Ultrastructural study of ensheathing cells in early development of olfactory axons.

Ultrastructural observations in the grey short-tailed opossum (Monodelphis domestica) and rat revealed that ensheathing cells were intimately related to the early formation of olfactory axons. Whilst the axons were still in the olfactory epithelium, they were enveloped by ensheathing cell processes which formed a cradle-like structure on the basal side of the epithelium. Continued downgrowth of the axons towards the lamina propria resulted in an evagination with the ensheathing cell process or cell body in direct contact with the basal lamina. Subsequently the basal lamina became fragmented, and the newly formed olfactory nerve emerged from the olfactory epithelium. As the olfactory nerve grew, it was observed that the ensheathing cell process always extended ahead of the axons while axon terminals moving ahead of ensheathing cells were never observed. The findings in this study suggest that ensheathing cells play a role in regulating and promoting olfactory axon growth.