Cerebellar-induced Locomotion: Reticulospinal Control of Spinal Rhythm Generating Mechanism in Cats

In a decerebrate cat (locomotor preparation), stimulation of a restricted region along the midline cerebellar white matter has been found to evoke generalized augmentation of postural muscle tone on a stationary surface (Asanome et al. 1998. Neurosci. Res. 30: 257-269) and "controlled" locomotion on the surface of a moving treadmill. Characteristics of cerebellar-evoked locomotion were similar to those of mesencephalic locomotor region-evoked "controlled" locomotion on the same animal. Microinjection of a neural tracer (CTb-HRP) into the lesioned stimulus site of the cerebellar white matter resulted in both retrograde labelling of cells in the fastigial nuclei, bilaterally, and anterograde labeling of fibers descending to the brain stem. These results indicated that the effective cerebellar stimulus site (cerebellar locomotor region) corresponded to the midline region of the hook bundle of Russell (Rasmussen, A. T., 1933. J. Comp. Neurol. 57: 165-197), through which crossed fastigioreticular, fastigiovestibular, and fastigiospinal fibers pass. In this study, contribution of reticulospinal systems to the control of cerebellar-evoked locomotion was extensively studied. By stimulating the cerebellar locomotor region and the MLR in the same animal, a majority of antidromically identified pontomedullary reticulospinal cells were synaptically activated. The results of the present study demonstrated that fastigial cells with crossed fastigioreticular fibers and reticulospinal fibers play a crucial role in the control of posture and locomotion in the locomotor preparation.