Threshold of ventral root stimulation to produce the IS-spike with the M-spike is higher than that to produce the IS-spike without the M-spike in the same cat motoneuron

抄録

In cats, anesthetized with pentobarbital sodium and immobilized with d-tubocurarine, it was discovered by changing the strength of L 7 or S 1 ventral root (VR) stimulation that the stimulation could produce in the same motoneuron the IS-spike, i.e., the spike of the initial segment, either via the M-spike or without the M-spike, which is believed to be the spike of the node of Ranvier as recorded in the soma. It was shown by simultaneously recording the compound action potential of the L 7 or S 1 ventral root that the threshold of VR stimulation to produce the IS-spike via the M-spike was higher than that to produce it without the M-spike in all the 18 motoneurons in which the threshold was studied. With weaker stimulation the M-spike was not produced and the IS-spike arose from a potential smaller than the M-spike (the M-potential) or directly from the baseline. The M-potential could also trigger the M-spike. These results disclose the possibility that the M-spike originates not in the axon, but somewhere else such as the dendrite. (J Nippon Med Sch 1997; 64: 314-322)