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The effect of ritanserin on dopamine (DA) re-uptake and efflux was studied in rat frontal cortex synaptosomes. When compared to other 5HT[sub 2] receptor antagonists such as ketanserin and risperidone or DA D[sub 2] receptor antagonists such as haloperidol and raclopride, the effect of ritanserin proved to be more potent. Ritanserin blocked the DA transporter with a K[sub i] of 0.18 ± 0.06 µM, similar to cocaine (0.11 ± 0.005 µM), while ketanserin had a K[sub i] of 0.93 ± 0.045; haloperidol of 2.07 ± 0.12; risperidone of 18.01 ± 0.62 and raclopride of 24.01 ± 1.55. In addition, 15 min from its local application to the synaptosomes, ritanserin potently released [³]H-DA leaving only 29.6 ± 1.6% of DA content, while ketanserin effect was equal to 46.5 ± 0.9%; haloperidol to 70.4 ± 2.2% and risperidone to 73.9 ± 1.5%, all tested at the dose of 10 µM. Cocaine had no effect on DA efflux. These results suggest that ritanserin has a intrinsic dopaminergic effect which may help to explain its reported improvement on mood, cognition and negative symptoms of schizophrenia. [ABSTRACT FROM AUTHOR]