ORIGIN OF THE NEGATIVE POTENTIAL SHIFT OF ALL-OR-NOTHING CHARACTER IN THE CEREBELLAR CORTEX OF THE RABBIT

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1. The negative potential shift, having variable durations (from 250 msec to several sec) and occurring in all-or-nothing fashion by white matter stimulation, was studied with the microelectrode in the cerebellum of the rabbit anaesthetized with Nembutal. The shift ranged from several to 60 mV in magnitude. The shift was recorded from the molecular layer as well as from the layer of Purkinje cell bodies, but never observed in the white matter.
2. The shift was always preceded by the sequential spike discharge of the Purkinje cell dendrites, but did not influence the excitability of the dendrites. Furthermore, no intracellular potentials were ever recorded from the Purkinje cell dendrites and cell bodies, which could account for the long-lasting potential shif t. These results show that the shift is recorded when the microelectrode tip is positioned close to the Purkinje cell membrane, but it does not originate in the Purkinje cell. All other nerve cells in the cerebellar cortex are also excluded as candidates for possible site of origin of the shift because they are physically not in a close relationship with the Purkinje cell dendrites. Possible site of origin of the shift was discussed.
3. During the shift amplitude of the spike of the Purkinje cell dendrites increased and positive-negative spikes of its cell body were converted into monophasic-positive spikes. Possible mechanism for this phenomenon was discussed.