Anxiolytic-like effects of antidepressants after acute administration in a four-plate test in mice.

The four-plate test (FPT) is an animal model of anxiety based on stress caused by unconditioned fear. An increase of spontaneous punished behavior was used as a measure to determine the anxiolytic effects of various antidepressants (ADs). In the present study. ADs with different mechanisms of action, including tricyclics, selective serotonin reuptake inhibitors (SSRIs), a monoamine oxidase inhibitor (MAOI), and atypicals, were studied in the FPT to evaluate their anxiolytic-like effects following acute administration. The number of punished crossings was dramatically increased by the SSRIs citalopram, fluvoxamine, and paroxetine, but not fluoxetine. The mixed 5-HT/NE reuptake inhibitors, milnacipran and venlafaxine, also demonstrated strong antipunishment effects. The specific NE reuptake inhibitors, desipramine and maprotiline, and the atypical AD trazodone, enhanced freezing behavior, suggesting anxiogenic-like behavior. It was concluded that, in the FPT, a model based on spontaneous response, where animals are exposed to an aversive environment from which they can only escape by being motionless, this kind of behavior might be related to anticipatory anxiety. In this situation, ADs acting preferentially on 5-HT transmission possessed clear anxiolytic like effects. The balance between the two transmitters, 5-HT and NE, seemed to be a crucial factor.