Subsecond spontaneous catecholamine release in mesenteric lymph node ex vivo

Measuring the dynamics of neurochemical‐regulated immunity, particularly in the gut, has been a growing interest over the last several years because of its important implications in gastrointestinal inflammation, neurodegeneration, and even depression. Sympathetic noradrenergic nerves innervate the gastrointestinal tract and resident immune organs, including the mesenteric lymph nodes (MLN) and Peyer's patches. Previous research has suggested that neuronal inputs in the MLN release norepinephrine (NE) at neural‐immune synapses to regulate immune function. The current immunological techniques do not have the appropriate temporal or spatial resolution to monitor this dynamic process in real‐time, within specific regions of intact lymphoid organs. Monitoring dynamic neural signaling within intact immune organs, in real‐time, would facilitate a deeper understanding of neuroimmune communication and would allow the mechanism of rapid immunomodulation to be elucidated. Here, we overcome this technological barrier by coupling real‐time neurochemical detection using fast‐scan cyclic voltammetry (FSCV) in live MLN slices from C57BL/6 mice. We have discovered rapid, spontaneous catecholamine transients in the T‐cell zone of the MLN which are on the order of a few hundred nanomolar, rapid (a few seconds), and frequent (every 20‐s). We demonstrate that the β2‐adrenergic receptor and the classic catecholamine transporters (DAT and NET) play a minor role in transient regulation in the MLN suggesting that regulation at the neural‐immune synapse is quite complicated and further mechanistic studies are needed. Overall, these findings provide direct evidence for rapid neurochemical events in the MLN which could have a major impact on our understanding of neurochemical‐regulated immunomodulation in the gut. Sympathetic nerves innervate the mesenteric lymph node in the gut to provide a direct communication pathway between the nervous system and the immune system. To date, measurements of neurochemical signaling in real‐time within intact immune tissue have not been possible. Here, we have used fast‐scan cyclic voltammetry at carbon‐fiber microelectrodes to measure rapid catecholamine transients within ex vivo slices of the mesenteric lymph node. This work provides critical information into the dynamics of neuroimmune communication and will enable the mechanisms and function of neurochemical‐regulated immunity to be probed with exquisite spatiotemporal control in the future.