The responses evoked by peripheral nerve stimulation in the c1 and c3 zones of the cerebellar cortex have been examined in barbiturate-anaesthetized cats. The responses evoked via the spino-olivocerebellar pathways (SOCPs), which terminate in the cortex as climbing fibres, were recorded as positive multiunit field potentials from the cerebellar surface of lobule V. 2. Low-strength conditioning stimulation of the superficial radial, ulnar or median nerve frequently modified the climbing fibre-mediated responses evoked by a subsequent test stimulus to one of the other nerves. In most cases this modification involved a depression of the evoked response. The depression was not dependent on the conditioning stimulus evoking climbing fibre-mediated responses in the cortex. 3. The depression of the evoked responses increased as the conditioning stimulus intensity was raised within the range of 1.1-1.5 x threshold (1.1-1.5T). 4. Topical application of bicuculline to the surface of the dorsal column nuclei reduced the depression evoked by conditioning stimulation and it is therefore concluded that GABAergic inhibition in the cuneate nucleus contributes to the depression. 5. The inhibition is discussed in relation to its possible contribution to movement-related regulation of the excitability of SOCPs which occurs during locomotion in awake cats.
