Innate liking and disgust reactions elicited by intraoral capsaicin in male mice

Liking and disgust are the primary positive and negative emotions, respectively, and are crucial for taking nutrients and avoiding toxins. These emotions are induced by multimodal stimuli, such as taste, olfactory, and somatosensory inputs, and their dysregulation is evident in various psychiatric disorders. To understand the biological basis of liking and disgust, it is crucial to establish an animal model that allows for objective measurement of liking and disgust in response to multimodal stimuli. The only readout shared in many species including humans for liking and disgust has been the taste reactivity. However, the readouts for non-taste stimuli-induced emotions remain unestablished. Here, we show that intraoral administration of capsaicin, a chemosomatosensory stimulus, elicits orofacial and somatic reactions in male mice which are similar to those observed in taste reactivity. Capsaicin induced liking reactions at low concentrations and disgust reactions at high concentrations. Capsaicin-induced disgust reactions consisted of various reactions, including gaping and forelimb flailing, with the proportion of each reaction among disgust reactions similar to that induced by bitter and sour stimuli. These findings indicate that the orofacial and somatic reactions defined as taste reactivity are elicited not only by taste stimuli but also by intraoral chemosomatosensory stimuli, suggesting that taste reactivity can be renamed as orosensory reactivity. Understanding the biological basis of orosensory reactivity would advance our comprehension of the fundamental mechanisms underlying liking and disgust across different sensory modalities.