Carbonic anhydrase activity in the frontal lobe of human brain

Carbonic anhydrase (CA) plays an important role in many biological processes. Recent technological advances have demonstrated the feasibility of measuring CA activity in the occipital lobe of human subjects in vivo. In this work we report, for the first time, in vivo measurement of CA activity in the frontal lobe of human brain, where structural and function abnormalities are strongly associated with symptoms of major psychiatric disorders. Despite the much larger magnetic field distortion in the frontal lobe, the pseudo first‐order bicarbonate dehydration rate constant was determined with high precision using in vivo 13C magnetic resonance magnetization transfer spectroscopy following oral administration of [U‐13C6]glucose. Nuclear Overhauser effect pulses were used to increase the signal‐to‐noise ratio; no proton decoupling was applied. The unidirectional dehydration rate constant of bicarbonate was found to be 0.26 ± 0.07 s−1, which is not statistically different from the dehydration rate constant in the occipital lobe determined in our previous study, indicating that CA activity in the two brain regions is essentially indistinguishable. These results demonstrate the feasibility of characterizing CA activity in the frontal lobe for future psychiatric studies.