Neuronal structures of the brainstem participating in postural suppression in cats.

Two histochemical tracer techniques (a horseradish peroxidase and a Phaseolus vulgaris leucoagglutinin axonal flow technique) were employed to determine the cells of origin, axonal trajectories and terminals of fibers of passage through the dorsal tegmental field (DTF) in the pons along the midline (Horsley-Clarke coordinates, P 3 to P 7, LR 0, H - 4.5 to H - 6.0). Stimulation of the DTF area results in the postural suppression in both acute decerebrate, reflexively standing cats and freely moving awake cats. With these techniques, we have been able to demonstrate that in addition to pontine reticular cells, many cells in the dorsolateral pontine tegmentum, including the LC-complex, project their axons to the rostral part of the midline DTF area, and that descending axons from the nucleus reticularis pontis oralis pass through the DTF area and terminate on cells in the nucleus reticularis pontis caudalis and the nucleus reticularis gigantocellularis. Among those cells in the nucleus reticularis gigantocellularis, a great number of giant cells project to the lumbar spinal cord. The functional roles of these neuronal structures are discussed in relation to the results obtained by chemical stimulation of the pontine structures.