SEROTONIN RECEPTORS REGULATING TRANSMITTER RELEASE

The effects of serotonin (5-HT) and of various serotonergic agents on the release of 3H-acetylcholine (3H-ACh) and of endogenous glutamate (GLU) have been studied in rat hippocampal and cerebellar synaptosomes and slices depolarized with KCl or stimulated electrically. The results allow to conclude that: a) hippocampal cholinergic terminals are endowed with a tonically activated inhibitory 5-HT receptor which appears to belong to the 5-HT1B subtype; b) cerebellar GLU release appears to be tonically inhibited by 5-HT through the activation of both 5-HT1 and 5-HT2 receptors. The 5-HT1 receptors are located on GLU terminals (parallel fibers); they do not conform to the criteria defining the known 5-HT binding sites and might therefore represent a novel subtype of the 5-HT2 receptor. The possible localization of the 5-HT receptors is discussed.