Rose odor can innately counteract predator odor.

When animals smell a predator odor such as 2,5-Dihydro-2,4,5-trimethylthiazoline (TMT), even if it is a novel substance, the hypothalamo-pituitary-adrenal (HPA) axis is activated, causing stress-like behaviors. Although the medial part of the bed nucleus of stria terminalis (mBST) is known to be involved in this process, the mechanism remains unclear. Moreover, it is unknown whether there is any odor that can counteract the predator odor, even when the odorants are novel substances for the animals. In this study, we assessed whether rose odor can counteract by counting the number of activated neurons in mice brain following the presentation of rose odor with or without TMT for 30 min. The number of activated cells in the mBST and in the ventrorostral part of the anterior piriform cortex (APC) was significantly reduced by a mixture of TMT and rose odor; however, no significant differences were noted in the dorsal part of the APC and in the olfactory bulb (OB) following TMT presentation with or without rose odor. The results suggest that rose odor may counteract the TMT-induced stress response in the OB and/or APC and suppress the neural circuit to the mBST. It also indicates that there are some odors that can innately counteract predator odor, even when they have not been experienced before.