We will study the rostral scratch, the pocket scratch, and the flexion reflex in the turtle with a complete transection of the spinal cord just posterior to the forelimb enlargement. Each of these cutaneous reflexes displays a distinct pattern of hindlimb motor neuron activation in response to tactile stimulation within a specific receptive field. We will record motor neuron activation patterns in a preparation immobilized by neuromuscular blockade. Spinal cord circuitry in this preparation, in the absence of movement-related sensory feedback, selects and generates an appropriate motor pattern for each specific stimulus: the circuitry makes a motor pattern decision and then produces that motor pattern. Our experiments will reveal spinal cord neuronal mechanism responsible for these processes. We will use several experimental strategies to study these mechanisms. First, we will study the anatomical and physiological properties of a specific class of spinal cord neuron, the set of propriospinal neurons with descending axons. We will use these data to test specific hypotheses about the characteristics of spinal neurons involved in the selection and generation of scratch reflex motor patterns. Second, we will continue our characterization of the contributions of glutamate receptors to cutaneous reflexes. We will examine the relative contributions of non-NMDA and NMDA receptors to each component of the flexion reflex. We will determine the contribution of each class of glutamate receptors to rostral scratch motor pattern generation. Third, we will measure the contribution of glutamate receptors to the activation of propriospinal neurons involved in the flexion reflex and in the rostral scratch reflex. In each specific aim, we will obtain information concerning the neuronal mechanisms responsible for cutaneous sensorimotor integration in the spinal cord. Turtle spinal cord is similar to that of other vertebrates, including humans. The mechanisms we will reveal may serve as working hypotheses for studies of spinal cord sensorimotor integration in other vertebrates.
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