Cerebello-cerebellar responses mediated via climbing fibres

The results of impulse collision experiments have been satisfactorily accounted for by postulating that the climbing fibre afferents branch widely after entering the cerebellum, and the earlier response arose as a result of axon reflexes and the later response as an result of orthodromic impulses generated by the cells of origin of the fibres.

Abstract

A sequence of three evoked potentials was recorded on the paramedian lobule of the cat cerebellum following single shock stimulation of the intermediate portion of the ipsilateral anterior lobe. The second and third responses have been analysed using micro-electrode recording techniques and each was shown to reflect near-synchronous climbing fibre activation of many Purkinje cells in the paramedian lobule. The first response has not been fully studied but did not involve the climbing fibres. The first climbing fibre evoked potential was constant in amplitude and latency and able to follow at stimulation frequencies as high as 350/sec. It was scarcely affected by section of the ipsilateral cerebellar peduncles. The second was very variable in amplitude, never followed at frequencies greater than c. 10/sec and was completely abolished by pedunculotomy. Intracellular recordings from Purkinje cells showed that the first climbing fibre response was associated with a single excitatory post-synaptic potential but the second with excitatory post-synaptic potentials which were usually multiple. The above characteristics, together with the results of impulse collision experiments, have been satisfactorily accounted for by postulating that the climbing fibre afferents branch widely after entering the cerebellum. The earlier response arose as a result of axon reflexes and the later response as a result of orthodromic impulses generated by the cells of origin of the fibres. Evidence is presented which suggests that some at least of these cells were situated in the inferior olive.