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Stimulated changes in localized cerebral energy consumption under anesthesia
R G Shulman1, D L Rothman, F Hyder
1Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06510, USA.
Summary
Anesthesia lowers resting brain glucose use, causing larger activation increases. Total brain glucose metabolism, not just the change, reflects true activity during stimulation.
Area of Science:
- Neuroscience
- Metabolic Imaging
Background:
- Focal changes in cerebral metabolic rate of glucose utilization (CMRglc) during sensory activation are smaller in awake animals (10-50%) compared to anesthetized animals (50-250%).
- Resting CMRglc is lower under anesthesia, but activation-induced CMRglc levels are similar between anesthetized and non-anesthetized states.
Purpose of the Study:
- To investigate the impact of anesthesia on cerebral glucose metabolism during sensory activation.
- To clarify the relationship between glucose oxidation, neurotransmitter cycling, and brain energy consumption.
Main Methods:
- Utilized 13C Nuclear Magnetic Resonance (NMR) spectroscopy to measure CMRglc.
- Quantified the flux of the glutamate/gamma-aminobutyric acid/glutamine neurotransmitter cycle (Vcycle) and its relation to oxidative CMRglc.
Main Results:
- Anesthesia reduces resting CMRglc, leading to larger apparent increments during activation.
- Approximately 80% of brain energy consumption, both resting and during stimulation, is attributed to Vcycle.
- Incremental changes in CMRglc (DeltaCMRglc) can localize neurotransmitter activity, but total CMRglc reflects the magnitude of activity.
Conclusions:
- The observed differences in activation-induced CMRglc are explained by reduced resting metabolism under anesthesia.
- Total localized CMRglc, rather than the incremental change, accurately represents the magnitude of brain activity during functional responses.