Intracellularly recorded responses of the cerebellar Purkinje cells

Abstract

1. Intracellular recording from Purkinje cells has been employed in investigating the excitatory and inhibitory synaptic action that is exerted on these cells by the mossy fibre input into the cerebellum. 2. These synaptic actions are evoked not directly by the mossy fibres, but probably always through granule cells and their axons, the parallel fibres. The intracellular records conform with the anatomical evidence that the parallel fibres directly exert a powerful synaptic excitatory action on Purkinje cells, and that the inhibitory pathway occurs via an inhibitory interneurone — a basket cell or a stellate cell. Direct stimulation of parallel fibres gives intracellular potentials closely resembling those produced by deep stimulation of mossy fibres. 3. As would be expected, direct stimulation of parallel fibres produces an EPSP with a latency 1 to 2 msec briefer than the IPSP. The IPSP has a duration usually in excess of 100 msec. The EPSP appears to be briefer, though its superposition on the IPSP greatly reduces its apparent duration. Neutralization of the IPSP by appropriate membrane polarization or by intracellular chloride injection reveals an EPSP duration of up to 50 msec. 4. The IPSP is typically affected by polarizing currents; reduced and even inverted by hyperpolarizing currents, and increased by depolarizing currents. The IPSP is converted to a depolarizing response by excess of intracellular chloride. It must therefore be generated by an increased ionic permeability of the inhibitory subsynaptic membrane, chloride ions being importantly concerned. 5. Often small irregular IPSPs can be observed occurring spontaneously, and they react to polarizing currents and to chloride injections in a manner identical to the evoked IPSPs. It is concluded that they are generated by the spontaneous discharges of basket cells. 6. A brief account is given of various spontaneous rhythmic responses of impaled Purkinje cells, and of the effect of synaptic inhibitory action upon them. 7. There is a general discussion of these findings in relation to the various neural pathways and neural mechanisms that have been postulated in the light of the preceding investigations.