Lactate and glutamate dynamics during prolonged stimulation of the rat barrel cortex suggest adaptation of cerebral glucose and oxygen metabolism

A better understanding of BOLD responses stems from a better characterization of the brain's ability to metabolize glucose and oxygen. Non-invasive techniques such as functional magnetic resonance spectroscopy (fMRS) have thus been developed allowing for the reproducible assessment of metabolic changes during barrel cortex (S1BF) activations in rats. The present study aimed at further exploring the role of neurotransmitters on local and temporal changes in vascular and metabolic function in S1BF. fMRS and fMRI data were acquired sequentially in α-chloralose anesthetized rats during 32-min rest and trigeminal nerve stimulation periods. During stimulation, concentrations of lactate (Lac) and glutamate (Glu) increased in S1BF by 0.23 ± 0.05 and 0.34 ± 0.05 μmol/g respectively in S1BF. Dynamic analysis of metabolite concentrations allowed estimating changes in cerebral metabolic rates of glucose (ΔCMRGlc) and oxygen (ΔCMRO2). Findings confirmed a prevalence of oxidative metabolism during prolonged S1BF activation. Habituation led to a significant BOLD magnitude decline as a function of time while both total ΔCMRGlc and ΔCMRO2 remained constant revealing adaptation of glucose and oxygen metabolisms to support ongoing trigeminal nerve stimulation.