Neuro-immune regulation of sepsis-associated delirium via the PBN-CeA-spleen axis.

BACKGROUND: Sepsis associated delirium (SAD) is the most prevalent manifestation of acute brain dysfunction in sepsis, yet its central regulatory mechanisms remain incompletely understood. As researchers have progressively explored the brain-spleen axis and neuroimmunity, this study aimed to investigate the role of the parabrachial nucleus (PBN)-central amygdala (CeA)-spleen axis in the pathogenesis of SAD. METHODS: In a mouse model of SAD induced by intraperitoneal injection of lipopolysaccharide (LPS, 10 mg/kg), we identified activation patterns in both the PBN and CeA using immunofluorescence analysis. We subsequently investigated direct anatomical connections between these regions through bidirectional neural tracing, followed by functional interrogation using fiber photometry and electrophysiological recordings. Finally, we evaluated the effect of targeted inhibition of the PBN-CeA pathway on delirium in septic mice through behavioral assays. Additionally, enzyme-linked immunosorbent assay (ELISA) and flow cytometry were employed for immunological profiling. RESULTS: We observed a significant increase in c-Fos expression in both the PBN and CeA, and confirmed a direct anatomical connection between these regions. Fiber photometry and electrophysiological recordings revealed that LPS stimulation activated CeA neurons and splenic sympathetic nerves. In addition, targeted inhibition of the PBN-CeA pathway mitigated CeA calcium dynamics and reduced spontaneous splanchnic nerve discharge. Behavioral assays showed that splenic denervation and inhibition of the PBN-CeA pathway attenuated delirium-like behaviors in septic mice. ELISA and flow cytometry demonstrated that these interventions reversed splenic proinflammatory cytokines (tumor necrosis factor-alpha [TNF-α], interleukin [IL]-1β, IL-6, and IL-10, interferon-gamma [IFN-γ]) and norepinephrine (NE) while restoring immune cell composition and enhancing natural killer (NK) cell function. CONCLUSION: The PBN-CeA-splenic axis plays a critical neuroimmune conduit linking central neural circuits to peripheral immune modulation, offering new mechanistic insight into the neural regulation of systemic inflammation and the pathogenesis of SAD.