POSTSYNAPTIC INHIBITION OF CEREBELLAR PURKINJE CELLS

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Abstract
In anaesthetized cats the exposed cerebellar vermis was activated by means of 2 pairs of stimulating electrodes, 1 on the Surface of a folium giving a beam of excited parallel fibers for several millimeters along the length of that folium, and one in the region of the fastigial nucleus exciting the axons of the Purkinje (P) cells. When observed by intracellular recording every P-cell responded to the beam of excited parallel fibers by a large (up to 10 mV) and prolonged (100 to 200 msec) inhibitory postsynaptic potential that powerfully inhibited the spontaneous and evoked responses of that cell. The extracellular potential field generated by parallel fiber activation showed 2 main components: an excitatory action giving a sharp initial negativity (maximum at 0.2 mm) and a later slower positive wave (maximum at 0.3 to 0.4 mm). Both in its depth profile and its time course this positive wave corresponds to the extracellular counterpart of P-cell IPSPs [inhibitory post-synaptic potential]. The positive field potential extends transversely across the folium far beyond the excited beam of parallel fibers. This finding, together with the maximum observed at the depth of the somas of the P-cell, points to the basket cells, with their transversely oriented axons, as being the inhibitory interneurons acting by their synapses on the P-cell soma and axonal origin. In preliminary experiments their repetitive discharges were recorded.