Electrochemistry of neuropeptides: a possible method for assay and in vivo detection

The electrochemical activity of catechol and indoleamines has been utilized to develop sensitive assays for amine neuro-transmitters and metabolites. We present evidence that several neuropeptides are electrochemically active and that this property may be used to develop peptide assays similar in sensitivity to those available for the amines. The electrochemical activity of twenty synthetic neuropeptides and their constituent amino acids were tested in buffered solutions using differential pulse voltammetry (DPV) and micro-carbon paste working electrodes. The studies show that peptides which are electroactive include Met-and Leu-enkephalin, the cholecystokinins (CCK-8, CCK-4), caerulein, neurotensin, gonadotrophin releasing hormone (LH-RH), α-melanocyte stimulating hormone (αMSH), somatostatin and vasopressin. The electrochemical oxidation potentials of these peptides are distinct and separable from those of the amines and are apparently associated with the presence and combination of specific amino acids (tyrosine, tryptophan and cysteine) in the peptide sequence. DPV $\text{in vitro}$ was used to demonstrate the presence of 5-hydroxytryptamine and caerulein in extracts of amphibian skin. With electrodes implanted in the rat striatum DPV $\text{in vivo}$ exhibited oxidation potentials which may relate to neuropeptide oxidation.