The secondary spikes of climbing fibre responses recorded from Purkinje cell somata in cat cerebellum.

Extracellularly recorded climbing fibre responses in Purkinje cell somata in the cerebellar cortex were investigated in cats deeply anaesthetized with barbiturate. The effects on the amplitude of initial and secondary spikes of preceding climbing fibre activation, on-beam parallel fibre activation and off-beam parallel fibre activation were studied. When a climbing fibre response was preceded by climbing fibre activation there was a decrease in the amplitude of the initial spike of the second response at intervals up to 25 ms and little effect at longer intervals. Secondary spike amplitude was greatly increased at intervals up to 100 ms. When a complex spike was preceded by on-beam parallel fibre activation there was a decrease in the initial spike amplitude at short intervals and an increase in the amplitude at long intervals. Secondary spike amplitude was increased up to 150 ms after an on-beam parallel fibre volley. When a complex spike was preceded by off-beam parallel fibre stimulation there was an increase in initial spike amplitude at intervals up to about 200 ms and a decrease in secondary spike amplitude at intervals up to about 150 ms. The results show that the amplitude of the secondary spikes can be modified by a preceding input to the Purkinje cell. The results also suggest that the secondary spikes are generated in the Purkinje cell dendrites and the initial spike in the soma.