Stimulation of a Restricted Region in the Midline Cerebellar White Matter Evokes Coordinated Quadrupedal Locomotion in the Decerebrate Cat

Department of Biological Control System, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8585, Japan Mori, Shigemi, Toshihiro Matsui, Bunya Kuze, Mitsuru Asanome, Katsumi Nakajima, and Kiyoji Matsuyama. Stimulation of a Restricted Region in the Midline Cerebellar White Matter Evokes Coordinated Quadrupedal Locomotion in the Decerebrate Cat. J. Neurophysiol. 82: 290-300, 1999. In the reflexively standing acute decerebrate cat, we have previously shown that pulse train microstimulation of the hook bundle of Russel in the midline of the cerebellar white matter, through which crossed fastigiofugal fibers decussate, augments the postural tone of neck, trunk, fore-, and hindlimb extensor muscles. In the present study we examined the possible role of such stimulation in evoking locomotion as the animal is supported by a rubber hammock with its feet contacting the moving surface of a treadmill. We were able to provoke well-coordinated, bilaterally symmetrical, fore- and hindlimb movements, whose cycle time and pattern were controlled by appropriate changes in stimulus intensity and treadmill speed. We carefully and systematically mapped this cerebellar locomotor region (CLR) through repeated dorsoventral penetrations with a glass-coated tungsten microelectrode in a single animal and between animals. We found that the optimal locus for evoking locomotion was centered on the midline, at Horsley-Clarke coordinates H0 and P7.0, and extended over a rostrocaudal and dorsolateral range of ~0.5 mm. The lowest effective stimulus intensity at the optimal site was in the range of 5-8 µA. Along penetration tracks to left or right of the midline, effective stimulus intensity increased and evoked locomotor patterns were no longer symmetrical, but rather shifted toward the contralateral limbs. In the same animals, controlled locomotion was evoked by stimulating the mesencephalic locomotor region (MLR). With concomitant stimulation of the optimal sites in the CLR and the MLR, each at subthreshold strength, locomotor movements identical to those seen with suprathreshold stimulation of each site alone were evoked. With concomitant stimulation at suprathreshold strength for each site, locomotion became vigorous, with a shortened cycle time. After making ablative lesions at either the CLR or MLR (unilateral or bilateral), controlled locomotion was still evoked at the prior stimulus strength by stimulating the remaining site. Together, these results demonstrate th