Anomalously high concentrations of brain extracellular uric acid detected with chronically implanted probes: implications for in vivo sampling techniques

• Published in: Journal of neurochemistry Vol. 57; no. 1; p. 22
• Main Authors: O'Neill, R D, Gonzalez-Mora, J L, Boutelle, M G, Ormonde, D E, Lowry, J P, Duff, A, Fumero, B, Fillenz, M, Mas, M
• Format: Journal Article
• Language: English
• Published: England 01.07.1991
• Subjects: Animals; Brain - metabolism; Carbon; Dialysis; Electrochemistry - methods; Electrodes, Implanted; Extracellular Space - metabolism; Male; Osmolar Concentration; Rats; Rats, Inbred Strains; Time Factors; Uric Acid - metabolism
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1111/j.1471-4159.1991.tb02094.x

The height of peak 2, h2, recorded using linear sweep voltammetry with 350-micron-diameter carbon paste electrodes in rat striatum was measured from the day of implantation (day 0) to 4 months after surgery. The value of h2 was at a minimum on day 0 (0.6 +/- 0.2 nA; n = 20), rose sharply to a maximum on day 2 (6.3 +/- 0.9 nA; n = 12), and decreased to a stable level by day 7 (3.3 +/- 0.7 nA; n = 16), which lasted for 4 months (3.2 +/- 0.6 nA; n = 9). These changes were shown by microinfusion of uricase to be due to variations in the concentrations of extracellular uric acid, although h2 appears to have a small baseline contribution of approximately 0.3 nA from 5-hydroxyindoleacetic acid. The stable value of h2 recorded under chronic conditions was estimated to correspond to a minimal uric acid concentration of 50 mumol/L, which represents a 10-fold increase in the extracellular level of this purine metabolite compared with the initial (acute) value. Very similar results were obtained using a microdialysis technique that detected uric acid directly. These estimates of striatal uric acid concentration are in marked contrast to those obtained using 40-micron diameter carbon fiber electrodes, which showed a decrease from the acute preparation to less than 1 mumol/L under chronic conditions. Large values of h2 were also recorded with chronically implanted paste electrodes in the hippocampus and frontal cortex.