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 promoter protease nexin-1 (PN-1) is expressed in Schwann cell precursors and astroblasts during embryogenesis. In the adult nervous system, PN-1 persists in the Schwann cells and olfactory glia only. Light-microscopic immunohistochemistry has revealed the presence of PN-1 in the olfactory mucosa and in the nerve fiber layer of the olfactory bulb. The present electron-microscopic study of the gerbil olfactory bulb confirms the occurrence of PN-1 in ensheathing cells of the olfactory nerve fiber layer, a special type of glia which envelopes olfactory axons. In addition, PN-1 is contained in typical astrocytes of the nerve fiber layer 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 renewal of olfactory receptor neurons.