137 Light-mediated Vagus Nerve Stimulation Inhibits Pro-inflammatory Cytokine Production in Acute Endotoxemia

INTRODUCTION: Vagus nerve stimulation (VNS) is a form of neuromodulation being explored to treat chronic inflammatory conditions by activating the inflammatory reflex, an arc reducing proinflammatory cytokine release through efferent cholinergic signaling. Current VNS approaches are primarily invasive and use electricity, but alternatives may improve vagal fiber specificity and eliminate surgical risks. Red-light optogenetics, a biological tool utilizing red light-activatable channelrhodopsins (ReaChR), can selectively activate genetically-modified neurons transdermally with light. Here, we show that ReaChR activation of cholinergic vagal fibers reduces cytokine production in a model of acute inflammation. METHODS: Vagus nerve cholinergic fibers were selectively activated using ReaChR expressed on choline acetyltransferase-expressing (ChAT) fibers in transgenic ChAT-ReaChR mice. Sensory afferent vagal fibers were activated in a separate cohort of transient receptor potential vanilloid subfamily member 1 (TRPV1)-ReaChR mice. Lipopolysaccharide (LPS) was injected intraperitoneally under anesthesia to induce acute endotoxemia, as measured by elevated tumor necrosis factor-alpha (TNFa). A 635nm fiber optic was targeted onto an isolated, cervical vagus for optogenetic VNS post-LPS administration. RESULTS: Selective ReaChR activation of cholinergic fibers in the cervical vagus nerve stimulates the inflammatory reflex to inhibit splenic TNFa production to bacterial LPS (ChAT-ReaChR: 1.27 ± 1.44 pg/ug; control: 4.26 ± 0.97 pg/ug, p < 0.001), but no significant differences were observed in serum (ChAT-ReaChR: 538 ± 216 pg/ml; littermate: 447 ± 206 pg/ml, p = 0.81). In contrast to efferent activation, ReaChR stimulation of afferent subsets (TRPV1+) failed to show cytokine regulation in splenic nor in serum .Approximate 20% baseline heart rate drop was seen during both ChAT+ and TRPV1+ fiber excitation, but only cholinergic activation sustained bradycardia throughout the stimulation period. CONCLUSIONS: Red-light optogenetic activation of cholinergic vagal fibers reduces splenic inflammatory cytokine production in murine endotoxemia and holds potential as a non-invasive, light-mediated VNS approach.