Noradrenergic action in the developing rat cerebellum: interaction between norepinephrine and synaptically-evoked responses of immature Purkinje cells.

This study was designed to characterize the influence of norepinephrine (NE), a putative cerebellar neurotransmitter, on immature synaptic activity during early postnatal periods of the developing cerebellar cortex. Norepinephrine was applied by microiontophoresis to single, young Purkinje cells to assess its effects on spontaneous and synaptically-mediated activities. Data from these studies indicate that the catecholamine exerts a profound modulatory-type influence on Purkinje cell responsiveness to activation of newly-established inputs. NE augmented climbing fiber-elicited excitatory burst responses by postnatal day 5 and enhanced 'off-beam' inhibitory activity by postnatal day 9, as soon as basket and stellate interneurons became functional. The functional implications of this noradrenergic facilitating effect, which is present throughout the maturation of the cerebellar cortical network, are discussed in terms of its possible contribution to the wiring of a definitive neuronal circuit.