Mechanism of olfactory masking in the sensory cilia.

Olfactory masking has been used to erase the unpleasant sensation in human cultures for a long period of history. Here, we show a positive correlation between the human masking and the odorant suppression of the transduction current through the cyclic nucleotide-gated (CNG) and Ca2+-activated Cl- (Cl(Ca)) channels. Channels in the olfactory cilia were activated with the cytoplasmic photolysis of caged compounds, and their sensitiveness to odorant suppression was measured with the whole cell patch clamp. When 16 different types of chemicals were applied to cells, cyclic AMP (cAMP)-induced responses (a mixture of CNG and Cl(Ca) currents) were suppressed widely with these substances, but with different sensitivities. Using the same chemicals, in parallel, we measured human olfactory masking with 6-rate scoring tests and saw a correlation coefficient of 0.81 with the channel block. Ringer's solution that was just preexposed to the odorant-containing air affected the cAMP-induced current of the single cell, suggesting that odorant suppression occurs after the evaporation and air/water partition of the odorant chemicals at the olfactory mucus. To investigate the contribution of Cl(Ca), the current was exclusively activated by using the ultraviolet photolysis of caged Ca, DM-nitrophen. With chemical stimuli, it was confirmed that Cl(Ca) channels were less sensitive to the odorant suppression. It is interpreted, however, that in the natural odorant response the Cl(Ca) is affected by the reduction of Ca2+ influx through the CNG channels as a secondary effect. Because the signal transmission between CNG and Cl(Ca) channels includes nonlinear signal-boosting process, CNG channel blockage leads to an amplified reduction in the net current. In addition, we mapped the distribution of the Cl(Ca) channel in living olfactory single cilium using a submicron local [Ca2+]i elevation with the laser photolysis. Cl(Ca) channels are expressed broadly along the cilia. We conclude that odorants regulate CNG level to express masking, and Cl(Ca) in the cilia carries out the signal amplification and reduction evenly spanning the entire cilia. The present findings may serve possible molecular architectures to design effective masking agents, targeting olfactory manipulation at the nano-scale ciliary membrane.

The Use of Semantic Differential Scaling to Define the Multi-Dimensional Representation of Odors.

The mental representation elicited by smelling an odor often consists of multiple sensory and affective dimensions, yet, the richness of this elaboration is difficult to capture using methods to rate the intensity of these factors in isolation. Attempts to use language descriptors for olfactory experience have also been shown to be rather limited; among non-specialists, there is no universally accepted system for describing odors, leading to greater reliance on specific item associations. In this study we explored the utility of semantic differential scaling for illustrating the various dimensions of olfactory experience. 300 volunteers rated thirty distinct odorants using 50 SDS adjectives. Three factors emerged from the analysis (based on 17 adjective-pairs) accounting for 53% of the variance, and corresponding to the evaluation, potency and activity dimensions identified for other stimulus types. SD scaling appears to be a viable method for identifying the multiple dimensions of mental representation evoked when smelling an odorant and may prove a useful tool for both consumer and basic research alike. PRACTICAL APPLICATIONS: Although numerous methods of classifying odors have been developed, little agreement has been achieved on the dimensions that are useful to both basic and consumer research. The identification of a set of Semantic Differential adjectives which are relevant to olfactory experience can become a useful tool for classifying the qualitative and affective basis on which odorants differ.. In particular, the degree to which odorants evokes multi-dimensional representations from other sensory modalities (visual, auditory, somatosensory or gustatory), can be usefully applied in the arena of product development both within and across cultures.