Optogenetic Stimulation of Cholinergic Neurons in the Brainstem Induces Splenic Nerve Activity and Attenuates Systemic Inflammation

Abstract

The inflammatory reflex is a well‐defined neural circuit composed of afferent and efferent fibers that travel via the vagus nerve to regulate peripheral tumor necrosis factor (TNF) production. Electrical stimulation of the efferent fibers reduces splenic TNF output in an animal model of endotoxemia. However, the exact origin of these vagus nerve fibers in the brainstem and the means by which they innervate the spleen to modulate TNF levels is not yet understood. Using optogenetics, we selectively stimulated cholinergic neurons in the dorsal motor nucleus of the vagus nerve (DMV), the autonomic brainstem nucleus from which the efferent vagus nerve fibers originate. A fiber‐optic cannula was inserted using stereotactic guidance into the DMV of transgenic mice expressing channelrhodopsin under the choline acetyltransferase promoter (ChAT‐ChR2‐EYFP). Mice were subjected to either optogenetic or sham stimulation (n=20 per group) for five minutes (473nm laser, 20Hz, 25% duty cycle). After 24 hours, animals were subjected to endotoxemia by intraperitoneal administration of lipopolysaccharide (0.25mg/kg), blood was collected after 90 minutes, and serum TNF was quantitated. Optogenetic stimulation of the cholinergic neurons in the DMV of ChAT‐ChR2‐EYFP mice significantly decreased endotoxin‐induced serum TNF levels compared to sham controls (p=0.0004). Splenic nerve activity, recorded during DMV stimulation using a cuffed two‐channel electrode, was significantly increased over baseline (p=0.0002). Blocking the signals transmitted in the vagus nerve by adding bupivacaine, a sodium channel antagonist, eliminated this effect (p=0.0028), implicating a functional synapse between the vagus and splenic nerves. These studies provide the first direct evidence for the central origin of the efferent vagus nerve fibers regulating TNF production during endotoxemia and suggest novel anti‐inflammatory approaches based on targeting DMV cholinergic signaling.Support or Funding InformationThis study was funded by NIH/NIGMS/NIAID.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.