Serotonin uptake and release from rat cerebellum in vitro

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Abstract
Serotonin (5‐HT) uptake and release were analyzed in cerebellar fractions. Cerebellar P2 fractions and molecular layer homogenates are able to accumulate exogenous 5‐HT through an Na‐dependent, high‐affinity transport system. Molecular layer 5‐HT uptake, however, was totally dependent upon Na+, whereas the accumulation of the amine by P2 fractions from whole cerebellum was also carried out by an Na‐independent transport system. Ca++‐dependent release of recently accumulated 5‐HT was observed in both P2 fractions and molecular layer homogenates when depolarizing conditions were used. This release was blocked by ruthenium red and Mg++, two inhibitors of the Ca++ entry to the nerve endings induced by depolarization. The molecular layer homogenates released twice as much 5‐HT as did cerebellar P2 fractions, indicating that serotoninergic boutons in the cerebellar cortex might be located in the molecular layer. Our results suggest that 5‐HT might play a transmitter role in the cerebellum.