Neuro-Inflammatory and Behavioral Changes Are Selectively Reversed by (Zembrin) and Mesembrine in Male Rats Subjected to Unpredictable Chronic Mild Stress.

(ST) induces antidepressant and anxiolytic effects, purportedly by monoamine regulation, anti-inflammatory and antioxidant properties, and phosphodiesterase 4 (PDE4) inhibition. These multimodal actions have not been demonstrated in an animal model of major depressive disorder. Wistar rats (both sexes) were subjected to 8-week unpredictable chronic mild stress, subsequently receiving saline, a standardized ST extract, Zembrin 25 and 12.5 mg/kg (ZEM25 and ZEM12.5), its primary alkaloid mesembrine (MES), or escitalopram (20 mg/kg) for 36 days. Sucrose preference, open field, Barnes maze, and forced swim tests were performed, with cortico-hippocampal monoamines, inflammatory and oxidative stress markers analyzed post-mortem. Male, but not female rats, presented with increased anhedonia and anxiety but not despair. Males presented with increased hippocampal PDE4B expression, increased dopamine metabolites, and decreased cortical serotonin. In males, ZEM12.5 decreased anhedonia- and anxiety-like behavior, decreased cortical and hippocampal PDE4B, and increased plasma interleukin-10. MES induced a transient decrease in anhedonia-like behavior and increased hippocampal serotonergic and cortical dopaminergic activity, whilst decreasing hippocampal PDE4B. ZEM25 increased plasma interleukin-10 but decreased cortical glutathione, indicating paradoxical anti-inflammatory and prooxidant effects. ZEM12.5 and MES more effectively addressed anxious-depressive-like behavior and stress-induced inflammation and monoaminergic alterations, respectively. Multitargeted actions on monoamines, redox-inflammation, and PDE4 may provide ST with antidepressant effects across multiple symptom domains, although mutually synergistic/antagonistic effects of constituent alkaloids should be considered.