Mapping the corticoreticular pathway from cortex-wide anterograde axonal tracing in the mouse

Abstract

The corticoreticular pathway (CRP) has been implicated as an important mediator of motor recovery and rehabilitation after central nervous system damage. However, its origins, trajectory and laterality are not well understood. This study mapped the mouse CRP in comparison with the corticospinal tract (CST). We systematically searched the Allen Mouse Brain Connectivity Atlas (© 2011 Allen Institute for Brain Science) for experiments that used anterograde tracer injections into the right isocortex in mice. For each eligible experiment (N=607), CRP and CST projection strength were quantified by the tracer volume reaching the reticular formation motor nuclei (RFmotor) and pyramids respectively. Tracer density in each brain voxel was also correlated with RFmotor versus pyramids projection strength to explore the relative trajectories of the CRP and CST. We found significant CRP projections originating from the primary and secondary motor cortices, anterior cingulate, primary somatosensory cortex and medial prefrontal cortex. Compared with the CST, the CRP had stronger projections from each region except the primary somatosensory cortex. Ipsilateral projections were stronger than contralateral for both tracts (above the pyramidal decussation), but the CRP projected more bilaterally than the CST. The estimated CRP trajectory was anteromedial to the CST in the internal capsule and dorsal to the CST in the brainstem. Our findings reveal a widespread distribution of CRP origins and confirm strong bilateral CRP projections, theoretically increasing the potential for partial sparing after brain lesions and contralesional compensation after unilateral injury.

Evaluating the neural underpinnings of motivation for walking exercise

“…Unlike SMA and PMd, SFG9m is not typically considered a motor region, but this finding adds to a growing body of evidence that SFG9m may indeed be a novel motor area, or at least highly relevant to walking function. 28,29,59,60 For example, the medial prefrontal cortex (including SFG9m) was recently found to be a major origin of a key descending projection for gross motor functions like walking (the cortico-reticulo-spinal pathway). 59,60 The current study cannot determine whether SFG9m exerted any direct effects on walking through the cortico-reticulo-spinal pathway and/or indirect effects via connections with established motor regions of the cortex (M1-LL, SMA, PMd).…”

“…28,29,59,60 For example, the medial prefrontal cortex (including SFG9m) was recently found to be a major origin of a key descending projection for gross motor functions like walking (the cortico-reticulo-spinal pathway). 59,60 The current study cannot determine whether SFG9m exerted any direct effects on walking through the cortico-reticulo-spinal pathway and/or indirect effects via connections with established motor regions of the cortex (M1-LL, SMA, PMd). Given the correlational nature of this result, it is also possible that SFG9m did not exert any effects on walking (non-causal/confounded association) or that faster walking somehow led to greater SFG9m activation (reverse causality).…”

“…Unlike SMA and PMd, SFG9m is not typically considered a motor region, but this finding adds to a growing body of evidence that SFG9m may indeed be a novel motor area, or at least highly relevant to walking function. 28, 29, 59, 60 For example, the medial prefrontal cortex (including SFG9m) was recently found to be a major origin of a key descending projection for gross motor functions like walking (the cortico-reticulo-spinal pathway). 59, 60…”

“…28, 29, 59, 60 For example, the medial prefrontal cortex (including SFG9m) was recently found to be a major origin of a key descending projection for gross motor functions like walking (the cortico-reticulo-spinal pathway). 59, 60…”