OLFACTORY-BULB ENSHEATHING GLIA - A UNIQUE CELL-TYPE WITH AXONAL GROWTH-PROMOTING PROPERTIES

The olfactory bulb (OB) is a structure of the central nervous system ( CNS) in which axonal growth occurs throughout the lifetime of the orga nism. A major difference between the OB and the remaining CNS is the p resence of ensheathing glia in the first two layers of the OB. Ensheat hing 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 t he study of this cell type interesting for understanding the mechanism s underlying axonal regeneration. Several groups have studied OB enshe athing cells extensively in an attempt to classify them within any of the known glial groups. However, this cell type does not exhibit the p henotypic 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 th e properties that involve them in axonal regeneration. The evidence su ggests that ensheathing glia are unique, have their own identity, and do not belong to any previously described glial type. (C) 1995 Wiley-L iss, Inc.