Real-time monitoring of brain energy metabolism in vivo using microelectrochemical sensors: the effects of anesthesia

Rats were implanted in the striatum with a Pt/Ir electrode for measurement of regional cerebral blood flow (rCBF) (H-2 clearance technique), a carbon paste electrode for monitoring tissue oxygen and a glucose biosensor for mo nitoring extracellular glucose. Changes in all three parameters were record ed in response to the intraperitoneal (i.p.) administration of the anesthet ics chloral hydrate (350 mg/kg), sodium pentobarbitone (60 mg/kg) and ketam ine (200 mg/kg). An i.p. injection of normal saline, given as a control for the injection of the anesthetics, produced a parallel increase in rCBF and tissue oxygen accompanied by a brief decrease in extracellular glucose. Ch anges in tissue oxygen reflected the changes in rCBF; there was a decrease in both after sodium pentobarbitone, a decrease followed by a rebound after ketamine and a transient increase after chloral hydrate, All three anesthe tics produced a decrease in extracellular glucose. The disparity between th e changes in glucose and the changes in rCBF and oxygen suggests that durin g anesthesia, the reduction in extracellular glucose is not due to a reduct ion in the direct delivery of glucose from the blood vascular system. These results also indicate that levels of enzymatic substrates and mediators, w hich are intrinsic to the design and operation of amperometric biosensors, are clearly altered in a complex manner by anesthesia and suggest that caut ion should be exercised in extrapolating data from acute anesthetized exper iments to normal physiology. (C) 2001 Elsevier Science B.V. All rights rese rved.