The long term goal of our research has been to explore the spinal cord and the brain stem of the lamprey as models for the functional organization of neurons in the vertebrate CNS. The specific objective of the present proposal is to determine the neural basis for central pattern generation of the well-defined behaviors of swimming and breathing in the lamprey. Intracellular recording and stimulation will be used to find candidate generator interneurons which both have oscillatory membrane potentials and evoke changes in the intensity and timing of motor bursts in ventral roots during fictive swimming. Paired intracellular electrodes will be used to determine unitary synaptic interactions between these candidate generator interneurons and previously identified neurons to construct a progressively more complete functional and morphological circuit diagram of the spinal cord which produces swimming activity. Intrinsic pacemaker properties, including the role of Ca-dependent K conductance, will be tested in candidate generator interneurons for swimming and particularly for respiration. The morphology of candidate generator interneurons will be determined by intracellular peroxidase and dye marking. The detailed information of types of interneurons, synaptic connections, membrane properties, and quantitative physiological parameters will be integrated to construct testable models for central pattern generation of locomotion and breathing in a simpler vertebrate.