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Akihiro Takano

Publications and source records attributed to Akihiro Takano.

At least 19 recordsLinked to original sources

Memory and frontal lobe functions; possible relations with dopamine D2 receptors in the hippocampus.

Cerebral cortical regions are thought to be important for cognitive functions such as memory and executive function. Although the functional associations between dopamine D2 receptors and motor and cognitive functions have been extensively examined in the striatum using positron emission tomography (PET), the role of dopamine D2 receptors in extrastriatal regions has been unexplored. We aimed to investigate the relationship between dopamine D2 receptors in extrastriatal regions and the performance of a broad spectrum of cognitive functions including memory, language, attention, and executive function in healthy subjects. Extrastriatal dopamine D2 receptors were measured in 25 male subjects using PET with [(11)C]FLB457. After the PET scans, a battery of neuropsychological tests was administered to all subjects. We found that the binding potential (BP) of [(11)C]FLB457 in the hippocampus was positively correlated with memory function. Furthermore, BP of [(11)C]FLB457 in the hippocampus, but not in the prefrontal cortex, was associated with frontal lobe functions such as executive function and verbal fluency. Our findings suggest that dopamine D2 receptors in the hippocampus might affect the local hippocampal function, but also brain functions outside the hippocampus such as the prefrontal cortex.

Adult↗

Changes in central 5-HT(1A) receptor binding in mesial temporal epilepsy measured by positron emission tomography with [(11)C]WAY100635.

OBJECTIVE: The possible involvement of the brain 5-HT(1A) receptor in epilepsy has been indicated in animal seizure models. Recent in vivo neuroimaging studies demonstrated decreased 5-HT(1A) receptor binding in epilepsy. Using positron emission tomography (PET) with [(11)C]WAY100635, we investigated 5-HT(1A) receptor binding in patients with mesial temporal lobe epilepsy and aimed to clarify the involvement of the brain 5-HT(1A) receptor system in epilepsy. METHOD: PET measurements with [(11)C]WAY100635 were performed on 23 healthy volunteers and 13 patients who were diagnosed with mesial temporal lobe epilepsy based on clinical symptoms and electroencephalogram (EEG) findings. They had non-lesional mesial temporal lobe epilepsy with unilateral EEG foci and no hippocampal atrophy on magnetic resonance imaging. The binding potential (BP) of [(11)C]WAY100635 was calculated by the reference tissue model method. Data were analyzed for each region of interest (ROI) and on a voxel-by-voxel basis by statistical parametric mapping (SPM) system. RESULTS: ROI and voxel-based analyses consistently demonstrated that 5-HT(1A) receptor BP was significantly decreased in the temporal lobe, hippocampus and amygdala on the ipsilateral side of the EEG focus compared to controls. In addition, decreased 5-HT(1A) receptor BP was also observed on the contralateral side of the amygdala. CONCLUSION: 5-HT(1A) receptor binding in patients with mesial temporal lobe epilepsy decreased predominantly in the ipsilateral mesial temporal lobe structures but also in the contralateral side. The imaging of 5-HT(1A) receptor binding by PET detects functional changes of the limbic system in mesial temporal lobe epilepsy, proving to be a sensitive and useful method.

Adult↗

Role of ventral striatal dopamine D1 receptor in cigarette craving.

BACKGROUND: Several theories of cigarette craving suggest that dopaminergic function in the ventral striatum plays an important role. The objective of this study was to determine correlations between craving-related brain activation and dopamine D1 receptor (D1R) binding in smokers. METHODS: Twelve smokers and 12 nonsmoking controls underwent [(15)O]H(2)O-positron emission tomography activation study and D1R-binding study using [(11)C]SCH 23390, and the correlations between receptor binding and cue-induced regional cerebral blood flow (rCBF) changes were assessed. Consecutive D1R-binding changes were examined during a period of 6 months of postsmoking abstinence in five smokers. RESULTS: Cue-induced activation was observed in the left ventral striatum including the nucleus accumbens in smokers. D1R binding in the ventral striatum showed a negative relationship with cue-induced craving and rCBF changes. D1R binding was significantly low in smokers, and there was a trend of increase after smoking abstinence. CONCLUSIONS: D1R binding and cue-induced rCBF changes in the ventral striatum suggest the important role of D1R in this region in cigarette craving.

Adult↗

Effects of repetitive transcranial magnetic stimulation on [11C]raclopride binding and cognitive function in patients with depression.

BACKGROUND: Several studies have demonstrated that repetitive transcranial magnetic stimulation (rTMS) elicits moderate antidepressant effects. Several previous studies suggested that the dopaminergic system might be related to this therapeutic action of rTMS. We attempted to determine the effects of chronic rTMS on central dopaminergic function in depression using positron emission tomography (PET) with [11C]raclopride. METHODS: Nine patients with depression were treated with 10 daily sessions of rTMS (10 Hz, 5 s train, 20 trains at 100% motor threshold per session) over the left dorsolateral prefrontal cortex (DLPFC). Each patient underwent two [11C]raclopride PET scans and neuropsychological tests - before rTMS and 1 day after rTMS. RESULTS: In five patients, the Hamilton Rating Scale for Depression (HRSD) significantly decreased. Patients showed significant improvement in verbal memory following rTMS. There were no changes in [11C]raclopride binding in the caudate nucleus and putamen after rTMS treatment. LIMITATIONS: Our sample size was limited, and our study was an open trial lacking sham-treated controls. CONCLUSION: This study suggests that rTMS may be effective for the treatment of depression and also may improve verbal memory function. We observed no changes in [11C]raclopride binding, suggesting that there was no measurable increase in the release of dopamine at the second PET scan. Several animal studies and healthy human studies have indicated that dopamine can be released soon after acute rTMS. Our results suggest that release of striatal dopamine induced by rTMS may be only transient, or that dopamine release may be attenuated following chronic rTMS.

Adult↗

Quantitative analysis for estimating binding potential of the peripheral benzodiazepine receptor with [(11)C]DAA1106.

[(11)C]DAA1106 is a potent and selective ligand for the peripheral benzodiazepine receptor (PBR) with high affinity. It has been reported that the density of PBR is related to brain damage, so a reliable tracer method for the evaluation of PBR would be of use. We evaluated a quantification method of [(11)C]DAA1106 binding in simulated data and human brain data. In the simulation study, the reliability of parameters estimated from the nonlinear least-squares (NLS) method, graphical analysis (GA), and multilinear analysis (MA) was evaluated. In GA, variation of the estimated distribution volume (DV) was small. However, DV was underestimated as noise increased. In MA, bias was smaller, and variation of the estimated DV was larger than in GA. In NLS, although variation was larger than in GA, it was small enough in regions of interest analysis, and not only DV but also binding potential (BP), determined from the k(3)/k(4) without any constraint, could be estimated. The variation of BP estimated with NLS became larger as k(3) or k(4) became smaller. In human studies with normal volunteers, regions of interest were drawn on several brain regions, BP was calculated by NLS, and DV was also estimated by NLS, GA, and MA. As a result, DVs estimated with each method were well correlated. However, there was no correlation between BP with NLS and DV with NLS, GA, and MA, because of the variation of K(1)/k(2) between individuals. In conclusion, BP is estimated most reliably by NLS with the two-tissue compartment model.

Acetamides↗

A dose-finding study of duloxetine based on serotonin transporter occupancy.

RATIONALE: Positron emission tomography (PET) has been utilized for determining the dosage of antipsychotic drugs. To evaluate the dosage of antidepressants such as selective serotonin reuptake inhibitors, serotonin transporter occupancy (5-HTT) is also a useful index. OBJECTIVES: We investigated the degree of 5-HTT occupancy with different doses of the antidepressant duloxetine and the time-course of 5-HTT occupancy using PET. METHODS: PET scans with [11C]DASB were performed before and after a single administration of duloxetine (5-60 mg), and three consecutive scans were performed after a single dose or repeated doses of 60 mg of duloxetine. RESULTS: 5-HTT occupancies by duloxetine were increased by 35.3 to 86.5% with dose and plasma concentration increments. The ED50 value of 5-HTT occupancy was 7.9 mg for dose and 3.7 ng/ml for plasma concentration. In the time-course of 5-HTT occupancy, mean occupancies were 81.8% at 6 h, 71.9% at 25 h, and 44.9% at 53 h after a single administration, and 84.3% at 6 h, 71.9% at 49 h, and 47.1% at 78 h after repeated administrations. CONCLUSIONS: Based on 5-HTT occupancy, 40 mg and more of duloxetine was needed to attain 80% occupancy, and 60 mg of duloxetine could maintain a high level of 5-HTT occupancy with a once-a-day administration schedule.

Adult↗

Effects of image reconstruction algorithm on neurotransmission PET studies in humans: comparison between filtered backprojection and ordered subsets expectation maximization.

OBJECTIVES: Both reconstruction algorithms, filtered backprojection (FBP) and ordered subsets expectation maximization (OSEM), are widely used in clinical positron emission tomography (PET) studies. Image reconstruction for most neurotransmission PET scan data is performed by FBP, while image reconstruction for whole-body [18F]FDG scan data is usually performed by OSEM. Although several investigators have compared FBP and OSEM in terms of the quantification of regional radioactivity and physiological parameters calculated from PET data, only a few studies have compared the two reconstruction algorithms in PET studies that estimate neurotransmission, i.e., neuroreceptor and neurotransporter binding. In this study we compared mean regional radioactivity concentration in the late phase and binding potential (BP) between FBP and OSEM algorithms in neurotransmission PET studies for [11C]raclopride and [11C]DASB. METHODS: Dynamic PET scans with [11C]raclopride in 3-dimensional mode were performed on seven healthy subjects. Dynamic PET scans with [11C]DASB in 2-dimensional mode were performed on another seven subjects. OSEM images were post-filtered so that its transverse spatial resolution became similar to that of FBP with the same Hanning filter (Kernel FWHM 6 mm). In both PET studies we calculated the BP of [11C]raclopride and [11C]DASB by a reference tissue model for each ROI (region of interest). RESULTS: There was no significant difference in mean regional radioactivity concentration between FBP and OSEM for [11C]raclopride and [11C]DASB. Only +2.4 - +3.2%, but still a significant difference in BP of [11C]raclopride between FBP and OSEM was observed in the striatum. There was no significant difference in BP between FBP and OSEM in other than the striatum for [11C]raclopride and in all regions for [11C]DASB. In addition, there was no significant difference in root mean square error between FBP and OSEM when BP was calculated. CONCLUSIONS: The BP values were similar between FBP and OSEM algorithms with [11C]raclopride and [11C]DASB. This study indicates that OSEM can be used for human neurotransmission PET studies for calculating BP although OSEM was not necessarily superior to FBP in the present study.

Adult↗

Time course of in vivo 5-HTT transporter occupancy by fluvoxamine.

The pharmacokinetics of drugs with specific binding sites in the brain needs to be evaluated at these sites. In this study, we measured the time course of the selective serotonin reuptake inhibitor fluvoxamine in the human brain based on serotonin transporter (5-HTT) occupancy by positron emission tomography. Consecutive positron emission tomography scans were performed using [11C]3-amino-4-(2-dimethylaminomethyl-phenylsulfanyl)-benzonitrile before, 5 hours, 26 hours, and 53 hours after 50 mg of fluvoxamine administration in 6 healthy male volunteers (mean, 24.3 +/- 4.8 years). Quantification was performed using the multilinear reference tissue model 2. Mean 5-HTT occupancies were 72.9% +/- 4.9% at 5 hours, 50.3% +/- 11.0% at 26 hours, and 24.7% +/- 15.3% at 53 hours, and plasma concentrations were 13.9 +/- 5.5 ng/mL at 5 hours, 5.1 +/- 3.2 ng/mL at 26 hours, and 1.5 +/- 1.7 ng/mL at 53 hours. The relationship between the plasma concentration of fluvoxamine and 5-HTT occupancy at these different time points was fitted to the law of mass action.

Adult↗

Quantitative analysis of dopamine synthesis in human brain using positron emission tomography with L-[beta-11C]DOPA.

BACKGROUND AND OBJECTIVES: To estimate the presynaptic function of the central dopaminergic system, the rate of endogenous dopamine synthesis has been measured by using L-[beta-C]DOPA or 6-[F]fluoro-L-DOPA with positron emission tomography. However, the regional kinetics of L-[beta-C]DOPA in human brain have not been investigated in detail. In the present study, the regional kinetics of L-[beta-C]DOPA in normal human brain and the accuracy of the method for quantifying L-[beta-C]DOPA kinetics, employing reference regions, were investigated. METHODS: After intravenous injection of L-[beta-C]DOPA, dynamic scanning was performed on ten healthy subjects for 89 min. The overall uptake rate constant K was calculated by the kinetic and graphical approaches, in which the occipital cortex was used as a reference brain region. RESULTS: Regional distribution of K was similar to those of dopamine D2 receptor. A significant negative correlation was observed between the neutral amino acid concentration in plasma and the influx rate constant through the blood-brain barrier (K1). The K values calculated by graphical approach were in good agreement with the values calculated by kinetic approach for both experimental and simulated data. CONCLUSIONS: The regional distribution of K corresponds to that of the nigrostriatal and mesolimbic dopaminergic system. Negative correlation between neutral amino acid concentration and K1 supports the suggestion that L-DOPA is transported in a competitive fashion via the same carrier system as neutral amino acids at the blood-brain barrier. Because the graphical approach can obviate the need for an arterial input function, it is useful for investigating the rate of regional dopamine synthesis in neuropsychiatric and neurodegenerative diseases.

Adult↗

Quantitative analyses of 18F-FEDAA1106 binding to peripheral benzodiazepine receptors in living human brain.

UNLABELLED: N-(5-Fluoro-2-phenoxyphenyl)-N-(2-(18)F-fluoroethyl-5-methoxybenzyl)acetamide ((18)F-FEDAA1106) is a potential PET ligand with highly selective and specific binding to peripheral benzodiazepine receptor (PBR). It has been reported that the regional density of PBR in the brain is increased in several neurodegenerative and psychiatric disorders. Thus, a reliable tracer method for evaluating PBR would be of use clinically and for research. To our knowledge, this is the first study to investigate the (18)F-FEDAA1106 binding to PBR in living human brain by PET. We also aimed to evaluate various analytic methods to quantify the density of PBR. METHODS: PET studies with (18)F-FEDAA1106 were performed on 7 healthy men. Volumes of interest (VOIs) were drawn on PET images. In each VOI, binding potential (BP) was calculated by nonlinear least-squares (NLS) fitting based on the 2-tissue compartment model, and the distribution volume (DV) was also estimated by NLS, Logan plot, and multilinear analysis (MA) methods. To estimate errors in calculation of BP and DV, simulation studies were also performed. RESULTS: The DVs estimated with each of the methods were significantly correlated. There was also significant correlation between BP with NLS and DV with NLS, Logan plot, or MA. But the interindividual differences in the distribution volume of the free and nonspecific binding compartment (K(1)/k(2)) were relatively large. In a simulation study, variation of the DV estimated by Logan plot was relatively small, but it was underestimated as the noise increased. By MA, the bias of DV was smaller, but the variation of DV was larger than by Logan plot. Within a 3% noise level, there was almost no difference between Logan plot and MA in both bias and variation. DVs estimated by both Logan plot and MA were underestimated by 10%-20%. Although the variation of DV was larger by NLS than by Logan plot, it was small enough in the noise level of VOI analysis, and the bias of DV was 0%-2%. CONCLUSION: The simulation studies indicated that NLS is a suitable method for the estimation of (18)F-FEDAA1106 binding to PBRs.

Acetamides↗

Evaluation of in vivo P-glycoprotein function at the blood-brain barrier among MDR1 gene polymorphisms by using 11C-verapamil.

UNLABELLED: P-glycoprotein (P-gp) is a membrane protein that functions as an adenosine triphosphate-dependent efflux pump for xenobiotics at the blood-brain barrier (BBB). Polymorphisms of MDR1 gene have been reported to be associated with the expression level of P-gp. (11)C-Verapamil is considered to be one of the suitable radioligands for evaluating P-gp functions. However, the metabolites of verapamil might complicate the quantitative analysis because of their possible brain penetration. In the present study, we investigated the P-gp functional differences at the BBB between the haplotypes (1236TT, 2677TT, 3435TT vs. 1236CC, 2677GG, 3435CC) of the MDR1 gene with different quantitative analyses of (11)C-verapamil. METHODS: Thirty-three healthy male volunteers were enrolled in this study after identification of the haplotypes of the MDR1 gene. Brain PET scans with (11)C-verapamil were performed for 16 min. Integration plot analysis, which yields brain uptake clearance, was performed with the first 3-min data. Integration plot analysis was then compared with several other quantitative analyses with 16-min data (1-input, 1-tissue compartment model, and the area under the curve ratio (AUC(ratio)) between brain and plasma). RESULTS: In the integration plot, there was no difference in the absolute values of brain uptake clearance (CL(uptake)) between the haplotypes; CL(uptake) of (11)C-verapamil for the haplotypes (1236TT, 2677TT, 3435TT vs. 1236CC, 2677GG, 3435CC) were 0.053 +/- 0.011 and 0.051 +/- 0.011 mL/g/min, respectively. CL(uptake) of (11)C-verapamil in the integration plot was significantly correlated with K1 and DV(K1/k2) (DV is distribution volume; K1 and k2 are plasma and tissue rate constants) in the 1-input, 1-tissue compartment model and the AUC(ratio). CONCLUSION: On the basis of the several quantitative analyses of (11)C-verapamil, the assumption that the function of P-gp at the BBB is different between the haplotypes (3 single nucleotide polymorphisms: C1236T, G2677T, and C3435T) of MDR1 gene was not supported.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

Quantitative analysis of 11C-verapamil transfer at the human blood-brain barrier for evaluation of P-glycoprotein function.

UNLABELLED: P-glycoprotein in the blood-brain barrier (BBB) has been found to be associated with several types of neurologic damage. (11)C-Verapamil has been used for in vivo imaging of P-glycoprotein function in the BBB by PET, but metabolites in plasma complicate the quantitative analysis of human studies. In this study, we validated the quantification methods of (11)C-verapamil transfer from plasma to the brain in humans. METHODS: The transfer rate constant from plasma to the brain, K(1), was estimated by nonlinear least squares (NLS) with a 2-input compartment model, including the permeation of the main metabolite in plasma at the BBB, and with a 1-input compartment model using only 15-min data that contained little metabolite in plasma. K(1) was also estimated by graphical analysis of an integration plot that uses only early-time data, before the appearance of metabolites, and the estimated K(1) was compared with that obtained by the NLS method. In the simulation study, the reliability of parameter estimates in the graphical analysis method was investigated for various values of rate constants, time ranges of parameter estimations, and noise levels. RESULTS: (11)C-Verapamil in plasma gradually converted to its metabolites, and about 45% of the radioactivity in the plasma specimen was associated with (11)C-verapamil metabolites at 30 min after injection. Although K(1) estimated from graphical analysis was slightly smaller than that by NLS, there was strong correlation among the K(1) values obtained by these 3 methods. In the simulation study, for graphical analysis, the differences between the true and mean of K(1) estimates became larger and the coefficient of variation (COV) of K(1) estimates became smaller as the end time of linear regression became later. The COV of graphical analysis was almost equal to that of NLS with the 1-input compartment model. CONCLUSION: The transfer of (11)C-verapamil from plasma to the brain was able to be quantitatively estimated by graphical analysis because this method can provide K(1) from the data of the initial few minutes without considering the effect of the metabolites in plasma.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

The antipsychotic sultopride is overdosed--a PET study of drug-induced receptor occupancy in comparison with sulpiride.

Conventional antipsychotics tend to elicit extrapyramidal symptoms at clinical doses, but dose optimization could reduce the risk of such side-effects. In-vivo receptor-binding studies have suggested that 70-80% of dopamine D2 receptor occupancy provides the desired antipsychotic effects without extrapyramidal symptoms. In terms of dose optimization based on the occupancy, there has not been enough supporting data regarding the clinical doses of the respective antipsychotics. In this study, we measured dopamine D2 receptor occupancy of two conventional benzamide antipsychotics, sulpiride and sultopride, using positron emission tomography, to investigate the rationale of their clinical dose. Although they are prescribed at similar doses (300-1200 mg), the doses required to obtain similar receptor occupancy (70-80%) were quite different: 1010-1730 mg for sulpiride but 20-35 mg for sultopride. In terms of dose, sultopride has about 50 times greater potency than sulpiride based on dopamine D2 receptor occupancy. Evidence for the optimal doses of conventional antipsychotics based on dopamine D2 receptor occupancy would be helpful for rational antipsychotic therapy.

Adult↗

Effects of dopaminergic and serotonergic manipulation on emotional processing: a pharmacological fMRI study.

Recent neuroimaging studies have demonstrated abnormal central emotional processing in psychiatric disorders. The dopamine (DA) systems and serotonin (5-HT) systems are the main target of psychopharmacotherapy. DA D2 receptor antagonists and selective serotonin reuptake inhibitors (SSRIs) are widely used in psychiatric practice. Investigating the effects of these drugs on emotional processing should lead to a better understanding of the pathophysiology and pharmacotherapy of neuropsychiatric disorders. We aimed to examine effects of dopaminergic and serotonergic manipulation on neural responses to unpleasant pictures in healthy volunteers using pharmacological fMRI. Thirteen healthy male subjects participated in a single-blind, randomized, placebo-controlled design study. Each subject participated in three fMRI sessions. In each session, participants were orally administered either 25 mg of sultopride or 50 mg of fluvoxamine or placebo prior to scanning, and neural responses to unpleasant and neutral pictures were recorded. Despite no significant differences being found in the subjective ratings of affective pictures across three sessions, compared to placebo, acute treatments of DA D2 receptor antagonists and SSRIs commonly attenuated the amygdala activity, although both treatments had slightly different modulatory effects on other components of the neural circuit of emotional processing. This study has shown that even acute treatment of drugs that manipulate neurotransmitter systems could affect brain activation associated with emotional processing in human brain. At the same time, our findings suggest that pharmacological fMRI could be a powerful tool for investigating the neurophysiological properties of drugs targeting neuropsychiatric disorders.

Adult↗

Time course of dopamine D2 receptor occupancy by clozapine with medium and high plasma concentrations.

Most antipsychotics were thought to induce antipsychotic action at an excess of 70% striatal dopamine D2 receptor occupancy, while the clinical dose of clozapine was reported to show less than 60% occupancy. High-dose clozapine could occupy as high as 80% of striatal dopamine D2 receptor in monkey PET studies. Although the time course of dopamine D2 receptor occupancy is an important property of antipsychotics, that by clozapine has not been investigated in a clinical setting. We measured the time course of extrastriatal dopamine D2 receptor occupancy with different doses of clozapine and evaluated whether the measured occupancies fitted the binding theory. Three consecutive PET scans with [11C]FLB 457 were performed for two patients with schizophrenia, chronically taking 600 mg/day and 200 mg/day of clozapine, respectively. Series of occupancies were also measured in combination with fluvoxamine or paroxetine in one patient. Dopamine D2 receptor occupancies were also simulated using individual clozapine plasma data and previously determined in vivo ED50 value. The occupancy of one patient with high plasma concentration (1207 ng/ml at peak time) was around 75% at peak and around 60% after 26 h. Another patient with medium plasma concentration (649 ng/ml at peak time) showed less than 50% occupancy at peak, decreasing to 15% after 25 h. The measured occupancy values fitted well with the simulated occupancy values. At high plasma concentration, clozapine can induce high extrastriatal dopamine D2 receptor occupancy in the human brain, and this finding fitted well with the theoretical estimation.

Adult↗

Abnormal effective connectivity of dopamine D2 receptor binding in schizophrenia.

Receptor binding has been examined region by region in both in vitro and in vivo studies, but less attention has been paid to the connectivity of regional receptor binding despite the fact that neurophysiological studies have indicated an extensive inter-regional connectivity. In this study, we investigated the connectivity of regional dopamine D2 receptor binding in positron emission tomography data from 10 drug-naive patients with schizophrenia and 19 healthy controls. We applied a structural equation method to regional receptor binding. The results indicated that the network models of the patients and normal subjects were significantly different. As to the individual path coefficients, (a) connectivity between cortical regions was different between groups; (b) connectivity from the prefrontal cortex, parietal cortex, and thalamus to the anterior cingulate differed from that in controls; and (c) connectivity from the prefrontal cortex to the anterior cingulate and thalamus via the hippocampus was observed in normal subjects but not in patients. These results suggest that a systems-level change reflected in the connectivity of D2 receptor binding is present in schizophrenia.

Adult↗