Effects of GABA and diazepam on 3H-serotonin release from hippocampal synaptosomes

The effects of GABA and diazepam on the spontaneous and potassium-evoked release of 3H-5-HT from rat hippocampal synaptosomes, preloaded by incubation with 3H-5-HT, have been investigated. Both GABA and diazepam independently increased the spontaneous release of 5-HT whereas they blocked the calcium-dependent, potassium-evoked release. However diazepam antagonised the GABA-mediated increase in spontaneous release but enhanced the inhibitory effects of GABA on potassium-stimulated release. The results suggest that 5-HT release in the hippocampus is under the presynaptic control of GABA and that diazepam may selectively enhance the inhibitory effect of GABA on the evoked release of 5-HT.