Chemical Senses Advance Access originally published online on September 1, 2005
Chemical Senses 2005 30(8):627-642; doi:10.1093/chemse/bji056
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Determinants for Nasal Trigeminal Detection of Volatile Organic Compounds
1 Chemosensory Perception Laboratory, Department of Surgery (Otolaryngology), University of California, San Diego, La Jolla, CA 92093-0957, USA and 2 Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
Correspondence to be sent to: J. Enrique Cometto-Muñiz, Chemosensory Perception Laboratory, Department of Surgery (Otolaryngology), University of California, San Diego, 9500 Gilman Drive, Mail Code 0957, La Jolla, CA 92093-0957, USA. e-mail: ecometto{at}ucsd.edu
We explored the influence of methodological and chemical parameters on the detection of nasal chemesthesis (i.e., trigeminal stimulation) evoked by volatile organic compounds (VOCs). To avoid odor biases, chemesthesis was probed via nasal pungency detection in anosmics and via nasal localization (i.e., lateralization) in normosmics, in both cases using forced-choice procedures. In the experiments with anosmics, 12 neat VOCs were selected based on previous reports of lack of chemesthetic response. Although none of the VOCs reached 100% detection, detectability and confidence of detection were higher when using a glass vessel system adapted with nosepieces to fit the nostrils tightly than when using wide-mouth glass jars. Half the stimuli were detected well above chance and half were not. When the latter were tested again after being heated to 37°C, that is, body temperature (from room temperature, 23°C), to increase their vapor concentration, only one, octane, significantly increased its detectability. Chemesthesis gauged with normosmics mirrored that with anosmics. Gas chromatography measurements showed that, even at 23°C, the saturated vapor concentrations of the undetected stimuli, except vanillin, were well above the respective calculated nasal pungency threshold (NPT) from an equation that, in the past, had accurately described and predicted NPTs. We conclude that, except for octane and perhaps vanillin, the failure of the other four VOCs to precipitate nasal chemesthesis rests on a chemical–structural limitation, for example, the molecules lack a key property to fit a receptor pocket, rather than on a concentration limitation, for example, the vapor concentration is too low to reach a threshold value.
Key words: anosmics, chemical irritation cutoff, nasal localization or lateralization, nasal pungency, structure–activity in chemesthesis, trigeminal nerve
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