Odor masking in the rat.

A computer controlled behavioral apparatus and olfactometer were used to determine the olfactory threshold of rats for propionic acid and to determine their ability to discriminate propionic acid in binary mixtures that contained the dissimilar odorants, limonene or carvone, or a similar odorant, acetic acid. The concentration of propionic acid that rats required to discriminate this substance from the other odorants was substantially above that of the threshold concentration, the increase being greatest with acetic acid. The increased levels of propionic acid needed for detection of this odorant in mixtures is attributed to masking by the other components. This study represents the first time behavioral methods have been used to demonstrate masking with odor mixtures in a rodent. The results indicate that it should be possible to use behavioral methods to define conditions for odor masking in animals so that physiological studies of the underlying mechanisms can be achieved.