Selective effects of apomorphine on dorsal raphe neurons: a cytofluorimetric study

Using a quantitative cytofluorimetric method to detect changes in the intracellular levels of serotonin (5-HT) in individual neurons in rat brain, we have found that the dopaminergic agonist apomorphine increases 5-HT content of dorsal raphe cell bodies without affecting cells in the median raphe nucleus. Liquid chromatographic studies revealed that apomorphine also elevated the concentrations of both 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in striatum, the projection site for dorsal raphe neurons. Conversely, the dopaminergic antagonist haloperidol, at a dose of 0.8 mg/kg, decreased 5-HT levels in dorsal raphe cells. A lower dose of haloperidol (0.4 mg/kg), which had no significant effect alone, completely blocked the effect of apomorphine in the dorsal raphe. These results support the hypothesis that the effects of apomorphine on serotonergic neurons are secondary to dopamine receptor stimulation.