Endogenous serotonin stimulates striatal dopamine release in conscious rats

Serotonin (5-HT) and dopamine (DA) are established neurotransmitters in the brain. This study examined whether, in conscious, free-moving rats, increased concentrations of endogenous 5-HT in extracellular fluid of the corpus striatum affect local release of endogenous DA. Administration of the 5-HT reuptake blocker alaproclate via a microdialysis probe increased striatal dialysate levels of DA and its metabolites dihydroxyphenylacetic acid and homovanillic acid as well as levels of 5-HT and the 5-HT metabolite 5-hydroxyindoleacetic acid. Whereas DA reuptake blockade with GBR-12909 did not prevent these effects of alaproclate, serotonergic ablation by i.c.v. administration of 5,7-dihydroxytryptamine markedly decreased basal levels of 5-HT and 5-hydroxyindoleacetic acid and abolished the effects of alaproclate on dialysate levels of DA, 5-HT and their metabolites. The results are consistent with a stimulatory action of endogenous 5-HT on striatal DA release in conscious animals.