The major goal of this proposal is to understand the mechanisms and the general principles involved in sensory informationprocessing. The proper function of the sensory systems is crucial to our health and well being. Numerous neurological and psychiatric disorders, such as schizophrenia, autism, attention deficit hyperactivity disorder (ADHD) and depression, all manifest defects in sensory responses. Sensory deficit is also the earliest sign of Parkinson's and Alzheimer's diseases. The study of the sensory systems will enable us to understand how the brain functions and help us to use this knowledge for diagnostic and therapeutic applications. To achieve this goal, one must study the neural circuitry that detects and integrates sensory input and elicits distinct behavioral output. In vertebrates, innate behaviors such as mating rituals and territorial aggression are largely elicited by the detection of pheromone cues through the vomeronasal organ. These behaviors are robust and stereotyped and their expression critically depends on the correct identification of pheromones. The neural circuits involved in pheromone detection are largely genetically determined. There is an intrinsic link between sensory input and behavior responses in the vomeronasal system, making it an attractive and tractable circuitry to understand sensory processing. In this study, we test the hypothesis that sensory information is encoded in the pattern of activation by different pheromones in the sensory cells. This information is further represented in the brain by the topographic projection from these neurons to allow an animal to discriminate gender, strain and the social and reproductive status of other individuals. We will first develop transgenic animals expressing calcium indicators in the sensory neurons to identify cells that respond to specific pheromones. Combining fluorescent imaging, mouse genetics and molecular biology, we will then identify the pheromone receptor gene these cells express. Third, we will trace the information flow by mapping the vomeronasal pathway with genetic labeling experiments. Finally, we will genetically inactivate subpopulations of neurons in the vomeronasal pathway to elucidate their functional contribution to pheromone perception. This functional mapping of the vomeronasal circuit will provide insight into how the sensory system detects, parses and integrates information to elicit specific behaviors.