Spleen voltammetry assesses in real time norepinephrine release elicited by autonomic stimulation

BackgroundThe noradrenergic innervation of the spleen is implicated in the autonomic control of inflammation and has been the target of neurostimulation therapies for inflammatory diseases. However, there is no real-time marker of its successful activation, which hinders the optimization of anti- inflammatory neurostimulation therapies and mechanistic studies in anti-inflammatory neural circuits. MethodsIn mice, we performed fast-scan cyclic voltammetry (FSCV) in the spleen during intravascular injections of norepinephrine (NE), or during stimulation of the vagus, splanchnic, or splenic nerves. We defined the stimulus-elicited charge generated at the oxidation potential for NE ([~]0.8 V) as the "NE voltammetry signal" and quantified the dependence of the signal on NE or nerve stimulation dose. We correlated the NE voltammetry signal in response to splenic nerve stimulation (SpNS) with the latters anti-inflammatory effect in a model of lipopolysaccharide- (LPS) induced endotoxemia, quantified as suppression of TNF release. ResultsWe found that the NE voltammetry signal is proportional to injected amount and estimated peak NE concentration, with 0.3 M detection threshold. In response to SpNS, the signal increases within seconds, returns to baseline minutes later and is blocked by interventions that deplete NE or inhibit NE release. The signal is elicited by efferent, but not afferent, electrical or optogenetic vagus nerve stimulation, and by splanchnic nerve stimulation. The magnitude of the signal during SpNS is inversely correlated with subsequent TNF suppression in endotoxemia and explains 40% of the variance in TNF measurements. ConclusionFSCV in the spleen provides a marker for real-time monitoring of anti-inflammatory activation of the splenic innervation during autonomic stimulation.