Localisation of Spinal Neurons Activated during Locomotion Using the C-fos Immunohistochemical Method

The c-fos immunohistochemical method of activity-dependent labelling was used to localise locomotor activated neurons in the adult cat spinal cord. In decerebrate cats, treadmill locomotion was evoked by electrical stimulation of the mesencephalic locomotor region (MLR). Spontaneous or MLR-evoked fictive locomotion was produced in decerebrate animals paralysed with a neuromuscular blocking agent. After bouts of locomotion during a 7-9 hour time period, the animals were perfused and the L3-S1 spinal cord segments removed for immunohistochemistry. Control animals were subjected to the same surgical procedures but no locomotor task. Labelled cells were concentrated in Rexed's laminae III and IV of the dorsal horn, and laminae VII, VIII and X of the intermediate zone/ventral horn after treadmill locomotion. Cells in laminae VII, VIII and X were labelled after fictive locomotion, but labelling in the dorsal horn was much reduced. In control animals, c-fos labelling was a small fraction of that observed in the locomotor animals. The results suggest that labelled cells in laminae VII, VIII and X are pre-motor interneurons involved in the production of locomotion, while the laminae III and IV cells are those activated during locomotion due to afferent feedback from the moving limb. c-fos labelled cells were most numerous in the L5 – L7 segments, consistent with the distribution of locomotor activated neurons detected through the use of MLR-evoked field potentials (Noga et al. 1995).