Differential pulse voltammetry in vivo with working carbon fiber electrodes: 5-hydroxyindole compounds or uric acid detection?

Differential pulse voltammetry was performed in rats chronically implanted with carbon fiber electrodes in the caudate (n.Cd) and raphe dorsalis (n.RD) nuclei. The electrochemical signal obtained at the +300 mV potential (peak 3) in animals implanted for more than one week (long term chronic conditions, greater than 7 days) could be dependent upon the extracellular fraction of 5-hydroxyindolacetic acid (5-HIAA) since a single injection of Pargyline is sufficient to suppress it in n.Cd and n.RD. This result was obtained despite the tendency of Pargyline to increase n.Cd and n.RD endogenous concentrations of Uric Acid (UA) measured by High Performance Liquid Chromatography (HPLC). In contrast, in animals implanted for less than one week (short term chronic conditions, less than 7 days) peak 3 recorded in the same structure could be dependent upon extracellular fractions of 5-HIAA and UA since consecutive injections of Pargyline and Allopurinol are necessary to suppress this signal. The source of extracellular UA measured in brain by voltammetry, in such short term chronic conditions, might result from surgical trauma.