Electrical Stimulation of the Dorsal Motor Nucleus of the Vagus Attenuates Serum Pro‐Inflammatory Cytokine Levels in Murine Models of Endotoxemia and Sepsis

Abstract

The inflammatory reflex is a vagus nerve‐mediated and brainstem‐integrated physiological mechanism that regulates immunity and inflammation (Annu Rev Immunol, 2018, 36:783). The efferent vagus nerve originates in brainstem nuclei, including the dorsal motor nucleus of the vagus (DMN). Recently, it was shown that optogenetic stimulation of cholinergic DMN neurons inhibits serum TNF levels during endotoxemia (Proc Natl Acad Sci USA, 2020, 117(47):29803). However, the effects of electrical DMN stimulation on cytokine levels in inflammatory conditions have not been previously evaluated. To provide insight, we examined the effect of electrical DMN stimulation in mice with endotoxemia and cecal ligation and puncture (CLP)‐induced polymicrobial sepsis. In the endotoxemia model, 10–12‐week‐old male C57BL/6 mice (n=14‐20 per group) were anesthetized using isoflurane and the head was positioned on a stereotaxic frame. A surgical intervention and a stereotaxic‐guided approach were used to insert a concentric bipolar electrode into the left DMN. Electrical stimulation (50 μA, 30 Hz, 260 μs) or sham stimulation was performed for five mins, followed by lipopolysaccharide (LPS, 0.5 mg/kg) i.p. administration. The mice were euthanized 90 mins after LPS and blood (via cardiac puncture) was collected and processed for cytokine analysis. In the CLP model, DMN stimulation or sham stimulation was performed as described above immediately after subjecting mice (n=14‐20 per group) to CLP, i.e., following a midline laparotomy in anesthetised mice, the cecum was isolated and the distal end was ligated and punctured. 24h later, the mice were euthanised and blood was collected and processed for analysis. In mice with endotoxemia, electrical DMN stimulation significantly decreased serum TNF (p = 0.0069) and IL‐6 (p = 0.0427) levels compared with sham stimulation. In addition, electrical DMN stimulation increased the serum levels of the anti‐inflammatory cytokine IL‐10 (p = 0.0284). In mice with CLP, electrical DMN stimulation resulted in significantly lower serum TNF levels compared with sham stimulation (p = 0.0291). These results indicate for the first time that electrical DMN stimulation alters circulating pro‐inflammatory and anti‐inflammatory levels in murine endotoxemia and sepsis. These findings are of interest for further development of bioelectronic approaches targeting DMN for therapeutic benefit in conditions, characterised by immune dysregulation and inflammation.

Dorsal Motor Vagal Neurons Can Elicit Bradycardia and Reduce Anxiety-Like Behavior

“…Despite these anatomical studies, functional studies remain conflicting. Some argue that direct electrical stimulation of DMV does not change chronotropy (Geis and Wurster, 1980; Laughton and Powley, 1987), while others demonstrate local activation (chemical, electrical, optogenetic, or chemogenetic) elicits bradycardias even if only modestly (Falvey et al, 2023; Machhada et al, 2020; Machhada et al, 2016; Sporton et al, 1991; Thompson et al, 2023). However, no activation technique in awake animals used to date rules out incidental stimulation of either neighboring nucleus tractus solitarius (NTS) neurons or inhibitory interneurons within DMV.…”