GLIAL PROGENITOR CELLS OF THE NERVE-FIBER LAYER OF THE OLFACTORY-BULB- EFFECT OF ASTROCYTE GROWTH MEDIA

There are two morphologically distinct types of glial cells (i.e., ens heathing cells and astrocytes) in the nerve fiber layer (NFL) of the a dult mammalian olfactory bulb. Ensheathing cells provide ensheathment for olfactory axons, whereas astrocytes occupy the interfascicular spa ces of the olfactory NFL. During embryonic development, however, only one type of glial cell is found in this layer of the olfactory bulb, n amely, the ensheathing cell. Even though ensheathing cells take up res idence within the CNS, they are actually derived from the olfactory pl acode. Far less is known about the developmental origin of interfascic ular astrocytes, which arise either from the glial progenitor cells th at give rise to ensheathing cells or from astrocyte precursor cells th at migrate into the NFL from deeper layers of the bulb primordium. In the present study, enriched populations of ensheathing cells were grow n in vitro in media known to promote the growth and differentiation of astrocytes to determine whether ensheathing cell progenitors could di fferentiate into astrocytes. These media failed to induce the appearan ce of astrocytes in the ensheathing cell cultures. It was concluded th at the astrocytes of the NFL most likely arise from progenitor cells t hat migrate into this layer from deeper parts of the developing bulb.