Influence of antipsychotics and serotonin antagonists on presynaptic receptors modulating the release of serotonin in synaptosomes of the nucleus accumbens of rats.

In the nucleus accumbens of rats the release of [3H]serotonin (5-HT) from superfused synaptosomes stimulated by 30 mM K+ was investigated. In the presence of 40 microM of the uptake inhibitor cocaine the release of [3H]5-HT was inhibited by 5-HT in a concentration-dependent manner (IC50 = 0.45 microM). The maximum inhibitory effect of 5-HT was 54% of controls. The inhibition of K+-stimulated release of [3H]5-HT induced by 5-HT was antagonized completely by methiothepine and clozapine, respectively, whereas methysergide had only a weak antagonizing effect in a concentration of 20 microM or less, haloperidol was ineffective. Furthermore, the synaptosomal K+-stimulated release of [3H]5-HT was also inhibited by dopamine (DA) in a concentration-dependent manner (IC50 = 0.1 microM). This inhibitory effect was antagonized by antipsychotic drugs, the rank order of antagonistic potencies was sulpiride greater than haloperidol greater than clozapine; methiothepine was ineffective. The experimental system (the K+-stimulated synaptosomal release of [3H]5-HT seems to be a suitable model for differentiating dopaminergic and/or serotonergic components of antipsychotics or other drugs on presynaptic receptors.