Effects of acute or chronic administration of substituted benzamides in experimental models of depression in rats

The effects of substituted benzamides, sulpiride and raclopride on experimental models of depression were studied in male rats after acute or chronic administration in comparison to those of the classical antidepressant, clomipramine. In contrast to clomipramine (50 mg/kg), acute doses of sulpiride or raclopride (1 or 5 mg/kg) failed to change the behavioral response of animals tested in the despair (constrained swim) test or in the model of reserpine-induced changes in the open field behavior. These doses also did not modify the grooming response of rats exposed to a novel environment. Sulpiride or raclopride 10 mg/kg increased the immobility time in the despair test and reduced novelty-induced grooming. The repeated injection for 21 days of sulpiride or raclopride (1 or 5 mg/kg, but not 10 mg/kg) induced a reduction of the immobility period during the constrained swim test similar to that following the chronic treatment with clomipramine 50 mg/kg. This appeared to be a clear-cut reversed dose-response relationship for both substituted benzamides, being the dose potency 1 mg/kg>5 mg/kg>10 mg/kg. Raclopride was more potent than sulpiride in this respect. Furthermore, like clomipramine, sulpiride (1 or 5 mg/kg) and raclopride (1 mg/kg) antagonized reserpine-induced changes in the open field behavior and enhanced novelty-induced grooming. These results indicate that, in contrast to acute injection, repeated administration of small doses of the substituted benzamides, sulpiride or raclopride induce an effect similar to that of the classical antidepressant, clomipramine. The reverse dose-response relationship suggests that these drugs in small doses act on presynaptic dopamine D2 receptors. This may be consistent with a postsynaptic action of greater doses that exert sedative effects and increase immobility time in the despair test