Effects of nicotine on regional cerebral glucose metabolism in awake resting tobacco smokers

Abstract

Eleven healthy tobacco smoking adult male volunteers of mixed race were tobacco abstinent overnight for this study. In each subject, positron emission tomographic images of regional cerebral metabolism of glucose with [ 18F]fluorodeoxyglucose were obtained in two conditions in the morning on different days: about 3 min after approximately 1–2 mg of nasal nicotine spray and after an equivalent volume of an active placebo spray of oleoresin of pepper in a random counterbalanced design. A Siemens/CTI 931/08-12 scanner with the capability of 15 horizontal brain slices was used. The images were further converted into a standard uniform brain format in which the mean data of all 11 subjects were obtained. Images were analysed in stereotactic coordinates using pixel-wise t statistics and a smoothed Gaussian model. Peak plasma nicotine levels varied three-fold and the areas under the curve 0–30 min varied seven-fold among the individual subjects. Nicotine caused a small overall reduction in global cerebral metabolism of glucose but, when the data were normalized, several brain regions showed relative increases in activity. Cerebral structures specifically activated by nicotine (nicotine minus pepper, Z score >4.0) included: left inferior frontal gyrus, left posterior cingulate gyrus and right thalamus. The visual cortex, including the right and left cuneus and left lateral occipito-temporal gyrus fusiformis, also showed an increase in regional cerebral metabolism of glucose with Z scores >3.6. Structures with a decrease in regional cerebral metabolism of glucose (pepper minus nicotine) were the left insula and right inferior occipital gyrus, with Z scores >3.5. Especially important is the fact that the thalamus is activated by nicotine. This is consistent with the high density of nicotinic cholinoceptors in that brain region. However, not all brain regions affected by nicotine are known to have many nicotinic cholinoceptors. The results are discussed in relation to the cognitive effects of nicotine.