Journal of Neuroscience, Vol 15, 990-1000, Copyright © 1995 by Society for Neuroscience
Soluble factors from the olfactory bulb attract olfactory Schwann cells
KL Liu, MI Chuah and KK Lee
Department of Anatomy, Chinese University of Hong Kong, Shatin, N.T.
Olfactory Schwann cells (OSCs) extend processes that ensheathe bundles of
olfactory axons as they course from the olfactory epithelium to the
olfactory bulb (OB). Results of morphological and immunohistochemical
studies have led to speculation that OSCs may be involved in guiding the
olfactory axons to their target tissue. In this study we have explored 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 into
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 toward the
presumptive OB. Cocultures of neonatal OB explants on OSC monolayers showed
that the OSCs were attracted to the OB and formed a ring-like aggregate
around the explant after 48 hr culture. This attraction was absent when a
piece of cerebrum was used in place of the OB. When medium conditioned by
neonatal OBs was placed in the lower compartment of the chemotaxis chamber,
OSCs seeded in the upper compartment migrated through the pores of the
nucleopore filter to reach the underside which was in contact with the
conditioned medium. After 6 hr of incubation, scanning electron microscopy
was performed on the underside of the nucleopore filters. Cell counts of
OSCs showed that the cell density was significantly higher when medium
conditioned by OBs was used instead of unconditioned medium or medium
conditioned by cerebrum. The results of these experiments show that the
OSCs migrate toward the OB under the influence of soluble factor(s)
secreted by the target tissue.