In vitro characterization of olfactory ensheathing cells from the olfactory mucosa and olfactory bulb

Olfactory ensheathing cells (OECs), which surround fascicles of numerous unmyelinated olfactory axons, are regarded as a promising tool for the repair of the injured nervous system. Implantation of cultured OECs into the damaged spinal cord of adult rats has been shown to mediate some degree of axonal remyelination. This observation is curious because OECs do not myelinate axons in their native environment. We, however, believe that primary OEC cultures isolated from the olfactory system may be contaminated with Schwann cells (SCs), which could account for the remyelination of central axons seen following OEC intraspinal implantation. We have recently determined that calponin, an actin-binding protein, is expressed by OECs and not by Schwann cells, thus providing us with the first definitive phenotypic marker for these cells. In this study, primary cultures of adult rat olfactory mucosa and olfactory bulb were established and immunostained for the p75 neurotrophin receptor (p75NTR), calponin, S100, and glial fibrillary acidic protein (GFAP). Both types of cultures possessed OECs (which were identified as having positive immunostaining for p75NTR, calponin, S 100, and GFAP), and SCs (which were identified as having positive immunostaining for p75NTR, S100, and GFAP, but lacking calponin immunostaining). Our results reveal that two populations of p75NTR-positive cells exist in primary cultures of the rat olfactory mucosa and bulb: calponin-positive OECs and calponin-negative SCs. Since olfactory tissues likely yield a mixed glial population, the idea that OECs are capable of de novo myelin synthesis after intraspinal implantation should be re-evaluated.