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Frankle WG, Narendran R, Wood AT, Suto F, Himes ML, Kobayashi M, Ohno T, Yamauchi A, Mitsui K, Duffy K, Bruce M. Brain translocator protein occupancy by ONO-2952 in healthy adults: A Phase 1 PET study using [11C]PBR28. Synapse 2017; 71. [DOI: 10.1002/syn.21970] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Revised: 02/10/2017] [Accepted: 02/22/2017] [Indexed: 11/12/2022]
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Anand V, Narendran R. Characteristics of recursive backstepping algorithm and active damping of oscillations in feedback linearization for electromechanical system with extended stability analysis and perturbation rejection. ISA TRANSACTIONS 2016; 64:365-372. [PMID: 27346332 DOI: 10.1016/j.isatra.2016.06.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2016] [Accepted: 06/07/2016] [Indexed: 06/06/2023]
Abstract
In this paper, a technique for estimation of state variables and control of a class of electromechanical system is proposed. Initially, an attempt is made on rudimentary pole placement technique for the control of rotor position and angular velocity profiles of Permanent Magnet Stepper Motor. Later, an alternative approach is analyzed using feedback linearization method to reduce the error in tracking performances. A damping control scheme was additionally incorporated into the feedback linearization system in order to nullify the persistent oscillations present in the system. Furthermore, a robust backstepping controller with high efficacy is put forth to enhance the overall performance and to carry out disturbance rejection. The predominant advantage of this control technique is that it does not require the DQ Transformation of the motor dynamics. A Lyapunov candidate was employed to ensure global asymptotical stability criterion. Also, a nonlinear observer is presented to estimate the unknown states namely load torque and rotor angular velocity, even under load uncertainty conditions. Finally, the performances of all the aforementioned control schemes and estimation techniques are compared and analyzed extensively through simulation.
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Krystal JH, Abi-Dargham A, Akbarian S, Arnsten AFT, Barch DM, Bearden CE, Braff DL, Brown ES, Bullmore ET, Carlezon WA, Carter CS, Cook EH, Daskalakis ZJ, DiLeone RJ, Duman RS, Grace AA, Hariri AR, Harrison PJ, Hiroi N, Kenny PJ, Kleinman JE, Krystal AD, Lewis DA, Lipska BK, Marder SR, Mason GF, Mathalon DH, McClung CA, McDougle CJ, McIntosh AM, McMahon FJ, Mirnics K, Monteggia LM, Narendran R, Nestler EJ, Neumeister A, O’Donovan MC, Öngür D, Pariante CM, Paulus MP, Pearlson G, Phillips ML, Pine DS, Pizzagalli DA, Pletnikov MV, Ragland JD, Rapoport JL, Ressler KJ, Russo SJ, Sanacora G, Sawa A, Schatzberg AF, Shaham Y, Shamay-Tsoory SG, Sklar P, State MW, Stein MB, Strakowski SM, Taylor SF, Turecki G, Turetsky BI, Weissman MM, Zachariou V, Zarate CA, Zubieta JK. Constance E. Lieber, Theodore R. Stanley, and the Enduring Impact of Philanthropy on Psychiatry Research. Biol Psychiatry 2016; 80:84-86. [PMID: 27346079 PMCID: PMC6150945 DOI: 10.1016/j.biopsych.2016.05.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Revised: 05/09/2016] [Accepted: 05/09/2016] [Indexed: 10/21/2022]
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Narendran R, Tumuluru D, May MA, Chowdari KV, Himes ML, Fasenmyer K, Frankle WG, Nimgaonkar VL. Cortical Dopamine Transmission as Measured with the [11C]FLB 457 - Amphetamine PET Imaging Paradigm Is Not Influenced by COMT Genotype. PLoS One 2016; 11:e0157867. [PMID: 27322568 PMCID: PMC4913897 DOI: 10.1371/journal.pone.0157867] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2016] [Accepted: 06/06/2016] [Indexed: 11/18/2022] Open
Abstract
Basic investigations link a Val158Met polymorphism (rs4680) in the catechol-O-methyltransferase (COMT) gene to not only its enzymatic activity, but also to its dopaminergic tone in the prefrontal cortex. Previous PET studies have documented the relationship between COMT Val158Met polymorphism and D1 and D2/3 receptor binding potential (BP), and interpreted them in terms of dopaminergic tone. The use of baseline dopamine D1 and D2/3 receptor binding potential (BPND) as a proxy for dopaminergic tone is problematic because they reflect both endogenous dopamine levels (a change in radiotracer's apparent affinity) and receptor density. In this analysis of 31 healthy controls genotyped for the Val158Met polymorphism (Val/Val, Val/Met, and Met/Met), we used amphetamine-induced displacement of [11C]FLB 457 as a direct measure of dopamine release. Our analysis failed to show a relationship between COMT genotype status and prefrontal cortical dopamine release. COMT genotype was also not predictive of baseline dopamine D2/3 receptor BPND.
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Weidner LD, Paris A, Frankle WG, Narendran R. Safety of Oral Amphetamine Administered during Positron Emission Tomography Scans in Medically Screened Humans. PLoS One 2015; 10:e0140647. [PMID: 26656737 PMCID: PMC4685985 DOI: 10.1371/journal.pone.0140647] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2015] [Accepted: 09/28/2015] [Indexed: 02/07/2023] Open
Abstract
Changes in endogenous dopamine levels can be detected in humans using positron emission tomography scans by measuring the amount by which a specific D2/3 radioligand is displaced. In some cases, a challenge drug such as amphetamine is introduced to increase the amount of dopamine released into the synaptic cleft. Although intravenous amphetamine is often utilized, oral amphetamine has been shown to be just as effective in increasing endogenous dopamine levels. Based on our own use of oral amphetamine as a challenge drug, we have retroactively reviewed our study charts to determine the cardiovascular safety of 0.5 mg kg-1 oral d-amphetamine. Of 172 amphetamine administrations in 144 individuals, only 2.8% of subjects experienced any transient adverse effects. In addition, we found no clinically relevant differences in increases of vital signs between healthy controls and patients. We therefore reaffirm the safety of 0.5 mg kg-1 oral amphetamine in subjects previously screened for cardiovascular risk factors.
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Frankle WG, Cho RY, Prasad KM, Mason NS, Paris J, Himes ML, Walker C, Lewis DA, Narendran R. In vivo measurement of GABA transmission in healthy subjects and schizophrenia patients. Am J Psychiatry 2015; 172:1148-59. [PMID: 26133962 PMCID: PMC5070491 DOI: 10.1176/appi.ajp.2015.14081031] [Citation(s) in RCA: 77] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVE Postmortem studies in schizophrenia reveal alterations in gene products that regulate the release and extracellular persistence of GABA. However, results of in vivo studies of schizophrenia measuring total tissue GABA with magnetic resonance spectroscopy (MRS) have been inconsistent. Neither the postmortem nor the MRS studies directly address the physiological properties of GABA neurotransmission. The present study addresses this question through an innovative positron emission tomography (PET) paradigm. METHOD The binding of [(11)C]flumazenil, a benzodiazepine-specific PET radiotracer, was measured before and after administration of tiagabine (0.2 mg/kg of body weight), a GABA membrane transporter (GAT1) blocker, in 17 off-medication patients with schizophrenia and 22 healthy comparison subjects. Increased extracellular GABA, through GAT1 blockade, enhances the affinity of GABAA receptors for benzodiazepine ligands, detected as an increase in [(11)C]flumazenil tissue distribution volume (VT). RESULTS [(11)C]Flumazenil VT was significantly increased across all cortical brain regions in the healthy comparison group but not in the schizophrenia group. This lack of effect was most prominent in the antipsychotic-naive schizophrenia group. In this subgroup, [(11)C]flumazenil ΔVT in the medial temporal lobe was correlated with positive symptoms, and baseline [(11)C]flumazenil VT in the medial temporal lobe was negatively correlated with visual learning. In the healthy comparison group but not the schizophrenia group, [(11)C]flumazenil ΔVT was positively associated with gamma-band oscillation power. CONCLUSIONS This study demonstrates, for the first time, an in vivo impairment in GABA transmission in schizophrenia, most prominent in antipsychotic-naive individuals. The impairment in GABA transmission appears to be linked to clinical symptoms, disturbances in cortical oscillations, and cognition.
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Slifstein M, van de Giessen E, Van Snellenberg J, Thompson JL, Narendran R, Gil R, Hackett E, Girgis R, Ojeil N, Moore H, D’Souza D, Malison RT, Huang Y, Lim KP, Nabulsi N, Carson RE, Lieberman JA, Abi-Dargham A. Deficits in prefrontal cortical and extrastriatal dopamine release in schizophrenia: a positron emission tomographic functional magnetic resonance imaging study. JAMA Psychiatry 2015; 72:316-24. [PMID: 25651194 PMCID: PMC4768742 DOI: 10.1001/jamapsychiatry.2014.2414] [Citation(s) in RCA: 259] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
IMPORTANCE Multiple lines of evidence suggest a deficit in dopamine release in the prefrontal cortex (PFC) in schizophrenia. Despite the prevalence of the concept of prefrontal cortical hypodopaminergia in schizophrenia, in vivo imaging of dopamine release in the PFC has not been possible until now, when the validity of using the positron emission tomographic D2/3 radiotracer carbon 11-labeled FLB457 in combination with the amphetamine paradigm was clearly established. OBJECTIVES To (1) test amphetamine-induced dopamine release in the dorsolateral PFC (DLPFC) in drug-free or drug-naive patients with schizophrenia (SCZ) and healthy control (HC) individuals matched for age, sex, race/ethnicity, and familial socioeconomic status;(2) test blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging activation during a working memory task in the same participants; and (3) examine the relationship between positron emission tomographic and functional magnetic resonance imaging outcome measures. DESIGN, SETTING AND PARTICIPANTS Positron emission tomographic imaging with carbon 11-labeled FLB457 before and following 0.5 mg/kg of amphetamine by mouth. Blood oxygenation level-dependent functional magnetic resonance imaging during the self-ordered working memory task. Twenty patients with schizophrenia recruited from the inpatient and outpatient research facilities at New York State Psychiatric Institute and 21 healthy control individuals participated, and data were acquired between June 16, 2011, and February 25, 2014. MAIN OUTCOMES AND MEASURE The percentage change in binding potential (∆BPND) in the DLPFC following amphetamine, BOLD activation during the self-ordered working memory task compared with the control task, and the correlation between these 2 outcome measures. RESULTS We observed significant differences in the effect of amphetamine on DLPFC BPND (mean [SD], ∆BPND in HC: -7.5% [11%]; SCZ: +1.8% [11%]; P = .01); a generalized blunting in dopamine release in SCZ involving most extrastriatal regions and the midbrain; and a significant association between ∆BPND and BOLD activation in the DLPFC in the overall sample including patients with SCZ and HC individuals. CONCLUSIONS AND RELEVANCE To our knowledge, these results provide the first in vivo evidence for a deficit in the capacity for dopamine release in the DLPFC in SCZ and suggest a more widespread deficit extending to many cortical and extrastriatal regions including the midbrain. This contrasts with the well-replicated excess in dopamine release in the associative striatum in SCZ and suggests a differential regulation of striatal dopamine release in associative striatum vs extrastriatal regions. Furthermore, dopamine release in the DLPFC relates to working memory-related activation of this region, suggesting that blunted release may affect frontal cortical function.
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Narendran R, Jedema HP, Lopresti BJ, Mason NS, Himes ML, Bradberry CW. Decreased vesicular monoamine transporter type 2 availability in the striatum following chronic cocaine self-administration in nonhuman primates. Biol Psychiatry 2015; 77:488-92. [PMID: 25062684 PMCID: PMC4275417 DOI: 10.1016/j.biopsych.2014.06.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Revised: 05/13/2014] [Accepted: 06/11/2014] [Indexed: 12/16/2022]
Abstract
BACKGROUND Consistent with postmortem data, in a recent positron emission tomography study, we demonstrated less [(11)C]-(+)-dihydrotetrabenazine ([(11)C]DTBZ) binding to striatal vesicular monoamine transporter type 2 (VMAT2) in cocaine abusers compared with control subjects. A major limitation of these between-group comparison human studies is their inability to establish a causal relationship between cocaine abuse and lower VMAT2. Furthermore, studies in rodents that evaluated VMAT2 binding before and after cocaine self-administration do not support a reduction in VMAT2. METHODS To clarify these discrepant VMAT2 findings and attribute VMAT2 reduction to cocaine abuse, we imaged four rhesus monkeys with [(11)C]DTBZ positron emission tomography before and after 16 months of cocaine self-administration. [(11)C]DTBZ binding potential in the striatum was derived using the simplified reference tissue method with the occipital cortex time activity curve as an input function. RESULTS Chronic cocaine self-administration led to a significant (25.8 ± 7.8%) reduction in [(11)C]DTBZ binding potential. CONCLUSIONS In contrast to the cocaine rodent investigations that do not support alterations in VMAT2, these results in nonhuman primates clearly demonstrated a reduction in VMAT2 binding following prolonged exposure to cocaine. Lower VMAT2 implies that fewer dopamine storage vesicles are available in the presynaptic terminals for release, a likely factor contributing to decreased dopamine transmission in cocaine dependence. Future studies should attempt to clarify the clinical significance of lower VMAT2 in cocaine abusers, for example, its relationship to relapse and vulnerability to mood disorders.
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Narendran R, Mason NS, Paris J, Himes ML, Douaihy AB, Frankle WG. Decreased prefrontal cortical dopamine transmission in alcoholism. Am J Psychiatry 2014; 171:881-8. [PMID: 24874293 PMCID: PMC4119559 DOI: 10.1176/appi.ajp.2014.13121581] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
OBJECTIVE Basic studies have demonstrated that optimal levels of prefrontal cortical dopamine are critical to various executive functions such as working memory, attention, inhibitory control, and risk/reward decisions, all of which are impaired in addictive disorders such as alcoholism. Based on this and imaging studies of alcoholism that have demonstrated less dopamine in the striatum, the authors hypothesized decreased dopamine transmission in the prefrontal cortex in persons with alcohol dependence. METHOD To test this hypothesis, amphetamine and [11C]FLB 457 positron emission tomography were used to measure cortical dopamine transmission in 21 recently abstinent persons with alcohol dependence and 21 matched healthy comparison subjects. [11C]FLB 457 binding potential, specific compared to nondisplaceable uptake (BPND), was measured in subjects with kinetic analysis using the arterial input function both before and after 0.5 mg kg-1 of d-amphetamine. RESULTS Amphetamine-induced displacement of [11C]FLB 457 binding potential (ΔBPND) was significantly smaller in the cortical regions in the alcohol-dependent group compared with the healthy comparison group. Cortical regions that demonstrated lower dopamine transmission in the alcohol-dependent group included the dorsolateral prefrontal cortex, medial prefrontal cortex, orbital frontal cortex, temporal cortex, and medial temporal lobe. CONCLUSIONS The results of this study, for the first time, unambiguously demonstrate decreased dopamine transmission in the cortex in alcoholism. Further research is necessary to understand the clinical relevance of decreased cortical dopamine as to whether it is related to impaired executive function, relapse, and outcome in alcoholism.
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Jedema HP, Narendran R, Bradberry CW. Amphetamine-induced release of dopamine in primate prefrontal cortex and striatum: striking differences in magnitude and timecourse. J Neurochem 2014; 130:490-7. [PMID: 24749782 DOI: 10.1111/jnc.12743] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2014] [Revised: 04/08/2014] [Accepted: 04/10/2014] [Indexed: 01/18/2023]
Abstract
The psychostimulant amphetamine (AMPH) is frequently used to increase catecholamine levels in attention disorders and positron emission tomography imaging studies. Despite the fact that most radiotracers for positron emission tomography studies are characterized in non-human primates (NHPs), data on regional differences of the effect of AMPH in NHPs are very limited. This study examined the impact of AMPH on extracellular dopamine (DA) levels in the medial prefrontal cortex and the caudate of NHPs using microdialysis. In addition to differences in magnitude, we observed striking differences in the temporal profile of extracellular DA levels between these regions that can likely be attributed to differences in the regulation of dopamine uptake and biosynthesis. The present data suggest that cortical DA levels may remain elevated longer than in the caudate which may contribute to the clinical profile of the actions of AMPH. Using microdialysis probes implanted in the cortex and caudate region of non-human primate brains, we observed in vivo differences in the magnitude and temporal profile of extracellular dopamine levels in response to intravenous amphetamine administration.
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Forbes EE, Rodriguez EE, Musselman S, Narendran R. Prefrontal response and frontostriatal functional connectivity to monetary reward in abstinent alcohol-dependent young adults. PLoS One 2014; 9:e94640. [PMID: 24804780 PMCID: PMC4012954 DOI: 10.1371/journal.pone.0094640] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Accepted: 03/17/2014] [Indexed: 11/19/2022] Open
Abstract
Although altered function in neural reward circuitry is widely proposed in models of addiction, more recent conceptual views have emphasized the role of disrupted response in prefrontal regions. Changes in regions such as the orbitofrontal cortex, medial prefrontal cortex, and dorsolateral prefrontal cortex are postulated to contribute to the compulsivity, impulsivity, and altered executive function that are central to addiction. In addition, few studies have examined function in these regions during young adulthood, when exposure is less chronic than in typical samples of alcohol-dependent adults. To address these issues, we examined neural response and functional connectivity during monetary reward in 24 adults with alcohol dependence and 24 psychiatrically healthy adults. Adults with alcohol dependence exhibited less response to the receipt of monetary reward in a set of prefrontal regions including the medial prefrontal cortex, lateral orbitofrontal cortex, and dorsolateral prefrontal cortex. Adults with alcohol dependence also exhibited greater negative correlation between function in each of these regions and that in the nucleus accumbens. Within the alcohol-dependent group, those with family history of alcohol dependence exhibited lower mPFC response, and those with more frequent drinking exhibited greater negative functional connectivity between the mPFC and the nucleus accumbens. These findings indicate that alcohol dependence is associated with less engagement of prefrontal cortical regions, suggesting weak or disrupted regulation of ventral striatal response. This pattern of prefrontal response and frontostriatal connectivity has consequences for the behavior patterns typical of addiction. Furthermore, brain-behavior findings indicate that the potential mechanisms of disruption in frontostriatal circuitry in alcohol dependence include family liability to alcohol use problems and more frequent use of alcohol. In all, these findings build on the extant literature on reward-circuit function in addiction and suggest mechanisms for disrupted function in alcohol dependence.
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Narendran R, Jedema HP, Lopresti BJ, Mason NS, Gurnsey K, Ruszkiewicz J, Chen CM, Deuitch L, Frankle WG, Bradberry CW. Imaging dopamine transmission in the frontal cortex: a simultaneous microdialysis and [11C]FLB 457 PET study. Mol Psychiatry 2014; 19:302-10. [PMID: 23439486 PMCID: PMC3706503 DOI: 10.1038/mp.2013.9] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/18/2012] [Revised: 12/14/2012] [Accepted: 01/02/2013] [Indexed: 12/25/2022]
Abstract
In a recent human positron emission tomography (PET) study we demonstrated the ability to detect amphetamine-induced dopamine (DA) release in the prefrontal cortex as a reduction in the binding of the DA D(2/3) radioligand [(11)C]FLB 457. A key requirement for validating this paradigm for use in clinical studies is demonstrating that the changes in [(11)C]FLB 457 binding observed with PET following amphetamine are related to changes in dialysate DA concentration as measured with microdialysis. Microdialysis and PET experiments were performed to compare, in five rhesus monkeys, amphetamine-induced DA release and [(11)C]FLB 457 displacement in the frontal cortex after three doses of amphetamine (0.3 mg kg(-1), 0.5 mg kg(-1) and 1.0 mg kg(-1)). Amphetamine led to a significant dose-dependent increase in dialysate (0.3 mg kg(-1): 999±287%; 0.5 mg kg(-1): 1320±432%; 1.0 mg kg(-1): 2355±1026%) as measured with microdialysis and decrease in [(11)C]FLB 457 binding potential (BP(ND), 0.3 mg kg(-1): -6±6%; 0.5 mg kg(-1): -16±4%; 1.0 mg kg(-1): -24±2%) as measured with PET. The relationship between amphetamine-induced peak ΔDA and Δ[(11)C]FLB 457 BP(ND) in the frontal cortex was linear. The results of this study clearly demonstrate that the magnitude of dialysate DA release is correlated with the magnitude of the reduction in [(11)C]FLB 457 BP(ND) in the frontal cortex. The use of the [(11)C]FLB 457-amphetamine imaging paradigm in humans should allow for characterization of prefrontal cortical DA release in neuropsychiatric disorders such as schizophrenia and addiction.
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Narendran R, Frankle WG, Mason NS, Muldoon MF, Moghaddam B. Improved working memory but no effect on striatal vesicular monoamine transporter type 2 after omega-3 polyunsaturated fatty acid supplementation. PLoS One 2012; 7:e46832. [PMID: 23056476 PMCID: PMC3463539 DOI: 10.1371/journal.pone.0046832] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Accepted: 09/06/2012] [Indexed: 12/04/2022] Open
Abstract
Studies in rodents indicate that diets deficient in omega-3 polyunsaturated fatty acids (n–3 PUFA) lower dopamine neurotransmission as measured by striatal vesicular monoamine transporter type 2 (VMAT2) density and amphetamine-induced dopamine release. This suggests that dietary supplementation with fish oil might increase VMAT2 availability, enhance dopamine storage and release, and improve dopamine-dependent cognitive functions such as working memory. To investigate this mechanism in humans, positron emission tomography (PET) was used to measure VMAT2 availability pre- and post-supplementation of n–3 PUFA in healthy individuals. Healthy young adult subjects were scanned with PET using [11C]-(+)-α-dihydrotetrabenzine (DTBZ) before and after six months of n–3 PUFA supplementation (Lovaza, 2 g/day containing docosahexaenonic acid, DHA 750 mg/d and eicosapentaenoic acid, EPA 930 mg/d). In addition, subjects underwent a working memory task (n-back) and red blood cell membrane (RBC) fatty acid composition analysis pre- and post-supplementation. RBC analysis showed a significant increase in both DHA and EPA post-supplementation. In contrast, no significant change in [11C]DTBZ binding potential (BPND) in striatum and its subdivisions were observed after supplementation with n–3 PUFA. No correlation was evident between n–3 PUFA induced change in RBC DHA or EPA levels and change in [11C]DTBZ BPND in striatal subdivisions. However, pre-supplementation RBC DHA levels was predictive of baseline performance (i.e., adjusted hit rate, AHR on 3-back) on the n-back task (y = 0.19+0.07, r2 = 0.55, p = 0.009). In addition, subjects AHR performance improved on 3-back post-supplementation (pre 0.65±0.27, post 0.80±0.15, p = 0.04). The correlation between n-back performance, and DHA levels are consistent with reports in which higher DHA levels is related to improved cognitive performance. However, the lack of change in [11C]DBTZ BPND indicates that striatal VMAT2 regulation is not the mechanism of action by which n–3 PUFA improves cognitive performance.
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Huang Y, Narendran R, Bischoff F, Guo N, Bae SA, Hwang DR, Lesage AS, Laruelle M. Synthesis and characterization of two PET radioligands for the metabotropic glutamate 1 (mGlu1) receptor. Synapse 2012; 66:1002-14. [PMID: 22927303 DOI: 10.1002/syn.21606] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2012] [Accepted: 08/20/2012] [Indexed: 11/09/2022]
Abstract
The metabotropic glutamate 1 receptor (mGlu1) is an important protein in the regulation of glutamate transmission in the brain, and believed to be involved in disorders such as ischemia, epilepsy, neuropathic pain, anxiety, and schizophrenia. The goal of this study was to evaluate two selective mGlu1 antagonists [(11) C]3 and [(18) F]4 as potential PET radioligands for the in vivo imaging of the mGlu1 receptor. Biodistribution studies in rats indicated high uptake of [(11) C]3 and [(18) F]4 in the brain. The highest activity level was found in the cerebellum, followed by striatum, hippocampus, frontal cortex, and medulla, in a pattern consistent with the distribution of mGlu1 receptor in rat. At 30 min postinjection, the activity ratio of cerebellum to medulla was 4.5 for [(11) C]3, indicating a high degree of specific binding, while specific binding was lower for [(18) F]4 (cerebellum to medulla activity ratio of 2.0). Moreover, binding of the radioligands [(11) C]3 and [(18) F]4 in mGlu1 receptor-rich region such as cerebellum was blocked by pretreatment of the rats with their respective unlabeled compound or the selective mGlu1 antagonist (compound 5, 2 mg/kg each), but not by the selective mGlu2 antagonist LY341495, or the selective mGlu5 antagonist MPEP (2 mg/kg), thus indicating the binding specificity and selectivity of [(11) C]3 and [(18) F]4 to the mGlu1 receptor. However, in imaging experiments in baboons [(11) C]3 displayed a small specific binding signal only in the cerebellum, while the specific binding of [(18) F]4 was difficult to detect. Species differences in receptor density and affinity of the radioligands in large part account for the differences in the behavior of [(11) C]3 and [(18) F]4 in rats and baboons. Radioligands with higher affinity and/or lower lipophilicity are needed to successfully image the mGlu1 receptor in humans.
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Laymon CM, Narendran R, Mason NS, Carney JP, Lopresti BJ, Mathis CA, Mountz JM, Sashin D, Frankle WG. Human biodistribution and dosimetry of the PET radioligand [¹¹C]flumazenil (FMZ). Mol Imaging Biol 2012; 14:115-22. [PMID: 21365327 DOI: 10.1007/s11307-011-0478-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
PURPOSE We measure the whole-body distribution of IV injected [¹¹C]Flumazenil (FMZ) as a function of time in adult subjects and determine the absorbed radiation doses. PROCEDURES After injection with 770 MBq of [¹¹C]FMZ (nominal), each of six subjects underwent nine consecutive whole body PET scans. Twelve source organs were identified using PET attenuation and emission images. Activity within each organ as a function of time was determined from the sequence of the nine PET scans. Source organ time activity curves were integrated and normalized by the injected dose to yield source organ residence times for the no voiding situation. Separate bladder residence-time calculations were performed for the cases of a 1- and a 2-h voiding interval. Using the source organ residence times as input, the program OLINDA/EXM (Stabin et al. in J Nucl Med. 46:1023-1027, 2005) was used to perform dosimetry calculations for the various body organs and for the whole body. RESULTS For the no voiding situation, the average whole-body radiation equivalent dose was 3.02 × 10⁻³ mSv/MBq of injected [¹¹C]FMZ. The average effective dose and effective dose equivalent was 7.57 × 10⁻³ and 1.12 × 10⁻² mSv MBq⁻¹, respectively. The organ receiving the highest equivalent dose was the urinary bladder wall with an average of 6.32 × 10⁻² mSv MBq⁻¹. CONCLUSION On average, the administration of less than 790 MBq (21 mCi) of [¹¹C]FMZ yields (no voiding model) an organ equivalent dose of under 50 mSv [the single dose limit for research studies under US regulations (21CFR361.1) to body organs other than blood forming organs, gonads or the lens of the eye] to all organs. Equivalent dose to the blood forming organs and gonads from a 790 MBq administered FMZ dose is well under the 30 mSv limit provided under 21CFR361.1. Additionally, administration of less than 1320 MBq (35.7 mCi) yields an effective dose [International Commission on Radiation Protection (ICRP) 60 tissue weighting scheme] of under 10 mSv, which is the ICRP IIb (minor to intermediate) risk category limit.
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Narendran R, Martinez D, Mason NS, Lopresti BJ, Himes ML, Chen CM, May MA, Price JC, Mathis CA, Frankle WG. Imaging of dopamine D2/3 agonist binding in cocaine dependence: a [11C]NPA positron emission tomography study. Synapse 2012; 65:1344-9. [PMID: 21780185 DOI: 10.1002/syn.20970] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
OBJECTIVE Positron emission tomography (PET) studies performed with [(11) C]raclopride have consistently reported lower binding to D(2/3) receptors and lower amphetamine-induced dopamine (DA) release in cocaine abusers relative to healthy controls. A limitation of these studies that were performed with D(2/3) antagonist radiotracers such as [(11) C]raclopride is the failure to provide information that is specific to D(2/3) receptors configured in a state of high affinity for the agonists (i.e., D(2/3) receptors coupled to G-proteins, D(2/3 HIGH) ). As the endogenous agonist DA binds with preference to D(2/3 HIGH) relative to D(2/3 LOW) receptors (i.e., D(2/3) receptors uncoupled to G-proteins) it is critical to understand the in vivo status of D(2/3 HIGH) receptors in cocaine dependence. Thus, we measured the available fraction of D(2/3) (HIGH) receptors in 10 recently abstinent cocaine abusers (CD) and matched healthy controls (HC) with the D(2/3) antagonist and agonist PET radiotracers [(11) C]raclopride and [(11) C]NPA. METHODS [(11) C]raclopride and [(11) C]NPA binding potential (BP) (BP(ND) ) in the striatum were measured with kinetic analysis using the arterial input function. The available fraction of D(2/3 HIGH) receptors, i.e., % R(HIGH) available = D(2/3 HIGH) /(D(2/3 HIGH) + D(2/3 LOW) ) was then computed as the ratio of [(11) C]NPA BP(ND) /[(11) C]raclopride BP(ND) . RESULTS No differences in striatal [(11) C]NPA BP(ND) (HC = 1.00 ± 0.17; CD = 0.97 ± 0.17, P = 0.67) or available % R(HIGH) (HC = 39% ± 5%; CD = 41% ± 5%, P = 0.50) was observed between cocaine abusers and matched controls. CONCLUSIONS The results of this [(11) C]NPA PET study do not support alterations in D(2/3 HIGH) binding in the striatum in cocaine dependence.
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Bailer UF, Narendran R, Frankle WG, Himes ML, Duvvuri V, Mathis CA, Kaye WH. Amphetamine induced dopamine release increases anxiety in individuals recovered from anorexia nervosa. Int J Eat Disord 2012; 45:263-71. [PMID: 21541980 PMCID: PMC3151352 DOI: 10.1002/eat.20937] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 03/13/2011] [Indexed: 11/11/2022]
Abstract
OBJECTIVE Genetic, pharmacologic, and physiological data suggest that individuals with anorexia nervosa (AN) have altered striatal dopamine (DA) function. METHOD We used an amphetamine challenge and positron emission tomography [(11) C]raclopride paradigm to explore DA striatal transmission in 10 recovered (REC) AN compared with 9 control women (CW). RESULTS REC AN and CW were similar for baseline, postamphetamine [(11) C]raclopride binding potential (BP(ND) ) and change (Δ) in BP(ND) for all regions. In CW, ventral striatum Δ BP(ND) was associated with euphoria (r = -0.76; p = 0.03), which was not found for REC AN. Instead, REC AN showed a significant relationship between anxiety and Δ BP(ND) in the precommissural dorsal caudate (r = -0.62, p = 0.05). DISCUSSION REC AN have a positive association between endogenous DA release and anxiety in the dorsal caudate. This finding could explain why food-related DA release produces anxiety in AN, whereas feeding is pleasurable in healthy participants.
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Frankle WG, Cho RY, Mason NS, Chen CM, Himes M, Walker C, Lewis DA, Mathis CA, Narendran R. [11C]flumazenil binding is increased in a dose-dependent manner with tiagabine-induced elevations in GABA levels. PLoS One 2012; 7:e32443. [PMID: 22384252 PMCID: PMC3288104 DOI: 10.1371/journal.pone.0032443] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2011] [Accepted: 01/26/2012] [Indexed: 01/14/2023] Open
Abstract
Evidence indicates that synchronization of cortical activity at gamma-band frequencies, mediated through GABA-A receptors, is important for perceptual/cognitive processes. To study GABA signaling in vivo, we recently used a novel positron emission tomography (PET) paradigm measuring the change in binding of the benzodiazepine (BDZ) site radiotracer [11C]flumazenil associated with increases in extracellular GABA induced via GABA membrane transporter (GAT1) blockade with tiagabine. GAT1 blockade resulted in significant increases in [11C]flumazenil binding potential (BPND) over baseline in the major functional domains of the cortex, consistent with preclinical studies showing that increased GABA levels enhance the affinity of GABA-A receptors for BDZ ligands. In the current study we sought to replicate our previous results and to further validate this approach by demonstrating that the magnitude of increase in [11C]flumazenil binding observed with PET is directly correlated with tiagabine dose. [11C]flumazenil distribution volume (VT) was measured in 18 healthy volunteers before and after GAT1 blockade with tiagabine. Two dose groups were studied (n = 9 per group; Group I: tiagabine 0.15 mg/kg; Group II: tiagabine 0.25 mg/kg). GAT1 blockade resulted in increases in mean (± SD) [11C]flumazenil VT in Group II in association cortices (6.8±0.8 mL g−1 vs. 7.3±0.4 mL g−1;p = 0.03), sensory cortices (6.7±0.8 mL g−1 vs. 7.3±0.5 mL g−1;p = 0.02) and limbic regions (5.2±0.6 mL g−1 vs. 5.7±0.3 mL g−1;p = 0.03). No change was observed at the low dose (Group I). Increased orbital frontal cortex binding of [11C]flumazenil in Group II correlated with the ability to entrain cortical networks (r = 0.67, p = 0.05) measured via EEG during a cognitive control task. These data provide a replication of our previous study demonstrating the ability to measure in vivo, with PET, acute shifts in extracellular GABA.
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Narendran R, Lopresti BJ, Martinez D, Mason NS, Himes M, May MA, Daley DC, Price JC, Mathis CA, Frankle WG. In vivo evidence for low striatal vesicular monoamine transporter 2 (VMAT2) availability in cocaine abusers. Am J Psychiatry 2012; 169:55-63. [PMID: 22193525 PMCID: PMC3405490 DOI: 10.1176/appi.ajp.2011.11010126] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVE Positron emission tomography (PET) imaging studies in cocaine abusers have shown that low dopamine release in the striatum following an amphetamine challenge is associated with higher relapse rates. One possible mechanism that might lead to lower amphetamine-induced dopamine release is low availability of dopamine storage vesicles in the presynaptic terminals for release. Consistent with this hypothesis, postmortem studies have shown low levels of vesicular monoamine transporter, type 2 (VMAT2), the membrane protein that regulates the size of the vesicular dopamine pool, in cocaine abusers relative to healthy subjects. To confirm the postmortem findings, the authors used PET and the VMAT2 radioligand [¹¹C]-(+)-dihydrotetrabenazine (DTBZ) to assess the in vivo VMAT2 availability in a group of 12 recently abstinent cocaine-dependent subjects and matched healthy comparison subjects. METHOD [¹¹C]DTBZ nondisplaceable binding potential (BP(ND)) was measured by kinetic analysis using the arterial input function or, if arterial input was unavailable, by the simplified reference tissue method. RESULTS [¹¹C]DTBZ BP(ND) was significantly lower in the cocaine abusers than in the comparison subjects in the limbic striatum (10.0% lower), associative striatum (-13.4%), and sensorimotor striatum (-11.5%). CONCLUSIONS The results of this in vivo PET study confirm previous in vitro reports of low VMAT2 availability in the striatum of cocaine abusers. It also suggests a compensatory down-regulation of the dopamine storage vesicles in response to chronic cocaine abuse and/or a loss of dopaminergic terminals. Further research is necessary to understand the clinical relevance of this observation to relapse and outcome in abstinent cocaine abusers.
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Narendran R, Mason NS, Chen CM, Himes M, Keating P, May MA, Rabiner EA, Laruelle M, Mathis CA, Frankle WG. Evaluation of dopamine D₂/₃ specific binding in the cerebellum for the positron emission tomography radiotracer [¹¹C]FLB 457: implications for measuring cortical dopamine release. Synapse 2011; 65:991-7. [PMID: 21360596 DOI: 10.1002/syn.20926] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2011] [Revised: 02/03/2011] [Accepted: 02/04/2011] [Indexed: 11/06/2022]
Abstract
In a recent positron emission tomography (PET) study, we demonstrated the ability to measure amphetamine-induced dopamine (DA) release in the human cortex with the DA D₂/₃ radioligand [¹¹C]FLB 457. As previous studies in animals have shown that a relatively high fraction of the [¹¹C]FLB 457 signal in the cerebellum represents specific binding to D₂/₃ receptors, there was concern that the use of the cerebellum as a measure of nonspecific binding (i.e., reference region) to derive [¹¹C]FLB 457 binding potential (BP) (BP(ND) ) would bias cortical DA release measurements. Thus, we evaluated the fractional contribution of specific binding to D₂/₃ receptors in the human cerebellum for [¹¹C]FLB 457. Six healthy human subjects (5M/1F) were studied twice with [¹¹C]FLB 457, once at baseline and again following a single oral dose of 15 mg of aripiprazole, a D₂/₃ partial agonist. [¹¹C]FLB 457 distribution volume (V(T) ) was estimated using kinetic analysis in the cortical regions of interest and potential reference regions. The change in [¹¹C]FLB 457 V(T) following aripiprazole ranged from -33 to -42% in the cortical regions of interest (ROIs). The aripiprazole-induced change in [¹¹C]FLB 457 V(T) in three potential reference regions suggests significant specific binding the cerebellum (CER, -17 ± 12%), but not pons (PON, -10 ± 10%) and centrum semiovale (CESVL, -3 ± 12%). Nevertheless, a reanalysis of the published [¹¹C]FLB 457 test-retest and amphetamine studies suggests that the use of the PON V(T) and CESVL V(T) as an estimate of nonspecific binding to derive [¹¹C]FLB 457 BP(ND) in DA release studies is unlikely to be successful because it leads to less reproducible outcome measures, which in turn diminishes the ability to measure DA release in the cortex. D₂/₃ blocking studies with aripiprazole and [¹¹C]FLB 457 suggest specific binding to D₂/₃ receptors in the cerebellum. These data also suggest that the contribution of specific binding to D₂/₃ receptors in the cerebellum is lower than that in the cortical ROIs and that CER V(T) is mostly representative of nonspecific binding. Nevertheless, caution is advised when using reference tissue methods that rely solely on the cerebellum signal as an input function to quantify [¹¹C]FLB 457 BP(ND).
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Narendran R, Mason NS, May MA, Chen CM, Kendro S, Ridler K, Rabiner EA, Laruelle M, Mathis CA, Frankle WG. Positron emission tomography imaging of dopamine D₂/₃ receptors in the human cortex with [¹¹C]FLB 457: reproducibility studies. Synapse 2011; 65:35-40. [PMID: 20506186 DOI: 10.1002/syn.20813] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
In a recent PET study, we demonstrated the ability to measure amphetamine-induced DA release in the human cortex with the relatively high affinity dopamine D₂/₃ radioligand [¹¹C]FLB 457 (Narendran et al., [2009] Synapse 63:447-461). The aim of this study was to evaluate the reproducibility and reliability of [¹¹C]FLB 457 in the same imaging paradigm we used to measure amphetamine-induced DA transmission. Six healthy human subjects (three males/three females)were studied twice with [¹¹C]FLB 457, once at baseline and again 3 h following the end of the baseline scan. D₂/₃ receptor binding parameters were estimated using a two-tissue compartment kinetic analysis in the cortical regions of interest and cerebellum (reference region). The test-retest variability and intraclass correlation coefficient were assessed for distribution volume (VT), binding potential relative to plasma concentration (BP(P)), and binding potential relative to non-displaceable uptake (BP(ND)) of [¹¹C]FLB 457. The test-retest variability of [¹¹C]FLB 457 VT, BPP, and BP(ND) were ≤15%, consistent with the published test-retest variability for this ligand in other brain regions (Sudo et al., [2001] Nucl Med Commun 22:1215-1221; Vilkman et al., [2000] Eur J Nucl Med 27:1666-1673). In addition, no significant decrease in [¹¹C]FLB457 BP(ND) was observed in the second scan compared to the first one. This suggests that the contribution of carryover mass of [¹¹C]FLB 457 to the measured reduction in[¹¹C]FLB 457 BP(ND) following amphetamine was relatively low. These data support the further validation of [¹¹C]FLB 457 as a tool to measure amphetamine-induced dopamine release in the human cortex.
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Frankle WG, Mason NS, Rabiner EA, Ridler K, May MA, Asmonga D, Chen CM, Kendro S, Cooper TB, Mathis CA, Narendran R. No effect of dopamine depletion on the binding of the high-affinity D2/3 radiotracer [11C]FLB 457 in the human cortex. Synapse 2010; 64:879-85. [DOI: 10.1002/syn.20806] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Martinez D, Orlowska D, Narendran R, Slifstein M, Liu F, Kumar D, Broft A, Van Heertum R, Kleber HD. Dopamine type 2/3 receptor availability in the striatum and social status in human volunteers. Biol Psychiatry 2010; 67:275-8. [PMID: 19811777 PMCID: PMC2812584 DOI: 10.1016/j.biopsych.2009.07.037] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/18/2008] [Revised: 07/23/2009] [Accepted: 07/28/2009] [Indexed: 11/27/2022]
Abstract
BACKGROUND Previous positron emission tomography (PET) imaging studies in nonhuman primates have shown that striatal dopamine type 2/3 (D(2/3)) receptors correlate with social hierarchy in monkeys and that dominant animals exhibit higher levels of D(2/3) receptor binding. The goal of the present study was to examine this phenomena in human subjects using PET and the radiotracer [(11)C]raclopride. METHODS Fourteen healthy volunteers were scanned with [(11)C]raclopride to measure D(2/3) receptor binding potential (BP). Social status was assessed using the Barratt Simplified Measure of Social Status. In addition, participants were asked to assess their level of social support using the Multidimensional Scale of Perceived Social Support (MSPSS). RESULTS A correlation was seen between social status and dopamine D(2/3) receptors, where volunteers with the higher status had higher values for [(11)C]raclopride BP. A similar correlation was seen with the perceived social support, where higher [(11)C]raclopride BP correlated with higher scores on the MSPSS. CONCLUSIONS The results of this study support the hypothesis that social status and social support is correlated with D(2/3) receptor binding.
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Narendran R, Mason NS, Laymon CM, Lopresti BJ, Velasquez ND, May MA, Kendro S, Martinez D, Mathis CA, Frankle WG. A comparative evaluation of the dopamine D(2/3) agonist radiotracer [11C](-)-N-propyl-norapomorphine and antagonist [11C]raclopride to measure amphetamine-induced dopamine release in the human striatum. J Pharmacol Exp Ther 2010; 333:533-9. [PMID: 20103586 DOI: 10.1124/jpet.109.163501] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
(-)-N-Propyl-norapomorphine (NPA) is a full dopamine D(2/3) receptor agonist, and [(11)C]NPA is a suitable radiotracer to image D(2/3) receptors configured in a state of high affinity for agonists with positron emission tomography (PET). In this study, the vulnerability of the in vivo binding of [11C]NPA to acute fluctuation in synaptic dopamine was assessed with PET in healthy humans and compared with that of the reference D(2/3) receptor antagonist radiotracer [11C]raclopride. Ten subjects (eight females and two males) were studied on two separate days, a minimum of 1 week apart, both with [11C]raclopride and [11C]NPA at baseline and after the administration of 0.5 mg x kg(-1) oral d-amphetamine. Kinetic modeling with an arterial input function was used to derive the binding potential relative to nonspecific uptake (BPND) in the ventral striatum (VST), caudate (CAD), and putamen (PUT). [11C]Raclopride BPND was significantly reduced by 9.7 +/- 4.4, 8.4 +/- 4.2, and 14.7 +/- 4.8% after amphetamine administration in the VST, CAD, and PUT. [11C]NPA BPND was also reduced significantly, by 16.0 +/- 7.0, 16.1 +/- 6.1, and 21.9 +/- 4.9% after the same dose of amphetamine in the VST, CAD, and PUT. Although these results suggest that [11C]NPA is more vulnerable to endogenous competition by dopamine compared with [11C]raclopride by a factor of 1.49 to 1.90, the same data for a related outcome measure, binding potential relative to plasma concentration, was not significant. Nevertheless, these data add to the growing literature that suggests D(2/3) agonist radiotracers are more vulnerable to endogenous competition by dopamine than existing D(2/3) antagonist radiotracers.
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Abstract
Previous studies have shown that imaging with positron emission tomography (PET) and single photon emission computed tomography (SPECT) radiotracers that are specific for brain dopamine receptors can be used to indirectly image the change in the levels of neurotransmitters within the brain. Most of the studies in addiction have focused on dopamine, since the dopamine neurons that project to the striatum have been shown to play a critical role in mediating addictive behavior. These imaging studies have shown that increased extracellular dopamine produced by psychostimulants can be measured with PET and SPECT. However, there are some technical issues associated with imaging changes in dopamine, and these are reviewed in this chapter. Among these are the loss of sensitivity, the time course of dopamine pulse relative to PET and SPECT imaging, and the question of affinity state of the receptor. In addition, animal studies have shown that most drugs of abuse increase extracellular dopamine in the striatum, yet not all produce a change in neurotransmitter that can be measured. As a result, imaging with a psychostimulant has become the preferred method for imaging presynaptic dopamine transmission, and this method has been used in studies of addiction. The results of these studies suggest that cocaine and alcohol addiction are associated with a loss of dopamine transmission, and a number of studies show that this loss correlates with severity of disease.
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