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Aromatase, the last and obligatory enzyme catalyzing estrogen biosynthesis from androgenic precursors, can be labeled in vivo with 11 Cvorozole. Aromatase inhibitors are widely used in breast cancer and other endocrine conditions. The present study aimed to provide baseline information defining aromatase distribution in healthy men and women, against which its perturbation in pathologic situations can be studied. Methods: 11C-vorozole (111–296 MBq/subject) was injected intravenously in 13 men and 20 women (age range, 23–67 y). PET data were acquired over a 90-min period. Each subject had 4 scans, 2 per day separated by 2–6 wk, including brain and torso or pelvis scans. Young women were scanned at 2 discrete phases of the menstrual cycle (midcycle and late luteal). Men and postmenopausal women were also scanned after pretreatment with a clinical dose of the aromatase inhibitor letrozole. Time–activity curves were obtained, and standardized uptake values (SUV) were calculated for major organs including brain, heart, lungs, liver, kidneys, spleen, muscle, bone, and male and female reproductive organs (penis, testes, uterus, ovaries). Organ and whole-body radiation exposures were calculated using OLINDA software. Results: Liver uptake was higher than uptake in any other organ but was not blocked by pretreatment with letrozole. Mean SUVs were higher in men than in women, and brain uptake was blocked by letrozole. Male brain SUVs were also higher than SUVs in any other organ (ranging from 0.48 ± 0.05 in lungs to 1.5 ± 0.13 in kidneys). Mean ovarian SUVs (3.08 ± 0.7) were comparable to brain levels and higher than in any other organ. Furthermore, ovarian SUVs in young women around the time of ovulation (midcycle) were significantly higher than those measured in the late luteal phase, whereas aging and cigarette smoking reduced 11 C-vorozole uptake. Conclusion: PET with 11 C-vorozole is useful for assessing physiologic changes in estrogen synthesis capacity in the human body. Baseline levels in breasts, lungs, and bones are low, supporting further investigation of this tracer as a new tool for detection of aromatase-overexpressing primary tumors or metastases in these organs and optimization of treatment in cancer and other disorders in which aromatase inhibitors are useful.

Dopamine D3 receptor (D3R) antagonists may be effective medications for multiple substance use disorders (SUDs). However, no selective D3R antagonists are currently available for clinical testing. Buspirone, originally characterized as a 5-HT1A partial agonist and used as an anxiolytic, also binds to D3R and D4R with high affinity, with lower affinity to D2R, and interferes with cocaine reward. Here we used PET with [ 11 C]PHNO (D3R-preferring radioligand), [ 11 C]raclopride (D2R/D3R radioligand) and [ 11 C]NNC-112 (D1R radioligand) to measure occupancy of oral and parenteral buspirone in the primate brain. Intramuscular buspirone (0.19 and 0.5 mg/kg) blocked both [ 11 C]PHNO and [ 11 C]raclopride binding to striatum, exhibiting high occupancy (50–85%) at 15 min and rapid wash-out over 2–6 h. In contrast, oral buspirone (3 mg/kg) significantly blocked [ 11 C]PHNO binding in D3-rich regions (globus pallidum and midbrain) at 3 h, but had minimal effects on [ 11 C]raclopride binding (28–37% at 1 h and 10% at 3 h). Buspirone did not block [ 11 C]NNC-112. Our findings provide evidence that i.m. buspirone blocks D3R and D2R, whereas oral buspirone is more selective towards D3R blockade in vivo, consistent with extensive first pass metabolism and supporting the hypothesis that its metabolites (5- and 6′-hydroxybuspirone) merit evaluation for treating SUDs. They also indicate that for oral buspirone to achieve greater than 80% sustained D3R occupancy, as might be needed to treat addiction, higher doses (at least three-fold) than those used to treat anxiety (maximal 60 mg) will be required. Nonetheless, based on previous clinical studies, these doses would be safe and well tolerated.

To explore the role of endogenous GABA in NMDA antagonist induced dopamine (DA) release, we used in vivo microdialysis to study the effects of pretreatment with gamma-vinyl GABA (GVG) on phencyclidine (PCP)-induced DA release in terminal regions of midbrain DA neurons. GVG, an irreversible inhibitor of the GABA catabolizing enzyme GABA-AT, significantly reduced the DA response to PCP (7.0 mg/kg) in freely moving animals. Preferential increases in PCP-induced DA release in the PFC (four-fold those of NAcc) were dose-dependently inhibited by acute pretreatment with GVG at doses of 150 (51% inhibition), 300 (68% inhibition), and 500 (82% inhibition) mg/kg, whereas NAcc PCP-induced DA activity was unresponsive to 150 mg/kg and only partially inhibited by 300 and 500 mg/kg. Subchronic treatment with GVG did not enhance the inhibitory capacity of the GABAergic system. While GVG evidently modulates PCP-induced increases in mesocorticolimbic DA transmission, the character of this modulation is regionally specific, with cortical NMDA-antagonist induced increases appearing more sensitive to inhibition by endogenous GABA than subcortical areas.

The graphical analysis method, which transforms multiple time measurements of plasma and tissue uptake data into a linear plot, is a useful tool for rapidly obtaining information about the binding of radioligands used in PET studies. The strength of the method is that it does not require a particular model structure. However, a bias is introduced in the case of noisy data resulting in the underestimation of the distribution volume (DV), the slope obtained from the graphical method. To remove the bias, a modification of the method developed by Feng et al. (1993) , the generalized linear least squares (GLLS) method, which provides unbiased estimates for compartment models was used. The one compartment GLLS method has a relatively simple form, which was used to estimate the DV directly and as a smoothing technique for more general classes of model structures. In the latter case, the GLLS method was applied to the data in two parts, that is, one set of parameters was determined for times 0 to T1 and a second set from T1 to the end time. The curve generated from these two sets of parameters then was used as input to the graphical method. This has been tested using simulations of data similar to that of the PET ligand [11C]- d-threo-methylphenidate (MP, DV = 35 mL/mL) and 11C raclopride (RAC, DV = 1.92 mL/mL) and compared with two examples from image data with the same tracers. The noise model was based on counting statistics through the half-life of the isotope and the scanning time. Five hundred data sets at each noise level were analyzed. Results (DV) for the graphical analysis (DVg), the nonlinear least squares (NLS) method (DVnls), the one-tissue compartment GLLS method (DVf), and the two part GLLS followed by graphical analysis (DVfg) were compared. DVFG was found to increase somewhat with increasing noise and in some data sets at high noise levels no estimate could be obtained. However, at intermediate levels it provided a good estimation of the true DV. This method was extended to use a reference tissue in place of the input function to generate the distribution volume ratio (DVR) to the reference region. A linearized form of the simplified reference tissue method of Lammertsma and Hume (1996) was used. The DVR generated directly from the model (DVRfl) was compared with DVRfg (determined from a “smoothed” uptake curve as for DVfg) using the graphical method.

Objective: This study was undertaken to measure serotonergic modulation of dopamine in vivo by using positron emission tomography (PET), a radiotracer for the striatal dopamine D2 receptor ([11C]raclopride), and a pharmacologic challenge of the serotonin system (d,l-fenfluramine). Method: Two PET studies using [11C]raclopride were performed in 11 normal male subjects before administration of the serotonin-releasing agent and reuptake inhibitor fenfluramine (60 mg p.o.) and 3 hours afterward. A graphical analysis method was used with the [11C]raclopride data to derive the distribution volume of D2 receptors. Plasma levels of fenfluramine, norfenfluramine, homovanillic acid (HVA), cortisol, and prolactin were determined. Results: Levels of fenfluramine and prolactin were elevated 2 hours after fenfluramine administration and remained significantly elevated during the second scan, while levels of HVA and cortisol were not altered significantly during the time of scanning. A significant decrease in the specific binding (striatum) and the nonspecific binding subtracted from the specific binding (striatum minus cerebellum) of [11C]raclopride was observed. The rate of metabolism of [11C]raclopride and the nonspecific binding (cerebellum) were not significantly altered by the fenfluramine intervention. Conclusions: The observed decrease in [11C]raclopride binding is consistent with an increase in dopamine concentrations and with the ability of serotonin to stimulate dopamine activity. The ability to measure serotonergic modulation of dopamine in vivo may have implications for the study of etiologic and therapeutic mechanisms in schizophrenia, major depressive disorder, obsessive-compulsive disorder, and substance abuse. (Am J Psychiatry 1997; 154:490‐496)

GABA modulates dopamine concentrations in the nucleus accumbens and corpus striatum. Using in vivo microdialysis techniques we examined this modulatory role and the extent to which three different GABAergic drugs can attenuate cocaine's ability to increase extracellular dopamine concentrations and gross locomotor activity. Ethanol, lorazepam (Ativan), and gamma-vinyl GABA (GVG) significantly and dose-dependently attenuated cocaine-induced dopamine release in the corpus striatum of freely moving animals. Unlike ethanol or lorazepam, however, GVG is not a sedative hypnotic in the doses used, and hence the strategy of selectively increasing GABAergic activity by suicide inhibition of the catabolic enzyme, GABA-transaminase, offers the unique advantage of attenuating cocaine-induced dopamine release without the apparent side effects typically associated with sedative hypnotics.

Neuroimaging techniques, including positron emission tomography (PET), are widely used in clinical settings and in basic neuroscience research. Education in these methods and their applications may be incorporated into curricula to keep pace with this expanding field. Here, we have developed pedagogical materials on the fundamental principles of PET that incorporate a hands-on laboratory activity to view and analyze human brain scans. In this activity, students will use authentic PET brain scans generated from original research at Brookhaven National Laboratory (Volkow et al., 2009) to explore the neurobiological effects of a drug on the dopamine system. We provide lecture and assignment materials (including a 50-minute PowerPoint presentation introducing PET concepts), written background information for students and instructors, and explicit instructions for a 4-hour, computer-based laboratory to interested educators. Also, we discuss our experience implementing this exercise as part of an advanced undergraduate laboratory course at Stony Brook University in 2010 and 2011. Observing the living human brain is intriguing, and this laboratory is designed to illustrate how PET neuroimaging techniques are used to directly probe biological processes occurring in the living brain. Laboratory course modules on imaging techniques such as PET can pique the interest of students potentially interested in neuroscience careers, by exposing them to current research methods. This activity provides practical experience analyzing PET data using a graphical analysis method known as the Logan plot, and applies core neuropharmacology concepts. We hope that this manuscript inspires college instructors to incorporate education in PET neuroimaging into their courses.

Several studies have documented a strong association between smoking and depression. Because cigarette smoke has been reported to inhibit monoamine oxidase (MAO) A in vitro and in animals and because MAO A inhibitors are effective antidepressants, we tested the hypothesis that MAO A would be reduced in the brain of cigarette smokers. We compared brain MAO A in 15 nonsmokers and 16 current smokers with [ 11 C]clorgyline and positron emission tomography (PET). Four of the nonsmokers were also treated with the antidepressant MAO inhibitor drug, tranylcypromine (10 mg/day for 3 days) after the baseline PET scan and then rescanned to assess the sensitivity of [ 11 C]clorgyline binding to MAO inhibition. MAO A levels were quantified by using the model term λk 3 which is a function of brain MAO A concentration. Smokers had significantly lower brain MAO A than nonsmokers in all brain regions examined (average reduction, 28%). The mean λ k 3 values for the whole brain were 0.18 ± 0.04 and 0.13 ± 0.03 cc brain (ml plasma ) −1 min −1 for nonsmokers and smokers, respectively; P < 0.0003). Tranylcypromine treatment reduced λ k 3 by an average of 58% for the different brain regions. Our results show that tobacco smoke exposure is associated with a marked reduction in brain MAO A, and this reduction is about half of that produced by a brief treatment with tranylcypromine. This suggests that MAO A inhibition needs to be considered as a potential contributing variable in the high rate of smoking in depression and in the development of more effective strategies for smoking cessation.

A commercial laboratory robot system (Zymate PyTechnology II Laboratory Automation System) was interfaced to standard and custom laboratory equipment and programmed to perform rapid radiochemical assays necessary for plasma input function determination in quantitative PET studies in humans and baboons. A Zymark XP robot arm was used to carry out two assays: (1) the determination of total plasma radioactivity concentrations in a series of small-volume whole blood samples and (2) the determination of unchanged (parent) radiotracer in plasma using only solid phase extraction methods. Steady state robotic throughput for determination of total plasma radioactivity in whole blood samples (0.350 mL) is 14.3 samples/h, which includes automated centrifugation, pipetting, weighing and radioactivity counting. Robotic throughput for the assay of parent radiotracer in plasma is 4–6 samples/h depending on the radiotracer. Percents of total radioactivities present as parent radiotracers at 60 min. postinjection of 25 ± 5.0 ( N = 25), 26 ± 6.8 ( N = 68), 13 ± 4.4 ( N = 30), 32 ± 7.2 ( N = 18), 16 ± 4.9 ( N = 20), were obtained for carbon-11 labeled benztropine, raclopride, methylphenidate, SR 46349B (trans, 4-[(3Z)3-(2-dimethylamino-ethyl) oxyimino-3 (2-fluorophenyl)propen-1-yl]phenol), and cocaine respectively in baboon plasma and 84 ± 6.4 ( N = 9), 18 ± 11 ( N = 10), 74 ± 5.7 ( N = 118) and 16 ± 3.7 ( N = 18) for carbon-11 labeled benztropine, deprenyl, raclopride, and methylphenidate respectively in human plasma. The automated system has been used for more than 4 years for all plasma analyses for 7 different C-11 labeled compounds used routinely in our laboratory. The robotic radiotracer assay runs unattended and includes automated cleanup procedures that eliminates all human contact with plasma-contaminated containers.

Positron emission tomography and in vivo microdialysis were used to study serotonin's role in modulating striatal dopamine. Serial PET studies were performed in adult female baboons at baseline and following drug treatment, using the dopamine (D2) selective radiotracer, 11C-raclopride. The serotonergic system was manipulated by administration of the selective 5-HT reuptake inhibitor, citalopram, or by serotonergic (5-HT2) receptor blockade (using altanserin, a 5-HT2 antagonist). 11C-Raclopride time-activity data from striatum and cerebellum were combined with plasma arterial input functions and analyzed by calculating a distribution volume as described previously (Logan et al., 1990). Additionally, in vivo microdialysis studies were performed in awake freely moving rats using similar pharmacologic challenges plus SR 46349B, a new highly selective 5-HT2 receptor antagonist. Altanserin and SR 46349B increased extracellular striatal dopamine concentrations (35% and 910%, respectively) while altanserin decreased striatal 11C-raclopride binding (37%). Citalopram, however, decreased extracellular striatal dopamine concentrations (50%) and increased 11C-raclopride binding (33%). These data demonstrate that 5- HT-selective drugs produce changes in striatal dopamine that can be measured noninvasively with PET. Furthermore, the PET data obtained from anesthetized baboons is consistent with in vivo microdialysis data obtained from awake and freely moving rats. Finally, these studies have implications for understanding the therapeutic efficacy of atypical neuroleptics and their utility for treating schizophrenia and affective disorders.

Alcohol intoxication results in marked reductions in brain glucose metabolism, which we hypothesized reflect not just its GABAergic enhancing effects but also the metabolism of acetate as an alternative brain energy source. To test this hypothesis we separately assessed the effects of alcohol intoxication on brain glucose and acetate metabolism using Positron Emission Tomography (PET). We found that alcohol intoxication significantly decreased whole brain glucose metabolism (measured with FDG) with the largest decrements in cerebellum and occipital cortex and the smallest in the thalamus. In contrast, alcohol intoxication caused a significant increase in [1-(11)C]acetate brain uptake (measured as standard uptake value, SUV), with the largest increases occurring in the cerebellum and the smallest in the thalamus. In heavy alcohol drinkers [1-(11)C]acetate brain uptake during alcohol challenge tended to be higher than in occasional drinkers (p

L-Deprenyl (Selegeline) is an enzyme-activated irreversible inhibitor of monoamine oxidase B (MAO B; EC 1.4.3.4). It is used to treat Parkinson's disease at a dose of 5 mg twice a day. Since enzyme inhibition is irreversible, the recovery of functional enzyme activity after withdrawal from L-deprenyl requires the synthesis of new enzyme. We have measured a 40 day half-time for brain MAO B synthesis in Parkinson's disease and in normal subjects after withdrawal from L-deprenyl. This is the first measurement of the synthesis rate of a specific protein in the living human brain. L-Deprenyl is currently used by 50,000 patients with Parkinson's disease in the United States and its use is expected to increase with reports that it may be beneficial in Alzheimer's disease. The slow turnover of brain MAO B suggests that the current clinical dose of L-deprenyl may be excessive and that the clinical efficacy of reduced dosing should be evaluated. Such an evaluation may have mechanistic importance as well as an impact on reducing the side effects and the costs arising from excessive drug use. © 1994 Wiley-Liss, Inc.1

We synthesized the o-, m- and p-bromo derivatives of dl-threo-methylphenidate from the corresponding bromophenylacetonitriles by modification of the literature synthesis of methylphenidate (Panizzon, Helv. Chim. Acta 1944, 27, 1748). In in vitro binding assays all three dl-threo bromo compounds had higher affinities than methylphenidate for dopamine transporter sites labeled with [3H]2 beta-carbomethoxy-3 beta-(4-fluorophenyl)tropane ([3H]WIN 35,428; IC50 = 13, 4, 20 and 82 nM for o-, m-, and p-bromo compounds, and unsubstituted methylphenidate, respectively). They also bound more strongly than methylphenidate to norepinephrine reuptake sites labeled with [3H]nisoxetine (IC50 = 32, 20, 31 and 440 nM, respectively), but were weak ligands (IC50 > or = 1 microM) at the serotonin transporter labeled with [3H]paroxetine. In addition, the bromine substituted derivatives demonstrated similar activity to methylphenidate in vivo in rodents in terms of inhibition of heart uptake of [3H](-)-norepinephrine, elevation of striatal extracellular dopamine, and stimulation of locomotor activity.

Positron emission tomography (PET), [11C]cocaine, and (–)-6-[18F]fluoronorepinephrine [(-)-6-[18F]NE] were used to determine the extent to which the binding of labeled cocaine in the baboon heart represents binding to the norepinephrine transporter and to characterize the functional consequences of cocaine administration on the norepinephrine transporter. Peak heart binding of [11C] cocaine was high (0.038-0.055%/g) and clearance was rapid (t1/2 from peak: 2.5–9 min) for both tracer doses and a pharmacological dose. The binding of a tracer dose of labeled cocaine could not be inhibited by desipramine, tomoxetine, cocaine, nomifensine, or benztropine. The behavior of a pharmacological dose of [11C]cocaine could not be distinguished from a tracer dose and also could not be inhibited by tomoxetine. However, pretreatment with cocaine profoundly inhibited norepinephrine uptake as assessed by (–)-6-[18F]NE. Recovery was slow with only 48% of the baseline (–)-6-[18F]NE uptake being recovered by 78 minutes after cocaine administration. [11C]Benzoylecgonine, a vasoactive metabolite of cocaine, showed negligible retention in heart. The results of this study (i.e., the rapid clearance of cocaine from the heart, the inability to inhibit cocaine binding with desipramine and tomoxetine, and its relatively long-lasting effects on norepinephrine uptake) reinforce the need to understand the link between cocaine pharmacokinetics and norepinephrine transporter function and its relationship to cardiotoxicity. © 1994 Wiley-Liss, Inc.

Metergoline, a serotonin receptor antagonist, was labeled with carbon-11 in order to evaluate its pharmacokinetics and distribution in non-human primates using positron emission tomography. [{sup 11}C]Metergoline had moderate brain uptake and exhibited heterogeneous specific binding, which was blocked by pretreatment with metergoline and altanserin throughout the cortex. Non-specific binding and insensitivity to changes in synaptic serotonin limit its potential as a PET radiotracer. However, the characterization of [{sup 11}C]metergoline pharmacokinetics and binding in the brain and peripheral organs using PET improves our understanding of metergoline drug pharmacology.

Introduction PET imaging in plants is receiving increased interest as a new strategy to measure plant responses to environmental stimuli and as a tool for phenotyping genetically engineered plants. PET imaging in plants, however, poses new challenges. In particular, the leaves of most plants are so thin that a large fraction of positrons emitted from PET isotopes ( 18 F, 11 C, 13 N) escape while even state-of-the-art PET cameras have significant partial-volume errors for such thin objects. Although these limitations are acknowledged by researchers, little data have been published on them. Methods Here we measured the magnitude and distribution of escaping positrons from the leaf of Nicotiana tabacum for the radionuclides 18 F, 11 C and 13 N using a commercial small-animal PET scanner. Imaging results were compared to radionuclide concentrations measured from dissection and counting and to a Monte Carlo simulation using GATE (Geant4 Application for Tomographic Emission). Results Simulated and experimentally determined escape fractions were consistent. The fractions of positrons (mean±S.D.) escaping the leaf parenchyma were measured to be 59±1.1%, 64±4.4% and 67±1.9% for 18 F, 11 C and 13 N, respectively. Escape fractions were lower in thicker leaf areas like the midrib. Partial-volume averaging underestimated activity concentrations in the leaf blade by a factor of 10 to 15. Conclusions The foregoing effects combine to yield PET images whose contrast does not reflect the actual activity concentrations. These errors can be largely corrected by integrating activity along the PET axis perpendicular to the leaf surface, including detection of escaped positrons, and calculating concentration using a measured leaf thickness.

A reliable remote water target loading system has been designed and fabricated around the operation of a single pneumatic syringe dispenser that accesses one of two water reservoirs, filling one or more targets depending on the system configuration. For multiple radionuclide configuration, reservoirs are filled with 18O-enriched water for [18F]fluoride production, and natural abundance water for [13N]nitrate and [13N]nitrite production. When actuated, the system withdraws a calibrated volume of water from a selected reservoir, and automatically dispenses that charge through a short transfer line to the appropriate target. A second actuation then forces the dispenser to purge itself of residual water by dispensing a charge of helium gas through the same line thus completing the transfer of water to the target volume. Direct liquid level sensing inside the target, utilizing the specific resistance response of water, signals the operator that the target is loaded. For single radionuclide configuration, one or both reservoirs can be used with the same type of water, while dispensing is directed to a single target.

Reversible inhibitors of monoamine oxidase-A (RIMA) inhibit the breakdown of three major neurotransmitters, serotonin, norepinephrine and dopamine, offering a multi-neurotransmitter strategy for the treatment of depression. CX157 (3-fluoro-7-(2,2,2-trifluoroethoxy)phenoxathiin-10,10-dioxide) is a RIMA, which is currently in development for the treatment of major depressive disorder. We examined the degree and reversibility of the inhibition of brain monoamine oxidase-A (MAO-A) and plasma CX157 levels at different times after oral dosing to establish a dosing paradigm for future clinical efficacy studies, and to determine whether plasma CX157 levels reflect the degree of brain MAO-A inhibition. Brain MAO-A levels were measured with positron emission tomography (PET) imaging and [(11)C]clorgyline in 15 normal men after oral dosing of CX157 (20-80 mg). PET imaging was conducted after single and repeated doses of CX157 over a 24-h time course. We found that 60 and 80 mg doses of CX157 produced a robust dose-related inhibition (47-72%) of [(11)C]clorgyline binding to brain MAO-A at 2 h after administration and that brain MAO-A recovered completely by 24 h post drug. Plasma CX157 concentration was highly correlated with the inhibition of brain MAO-A (EC(50): 19.3 ng/ml). Thus, CX157 is the first agent in the RIMA class with documented reversible inhibition of human brain MAO-A, supporting its classification as a RIMA, and the first RIMA with observed plasma levels that can serve as a biomarker for the degree of brain MAO-A inhibition. These data were used to establish the dosing regimen for a current clinical efficacy trial with CX157.

MS-275 (Entinostat) is a histone deacetylase (HDAC) inhibitor currently in clinical trials for the treatment of several types of cancer. Recent reports have noted that MS-275 can cross the blood brain barrier (BBB) and cause region specific changes in rodent brain histone acetylation. To characterize the pharmacokinetics and distribution of MS-275 in the brain using positron emission tomography (PET), we labeled the carbamate carbon of MS-275 with carbon-11. Using PET, we determined that [(11)C]MS-275 has low uptake in brain tissue when administered intravenously to non-human primates. In rodent studies, we observed that pharmacokinetics and brain accumulation of [(11)C]MS-275 were not changed by the co-administration of large doses of unlabeled MS-275. These results, which both highlight the poor brain penetration of MS-275, clearly suggest its limitation as a therapeutic agent for the central nervous system (CNS). Moreover, our study demonstrates the effectiveness of PET at providing brain pharmacokinetic data for HDAC inhibitors. These data are important not only for the development of new compounds for peripheral cancer treatment (where CNS exclusion is often advantageous), but also for the treatment of neurological disorders (where CNS penetration is critical).

PR04.MZ was designed as a highly selective dopamine transporter inhibitor, derived from natural cocaine. Its binding profile indicates that [{sup 11}C]PR04.MZ may be suited as a PET radioligand for the non-invasive exploration of striatal and extrastriatal DAT populations. As a key feature, its structural design facilitates both, labelling with fluorine-18 at its terminally fluorinated butynyl moiety and carbon-11 at its methyl ester function. The present report concerns the efficient [{sup 11}C]MeI mediated synthesis of [{sup 11}C]PR04.MZ from an O-desmethyl precursor trifluoroacetic acid salt with Rb{sub 2}CO{sub 3} in DMF in up to 95 {+-} 5% labelling yield. A preliminary {mu}PET-experiment demonstrates the reversible, highly specific binding of [{sup 11}C]PR04.MZ in the brain of a male Sprague-Dawley rat.

Modafinil, a wake-promoting drug used to treat narcolepsy, is increasingly being used as a cognitive enhancer. Although initially launched as distinct from stimulants that increase extracellular dopamine by targeting dopamine transporters, recent preclinical studies suggest otherwise.To measure the acute effects of modafinil at doses used therapeutically (200 mg and 400 mg given orally) on extracellular dopamine and on dopamine transporters in the male human brain.Positron emission tomography with [(11)C]raclopride (D(2)/D(3) radioligand sensitive to changes in endogenous dopamine) and [(11)C]cocaine (dopamine transporter radioligand) was used to measure the effects of modafinil on extracellular dopamine and on dopamine transporters in 10 healthy male participants. The study took place over an 8-month period (2007-2008) at Brookhaven National Laboratory.Primary outcomes were changes in dopamine D(2)/D(3) receptor and dopamine transporter availability (measured by changes in binding potential) after modafinil when compared with after placebo.Modafinil decreased mean (SD) [(11)C]raclopride binding potential in caudate (6.1% [6.5%]; 95% confidence interval [CI], 1.5% to 10.8%; P = .02), putamen (6.7% [4.9%]; 95% CI, 3.2% to 10.3%; P = .002), and nucleus accumbens (19.4% [20%]; 95% CI, 5% to 35%; P = .02), reflecting increases in extracellular dopamine. Modafinil also decreased [(11)C]cocaine binding potential in caudate (53.8% [13.8%]; 95% CI, 43.9% to 63.6%; P.001), putamen (47.2% [11.4%]; 95% CI, 39.1% to 55.4%; P.001), and nucleus accumbens (39.3% [10%]; 95% CI, 30% to 49%; P = .001), reflecting occupancy of dopamine transporters.In this pilot study, modafinil blocked dopamine transporters and increased dopamine in the human brain (including the nucleus accumbens). Because drugs that increase dopamine in the nucleus accumbens have the potential for abuse, and considering the increasing use of modafinil, these results highlight the need for heightened awareness for potential abuse of and dependence on modafinil in vulnerable populations.

Introduction The only radiotracer available for the selective imaging of muscarinic M2 receptors in vivo is 3-(3-{3-[ 18 F]fluoropropyl)thio}-1,2,5-thiadiazol-4-yl)-1,2,5,6-tetrahydro-1-methylpyridine) ([ 18 F]FP-TZTP). We have prepared and labeled 3-(3-(3-fluoropropylthio)-1,2,5-thiadiazol-4-yl)-1,2,5,6-tetrahydro-1-methylpyridne (FP-TZTP, 3 ) and two other TZTP derivatives with 11 C at the methylpyridine moiety to explore the potential of using 11 C-labeled FP-TZTP for positron emission tomography imaging of M2 receptors and to compare the effect of small structural changes on tracer pharmacokinetics (PK) in brain and peripheral organs. Methods 11 C-radiolabeled FP-TZTP, 3-(3-propylthio)-TZTP ( 6 ) and 3,3,3-(3-(3-trifluoropropyl)-TZTP ( 10) were prepared, and log D, plasma protein binding (PPB), affinity constants, time-activity curves (TACs), area under the curve (AUC) for arterial plasma, distribution volumes (DV) and pharmacological blockade in baboons were compared. Results Values for log D, PPB and affinity constants were similar for 3 , 6 and 10 . The fraction of parent radiotracer in the plasma was higher and the AUC lower for 10 than for 3 and 6 . TACs for brain regions were similar for 3 and 6 , which showed PK similar to the 18 F tracer, while 10 showed slower uptake and little clearance over 90 min. DVs for 3 and 6 were similar to the 18 F tracer but higher for 10 . Uptake of the three tracers was significantly reduced by coinjection of unlabeled 3 and 6 . Conclusion Small structural variations on the TZTP structure greatly altered the PK in brain and behavior in blood with little change in the log D, PPB or affinity. The study suggests that 11 C-radiolabeled 3 will be a suitable alternative to [ 18 F]FP-TZTP for translational studies in humans.

(3E)-3-[(2,4-dimethoxyphenyl)methylene]-3,4,5,6-tetrahydro-2,3'-bipyridine (GTS-21), a partial alpha7 nicotinic acetylcholine receptor agonist drug, has recently been shown to improve cognition in schizophrenia and Alzheimer's disease. One of its two major demethylated metabolites, 4-OH-GTS-21, has been suggested to contribute to its therapeutic effects.We labeled GTS-21 in two different positions with carbon-11 ([2-methoxy-(11)C]GTS-21 and [4-(11)C]GTS-21) along with two corresponding demethylated metabolites ([2-methoxy-(11)C]4-OH-GTS-21 and [4-methoxy-(11)C]2-OH-GTS-21) for pharmacokinetic studies in baboons and mice with positron emission tomography (PET).Both [2-(11)C]GTS-21 and [4-methoxy-(11)C]GTS-21 showed similar initial high rapid uptake in baboon brain, peaking from 1 to 3.5 min (0.027-0.038%ID/cc) followed by rapid clearance (t(1/2)15 min), resulting in low brain retention by 30 min. However, after 30 min, [2-methoxy-(11)C]GTS-21 continued to clear while [4-methoxy-(11)C]GTS-21 plateaued, suggesting the entry of a labeled metabolite into the brain. Comparison of the pharmacokinetics of the two labeled metabolites confirmed expected higher brain uptake and retention of [4-methoxy-(11)C]2-OH-GTS-21 (the labeled metabolite of [4-methoxy-(11)C]GTS-21) relative to [2-methoxy-(11)C]4-OH-GTS-21 (the labeled metabolite of [2-methoxy-(11)C]GTS-21), which had negligible brain uptake. Ex vivo studies in mice showed that GTS-21 is the major chemical form in the mouse brain. Whole-body dynamic PET imaging in baboon and mouse showed that the major route of excretion of C-11 is through the gallbladder.The major findings are as follows: (a) extremely rapid uptake and clearance of [2-methoxy-(11)C]GTS-21 from the brain, which may need to be considered in developing optimal dosing of GTS-21 for patients, and (b) significant brain uptake of 2-OH-GTS-21, suggesting that it might contribute to the therapeutic effects of GTS-21. This study illustrates the value of comparing different label positions and labeled metabolites to gain insight on the behavior of a central nervous system drug and its metabolites in the brain, providing an important perspective on drug pharmacokinetics.

Medically refractory seizures cause inflammation and neurodegeneration. Seizure initiation thresholds have been linked in mice to the serine protease tissue plasminogen activator (tPA); mice lacking tPA exhibit resistance to seizure induction, and the ensuing inflammation and neurodegeneration are similarly suppressed. Seizure foci in humans can be examined using PET employing 2-deoxy-2[18F]fluoro- d -glucose (18FDG) as a tracer to visualize metabolic dysfunction. However, there currently exist no such methods in mice to correlate measures of brain activation with behavior. Using a novel method for small animal PET data analysis, we examine patterns of 18FDG uptake in wild-type and tPA−/− mice and find that they correlate with the severity of drug-induced seizure initiation. Furthermore, we report unexpected activations that may underlie the tPA modulation of seizure susceptibility. The methods described here should be applicable to other mouse models of human neurological disease.

Results from human studies with the PET radiotracer ( S , S )-[ 11 C] O -methyl reboxetine ([ 11 C]( S , S )-MRB), a ligand targeting the norepinephrine transporter (NET), are reported. Quantification methods were determined from test/retest studies, and sensitivity to pharmacological blockade was tested with different doses of atomoxetine (ATX), a drug that binds to the NET with high affinity ( K i =2–5 nM). Methods Twenty-four male subjects were divided into different groups for serial 90-min PET studies with [ 11 C]( S , S )-MRB to assess reproducibility and the effect of blocking with different doses of ATX (25, 50 and 100 mg, po). Region-of-interest uptake data and arterial plasma input were analyzed for the distribution volume (DV). Images were normalized to a template, and average parametric images for each group were formed. Results [ 11 C]( S , S )-MRB uptake was highest in the thalamus (THL) and the midbrain (MBR) [containing the locus coeruleus (LC)] and lowest for the caudate nucleus (CDT). The CDT, a region with low NET, showed the smallest change on ATX treatment and was used as a reference region for the DV ratio (DVR). The baseline average DVR was 1.48 for both the THL and MBR with lower values for other regions [cerebellum (CB), 1.09; cingulate gyrus (CNG) 1.07]. However, more accurate information about relative densities came from the blocking studies. MBR exhibited greater blocking than THL, indicating a transporter density ∼40% greater than THL. No relationship was found between DVR change and plasma ATX level. Although the higher dose tended to induce a greater decrease than the lower dose for MBR (average decrease for 25 mg=24±7%; 100 mg=31±11%), these differences were not significant. The different blocking between MBR (average decrease=28±10%) and THL (average decrease=17±10%) given the same baseline DVR indicates that the CDT is not a good measure for non-NET binding in both regions. Threshold analysis of the difference between the average baseline DV image and the average blocked image showed the expected NET distribution with the MBR (LC) and hypothalamus>THL>CNG and CB, as well as a significant change in the supplementary motor area. DVR reproducibility for the different brain regions was ∼10%, but intersubject variability was large. Conclusions The highest density of NETs was found in the MBR where the LC is located, followed by THL, whereas the lowest density was found in basal ganglia (lowest in CDT), consistent with the regional localization of NETs in the nonhuman primate brain. While all three doses of ATX were found to block most regions, no significant differences between doses were found for any region, although the average percent change across subjects of the MBR did correlate with ATX dose. The lack of a dose effect could reflect a low signal-to-noise ratio coupled with the possibility that a sufficient number of transporters were blocked at the lowest dose and further differences could not be detected. However, since the lowest (25 mg) dose is less than the therapeutic doses used in children for the treatment of attention-deficit/hyperactivity disorder (∼1.0 mg/kg/day), this would suggest that there may be additional targets for ATX's therapeutic actions.

Context Predisposition to alcoholism is likely an interaction between genetic and environmental factors that confer vulnerability and protection. Alcoholic subjects have low levels of dopamine D 2 receptors in striatum, and increasing D 2 receptor levels in laboratory animals reduces alcohol consumption. Objectives To test whether high levels of D 2 receptors may be protective against alcoholism and whether this is mediated by their modulation of activity in orbitofrontal cortex and cingulate gyrus (regions involved in salience attribution, emotional reactivity, and inhibitory control). Design Research (nonalcoholic subjects with a family history of alcoholism) and comparison (nonalcoholic subjects with a negative family history) sample. Setting Outpatient setting. Participants Fifteen nonalcoholic subjects who had an alcoholic father and at least 2 other first- or second-degree relatives who were alcoholics (family-positive group) and 16 nonalcoholic controls with no family history of alcoholism (family-negative group). Main Outcome Measures Results of positron emission tomography with raclopride C 11 to assess D 2 receptors and with fludeoxyglucose F 18 to assess brain glucose metabolism (marker of brain function). Personality measures were obtained with the Multidimensional Personality Questionnaire. Results Availability of D 2 receptors was significantly higher in caudate and ventral striatum in family-positive than family-negative subjects. In family-positive but not family-negative subjects, striatal D 2 receptors were associated with metabolism in anterior cingulate (Brodmann area 24/25) and orbitofrontal (Brodmann area 11) and prefrontal (Brodmann area 9/10) cortices, and with personality scores of positive emotionality. Conclusions The higher-than-normal D 2 receptor availability in nonalcoholic members of alcoholic families supports the hypothesis that high levels of D 2 receptors may protect against alcoholism. The significant associations between D 2 receptors and metabolism in frontal regions involved with emotional reactivity and executive control suggest that high levels of D 2 receptors could protect against alcoholism by regulating circuits involved in inhibiting behavioral responses and in controlling emotions.

Publisher Summary Small-animal positron emission tomography (PET) is becoming an increasingly common tool to explore biological function noninvasively, particularly in the neurosciences. Quantitative imaging of complex biological processes is a critical technology of the post-sequencing era. In particular, PET, using small-animal models, has emerged as a powerful technique to explore physiology in a flexible, noninvasive, and quantitative way. With the recent advent of commercial high-resolution, small-animal imagers, such as the micro- PET scanners from Siemens, functional imaging of rodent models using PET has found increasing acceptance. An essential first step in a quantitative PET study is the generation of a faithful representation of the radioactivity distribution in the subject as a function of time, which can be subsequently interpreted in terms of biological processes using methods such as tracer kinetic modeling. The development of methods to improve image quantification is an important endeavor because the accuracy of the input images is critical to the effectiveness of such models.

Children and adolescents will readily abuse household products that contain solvents such as toluene. It is likely that reinforcing exposures to toluene alter brain glucose metabolism. Using an animal model of drug reinforcement, we sought to identify a metabolic signature of toluene abuse in the adolescent rodent brain. Small animal PET (microPET), in combination with the glucose analog radiotracer, 18FDG, were used to evaluate the metabolic consequences of inhaled toluene. The exposure protocol paralleled our previously established method for assessing the conditioned reinforcing effects of toluene (5,000 ppm) using the conditioned place preference (CPP) paradigm. Animals were scanned at baseline and 2 h after the last exposure. Follow-up 18FDG scans occurred 1 day, 3 weeks, and 2 months later. Results: After six pairings, 38% of the animals preferred the toluene paired chamber and 25% were averse. The immediate metabolic effect in toluene-exposed animals was a 20% decline in whole brain 18FDG uptake. Twenty-four hours following the last exposure, the whole brain decline was 40%, and 2 months later, the decline was 30% of pretoluene levels. A region-by-region analysis demonstrated significant additional decreases in the pons, cerebellum, striatum, midbrain, temporal cortex, and hippocampus. Two months after toluene cessation, regions of complete metabolic recovery were the thalamus and cerebellum; however, the temporal cortex did not recover. Brain uptake of 18FDG appears to be a useful tool for examining the metabolic impact of toluene abuse, which include a profound decline followed by region-specific recovery after cessation.

Smokers have reduced levels of brain monoamine oxidase A (MAO A) leading to speculation that MAO A inhibition by tobacco smoke may underlie some of the neurophysiologic effects of smoking. Because smoking exposes peripheral organs as well as the brain to MAO A-inhibitory compounds, we determined whether smokers would also have reduced MAO A in peripheral organs.We measured MAO A in peripheral organs in a group of 9 smokers and compared it with a group of nonsmokers studied previously. MAO A was measured using PET and serial scans with the MAO A-specific radiotracers (11)C-clorgyline and deuterium-substituted (11)C-clorgyline ((11)C-clorgyline-D2) using the deuterium isotope effect to assess binding specificity. The time course of radiotracer in the arterial plasma was also measured and data from the tissue time-activity curves and the arterial input function were analyzed using a 3-compartment model to estimate k(3), which represents the rate-limiting step for the irreversible binding of labeled clorgyline to MAO A.Tracer uptake at plateau was reduced with deuterium substitution for the heart, lungs, and kidneys, indicating specificity for MAO. There was no difference in organ uptake at plateau between nonsmokers and smokers though, for the smokers, the efflux of tracer from peak uptake to plateau was slower for the lungs. The area under the time-activity curve for the arterial plasma was also significantly reduced for smokers versus nonsmokers and the reduction occurred in the first few minutes after radiotracer injection. Smokers had an approximately 50% reduction in k(3) when compared with nonsmokers; however, k(3) did not differ for nonsmokers and smokers for the heart and the kidneys.Because MAO A breaks down serotonin, norepinephrine, dopamine, and tyramine, and because the lung is a major metabolic organ in degrading some of these substances, reduced lung MAO A may contribute to some of the physiologic effects of smoking. This study also revealed that the concentration of the radiotracers in the arterial plasma is significantly lower for the smoker versus the nonsmoker and that this appears to be caused in part by retention of the radiotracer in lungs. If this is generally true for other substances that are administered intravenously, then this needs to be considered as a variable that may contribute to different short-term behavioral responses to intravenously administered drugs for nonsmokers versus smokers.

Introduction Acetone is an ubiquitous ingredient in many household products (e.g., glue solvents, air fresheners, adhesives, nail polish, and paint) that is putatively abused; however, there is little empirical evidence to suggest that acetone alone has any abuse liability. Therefore, we systematically investigated the conditioned response to inhaled acetone in a place conditioning apparatus. Method Three groups of male, Sprague–Dawley rats were exposed to acetone concentrations of 5000, 10,000 or 20,000 ppm for 1 h in a conditioned place preference apparatus alternating with air for 6 pairing sessions. A place preference test ensued in an acetone-free environment. To test the preference of acetone as a function of pairings sessions, the 10,000 ppm group received an additional 6 pairings and an additional group received 3 pairings. The control group received air in both compartments. Locomotor activity was recorded by infrared photocells during each pairing session. Results We noted a dose response relationship to acetone at levels 5000–20,000 ppm. However, there was no correlation of place preference as a function of pairing sessions at the 10,000 ppm level. Locomotor activity was markedly decreased in animals on acetone-paired days as compared to air-paired days. Conclusion The acetone concentrations we tested for these experiments produced a markedly decreased locomotor activity profile that resemble CNS depressants. Furthermore, a dose response relationship was observed at these pharmacologically active concentrations, however, animals did not exhibit a positive place preference.

Introduction One strength of small animal imaging is the ability to obtain longitudinal measurements within the same animal, effectively reducing the number of animals needed and increasing statistical power. However, the variability of within-rodent brain glucose uptake after an intraperitoneal injection across an extended time has not been measured. Methods Small animal imaging with 2-deoxy-2-[ 18 F]-fluoro-d-glucose ( 18 FDG) was used to determine the variability of a 50-min brain 18 FDG uptake following an intraperitoneal injection over time in awake male and female Sprague–Dawley rodents. Results After determining the variability of an intraperitoneal injection in the awake rat, we found that normalization of brain 18 FDG uptake for (1) injected dose and body weight or (2) body weight, plasma glucose concentration and injected dose resulted in a coefficient of variation (CV) of 15%. However, if we normalized regional uptake to whole brain to compare relative regional changes, the CV was less than 5%. Normalized cerebral 18 FDG uptake values were reproducible for a 2-week period in young adult animals. After 1 year, both male and female animals had reduced whole-brain uptake, as well as reduced regional hippocampal and striatal 18 FDG uptake. Conclusion Overall, our results were similar to findings in previous rodent and human clinical populations; thus, using a high throughput study with intraperitoneal 18 FDG is a promising preclinical model for clinical populations. This is particularly relevant for measuring changes in brain function after experimental manipulation, such as long-term pharmacological administration.

Anorexia nervosa is a life-threatening psychiatric disorder characterized by severe weight loss and high rates of comorbidity and mortality. The current study assessed the feasibility of using microPET imaging to study the effects of chronic food restriction in an animal model of anorexia nervosa. To establish preliminary support for this model, we hypothesized that chronic food restriction would decrease relative 2-deoxy-2-[18F]fluoro-D-glucose (18FDG) uptake in the rat, in effect modeling cerebral glucose hypometabolism reported in the clinical population of anorexia nervosa. Nine adolescent Wistar female rats received a baseline 18FDG scan. The control group received free access to food for a period of 25 days. The food restricted (FR) group received 40% of their baseline daily food intake until a 30% weight loss occurred; body weight was then maintained at 70% of baseline by adjusting daily food intake. The FR group also had free access to a running wheel for a mean period of 10.8 ± 6.1 days. Both groups received a follow-up 18FDG scan. Relative 18FDG uptake was significantly increased in the cerebellum and significantly decreased in the hippocampus and striatum in the FR group compared to controls. Moreover, there was a trend towards a decrease in relative 18FDG uptake in the thalamus in the FR compared to control group. This is the first study to establish support for the use of microPET imaging in an animal model of anorexia nervosa as a means for studying the neurobiological changes that occur due to chronic food restriction. Synapse 57:85–90, 2005. © 2005 Wiley-Liss, Inc.

The development of automated systems supporting the production and application of PET radiopharmaceuticals has been an important focus of researchers since the first successes of using carbon-11 (Comar et al., 1979) and fluorine-18 (Reivich et al., 1979) labeled compounds to visualize functional activity of the human brain. These initial successes of imaging the human brain soon led to applications in the human heart (Schelbert et al., 1980), and quickly radiochemists began to see the importance of automation to support PET studies in humans (Lambrecht, 1982; Langstrom et al., 1983). Driven by the necessity of controlling processes emanating high fluxes of 511 KeV photons, and by the tedium of repetitive syntheses for carrying out these human PET investigations, academic and government scientists have designed, developed and tested many useful and novel automated systems in the past twenty years. These systems, originally designed primarily by radiochemists, not only carry out effectively the tasks they were designed for, but also demonstrate significant engineering innovation in the field of laboratory automation.

The phenomenon of inhalant abuse is a growing problem in the US and many countries around the world. Yet, relatively little is known about the pharmacokinetic properties of inhalants that underlie their abuse potential. While the synthesis of 11C-labeled toluene, acetone and butane has been proposed in the literature, none of these compounds has been developed as radiotracers for PET studies. In the present report we extend our previous studies with [11C]toluene to include [11C]acetone and [11C]butane with the goal of comparing the pharmacokinetic profiles of these three volatile abused substances. Both [11C]toluene and [11C]acetone were administered intravenously and [11C]butane was administered via inhalation to anesthesized baboons. Rapid and efficient uptake of radiolabeled toluene and acetone into the brain was followed by fast clearance in the case of toluene and slower kinetics in the case of acetone. [11C]Butane was detected in the blood and brain following inhalation, but the levels of radioactivity in both tissues dropped to half of the maximal values over the period of less than a minute. To our knowledge, this is the first reported study of the in vivo brain pharmacokinetics of labeled acetone and butane in nonhuman primates. These data provide insight into the pharmacokinetic features possibly associated with the abuse liability of toluene, acetone and butane.

In the field of small animal positron emission tomography (PET), the assumptions underlying human and primate kinetic models may not be sustained in rodents. That is, the threshold dose at which a pharmacologic response occurs may be lower in small animals. In order to define this relationship, we combined microPET imaging using 11C-raclopride with microdialysis measures of extracellular fluid (ECF) dopamine (DA). In addition, we performed a series of studies in which a known mass of raclopride was microinfused into one striatum prior to a high specific activity (SA) systemic injection of 11C-raclopride. This single-injection approach provided a high and low SA region of radiotracer binding in the same animal during the same scanning session. Our data demonstrate that the binding potential (BP) declines above 3.5 pmol/ml (0.35 microg), with an ED50 of 8.55+/-5.62 pmol/ml. These data also provide evidence that BP may be compromised by masses of raclopride below 2.0 pmol/ml (0.326 microg). Increases in ECF DA were produced by mass doses of raclopride over 3.9 pmol/ml (0.329 microg) with an ED50 of 8.53+/-2.48 pmol/ml. Taken together, it appears that an optimal range of raclopride mass exists between 2.0 and 3.5 pmol/ml, around which the measured BP can be compromised by system sensitivity, endogenous DA, or excessive competition with unlabeled compound.

Publisher Summary This chapter describes the binding potential computed for 15 [11C]raclopride studies in the rat striatum using the micro-PET R4. In two of these studies, a 1-mg/kg blocking dose of raclopride was coadministered with the tracer to measure nonspecific binding of the tracer. The remaining studies were carried out with varying doses of [11C]raclopride of varying specific activity. Data are summarized as the binding potential as a function of raclopride mass injected. The curve is the best fit to a single-site ligand receptor model allowing for fitting of the modified equilibrium constants. Image data were corrected for spillover from the intraorbital lachrymal glands but were not corrected for partial volume averaging. The microPET R4, with a FWHM resolution is expected to give a truer measure of striatal [11C]raclopride concentration, and therefore, gives a larger binding potential. Determinations of binding potential using the graphical method were compared with the values obtained using a compartmental model without blood sampling. The results support the use of the noninvasive graphical analysis methodology with [11C]raclopride, and the microPET R4 to measure dopamine receptor availability in the rat striatum.

Human brain function is frequently being studied by subtracting two brain images of the same subject, one obtained while resting and the other one while his brain is activated by either a motor task, a cognitive activity, the effects of a medication, or drug abuse. The activation signal has noise induced both by the camera and the patient, i.e. daily metabolic variability, patient positioning errors, etc. The present methodology allows the determination of faint activation signals by finding sharper error bounds in the error induced in the signal by each separate source of noise in the image, combining them later for a final bound on the noise to assess the signal's statistical significance. Using simple concepts from numerical analysis and directional statistics, we present a general methodology to analyze the effect that spatial registration errors have on each pixel's signal to noise ratio. This approach to signal analysis is valid for most imaging modalities and registration methods. Experimental results are given for 48 subjects, using Positron Emission Tomography (PET) brain images spatially registered with the Centroidal Principal Axes registration method. >

The construction of parametric positron emission tomography images of enzyme or receptor concentration obtained using irreversibly binding radiotracers presents problems not usually encountered with reversibly binding radiotracers. Difficulties are most apparent in brain regions having low blood flow and/or high enzyme or receptor concentration and are exacerbated with noisy data. This is especially true when minimal doses of radiotracer are administered. A comparison was recently reported of the irreversible monoamine oxidase A (MAO A) radiotracers [11C]clorgyline (CLG) and deuterium-substituted [11C]clorgyline (CLG-D) in the human brain using region of interest (ROI) analysis in which the authors observed an unexpected loss of image contrast with CLG-D compared with CLG. In order to more fully investigate patterns of binding of these irreversibly binding radiotracers, a strategy was devised to reduce noise in the generation of parametric images of the model term related to enzyme or receptor concentration. The generalized linear least squares (GLLS) method of Feng et al. (1995) , a rapid linear method that is unbiased, was used for image-wide parameter estimation. Since GLLS can fail in the presence of large amounts of noise, local voxels were grouped within the image to increase the signal, and the GLLS method was combined with the standard nonlinear estimation methods when necessary. Voxels were grouped together depending on their proximity and whether they fell within a specified range of the time-integrated image. It was assumed that voxels meeting both criteria are functionally related. Simulations reflecting varying enzyme concentrations were performed to assess precision and accuracy of parameter estimates in the presence of varying amounts of noise. Using this approach, images were generated of the combination parameter λ k3 (λ = K1/ k2, where K1 and k2 are plasma-to-tissue and tissue-to-plasma transport constants, respectively) that is related to enzyme concentration as well as images of the transport constant K1 for individual subjects. Reasonably high-quality images of both K1 and λ k3 were obtained for CLG and CLG-D for individual subjects even with low injected doses averaging 6 mCi. While there were no differences in the K1 images, the λ k3 images revealed the loss of contrast previously reported for CLG-D using the ROI analysis. This method should be generalizable to other tracers and should facilitate the analysis of group differences.

The use of mice with targeted gene deletions (knockouts [KOs]) provides an important tool to investigate the mechanisms underlying behavior, neuronal development, and the sequella of neuropsychiatric diseases. MRI has been used to image brain structural changes in KO mice but, to our knowledge, the feasibility of using PET to investigate brain neurochemistry in KO mice has not been demonstrated.We have evaluated the sensitivity of the microPET to image dopamine D2 receptor (DRD2) KO mice (D2-/-). PET measurements were performed in wild-type (D2+/+) mice and KO (D2-/-) mice using a microPET scanner. Briefly, each animal was anesthetized and injected intravenously with (11)C-raclopride, a DRD2-specific ligand, and dynamic PET scanning was performed for 60 min.The (11)C-raclopride images of the KO mice showed significantly lower binding in the striatum (ST) than those of the wild-type (WT) mice, which was confirmed by the time-activity curves that revealed equivalent binding in the ST and cerebellum (CB) in KO mice, whereas the WT mice had significantly higher binding in the ST than in the CB. The ST/CB ratio was significantly higher in WT mice than in KO mice (ST/CB = 1.33 +/- 0.13 and 1.05 +/- 0.03, respectively; P0.002; n = 10). The microPET images were compared qualitatively with conventional autoradiography images.These data support the use of microPET as an effective in vivo imaging tool for studying noninvasively KO mice. These same tools can be extended to investigate other genetically engineered murine models of disease. Future studies will seek to use microPET to investigate the relationships between genes, neuronal activity, and behavior.

Monoamine oxidase (MAO) regulates neurotransmitter concentration in the brain and is also an important detoxifying enzyme in peripheral organs. It occurs in 2 subtypes, MAO A and MAO B. Their relative ratios in different organs are variable, depending on the particular organ and species, making it difficult to extrapolate measures from animals to humans. The purpose of this study was to investigate the feasibility of imaging MAO B in peripheral organs in humans with PET.Nine healthy subjects (7 males, 2 females; mean age +/- SD, 37 +/- 7 y) received 2 dynamic PET studies of the torso area 2 h apart with 11C-L-deprenyl and deuterium-substituted 11C-L-deprenyl (11C-L-deprenyl-D2). Time-activity curves for heart, lungs, liver, kidneys, and spleen and arterial plasma input were measured for each study. The uptake at plateau and the incorporation quotient (IQ = uptake/plasma input) as well as model terms K1 (which is a function of blood flow) and k3 and lambdak3 (which are kinetic terms proportional to MAO B) were compared to identify organs that showed reduced values with deuterium substitution (deuterium isotope effect) characteristic of MAO B. In addition, a sensitivity analysis compared the 2 tracers with respect to their ability to quantify MAO B.Heart, lungs, kidneys, and spleen showed a robust deuterium isotope effect on uptake, IQ, k3, and lambdak3. The arterial plasma input function was significantly larger for 11C-L-deprenyl-D2 than for 11C-L-deprenyl. Liver time-activity curves were not affected by deuterium substitution and model terms could not be estimated. In organs showing an isotope effect, lambdak3 showed the rank order: kidneysor= heartlungs = spleen. A sensitivity analysis showed that 11C-L-deprenyl-D2 is a better index of MAO activity than 11C-L-deprenyl.This study demonstrates that (a) the deuterium isotope effect is useful in assessing the binding specificity of labeled deprenyl to peripheral MAO B; (b) MAO B can be visualized and quantified in the heart, lungs, kidneys, and spleen but not in the liver; (c) with the exception of the liver, which cannot be measured, MAO B activity is highest in the kidneys and heart; and (d) quantitation in organs having high levels of MAO B is improved by the use of 11C-L-deprenyl-D2, similar to prior studies on the brain. This study indicates that 11C-L-deprenyl-D2 will be useful for measuring the effects of different variables, including tobacco smoke exposure on MAO B activity in peripheral organs in humans.

doi:10.1017/S1461145714000194, Published by Cambridge University Press, 28 March 2014. In the article above there …

It is widely held that the reinforcing and dependence-producing properties of nicotine rely on activation of the mesocorticolimbic dopamine (DA) system. This notion is primarily derived from demonstrations that lesions of ventral tegmental area (VTA) DA neurons projecting to the nucleus accumbens (NAcc) can reduce both locomotor activation and the reinforcing effects of nicotine (Clarke et al., 1988; Corrigall et al., 1992). However, it appears that pharmacologically targeting isolated DA receptors is not sufficient to reduce symptoms associated with nicotine dependence (Di Chiara, 2000; Kameda et al., 2000). Recent studies suggest that N-methyl-D-aspartate (NMDA) glutamate receptor activation within the VTA may be required for nicotine to stimulate DA release in the NAcc (LeikolaPelho and Jackson, 1992; Nisell et al., 1994; Shim et al., 2001), consistent with demonstrations that microinfusion of ionotropic glutamate receptor antagonists reduces nicotine-induced increases in neurochemical and locomotor activity (Schilstrom et al., 1998; Svensson et al., 1998). It has been proposed that this effect is mimicked by noradrenergic neurons, such that nicotine-induced increases in norepinephrine (NE) activity, associated with its cognition-enhancing effects, is mediated by glutamatergic transmission (Chen and Engberg, 1989; Erhardt et al., 2000). Alternatively, it has been proposed that augmented NAcc DA activity is the result of a disinhibited system, where increasing the activity of GABAergic interneurons modulates rewardrelated neurochemical and behavioral changes induced by nicotine (Corrigall et al., 2000; Dewey et al., 1999; Kawahara et al., 1999). Consistent with this, studies in our laboratory (Dewey et al., 1999; Schiffer et al., 2000) and others (Bevins et al., 2001) have demonstrated that pretreatment with g-vinyl GABA (GVG), which blocks GABA degredation, modulates nicotine-induced increases in DA and craving for nicotine in animal models. It follows that if both decreasing excitatory activity with glutamatergic antagonists and increasing inhibitory activity with GABA agonists can reduce nicotineinduced increases in DA, a drug which possesses both mechanisms might also suppress nicotine-induced increases in neurotransmitter activity. Topiramate (Topomaxt) was developed as an anticonvulsant and is well tolerated in humans, with some evidence of relieving symptoms associated with bipolar disorder and obesity (Gordon and Price, 1999; Teter et al., 2000). Topiramate reduces EAA activity by antagonizing ionotropic alpha-amino-3-hydroxy-5-metyloisoxazolo-4-propionate (AMPA)/kainate glutamate receptors (Gibbs et al., 2000; Skradski and White, 2000). Further, considerable evidence indicates topiramate increases brain GABA levels (Petroff et al., 1999, 2001; White et al., 1997), possibly by activating a novel site on the GABAA receptor complex (Czuczwar and Patsalos, 2001). In the present study, we used in vivo microdialysis to explore the effects of acute pretreatment with topiramate (25 mg/kg or 50 mg/kg) on increases in mesolimbic extracellular DA, NE, and serotonin (5-HT) activity following a subcutaneous dose of nicotine (0.4 mg/kg). Further, we present the effects of topiramate (75 mg/kg) on nicotine-induced DA release in animals pretreated with nicotine for 14 days. Details of microdialysis methods can be found in Dewey et al. (1999). Briefly, 2 days prior to the microdialysis experiments, siliconized guide cannulae were implanted targeting the NAcc ( A 5 1 1.5 mm, L 5 2 1.0 mm, V 5 2 5.6 mm). Pretreated animals received their last dose of nicotine on the day before the surgery, 2 days prior to the microdialysis study. Dialysate samples were assayed for monoamine content by

[11C]Clorgyline selectively binds to MAO A in the human brain. This contrasts with a recent report that [11C]clorgyline (in contrast to other labeled MAO A inhibitors) is not retained in the rhesus monkey brain [4]. To explore this difference, we compared [11C]clorgyline in the baboon brain before and after clorgyline pretreatment and we also synthesized deuterium substituted [11C]clorgyline (and its nor-precursor) for comparison. [11C]Clorgyline was not retained in the baboon brain nor was it influenced by clorgyline pretreatment or by deuterium substitution, contrasting to results in humans. This suggests a species difference in the susceptibility of MAO A to inhibition by clorgyline and represents an unusual example of where the behavior of a radiotracer in the baboon brain does not predict its behavior in the human brain.

We measured the concentration of brain monoamine oxidase B (MAO B; EC 1.4.3.4) in 8 smokers and compared it with that in 8 non-smokers and in 4 former smokers using positron emission tomography (PET) and deuterium substituted [11C]L-deprenyl ([11C]L-deprenyl-D2) as a radiotracer for MAO B. Smokers had significantly lower brain MAO B than non-smokers as measured by the model term lambda k3 which is a function of MAO B activity. Reductions were observed in all brain regions. Low brain MAO B in the cigarette smoker appears to be a pharmacological rather than a genetic effect since former smokers did not differ from non-smokers. Brain MAO B inhibition by cigarette smoke is of relevance in light of the inverse association between smoking and Parkinson's disease and a high prevalence of smoking in psychiatric disorders and in substance abuse. Though nicotine is at the core of the neuropharmacological actions of tobacco smoke, MAO B inhibition may also be an important variable in understanding and treating tobacco smoke addiction.

The distribution volume ratio (DVR), which is a linear function of receptor availability, is widely used as a model parameter in imaging studies. The DVR corresponds to the ratio of the DV of a receptor-containing region to a nonreceptor region and generally requires the measurement of an arterial input function. Here we propose a graphical method for determining the DVR that does not require blood sampling. This method uses data from a nonreceptor region with an average tissue-to-plasma efflux constant k2 to approximate the plasma integral. Data from positron emission tomography studies with [15C]raclopride (n = 20) and [11C] d-threo-methylphenidate ([11C]dMP) (n = 8) in which plasma data were taken and used to compare results from two graphical methods, one that uses plasma data and one that does not. k2 was 0.163 and 0.051 min−1 for [11C]raclopride and [11C]dMP, respectively. Results from both methods were very similar, and the average percentage difference between the methods was −0.11% for [11C]raclopride and 0.46% for [11C]dMP for DVR of basal ganglia (BG) to cerebellum (CB). Good agreement between the two methods was also achieved for DVR images created by both methods. This technique provides an alternative method of analysis not requiring blood sampling that gives equivalent results for the two ligands studied. It requires initial studies with blood sampling to determine the average kinetic constant and to test applicability. In some cases, it may be possible to neglect the b̅2 term if the BG/CB ratio becomes reasonably constant for a sufficiently long period of time over the course of the experiment.

Our goal was to assess the utility of MR-PET image coregistration to quantify dopamine D{sub 2} receptors in striatum. Twenty-nine normal subjects were investigated with PET and [{sup 11}C]raclopride and with MRI. D{sub 2} receptors were quantified using the ratio of the distribution volume in striatum to that in cerebellum. Measures obtained using regions selected directly from the PET images were compared with those obtained from MR images and then projected to coregistered PET images. There were no differences between measures selected from the PET images (3.9 {+-} 0.5) and those from the MR images (3.9 {+-} 0.65). The values for these two measures were significantly correlated and corresponded to r = 0.9, P < 0.0001. Regions of interest selected directly from PET images, where there is a large contrast between the region of interest and background, as for the case of dopamine D{sub 2} ligands, are almost identical to those obtained from coregistered MR images. 24 refs., 4 figs., 1 tab.

The massive health problem associated with cigarette smoking is exacerbated by the addictive properties of tobacco smoke and the limited success of current approaches to cessation of smoking. Yet little is known about the neuropharmacological actions of cigarette smoke that contribute to smoking behaviour, or why smoking is so prevalent in psychiatric disorders and is associated with a decreased risk of Parkinson's disease. Here we report that brains of living smokers show a 40% decrease in the level of monoamine oxidase B (MAO B; EC 1.4.3.4) relative to non-smokers or former smokers. MAO B is involved in the breakdown of dopamine, a neurotransmitter implicated in reinforcing and motivating behaviours as well as movement. MAO B inhibition is therefore associated with enhanced activity of dopamine, as well as with decreased production of hydrogen peroxide, a source of reactive oxygen species. We propose that reduction of MAO B activity may synergize with nicotine to produce the diverse behavioural and epidemiological effects of smoking.

Dual-modality imaging, using Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET) simultaneously, is a powerful tool to gain valuable information correlating structure with function in biomedicine. The advantage of this dual approach is that the strengths of one modality can balance the weaknesses of the other. However, success of this technique requires developing imaging probes suitable for both. Here, we report on the development of a nanoparticle labeling procedure via covalent bonding with carbon-11 PET isotope. Carbon-11 in the form of [(11)C]methyl iodide was used as a methylation agent to react with carboxylic acid (-COOH) and amine (-NH2) functional groups of ligands bound to the nanoparticles (NPs). The surface coating ligands present on superparamagnetic iron-oxide nanoparticles (SPIO NPs) were radiolabeled to achieve dual-modality PET/MR imaging capabilities. The proof-of-concept dual-modality PET/MR imaging using the radiolabeled SPIO NPs was demonstrated in an in vivo experiment.

We report here a simple apparatus for remote trapping and processing of H2[15O] produced from the N2/H2 target. The system performs a three step operation for H2[15O] delivery at the PET imaging facility which includes the following: (i) collecting the radiotracer in sterile water; (ii) adjusting preparation pH through removal of radiolytically produced ammonia, while at the same time adjusting solution isotonicity; and (iii) delivery of the radiotracer preparation to the injection syringe in a sterile and pyrogen-free form suitable for human studies. The processing apparatus is simple, can be remotely operated and fits inside a Capintec Dose Monitoring Chamber for direct measurement of accumulated radioactivity. Using this system, 300 mCi of H2[15O] (15 μA of 8 MeV D+ on target) is transferred from target through 120 m × 3.18 mm o.d. Impolene tubing to yield 100 mCi of H2[15O] which is isotonic, neutral and suitable for human studies. A remote hydraulically driven system for i.v. injection of the H2[15O] is also described. The device allows for direct measurement of syringe dose while filling, and for easy, as well as safe transport of the injection syringe assembly to the patient's bedside via a shielded delivery cart. This cart houses a hydraulic piston that allows the physician to “manually” inject the radiotracer without directly handling the syringe.