Saltiel P, Tresch M C, Bizzi E
Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
J Neurophysiol. 1998 Nov;80(5):2323-39. doi: 10.1152/jn.1998.80.5.2323.
Previous work using electrical microstimulation has suggested the existence of modules subserving limb posture in the spinal cord. In this study, the question of modular organization was reinvestigated with the more selective method of chemical microstimulation. N-methyl--aspartate (NMDA) iontophoresis was applied to 229 sites of the lumbar spinal cord gray while monitoring the isometric force output of the ipsilateral hindlimb at the ankle. A force response was elicited from 69 sites. At 18 of these sites, tonic forces were generated and rhythmic forces at 44. In the case of tonic forces, their directions clustered along four orientations: lateral extension, rostral flexion, adduction, and caudal extension. For the entire set of forces (tonic and rhythmic), the same clusters of orientations were found with the addition of a cluster directed as a flexion toward the body. This distribution of force orientations was quite comparable to that obtained with electrical stimulation at the same sites. The map of tonic responses revealed a topographic organization; each type of force orientation was elicited from sites that grouped together in zones at distinct rostrocaudal and depth locations. In the case of rhythmic sequences of force orientations, some were distinctly more common, whereas others were rarely elicited by NMDA. Mapping of the most common rhythms showed that each was elicited from two or three regions of the cord. These regions were close in location to the tonic regions that produced those forces that represented components specific to that rhythm. There was an additional caudal region from which the different rhythms also could be elicited. Taken together, these results support the concept of a modular organization of the motor system in the frog's spinal cord and delineate the topography of these modules. They also suggest that these modules are used by the circuitry underlying rhythmic pattern generation by the spinal cord.
先前使用电微刺激的研究表明，脊髓中存在着服务于肢体姿势的模块。在本研究中，采用更具选择性的化学微刺激方法，对模块组织问题进行了重新研究。在监测同侧后肢踝关节等长力输出的同时，将N-甲基-D-天冬氨酸（NMDA）离子导入法应用于229个腰脊髓灰质位点。从69个位点引发了力反应。其中18个位点产生了张力，44个位点产生了节律性力。在产生张力的情况下，其方向沿四个方向聚集：外侧伸展、头侧屈曲、内收和尾侧伸展。对于所有的力（张力和节律性力），除了一个朝向身体屈曲的方向簇外，发现了相同的方向簇。这种力方向的分布与在相同位点进行电刺激所获得的分布相当。张力反应图谱揭示了一种拓扑组织；每种力方向类型都是从在不同的头尾和深度位置区域中聚集在一起的位点引发的。在力方向的节律性序列情况下，有些明显更常见，而其他的则很少由NMDA引发。对最常见节律的图谱分析表明，每种节律都是从脊髓的两三个区域引发的。这些区域在位置上靠近产生代表该节律特定成分的力的张力区域。还有一个额外的尾侧区域，也可以从该区域引发不同的节律。综上所述，这些结果支持了青蛙脊髓运动系统模块组织的概念，并描绘了这些模块的拓扑结构。它们还表明，这些模块被脊髓节律模式生成的基础电路所利用。
