THE NEURITE GROWTH-PROMOTING PROTEASE NEXIN-1 IN GLIAL-CELLS OF THE OLFACTORY-BULB OF THE GERBIL - AN ULTRASTRUCTURAL-STUDY

The glia-derived serine protease inhibitor and neurite outgrowth promo tor protease nexin-1 (PN-1) is expressed in Schwann cell precursors an d astroblasts during embryogenesis. In the adult nervous system, PN-1 persists in the Schwann cells and olfactory glia only. Light-microscop ic immunohistochemistry has revealed the presence of PN-1 in the olfac tory mucosa and in the nerve fiber layer of the olfactory bulb. The pr esent electron-microscopic study of the gerbil olfactory bulb confirms the occurrence of PN-1 in ensheathing cells of the olfactory nerve fi ber layer, a special type of glia which envelops olfactory axons. In a ddition, PN-1 is contained in typical astrocytes of the nerve fiber la yer and of the glomerular layer. It is inferred that synthesis of PN-1 in the olfactory bulbs is maintained throughout adulthood because its neurite outgrowth promoting action is required for the continuous ren ewal of olfactory receptor neurons.