Glucose-6-phosphate dehydrogenase and NADPH-consuming enzymes in the rat olfactory bulb

The resistance to oxidative stress is a multifactorial reaction involving the clustering of transcriptionally regulated genes. Because glucose-6-phosphate dehydrogenase (G6PD), the principal enzyme responsible for reducing power, is highly expressed in the olfactory bulb (OB), it is of interest to verify whether other enzymes utilizing NADPH are also highly expressed. The level and localization of G6PD- and NADPH-consuming enzymes, such as NADPH-cytochrome P450 oxidoreductase (P450R), glutathione reductase (GR), and NADPH-diaphorase (NADPH-d), were analyzed in the rat olfactory bulb (OB) by quantitative histochemistry and immunohistochemistry. The highest concentration of G6PD, P450R, and GR was observed in the olfactory nerve layer (ONL), suggesting a correlation in the expression of these enzymes at the gene level. Correlation in staining intensity between G6PD and NADPH-d activities occurred only in part of the ONL, some glomeruli, and scattered periglomerular cells. This peculiar distribution of NADPH-d could reflect a spatial patterning of the nose to bulb projections. Taken together, these results indicate that G6PD expression in the ONL could be related to the importance of generating a substantial supply of NADPH to sustain the detoxifying systems represented by GR and P450R reactions and, only in discrete zones, by NADPH-d activity.