Loss of respiratory function is one of the leading causes of death following spinal cord injury (SCI). Existing studies have demonstrated that pre-phrenic interneurons (PPIN’s) can be recruited into the phrenic motor neuron (PhMN) pathway following cervical SCI and may contribute to respiratory recovery, but there is still a lack of information detailing the nature of these changes and the extent they may improve diaphragm function. This project aims to validate a method of utilizing neuronal tracers to further characterize the intact respiratory circuitry.
This study was carried out using a rat model. A fluorophore-conjugated retrograde neuronal tracer (cholera toxin B) was applied directly to different subregions of the hemidiaphragm. Sagittal sections of cervical spinal cord were imaged, and the positions of labeled PhMN cell bodies were mapped.
Innervation of the hemidiaphragm is distributed topographically along the ventrodorsal axis with the ventral, medial, and dorsal subregions being preferentially innervated by PhMNs residing in C3, C4, and C5 respectively. Although our method roughly approximated this distribution, we were unable to achieve discrete labeling.
It was difficult to keep the tracers from spreading beyond the confines of each subregion, likely due to the diaphragm not being dry enough during application. In the future we plan to refine and use this method with another tracer that will allow visualization of PPIN’s and apply it to a cervical SCI model to examine how this circuitry is remodeled. Further understanding of PPIN plasticity may also reveal novel therapeutic targets to enhance the endogenous recovery process.
Recommended CitationThomas, Samantha and Lepore, Angelo, "Development of a method using retrograde neuronal tracers to neuroanatomically characterize respiratory neural circuitry" (2021). Phase 1. Paper 17.