Nitric oxide synthase, cGMP, and NO-mediated cGMP production in the olfactory bulb of the rat

High levels of nitric oxide synthase and cyclic 3', 5'-guanosine monophosphate (cGMP) in the olfactory bulb suggest that nitric oxide, acting as a diffusible intercellular messenger molecule inducing increased synthesis of cGMP, plays an important role in olfaction. The localization of cGMP after sodium nitroprusside stimulation of in vitro slices of rat olfactory bulb was compared with the distribution of nicotinamide adenine dinucleotide phosphate-diaphorase, nitric oxide synthase, and glial fibrillary acidic protein. cGMP was detected immunohistochemically in cryostat sections. In the presence of the phosphodiesterase blocker isobutyl methylxanthine, cGMP was present in neurons in the glomerular layer, axons in the external and internal plexiform layers, and in a few somata and axons of the granule cell layer. This staining was blocked by N(G)-nitro-L-arginine methylester hydrochloride or hemoglobin. After sodium nitroprusside stimulation, the olfactory nerve layer was intensely stained, as were the glomeruli and periglomerular cells. In the external plexiform layer, axonal staining was increased substantially, and there were occasional multipolar cGMP-positive neurons. In the internal plexiform and granule cell layers, axonal staining was greatly increased. Many granule cells were also cGMP positive after sodium nitroprusside stimulation. cGMP and nitric oxide synthase-positive neuronal overlapped in the glomerular and granule cell layers, but staining was not colocalized. cGMP was not found in astrocytes. The glutamatergic antagonists D-2-amino-5-phosphonovalerate and 6-cyano-7-nitroquinoxaline caused differential inhibition of cGMP accumulation in layers of the olfactory bulb. These findings support the hypothesis that nitric oxide is an intercellular messenger in the olfactory bulb (Breer and Shepherd [1993] Trends Neurosci. 16:5-9).