Minimum Odorant Concentrations Detectable by the Dog and Their Implications for Olfactory Receptor Sensitivity
In the absence of other cues, the sooner an animal detects, recognizes and responds to certain odorants entering its environment, the better will be its chances of survival. Faced with such evolutionary pressures, the ability to detect odorants, in some species at least, may well have approached or reached absolute theoretical limits. This seems to be true of the silk moth, Bombyx mori. The male will respond, behaviorally, to the female sex attractant, Bombykol, when 104 molecules/cm3 are present in air currents flowing at 60cm3/s over 2 s. Experiments with tritiated Bombykol suggest that this corresponds to about one molecule per sense cell (Schneider, et al., 1968; Schneider, 1969). In mammals, however, delivery of odorant molecules to the receptors depends on the flow of air through respiratory airways and across extensive mucous surfaces. These and other variables compound the difficulty of assessing the sensitivity of individual receptors or sites. It is nevertheless valuable to attempt such an estimate not only for its intrinsic interest but also for the light it may throw on olfactory mechanisms, and for the framework it provides in defining the nature and diversity of events that limit access of odorant molecules to receptor sites. Ultimately such information may also assist in evaluating whether, in a specific context, a given odorant is present in sufficient concentration to elicit a pattern of behavior.
KeywordsOlfactory Receptor Receptor Site Olfactory Epithelium Caprylic Acid Odorant Molecule
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