Abstract
Propriospinal interneurons (INs) communicate information over short and long distances within the spinal cord. They act to coordinate different parts of the body by linking motor circuits that control muscles across the forelimbs, trunk, and hindlimbs. Their role in coordinating locomotor circuits near and far may be invaluable to the recovery of locomotor function lost due to injury to the spinal cord where the flow of motor commands from the brain and brainstem to spinal motor circuits is disrupted. The formation and activation of circuits established by spared propriospinal INs may promote the re-emergence of locomotion. In light of progress made in animal models of spinal cord injury (SCI) and in human patients, we discuss the role of propriospinal INs in the intact spinal cord and describe recent studies investigating the assembly and/or activation of propriospinal circuits to promote recovery of locomotion following SCI.
Highlights
Successful locomotion depends upon the precise coordination of multiple muscles across numerous joints and limbs, as well as the simultaneous engagement of multiple trunk and stabilizing muscles (Frigon, 2017)
While no long descending propriospinal axons from cervical dorsal IN type 3 (dI3) INs to lumbar segments have been found (Ruder et al, 2016), transsynaptic tracing experiments from the mouse quadriceps muscle found that dI3 INs project from adjacent lumbar segments (55% L1–L2, 6% L3, 39% L4–L6) to the flexor motoneuron pool, suggesting a moderately dispersed pattern of short propriospinal connectivity (Stepien et al, 2010). dI3 IN loss-of-function resulted in minor disturbances in locomotor gait in mice (Bui et al, 2016), which may speak to the distributed integration of sensory input among different spinal populations
More generally, there is an abundance of literature implicating propriospinal INs in the recovery of locomotion after spinal cord injury (SCI), a topic that will be explored in depth below
Summary
Propriospinal interneurons (INs) communicate information over short and long distances within the spinal cord. They act to coordinate different parts of the body by linking motor circuits that control muscles across the forelimbs, trunk, and hindlimbs. Their role in coordinating locomotor circuits near and far may be invaluable to the recovery of locomotor function lost due to injury to the spinal cord where the flow of motor commands from the brain and brainstem to spinal motor circuits is disrupted.
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