Localization of a sub-population of commissural cells active in treadmill locomotion in the adult rat thoracolumbar spinal cord
The aim of this study was to identify a selective population of commissural neurons in the adult rat spinal cord that were active during treadmill locomotion. Fluorogold, a retrograde neuroanatomical tracer was combined with the immunocytochemical localization of the activity dependant cellular marker c-fos protein in an in vivo animal. We observed that the commissural neurons that were activated during locomotion are distributed from spinal segments T13 to L6. They are located primarily in Rexed's laminae VII & X of the intermediate zone and lamina VIII of the ventral horn. No c-fos and fluorogold double labeled cells were observed in the experimental animals that did not perform the treadmill locomotor task. This suggests that the identified neurons are specifically activated by the locomoter task. We also observed that ipsi-lateral propriospinal cells, known to have extensive synaptic connections within the spinal cord, were also active during treadmill locomotion. These identified commissural cells are active during physiological locomotion and they may mediate left/right alternating rhythmic patterns and represent an important component of the spinal central pattern generator (CPG).