Increased oxygen consumption in the somatosensory cortex of α-chloralose anesthetized rats during forepaw stimulation determined using MRS at 11.7 Tesla

The significance of changes in cerebral oxygen consumption in focally activated brain tissue is still controversial. Since the rate of cerebral oxygen consumption is tightly coupled to that of tricarboxylic acid cycle which can be measured from the turnover kinetics of [4-13C]glutamate using in vivo 1H{13C} magnetic resonance spectroscopy, changes in tricarboxylic acid cycle flux rate were assessed in primary somatosensory cortex of α-chloralose anesthetized rats during electrical forepaw stimulation. With markedly improved 1H{13C} magnetic resonance spectroscopy technique and the use of high magnetic field strength of 11.7 T accessible to the current study, [4-13C]glutamate at 2.35 ppm was spectrally resolved from overlapping resonances of [4-13C]glutamine at 2.46 ppm and [2-13C]GABA at 2.28 ppm as well as the more distal [3-13C]glutamate and [3-13C]glutamine. The results showed a significantly increased VTCA in focally activated primary somatosensory cortex during forepaw stimulation, corresponding to approximately 51 ± 27% (n = 6, mean ± SD) increase in cerebral oxygen consumption rate. Considering the high efficiency in producing adenosine triphosphate by oxidative metabolism of glucose, the results demonstrate that aerobic oxidative metabolism provides the majority of energy required for cerebral focal activation in α-chloralose anesthetized rats subjected to forepaw stimulation.