Physiological studies on the development of neuronal mechanisms generating locomotion in the rat spinal cord

点击翻译按钮获取中文摘要

Effects of N-methyl-D,L-aspartate (NMA) on the generation of locomortor activity were studied using isolated lumbar spinal cord-hind limb preparations in new-born rats.Electromyographic activities were recorded from the ankle flexor and extensor muscles of both sides. Bath-applied NMA (10-30 <micrn>M) evoked alternating rhythmic activity between the flexors and extensors. The frequency of the rhythmic activity in each muscle depended on the NMA dose. The mean burst duration in extensors was considerably longer than that in flexors at low concentrations of NMA. When the NMA dose was increased, the mean burst duration in extensors markedly decreased, compared with that in flexors. The activity in the corresponding muscles of the two hind limbs always occurred alternatingly within the concentration ranged described above. This pattern of muscle activity was not affected by the dorsal root transection. The NMA-induced rhythmic activity was also observed after the spinal cord was split mid- … More sagittally. However, the frequency of the rhythmic activity was significantly lower and the mean burst duration in each muscle much longer than those before splitting. It was concluded that central rhythm generators, activated by NMA, exist in both sides of the lumbar spinal cord.The development of rhythmic motor activity was also studied using isolated lumbar spinal cord preparations of rat fetuses. Rhythmic motor activity was evoked by bath application of NMA and recorded through the ventral roots on both sides of the lumbar spinal cord. It was found that rhythmic activity in the ventral roots was elicited by bath-applied NMA at and after E15.5. The mean frequency of the rhythmic activity increased with age. The rhythythmic activity was also evoked at all stages after splitting the spinal cord midsagitally, indicating that each side of the spinal cord has neuronal circuits for rhythm generation even at the fetal stage.the phase relationship of the rhythmic activities between the two sides of the ventral roots was synchrous st E15.5 and E16.5, independent at E17.5 and alternating at @18.5-20.5. At E17.5. the addition of strvchnine changed the independent rhythimic activities between the two sides to a synchrounous pattern, while at earlier stages it had no effect. This suggets that some inhibitory pathways to play an inportant role of functional couplimg between the two sides of neuronal circuits at this stage. Less