NITRIC-OXIDE SYNTHASE IN THE OLFACTORY MUCOSA OF THE LARVAL SEA LAMPREY (PETROMYZON-MARINUS)

The use of nitric oxide, a product of enzymatic reduction of L-arginin e by nitric oxide synthase, as a modulator of processes within the olf actory mucosa was investigated in larval sea lampreys, extant fish of ancient vertebrate origin. In the present study, we demonstrated that the sea lamprey olfactory mucosa is specifically sensitive to L-argini ne, that the L-arginine responses are inhibited by an inhibitor of nit ric oxide synthase, Nw-nitro-L-arginine, and that nitric oxide synthas e is present in olfactory receptor cells, sustentacular cells, and bas al cells. Electron microscopic examination using NADPH-diaphorase hist ochemistry revealed intense labeling within secretory vesicles of sust entacular cells and in proximity to mitochondria within olfactory rece ptor cell dendrites and sustentacular cells. At the base of the olfact ory epithelium, NADPH-diaphorase staining was intense in the perinucle ar cytoplasm of a subpopulation of basal cells, moderate in sustentacu lar cell foot processes, and scattered in olfactory receptor cell axon s. Throughout axons in the olfactory epithelium and the lamina propria , labeling predominated in axonal profiles with mitochondria. These ph ysiological and ultrastructural studies imply that in sea lamprey larv ae, nitric oxide modulates peri-receptor events of L-arginine chemosti mulation, olfactory receptor cell axonal activity, and developmental p rocesses. (C) 1996 Wiley-Liss, Inc.