Boldine Mitigates Chronic Unpredictable Stress-Induced Depression by Suppressing Serotonin 3A Receptor-Calcium/Calmodulin-Dependent Protein Kinase II Signaling and Nucleotide-Binding Domain Leucine-Rich Repeat Protein 3 Inflammasome in the Hippocampus.

Major depressive disorder is a debilitating condition linked to dysregulated serotonin (5-HT) signaling, neuroinflammation, and oxidative stress. Boldine (BDN), a natural aporphine alkaloid with antioxidant and neuroprotective properties, might have antidepressant potential, which is still unexplored. This study investigates the effects of BDN on chronic unpredictable stress (CUS)-induced depression-like behavior in male Wistar rats. It focuses on neuroinflammation, oxidative stress, monoamine levels, and 5-HT3A receptor modulation. Rats were subjected to CUS for 42 days and treated with BDN (20, 40, or 80 mg/kg, po) or vortioxetine (VORT, 20 mg/kg, p.o) from the 22nd to 42nd day. Behavioral assessments (sucrose preference test, forced swim test, hole board test) revealed that BDN significantly alleviated anhedonia, despair, and anxiety-like behaviors. CUS increased serum and hippocampal cortisol, oxidative stress (elevated malondialdehyde, reduced glutathione, superoxide dismutase, catalase), and pro-inflammatory markers (NLRP3, IL-1β), which BDN effectively normalized. High-performance liquid chromatographic analysis of the brain region showed that BDN restored hippocampal dopamine, norepinephrine, and serotonin levels. RT-PCR analysis demonstrated that BDN downregulated hippocampal Htr3a, CAMKII and upregulated Htr1a gene expression, suggesting serotonergic modulation. Histopathological evaluation confirmed BDN neuroprotective effects preventing CUS-induced neuronal damage in the CA1 and CA3 hippocampal regions. These findings indicate that BDN exerts antidepressant effects by mitigating oxidative stress, suppressing NLRP3-mediated neuroinflammation, normalizing HPA axis hyperactivity, and modulating 5-HT receptor signaling. Thus, BDN represents a promising multitarget therapeutic candidate for stress-related depression.