The therapeutic mechanism of transcranial iTBS on nerve regeneration and functional recovery in rats with complete spinal cord transection

Front Immunol. 2023 Jun 14:14:1153516. doi: 10.3389/fimmu.2023.1153516. eCollection 2023.

Abstract

Background: After spinal cord transection injury, the inflammatory microenvironment formed at the injury site, and the cascade of effects generated by secondary injury, results in limited regeneration of injured axons and the apoptosis of neurons in the sensorimotor cortex (SMC). It is crucial to reverse these adverse processes for the recovery of voluntary movement. The mechanism of transcranial intermittent theta-burst stimulation (iTBS) as a new non-invasive neural regulation paradigm in promoting axonal regeneration and motor function repair was explored by means of a severe spinal cord transection.

Methods: Rats underwent spinal cord transection and 2 mm resection of spinal cord at T10 level. Four groups were studied: Normal (no lesion), Control (lesion with no treatment), sham iTBS (lesion and no functional treatment) and experimental, exposed to transcranial iTBS, 72 h after spinal lesion. Each rat received treatment once a day for 5 days a week; behavioral tests were administered one a week. Inflammation, neuronal apoptosis, neuroprotective effects, regeneration and synaptic plasticity after spinal cord injury (SCI) were determined by immunofluorescence staining, western blotting and mRNA sequencing. For each rat, anterograde tracings were acquired from the SMC or the long descending propriospinal neurons and tested for cortical motor evoked potentials (CMEPs). Regeneration of the corticospinal tract (CST) and 5-hydroxytryptamine (5-HT) nerve fibers were analyzed 10 weeks after SCI.

Results: When compared to the Control group, the iTBS group showed a reduced inflammatory response and reduced levels of neuronal apoptosis in the SMC when tested 2 weeks after treatment. Four weeks after SCI, the neuroimmune microenvironment at the injury site had improved in the iTBS group, and neuroprotective effects were evident, including the promotion of axonal regeneration and synaptic plasticity. After 8 weeks of iTBS treatment, there was a significant increase in CST regeneration in the region rostral to the site of injury. Furthermore, there was a significant increase in the number of 5-HT nerve fibers at the center of the injury site and the long descending propriospinal tract (LDPT) fibers in the region caudal to the site of injury. Moreover, CMEPs and hindlimb motor function were significantly improved.

Conclusion: Neuronal activation and neural tracing further verified that iTBS had the potential to provide neuroprotective effects during the early stages of SCI and induce regeneration effects related to the descending motor pathways (CST, 5-HT and LDPT). Furthermore, our results revealed key relationships between neural pathway activation, neuroimmune regulation, neuroprotection and axonal regeneration, as well as the interaction network of key genes.

Keywords: intermittent theta-burst stimulation (iTBS); motor pathway; nerve regeneration; neuroprotection; spinal cord injury; synaptic plasticity.

Publication types

  • Research Support, Non-U.S. Gov't
  • Comment

MeSH terms

  • Animals
  • Gastropoda*
  • Nerve Regeneration
  • Neuroprotective Agents*
  • Rats
  • Serotonin
  • Spinal Cord Injuries* / therapy

Substances

  • Neuroprotective Agents
  • Serotonin

Grants and funding

This research was supported by grants from the National Key R&D Program of China, No. 2022YFA1105900 (to B-QL); the Chinese National Natural Science Foundation (Grant No. 81891003 to Y-SZ, 81971157 to B-QL and 81101462 to L-XZ); the Natural Science Foundation of Guangdong Province, China, No. 2021B1515020045 (to B-QL);the National Natural Science Foundation of Liaoning Province, No. 2019-KF-01-06 (to L-XZ), the Key Research and Development Program of the Ministry of Science and Technology of China No. 2020YFC2005703 and No. 2020YFC2007604 (to L-XZ).