9630805 Norekian All animals are engaged in a wide variety of behaviors. Many behaviors are mutually exclusive since they follow different goals and might involve opposite movements of the same body parts. Given a choice between two or more behaviors at the same time, one behavior usually takes precedence over the others. This behavior is considered to be dominant over the other behaviors. Unrelated and competing behaviors are organized in a priority sequence in each animal, termed a behavioral hierarchy. Understanding of how a behavioral choice is made, why switching between different behaviors occurs and what are the neural mechanisms which reorganize the behavioral repertoire of all animals in a hierarchical manner represents a central issue in behavioral neurobiology. Most advantageous for investigation of this issue are preparations in which behaviors are relatively simple and well defined and the underlying neural circuits are identified and characterized. Invertebrate preparations were found to be particularly useful for these neuroethological investigations. The pteropod mollusc Clione limacina appears to be an excellent model system for such neuroethological studies since it has a few basic, very well-defined, mutually exclusive behaviors, such as feeding, withdrawal, escape swimming, egg laying and mating, as well as relatively simple, well-studied neural circuits producing them. The simplicity of the preparation, including its behaviors and underlying neural circuits, makes it possible to draw direct connections between the activities of individual neurons and behavioral outputs. This task is much more difficult, if at all possible, in complex organisms such as vertebrates. A focused investigation of one simple animal by the present project will enable an integrated understanding of neural interactions and modulatory changes in the central nervous system which underlie the behavioral choice and dominance of one behavior over others. Knowledge of neural circuits producing specific behaviors in Clione allows the timely description of interconnections between neural networks, that determine the reorganization of the behavioral repertoire in a priority sequence (behavioral hierarchy). The main principals of this reorganization and the underlying neural mechanisms appear to be similar not only among invertebrates including Clione, but also in vertebrate animals. Therefore, knowledge obtained in the Clione preparation would have broad theoretical value.
