Potentiation of the effects of raclopride on sucrose consumption by the 5-HT2 antagonist ritanserin.

We examined the effects on sucrose consumption of a dopamine (DA) D2/D3 antagonist (raclopride, 0-0.3 mg/kg), a serotonin 5-HT2/2c antagonist (ritanserin, 0-0.4 mg/kg), and raclopride (0.15 mg/kg) combined with ritanserin (0-0.4 mg/kg). Three different concentrations of sucrose solution (0.7%, 7.0% and 34%) were tested. The concentration-intake function in drug-free rats was an inverted-U, with 7.0% sucrose supporting the highest intake. Raclopride (0.3 mg/kg) inhibited intake of 7.0% sucrose, but its effect on 0.7% sucrose fell short of significance (P < 0.06) and intake of 34% sucrose was unchanged. Ritanserin did not affect sucrose intake when given on its own, but synergized with a previously ineffective dose of raclopride (0.15 mg/kg) so as to cause a significant inhibition of 7.0% sucrose intake and increase in 34% sucrose intake. These data indicate that 5-HT2 antagonism potentiated the behavioural effects of raclopride and we speculate that this interaction might contribute to the efficacy of atypical neuroleptic drugs.