Olfactory bulb ensheathing glia: A unique cell type with axonal growth‐promoting properties

Abstract

The olfactory bulb (OB) is a structure of the central nervous system (CNS) in which axonal growth occurs throughout the lifetime of the organism. A major difference between the OB and the remaining CNS is the presence of ensheathing glia in the first two layers of the OB. Ensheathing glia display properties that might be involved in the process of regeneration and they appear to be responsible for the permissibility of the adult OB to axonal growth. In fact, transplants of ensheathing glia can be used as promoters of axonal regeneration within the adult CNS. The axonal growth-promoting properties of ensheathing glia make the study of this cell type interesting for understanding the mechanisms underlying axonal regeneration. Several groups have studied OB ensheathing cells extensively in an attempt to classify them within any of the known glial groups. However, this cell type does not exhibit the phenotypic features of any glial population described thus far. In this article we review the characteristics that differentiate ensheathing glia from other peripheral and central glial populations as well as the properties that involve them in axonal regeneration. The evidence suggests that ensheathing glia are unique, have their own identity, and do not belong to any previously described glial type.

d-Serine as a Neuromodulator: Regional and Developmental Localizations in Rat Brain Glia Resemble NMDA Receptors

“…The highest densities of D-serine in the brain occur in the AOB, in specialized glia that surround axons of the vomeronasal fibers that project from the vomeronasal organ to olfactory glomeruli (Raisman, 1985;Ramon-Cueto and Valverde, 1995). This fiber system mediates the actions of pheromones on reproductive behavior (Halpern, 1987).…”

Migratory properties of cultured olfactory ensheathing cells by single-cell migration assay

“…This remarkable regenerative property of the olfactory system is thought to be in part due to a special type of glia cells [2,3], the olfactory ensheathing cells (OECs), which support and guide the growth of olfactory axons and ensheath the bundles of olfactory nerves that extend from the olfactory epithelium to the olfactory bulb [4]. Owing to these unique roles, OEC transplantation has emerged as a promising experimental therapy for axonal injuries and demyelinating disease [5].…”

Olfactory ensheathing cells: Historical perspective and therapeutic potential

“…This dichotomy in the success of axonal growth appears due, at least in part, to the different glial cell environments through which olfactory and nonolfactory axons must grow (Doucette, 1990(Doucette, , 1995Ramon-Cueto and Valverde, 1995;Franklin and Barnett, 1997;Fawcett, 1998;. Macroglia of the CNS play a major role in the normally abortive regeneration of nonolfactory CNS axons, due most likely both to the presence of inhibitory molecules as well as to the lack of sufficient growth promoting molecules (Reier and Houle, 1988;Hoke and Silver, 1994;GebickeHaerter et al, 1996;Moore and Thanos, 1996;Frisen, 1997;Ridet et al, 1997).…”

“…The driving force behind these experiments was to manipulate the cellular environment of the lesion site in the brain or spinal cord so as to create one more conducive to supporting axonal growth across the lesion and into the tissue on the distal side. Even though, as mentioned above, macroglia of the CNS appear to play a major role in the abortive regeneration of axons in the brain and spinal cord (Liuzzi and Lasek, 1987;Reier and Houle, 1988;Reier et al, 1989;Fawcett, 1991;Hatten et al, 1991), it was hypothesized that the presence of OECS would create a more favourable and supportive environment for axonal growth (Doucette, 1990(Doucette, , 1995Wozniak, 1993;Ramon-Cueto and Valverde, 1995;Franklin and Barnett, 1997).…”