Organization and Function of the Extra-Bulbar Olfactory Pathway

Michigan State University, East Lansing MI

Investigators

Abstract

Evolutionary changes in the nervous system offer a tremendous opportunity to understand the relationship between the nervous system and behavior. When new brain structures are created, what does this do to an organism's behavior? How do these new structures interact with other portions of the nervous system? We are using the vertebrate olfactory system (the system responsible for the sense of smell) as a model for examining evolutionary changes in the nervous system. To this end, we are exploring the organization of the olfactory system in a variety of vertebrate animals. Recently, scientists have learned that receptor cells in the nose of some fishes and amphibians are connected to the a region in the base of the forebrain, instead of to the olfactory bulbs, as is usual for these cells. The structure of this newly-discovered subsystem, the "extra-bulbar pathway," is poorly understood, and its function has not been investigated. In the proposed experiments, the location of the receptor cells of the extra-bulbar pathway within the nose will be examined in adult axolotls (Ambystoma mexicanum), a salamander species that lives in water throughout its life. Single-cell electrophysiological recording methods will be used to study the odorant response properties of the receptor cells of the extra-bulbar pathway in axolotls. These experiments will allow us to examine the function of the extra-bulbar pathway, and to test an interesting hypothesis that suggests that the extra-bulbar pathway functions in detection of pheromones. Pheromones are chemicals produced by animals that carry information to other members of the same species to tell them about the producer's sex or reproductive status. These experiments will provide the first clear description of the organization and function of the extra-bulbar pathway. This research has important implications for our understanding of the ways in which odorant information is converted into electrical signals in olfactory receptor cells, as well as the way odorant information is processed in the olfactory bulbs, potentially shedding light on the neural mechanisms underlying odor perception.