On the significance of brain extracellular uric acid detected with in-vivo monitoring techniques: a review.

The concentration of uric acid [UA] in the extracellular fluid (ECF) estimated with in-vivo voltammetry and microdialysis data is compared for probes of different diameters from the day of implantation (acute) to several days (chronic) or even months after surgery. For small probes (diameter < 160 microns) the acute [UA] of ca. 5 microM decreased significantly to ca. 1 microM under chronic conditions. For larger probes (e.g., 320-microns diameter) the acute [UA] was also ca. 5 microM, but this value significantly increased to ca. 50 microM under chronic conditions. Associated with this difference in [UA], there were parallel differences in the extent of gliosis around the probes. These findings are discussed in terms of possible sources of extracellular UA and their implications for in-vivo monitoring techniques in behaving animals.