David Ladle (Advisor), Larry Ream (Committee Member), Patrick Sonner (Committee Member)
Master of Science (MS)
Proprioception allows sensory information about muscle position and length to enter the CNS without the aid of visual cues. One type of fiber that carries this information is the Ia afferent, which innervates muscle spindles that respond to mechanical perturbation in muscle. Ia fibers are known to synapse with Ia interneurons (INs) and motor neurons (MNs), setting up important circuits which affect movement. Another type of IN is the Renshaw cell (RC), which is located in the ventral part of lamina VII of the spinal cord and is critical for the functionality of the recurrent inhibitory circuit. In addition to sending inhibitory axons to MNs, RCs were recently discovered to receive monosynaptic Ia afferent connections. Sensory connections increase from birth through postnatal day (P) 15 in a mouse model, and then decline functionally into adulthood. The functional relevance and possible muscle-specific patterns of sensory connectivity with RCs is poorly understood. To investigate this question, we mapped the connections of proprioceptive afferents of quadriceps and obturator nerves (with fluorescent dextran retrograde tracing) onto immunohistochemically defined RCs in neonatal mice (P0 or P1). We hypothesized the quadriceps and obturator afferents would contact different populations of RCs, implying selective activation. Our results indicate RCs are almost twice as likely to receive obturator sensory contacts as quad contacts at this stage, and that there is a population of RCs which receive contacts from both types of afferents. A possible explanation is that synaptic contact patterns may change in the course of postnatal development to eliminate convergent inputs from both types of afferents. Alternatively, all RCs may be contacted by afferents from various muscle nerves to allow for generalized feedforward inhibition during early postnatal development.
Department or Program
Department of Neuroscience, Cell Biology & Physiology
Year Degree Awarded
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