Abstract
The descending corticospinal (CS) projection has been considered a key element for motor control, which results from direct and indirect modulation of spinal cord pre-motor interneurons in the intermediate gray matter of the spinal cord, which, in turn, influences motoneurons in the ventral horn. The CS tract (CST) is also involved in a selective and complex modulation of sensory information in the dorsal horn. However, little is known about the spinal network engaged by the CST and the organization of CS projections that may encode different cortical outputs to the spinal cord. This study addresses the issue of whether the CS system exerts parallel control on different spinal networks, which together participate in sensorimotor integration. Here, we show that in the adult rat, two different and partially intermingled CS neurons in the sensorimotor cortex activate, with different time latencies, distinct spinal cord neurons located in the dorsal horn and intermediate zone of the same segment. The fact that different populations of CS neurons project in a segregated manner suggests that CST is composed of subsystems controlling different spinal cord circuits that modulate motor outputs and sensory inputs in a coordinated manner.
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Abbreviations
- CST:
-
Corticospinal tract
- CS:
-
Corticospinal
- PAD:
-
Primary afferent depolarization
- EFPs:
-
Evoked field potentials
- SD:
-
Standard deviation
- M1:
-
Primary motor cortex
- S1:
-
Primary somatosensory cortex
- M2:
-
Secondary motor cortex
- S2:
-
Secondary somatosensory cortex
- HL:
-
Hind limb
- FL:
-
Fore limb
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Acknowledgements
We thank Jessica Gonzalez Norris for revising the grammatical aspects of the manuscript; Cutberto Dorado, Nydia Hernández, Alejandra Castilla, Martín García Servin, Adriana Gonzalez Gallardo, and Anaid Antaramian for technical assistance as well as Edna Hurtado who performed preliminary experiments. Supported by grants from CONACYT Fronteras de la Ciencia 846 (GRP) and 181508 (LC) and PAPIIT (IN200615). Rafael Olivares Moreno is a doctoral student from Programa de Doctorado en Ciencias Biomédicas, Universidad Nacional Autónoma de México (UNAM) and received fellowship 317553 from CONACYT.
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Supplementary material 1 Supplementary Fig. 1 Relationship between the number of pulses of the cortical stimulation train and amplitude of the intraspinal LFP. Relationship between the number of pulses of the cortical stimulation train and magnitude of the short-latency (green triangles) and long-latency (red circles) components of the intraspinal EFP. The continuous lines are the respective best sigmoidal fittings. Inset shows representative superimposed averaged (n = 16) intraspinal EFPs produced with 1, 3, and 5 pulses in the same experiment. Green and red arrows indicate short- and long-latency components of the EFP, respectively (TIFF 5214 kb)
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Supplementary material 2 Supplementary Fig. 2 Spinal cord injection sites of all the experiments analyzed. a Cervical spinal cord sections showing the core of the neuronal tracer’s injection sites (dashed lines) in three different experiments (cholera toxin subunit B conjugated with Alexa 488 in green and Alexa 594 in red). b Average of the injection site areas corresponding to DH and IZ. c–d The same but for the injections in lumbar segments. The measured areas of the injection sites in cervical and lumbar segments show a similar size (p > 0.5, Mann–Whitney U). Scale bars 500 µm (TIFF 30694 kb)
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Supplementary material 3 Supplementary video 1 Identification of retrogradely labeled CS cells in large-scale mosaic images (WMV 5799 kb)
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Supplementary material 4 Supplementary video 2 3D model of the rat brain showing the landmarks and density maps of the CS cells projecting to the dorsal horn (red) and intermediate zone (green) (WMV 7651 kb)
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Olivares-Moreno, R., Moreno-Lopez, Y., Concha, L. et al. The rat corticospinal system is functionally and anatomically segregated. Brain Struct Funct 222, 3945–3958 (2017). https://doi.org/10.1007/s00429-017-1447-6
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DOI: https://doi.org/10.1007/s00429-017-1447-6