Antinociceptive effects of serotonergic reuptake inhibitors in mice

The antinociceptive effects of three predominantly serotonergic reuptake inhibitors, alaproclate, citalopram and clomipramine, were examined in mice using the hot-plate, formalin and substance P tests. The effects were compared with those of the noradrenergic reuptake inhibitor, desipramine. Different profiles in the three nociceptive tests were found for all four drugs, using doses of 10 and 40 mg/kg. The selective serotonergic reuptake inhibitor, alaproclate, seemed to have the least antinociceptive effects, and was the only drug that was ineffective in the hot-plate test. The other selective drug, citalopram, had a stronger effect than alaproclate in the substance P test, but in the formalin test, both drugs were approximately equally effective. Clomipramine differed from citalopram by being more effective in the formalin test. These findings thus indicate that selective inhibitors of the uptake of 5-HT have weaker antinociceptive effects than less selective drugs. Desipramine seemed to be no less effective than the serotonergic drugs and was the most potent drug in the hot-plate test.