The pheromone darcin drives a circuit for innate and reinforced behaviours

Organisms have evolved diverse behavioural strategies that enhance the likelihood of encountering and assessing mates¹. Many species use pheromones to communicate information about the location, sexual and social status of potential partners². In mice, the major urinary protein darcin—which is present in the urine of males—provides a component of a scent mark that elicits approach by females and drives learning^3,4. Here we show that darcin elicits a complex and variable behavioural repertoire that consists of attraction, ultrasonic vocalization and urinary scent marking, and also serves as a reinforcer in learning paradigms. We identify a genetically determined circuit—extending from the accessory olfactory bulb to the posterior medial amygdala—that is necessary for all behavioural responses to darcin. Moreover, optical activation of darcin-responsive neurons in the medial amygdala induces both the innate and the conditioned behaviours elicited by the pheromone. These neurons define a topographically segregated population that expresses neuronal nitric oxide synthase. We suggest that this darcin-activated neural circuit integrates pheromonal information with internal state to elicit both variable innate behaviours and reinforced behaviours that may promote mate encounters and mate selection.