State-dependent modulation of odor valence and social behaviour via the main olfactory pathway
1 Institute of Physiology II, Faculty of Medicine, University Clinic Bonn (UKB), University of Bonn, Bonn, Germany
The olfactory system translates the detection of volatile chemicals (odours) into perceptual features such as odour identity, intensity, and valence to generate appropriate behavioural responses. Odour valence is a particularly critical feature as it elicits appropriate aversion and attraction – motivated behaviours that are crucial for survival. Importantly, odour valence can be significantly modulated by several factors including internal state (e.g., hormonal status), context and experience. Despite its importance, the mechanisms underlying the encoding and modulation of odour valence remain poorly understood. Moreover, previous studies investigating valence modulation have almost exclusively focused on artificially (conditioned) valence changes. Thus, how untrained (innate) odour valence is encoded and modulated by naturally occurring changes, e.g. the internal state of the animal, remains largely elusive. Here, we identified a naturally occurring switch in innate valence responses towards a volatile social odour that is dependent on the neuroendocrine state. In this model, 1) the response of female mice to the male social cue trimethylamine (TMA) significantly depends on the estrus-state; 2) This behavioral switch depends on a defined receptor, TAAR5, which is expressed in the main olfactory system and is specifically activated by TMA; 3) This switch in behavior is specific to TMA. This naturally occurring switch in odor valence provides a unique opportunity to study a non-conditioned, potentially inducible change in perception.