Anomalously high concentrations of brain extracellular uric acid detected with chronically implanted probes: implications for in vivo sampling techniques.
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.(ABSTRACT TRUNCATED AT 250 WORDS)
O'Neill
R D
RD
Department of Chemistry, University College, Dublin, Ireland.
Gonzalez-Mora
J L
JL
Boutelle
M G
MG
Ormonde
D E
DE
Lowry
J P
JP
Duff
A
A
Fumero
B
B
Fillenz
M
M
Mas
M
M
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002244:Carbon; D003956:Dialysis; D004563:Electrochemistry / Q000379:methods*; D004567:Electrodes, Implanted; D005110:Extracellular Space / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors; D014527:Uric Acid / Q000378:metabolism*
D014527:Uric Acid; D002244:Carbon