Re-evaluating NADPH-diaphorase histochemistry as an indicator of nitric oxide synthase: an examination of the olfactory system of coho salmon (Oncorhynchus kisutch).
The NADPH-diaphorase (NADPH-d) histochemical technique is commonly used to localize the nitric oxide (NO)-producing enzyme NO synthase (NOS) in neural tissues. In the olfactory tissues of vertebrates, however, NADPH-d staining can be present without the detection of NOS by other methods. We used pharmacological controls to determine whether NADPH-d staining was indicative of NOS in olfactory tissues from coho salmon (Oncorhynchus kisutch). We also compared NADPH-d staining with immunoreactivity to NOS. NADPH-d staining localized to the olfactory epithelium and to the glomerular layer of the olfactory bulb. Two NOS inhibitors, L-N-nitroarginine and L-N-methyl-L-arginine, failed to block this staining, but the less specific flavin-binder, diphenylene iodonium chloride, decreased or eliminated NADPH-d staining in all olfactory tissues. Immunoreactivity to NOS was present in short axon cells of the bulb, but was absent from the epithelium. Our findings show that NADPH-d staining was not representative of NOS in the olfactory tissues of salmon.
Lema
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Section of Neurobiology, Physiology, and Behavior, University of California, 1 Shields Avenue, Davis, CA 95616, USA. sclema@ucdavis.edu
Nevitt
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GA
D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology; D009252:NADPH Dehydrogenase / Q000032:analysis*; D019001:Nitric Oxide Synthase / Q000032:analysis* / Q000037:antagonists & inhibitors; D019335:Nitroarginine / Q000494:pharmacology; D009833:Olfactory Pathways / Q000201:enzymology*; D017684:Oncorhynchus kisutch; D019323:omega-N-Methylarginine / Q000494:pharmacology
D004791:Enzyme Inhibitors; D019335:Nitroarginine; D019323:omega-N-Methylarginine; D019001:Nitric Oxide Synthase; D009252:NADPH Dehydrogenase