Elevated intracellular levels of cAMP induce olfactory ensheathing cells to express GAL-C and GFAP but not MBP.

The primary olfactory pathway contains non-myelinating glial cells, called ensheathing cells, that exhibit a variety of phenotypes depending on their immediate environment. In vivo, these cells normally possess a mixture of astrocyte- and Schwann cell-specific phenotypic features. When co-cultured with dorsal root ganglion neurons, their phenotype can become more like that of a myelinating Schwann cell. The objective of this study was to determine whether ensheathing cells would express a myelinating phenotype in culture in the absence of neurons but in the presence of cAMP analogues that are known to induce the expression of myelin associated molecules in Schwann cell cultures. The ensheathing cell cultures were initiated using the nerve fiber layers of Theiler stage 23 rat olfactory bulb primordia and were fed for 1 day to 3 weeks with serum containing (1% or 10% FBS) or serum-free media to which was added different concentrations of dBcAMP (0.1 to 1 mM) or forskolin (10 microM). These cultures were double-labelled with a rabbit polyclonal antibody to S100 in combination with mouse anti-GAL-C (O1 and BRD1 hybridomas) or anti-MBP monoclonal antibodies. The remaining cultures were double-labeled with a rabbit polyclonal antibody to GFAP in combination with the BRD1 antibody. Treatment with dBcAMP or forskolin failed to induce ensheathing cells to express MBP regardless of the concentration. On the other hand, the treatment induced approximately one tenth of the cells to express GAL-C, and virtually all of the cells to express GFAP. These results indicate that although ensheathing cells can synthesize myelin associated molecules, the cAMP second messenger system appears to play a lesser role in controlling the expression of a myelinating phenotype in ensheathing cells than it does in Schwann cells.