Comparison of behavioral effects of moclobemide and deprenyl during forced swimming

The present study compared the antiimmobility effects of l-deprenyl (DEP) and moclobemide (MOC) to the classic antidepressant imipramine (IMI), using an ethological approach. To investigate the degree of MAO-B inhibition by DEP and MOC, combination of treatments of ineffective doses of phenylethylamine (PHEA) with DEP or with MOC were administered in three doses before immobility was tested in the forced-swimming paradigm. Tests were videotape recorded for analysis of the frequency and duration of the behaviors during the procedure. There was a significant, dose-dependent decrease in immobility duration and an increase in mobility duration of rats treated with IMI. Both active behaviors of climbing and swimming were equally enhanced by the tricyclic antidepressant, climbing behavior composing 75% of the mobile behaviors. The intermediate doses of the MAOIs tested, DEP 0.25 mg/kg and MOC 30 mg/kg, decreased immobility and increased mobility. The antiimmobility effect of DEP was due to longer climbing behavior while MOC enhanced swimming duration. No behavioral changes were seen with the administration of the lower and higher doses of the MAOI. Potentiation of the antiimmobility effects was observed when ineffective doses of PHEA and of DEP or MOC were administered in combination. Differences between the MAO inhibitors on the active behaviors were also observed when administered with PHEA; DEP and PHEA significantly increased climbing and MOC and PHEA increased swimming. This preclinical evaluation of selective MAO inhibitors indicates that both MAO-A and MAO-B inhibitors have antidepressant effects. However, to clearly demonstrate that these antiimmobility effects are a consequence of increased brain concentrations of any one of the several monoamines implicated in the mechanism of action of DEP or MOC should be the subject of future studies.