The long term goal of the proposed project is to understand how nervous systems control movement. Somatic motor neurons are commonly used in more than one movement and can be activated in a variety of spatial and temporal patterns. In general, motor neurons are driven by a population of premotor interneurons. How are the premotor interneurons organized and activated to yield different motor patterns? Are the neurons which comprise the pattern generator for one behavior involved in the generation of other motor responses? If so, by what mechanisms can a set of neurons connected together to subserve one motor function be reorganized to participate other motor patterns? To address these questions we will concentrate on the organization of interneurons and motor neurons within the CNS of the mollusc, Tritonia diomedea, as a model system. Our experimental approach is divided into three areas. Using intracellular recordings, the firing patterns of identified premotor interneurons and motor neurons will be characterized quantitatively during three different behaviors: swimming, reflexive withdrawals, and feeding. Each of these behaviors involves a common pool of motor neurons activated in three different patterns. A second series of experiments focuses on cellular and synaptic mechanisms for pattern generation and includes i) a network analysis of the synaptic connectivity between and integrative properties of the interneurons and motor neurons, ii) analysis of sensory input pathways to this motor system, and (iii) identification of modulatory sites within the motor network. Finally the network of interneurons and motor neurons will be reconstructed by digital computer simulation to provide insights into the interaction and role of cellular and synaptic properties in the generation of multiple, complex motor patterns. These experiments should uncover principles of motor system organization which will be applicable to more complex systems in which this level of cellular analysis is not possible.
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