The metabolic basis of brain activation remains an unsettled question because of recent results suggesting that anaerobic glycolysis provides the additional energy required for activation The rat brain will be studied by in vivo NMR at 7.OT in order to understand the metabolic basis of brain activity. The somatosensory cortex will be activated by a forepaw stimulation protocol which has already been established. The fMRI of the activation will be measured at shorter times after the stimulation and by gradient echo and T1 weighted imaging so as to understand its mechanism. Instrumental improvements of transmitter/receiver coils, gradients and pulse sequences will be implemented so as to improve sensitivity and spatial resolution. 1H NMR spectroscopy will be used to measure localized glucose and lactate pools and their changes during forepaw stimulation. During 1-13C glucose infusion the turnover of glucose, lactate and glutamate will be measured by our well established Proton Observe Carbon Edit sequence. These measurements will be interpreted by a quantitative model to give deltaCMRO(glucose), deltaCMRO2 and changes of lactate during stimulation so as to quantify the contribution of anaerobic glycolysis to the energy. Brain extracts of metabolites and of hexokinase in the somatosensory cortex will be made comparing resting conditions with forepaw stimulation. Mitochondrial and cytosolic isoforms of the enzyme will be tested separately in order to complete our understanding of their control by glucose-6-phosphate and glucose-l,6-bisphosphate. Control of the flux by hexokinase will be calculated from these values using control theory approach. Finally 13C NMR measurements of larger volumes of brain will evaluate changes in the TCA cycle activity and the flux from glutamate to glutamine at different levels of alpha-chloralose anesthesia. The hypotheses that glutamine synthesis is regulated by glutamate release from neurons to glia as a neurotransmitter will be tested by measuring the relative rates of glutamate and glutamine labeling by a label that originates in the glia and by inhibiting glutamate release by carbetapentane. A coherent study of brain activation, glucose and oxygen consumption and flux control by hexokinase is proposed that can be accomplished in the rat and will answer questions about the energetics of rat and human cerebral metabolism.
Showing the most recent 10 out of 85 publications
