From models to mechanisms: Odorant communication as a key determinant of social behavior in rodents during illness-associated states

Pheromones and other social odor cues convey rich information among rodents. Social investigation is described as a key element in olfactory communication, which involves motivated approaches to conspecifics and other socially relevant stimuli. This behavior is activated by the detection of social cues to gather information about conspecifics for subsequent strategies such as avoidance or further approach, thereby determining the extent and nature of physical contact that ensues. This feature indicates a useful way for describing the process of social communication in distance-based manner. In particular, airborne odorant signals in rodent species guide social investigation at a distance, and provide information regarding the health status of the odor donors. In this review, we will address the role of the inflammatory response in the release of odor cues that involve information about several illness-associated conditions (bacterial or parasitic infection, stressor exposure, etc.). We will provide an overview of how sex and developmental epoch in odor donors serve as predictors of subsequent social behavior. We conclude that inflammatory processes have a profound impact on social behavior through a direct effect on the sick individual (i.e., reduced motivation to engage in social interaction), while the release of illness-related, aversive odor cues from the sick individual serves to inhibit social investigation by healthy conspecifics. Together, this dual impact of acute illness is thought to minimize disease transmission across individuals and promote healthy group living.