Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Comparative Study
. 2010 Dec 1;30(48):16391-8.
doi: 10.1523/JNEUROSCI.2527-10.2010.

Enzymatic conversion of odorants in nasal mucus affects olfactory glomerular activation patterns and odor perception

Ayumi Nagashima  1 , Kazushige Touhara
Affiliations
Comparative Study

Enzymatic conversion of odorants in nasal mucus affects olfactory glomerular activation patterns and odor perception

Ayumi Nagashima et al. J Neurosci. .

Abstract

Odor information is decoded by a combination of odorant receptors, and thus transformed into discrete spatial patterns of olfactory glomerular activity. It has been found, however, that for some odorants, there are differences between the ligand specificity of an odorant receptor in vitro and its corresponding glomerulus in vivo. These observations led us to hypothesize that there exist prereceptor events that affect the local concentration of a given odorant in the nasal mucus, thus causing the apparent specificity differences. Here we show that odorants with functional groups such as aldehydes and esters are targets of metabolic enzymes secreted in the mouse mucus, resulting in their conversion to the corresponding acids and alcohols. The glomerular activation patterns elicited by an enzyme-targeted odorant in the olfactory bulb was different in the presence of an enzyme inhibitor in the mucosa, suggesting that the enzymatic conversion occurs fast enough to affect recognition of the odorant at the levels of olfactory sensory neurons. Importantly, olfactory discrimination tests revealed that mice behaviorally trained to associate an enzyme-targeted odorant to sugar rewards could not discriminate the odorant after treatment with the enzyme inhibitor. These results reveal that the enzymatic conversion of odorants in the nasal mucus appears be fast enough to affect olfactory perception, which sheds light on the previously unappreciated role of nasal mucosal enzymes in odor sensation.

PubMed Disclaimer

Figures

Figure 1.
Figure 1.
GC/MS analysis for the enzymatic conversion of benzaldehyde and acetyl isoeugenol in nasal mucus. A, Total ion chromatograms of the organic extracts from Ringer's solution (black line, top panel), nasal mucus (red line, middle panel), and heated nasal mucus (blue line, bottom panel), each incubated with benzaldehyde. The extracted ion chromatogram of the molecular ion peak of benzoic acid (m/z 122) is shown as the inset. Peaks for benzaldehyde, benzyl alcohol, and benzoic acid are shown by arrowheads. B, Total ion chromatograms of the organic extracts from Ringer's solution (black line, top panel), nasal mucus (red line, middle panel), and heated nasal mucus (blue line, bottom panel), each incubated with acetyl isoeugenol (AIEG). Peaks for AIEG and isoeugenol (IEG) are shown by arrowheads.
Figure 2.
Figure 2.
Structure–activity relationships of the enzyme reactions in nasal mucus of odorants with an aldehyde or acetate group. A, The percentage of converted odorants with an aldehyde group (conversion ratio) was plotted as the mean ± SEM (n = 3). B, The percentage of converted odorants with an acetate group (conversion ratio) was plotted as the mean ± SEM (n = 3). C, The compounds not converted.
Figure 3.
Figure 3.
The in vivo enzymatic conversions of benzaldehyde and acetyl isoeugenol in the nasal cavity. A, Total ion chromatogram of the benzaldehyde sample recovered from the nasal cavity. Upper panel, Control benzaldehyde; lower panel, the sample retrieved from the nasal cavity after perfusion. Extracted ion chromatogram of the molecular ion peak of benzoic acid (m/z 122) is shown as the inset. Peaks for benzaldehyde, benzyl alcohol, and benzoic acid are shown by arrowheads. B, Total ion chromatogram of the acetyl isoeugenol (AIEG) sample recovered from the nasal cavity. Upper panel, Control AIEG; lower panel, the sample retrieved from the nasal cavity after perfusion. Peaks for AIEG and isoeugenol (IEG) are shown by arrowheads. C, Extracted ion chromatogram of the molecular ion peaks m/z 122, 108, 106, 105, 94, and 79 of the nasal mucus sample obtained from mice that naturally inhaled benzaldehyde vapor. D, Extracted ion chromatogram of the molecular ion peak m/z 164 of the nasal mucus sample obtained from mice that naturally inhaled AIEG vapor. The samples in C and D were analyzed by GC/MS-SIM.
Figure 4.
Figure 4.
Effects of inhibitors for carboxylesterase and carbonic anhydrase on acetyl isoeugenol–isoeugenol conversion in nasal mucus. A, Dose-dependent inhibition by carboxylesterase inhibitor BNPP, but not by carbonic anhydrase inhibitor AZ. The mean conversion ratio was shown as percentage ± SEM (n = 3). Statistics, One-way ANOVA and post hoc test (Dunnett's test), *p < 0.05; ***p < 0.001. B, Analysis of the enzymatic activity of nasal mucus collected 1 d after application of Ringer's solution (left panel), AZ (middle panel), or BNPP (right panel) in the nasal cavity. C, The amount of nonconverted acetyl isoeugenol (AIEG) remaining 1 d after application of AZ or BNPP upon odorant perfusion into the nasal cavity. Statistics, One-way ANOVA and post hoc test (Dunnett's test), **p < 0.01.
Figure 5.
Figure 5.
Comparison of odorant-evoked glomerular activation patterns stimulated with acetyl isoeugenol before and after the application of inhibitor. A, Glomerular Ca2+ responses to acetyl isoeugenol (AIEG) before/after the application of BNPP shown as pseudocolored images. Left, Fluorescent image of the olfactory bulb. Middle images, Pseudocolored images of the olfactory bulb before and after the application of BNPP showing the glomerular activation patterns; red corresponds to the greatest response. The data from three animals (#1, #2, #3) are shown. Right, Schematic illustrations of glomerular activation patterns in pseudocolored images. The filled circles indicate glomeruli activated by AIEG, while the glomeruli with open circles are the ones that responded to AIEG only after BNPP application. Some extra glomeruli are activated by AIEG after BNPP treatment. B, Glomerular Ca2+ responses to acetyl isoeugenol (AIEG) before/after the application of AZ shown as pseudocolored images. Left, Fluorescent image of the olfactory bulb. Middle images, Pseudocolored images of the olfactory bulb before and after the application of AZ showing the glomerular activation patterns. The data from two animals (#4, #5) are shown. Right, Schematic illustrations of glomerular activation patterns in pseudocolored images. The filled circles indicate glomeruli activated by AIEG. There was no effect of AZ treatment on glomerular activation patterns.
Figure 6.
Figure 6.
Effects of enzymatic conversion on the recognition of acetyl isoeugenol (AIEG) in a behavioral context. Mice were trained for 4 d to associate a reward (sugar grains) with either of two odorants. After 4 d of training, BNPP or AZ was applied to the nasal cavities of the mice. On day 5, investigation times were measured for each pair of odorants without the sugar reward. Mean investigation times (in seconds) ± SEM during the 2 min test period are shown as bar graphs for odorants paired with the sugar reward [odor (+), gray bars], and unpaired odorants [odor (−), white bars]. A, Eugenol (EG) versus pentanol; B-1, EG versus AIEG; B-2, pentanol versus AIEG; B-3, 2-heptanone versus AIEG; C, IEG versus AIEG. Statistics, Paired t test was used for two related samples (pair of odorants in each group); *p < 0.05, **p < 0.01 (black asterisk). Non-repeated-measures ANOVA for three independent groups (control, AZ, BNPP group) and post hoc test (Dunnett's test), *p < 0.05, **p < 0.01 (gray asterisk).
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Badonnel K, Denis JB, Caillol M, Monnerie R, Piumi F, Potier MC, Salesse R, Baly C. Transcription profile analysis reveals that OBP-1F mRNA is downregulated in the olfactory mucosa following food deprivation. Chem Senses. 2007;32:697–710. - PubMed
    1. Ben-Arie N, Khen M, Lancet D. Glutathione S-transferases in rat olfactory epithelium: purification, molecular properties and odorant biotransformation. Biochem J. 1993;292:379–384. - PMC - PubMed
    1. Bogdanffy MS, Randall HW, Morgan KT. Biochemical quantitation and histochemical localization of carboxylesterase in the nasal passages of the Fischer-344 rat and B6C3F1 mouse. Toxicol Appl Pharmacol. 1987;88:183–194. - PubMed
    1. Bogdanffy MS, Manning LA, Sarangapani R. High-affinity nasal extraction of vinyl acetate vapor is carboxylesterase dependent. Inhal Toxicol. 1999;11:927–941. - PubMed
    1. Brose H, Strotmann J, Breer H. List of abstracts from the XVIIIth Congress of European Chemoreception Research Organization, ECRO-2008: uptake of odorant binding proteins in the olfactory epithelium. Chem Senses. 2009;34:E58.

Publication types

Substances

LinkOut - more resources