Analysis of glucose and lactate in hippocampal dialysates of rats during the operant conditioned reflex using microdialysis.

Changes of extracellular glucose and lactate in hippocampus for freely moving rats during the operant conditioned reflex were examined simultaneously. Samples of the dialysate were assayed for both glucose and lactate using in vivo microdialysis and a microbore flow injection analysis-immobilized enzyme reactor-electrochemical detection (FIA-IMER-ECD) system. Microdialysis samplings were conducted in a Skinner box where lights were delivered as conditioned stimuli (CS) paired with foot shocks as unconditioned stimuli (US). In the treatment group the concentration of glucose and lactate showed no fluctuations during the whole process. However, in the control group in which the rats were exposed to many foot shocks, lactate levels decreased by 19% below baseline during the behavioral session and glucose showed a delayed decrease (by 18%). Compared with glucose, lactate can immediately indicate the dynamic changes in brain.