Increased Cerebral Uptake of [18F]Fluoro-Deoxyglucose but not [1-14C]Glucose Early following Traumatic Brain Injury in Rats

• Following experimental and clinical traumatic brain injury (TBI), the local cerebral metabolic rate of glucose (lCMRGlc) is commonly estimated using the 2-[18F]fluoro-2-deoxy-D-glucose (FDG) method. The adequate estimation of lCMRGlc using FDG requires a correction factor, the lumped constant (LC), to convert FDG net uptake into lCMRGlc. The LC, and thus lCMRGlc calculations, requires a "steady state" that may be disrupted following TBI. In the present report, we hypothesized that [1-14C]glucose uptake would accurately reflect glucose dynamics early post-injury and was compared to the regional uptake of FDG in 44 rats subjected to moderate (2.4-2.6 atm) lateral fluid percussion brain injury (FPI) or sham injury. Cortical energy state and adenylate (ATP, ADP, AMP) levels were also measured. Early (7-42 min) after FPI, FDG uptake was increased in the ipsilateral cortex and hippocampus (p<0.05). In contrast, no change in [1-14C]glucose uptake (7 and 17 min) or cortical adenylate content (42 min post-injury) was observed. At 12 hours following FPI, the ipsilateral FDG and [1-14C]glucose uptake was decreased in the cortex and hippocampus and the ipsilateral cortical ATP concentration was decreased in comparison to sham-injured controls (p<0.05). Under the present experimental conditions, the rate of cerebral uptake of FDG and of [1-14C]glucose differs, and indicate that following TBI, regional changes in the LC may occur in the immediate, but not in the late, post-injury phase. These results should be considered when interpreting results obtained using FDG for the estimation of lCMRGlc early following experimental TBI.

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