Sensory detection of glutaraldehyde in drinking water-emergence of sensitivity and specific anosmia

Olfactory Deprivation and Enrichment: An Identity of Opposites?

The effects of deprivation and enrichment on the electroolfactogram of mice were studied through the paradigms of unilateral naris occlusion and odor induction, respectively. Deprivation was shown to cause an increase in electroolfactogram amplitudes after 7 days. We also show that unilateral naris occlusion is not detrimental to the gross anatomical appearance or electroolfactogram of either the ipsilateral or contralateral olfactory epithelium even after year-long survival periods, consistent with our previous assumptions. Turning to induction, the increase in olfactory responses after a period of odor enrichment, could not be shown in CD-1 outbred mice for any odorant tried. However, consistent with classical studies, it was evident in C57BL/6J inbred mice, which are initially insensitive to isovaleric acid. As is the case for deprivation, enriching C57BL/6J mice with isovaleric acid causes an increase in their electroolfactogram response to this odorant over time. In several experiments on C57BL/6J mice, the odorant specificity, onset timing, recovery timing, and magnitude of the induction effect were studied. Considered together, the current findings and previous work from the laboratory support the counterintuitive conclusion that both compensatory plasticity in response to deprivation and induction in response to odor enrichment are caused by the same underlying homeostatic mechanism, the purpose of which is to preserve sensory information flow no matter the odorant milieu. This hypothesis, the detailed evidence supporting it, and speculations concerning human odor induction are discussed.

Tale of two isomers: complexities of human odor perception for cis- and trans-4-methylcyclohexane methanol from the chemical spill in West Virginia

Application of gas chromatography with mass spectrometric and human olfactory "sniffer" detectors reveals the nature of odorous chemicals from an industrial chemical spill. Crude 4-methylcyclohexane methanol (4-MCHM) spilled in a river and then contaminated drinking water and air for over 300000 consumers living in West Virginia. Olfactory gas chromatography allows investigators to independently measure the odor of chemical components in a mixture. Crude 4-MCHM is comprised of several major cyclohexane components, four of which have distinct isomer pairs. The cis- and trans-4-MCHM isomers are the only components to have distinct odors at the concentrations used in this study. The trans-4-MCHM is the dominant odorant with descriptors of "licorice" and "sweet". Trans-4-MCHM has an air odor threshold concentration of 0.060 ppb-v (95% CI: 0.040-0.091). The odor threshold concentrations are not influenced by gender or age but are lower by a factor of 5 for individuals with prior exposure compared to naïve subjects. Individual trans-4-MCHM odor threshold concentrations vary by more than a factor of 100. The cis-4-MCHM isomer has approximately a 2000-fold higher odor threshold concentration, different descriptors, and an even wider individual response range.

2-bromo-4-methylphenol, a compound responsible for iodine off-flavor in wines

This study focuses on an off-flavor in wines treated by an acidification technique involving ion-exchange resins. Applying reversed-phase HPLC on a C18 column to a contaminated wine extract resulted in 25 fractions in dilute alcohol medium, and only one, fraction 19, presented this off-flavor. Its composition was analyzed using gas chromatography coupled to olfactometry (GC-O) and mass spectrometry (GC-MS), leading to the identification of 2-bromo-4-methylphenol for the first time as a compound associated with an "iodine" aroma in white, rosé, and red table wines. Contaminated wines presented a wide range of levels, with maximum concentrations of 28900, 7556, and 48000 ng/L and minimum values of 260, 35, and 63 ng/L in white, rosé, and red wines, respectively. Sensory studies investigating 2-bromo-4-methylphenol gave very interesting results. Individual thresholds ranged from 0.15 to >77.4 ng/L in reverse osmosis water, from 0.4 to >193.5 ng/L in white wine, from 0.5 to >774 ng/L in rosé wine, and from 0.5 to >774 ng/L in red wine. The very wide distribution of individual thresholds suggested the presence of two populations, sensitive and nonsensitive, with a bimodal frequency distribution. The odor descriptions quoted by the more sensitive group characterized 2-bromo-4-methylphenol using terms with "iodine" connotations in both the reverse osmosis water and red wine matrices. The descriptors for commercial wines naturally affected by this defect were seafood, iodine, mud, and fish.

Experience-induced changes in taste identification of monosodium glutamate (MSG) are reversible

A few studies have reported experience-inducible changes in human taste and olfactory sensitivities. However, no study thus far has systematically characterized the stability of the enhanced sensitivities. In our previous study, we found increases in taste identification ability for monosodium glutamate (MSG) in subjects who had been briefly exposed to MSG in food for 10 days. Here, we tested the temporal stability of the enhanced taste identification ability. First, we exposed a group of 20 subjects to MSG in food and then compared their sensitivities to MSG with those of a control group. When tested on day 11 or 12, the mean MSG taste identification ability of the MSG-exposed group was significantly higher than the control group. Next, 11 of the subjects who were exposed to MSG in food initially, and then stopped being exposed performed significantly poorer in identifying MSG after 10 days of the nonexposure than they did 10 days before. In contrast, nine subjects who were exposed to MSG initially and continued being exposed maintained their high identification levels. These results support earlier finding of the plasticity in the taste identification of MSG and show that the enhanced identification ability can be reversed rapidly when MSG exposure is not sustained.

Olfactory perceptual learning: the critical role of memory in odor discrimination

The major problem in olfactory neuroscience is to determine how the brain discriminates one odorant from another. The traditional approach involves identifying how particular features of a chemical stimulus are represented in the olfactory system. However, this perspective is at odds with a growing body of evidence, from both neurobiology and psychology, which places primary emphasis on synthetic processing and experiential factors--perceptual learning--rather than on the structural features of the stimulus as critical for odor discrimination. In the present review of both psychological and sensory physiological data, we argue that the initial odorant feature extraction/analytical processing is not behaviorally/consciously accessible, but rather is a first necessary stage for subsequent cortical synthetic processing which in turn drives olfactory behavior. Cortical synthetic coding reflects an experience-dependent process that allows synthesis of novel co-occurring features, similar to processes used for visual object coding. Thus, we propose that experience and cortical plasticity are not only important for traditional associative olfactory memory (e.g. fear conditioning, maze learning, and delayed-match-to-sample paradigms), but also play a critical, defining role in odor discrimination.