Interaction between responses in Purkinje cells evoked by climbing fibre impulses and parallel fibre volleys in the cat.

The plateau-like depolarizing potentials evoked in Purkinje cell dendrites by impulses in climbing fibres (Ekerot & Oscarsson, 1981) were conditioned by single parallel fibre volleys and investigated by intra- and extracellular recording from cat cerebellar cortex. The conditioning parallel fibre volleys evoked predominantly inhibitory potentials of long duration in the Purkinje cell dendrites. Massive parallel fibre volleys, which may evoke plateau-like depolarizing potentials (Campbell, Ekerot, Hesslow & Oscarsson, 1983) were avoided. In proximal dendrites parallel fibre volleys preceding climbing fibre responses reduced or abolished the plateau potential, whereas the initial spike-like component of the climbing fibre responses was largely unaffected. Parallel fibre stimulation during already established plateau potentials immediately terminated the plateaus. In distal dendrites parallel fibre stimulation preceding climbing fibre responses reduced or abolished both the plateau potential and the initial component of the climbing fibre responses. Parallel fibre stimulation during established plateau potentials did not immediately terminate the plateau potentials but reduced their duration. The results of the present investigation suggest that single dendritic branches of Purkinje cells serve as independent integrators of mossy fibre and climbing fibre inputs.