3D imaging of supraspinal inputs to the thoracic and lumbar spinal cord mapped by retrograde tracing and light‐sheet microscopy. Issue 4 (22nd June 2022) - Lu, Tao
Abstract: The supraspinal inputs play a major role in tuning the hindlimb locomotion function. While most research on spinal cord injury (SCI) with rodents is based on thoracic segments, the difference in connectivity of the supraspinal centers to the thoracic and lumbar cord is still unknown. Here, we combined retrograde tracing and 3D imaging to map the connectivity of supraspinal neurons projecting to thoracic (T9‐vertebral) and lumbar (T13‐vertebral) spinal levels in adult female mice. We dissected the difference in connections of corticospinal neurons (CSNs), rubrospinal neurons, and reticulospinal neurons projecting to thoracic and lumbar cords. The ratio of double‐labeled neurons is higher in T13‐vertebral projection CSNs and parvocellular part of the red nucleus (RPC) than in T9‐vertebral projection. Using the Cre‐DIO system, we precisely targeted CSNs projecting to T9‐vertebral or T13‐vertebral. We found that abundant axon branches communicated with the red nucleus and reticular formation and distributed from cervical gray matter to the lumbar cord. Their collateral branches showed a distinct innervation pattern in thoracic and lumbar gray matters and a similar distribution pattern in the cervical spinal cord. These results revealed the difference in connectivity between the thoracic and lumbar projection supraspinal centers and clarified the collateralization of thoracic/lumbar projection CSNs throughout the brain and spinal cord. This study highlights brain‐spinal cord neural networks and the complexity of the axon terminals of spinal projection CSNs, which could contribute to the development of targeted therapeutic strategies connecting CST fibers and hindlimb function recovery. Cover Image for this issue: https://doi.org/10.1111/jnc.15414 Abstract : The spinal cords at thoracic vertebral levels of ninth and thirteenth are the important regions located in rostral and caudal positions of the lesion in spinal cord injury model. The difference in connectivity of the supraspinal neurons projecting to the thoracic and lumbar cords was demonstrated including corticospinal neurons (CSNs), rubrospinal neurons, and reticulospinal neurons. This study highlights brain‐spinal cord neural networks, which could contribute to the development of targeted therapeutic strategies connecting corticospinal tract fibers and hindlimb function recovery. Cover Image for this issue: https://doi.org/10.1111/jnc.15414