397. NEURAL MECHANISMS OF BRAIN-LYMPH NODES AXIS IN STRESS-INDUCED ANXIETY DISORDERS

Abstract Background Stress-linked psychiatric disorders, including anxiety disorder, are associated with systemic inflammation, and this peripheral inflammation contributes to the development of psychiatric symptoms. We have previously revealed the function of the "brain-lymph" axis in anxiety and found that regulating the activity of glutamatergic neurons in the red nucleus (RN) can affect anxiety-like behavior and the immune response of cervical lymph nodes (CLN). However, the neural mechanisms underlying how the brain and CLN interact to mediate anxious behaviors have not been clearly understood. Aims & Objectives Delineating the neurobiological mechanisms underlying "brain-lymph" axis regulation of stress-Induced anxiety: analysis of behavioral outcomes mediated by brain-cervical lymph node Communication. Method Restraint stress was used in this study. In vivo fiber photometry recordings combined with ex vivo patch-clamp electrophysiology were used to detect the function of neurons in RN. The functional relevance of this neural circuit was validated using complementary chemogenetic and optogenetic approaches to examine its role in stress-induced anxiety-like behavioral phenotypes and cervical lymph node inflammation. Molecular profiling of cervical lymph nodes was conducted following superior cervical ganglionectomy, combined with viral-mediated manipulations and pharmacological interventions to elucidate underlying mechanisms. Results In vivo fiber photometry recordings combined with ex vivo patch-clamp electrophysiology demonstrated stress-induced suppression of neuronal activity in the red nucleus. To delineate the neural circuits governing red nucleus (RN) function, we employed retrograde tracing using cholera toxin subunit B (CTB). Analysis of brain sections 3-7 days post-injection revealed afferent projections from multiple regions, including the primary motor cortex (M1) and central amygdala. Chemogenetic modulation of the M1-RN circuit demonstrated significant effects on anxiety-like behavioral phenotypes in rodents. Neurochemical analysis revealed significant elevation of norepinephrine content in cervical lymph nodes, suggesting sympathetic nervous system involvement. Superior cervical ganglionectomy experiments confirmed that sympathetic denervation significantly attenuated anxiety-like behaviors. Additionally, stress exposure induced upregulation of β2-adrenergic receptor (ADRB2) expression in cervical lymph nodes, suggesting that stress-induced noradrenergic activation may enhance lymph node inflammatory responses via ADRB2 signaling. Pharmacological intervention using ADRB2 antagonists resulted in reduced lymph node inflammation and ameliorated anxiety-like behaviors, supporting the functional significance of this pathway. To confirm the RN effect in stress-induced anxiety, we further analyzed the fMRI of stressed individuals. Compared with controls, stressed individuals exhibited significantly decreased FC in bilateral RN. Specifically, we found the decreased FC between left RN and left Mid Temporal Gyrus, left Mid Frontal Gyrus. We also found the decreased FC between right RN and left Mid Temporal Gyrus, right Mid Temporal Gyrus. These results confirmed that stress-induced red nucleus dysfunctions contributed to anxiety. Discussion & Conclusions We identified the M1-RN neural circuit as a critical mediator of stress-induced anxiety-like behaviors and cervical lymph node inflammatory responses. Mechanistic investigations revealed that stress-induced sympathetic activation promotes inflammatory cascades through noradrenergic signaling via β2-adrenergic receptors specifically expressed on CD8+ T lymphocytes within cervical lymph nodes. Importantly, sympathetic denervation significantly enhanced stress resilience, suggesting therapeutic potential through neuroimmune modulation. This study will provide novel targets for anxiety intervention.