Oxidative stress in brain tissue was measured experimentally in situ u
sing microdialysis to sample the extracellular environment for a lipid
peroxidation breakdown product and antioxidants. The extracellular co
ncentrations of the lipid peroxidation product malonaldehyde (MDA) and
the antioxidants ascorbic acid (AA) and uric acid (UA) were measured
in rat cortex and striatum in vivo using microdialysis coupled to HPLC
with UV detection. Tissue acidosis following ischaemia and epileptic
seizures may contribute to neuronal damage, which may be mediated by r
eactive oxygen species. Perfusion of microdialysis probes with acidic
artificial cerebrospinal fluid (pH 6) led to a significant increase in
the sampled concentration of MDA and the antioxidant ascorbic acid. S
imultaneous perfusion of ascorbate (5 mM) with acidic ACSF (pH 6) comp
letely attenuated the rise in lipid peroxidation. This study provides
in vivo evidence for acidosis induced oxidative stress in brain tissue
and an antioxidant action of ascorbate. The methodology described her
e can provide direct in vivo information in respect of oxidative stres
s in experimental situations. The method could equally be applied to t
he assessment of oxidative stress in a number of pathological models n
ot necessarily confined to the CNS.