SOLUBLE FACTORS FROM THE OLFACTORY-BULB ATTRACT OLFACTORY SCHWANN-CELLS

Olfactory Schwann cells (OSCs) extend processes that ensheathe bundles of olfactory axons as they course from the olfactory epithelium to th e olfactory bulb (OB). Results of morphological and immunohistochemica l studies have led to speculation that OSCs may be involved in guiding the olfactory axons to their target tissue. In this study we have exp lored this possibility by investigating the relationship between OSCs and the OB. Olfactory Schwann cells labelled with 1,1'-dioctadecyl 3,3 ,3',3'-tetramethylindocarbocyanine perchlorate (Dil) were injected int o the nasal region of E14 rat embryos and entire embryos were cultured for 24 hr. It was found in some embryos, that the OSCs had migrated t oward the presumptive OB. Cocultures of neonatal OB explants on OSC mo nolayers showed that the OSCs were attracted to the OB and formed a ri ng-like aggregate around the explant after 48 hr culture. This attract ion was absent when a piece of cerebrum was used in place of the OB. W hen medium conditioned by neonatal OBs was placed in the lower compart ment of the chemotaxis chamber, OSCs seeded in the upper compartment m igrated through the pores of the nucleopore filter to reach the unders ide which was in contact with the conditioned medium. After 6 hr of in cubation, scanning electron microscopy was performed on the underside of the nucleopore filters. Cell counts of OSCs showed that the cell de nsity was significantly higher when medium conditioned by OBs was used instead of unconditioned medium or medium conditioned by cerebrum. Th e results of these experiments show that the OSCs migrate toward the O B under the influence of soluble factor(s) secreted by the target tiss ue.