[18F]-Fluorodeoxyglucose Uptake in Lymphoid Tissue Serves as a Predictor of Disease Outcome in the Nonhuman Primate Model of Monkeypox Virus Infection.

Real-time bioimaging of infectious disease processes may aid countermeasure development and lead to an improved understanding of pathogenesis. However, few studies have identified biomarkers for monitoring infections using in vivo imaging. Previously, we demonstrated that positron emission tomography/computed tomography (PET/CT) imaging with [18F]-fluorodeoxyglucose (FDG) can monitor monkeypox disease progression in vivo in nonhuman primates (NHPs). In this study, we investigated [18F]-FDG-PET/CT imaging of immune processes in lymphoid tissues to identify patterns of inflammation in the monkepox NHP model and to determine the value of [18F]-FDG-PET/CT as a biomarker for disease and treatment outcomes. Quantitative analysis of [18F]-FDG-PET/CT images revealed differences between moribund and surviving animals at two sites vital to the immune response to viral infections, bone marrow and lymph nodes (LNs). Moribund NHPs demonstrated increased [18F]-FDG uptake in bone marrow 4 days postinfection compared to surviving NHPs. In surviving, treated NHPs, increase in LN volume correlated with [18F]-FDG uptake and peaked 10 days postinfection, while minimal lymphadenopathy and higher glycolytic activity were observed in moribund NHPs early in infection. Imaging data were supported by standard virology, pathology, and immunology findings. Even with the limited number of subjects, imaging was able to differentiate the difference between disease outcomes, warranting additional studies to demonstrate whether [18F]-FDG-PET/CT can identify other, subtler effects. Visualizing altered metabolic activity at sites involved in the immune response by [18F]-FDG-PET/CT imaging is a powerful tool for identifying key disease-specific time points and locations that are most relevant for pathogenesis and treatment.IMPORTANCE Positron emission tomography and computed tomography (PET/CT) imaging is a universal tool in oncology and neuroscience. The application of this technology to infectious diseases is far less developed. We used PET/CT imaging with [18F]-labeled fluorodeoxyglucose ([18F]-FDG) in monkeys after monkeypox virus exposure to monitor the immune response in lymphoid tissues. In lymph nodes of surviving monkeys, changes in [18F]-FDG uptake positively correlated with enlargement of the lymph nodes and peaked on day 10 postinfection. In contrast, the bone marrow and lymph nodes of nonsurvivors showed increased [18F]-FDG uptake by day 4 postinfection with minimal lymph node enlargement, indicating that elevated cell metabolic activity early after infection is predictive of disease outcome. [18F]-FDG-PET/CT imaging can provide real-time snapshots of metabolic activity changes in response to viral infections and identify key time points and locations most relevant for monitoring the development of pathogenesis and for potential treatment to be effective.

Dorsolateral caudate nucleus differentiates cocaine from natural reward-associated contextual cues.

Chronic drug administration induces neuroplastic changes within brain circuits regulating cognitive control and/or emotions. Following repeated pairings between drug intake and environmental cues, increased sensitivity to or salience of these contextual cues provoke conscious or unconscious craving and enhance susceptibility to relapse. To explore brain circuits participating in such experience-induced plasticity, we combined functional MRI with a preclinical drug vs. food self-administration (SA) withdrawal model. Specifically, two groups of rats were trained to associate odor cues with the availability of i.v. cocaine or oral sucrose, respectively. After 20 d of cocaine or sucrose SA followed by prolonged (30 d) forced abstinence, animals were presented with odor cues previously associated with or without (S+/S-) reinforcer (cocaine/sucrose) availability while undergoing functional MRI scans. ANOVA results demonstrate that a learning effect distinguishing S+ from S- was seen in the insula and nucleus accumbens, with the insula response reflecting the individual history of cocaine SA intake. A main effect of group, distinguishing cocaine from sucrose, was seen in the medial prefrontal cortex (infralimbic, prelimbic, and cingulate cortex) and dorsolateral striatum. Critically, only the dorsomedial striatum demonstrated a double dissociation between the two SA groups and learning (S+ vs. S-). These findings demonstrate altered cortico-limbic-striatal reward-related processing to learned, environment reward-associated contextual odor cues, which may serve as potential biomarkers for therapeutic interventions.

Withdrawal from long-term methamphetamine self-administration 'normalizes' neurometabolites in rhesus monkeys: a (1) H MR spectroscopy study.

(1) H magnetic resonance spectroscopy has demonstrated alterations in several neurometabolites in methamphetamine (METH)-dependent individuals in brain regions implicated in addiction. Yet, it is unclear whether these neurochemicals return to homeostatic levels after an individual abstains from drug use, a difficult question to address due to high recidivism and poor study retention in human subjects. We thus utilized a non-human primate model of addiction to explore the effects of long-term drug exposure and withdrawal on brain neurochemistry. Ten rhesus macaque monkeys on an active METH self-administration protocol (average use 4.6 ± 0.8 years, average daily intake between 0.4 and 1.2 mg/kg) and 10 age- and sex-matched drug-naive controls (CONT) served as subjects. Concentrations of several neurochemicals were evaluated at several timepoints following withdrawal from drug availability (10 monkeys at 1 week and 1 and 3 months, and 6 monkeys at 6 and 12 months; CONT examined at one timepoint). At 1 week following METH withdrawal, we found increases in myo-inositol in anterior cingulate cortex in the METH group relative to CONT. These alterations showed a linear pattern of decreased levels ('normalization') by 1 year of abstinence. We also found decreases in glutamine and Glx (composed mainly of glutamate and glutamine) in the caudate-putamen of the same animals at early withdrawal that showed a similar linear pattern of increasing concentration by 1 year. These results demonstrate that despite protracted, long-term use, neurochemical changes seen following long-term drug administration do not persist following prolonged abstinence, suggesting therapeutic effects of long-term withdrawal from drug use.

fMRI response in the medial prefrontal cortex predicts cocaine but not sucrose self-administration history.

Repeated cocaine exposure induces long-lasting neuroadaptations that alter subsequent responsiveness to the drug. However, systems-level investigation of these neuroplastic consequences is limited. We employed a rodent model of drug addiction to investigate neuroadaptations associated with prolonged forced abstinence after long-term cocaine self-administration (SA). Since natural rewards also activate the mesolimbic reward system in a partially overlapping fashion as cocaine, our design also included a sucrose SA group. Rats were trained to self-administer cocaine or sucrose using a fixed-ratio one, long-access schedule (6 h/day for 20 days). A third group of naïve, sedentary rats served as a negative control. After 30 days of abstinence, the reactivity of the reward system was assessed with functional magnetic resonance imaging (fMRI) following an intravenous cocaine injection challenge. A strong positive fMRI response, as measured by fractional cerebral blood volume changes relative to baseline (CBV%), was seen in the sedentary control group in such cortico-limbic regions as medial prefrontal cortex and anterior cingulate cortex. In contrast, both the cocaine and sucrose SA groups demonstrated a very similar initial negative fMRI response followed by an attenuated positive response. The magnitude of the mPFC response was significantly correlated with the total amount of reinforcer intake during the training sessions for the cocaine SA but not for the sucrose SA group. Given that the two SA groups had identical histories of operant training and handling, this region-specific group difference revealed by regression analysis may reflect the development of neuroadaptive mechanisms specifically related to the emergence of addiction-like behavior that occurs only in cocaine SA animals.

Temporary disruption of the rat blood-brain barrier with a monoclonal antibody: a novel method for dynamic manganese-enhanced MRI.

Manganese (Mn(2+)) has limited permeability through the blood-brain barrier (BBB). Opening the BBB such that a sufficient amount of Mn(2+) enters the extracellular space is a critical step for dynamic manganese-enhanced magnetic resonance imaging (ME-MRI) experiments. The traditional BBB opening method uses intracarotid hyperosmolar stress which results in suboptimal BBB opening, and practically is limited to nonsurvival experiments due to substantial surgical trauma. In the present ME-MRI study, we investigate the feasibility of opening the BBB with an antibody that targets the endothelial barrier antigen (EBA) specifically expressed by rat endothelial cells. Results demonstrate that intravenous infusion of the anti-EBA agent SMI-71 leads to BBB disruption of the whole brain as detected by ME-MRI and confirmed by Evans blue dye staining. Physiologically, injection of SMI-71 leads to a hypertensive response followed by a sustained hypotensive response in animals anesthetized with urethane alone. Incorporating isoflurane partially mitigated both pressor responses. In general, BBB disruption via intravenous infusion of SMI-71 is straightforward and obviates technical difficulties associated with intracarotid hyperosmolar stress, opening new possibilities for in vivo neuroimaging with ME-MRI. The data also suggest that ME-MRI may be used as an imaging method to assess BBB integrity complementary to the Evans blue dye method, a classical but highly invasive technique, permitting longitudinal assessment of the integrity of the BBB on the same animal.

NIDA522131, a new radioligand for imaging extrathalamic nicotinic acetylcholine receptors: in vitro and in vivo evaluation.

A novel radioligand, 6-chloro-3-((2-(S)-azetidinyl)methoxy)-5-(2-fluoropyridin-4-yl)pyridine (NIDA522131), for imaging extrathalamic nicotinic acetylcholine receptors (nAChRs) was characterized in vitro and in vivo using positron emission tomography. The K(d) and T(1/2) of dissociation of NIDA522131 binding measured at 37 degrees C in vitro were 4.9 +/- 0.4 pmol/L and 81 +/- 5 min, respectively. The patterns of radioactivity distribution in monkey brain in vivo was similar to that of 2-[(18)F]fluoro-3-(2(S)-azetidinylmethoxy)pyridine (2FA), a radioligand that has been successfully used in humans, and matched the alpha(4)beta(2)* nAChRs distribution. Comparison between [(18)F]NIDA522131 and 2FA demonstrated better in vivo binding properties of the new radioligand and substantially greater radioactivity accumulation in brain. Consistent with [(18)F]NIDA522131 elevated affinity for nAChRs and its increased lipophilicity, both, the total and non-displaceable distribution volumes were substantially higher than those of 2FA. Estimated binding potential values in different brain regions, characterizing the specificity of receptor binding, were 3-4 fold higher for [(18)F]NIDA522131 than those of 2FA. Pharmacological evaluation in mice demonstrated a toxicity that was comparable to 2FA and is in agreement with a 2300 fold higher affinity at alpha(4)beta(2)* versus alpha(3)beta(4)* nAChRs. These results suggest that [(18)F]NIDA522131 is a promising positron emission tomography radioligand for studying extrathalamic nAChR in humans.

Estimation of D2-like receptor occupancy by dopamine in the putamen of hemiparkinsonian Monkeys.

To advance understanding of the neurochemical changes in Parkinson's disease (PD), we compared D2-like dopamine receptor occupancy by dopamine in the control and lesioned putamen of four pig-tailed macaques treated unilaterally with MPTP. PET and in vitro binding techniques were used to measure binding potential (BP(*)) and density of D2-like dopamine receptors (B(max)), respectively. As would be expected in PD, relatively higher values of BP(*) and B(max) and less amphetamine-induced decrease in [(11)C]raclopride binding were observed in the lesioned compared with the contralateral putamen in each animal. The percent differences between lesioned and contralateral sides were similar whether the measurements were of [(11)C]raclopride BP(*) or B(max) values, measured in vivo and in vitro, respectively. As [(11)C]raclopride BP(*) is a measure of the density of D2-like dopamine receptors available for radioligand binding (i.e., not occupied by dopamine), these findings suggest that the fractional occupancy of receptors by endogenous dopamine in the lesioned putamen is nearly equal to that in the contralateral putamen. Therefore, the absolute number of receptors occupied by dopamine, which is a product of receptor density and fractional occupancy by dopamine, is greater in the lesioned than in the contralateral putamen. One possible explanation for the lack of differences in fractional occupancy of D2 receptors by dopamine (despite a loss in available dopamine) is a lesion-induced increase in a portion of low-affinity D2 receptors to a state of high affinity for dopamine.

Greater nicotinic acetylcholine receptor density in smokers than in nonsmokers: a PET study with 2-18F-FA-85380.

UNLABELLED: Assays of human postmortem brain tissue have revealed that smokers have greater densities of high-affinity nicotinic acetylcholine receptors (nAChRs) in several brain regions than do nonsmokers or exsmokers. Quantitative PET imaging of nAChRs in humans has recently been reported using the alpha4beta2* subtype-specific radioligand 2-(18)F-FA-85380 (2FA). METHODS: We used PET and 2FA to measure total volumes of distribution corrected for the free fraction of 2FA in plasma (V(T)/f(P)) in 10 nonsmokers and 6 heavy smokers (>14 cigarettes/d; abstinent for >36 h). Dynamic PET scans were performed over 8 h, commencing immediately after a bolus injection of 2FA. Anatomic sampling was performed on PET images that were coregistered to MR images acquired from each volunteer. Data were analyzed by Logan plots and by 1- and 2-tissue-compartment models using unbound, unmetabolized arterial 2FA concentration as the input function. RESULTS: All modeling methods yielded similar results. V(T)/f(P) was significantly higher in smokers than in nonsmokers in all brain regions tested, except the thalamus. We used measures of V(T)/f(P) and estimates of nondisplaceable volume of distribution and found 25%-200% higher values in smokers than in nonsmokers for the volume of distribution for the specific binding compartment in the frontal cortex, midbrain, putamen, pons, cerebellum, and corpus callosum. These findings were consistent with voxel-based analysis using statistical parametric mapping. CONCLUSION: Our findings suggest that PET with 2FA can be used to study the role of nicotine-induced upregulation of nAChRs in active smokers and during smoking cessation.

The Human Sodium Iodide Symporter as a Reporter Gene for Studying Middle East Respiratory Syndrome Coronavirus Pathogenesis.

Single photon emission computed tomography (SPECT) is frequently used in oncology and cardiology to evaluate disease progression and/or treatment efficacy. Such technology allows for real-time evaluation of disease progression and when applied to studying infectious diseases may provide insight into pathogenesis. Insertion of a SPECT-compatible reporter gene into a virus may provide insight into mechanisms of pathogenesis and viral tropism. The human sodium iodide symporter (hNIS), a SPECT and positron emission tomography reporter gene, was inserted into Middle East respiratory syndrome coronavirus (MERS-CoV), a recently emerged virus that can cause severe respiratory disease and death in afflicted humans to obtain a quantifiable and sensitive marker for viral replication to further MERS-CoV animal model development. The recombinant virus was evaluated for fitness, stability, and reporter gene functionality. The recombinant and parental viruses demonstrated equal fitness in terms of peak titer and replication kinetics, were stable for up to six in vitro passages, and were functional. Further in vivo evaluation indicated variable stability, but resolution limits hampered in vivo functional evaluation. These data support the further development of hNIS for monitoring infection in animal models of viral disease.IMPORTANCE Advanced medical imaging such as single photon emission computed tomography with computed tomography (SPECT/CT) enhances fields such as oncology and cardiology. Application of SPECT/CT, magnetic resonance imaging, and positron emission tomography to infectious disease may enhance pathogenesis studies and provide alternate biomarkers of disease progression. The experiments described in this article focus on insertion of a SPECT/CT-compatible reporter gene into MERS-CoV to demonstrate that a functional SPECT/CT reporter gene can be inserted into a virus.

Validation of an extracerebral reference region approach for the quantification of brain nicotinic acetylcholine receptors in squirrel monkeys with PET and 2-18F-fluoro-A-85380.

UNLABELLED: The aim of the present study was to explore the applicability of an extracerebral reference region for the quantification of cerebral receptors with PET. METHODS: Male squirrel monkeys underwent quantitative PET studies of cerebral nicotinic acetylcholine receptors (nAChRs) with 2-(18)F-fluoro-A-85380 (2-FA). Data from dynamic PET scans were analyzed with various compartment- and non-compartment-based models, including a simplified reference tissue model (SRTM). Nondisplaceable volume-of-distribution (VDnd) values were determined in regions of interest after the blockade of 2-FA-specific binding by nicotine infusion. Binding potential values, estimated with the cerebellum and muscle as reference regions, were compared and the reproducibility of measurements was determined. RESULTS: One- and 2-tissue-compartment modeling and linear graphic analysis provided similar total volume-of-distribution (VD(T)) values for each studied region. VD(T) values were high in the thalamus, intermediate in the cortex and midbrain, and low in the cerebellum and muscle, consistent with the distribution pattern of nAChR containing alpha(4) and beta(2) receptor subunits (alpha(4)beta(2)*). The administration of nicotine at 2 mg/kg/d via an osmotic pump resulted in a nearly complete saturation of 2-FA-specific binding and led to very small changes in volumes of distribution in the cerebellum and muscle (-9% +/- 4% [mean +/- SEM] and 0% +/- 6%, respectively), suggesting limited specific binding of the radioligand in these areas. VD(T) measured in muscle in 15 monkeys was reasonably constant (3.0 +/- 0.2, with a coefficient of variation of 8%). VDnd in studied brain regions exceeded VD(T) in muscles by a factor of 1.3. With this factor and with muscle as a reference region, BP* values calculated for studied brain regions with the SRTM were in good agreement with those obtained with the cerebellum as a reference region. Significant correlations were observed between BP* values estimated with these 2 approaches. The reproducibilities of BP* measurements obtained with the 2 methods were comparable, with coefficients of variation of less than 11% and 13% for the thalamus and the cortex, respectively. CONCLUSION: These results suggest that the accurate quantification of nAChRs can be performed with 2-FA and a reference region outside the brain, providing a novel approach for the quantification of brain receptors when no suitable cerebral reference region is available.

Cigarette smoking saturates brain alpha 4 beta 2 nicotinic acetylcholine receptors.

CONTEXT: 2-[18F]fluoro-3-(2(S)-azetidinylmethoxy) pyridine (2-F-A-85380, abbreviated as 2-FA) is a recently developed radioligand that allows for visualization of brain alpha 4 beta 2* nicotinic acetylcholine receptors (nAChRs) with positron emission tomography (PET) scanning in humans. OBJECTIVE: To determine the effect of cigarette smoking on alpha 4 beta 2* nAChR occupancy in tobacco-dependent smokers. DESIGN: Fourteen 2-FA PET scanning sessions were performed. During the PET scanning sessions, subjects smoked 1 of 5 amounts (none, 1 puff, 3 puffs, 1 full cigarette, or to satiety [2(1/2) to 3 cigarettes]). SETTING: Academic brain imaging center. PARTICIPANTS: Eleven tobacco-dependent smokers (paid volunteers). Main Outcome Measure Dose-dependent effect of smoking on occupancy of alpha 4 beta 2* nAChRs, as measured with 2-FA and PET in nAChR-rich brain regions. RESULTS: Smoking 0.13 (1 to 2 puffs) of a cigarette resulted in 50% occupancy of alpha 4 beta 2* nAChRs for 3.1 hours after smoking. Smoking a full cigarette (or more) resulted in more than 88% receptor occupancy and was accompanied by a reduction in cigarette craving. A venous plasma nicotine concentration of 0.87 ng/mL (roughly 1/25th of the level achieved in typical daily smokers) was associated with 50% occupancy of alpha 4 beta 2* nAChRs. CONCLUSIONS: Cigarette smoking in amounts used by typical daily smokers leads to nearly complete occupancy of alpha 4 beta 2* nAChRs, indicating that tobacco-dependent smokers maintain alpha 4 beta 2* nAChR saturation throughout the day. Because prolonged binding of nicotine to alpha 4 beta 2* nAChRs is associated with desensitization of these receptors, the extent of receptor occupancy found herein suggests that smoking may lead to withdrawal alleviation by maintaining nAChRs in the desensitized state.

Impact of short access nicotine self-administration on expression of α4ß2* nicotinic acetylcholine receptors in non-human primates.

RATIONALE: Although nicotine exposure upregulates the α4ß2* subtype of nicotinic acetylcholine receptors (nAChRs), the upregulation of nAChRs in non-human primates voluntarily self-administering nicotine has never been demonstrated. OBJECTIVES: The objective of the study is to determine if short access to nicotine in a non-human primate model of nicotine self-administration is sufficient to induce nAChRs upregulation. METHODS: We combined a nicotine self-administration paradigm with in vivo measure of α4ß2* nAChRs using 2-[(18)F]fluoro-A-85380 (2-FA) and positron emission tomography (PET) in six squirrel monkeys. PET measurement was performed before and after intravenous nicotine self-administration (unit dose 10 µg/kg per injection). Monkeys were trained to self-administer nicotine under a fixed-ratio (FR) schedule of reinforcement. Intermittent access (1 h daily per weekday) to nicotine was allowed for 4 weeks and levels of α4ß2* nAChRs were measured 4 days later. RESULTS: This intermittent access was sufficient to induce upregulation of α4ß2* receptors in the whole brain (31 % upregulation) and in specific brain areas (+36 % in amygdala and +62 % in putamen). CONCLUSIONS: These results indicate that intermittent nicotine exposure is sufficient to produce change in nAChRs expression.

Synthesis and structure-activity relationship of a novel series of aminoalkylindoles with potential for imaging the neuronal cannabinoid receptor by positron emission tomography.

A new series of CB(1) ligands with high binding affinity (K(i) = 0.7-100 nM) and moderate lipophilicity (cLogD(7.4)) in the range of 2.1-4.5 has been synthesized. A structure-activity relationship study demonstrated that for the studied set of aminoalkylindoles, the molecular dipole of the ground state conformation within the series was inversely related to the affinity. The racemic ligand with highest affinity (0.7 nM), 3-(4-fluoronaphthoyl)-1-(N-methylpiperidin-2-ylmethyl)indole, was radiolabeled with (18)F. This radioligand specifically labeled CB(1) receptors in mouse brain and accumulated in regions of high versus low CB(1) receptor density in a ratio of 1.6. The displaceable radioactivity of one enantiomer in the brains of mice determined in a pretreatment study using the CB(1) antagonist N-(piperidinyl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716) was nearly double that of the racemate for the same determination; therefore, the active enantiomer is a candidate for PET studies in animals. A pretreatement study for the other enantiomer found no displaceable radioactivity in the same group of mice; this result suggested the enantiomer was inactive.

2-[18F]F-A-85380: PET imaging of brain nicotinic acetylcholine receptors and whole body distribution in humans.

Noninvasive imaging of nicotinic acetylcholine receptors (nAChRs) in the human brain in vivo is critical for elucidating the role of these receptors in normal brain function and in the pathogenesis of brain disorders. Here we report the first in vivo visualization of human brain areas containing nAChRs by using PET and 2-[18F]fluoro-3-(2(S)azetidinylmethoxy)pyridine (2-[18F]FA). We acquired scans from six healthy non-smoking volunteers after i.v. bolus administration of 2-[18F]FA (1.6 MBq/kg or 0.043 +/- 0.002 mCi/kg). This dose was sufficient for visualizing nAChRs in the thalamus up to 5 h after injection. There were no adverse effects associated with administration of no-carrier-added 2-[18F]FA (1.3-10 pmol/kg). Consistent with the distribution of nAChRs in human brain, accumulated radioactivity was greatest in thalamus, intermediate in the midbrain, pons, cerebellum, and cortex; and least in white matter. As approximately 90% of the injected radioactivity was eliminated via the urine (biological half-life ca. 4 h), the urinary bladder wall received the highest radiation dose. The estimate of radiation dose equivalent to the urinary bladder wall (ca. 180 +/- 30 mSv/MBq or 0.7 rem/mCi with a 2.4 h void interval) suggests that multiple studies could be performed in a single subject. The results predict that quantitative PET imaging of nAChRs in human brain with 2-[18F]FA is feasible.

Modeling [(18)F]-FDG lymphoid tissue kinetics to characterize nonhuman primate immune response to Middle East respiratory syndrome-coronavirus aerosol challenge.

BACKGROUND: The pathogenesis and immune response to Middle East respiratory syndrome (MERS) caused by a recently discovered coronavirus, MERS-CoV, have not been fully characterized because a suitable animal model is currently not available. (18)F-Fluorodeoxyglucose ([(18)F]-FDG)-positron emission tomography/computed tomography (PET/CT) as a longitudinal noninvasive approach can be beneficial in providing biomarkers for host immune response. [(18)F]-FDG uptake is increased in activated immune cells in response to virus entry and can be localized by PET imaging. We used [(18)F]-FDG-PET/CT to investigate the host response developing in nonhuman primates after MERS-CoV exposure and applied kinetic modeling to monitor the influx rate constant (K i ) in responsive lymphoid tissue. METHODS: Multiple [(18)F]-FDG-PET and CT images were acquired on a PET/CT clinical scanner modified to operate in a biosafety level 4 environment prior to and up to 29 days after MERS-CoV aerosol exposure. Time activity curves of various lymphoid tissues were reconstructed to follow the [(18)F]-FDG uptake for approximately 60 min (3,600 s). Image-derived input function was used to calculate K i for lymphoid tissues by Patlak plot. RESULTS: Two-way repeated measures analysis of variance revealed alterations in K i that was associated with the time point (p < 0.001) after virus exposure and the location of lymphoid tissue (p = 0.0004). As revealed by a statistically significant interaction (p < 0.0001) between these two factors, the pattern of K i changes over time differed between three locations but not between subjects. A distinguished pattern of statistically significant elevation in K i was observed in mediastinal lymph nodes (LNs) that correlated to K i changes in axillary LNs. Changes in LNs K i were concurrent with elevations of monocytes in peripheral blood. CONCLUSIONS: [(18)F]-FDG-PET is able to detect subtle changes in host immune response to contain a subclinical virus infection. Full quantitative analysis is the preferred approach rather than semiquantitative analysis using standardized uptake value for detection of the immune response to the virus.

Effects of Fatty Acid Amide Hydrolase (FAAH) Inhibitors in Non-Human Primate Models of Nicotine Reward and Relapse.

Inhibition of the enzyme fatty acid amide hydrolase (FAAH) counteracts reward-related effects of nicotine in rats, but it has not been tested for this purpose in non-human primates. Therefore, we studied the effects of the first- and second-generation O-arylcarbamate-based FAAH inhibitors, URB597 (cyclohexyl carbamic acid 3'-carbamoyl-3-yl ester) and URB694 (6-hydroxy-[1,1'-biphenyl]-3-yl-cyclohexylcarbamate), in squirrel monkeys. Both FAAH inhibitors: (1) blocked FAAH activity in brain and liver, increasing levels of endogenous ligands for cannabinoid and α-type peroxisome proliferator-activated (PPAR-α) receptors; (2) shifted nicotine self-administration dose-response functions in a manner consistent with reduced nicotine reward; (3) blocked reinstatement of nicotine seeking induced by reexposure to either nicotine priming or nicotine-associated cues; and (4) had no effect on cocaine or food self-administration. The effects of FAAH inhibition on nicotine self-administration and nicotine priming-induced reinstatement were reversed by the PPAR-α antagonist, MK886. Unlike URB597, which was not self-administered by monkeys in an earlier study, URB694 was self-administered at a moderate rate. URB694 self-administration was blocked by pretreatment with an antagonist for either PPAR-α (MK886) or cannabinoid CB1 receptors (rimonabant). In additional experiments in rats, URB694 was devoid of THC-like or nicotine-like interoceptive effects under drug-discrimination procedures, and neither of the FAAH inhibitors induced dopamine release in the nucleus accumbens shell--consistent with their lack of robust reinforcing effects in monkeys. Overall, both URB597 and URB694 show promise for the initialization and maintenance of smoking cessation because of their ability to block the rewarding effects of nicotine and prevent nicotine priming-induced and cue-induced reinstatement.

Age-related decline in striatal volume in rhesus monkeys: assessment of long-term calorie restriction.

Using magnetic resonance imaging (MRI), we measured striatal volume in 22 male rhesus monkeys undergoing calorie restriction (CR) for 11-13 years and 38 monkeys who were fed ad libitum (CON). CR delays the onset of many age-related processes, and this study tested whether it would alter the age-related decline in striatal volume. The CON and CR groups were sub-divided into middle age (less than 24 years old) and old age groups. Contrary to expectation, volumes of the putamen (not the caudate nucleus) were larger bilaterally in the CON than in the CR group both at middle age and senescence. Regression analysis (region volume versus age) indicated bilateral age-related declines in putamen and caudate nucleus volumes in the old CON monkeys, but only for the putamen in the old CR monkeys. Because tests for slopes found no differences between the groups, the data do not establish an effect of CR. Further study, involving sequential imaging, is warranted in order to clarify the possible effects of CR on age-related changes in striatal volume.

5-substituted derivatives of 6-halogeno-3-((2-(S)-azetidinyl)methoxy)pyridine and 6-halogeno-3-((2-(S)-pyrrolidinyl)methoxy)pyridine with low picomolar affinity for alpha4beta2 nicotinic acetylcholine receptor and wide range of lipophilicity: potential probes for imaging with positron emission tomography.

Potential positron emission tomography (PET) ligands with low picomolar affinity at the nicotinic acetylcholine receptor (nAChR) and with lipophilicity (log D) ranging from -1.6 to +1.5 have been synthesized. Most members of the series, which are derivatives of 5-substituted-6-halogeno-A-85380, exhibited a higher binding affinity at alpha4beta2-nAChRs than epibatidine. An analysis, by molecular modeling, revealed an important role of the orientation of the additional heterocyclic ring on the binding affinity of the ligands with nAChRs. The existing nicotinic pharmacophore models do not accommodate this finding. Two compounds of the series, 6-[(18)F]fluoro-5-(pyridin-3-yl)-A-85380 ([(18)F]31) and 6-chloro-3-((2-(S)-azetidinyl)methoxy)-5-(2-[(18)F]fluoropyridin-5-yl)pyridine) ([(18)F]35), were radiolabeled with (18)F. Comparison of PET data for [(18)F]31 and 2-[(18)F]FA shows the influence of lipophilicity on the binding potential. Our recent PET studies with [(18)F]35 demonstrated that its binding potential values in Rhesus monkey brain were ca. 2.5 times those of 2-[(18)F]FA. Therefore, [(18)F]35 and several other members of the series, when radiolabeled, will be suitable for quantitative imaging of extrathalamic nAChRs.

Abstinence from cocaine and sucrose self-administration reveals altered mesocorticolimbic circuit connectivity by resting state MRI.

Previous preclinical studies have emphasized that drugs of abuse, through actions within and between mesocorticolimbic (MCL) regions, usurp learning and memory processes normally involved in the pursuit of natural rewards. To distinguish MCL circuit pathobiological neuroadaptations that accompany addiction from general learning processes associated with natural reward, we trained two groups of rats to self-administer either cocaine (IV) or sucrose (orally) followed by an identically enforced 30 day abstinence period. These procedures are known to induce behavioral changes and neuroadaptations. A third group of sedentary animals served as a negative control group for general handling effects. We examined low-frequency spontaneous fluctuations in the functional magnetic resonance imaging (fMRI) signal, known as resting-state functional connectivity (rsFC), as a measure of intrinsic neurobiological interactions between brain regions. Decreased rsFC was seen in the cocaine-SA compared with both sucrose-SA and housing control groups between prelimbic (PrL) cortex and entopeduncular nucleus and between nucleus accumbens core (AcbC) and dorsomedial prefrontal cortex (dmPFC). Moreover, individual differences in cocaine SA escalation predicted connectivity strength only in the Acb-dmPFC circuit. These data provide evidence of fronto-striatal plasticity across the addiction trajectory, which are consistent with Acb-PFC hypoactivity seen in abstinent human drug addicts, indicating potential circuit level biomarkers that may inform therapeutic interventions. They further suggest that available data from cross-sectional human studies may reflect the consequence of rather a predispositional predecessor to their dependence.

The effect of volume of interest definition on quantification of lymph node immune response to a monkeypox virus infection assessed by (18)F-FDG-PET.

BACKGROUND: 2-deoxy-2-[(18)F]fluoro-D-glucose-positron emission tomography ((18)F-FDG-PET) is applied in the clinic for infection assessment and is under consideration for investigating the inflammatory/immune response in lymphoid tissue in animal models of viral infection. Assessing changes in (18)F-FDG uptake of lymph nodes (LNs), primary lymphoid tissues targeted during viral infection, requires suitable methods for image analysis. Similar to tumor evaluation, reliable quantitation of the LN function via multiple (18)F-FDG-PET sessions will depend how the volume of interest is defined. Volume of interest definition has a direct effect on statistical outcome. The current study objective is to compare for the first time agreement between conventional and modified VOI metrics to determine which method(s) provide(s) reproducible standardized uptake values (SUVs) for (18)F-FDG uptake in the LN of rhesus macaques. METHODS: Multiple (18)F-FDG-PET images of LNs in macaques were acquired prior to and after monkeypox virus intravenous inoculation. We compared five image analysis approaches, SUVmax, SUVmean, SUVthreshold, modified SUVthreshold, and SUVfixed volume, to investigate the impact of these approaches on quantification of the changes in LN metabolic activity denoting the immune response during viral infection progression. RESULTS: The lowest data repeatability was observed with SUVmax. The best correspondence was between SUVfixed volume and conventional and modified SUVthreshold. A statistically significant difference in the LN (18)F-FDG uptake between surviving and moribund animals was shown using modified SUVthreshold and SUVfixed volume (adjusted p = 0.0037 and p = 0.0001, respectively). CONCLUSIONS: Quantification of the LN (18)F-FDG uptake is highly sensitive to the method applied for PET image analysis. SUVfixed volume and modified SUVthreshold demonstrate better reproducibility for SUV estimates than SUVmax, SUVmean, and SUVthreshold. SUVfixed volume and modified SUVthreshold are capable of distinguishing between groups with different disease outcomes. Therefore, these methods are the preferred approaches for evaluating the LN function during viral infection by (18)F-FDG-PET. Validation of multiple approaches is necessary to choose a suitable method to monitor changes in LN metabolic activity during progression of viral infection.