Olfactory ensheathing cells

Olfactory ensheathing glia (OEG), also known as olfactory ensheathing cells (OECs) or olfactory ensheathing glial cells, are a type of macroglia (radial glia) found in the nervous system. They are also known as olfactory Schwann cells because they ensheath the non-myelinated axons of olfactory neurons in a similar way to which Schwann cells ensheath non-myelinated peripheral neurons. They also share the property of assisting axonal regeneration. OEG are capable of phagocytosing axonal debris in vivo, and in vitro they phagocytose bacteria. Olfactory glia that express LYZ are thought to play an important role in immunoprotection in the mucosa, where neurons are directly exposed to the external environment. OEG have been tested successfully in experimental axonal regeneration in adult rats with traumatic spinal cord damage, and clinical trials are currently being conducted to obtain more information on spinal cord injuries and other neurodegenerative diseases.

In the peripheral nervous system OEG are dispersed within the olfactory epithelium and the olfactory nerve. In the central nervous system, OEG are found within the outer two layers of the olfactory bulb. During development, primitive olfactory neurons extend their axons from the olfactory placode, through the mesenchyme, towards the telencephalic vesicle. After reaching the telencephalic vesicle, a small layer of cells and axons cover the vesicle. Olfactory axons invade the basal lamina of the glia limitans and the olfactory bulb to create the olfactory nerve and glomerular layers. A fraction of the epithelial migrating precursors give rise to olfactory ensheathing glia that inhabit the olfactory nerve and glomerular layers. OEG and astrocytes interact with each other to form a new glia limitans. OEG are distinct from other glia in their developmental origin for they are present in the peripheral nervous system as well as the central nervous system. They also form on bundles of olfactory sensory neuron axons in a manner distinct from myelination.

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