MicroPET detection of enhanced 18F-FDG utilization by PKA inhibitor in awake rat brain

To obtain PET imaging of glucose metabolism in the brains of conscious rats, a method of rat head fixation was developed. PET measurement with microPET was performed for 60 min after 18F-FDG injection. Significant enhancement of glucose utilization in the right striatum was observed with infusion of Rp-adenosine-3,5-cyclic phosphorothioate triethylamine (Rp-cAMPS). FDG uptake increments were also seen in the ipsilateral frontal cortex and thalamus. As initial FDG uptake in the brain was not significantly altered by Rp-cAMPS, increased glucose metabolism might be due to an increase in the phosphorylation rate by hexokinase rather than the delivery process from plasma to the brain. In contrast to awake rats, the effect of Rp-cAMPS was abolished by anesthesia using chloral hydrate, indicating that neuronal activity has an important role in short term regulation of hexokinase activity through the cAMP/PKA system in the brain. These results strongly demonstrated the value of measuring glucose utilization in the brains of conscious rats.