Neuronal TLR4 overexpression in the medial prefrontal cortex is associated with neuroinflammation and depression-like behaviors in ovariectomized rats

Growing evidence implicates Toll-like receptor 4 (TLR4) expression in neuroinflammatory processes linked to depression pathogenesis, yet its role in perimenopausal depression remains unexplored. This study investigated concurrent changes in TLR4-related inflammatory mechanisms underlying depression-like behaviors following ovariectomy (OVX), focusing on the medial prefrontal cortex (mPFC). Sucrose preference and forced swim tests were used to assess anhedonia and behavioral despair, respectively. Quantitative analysis of TLR4/MyD88/NF-κB/p65 pathway components, pro-inflammatory cytokines (TNF-α, IL-6, IL-1β), and apoptosis marker caspase-3 in the mPFC was conducted via Western blotting, whereas dual immunofluorescence staining mapped TLR4 distribution in neurons and microglia. OVX induced depression-like behaviors, along with upregulation of the TLR4-MyD88-NF-κB signalling axis, increased pro-inflammatory cytokines levels, and higher caspase-3 expression in the mPFC. Dual immunofluorescence colocalisation analysis revealed TLR4 expression in both neurons and microglia, with selective neuronal enrichment post-OVX. Notably, the neuronal TLR4 expression profiles showed parallel alterations in apoptosis markers and cytokines. Intraperitoneal administration of ibudilast, a TLR4 inhibitor, significantly ameliorated depression-like behaviors, attenuated upregulation of the TLR4 pathway, and reduced neuroinflammatory markers in OVX rats. These results demonstrate that OVX induces neuronal TLR4 overexpression, which results in concurrent neuroinflammatory and apoptotic processes underlying depressive phenotypes. These findings support the therapeutic potential of TLR4 inhibitors for perimenopausal depression, particularly by targeting neuron-specific inflammatory cascades.