Activation of a Central Noradrenergic Projection to Cerebellum

RECENT histochemical studies have demonstrated abundant nerve fibres containing noradrenaline in rat cerebellar cortex 1,2 terminating predominantly on Purkinje cells 2 . An inhibitory function for these fibres is suggested by the uniform inhibition of the spontaneous discharge 3 and hyperpolarization of Purkinje cells (P cells) produced by microelectrophoretic application of noradrenaline (NA) 4 . Furthermore, the firing rate of Purkinje cells is generally increased after destruction by 6-hydroxy-dopamine of fibres containing NA 5 . Further characterization of the natural endogenous transmitter and its effect on P cells requires experimental activation of the proposed adrener-gic pathway, and identification of the origin of the NA projection to the cerebellum thus assumes critical importance. It has been suggested that the nerves containing catecholamine in rat cerebellar cortex arise largely from discrete bilateral nuclei of fluorescent cells in the dorsal medullary brain stem (the locus coeruleus, LC) 6,7 . We have reported that electrical stimulation in the area of the LC inhibits P cells 8 . We now report that this inhibitory response is evoked selectively from the NA-contain-ing cells of the LC, that the inhibitory effects are widespread and that the response closely resembles the electrophysiological effects produced by exogenous NA.