Kinetics of dopamine and noradrenaline transport in synaptosomes from cerebellum, striatum and frontal cortex of normal and reeler mice

Recent evidence indicates that the cerebellum has a dopaminergic system. In order to elucidate further the dopaminergic system in the cerebellum, we investigated the transport of dopamine (DA) in synaptosomal preparations of normal and reeler mice. For comparative purposes we also studied DA transport in synaptosomal preparations from striatum and frontal cortex and compared DA transport to nor‐adrenaline (NA) transport. [3H]‐DA transport into cerebellar synaptosomes was found to be a Na+‐dependent, two component system–a high affinity, low capacity and a low affinity, high capacity. In striatum [33H]‐DA is transported by a similar high but different low affinity component. Maximal velocities of both transport components in the striatum were higher than the corresponding ones in the cerebellum. In the frontal cortex we also observed two [3H]‐DA transport components with affinities significantly lower than those in cerebellum and striatum. [3H]‐NA transport into synaptosomes, prepared from the three brain regions studied, showed two transport components with similar Kt and Vmax values, except for the high affinity component in striatum whose affinity is lower. In reeler mice [3H]‐DA transport was different from normal only in the cerebellum where the maximal velocity for both transport components was significantly higher (2 x). In contrast, no significant difference was observed in the transport of [3H]‐NA. The accumulated [3H]‐DA from cerebellar slices was found to be releasable by K+ stimulation, in a Ca++‐dependent manner, and most of the released radioactivity was in the form of [3H]‐DA. These results indicate that in the cerebellum there is a low‐density dopaminergic system which is distinct from the corresponding noradrenergic system.