfactory receptor cells extended the longest pri mary neurites when cocultured with ensheathing cells. Neurite extension on hippocampal glia and laminin was less extensive than that observed on enshe athing cells but higher than that on poly-L-lysine. The neurite outgrowth-p romoting effect of ensheathing cells was, at least in part, mediated by dif fusible factors, because olfactory receptor cell neurite extension could al so be facilitated when receptor cells were cultured in ensheathing cell-con ditioned media. In contrast, cortical neurons extended neurites of equivale nt lengths on ensheathing and hippocampal glia. The results suggest that en sheathing cells may release factors that support the continuous outgrowth o f olfactory receptor cell axons and, therefore, the capacity of this pathwa y to recover from injury. GLIA 25:99-110, 1999. (C) 1999 Wiley-Liss, Inc.