Mapping brain glutamate in humans: sex differences in cigarette smokers

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PROJECT SUMMARY/ABSTRACT Smoking is the leading cause of preventable death and disease in the U.S. Women are disproportionately affected by smoking, as they not only have a higher risk of experiencing some health consequences of smoking, such as heart disease, but also suffer sex-specific health issues, including cervical cancer. Women have more difficulty maintaining long-term abstinence from smoking than men, possibly because they experience stronger withdrawal symptoms and greater relief of these symptoms after resumption of smoking. Despite their enhanced need for smoking-cessation therapies, current first-line treatments, such as nicotine replacement, are less effective for women than men. The underlying differences in brain function that drive these sex differences remain unknown, and understanding them can guide development of personalized smoking cessation therapies. Glutamatergic neurotransmission is a promising new target for smoking cessation therapy, but sex differences in glutamate levels across the brain, which can impact the efficacy of glutamatergic treatments, have not been investigated in smokers. Our preliminary data using single-voxel magnetic resonance spectroscopy (MRS), have revealed important sex differences in the relationships of glutamate in the dorsal anterior cingulate cortex (dACC), a region highly implicated in Tobacco Use Disorder, with sex (males vs. females) and smoking state (overnight abstinent vs. post-smoking) in smokers. Moreover, glutamate in the dACC is also associated with circulating estrogen, and possibly progesterone, in women who smoke. However, important relationships between glutamate in other brain regions and these factors are yet to be explored. Echo-planar spectroscopic imaging (EPSI), a state-of-the-art technique, permits measurement of glutamate in ~80 percent of the whole brain in vivo in humans. Given our preliminary results using single-voxel MRS, we now propose to test replicability of our finding in the dACC and to examine potential extension to other brain regions heavily implicated in the behavioral states of Tobacco Use Disorder - the anterior insula and thalamus. We will also perform exploratory analyses of relationships of glutamate across the brain with sex, smoking state, and ovarian hormones. Otherwise healthy, adult daily smokers (30 men and 30 women) will serve as participants for this study. They will be tested twice, after overnight (~12 h) abstinence from smoking and after smoking their first cigarette of the day. We will combine EPSI with analysis of circulating ovarian hormones in serum to address two specific aims: Aim 1. Determine relationships between brain glutamate, sex, and circulating ovarian hormones. Aim 2. Determine sex differences in acute effects of smoking on brain glutamate. The findings from this study will provide important empirical information regarding glutamate levels across the brain in smokers and help guide development of personalized, sex-specific smoking cessation therapies.