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Abstract:
Carvone enantiomers (d and l optical isomers) have been shown to be discriminable by humans even though the odor qualities are quite similar. Our experiment is based on a finding (J. Steroid Biochem. Molec. Biol. 1991;39(4B):621) that Concanavalin A (ConA) applied to a frog olfactory epithelium preparation blocks cAMP transduction induced by d- but not by l-carvone. We used standard operant conditioning methods to train animals to discriminate low odor concentrations of d-carvone from clean air, to discriminate l-carvone from clean air; or to discriminate between clean air and the odors of d-carvone, l-carvone, ethyl acetate and methacrylic acid. After perfusion of the nasal cavity with ConA, rats did not respond to d-carvone above or near chance level, while the l-carvone response was not affected at the same or higher ConA doses. However, for rats trained on both enantiomers and the two other unrelated odorants, the d-carvone response remained unaffected by ConA. These results suggest to us that: (1) ConA blocks at least one chiral receptor selective for d-carvone; (2) d-carvone odor quality is modified by ConA so that it is no longer recognized by rats trained on d-carvone only, while rats trained to generalize odors still respond to d-carvone.
