Melatonin is classically identified as a neurohormone secreted from the pineal gland to regulate circadian rhythm. In addition to its important role in the brain, evidence suggests that melatonin is released in the immune system to help regulate inflammation. In particular, regulation of immune responses in the gastrointestinal tract has received attention as a possible therapy for inflammatory bowel disease. Mesenteric lymph nodes are located in the walls of the intestines and are important for protection against pathogens; however, direct measurements of melatonin in this organ with selective electrochemical techniques have not been explored. Fast-scan cyclic voltammetry (FSCV) at carbon-fiber microelectrodes is an electrochemical technique which allows selective detection of analytes with subsecond temporal resolution. Here, we have developed a modified waveform using FSCV for selective detection of melatonin amongst common biological interferences. Melatonin’s oxidation products can diimerize and form a film on the electrode surface which leads to fouling; however, we have eliminated these byproducts by maintaining a positive holding potential and scanning at a rate of 600 V/s. The limit of detection for melatonin at our modified waveform is 40 nM, which is within physiological range. We demonstrate the validity of this method by detecting melatonin in 300-µm thick slices of live lymph node tissue, which have been immunostained to reveal structural organization of lymphocytes. Coupling real-time electrochemical recording with fluorescence microscopy provides quantitative detection within specific cell regions of the lymph node. Overall, we have developed the first method for detecting melatonin secretion with FSCV in live lymph node tissue.  Co-detection of melatonin and serotonin is possible with FSCV, which will allow mechanisms of co-regulation to be studied in the future.<br/>

Detection of melatonin dynamics in the immune system using fast-scan cyclic voltammetry

256th National Meeting (2018)

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