This year we started studies on 4 protocols and the fifth one is on hold due to the closure of the pharmacy at the clinical center. Research on radiotracer development is on hold pending construction of the radiotracer laboratory. This year we have also analyzed data from BNL and from open access brain imaging data sets. 1. Effects of Drugs in Human Brain - Effects of alcohol on brain glucose metabolism at rest and during stimulation: Acetate serves as an energy source for the brain predominantly for astrocytes, which express monocarboxylic acid transporters necessary for acetate transport. To assess if the brain restricted metabolism of acetate for resting energy requirements or whether it also metabolized acetate during task stimulation, we measured brain glucose metabolism (PET and 18FDG) and assessed effects of acute alcohol (compared to placebo) both when given during visual stimulation (VS) versus when given with no-stimulation (NS). Participants were tested four times and we compared heavy drinkers (HD) with controls (CT). Resting whole-brain glucose metabolism (placebo) was 13% lower in HD than in CT and alcohol-induced decreases of resting metabolism were larger in HD (20%) than CT (9%) and reductions were proportional to alcohol doses consumed; consistent with enhanced reliance on acetate metabolism with heavy alcohol use. In contrast, alcohol intoxication did not reduce glucose metabolic increases secondary to VS, in either group, indicating that alcohol did not change the rate of glucose metabolism needed for stimulation-induced activation. 2. Dopamine and Addiction - Gender Effects on Dopaminergic Reactivity in Cannabis Abusers (CA): To test whether CA have impaired reactivity to DA signaling we measured brain glucose metabolism using PET and 18FFDG at baseline (placebo) and after challenge with iv methylphenidate (MP) and compared 24 active CA (50% males) with 24 controls or CT (50% males) and alcohol compared the genders. At baseline CA had lower frontal metabolism than CT, which was associated with negative emotionality. The MP challenge also revealed group differences, which showed significantly blunted responses the CA in striatum, midbrain, thalamus, and cerebellum. MP-induced metabolic increases in striatum were negatively correlated with addiction severity. There were also significant genders effects, such that attenuated metabolic responses to MP were observed in female CA but not in males. Reduced baseline frontal metabolism along with attenuated DA reactivity could contribute to addiction severity in CA and females might be more sensitive to chronic cannabis than males. Recovery of striatal DA signaling in Methampethamine Abusers (MA). To assess if the loss of dopamine transporters (DAT) in MA reflect DA neuronal damage versus DAT downregulation, we used PET and 11Ccocaine to measure DAT, and 11Craclopride to measure DA release (quantified as differences in specific binding between placebo and MP), which was used as marker of DA neuronal function. MA (n=16), tested during early detoxification, had lower DAT (20-30%) than CT (n=15); whereas DA release was minimally reduced. In CT, DAT were positively correlated with DA release, consistent with DAT serving as markers of DA terminals whereas in MA, DAT showed a negative correlation (p=0.07) (lower DAT associated with larger DA increases), consistent with low DAT reflecting downregulation and reduced DA reuptake. The 9 MA who remained abstinent nine months later showed significant increases in DAT (20%) but no changes in MP-induced DA increases. In contrast, in CT, DAT did not change when retested 9 months later but MP-induced DA increases in ventral striatum were reduced (p=0.05). The loss of DAT in MA, which was not associated with reductions in DA release; as well as the recovery of DAT after detoxification, which was not associated with increases in DA release indicates that they did not reflect DA terminal degeneration. AKT1 gene and striatal D2R and DA release: The genetics of DA signaling are not well understood. Here we investigated the effect of a VNTR polymorphism in the AKT1 gene on striatal dopamine D2 receptors (D2R) and on DA release. We studied 91 healthy controls who underwent PET imaging with 11Craclopride after a placebo to assess D2R availability; and 54 of them also underwent a 11Craclopride scan after iv MP, to assess DA release. Effects of AKT1 genotype in striatal D2R were significant for caudate (p=0.001) and putamen (p=0.002), with LL > HL > HH; but no differences in ventral striatum. AKT1 genotype affected MP-induced DA release in ventral striatum (p=0.009), with HH > HL > LL. These results give evidence of AKT1role in modulating D2R and DA release. 3. Methodological studies - Dynamic metabolic measures: Inasmuch as resting fMRI BOLD fluctuations reflect varying neuronal activity, we tested whether we could detect corresponding fluctuations in brain glucose metabolism. We obtained dynamic FDG images (75 minutes) in 28 CT tested at rest. Seed-voxel correlations, independent component analysis (ICA), and functional connectivity density (FCD) were used to map metabolic connectivity density (MCD) and to assess connectivity hubs. MCD revealed regions with high metabolic connectivity (DMN areas and DLPFC) and low metabolic connectivity (cerebellum and temporal pole), that coincided with the regional pattern of aerobic glycolysis in brain. In contrast to fMRI BOLD, ICA on metabolic fluctuations did not reveal resting functional networks. Temporal evolution of resting brain functional connectivity metrics: Unaccounted temporal dynamics of resting- functional connectivity metrics challenges their potential as clinical biomarkers. Here we assessed scan time required to reach stable values for three connectivity metrics: seed-voxel correlations (FC), spatial independent component analyses (sICA), local FCD (lFCD). The necessary scan time to attenuate the effects of the temporal dynamics by 80% was shorter for lFCD (7 min) than for FC (11 min) or sICA (10 min). The lFCD metric being the most resilient to the effects of temporal dynamics could be particularly useful for pediatric and patient populations that dont tolerate long scans. Cost and Reactivity indices to characterize associations between functional connectivity and metabolism Though its assumed that there is a strong coupling between neuronal activity and glucose metabolism some brain regions deviate from this assumption. Here we characterized regional brain associations between metabolic supply and neuronal demand on two dimensions: a reactivity axis (positive indicates high supply/high demand and negative indicates low supply/low demand) and a cost axis (positive indicates high supply/low demand and negative indicates low/high demand) using lFCD, as marker of neuronal demand, and glucose metabolism as a marker of supply in 24 CT scanned with fMRI and PET-18FDG. The cost-reactivity contrast showed heterogeneity between brain regions and in a separate sample distinguished between controls and alcoholics indicating that cost and reactivity indices provide a new metric for studying brain diseases.
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