Oligopeptides and Polypeptides Impact Norepinephrine Detection in Lymphoid Tissue

Detection of neurochemicals voltammetrically can be challenging in complex matrices like tissue. Norepinephrine (NE) is a neurotransmitter in the brain and is directly released by the sympathetic nervous system in the periphery. Fast-scan cyclic voltammetry (FSCV) is an electrochemical technique previously used to detect NE from sympathetic neurons in lymphoid tissues. Mesenteric lymph nodes present a unique challenge to FSCV due to their complex tissue matrix, which includes immune cells and neurons. These cells release various neuropeptides, cytokines, and other chemical signaling molecules, which can interfere with FSCV. Notably, Neuropeptide Y (NPY) from sympathetic neurons, and Substance P (SubP) and Calcitonin Gene-Related Peptide (CGRP) from sensory neurons are common peptides that are released locally near NE sites. These peptides are regulated by and interact with NE through complex neuronal circuits, potentially impacting FSCV NE detection. We demonstrate that increasing levels of each peptide alter voltammetric NE detection. We observed that the NE oxidation potential shifts with each peptide in vitro, and NE cyclic voltammograms exhibit unique peak broadening specific to NPY compared to SubP and CGRP, indicating that each peptide affects the carbon fiber microelectrode (CFME) differently. Overall, we show significant convolution of voltammetric NE peaks in the presence of peptides, providing evidence that future developments in materials to reduce protein fouling could significantly improve the robustness and accuracy of NE FSCV detection.