Spontaneous Activity Of Central Neurons In Toads Small-Nerve Motor System

Spontaneous activities of the slow muscle system have been recorded from the forelimb muscles, the 3rd spinal ventral horn, and the midbrain of toad.1. On the forelimb muscles, slow muscle responses were observed by unipolar leading; in general from extensors and flexors in frequencies 7-12/sec. and 3-6/sec. respectively at rest. From symmetric muscles on the right and the left sides these were often observed discharging almost synchronously. However, their frequencies were varied according to changes in posture.2. Spontaneous spike discharges were led extracellularly from the 3rd spinal ventral horn with tungsten needles with a tip of about 1μ. These potentials were usually triphasic, and the 2nd negative spike as large as 250 μV was observed commonly. These rhythmic discharges appeared at 7.7/sec. in the mean, and there was found the correspondence to the slow muscle responses, and that synchronization was detected among almost extensors of the forelimbs.3. Similar spike discharges were also recorded from loci presumably belonging to the brain-stem reticular formation, which distributed uniformly in the mesencephalon and beneath rhomboid fossa. The potential was almost triphasic, the marked negative phase ranging up to about 250-300 μV, and the frequency was almost 7.9/sec. under the stationary condition. The frequency was almost equal to the rhythm of the muscle response in the forelimb, and there could be even found a correspondence between those two trains in simultaneous leading.4. Histograms have been plotted from intervals between successive discharges led from the brain-stem. The rhythmic discharges are characterized by a peak in the distribution of intervals, usually between 100 and 160, msec. The peak interval was transferred temporarily in the range from 70 to 50 msec. when the labyrinth was stimulated by means of rolling the body about 45°. Repetitive sloping stimuli were most effective, advancing the peak of the interval histogram to 30 msec. and consequently rhythmic activities of the slow system were accelerated in general to about 30/sec. in frequency in its muscles and their centers.