Soluble factors from the olfactory bulb attract olfactory Schwann cells

Abstract

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.

Slit-2 repels the migration of olfactory ensheathing cells by triggering Ca2+-dependent cofilin activation and RhoA inhibition

“…It has been shown that the OB secretes some soluble factors that might attract OEC migration from the OE towards the OB (Liu et al, 1995). Another potential guidance mechanism for OEC migration is that the OE might secrete some repellants to promote OEC migration toward the OB during early development.…”

Olfactory ensheathing cells are attracted to, and can endocytose, bacteria

“…Thus in doing so, OECs effectively penetrate the transition zone between the periphery and CNS [14,15]. It has been demonstrated that the directional cue for this migration may be due to soluble factors originating from the target tissue, the olfactory bulb [16]. Although the identity of olfactory bulb-derived factors has yet to be identified, a recent study showed that glial cell line-derived neurotrophic factor stimulates intercellular interaction of lamellipodial waves that contribute to OEC migration [17] and which may be critical for the establishment of olfactory axon projections between the nasal cavity and the brain.…”

Differential reaction of outgrowing olfactory neurites monitored in explant culture

“…This result indicates that the OB released long-range attractants, which may act in concert with permissive OEC cues. These bulb-derived attractants may be identical to the ones that attract OECs in early development (Liu et al, 1995), although it has to be kept in mind that substances may diffuse over longer distances in the culture dish than they might do in the tissue in vivo. Closer investigation of factors released by the precultured bulb and their potency to attract axons are now feasible, and their effect on the growth cone can be tested in live imaging experiments.…”