Whole-mount imaging of responses in mouse vomeronasal neurons

Experience-Dependent Plasticity Drives Individual Differences in Pheromone-Sensing Neurons

Different individuals exhibit distinct behaviors, but studying the neuronal basis of individuality is a daunting challenge. Here, we considered this question in the vomeronasal organ, a pheromone-detecting epithelium containing hundreds of distinct neuronal types. Using light-sheet microscopy, we characterized in each animal the abundance of 17 physiologically defined types, altogether recording from half a million sensory neurons. Inter-animal differences were much larger than predicted by chance, and different physiological cell types showed distinct patterns of variability. One neuronal type was present in males and nearly absent in females. Surprisingly, this apparent sexual dimorphism was generated by plasticity, as exposure to female scents or single ligands led to both the elimination of this cell type and alterations in olfactory behavior. That an all-or-none apparent sex difference in neuronal types is controlled by experience-even in a sensory system devoted to "innate" behaviors-highlights the extraordinary role of "nurture" in neural individuality.

A Molecular Code for Identity in the Vomeronasal System

In social interactions among mammals, individuals are recognized by olfactory cues, but identifying the key signals among thousands of compounds remains a major challenge. To address this need, we developed a new technique, component-activity matching (CAM), to select candidate ligands that "explain" patterns of bioactivity across diverse complex mixtures. Using mouse urine from eight different sexes and strains, we identified 23 components to explain firing rates in seven of eight functional classes of vomeronasal sensory neurons. Focusing on a class of neurons selective for females, we identified a novel family of vomeronasal ligands, steroid carboxylic acids. These ligands accounted for much of the neuronal activity of urine from some female strains, were necessary for normal levels of male investigatory behavior of female scents, and were sufficient to trigger mounting behavior. CAM represents the first step toward an exhaustive characterization of the molecular cues for natural behavior in a mammalian olfactory system.