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Functional redundancy of ventral spinal locomotor pathways
David N Loy1, David S K Magnuson, Y Ping Zhang
1The MD/PhD Program and Department of Neurological Surgery, University of Louisville School of Medicine, Louisville, Kentucky 40292, USA.
Summary
Identifying descending spinal cord tracts is key for spinal cord injury (SCI) repair. This study reveals that multiple pathways in the ventral white matter, not just the ventrolateral funiculus, are crucial for spontaneous locomotion.
Area of Science:
- Neuroscience
- Spinal Cord Injury Research
- Locomotion
Background:
- Identifying descending motor pathways is crucial for developing effective spinal cord injury (SCI) repair strategies.
- While reticulospinal tracts in the ventrolateral funiculus (VLF) are known to influence fictive locomotion, the specific white matter regions critical for spontaneous over-ground locomotion remain unclear due to varied recovery patterns in different species after ventral SCI.
Purpose of the Study:
- To investigate the contributions of myelinated tracts in the ventrolateral funiculus (VLF) and ventral columns (VC) to spontaneous over-ground locomotion in adult rats.
- To elucidate the role of specific white matter tracts in the ventral spinal cord in motor control and recovery after injury.
Main Methods:
- Adult rats received demyelinating lesions induced by ethidium bromide and photon irradiation in the VLF, VC, VLF-VC, or complete ventral white matter (CV).
- Locomotor behavior was assessed using open-field Basso, Beattie, and Bresnahan (BBB) scores and grid walking tests.
- Transcranial magnetic motor-evoked potentials (tcMMEPs) were recorded to evaluate axonal conduction integrity at 1, 2, and 4 weeks post-lesion.
Main Results:
- VLF lesions caused significant loss of tcMMEPs and moderate locomotor deficits (mean BBB score 18.0) without grid walking impairment.
- VC lesions did not significantly affect tcMMEPs but resulted in behavioral deficits similar to VLF lesions.
- Combined VLF-VC and CV lesions led to complete loss of tcMMEPs and severe locomotor impairment (mean BBB scores 12.7 and 6.5, respectively).
Conclusions:
- The findings suggest a diffuse organization of descending pathways within the ventral white matter, rather than a single critical tract.
- Multiple descending pathways in the ventral white matter collectively support spontaneous over-ground locomotion in intact animals.
- This diffuse system likely plays a significant role in locomotor function and potential recovery after spinal cord injury.