Spontaneous Odor Aversion in Mice

Mice were kept in their home cage, water-deprived, and habituated to receiving two bottles of water for 1-h/day for 3 days. Then, a simultaneous choice was performed between one bottle containing a scented solution, either iso-amyl acetate or benzaldehyde, diluted in water and one bottle with water only in order to evaluate spontaneous odor aversion. Indeed, if some concentrations of iso-amyl acetate (0.05%) and benzaldehyde (0.01%) solutions are well accepted and considered neutral for the mice when presented alone^{31 (link)}, animals prefer to consume water over these scented solutions when presented a choice^{58 (link),59 (link)}, this allows an evaluation of odor detection. Based on this protocol, we performed two sets of experiments using different concentrations of the odorized solution. The “highest concentrations” (iso-amyl acetate—0.05% and benzaldehyde—0.01%, Sigma-Aldrich) represent concentrations known to be perceived and equally consumed by mice and previously used in odor-conditioning protocols^{31 (link),59 (link)}. The “lowest concentrations” consist of the same solutions diluted 100 times (i.e., iso-amyl acetate—0.0005% and benzaldehyde—0.0001%). In order to promote the choice and decrease the random consumption of a solution, the odor used and the position (left or right) of the odorized solution were randomly assigned, and the top of the bottle lids were spaced about 3 cm from each other.