Fluoride transport in Arabidopsis thaliana plants is impaired in Fluoride EXporter (FEX) mutants.

Fluoride is an environmental toxin prevalent in water, soil, and air. A fluoride transporter called Fluoride EXporter (FEX) has been discovered across all domains of life, including bacteria, single cell eukaryotes, and all plants, that is required for fluoride tolerance. How FEX functions to protect multicellular plants is unknown. In order to distinguish between different models, the dynamic movement of fluoride in wildtype (WT) and fex mutant plants was monitored using [18F]fluoride with positron emission tomography. Significant differences were observed in the washout behavior following initial fluoride uptake between plants with and without a functioning FEX. [18F]Fluoride traveled quickly up the floral stem and into terminal tissues in WT plants. In contrast, the fluoride did not move out of the lower regions of the stem in mutant plants resulting in clearance rates near zero. The roots were not the primary locus of FEX action, nor did FEX direct fluoride to a specific tissue. Fluoride efflux by WT plants was saturated at high fluoride concentrations resulting in a pattern like the fex mutant. The kinetics of fluoride movement suggested that FEX mediates a fluoride transport mechanism throughout the plant where each individual cell benefits from FEX expression.

Imaging the brain's immune response to alcohol with [11C]PBR28 TSPO Positron Emission Tomography.

In humans, the negative effects of alcohol are linked to immune dysfunction in both the periphery and the brain. Yet acute effects of alcohol on the neuroimmune system and its relationships with peripheral immune function are not fully understood. To address this gap, immune response to an alcohol challenge was measured with positron emission tomography (PET) using the radiotracer [11C]PBR28, which targets the 18-kDa translocator protein, a marker sensitive to immune challenges. Participants (n = 12; 5 F; 25-45 years) who reported consuming binge levels of alcohol (>3 drinks for females; >4 drinks for males) 1-3 months before scan day were enrolled. Imaging featured a baseline [11C]PBR28 scan followed by an oral laboratory alcohol challenge over 90 min. An hour later, a second [11C]PBR28 scan was acquired. Dynamic PET data were acquired for at least 90 min with arterial blood sampling to measure the metabolite-corrected input function. [11C]PBR28 volume of distributions (VT) was estimated in the brain using multilinear analysis 1. Subjective effects, blood alcohol levels (BAL), and plasma cytokines were measured during the paradigm. Full completion of the alcohol challenge and data acquisition occurred for n = 8 (2 F) participants. Mean peak BAL was 101 ± 15 mg/dL. Alcohol significantly increased brain [11C]PBR28 VT (n = 8; F(1,49) = 34.72, p > 0.0001; Cohen's d'=0.8-1.7) throughout brain by 9-16%. Alcohol significantly altered plasma cytokines TNF-α (F(2,22) = 17.49, p < 0.0001), IL-6 (F(2,22) = 18.00, p > 0.0001), and MCP-1 (F(2,22) = 7.02, p = 0.004). Exploratory analyses identified a negative association between the subjective degree of alcohol intoxication and changes in [11C]PBR28 VT. These findings provide, to our knowledge, the first in vivo human evidence for an acute brain immune response to alcohol.

Lower dorsal putamen D2/3 receptor availability and amphetamine-induced dopamine release are related to poorer cognitive function in recently abstinent people who smoke and healthy controls.

INTRODUCTION: In the dopamine system, the mesolimbic pathway, including the dorsal striatum, underlies the reinforcing properties of tobacco smoking, and the mesocortical pathway, including the dorsolateral prefrontal cortex (dlPFC), is critical for cognitive functioning. Dysregulated dopamine signaling has been linked to drug-seeking behaviors and cognitbie deficits. The dorsal striatum and dlPFC are structurally and functionally connected and are the key regions for cognitive functioning. We recently showed that people who smoke have lower dlPFC dopamine (D2/3R) receptor availability than people who do not, which is related to poorer cognitive function. The goal of this study was to examine the same brain-behavior relationship in the dorsal striatum. METHODS: Twenty-nine (18 males) recently abstinent people who smoke and twenty-nine sex-matched healthy controls participated in two same-day [11C]-(+)-PHNO positron emission tomography scans before and after amphetamine administration to provoke dopamine release. D2/3R availability (binding potential; BPND) and amphetamine-induced dopamine release (%ΔBPND) were calculated. Cognition (verbal learning and memory) was assessed with the CogState computerized battery. RESULTS: There were no group differences in baseline BPND. People who smoke have a smaller magnitude %ΔBPND in dorsal putamen than healthy controls (p=0.022). People who smoke perform worse on immediate (p=0.035) and delayed (p=0.011) recall than healthy controls. In all people, lower dorsal putamen BPND was associated with worse immediate (p=0.006) and delayed recall (p=0.049), and lower %ΔBPND was related to worse delayed recall (p=0.022). CONCLUSION: Lower dorsal putamen D2/3R availability and function are associated with disruptions in cognitive function that may underlie difficulty with resisting smoking. IMPLICATIONS: This study directly relates dopamine imaging outcomes in the dorsal striatum to cognitive function in recently abstinent people who smoke cigarettes and healthy controls. The current work included a well-characterized subject sample in terms of demographics, smoking characteristics, and a validated neurocognitive test of verbal learning and memory. The findings of this study extend previous literature relating dopamine imaging outcomes to cognition in recently abstinent people who smoke and people who do not smoke, expanding our understanding of brain-behavior relationships.

In vivo evidence of lower synaptic vesicle density in schizophrenia.

Decreased synaptic spine density has been the most consistently reported postmortem finding in schizophrenia (SCZ). A recently developed in vivo measure of synaptic vesicle density estimated using the novel positron emission tomography (PET) ligand [11C]UCB-J is a proxy measure of synaptic density. In this study we determined whether [11C]UCB-J binding, an in vivo measure of synaptic vesicle density, is altered in SCZ. SCZ patients (n = 13, 3 F) and age-, gender-matched healthy controls (HCs) (n = 15, 3 F) underwent PET imaging using [11C]UCB-J and high-resolution research tomography (HRRT). [11C]UCB-J distribution volume (VT) and binding potential (BPND) were estimated using a 1T model with centrum-semiovale as the reference region. Relative to HCs, SCZ patients, showed significantly lower [11C]UCB-J BPND with significant differences in the frontal cortex (-10%, Cohen's d = 1.01), anterior cingulate (-11%, Cohen's d = 1.24), hippocampus (-15%, Cohen's d = 1.29), occipital cortex (-14%, Cohen's d = 1.34), parietal cortex (-10%, p = 0.03, Cohen's d = 0.85) and temporal cortex (-11%, Cohen's d = 1.23). These differences remained significant after partial volume correction. [11C]UCB-J BPND did not correlate with cumulative antipsychotic exposure or gray-matter volume. Consistent with the postmortem and in vivo findings, synaptic vesicle density is lower across several brain regions in SCZ. Frontal synaptic vesicle density correlated with psychosis symptom severity and cognitive performance on social cognition and processing speed. These findings indicate that [11C]UCB-J PET is a sensitive tool to detect lower synaptic density in SCZ and holds promise for future studies of early detection and disease progression.

Multimodal neuroimaging of metabotropic glutamate 5 receptors and functional connectivity in alcohol use disorder.

BACKGROUND: People recovering from alcohol use disorder (AUD) show altered resting brain connectivity. The metabotropic glutamate 5 (mGlu5) receptor is an important regulator of synaptic plasticity potentially linked with synchronized brain activity and a target of interest in treating AUD. The goal of this work was to assess potential relationships of brain connectivity at rest with mGlu5 receptor availability in people with AUD at two time points early in abstinence. METHODS: Forty-eight image data sets were acquired with a multimodal neuroimaging battery that included resting-state functional magnetic resonance imaging (fMRI) and mGlu5 receptor positron emission tomography (PET) with the radiotracer [18 F]FPEB. Participants with AUD (n = 14) were scanned twice, at approximately 1 and 4 weeks after beginning supervised abstinence. [18 F]FPEB PET results were published previously. Primary comparisons of fMRI outcomes were performed between the AUD group and healthy controls (HCs; n = 23) and assessed changes over time within the AUD group. Relationships between resting-state connectivity measures and mGlu5 receptor availability were explored within groups. RESULTS: Compared to HCs, global functional connectivity of the orbitofrontal cortex was higher in the AUD group at 4 weeks of abstinence (p = 0.003), while network-level functional connectivity within the default mode network (DMN) was lower (p < 0.04). Exploratory multimodal analyses showed that mGlu5 receptor availability was correlated with global connectivity across all brain regions (HCs, r = 0.41; AUD group at 1 week of abstinence, r = 0.50 and at 4 weeks, r = 0.46; all p < 0.0001). Furthermore, a component of cortical and striatal mGlu5 availability was correlated with connectivity between the DMN and salience networks in HCs (r = 0.60, p = 0.003) but not in the AUD group (p > 0.3). CONCLUSIONS: These preliminary findings of altered global and network connectivity during the first month of abstinence from drinking may reflect the loss of efficient network function, while exploratory relationships with mGlu5 receptor availability suggest a potential glutamatergic relationship with network coherence.

Recently Abstinent Smokers Exhibit Mood-Associated Dopamine Dysfunction in the Ventral Striatum Compared to Nonsmokers: A [11C]-(+)-PHNO PET Study.

INTRODUCTION: Chronic nicotine exposure desensitizes dopamine responses in animals, but it is not known if this occurs in human tobacco smokers. Deficits in dopamine function are likely to make smoking cessation difficult. We used positron emission tomography (PET) brain imaging with the dopamine D2/3 receptor agonist radioligand [11C]-(+)-PHNO to determine if abstinent smokers exhibit less amphetamine-induced dopamine release in the ventral striatum than nonsmokers, and whether this was associated with clinical correlates of smoking cessation. METHODS: Baseline [11C]-(+)-PHNO scans were acquired from smokers (n = 22, 7 female, abstinent 11 ± 9 days) and nonsmokers (n = 20, 7 female). A subset of thirty-seven participants (18 smokers) received oral amphetamine (0.5 mg/kg) three hours before a second [11C]-(+)-PHNO scan. Binding potential (BPND) (i.e., D2/3 receptor availability) was estimated at baseline and postamphetamine in the ventral striatum. Amphetamine-induced percent change in BPND was calculated to reflect dopamine release. Subjects also completed the Center for Epidemiologic Studies Depression Scale (CES-D). RESULTS: There were no group differences in baseline BPND. Amphetamine-induced percent change in BPND in the ventral striatum was significantly lower in abstinent smokers compared to nonsmokers (p=0.019; d=0.82). Higher CES-D scores were significantly associated with lower ventral striatal percent change in BPND for abstinent smokers (rs=-0.627, p=0.025). CONCLUSIONS: In conclusion, abstinent smokers exhibited significantly less amphetamine-induced dopamine release in the ventral striatum than nonsmokers. In abstinent smokers, worse mood was significantly associated with less striatal dopamine release. Our findings highlight a potential neural mechanism that may underlie negative mood symptoms during early abstinence. IMPLICATIONS: This study combined quantitative PET imaging and an amphetamine challenge to examine striatal dopamine function during early smoking cessation attempts. The findings demonstrate that recently abstinent tobacco smokers exhibit significant, mood-associated striatal dopamine dysfunction compared to nonsmokers. This study advances our knowledge of the neurobiology underlying early quit attempts, and bridges novel neural findings with clinically relevant symptoms of smoking cessation. These results may explain the challenge of maintaining long-term abstinence from smoking, and can lend insight into the development of treatment strategies for smoking cessation.

PET Imaging Estimates of Regional Acetylcholine Concentration Variation in Living Human Brain.

Acetylcholine (ACh) has distinct functional roles in striatum compared with cortex, and imbalance between these systems may contribute to neuropsychiatric disease. Preclinical studies indicate markedly higher ACh concentrations in the striatum. The goal of this work was to leverage positron emission tomography (PET) imaging estimates of drug occupancy at cholinergic receptors to explore ACh variation across the human brain, because these measures can be influenced by competition with endogenous neurotransmitter. PET scans were analyzed from healthy human volunteers (n = 4) and nonhuman primates (n = 2) scanned with the M1-selective radiotracer [11C]LSN3172176 in the presence of muscarinic antagonist scopolamine, and human volunteers (n = 10) scanned with the α4ß2* nicotinic ligand (-)-[18F]flubatine during nicotine challenge. In all cases, occupancy estimates within striatal regions were consistently lower (M1/scopolamine human scans, 31 ± 3.4% occupancy in striatum, 43 ± 2.9% in extrastriatal regions, p = 0.0094; nonhuman primate scans, 42 ± 26% vs. 69 ± 28%, p < 0.0001; α4ß2*/nicotine scans, 67 ± 15% vs. 74 ± 16%, p = 0.0065), indicating higher striatal ACh concentration. Subject-level measures of these concentration differences were estimated, and whole-brain images of regional ACh concentration gradients were generated. These results constitute the first in vivo estimates of regional variation in ACh concentration in the living brain and offer a novel experimental method to assess potential ACh imbalances in clinical populations.

Effect of age on brain metabotropic glutamate receptor subtype 5 measured with [18F]FPEB PET.

OBJECTIVE: Metabotropic glutamate receptor subtype 5 (mGluR5) is integral to the brain glutamatergic system and cognitive function. This study investigated whether aging is associated with decreased brain mGluR5 availability. METHODS: Cognitively normal participants (n = 45), aged 18 to 84 years, underwent [18F]FPEB positron emission tomography scans to quantify brain mGluR5. Distribution volume (VT) was computed using a venous or arterial input function and equilibrium modeling from 90 to 120 min. In the primary analysis, the association between age and VT in the hippocampus and association cortex was evaluated using a linear mixed model. Exploratory analyses assessed the association between age and VT in multiple brain regions. The contribution of gray matter tissue alterations and partial volume effects to associations with age was also examined. RESULTS: In the primary analysis, older age was associated with lower [18F]FPEB binding to mGluR5 (P = 0.026), whereas this association was not significant after gray matter masking or partial volume correction to account for age-related tissue loss. Post hoc analyses revealed an age-related decline in mGluR5 availability in the hippocampus of 4.5% per decade (P = 0.007) and a non-significant trend in the association cortex (P = 0.085). An exploratory analysis of multiple brain regions revealed broader inverse associations of age with mGluR5 availability, but not after partial volume correction. CONCLUSION: Reductions in mGluR5 availability with age appear to be largely mediated by tissue loss. Quantification of [18F]FPEB binding to mGluR5 may expand our understanding of age-related molecular changes and the relationship with brain tissue loss.

Identifying brain networks in synaptic density PET (11C-UCB-J) with independent component analysis.

BACKGROUND: The human brain is inherently organized into distinct networks, as reported widely by resting-state functional magnetic resonance imaging (rs-fMRI), which are based on blood-oxygen-level-dependent (BOLD) signal fluctuations. 11C-UCB-J PET maps synaptic density via synaptic vesicle protein 2A, which is a more direct structural measure underlying brain networks than BOLD rs-fMRI. METHODS: The aim of this study was to identify maximally independent brain source networks, i.e., "spatial patterns with common covariance across subjects", in 11C-UCB-J data using independent component analysis (ICA), a data-driven analysis method. Using a population of 80 healthy controls, we applied ICA to two 40-sample subsets and compared source network replication across samples. We examined the identified source networks at multiple model orders, as the ideal number of maximally independent components (IC) is unknown. In addition, we investigated the relationship between the strength of the loading weights for each source network and age and sex. RESULTS: Thirteen source networks replicated across both samples. We determined that a model order of 18 components provided stable, replicable components, whereas estimations above 18 were not stable. Effects of sex were found in two ICs. Nine ICs showed age-related change, with 4 remaining significant after correction for multiple comparison. CONCLUSION: This study provides the first evidence that human brain synaptic density can be characterized into organized covariance patterns. Furthermore, we demonstrated that multiple synaptic density source networks are associated with age, which supports the potential utility of ICA to identify biologically relevant synaptic density source networks.

Acute neuroimmune stimulation impairs verbal memory in adults: A PET brain imaging study.

Psychiatric and neurologic disorders are often characterized by both neuroinflammation and cognitive dysfunction. To date, however, the relationship between neuroinflammation and cognitive dysfunction remains understudied in humans. Preclinical research indicates that experimental induction of neuroinflammation reliably impairs memory processes. In this paradigm development study, we translated those robust preclinical findings to humans using positron emission tomography (PET) imaging with [11C]PBR28, a marker of microglia, and lipopolysaccharide (LPS), a potent neuroimmune stimulus. In a sample of 18 healthy adults, we extended our previous findings that LPS administration increased whole-brain [11C]PBR28 availability by 31-50%, demonstrating a robust neuroimmune response (Cohen's ds > 1.6). We now show that LPS specifically impaired verbal learning and recall, hippocampal memory processes, by 11% and 22%, respectively (Cohen's ds > 0.9), but did not alter attention, motor, or executive processes. The LPS-induced increase in [11C]PBR28 binding was correlated with significantly greater decrements in verbal learning performance in the hippocampus (r = -0.52, p = .028), putamen (r = -0.50, p = .04), and thalamus (r = -0.55, p = .02). This experimental paradigm may be useful in investigating mechanistic relationships between neuroinflammatory signaling and cognitive dysfunction in psychiatric and neurologic disorders. It may also provide a direct approach to evaluate medications designed to rescue cognitive deficits associated with neuroinflammatory dysfunction.

FDG PET imaging of vascular inflammation in post-traumatic stress disorder: A pilot case-control study.

The prevalence of cardiovascular diseases (CVD) is increased in subjects with post-traumatic stress disorder (PTSD). Vascular inflammation mediates CVD and may be assessed by 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) imaging. In this pilot study, we investigated whether subjects with PTSD have enhanced vascular and systemic inflammation compared to healthy controls, as assessed by FDG PET imaging. METHODS: A prospective group of 16 subjects (9 PTSD and 7 controls, age 34 ± 7) without prior history of CVD underwent FDG PET/CT imaging. The presence of PTSD symptoms at the time of the study was confirmed using PTSD checklist for DSM-5 (PCL5) questionnaire. Blood samples were collected to determine blood glucose, lipid and inflammatory biomarkers (tumor necrosis factor α, interleukin-1ß, and interleukin-6) levels. FDG signal in the ascending aorta, amygdala, spleen and bone marrow was quantified. RESULTS: The two groups matched closely with regards to cardiovascular risk factors. The inflammatory biomarkers were all within the normal range. There was no significant difference in FDG signal in the aorta (target to background ratio: 2.40 ± 0.29 and 2.34 ± 0.29 for control and PTSD subjects, difference: - 0.06, 95% confidence interval of difference: - 0.38 to 0.26), spleen, bone marrow, or amygdala between control and PTSD subjects. There was no significant correlation between aortic and amygdala FDG signal. However, a significant positive correlation existed between amygdala, splenic, and bone marrow FDG signal. CONCLUSION: This pilot, small study did not reveal any difference in vascular or systemic inflammation as assessed by FDG PET imaging between PTSD and healthy control subjects. Because of the small number of subjects, a modest increase in vascular inflammation, which requires larger scale studies to establish, cannot be excluded. The correlation between FDG signal in amygdala, spleen and bone marrow may reflect a link between amygdala activity and systemic inflammation.

Separating dopamine D2 and D3 receptor sources of [11C]-(+)-PHNO binding potential: Independent component analysis of competitive binding.

Development of medications selective for dopamine D2 or D3 receptors is an active area of research in numerous neuropsychiatric disorders including addiction and Parkinson's disease. The positron emission tomography (PET) radiotracer [11C]-(+)-PHNO, an agonist that binds with high affinity to both D2 and D3 receptors, has been used to estimate relative receptor subtype occupancy by drugs based on a priori knowledge of regional variation in the expression of D2 and D3 receptors. The objective of this work was to use a data-driven independent component analysis (ICA) of receptor blocking scans to separate D2-and D3-related signal in [11C]-(+)-PHNO binding data in order to improve the precision of subtype specific measurements of binding and occupancy. Eight healthy volunteers underwent [11C]-(+)-PHNO PET scans at baseline and at two time points following administration of the D3-preferring antagonist ABT-728 (150-1000 â€‹mg). Parametric binding potential (BPND) images were analyzed as four-dimensional image series using ICA to extract two independent sources of variation in [11C]-(+)-PHNO BPND. Spatial source maps for each component were consistent with respective regional patterns of D2-and D3-related binding. ICA-derived occupancy estimates from each component were similar to D2-and D3-specific occupancy estimated from a region-based approach (intraclass correlation coefficients â€‹> â€‹0.95). ICA-derived estimates of D3 receptor occupancy improved quality of fit to a single site binding model. Furthermore, ICA-derived estimates of the regional fraction of [11C]-(+)-PHNO binding related to D3 receptors was generated for each subject and values showed good agreement with region-based model estimates and prior literature values. In summary, ICA successfully separated D2-and D3-related components of the [11C]-(+)-PHNO binding signal, establishing this approach as a powerful data-driven method to quantify distinct biological features from PET data composed of mixed data sources.

Accuracy of arterial [18F]-Fluorodeoxyglucose uptake quantification: A kinetic modeling study.

2-deoxy-2- [18F] fluoro-D-glucose (FDG) PET is commonly used for the assessment of vessel wall inflammation. Guidelines for analysis of arterial wall FDG signal recommend the use of the average of maximal standardized uptake value (mean SUVmax) and target-to-blood (mean TBRmax) ratio. However, these methods have not been validated against a gold standard such as tissue activity ex vivo or net uptake rate of FDG (Ki) obtained using kinetic modeling. We sought to evaluate the accuracy of mean SUVmax and mean TBRmax for aortic wall FDG signal quantification in comparison with the net uptake rate of FDG. METHODS: Dynamic PET data from 13 subjects without prior history of cardiovascular disease who enrolled in a study of vascular inflammation were used for this analysis. Ex vivo measurement of plasma activity was used as the input function and voxel-by-voxel Patlak analysis was performed with t* = 20 minute to obtain the Ki image. The FDG signal in the ascending aortic wall was quantified on PET images following recent guidelines for vascular imaging to determine mean SUVmax and mean TBRmax. RESULTS: The Ki in the ascending aortic wall did not correlate with mean SUVmax (r = 0.10, P = NS), but correlated with mean TBRmax (r = 0.82, P < 0.001) (Figure 1B). Ki and Ki_max strongly correlated (R = 0.96, P < 0.0001) and similar to Ki, Ki_max did not correlate with mean SUVmax (r = 0.17, P = NS), but correlated with mean TBRmax (r = 0.83, P < 0.001). CONCLUSIONS: Kinetic modeling supports the use of mean TBRmax as a surrogate for the net uptake rate of FDG in the arterial wall. These results are relevant to any PET imaging agent, regardless of the biological significance of the tracer uptake in the vessel wall.

Approaches to PET Imaging of Glioblastoma.

Glioblastoma multiforme (GBM) is the deadliest type of brain tumor, affecting approximately three in 100,000 adults annually. Positron emission tomography (PET) imaging provides an important non-invasive method of measuring biochemically specific targets at GBM lesions. These powerful data can characterize tumors, predict treatment effectiveness, and monitor treatment. This review will discuss the PET imaging agents that have already been evaluated in GBM patients so far, and new imaging targets with promise for future use. Previously used PET imaging agents include the tracers for markers of proliferation ([11C]methionine; [18F]fluoro-ethyl-L-tyrosine, [18F]Fluorodopa,[18F]fluoro-thymidine, and [18F]clofarabine), hypoxia sensing ([18F]FMISO, [18F]FET-NIM, [18F]EF5, [18F]HX4, and [64Cu]ATSM), and ligands for inflammation. As cancer therapeutics evolve toward personalized medicine and therapies centered on tumor biomarkers, the development of complimentary selective PET agents can dramatically enhance these efforts. Newer biomarkers for GBM PET imaging are discussed, with some already in use for PET imaging other cancers and neurological disorders. These targets include Sigma 1, Sigma 2, programmed death ligand 1, poly-ADP-ribose polymerase, and isocitrate dehydrogenase. For GBM, these imaging agents come with additional considerations such as blood-brain barrier penetration, quantitative modeling approaches, and nonspecific binding.

Evaluation of (-)-[18 F]Flubatine-specific binding: Implications for reference region approaches.

We aimed to characterize changes in binding of (-)-[18 F]Flubatine to α4 ß2 *-nicotinic acetylcholine receptors (α4 ß2 *-nAChRs) during a tobacco cigarette smoking challenge. Displacement of (-)-[18 F]Flubatine throughout the brain was quantified as change in (-)-[18 F]Flubatine distribution volume (VT ), with particular emphasis on regions with low VT . Three tobacco smokers were imaged with positron emission tomography (PET) during a 210 min bolus-plus-constant infusion of (-)-[18 F]Flubatine. A tobacco cigarette was smoked in the PET scanner ∼125 min after the start of (-)-[18 F]Flubatine injection. Equilibrium analysis was used to estimate VT at baseline (90-120 min) and after cigarette challenge (180-210 min), at the time of greatest receptor occupancy by nicotine. Smoking reduced VT by 21 ± 9% (average ±SD) in corpus callosum, 17 ± 9% in frontal cortex, 36 ± 11% in cerebellum, and 22 ± 10% in putamen. The finding of displaceable (-)-[18 F]Flubatine binding throughout the brain is an important consideration for reference region-based quantification approaches with this tracer. We observed displacement of (-)-[18 F]Flubatine binding to α4 ß2 *-nicotinic acetylcholine receptors in corpus callosum by a tobacco cigarette challenge. We conclude that reference region approaches utilizing corpus callosum should first perform careful characterization of displaceable (-)-[18 F]Flubatine binding and nondisplaceable kinetics in this putative reference region.

Use of Electronic Cigarettes Leads to Significant Beta2-Nicotinic Acetylcholine Receptor Occupancy: Evidence From a PET Imaging Study.

Background: Electronic cigarettes (ECs) can influence nicotine addiction by delivering aerosolized nicotine. We investigated if nicotine from ECs is delivered to the brain ß2*-nicotinic acetylcholine receptors (ß2*-nAChR) and how this relates to the behavioral effects and nicotine delivery from cigarettes. Methods: Seven nicotine users participated in positron emission tomography (PET) studies with (-)-[18F]Flubatine before and after nicotine challenge with 0, 8, and 36 mg/ml nicotine in a 3.3 Volt, 1.5 Ohm EC or a standard tobacco cigarette. Craving was evaluated before and after product use. Results: Average ß2*-nAChR occupancy was higher after 36 mg/ml EC challenge compared to 8 mg/ml EC at trend level. Average ß2*-nAChR occupancy after tobacco cigarette smoking was 68 ± 18% and was not different compared with 8 mg/ml (64 ± 17%,) or 36 mg/ml (84 ± 3%) nicotine in EC users. Area under the curve (AUC) of blood nicotine level was higher in the cigarette smoking group compared with the 8mg/ml group (p = 0.03), but similar compared with the 36 mg/ml EC (p = 0.29). Drug craving was reduced after use of the tobacco cigarette, 8 mg/ml EC, and 36 mg/ml EC. Conclusions: In this novel investigation of EC effects at ß2*-nAChRs, we show that average ß2*-nAChR occupancy was higher after 36 mg/ml EC challenge compared with 8 mg/ml EC. Receptor occupancy and arterial blood nicotine levels after cigarette smoking were similar to 36 mg/ml EC use under controlled conditions. These findings suggest that the ECs studied here have abuse liability and may provide an adequate alternative nicotine delivery system for cigarette smokers. Implications: This is the first study to directly determine the neurologic effects of electronic cigarettes on human brain beta-2 nicotinic acetylcholine receptors using PET neuroimaging with (-)-[18F]Flubatine, a novel radiotracer. Our findings suggest that the e-cigarettes studied here have abuse liability and may provide an adequate alternative nicotine delivery system for cigarette smokers.

PET imaging of α7 nicotinic acetylcholine receptors: a comparative study of [18F]ASEM and [18F]DBT-10 in nonhuman primates, and further evaluation of [18F]ASEM in humans.

PURPOSE: The α7 nicotinic acetylcholine receptor (nAChR) is implicated in many neuropsychiatric disorders, making it an important target for positron emission tomography (PET) imaging. The first aim of this work was to compare two α7 nAChRs PET radioligands, [18F]ASEM (3-(1,4-diazabicyclo[3.2.2]nonan-4-yl)-6-([18F]fluorodibenzo[b,d]thiophene 5,5-dioxide) and [18F]DBT-10 (7-(1,4-diazabicyclo[3.2.2]nonan-4-yl)-2-([18F]fluorodibenzo[b,d]thiophene 5,5-dioxide), in nonhuman primates. The second aim was to assess further the quantification and test-retest variability of [18F]ASEM in humans. METHODS: PET scans with high specific activity [18F]ASEM or [18F]DBT-10 were acquired in three rhesus monkeys (one male, two female), and the kinetic properties of these radiotracers were compared. Additional [18F]ASEM PET scans with blocking doses of nicotine, varenicline, and cold ASEM were acquired separately in two animals. Next, six human subjects (five male, one female) were imaged with [18F]ASEM PET for 180 min, and arterial sampling was used to measure the parent input function. Different modeling approaches were compared to identify the optimal analysis method and scan duration for quantification of [18F]ASEM distribution volume (V T). In addition, retest scans were acquired in four subjects (three male, one female), and the test-retest variability of V T was assessed. RESULTS: In the rhesus monkey brain [18F]ASEM and [18F]DBT-10 exhibited highly similar kinetic profiles. Dose-dependent blockade of [18F]ASEM binding was observed, while administration of either nicotine or varenicline did not change [18F]ASEM V T. [18F]ASEM was selected for further validation because it has been used in humans. Accurate quantification of [18F]ASEM V T in humans was achieved using multilinear analysis with at least 90 min of data acquisition, resulting in V T values ranging from 19.6 ± 2.5 mL/cm3 in cerebellum to 25.9 ± 2.9 mL/cm3 in thalamus. Test-retest variability of V T was 11.7 ± 9.8%. CONCLUSIONS: These results confirm [18F]ASEM as a suitable radiotracer for the imaging and quantification of α7 nAChRs in humans.

[18 F]Nifene test-retest reproducibility in first-in-human imaging of α4ß2* nicotinic acetylcholine receptors.

The aim of this study was to examine the suitability of [18 F]nifene, a novel α4ß2* nicotinic acetylcholine receptor (nAChR) radiotracer, for in vivo brain imaging in a first-in-human study. METHODS: Eight healthy subjects (4 M,4 F;21-69,44 ± 21 yrs) underwent a [18 F]nifene positron emission tomography scan (200 ± 3.7 MBq), and seven underwent a second scan within 58 ± 31 days. Regional estimates of DVR were measured using the multilinear reference tissue model (MRTM2) with the corpus callosum as reference region. DVR reproducibility was evaluated with test-retest variability (TRV) and intraclass correlation coefficient (ICC). RESULTS: The DVR ranged from 1.3 to 2.5 across brain regions with a TRV of 0-7%, and did not demonstrate a systematic difference between test and retest. The ICCs ranged from 0.2 to 0.9. DVR estimates were stable after 40 min. CONCLUSION: The binding profile and tracer kinetics of [18 F]nifene make it a promising α4ß2* nAChR radiotracer for scientific research in humans, with reliable DVR test-retest reproducibility.

PET imaging evaluation of [(18)F]DBT-10, a novel radioligand specific to α7 nicotinic acetylcholine receptors, in nonhuman primates.

PURPOSE: Positron emission tomography (PET) radioligands specific to α7 nicotinic acetylcholine receptors (nAChRs) afford in vivo imaging of this receptor for neuropathologies such as Alzheimer's disease, schizophrenia, and substance abuse. This work aims to characterize the kinetic properties of an α7-nAChR-specific radioligand, 7-(1,4-diazabicyclo[3.2.2]nonan-4-yl)-2-[(18)F]-fluorodibenzo[b,d]thiophene 5,5-dioxide ([(18)F]DBT-10), in nonhuman primates. METHODS: [(18)F]DBT-10 was produced via nucleophilic substitution of the nitro-precursor. Four Macaca mulatta subjects were imaged with [(18)F]DBT-10 PET, with measurement of [(18)F]DBT-10 parent concentrations and metabolism in arterial plasma. Baseline PET scans were acquired for all subjects. Following one scan, ex vivo analysis of brain tissue was performed to inspect for radiolabeled metabolites in brain. Three blocking scans with 0.69 and 1.24 mg/kg of the α7-nAChR-specific ligand ASEM were also acquired to assess dose-dependent blockade of [(18)F]DBT-10 binding. Kinetic analysis of PET data was performed using the metabolite-corrected input function to calculate the parent fraction corrected total distribution volume (V T/f P). RESULTS: [(18)F]DBT-10 was produced within 90 min at high specific activities of 428 ± 436 GBq/µmol at end of synthesis. Metabolism of [(18)F]DBT-10 varied across subjects, stabilizing by 120 min post-injection at parent fractions of 15-55%. Uptake of [(18)F]DBT-10 in brain occurred rapidly, reaching peak standardized uptake values (SUVs) of 2.9-3.7 within 30 min. The plasma-free fraction was 18.8 ± 3.4%. No evidence for radiolabeled [(18)F]DBT-10 metabolites was found in ex vivo brain tissue samples. Kinetic analysis of PET data was best described by the two-tissue compartment model. Estimated V T/f P values were 193-376 ml/cm(3) across regions, with regional rank order of thalamus > frontal cortex > striatum > hippocampus > occipital cortex > cerebellum > pons. Dose-dependent blockade of [(18)F]DBT-10 binding by structural analog ASEM was observed throughout the brain, and occupancy plots yielded a V ND/f P estimate of 20 ± 16 ml/cm(3). CONCLUSION: These results demonstrate suitable kinetic properties of [(18)F]DBT-10 for in vivo quantification of α7-nAChR binding in nonhuman primates.

Nicotine and Nicotine Abstinence Do Not Interfere with GABAA Receptor Neuroadaptations During Alcohol Abstinence.

BACKGROUND: Alcohol dependence and tobacco smoking are highly comorbid, and treating both conditions simultaneously is controversial. Previously, we showed that tobacco smoking interferes with GABAA receptor neuroadaptations during alcohol withdrawal in humans, while this effect did not occur with continued nicotine use during alcohol abstinence in nonhuman primates. Here, we extend our previous work by measuring GABAA receptor availability with positron emission tomography (PET) during drug abstinence in nonhuman primates exposed to alcohol alone, nicotine and alcohol together, and alcohol abstinence with continued nicotine exposure. METHODS: Twenty-four adolescent male rhesus macaques orally self-administered alcohol and nicotine, available separately in water and saccharin, over 20 weeks. The groups included alcohol alone (n = 8); nicotine and alcohol with simultaneous abstinence (n = 8); nicotine and alcohol with alcohol abstinence while nicotine was still available (n = 8); and a pilot group of animals consuming nicotine alone (n = 6). Animals were imaged with [(11)C]flumazenil PET to measure binding potential (BPND), an index of GABAA receptor availability. Imaging occurred at baseline (drug-naíve), and following alcohol and/or nicotine cessation at 1 day, 8 days, and 12 weeks of abstinence. Generalized linear mixed models were used to examine the time course of [(11)C]flumazenil BPND during alcohol abstinence across groups. RESULTS: Animals consumed 3.95 ± 1.22 g/kg/d alcohol and 55.4 ± 35.1 mg/kg/d nicotine. No significant group effects were observed in [(11)C]flumazenil BPND during alcohol abstinence; however, a main effect of time was detected. Post hoc analyses indicated that all groups abstaining from alcohol exhibited significantly increased GABAA receptor availability at 1 day and 8 days (but not 12 weeks) of abstinence relative to baseline, while no changes in [(11)C]flumazenil BPND during nicotine abstinence alone were observed. CONCLUSIONS: These data indicate that neither nicotine nor nicotine abstinence interferes with GABAA receptor neuroadaptations during alcohol withdrawal. This conclusion is consistent with our previous study and does not contradict the use of nicotine replacement therapies or non-nicotinic-acting pharmaceuticals to quit smoking during alcohol withdrawal from a GABAergic perspective.