抄録
This study aimed to investigate characteristics of fore- and hindlimb locomotor movements evoked by stimulation to the midbrain in decerebrate rabbits. Under halothane anesthesia, adult rabbits (NZW, 2-3 kg) were surgically decerebrated at the precollicular-postmammillary level. The head was then fixed in a stereotaxic apparatus, and the body was supported by rubber belts. To evoke locomotion, 50-Hz stimuli (10-100 μA, 0.2 ms duration, 5-10 sec) were applied to the midbrain cuneiform nucleus, which corresponds to the mesencephalic locomotor region in cats, with Wood's-metal-filled glass microelectrodes. When the midbrain was stimulated, the left and right hindlimbs consistently exhibited nonalternating, rhythmic hopping movements. Even after the spinal hemisection at the lower thoracic level, the stimuli still evoked in phase rhythmic movements of bilateral hindlimbs. In contrast, left and right forelimbs basically displayed alternating locomotor movements when the midbrain was stimulated. In particular, after complete transection of the lower thoracic cord, the stimuli evoked purely reciprocal movements of bilateral forelimbs at any stimulus intensity. Despite such differences in fore- and hindlimb movement patterns, locomotor cycle frequency of fore- and hindlimbs was usually equal when the full hindlimb hopping was evoked. These findings suggest that spinal neuronal circuits involved in the generation of fore- and hindlimb locomotor patterns are tightly coupled, although they are constituted in a different manner. [J Physiol Sci. 2006;56 Suppl:S191]
