Dynamic, adaptive changes in MAO-A binding after alterations in substrate availability: an in vivo [11C]-harmine positron emission tomography study

Monoamine oxidase A (MAO-A) is an important target in the pathophysiology and therapeutics of major depressive disorder, aggression, and neurodegenerative conditions. We measured the effect of changes in MAO-A substrate on MAO-A binding in regions implicated in affective and neurodegenerative disease with [11C]-harmine positron emission tomography in healthy volunteers. Monoamine oxidase A VT, an index of MAO-A density, was decreased (mean: 14%±9%) following tryptophan depletion in prefrontal cortex (P<0.031), and elevated (mean: 17%±11%) in striatum following carbidopa–levodopa administration (P<0.007). These findings suggest an adaptive role for MAO-A in maintaining monoamine neurotransmitter homeostasis by rapidly compensating fluctuating monoamine levels

Salience network and parahippocampal dopamine dysfunction in memory-impaired Parkinson disease

Objective: Patients with Parkinson disease (PD) and mild cognitive impairment (MCI) are vulnerable to dementia and frequently experience memory deficits. This could be the result of dopamine dysfunction in corticostriatal networks (salience, central executive networks, and striatum) and/or the medial temporal lobe. Our aim was to investigate whether dopamine dysfunction in these regions contributes to memory impairment in PD. Methods: We used positron emission tomography imaging to compare D2 receptor availability in the cortex and striatal (limbic and associative) dopamine neuron integrity in 4 groups: memory‐impaired PD (amnestic MCI; n = 9), PD with nonamnestic MCI (n = 10), PD without MCI (n = 11), and healthy controls (n = 14). Subjects were administered a full neuropsychological test battery for cognitive performance. Results: Memory‐impaired patients demonstrated more significant reductions in D2 receptor binding in the salience network (insular cortex and anterior cingulate cortex [ACC] and the right parahippocampal gyrus [PHG]) compared to healthy controls and patients with no MCI. They also presented reductions in the right insula and right ACC compared to nonamnestic MCI patients. D2 levels were correlated with memory performance in the right PHG and left insula of amnestic patients and with executive performance in the bilateral insula and left ACC of all MCI patients. Associative striatal dopamine denervation was significant in all PD patients. Interpretation: Dopaminergic differences in the salience network and the medial temporal lobe contribute to memory impairment in PD. Furthermore, these findings indicate the vulnerability of the salience network in PD and its potential role in memory and executive dysfunction

On the relationship of first-episode psychosis to the amphetamine-sensitized state: a dopamine D2/3 receptor agonist radioligand study.

Schizophrenia is characterized by increased behavioral and neurochemical responses to dopamine-releasing drugs. This prompted the hypothesis of psychosis as a state of "endogenous" sensitization of the dopamine system although the exact basis of dopaminergic disturbances and the possible role of prefrontal cortical regulation have remained uncertain. To show that patients with first-episode psychosis release more dopamine upon amphetamine-stimulation than healthy volunteers, and to reveal for the first time that prospective sensitization induced by repeated amphetamine exposure increases dopamine-release in stimulant-naïve healthy volunteers to levels observed in patients, we collected data on amphetamine-induced dopamine release using the dopamine D2/3 receptor agonist radioligand [11C]-(+)-PHNO and positron emission tomography. Healthy volunteers (n = 28, 14 female) underwent a baseline and then a post-amphetamine scan before and after a mildly sensitizing regimen of repeated oral amphetamine. Unmedicated patients with first-episode psychosis (n = 21; 6 female) underwent a single pair of baseline and then post-amphetamine scans. Furthermore, T1 weighted magnetic resonance imaging of the prefrontal cortex was performed. Patients with first-episode psychosis showed larger release of dopamine compared to healthy volunteers. After sensitization of healthy volunteers their dopamine release was significantly amplified and no longer different from that seen in patients. Healthy volunteers showed a negative correlation between prefrontal cortical volume and dopamine release. There was no such relationship after sensitization or in patients. Our data in patients with untreated first-episode psychosis confirm the "endogenous sensitization" hypothesis and support the notion of impaired prefrontal control of the dopamine system in schizophrenia

Analysis of Variance in Neuroreceptor Ligand Imaging Studies

Radioligand positron emission tomography (PET) with dual scan paradigms can provide valuable insight into changes in synaptic neurotransmitter concentration due to experimental manipulation. The residual t-test has been utilized to improve the sensitivity of the t-test in PET studies. However, no further development of statistical tests using residuals has been proposed so far to be applied in cases when there are more than two conditions. Here, we propose the residual f-test, a one-way analysis of variance (ANOVA), and examine its feasibility using simulated [11C]raclopride PET data. We also re-visit data from our previously published [11C]raclopride PET study, in which 10 individuals underwent three PET scans under different conditions. We found that the residual f-test is superior in terms of sensitivity than the conventional f-test while still controlling for type 1 error. The test will therefore allow us to reliably test hypotheses in the smaller sample sizes often used in explorative PET studies

Isomerización de carbocianinas simétricas en solventes polares

Este trabajo de tesis describe aspectos de equilibrio y dinámicos relativos a la reacción de retro-isomeración de un catión carbocianina (3,3’-Dietiloxacarbocianina, DOCI) en distintos entornos: acetonitrilo, alcoholes alifáticos de diferente longitud de cadena y mezclas metanol (MeOH) - acetonitrilo (ACN). El amplio espectro de longitudes características relevantes en el problema, que van desde uniones intramoleculares del orden de 1-2 Å hasta distancias del orden del tamaño molecular, aproximadamente de 20 Å; juntamente con una significativa redistribución de la densidad electrónica que genera estados intermedios de elevada polaridad, hacen de este proceso un problema particularmente interesante, cuya descripción microscópica es compleja. El método de estudio es la dinámica molecular. Las simulaciones presentan un modelo, propio de esta tesis, cuyas principales características son: (i) un alto grado de detalle en la descripción del soluto, incorporando explícitamente todos los grados de libertad, (ii) la capacidad de cambios en la distribución electrónica conformes al valor de la coordenada de reacción, (iii) un solvente modelado como una colección de cargas parciales mantenidas a distancia fijas; (iv) para los solventes de mayor tamaño un modelo simplificado que reproduce las propiedades más relevantes que influyen el proceso reactivo tales como polaridad, características de empaquetamiento, autodifusión. El estudio del proceso reactivo fue abordado, como es usual en estos casos, mediante el cálculo de la constante de velocidad k iso. Su estimación es la resultante de dos contribuciones: la primera proveniente de la aplicación de la teoría del estado de transición; la segunda está relacionada con los efectos dinámicos involucrados en el proceso. Complementariamente, el estudio del equilibrio nos permitió obtener información referente a las estructuras de solvatación propias de los distintos estadios de la reacción (de productos y de transición). Por otro lado se realizaron simulaciones de no equilibrio desde las que se obtuvo información de la relajación simultánea de los grados de libertad y observables del soluto y del solvente. Las conclusiones del trabajo son: (i) la presencia de solvente polar siempre disminuye la energía libre de activación respecto de la intrínseca en vacío, la magnitud de esta reducción resulta de una competencia entre las interacciones soluto-solvente y solvente-solvente, la energía libre de activación de los alcoholes obtenida de los experimentos de simulación, reproduce la tendencia, anómala según el modelo de Kramer, observada en trabajos experimentales para la constante de velocidad, en las experiencias con mezclas ACN/MeOH se observó solvatación preferencial del solvente aprótico. Finalmente resulta importante establecer, a partir de los resultados aquí obtenidos, la importancia de la ponderación de los procesos microscópicos que acompañan el desarrollo de la reacción para lograr una interpretación del fenómeno global; estos aspectos son generalmente soslayados o reinterpretados en términos de propiedades macroscópicas al encarar el estudio de reacciones de este tipo.This work deals with equilibrium and dynamical aspects of the back-isomerization reaction of a carbocyanine cation (3,3’-Diethyloxacarbocyanine, DOCI) taking place in different solvents: acetonitrile, n-primary alcohols and mixtures of methanol (MeOH) and acetonitrile (ACN). The global description of the system is very complex due to the broad spectrum of relevant lengthscales in the problem, ranging from intramolecular bonds (with lengths in the order of 1 or 2 Å), to distances in the order of solute size (≈ 20 Å). In addition, an important redistribution of the electronic density that produces intermediate states of high polarity takes place as well. The methodolgy of study resorted on Molecular Dynamics techniques. The main characteristics of the model are: (i) a detailed model of the solute in which all degrees of freedom are explicitly included; (ii) the electronic distribution is allowed to change along the reaction coordinate; (iii) the solvents were considered as collection of partial charges kept at fix distances; (iv) for the largest solvent molecules, a simplified model was considered reproducing the most important properties that influence the reactive process, such as polarity, packing effects and self diffusion. Our approach to the study of the reaction included the computation of the rate constants. These rate constants are the result of two contributions: the first is the transition state theory estimate and, secondly corrections due to dynamical effects. Moreover, the equilibrium study provided information about solvation structures in the transition and product states. We have also performed non-equilibrium relaxations in which we monitored the simulataneous relaxation of the solute and the solvent degress of freedom. The mainly conclusions of this work are: (i) the presence of a solvent always produces a decrease of the free energy activation barrier with respect to the intrinsic barrier in vacuo. (ii) the value of this reduction is the result of a competition between the solute-solvent and solvent-solvent interactions, (iii) the computed activation free energies reproduces the observed trend of experimental rate constants, (iv) in the ACN/MeOH mixtures, we observed preferential solvation of the aprotic solvent.Fil:Rusjan, Pablo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

The relationship between subjective well-being and dopamine D-2 receptors in patients treated with a dopamine partial agonist and full antagonist antipsychotics

Antipsychotic drugs produce unpleasant subjective experiences, which have been associated with high levels of dopamine D2 receptor occupancy. Aripiprazole is a partial agonist antipsychotic, which is hypothesized to produce a different subjective experience profile compared to standard D2 antagonist antipsychotics. The aim of this study was to compare the effect of D2 occupancy produced by a partial agonist antipsychotic (aripiprazole) to that of antagonist antipsychotics (risperidone or olanzapine) on the subjective well-being of patients. Subjective well-being was measured using the Subjective Well-being under Neuroleptics Scale (SWN) and was related to dopamine D2 receptor occupancy using [11C]raclopride PET. Patients that were switched to aripiprazole showed improvement in their subjective well-being from 79.80 (S.D.=16.08) to 89.90 (S.D.=15.33), an effect that was sustained for 6 months. This sustained improvement was observed despite very high levels of DA D2 occupancy (82–99%), in contrast to the effects of antagonist antipsychotics on subjective well-being.peer-reviewe

Serotonin 2A Receptors and Visual Hallucinations in Parkinson Disease

International audienceBackground Complex visual hallucinations (VHs) occur in several pathologic conditions; however, the neural mechanisms underlying these symptoms remain unclear. Although dopamine may have a role, indirect evidence indicates that serotonin may also contribute to the pathogenesis of complex VHs, probably via involvement of the serotonin 2 receptor.Objective To examine for the first time in vivo changes in serotonin 2A receptor neurotransmission among patients having Parkinson disease (PD) with VHs.Design Case-control study.Setting Academic research.Patients Seven patients having PD with VHs and 7 age-matched patients having PD without VHs were recruited.Main Outcome Measures We used the selective serotonin 2A receptor ligand setoperone F 18 during positron emission tomography among nondemented patients having PD with VHs.Results Patients having PD with VHs demonstrate increased serotonin 2A receptor binding in the ventral visual pathway (including the bilateral inferooccipital gyrus, right fusiform gyrus, and inferotemporal cortex) as well as the bilateral dorsolateral prefrontal cortex, medial orbitofrontal cortex, and insula.Conclusions This pilot study provides the first in vivo evidence suggesting a role for serotonin 2A receptors in mediating VHs via the ventral visual pathway in PD. Treatment studies should be performed using selective serotonin 2A receptor antagonists, which have important implications for the clinical management of VHs and psychosis in PD.Visual hallucinations (VHs) are abnormal perceptions in the absence of an adequate visual stimulus. Complex well-formed VHs have been described in several pathologic conditions, including peduncular hallucinosis, schizophrenia, cortical Lewy body dementia, and Parkinson disease (PD). A potential common substrate for complex VHs in all of these conditions is suppression of normal inhibitory cortical inputs over the visual association cortex, leading to complex VHs as a “release phenomenon.”1 However, the neural mechanisms underlying VHs remain unclear. Although dopamine may have a role,2 indirect evidence indicates that serotonin may also contribute to the pathogenesis of complex VHs, probably via involvement of the serotonin 2 receptor. In fact, hallucinogenic lysergic acid diethylamide acts via serotonin 2A receptors,3 and atypical antipsychotics (eg, clozapine and quetiapine fumarate) that effectively reduce VHs, as well as dopamine receptor antagonists, are serotonin 2A and 2C receptor antagonists.4 In PD, this antipsychotic effect on VHs occurs at low dosages (approximately 10-fold less than in schizophrenia); at such dosages, there is high occupancy of serotonin 2A receptors and low occupancy of dopamine receptors.5 Together, these observations suggest that serotonin 2A receptors may be involved in VHs in PD; however, the pathogenesis underlying these phenomena and the potential action site of serotonin 2A ligands in reducing such symptoms is unknown to date. Therefore, the specific objective of this pilot study was to measure for the first time in vivo changes in serotonin 2A receptor binding using the selective serotonin 2A receptor ligand setoperone F 186 during positron emission tomography (PET) among age-matched nondemented patients having PD with well-formed VHs vs patients having PD without VHs

Monoamine oxidase A inhibitor occupancy during treatment of major depressive episodes with moclobemide or St. John’s wort: an [11C]-harmine PET study

Background Monoamine oxidase A (MAO-A) inhibitor antidepressants raise levels of multiple monoamines, whereas the selective serotonin reuptake inhibitors (SSRIs) only raise extracellular serotonin. Despite this advantage of MAO-A inhibitors, there is much less frequent development of MAO inhibitors compared with SSRIs. We sought to measure brain MAO-A occupancy after 6 weeks of treatment in depressed patients with a clinically effective dose of a selective MAO-A inhibitor and measure MAO-A occupancy after repeated administration of St. John’s wort, an herb purported to have MAO-A inhibitor properties. Methods Participants underwent 2 [11C]-harmine positron emission tomography scans. Healthy controls completed a test–retest condition, and depressed patients were scanned before and after repeated administration of moclobemide or St. John’s wort for 6 weeks at the assigned dose. We measured MAO-A VT, an index of MAO-A density, in the prefrontal, anterior cingulate and anterior temporal cortices, putamen, thalamus, midbrain and hippocampus. Results We included 23 participants (10 controls and 13 patients with major depressive disorder [MDD]) in our study. Monoamine oxidase A VT decreased significantly throughout all regions after moclobemide treatment in patients with MDD compared with controls (repeated-measures analysis of variance, F1,15 = 71.08–130.06, p < 0.001 for all regions, mean occupancy 74% [standard deviation 6%]). Treatment with St. John’s wort did not significantly alter MAO-A VT. Limitations The occupancy estimates are limited by the sample size of each treatment group; hence, our estimate for the overall moclobemide occupancy of 74% has a 95% confidence interval of 70%–78%, and we can estimate with 95% certainty that the occupancy of St. John’s wort is less than 5%. Conclusion For new MAO-A inhibitors, about 74% occupancy at steady-state dosing is desirable. Consistent with this, St. John’s wort should not be classified as an MAO-A inhibitor. The magnitude of MAO-A blockade during moclobemide treatment exceeds the elevation of MAO-A binding during illness by at least 30%, suggesting that the treatment effect should exceed the disease effect when designing selective anti-depressants for this target

Microglial activation in Parkinson’s disease using [18F]-FEPPA

Abstract Background Neuroinflammatory processes including activated microglia have been reported to play an important role in Parkinson’s disease (PD). Increased expression of translocator protein (TSPO) has been observed after brain injury and inflammation in neurodegenerative diseases. Positron emission tomography (PET) radioligand targeting TSPO allows for the quantification of neuroinflammation in vivo. Methods Based on the genotype of the rs6791 polymorphism in the TSPO gene, we included 25 mixed-affinity binders (MABs) (14 PD patients and 11 age-matched healthy controls (HC)) and 27 high-affinity binders (HABs) (16 PD patients and 11 age-matched HC) to assess regional differences in the second-generation radioligand [18F]-FEPPA between PD patients and HC. FEPPA total distribution volume (V T) values in cortical as well as subcortical brain regions were derived from a two-tissue compartment model with arterial plasma as an input function. Results Our results revealed a significant main effect of genotype on [18F]-FEPPA V T in every brain region, but no main effect of disease or disease × genotype interaction in any brain region. The overall percentage difference of the mean FEPPA V T between HC-MABs and HC-HABs was 32.6% (SD = 2.09) and for PD-MABs and PD-HABs was 43.1% (SD = 1.21). Conclusions Future investigations are needed to determine the significance of [18F]-FEPPA as a biomarker of neuroinflammation as well as the importance of the rs6971 polymorphism and its clinical consequence in PD