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Beyond antipsychotics: a twenty-first century update for preclinical development of schizophrenia therapeutics. Transl Psychiatry 2022; 12:147. [PMID: 35393394 PMCID: PMC8991275 DOI: 10.1038/s41398-022-01904-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Revised: 03/02/2022] [Accepted: 03/15/2022] [Indexed: 11/15/2022] Open
Abstract
Despite 50+ years of drug discovery, current antipsychotics have limited efficacy against negative and cognitive symptoms of schizophrenia, and are ineffective-with the exception of clozapine-against any symptom domain for patients who are treatment resistant. Novel therapeutics with diverse non-dopamine D2 receptor targets have been explored extensively in clinical trials, yet often fail due to a lack of efficacy despite showing promise in preclinical development. This lack of translation between preclinical and clinical efficacy suggests a systematic failure in current methods that determine efficacy in preclinical rodent models. In this review, we critically evaluate rodent models and behavioural tests used to determine preclinical efficacy, and look to clinical research to provide a roadmap for developing improved translational measures. We highlight the dependence of preclinical models and tests on dopamine-centric theories of dysfunction and how this has contributed towards a self-reinforcing loop away from clinically meaningful predictions of efficacy. We review recent clinical findings of distinct dopamine-mediated dysfunction of corticostriatal circuits in patients with treatment-resistant vs. non-treatment-resistant schizophrenia and suggest criteria for establishing rodent models to reflect such differences, with a focus on objective, translational measures. Finally, we review current schizophrenia drug discovery and propose a framework where preclinical models are validated against objective, clinically informed measures and preclinical tests of efficacy map onto those used clinically.
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2
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Chang NHS, Kumakura Y, Møller A, Linnet J, Bender D, Doudet DJ, Vafaee MS, Gjedde A. On the learning of addictive behavior: Sensation-seeking propensity predicts dopamine turnover in dorsal striatum. Brain Imaging Behav 2021; 16:355-365. [PMID: 34417966 PMCID: PMC8825434 DOI: 10.1007/s11682-021-00509-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/14/2021] [Indexed: 11/26/2022]
Abstract
We asked if sensation-seeking is linked to premorbid personality characteristics in patients with addictive disorders, or the characteristics follow the sensation-seeking activity. We interpreted the former as a state associated with normal rates of dopamine synthesis, and the latter as a trait of individuals with abnormally high rates of synthesis. We previously determined dopaminergic receptor density in striatum, and we now tested the hypothesis that an elevated dopaminergic condition with increased extracellular dopamine and receptor density follows increased dopamine synthesis capacity in highly sensation-seeking individuals, as measured by positron emission tomography of 18 men with tracer fluorodopa (FDOPA). We detected a site in left caudate nucleus where the volume of distribution of FDOPA-derived metabolites correlated negatively with FDOPA metabolite turnover, consistent with decreased metabolite breakdown in highly sensation-seeking subjects. High rates of sensation-seeking attenuated the dopamine turnover in association with a low rate of dopamine recycling, low dopamine oxidation, and elevated extracellular dopamine and receptors in caudate nucleus. In contrast, low rates of sensation-seeking were associated with rapid dopamine recycling, rapid dopamine oxidation, low extracellular dopamine, and low receptor density. We conclude that the modulation of dopaminergic neurotransmission associated with sensation-seeking is a state of sensation-seeking, rather than a trait of personality following abnormal regulation of dopaminergic neurotransmission.
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Affiliation(s)
- Natalie Hong Siu Chang
- Department of Clinical Research, University of Southern Denmark, Odense C, DK-5000 Denmark
| | - Yoshitaka Kumakura
- Department of Diagnostic Radiology and Nuclear Medicine, Saitama Medical University, 1981 Kamoda, Kawagoe, Saitama 350-8550 Japan
| | - Arne Møller
- Department of Nuclear Medicine and PET Centre, Aarhus University Hospital, DK-8200 Aarhus N, Denmark
| | - Jakob Linnet
- Gambling Disorder & BED Clinic, Department of Occupational and Environmental Medicine, Odense University Hospital, Odense C, Dk-5000 Denmark
| | - Dirk Bender
- Department of Nuclear Medicine and PET Centre, Aarhus University Hospital, DK-8200 Aarhus N, Denmark
| | - Doris J. Doudet
- Department of Nuclear Medicine and PET Centre, Aarhus University Hospital, DK-8200 Aarhus N, Denmark
- Department of Medicine, Division of Neurology, University of British Columbia, Vancouver, B.C. V6T 2B5 Canada
| | - Manouchehr Seyedi Vafaee
- Department of Clinical Research, BRIDGE, University of Southern Denmark, Odense M, DK-5230 Denmark
| | - Albert Gjedde
- Department of Neuroscience, University of Copenhagen, Copenhagen, DK-2200 Denmark
- Department of Clinical Medicine, University of Southern Denmark, Odense C, DK-5000 Denmark
- Translational Neuropsychiatry Unit, Aarhus University, Aarhus, DK-8000 Denmark
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3
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Ailuno G, Iacobazzi RM, Lopalco A, Baldassari S, Arduino I, Azzariti A, Pastorino S, Caviglioli G, Denora N. The Pharmaceutical Technology Approach on Imaging Innovations from Italian Research. Pharmaceutics 2021; 13:1214. [PMID: 34452175 PMCID: PMC8402236 DOI: 10.3390/pharmaceutics13081214] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Revised: 07/27/2021] [Accepted: 08/02/2021] [Indexed: 11/16/2022] Open
Abstract
Many modern therapeutic approaches are based on precise diagnostic evidence, where imaging procedures play an essential role. To date, in the diagnostic field, a plethora of agents have been investigated to increase the selectivity and sensitivity of diagnosis. However, the most common drawbacks of conventional imaging agents reside in their non-specificity, short imaging time, instability, and toxicity. Moreover, routinely used diagnostic agents have low molecular weights and consequently a rapid clearance and renal excretion, and this represents a limitation if long-lasting imaging analyses are to be conducted. Thus, the development of new agents for in vivo diagnostics requires not only a deep knowledge of the physical principles of the imaging techniques and of the physiopathological aspects of the disease but also of the relative pharmaceutical and biopharmaceutical requirements. In this scenario, skills in pharmaceutical technology have become highly indispensable in order to respond to these needs. This review specifically aims to collect examples of newly developed diagnostic agents connoting the importance of an appropriate formulation study for the realization of effective products. Within the context of pharmaceutical technology research in Italy, several groups have developed and patented promising agents for fluorescence and radioactive imaging, the most relevant of which are described hereafter.
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Affiliation(s)
- Giorgia Ailuno
- Department of Pharmacy, University of Genova, Viale Cembrano 4, 16148 Genova, Italy; (G.A.); (S.B.)
| | - Rosa Maria Iacobazzi
- Laboratory of Experimental Pharmacology, IRCCS Istituto Tumori “Giovanni Paolo II”, O. Flacco St., 70124 Bari, Italy; (R.M.I.); (A.A.)
| | - Antonio Lopalco
- Department of Pharmacy-Pharmaceutical Sciences, University of Bari “Aldo Moro”, Orabona St. 4, 70125 Bari, Italy; (A.L.); (I.A.)
| | - Sara Baldassari
- Department of Pharmacy, University of Genova, Viale Cembrano 4, 16148 Genova, Italy; (G.A.); (S.B.)
| | - Ilaria Arduino
- Department of Pharmacy-Pharmaceutical Sciences, University of Bari “Aldo Moro”, Orabona St. 4, 70125 Bari, Italy; (A.L.); (I.A.)
| | - Amalia Azzariti
- Laboratory of Experimental Pharmacology, IRCCS Istituto Tumori “Giovanni Paolo II”, O. Flacco St., 70124 Bari, Italy; (R.M.I.); (A.A.)
| | - Sara Pastorino
- Nuclear Medicine Unit, S. Andrea Hospital, via Vittorio Veneto 197, 19124 La Spezia, Italy;
| | - Gabriele Caviglioli
- Department of Pharmacy, University of Genova, Viale Cembrano 4, 16148 Genova, Italy; (G.A.); (S.B.)
| | - Nunzio Denora
- Department of Pharmacy-Pharmaceutical Sciences, University of Bari “Aldo Moro”, Orabona St. 4, 70125 Bari, Italy; (A.L.); (I.A.)
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4
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Feraco P, Donner D, Picori L, Rozzanigo U. Unusual diagnostic findings in temporal lobe epilepsy: A combined MRI and 18F-dopa case study. Eur J Radiol Open 2020; 7:100241. [PMID: 32695848 PMCID: PMC7365897 DOI: 10.1016/j.ejro.2020.100241] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Accepted: 06/06/2020] [Indexed: 12/27/2022] Open
Abstract
Onset Temporal Lobe Epilepsy may mimic a low-grade tumor at conventional MRI. Arterial Spin Labeling likely detect the epileptogenic focus even beyond 24 h after seizures. The knowledge of electroencephalographic findings is necessary when interpreting brain areas of tracer uptake. 18F-DOPA uptake may represent increased dopamine transport induced by seizures. 18F-DOPA tracer uptake is not always related to malignancy.
Temporal lobe epilepsy is the most common focal epilepsy in adults and often causes pharmacoresistant seizures. Magnetic resonance imaging (MRI) and PET studies have widely demonstrated a number of morphological and molecular abnormalities in epilepsy. However, considering the dopaminergic system, only a bilateral 18F-DOPA uptake reduction within the basal ganglia has been described. We report the unusual finding of increased 18F-DOPA uptake in a patient with focal recurrent seizures and "deja vu" experiences in the setting of cortical swelling detected at MRI exam. The final diagnosis was in in keeping with hippocampal sclerosis, confirmed during follow-up MR exams. In this case 18F-DOPA uptake may represent increased dopamine transport induced by seizures. Nuclear medicine physicians and radiologists should be aware of clinical and electroencephalographic findings when interpreting brain areas of tracer uptake, which are not always related to malignancy.
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Affiliation(s)
- Paola Feraco
- Neuroradiology Unit, S. Chiara Hospital, Trento, Italy.,University of Bologna, Department of Experimental, Diagnostic and Speciality Medicine (DIMES), Italy
| | - Davide Donner
- Nuclear Medicine Unit, S. Chiara Hospital, Trento, Italy
| | - Lorena Picori
- Nuclear Medicine Unit, S. Chiara Hospital, Trento, Italy
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5
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Jenkins PO, Mehta MA, Sharp DJ. Catecholamines and cognition after traumatic brain injury. Brain 2016; 139:2345-71. [PMID: 27256296 PMCID: PMC4995357 DOI: 10.1093/brain/aww128] [Citation(s) in RCA: 65] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2015] [Accepted: 04/20/2016] [Indexed: 01/11/2023] Open
Abstract
Cognitive problems are one of the main causes of ongoing disability after traumatic brain injury. The heterogeneity of the injuries sustained and the variability of the resulting cognitive deficits makes treating these problems difficult. Identifying the underlying pathology allows a targeted treatment approach aimed at cognitive enhancement. For example, damage to neuromodulatory neurotransmitter systems is common after traumatic brain injury and is an important cause of cognitive impairment. Here, we discuss the evidence implicating disruption of the catecholamines (dopamine and noradrenaline) and review the efficacy of catecholaminergic drugs in treating post-traumatic brain injury cognitive impairments. The response to these therapies is often variable, a likely consequence of the heterogeneous patterns of injury as well as a non-linear relationship between catecholamine levels and cognitive functions. This individual variability means that measuring the structure and function of a person’s catecholaminergic systems is likely to allow more refined therapy. Advanced structural and molecular imaging techniques offer the potential to identify disruption to the catecholaminergic systems and to provide a direct measure of catecholamine levels. In addition, measures of structural and functional connectivity can be used to identify common patterns of injury and to measure the functioning of brain ‘networks’ that are important for normal cognitive functioning. As the catecholamine systems modulate these cognitive networks, these measures could potentially be used to stratify treatment selection and monitor response to treatment in a more sophisticated manner.
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Affiliation(s)
- Peter O Jenkins
- 1 The Division of Brain Sciences, The Department of Medicine, Imperial College London, UK
| | - Mitul A Mehta
- 2 Department of Neuroimaging, Institute of Psychiatry, Psychology & Neuroscience, King's College London, UK
| | - David J Sharp
- 1 The Division of Brain Sciences, The Department of Medicine, Imperial College London, UK
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Pretze M, Wängler C, Wängler B. 6-[18F]fluoro-L-DOPA: a well-established neurotracer with expanding application spectrum and strongly improved radiosyntheses. BIOMED RESEARCH INTERNATIONAL 2014; 2014:674063. [PMID: 24987698 PMCID: PMC4058520 DOI: 10.1155/2014/674063] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Revised: 04/17/2014] [Accepted: 04/18/2014] [Indexed: 11/18/2022]
Abstract
For many years, the main application of [(18)F]F-DOPA has been the PET imaging of neuropsychiatric diseases, movement disorders, and brain malignancies. Recent findings however point to very favorable results of this tracer for the imaging of other malignant diseases such as neuroendocrine tumors, pheochromocytoma, and pancreatic adenocarcinoma expanding its application spectrum. With the application of this tracer in neuroendocrine tumor imaging, improved radiosyntheses have been developed. Among these, the no-carrier-added nucleophilic introduction of fluorine-18, especially, has gained increasing attention as it gives [(18)F]F-DOPA in higher specific activities and shorter reaction times by less intricate synthesis protocols. The nucleophilic syntheses which were developed recently are able to provide [(18)F]F-DOPA by automated syntheses in very high specific activities, radiochemical yields, and enantiomeric purities. This review summarizes the developments in the field of [(18)F]F-DOPA syntheses using electrophilic synthesis pathways as well as recent developments of nucleophilic syntheses of [(18)F]F-DOPA and compares the different synthesis strategies regarding the accessibility and applicability of the products for human in vivo PET tumor imaging.
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Affiliation(s)
- M. Pretze
- Molecular Imaging and Radiochemistry, Department of Clinical Radiology and Nuclear Medicine, Medical Faculty Mannheim of Heidelberg University, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany
| | - C. Wängler
- Biomedical Chemistry, Department of Clinical Radiology and Nuclear Medicine, Medical Faculty Mannheim of Heidelberg University, 68167 Mannheim, Germany
| | - B. Wängler
- Molecular Imaging and Radiochemistry, Department of Clinical Radiology and Nuclear Medicine, Medical Faculty Mannheim of Heidelberg University, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany
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7
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Stokes PRA, Benecke A, Puraite J, Bloomfield MAP, Shotbolt P, Reeves SJ, Lingford-Hughes AR, Howes O, Egerton A. Does human presynaptic striatal dopamine function predict social conformity? J Psychopharmacol 2014; 28:237-43. [PMID: 24257812 DOI: 10.1177/0269881113512037] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Socially desirable responding (SDR) is a personality trait which reflects either a tendency to present oneself in an overly positive manner to others, consistent with social conformity (impression management (IM)), or the tendency to view one's own behaviour in an overly positive light (self-deceptive enhancement (SDE)). Neurochemical imaging studies report an inverse relationship between SDR and dorsal striatal dopamine D₂/₃ receptor availability. This may reflect an association between SDR and D₂/₃ receptor expression, synaptic dopamine levels or a combination of the two. In this study, we used a [¹⁸F]-DOPA positron emission tomography (PET) image database to investigate whether SDR is associated with presynaptic dopamine function. Striatal [¹⁸F]-DOPA uptake, (k(i)(cer), min⁻¹), was determined in two independent healthy participant cohorts (n=27 and 19), by Patlak analysis using a cerebellar reference region. SDR was assessed using the revised Eysenck Personality Questionnaire (EPQ-R) Lie scale, and IM and SDE were measured using the Paulhus Deception Scales. No significant associations were detected between Lie, SDE or IM scores and striatal [¹⁸F]-DOPA k(i)(cer). These results indicate that presynaptic striatal dopamine function is not associated with social conformity and suggests that social conformity may be associated with striatal D₂/₃ receptor expression rather than with synaptic dopamine levels.
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Affiliation(s)
- Paul R A Stokes
- 1Centre for Neuropsychopharmacology, Division of Brain Sciences, Department of Medicine, Imperial College London, London, UK
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8
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Nature or nurture? Determining the heritability of human striatal dopamine function: an [18F]-DOPA PET study. Neuropsychopharmacology 2013; 38:485-91. [PMID: 23093224 PMCID: PMC3547199 DOI: 10.1038/npp.2012.207] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Striatal dopamine function is important for normal personality, cognitive processes and behavior, and abnormalities are linked to a number of neuropsychiatric disorders. However, no studies have examined the relative influence of genetic inheritance and environmental factors in determining striatal dopamine function. Using [18F]-DOPA positron emission tomography (PET), we sought to determine the heritability of presynaptic striatal dopamine function by comparing variability in uptake values in same sex monozygotic (MZ) twins to dizygotic (DZ) twins. Nine MZ and 10 DZ twin pairs underwent high-resolution [18F]-DOPA PET to assess presynaptic striatal dopamine function. Uptake values for the overall striatum and functional striatal subdivisions were determined by a Patlak analysis using a cerebellar reference region. Heritability, shared environmental effects and non-shared individual-specific effects were estimated using a region of interest (ROI) analysis and a confirmatory parametric analysis. Overall striatal heritability estimates from the ROI and parametric analyses were 0.44 and 0.33, respectively. We found a distinction between striatal heritability in the functional subdivisions, with the greatest heritability estimates occurring in the sensorimotor striatum and the greatest effect of individual-specific environmental factors in the limbic striatum. Our results indicate that variation in overall presynaptic striatal dopamine function is determined by a combination of genetic factors and individual-specific environmental factors, with familial environmental effects having no effect. These findings underline the importance of individual-specific environmental factors for striatal dopaminergic function, particularly in the limbic striatum, with implications for understanding neuropsychiatric disorders such as schizophrenia and addictions.
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9
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Egerton A, Demjaha A, McGuire P, Mehta MA, Howes OD. The test-retest reliability of 18F-DOPA PET in assessing striatal and extrastriatal presynaptic dopaminergic function. Neuroimage 2009; 50:524-531. [PMID: 20034580 DOI: 10.1016/j.neuroimage.2009.12.058] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2009] [Revised: 12/08/2009] [Accepted: 12/12/2009] [Indexed: 11/17/2022] Open
Abstract
Brain presynaptic dopaminergic function can be assessed using 18F-DOPA positron emission tomography (PET). Regional 18F-DOPA utilization may be used to index dopaminergic abnormalities over time or dopaminergic response to treatment in clinical populations. Such studies require prior knowledge of the stability of the 18F-DOPA signal in the brain regions of interest. Test-retest reliability was examined in eight healthy volunteers who each received two 18F-DOPA PET scans, approximately 2 years apart. 18F-DOPA utilization (k(i)(cer)) was determined using graphical analysis relative to a reference tissue input (Patlak and Blasberg, 1985). Reproducibility (measured as the within-subjects variation) and reliability (measured as intraclass correlation coefficients, ICCs) of 18F-DOPA k(i)(cer) were assessed in the structural and functional subdivisions of the striatum and select extrastriatal brain regions. Voxel-based median ICC maps were used to visualize the distribution of 18F-DOPA k(i)(cer) reliability across the brain. The caudate and putamen, and associative and sensorimotor, striatal subdivisions showed good reliability across the two scan sessions with bilateral ICCs ranging from 0.681 to 0.944. Reliability was generally lower in extrastriatal regions, with bilateral ICCs ranging from 0.235 in the amygdala to 0.894 in the thalamus. These data confirm the utility of 18F-DOPA PET in assessing dopaminergic function in the striatum and select extrastriatal areas but highlight the limitations in using this approach to measure dopaminergic function in low uptake extrastriatal brain areas. This information can be used to optimize the experimental design of future studies investigating changes in brain dopaminergic function with 18F-DOPA.
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Affiliation(s)
- Alice Egerton
- Psychiatric Imaging, Medical Research Council Clinical Sciences Centre, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, United Kingdom.,Division of Neurosciences & Mental Health, Imperial College London, United Kingdom.,Department of Psychological Medicine, Institute of Psychiatry, King's College London, London SE5 8AF, United Kingdom
| | - Arsime Demjaha
- Psychiatric Imaging, Medical Research Council Clinical Sciences Centre, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, United Kingdom.,Department of Psychological Medicine, Institute of Psychiatry, King's College London, London SE5 8AF, United Kingdom
| | - Philip McGuire
- Department of Psychological Medicine, Institute of Psychiatry, King's College London, London SE5 8AF, United Kingdom
| | - Mitul A Mehta
- Psychiatric Imaging, Medical Research Council Clinical Sciences Centre, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, United Kingdom.,Division of Neurosciences & Mental Health, Imperial College London, United Kingdom.,Department of Psychological Medicine, Institute of Psychiatry, King's College London, London SE5 8AF, United Kingdom
| | - Oliver D Howes
- Psychiatric Imaging, Medical Research Council Clinical Sciences Centre, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, United Kingdom.,Division of Neurosciences & Mental Health, Imperial College London, United Kingdom.,Department of Psychological Medicine, Institute of Psychiatry, King's College London, London SE5 8AF, United Kingdom
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10
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Mamo D, Remington G, Nobrega J, Hussey D, Chirakal R, Wilson AA, Baker G, Houle S, Kapur S. Effect of acute antipsychotic administration on dopamine synthesis in rodents and human subjects using 6-[18F]-L-m-tyrosine. Synapse 2004; 52:153-62. [PMID: 15034921 DOI: 10.1002/syn.20016] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Clinical effects of antipsychotic drugs are thought to be mediated primarily through antagonism of the dopamine D2 receptors. Recent studies have demonstrated increased aromatic decarboxylase activity following acute administration of dopamine D2 receptor antagonists both in vivo and ex vivo. However, this effect has never been demonstrated in human subjects. We studied the effect of acute antipsychotic administration on dopamine synthesis in rodents and healthy human subjects using 6-[18F]-L-m-tyrosine. In rats, we studied the effect of a single subcutaneous injection of haloperidol and risperidone on dopamine synthesis using 6-[18F]-L-m-tyrosine. In our human study, six healthy volunteers underwent two 6-[18F]-L-m-tyrosine PET scans, before and after 3 mg risperidone to measure the rate of accumulation of radioactivity in the striatum as an index of dopamine synthesis. The striatal/cerebellar radioactivity count ratio and the ratio of dopamine metabolites to dopamine concentration was significantly higher in all rodent treatment groups compared to controls. In the PET study we found no significant change in the rate of uptake in the striatum. Our results suggest that 6-[18F]-L-m-tyrosine PET may not be a useful tool in the study of the effect of antipsychotics on dopamine synthesis in human subjects.
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Affiliation(s)
- David Mamo
- Department of Psychiatry, University of Toronto, Canada.
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11
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Deep P, Kuwabara H, Gjedde A, Cumming P. The kinetic behaviour of [3H]DOPA in living rat brain investigated by compartmental modelling of static autoradiograms. J Neurosci Methods 1997; 78:157-68. [PMID: 9497012 DOI: 10.1016/s0165-0270(97)00147-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The kinetic behaviour of [3H]DOPA in living rat brain was investigated by compartmental modelling of measured activities from combined metabolite pools in a time-series (180 min) of static autoradiograms from right cerebral hemispheres. Two models of [3H]DOPA uptake and metabolism that incorporated the removal of the decarboxylation product, [3H]dopamine, from brain were significantly more accurate than a model in which [3H]dopamine accumulated irreversibly in situ. Present estimates of [3H]DOPA kinetic constants were compared to previously published results based on the analysis of measured activities from individual metabolite pools separated by chromatographic fractionation of [3H]DOPA metabolites in the left cerebral hemispheres of the same rats. Autoradiographic estimates of DOPA decarboxylase activity with respect to [3H]DOPA in brain (k3DOPA) were under-estimated several-fold relative to chromatographic estimates; this discrepancy is explained by post-mortem enzyme activity and omission of biological compartments from the models. However, autoradiographic estimates of the unidirectional blood-brain clearance of [3H]DOPA (K1DOPA) and monoamine oxidase activity with respect to [3H]dopamine in brain (k7DA') agreed with chromatographic estimates. This concordance represents the first empirical validation of compartmental modelling of autoradiographic data as a method for quantitatively investigating the kinetic behaviour of radiolabelled L-DOPA in living mammalian brain.
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Affiliation(s)
- P Deep
- Montreal Neurological Institute, McGill University, Quebec, Canada.
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