On the Nature of Positive Waves in Ventral Root Potential

Abstract

The ventral root potential (VRP) is recorded in general as a slow negative deflection, which indicates the negativity in the proximal portion of the ventral root in reference to its distal portion. We are already familiar with the positive slow potential in the sympathetic ganglia (5, 6, 10), but nothing has been reported concerning positive waves in VRP except the studies performed by Bernhard and Skoglund (1). They succeeded, by medullary stimulation, in obtaining positive VRP accompanied by predominant responses in extensor muscles, while the negative VRP was found to be always accompanied by responses predominant in the flexors. Some possible causes which may lead to these results were suggested by them, but no satisfactory account has yet been given for the reversal of the potential sign.In the course of the authors' research about the influence of polarizing currents on VRP, positive sloW potentials were found on occasion under certain experimental conditions. The findings seem to be worth reporting, because they might furnish a clue for the bearings of positive VRP on the mechanism of synaptic transmission. METHODSToads were used in all experiments. The spinal cord with attached roots was excised from the animal body and placed in an airtight chamber through which moist oxygen (sometimes 5% CO2 was added) was passed. The VRP and in some cases also the dorsal root potential (DRP) evoked by dorsal root stimulation were recorded routinely by means of a RC-coupled amplifier (half time : 0.5 sec.) and an oscilloscope. For stimulation, a thyratron stimulator coupled with an induction coil was used, which relayed electrically to the sweep circuit. In order to polarize motoneurones, constant currents were made to flow along a ventral root and the spinal cord ( fig. 1). The previous reports (8, 12) must be read for details. RESULTSThe occurrence of positive waves in VRP seemed to be facilitated firstly by cathodal polarization of motoneurone somata and secondly by its repeated orthodromic excitation. Also the intensity of the stimuli delivered to a dorsal root was proved to have some bearings on it. These conditions, however, were

The Electrical Activities of Single Motoneurones in Toad's Spinal Cord, Recorded With Intracellular Electrodes

“…Some of the positive deflections which have been often encountered. in ventral root potentials may originate from positive potentials set up in motoneurone somata, on which discussions were made in a separate report (Iwata and Araki,13). Iwata and Otani (12) analysed the ventral root potential into two components; the spike-like and the slow.…”