These experiments were made to study the mechanisms underlying the antidepressant-like effects of the beta(3) adrenoceptor agonist amibegron (SR58611A). To this purpose, the expression levels of the hippocampal cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB), brain-derived neurotrophic factor (BDNF), B-cell lymphoma-2 (Bcl-2) and Bax proteins were assessed, by using western blot analysis, in rats tested in the forced swim test (FST). Under basal conditions (no previous exposure to stressors), different groups of male Wistar rats received acutely or repeatedly (once/day for 7days) intraperitoneal (i.p.) injections of amibegron (1, 5 and 10mg/kg), the tricyclic antidepressant (TCA) clomipramine (50mg/kg), the selective serotonin reuptake inhibitor (SSRI) citalopram (15mg/kg) or their vehicles. The influence of stress-related conditions was studied in rats subjected to acute (4h) or repeated (4h/day for 7days) restraint stress, applied prior to the FST procedure. Compared to the control groups, both stressor procedures increased the immobility time in the FST and reduced hippocampal BDNF and Bcl-2/Bax ratio proteins expression, which were counteracted by amibegron (5 and 10mg/kg) treatment. Opposite effects were found in the CREB expression, since it was lower after acute and higher after repeated stress procedure, respectively. Again, these effects were reversed by amibegron treatment. Different results were obtained in animals treated with clomipramine or citalopram. Hence, it is likely that the observed behavioral effects of amibegron could be due, at least in part, to its action on hippocampal expression of neurotrophic and/or anti-apoptotic factors, supporting the hypothesis that beta(3) adrenoceptors may be a therapeutic target for the treatment of stress-related disorders.
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