EFFECTS OF MOCLOBEMIDE, A NEW GENERATION REVERSIBLE MAO-A INHIBITOR, IN A NOVEL ANIMAL-MODEL OF DEPRESSION

This study was designed to investigate the predictive validity of a recently described chronic mild-stress-induced anhedonia model of depression. In an intracranial self-stimulation (ICSS) paradigm, rats were allowed to self-stimulate in the ventral tegmental area. Stimulation frequency thresholds for ICSS responses were determined prior to, during, and after a 19-day period of exposure to a variety of mild, intermittent, unpredictable stressors. After nine days of mild stress, stimulation threshold was significantly increased, suggesting a gradual decrease in the rewarding properties of brain stimulation. This anhedonic state lasted throughout the stress period and slowly disappeared over a 10-day period after termination of the stress regimen. This stress-induced increase in ICSS threshold was not observed in rats that were stressed and concomitantly treated with the reversible inhibitor of monoamine oxidase type A (RIMA) moclobemide (20 mg/kg, b.i.d.). In nonstressed animals treated with vehicle or moclobemide, no significant change in ICSS occurred during the course of the experiment. These experimental results reinforce the value of this animal model with respect to its predictive and construct validity.