Spinal cholinergic neurons activated during locomotion: Localization and electrophysiological characterization

The objective of the present study was to determine the location of the cho linergic neurons activated in the spinal cord of decerebrate cats during fi ctive locomotion. Locomotion was induced by stimulation of the mesencephali c locomotor region (MLR). After bouts of locomotion during a 7-9 h period, the animals were perfused and the L-3-S-1 spinal cord segments removed. Cat s in the control group were subjected to the same surgical procedures but n o locomotor task. The tissues were sectioned and then stained by immunohist ochemical methods for detection of the c-fos protein and choline acetyltran sferase (ChAT) enzyme. The resultant c-fos labeling in the lumbar spinal co rd was similar to that induced by fictive locomotion in the cat. ChAT-posit ive cells also clearly exhibited fictive locomotion induced c-fos labeling. Double labeling with c-fos and ChAT was observed in cells within ventral l amina VII, VIII, and possibly IX. Most of them were concentrated in the med ial portion of lamina VII close to lamina X, similar in location to the par tition and central canal cells found by Barber and collaborators. The numbe r of ChAT and c-fos-labeled neurons was increased following fictive locomot ion and was greatest in the intermediate gray, compared with dorsal and ven tral regions. The results are consistent with the suggestion that cholinerg ic interneurons in the lumbar spinal cord are involved in the production of fictive locomotion. Cells in the regions positive for double-labeled cells were targeted for electrophysiological study during locomotion, intracellu lar filling, and subsequent processing for ChAT immunohistochemistry. Three cells identified in this way were vigorously active during locomotion in p hase with ipsilateral extension, and they projected to the contralateral si de of the spinal cord. Thus a new population of spinal cord cells can be de fined: cholinergic partition cells with commissural projections that are ac tive during the extension phase of locomotion.