Modification of parallel fibre-Purkinje cell transmission by long-term activation of climbing fibres.

Harmaline has been used to produce long-term activation of the climbing fibre projection to the cerebellar cortex and the effects on parallel fibre transmission to Purkinje cells were studied electrophysiologically. The climbing fibre activation produced a profound depression in parallel fibre transmission which could be sustained for a period of more than two days. It was found that ongoing climbing fibre activity was necessary to maintain the depression at the synaptic junctions because transmission returned to normal within a matter of minutes if the climbing fibre input to the Purkinje cell was removed. This finding suggests that climbing fibre impulses do not induce permanent modifications in the efficacy of parallel fibre synapses.