Basic NeuroscienceSimultaneous recording of hippocampal oxygen and glucose in real time using constant potential amperometry in the freely-moving rat

Amperometric sensors for oxygen and glucose allow for real time recording from the brain in freely-moving animals. These sensors have been used to detect activity- and drug-induced changes in metabolism in a number of brain regions but little attention has been given over to the hippocampus despite its importance in cognition and disease. Sensors for oxygen and glucose were co-implanted into the hippocampus and allowed to record for several days. Baseline recordings show that basal concentrations of hippocampal oxygen and glucose are 100.26 ± 5.76 μM and 0.60 ± 0.06 mM respectively. Furthermore, stress-induced changes in neural activity have been shown to significantly alter concentrations of both analytes in the hippocampus. Administration of O2 gas to the animals' snouts results in significant increases in hippocampal oxygen and glucose and administration of N2 gas results in a significant decrease in hippocampal oxygen. Chloral hydrate-induced anaesthesia causes a significant increase in hippocampal oxygen whereas treatment with the carbonic anhydrase inhibitor acetazolamide significantly increases hippocampal oxygen and glucose. These findings provide real time electrochemical data for the hippocampus which has been previously impossible with traditional methods such as microdialysis or ex vivo analysis. As such, these sensors provide a window into hippocampal function which can be used in conjunction with behavioural and pharmacological interventions to further elucidate the functions and mechanisms of action of the hippocampus in normal and disease states.

► We show that average concentrations of hippocampal oxygen and glucose are 100.26 ± 5.76 μM and 0.60 ± 0.06 mM respectively. ► We show that there are uncoupled changes in oxygen and glucose during neuronal activation. ► Anaesthesia and carbonic anhydrase inhibition both significantly increase hippocampal oxygen. ► Anaesthesia, dimethyl sulfoxide administration and carbonic anhydrase inhibition significantly increase hippocampal glucose. ► We show that changes in hippocampal metabolism can be detected in real time using constant potential amperometry.