Very short-term potentiation of climbing fiber effects on deep cerebellar nuclei neurons by conditioning stimulation of mossy fiber afferents.

Field potentials induced in deep cerebellar nuclei by the electrical stimulation of contralateral red, pontine and reticularis tegmenti pontis oralis nuclei, the restiform body and the inferior olive were recorded in the alert cat. Recording sites in interpositus and fastigial nuclei were selected with the aid of antidromic field potentials induced by red nucleus and restiform body stimulation, respectively. Pontine and reticularis tegmenti pontis oralis nuclei stimulation induced small, but constant amplitude, field potentials consisting of one or two negative waves. Control field potentials induced by inferior olive stimulation consisted of a negative wave at 2-3 ms followed by a late (4-6 ms) positivity. Conditioning stimuli applied to the pontine and reticularis tegmenti pontis oralis nuclei greatly enhanced the amplitude of the inferior olive-evoked synaptic field potential for a time window of about 40 ms. In contrast, inferior olive conditioning stimulation failed to modify the field potentials induced by pontine nuclei stimulation. These facilitatory effects on field potential amplitude showed no long-lasting modifications. The transient modification of inferior olive-induced field potentials could be related to attentional movements made by the animal to natural or electrically-induced sensory cues.