Striatal dopamine distribution in parkinsonian patients during life

Neuronal activity of human caudate nucleus and prefrontal cortex in cognitive tasks

Lesions of the caudate nucleus and prefrontal cortex may display similar cognitive deficits. Recent advances in cognitive neuroscience have clarified the functional role of prefrontal cortical areas in certain cognitive operations involved in simple language tasks. We have addressed the role of the caudate nucleus in tasks of lexical decision, semantic categorization, recognition memory, reading aloud and object naming by recording neuronal activity in patients with depth electrodes. During visual processing of words, caudate cells exhibited excitatory responses related to both semantic and phonological-articulatory encoding with non-overlapping time courses. The firing rate of the cells was increased when the semantic processing was required. This occurred within 400-600 ms after the stimulus onset, or within the first 200-300 ms of the delay period. The increased firing within 1000-1200 ms after the stimulus onset was related to the phonological processing. These responses turned out to be strikingly similar to those in Broca's area. Both reading aloud and explicit memory retrieval tasks elicited a sustained inhibition of firing of the same cells with a greater onset latency. Chronometric comparison of prefrontal, temporo-parietal and caudate activities in similar tasks relates the time course of these activations to the fronto-caudate anatomical loops and helps further understanding of the anatomy and circuitry involved in human cognition.

Orphan neurones and amine excess: the functional neuropathology of Parkinsonism and neuropsychiatric disease

The aetiology and treatment of Parkinsonism is currently conceptualised within a dopamine (DA) deficiency-repletion framework. Loss of striatal DA is thought to cause motor impairment of which tremor, bradykinaesia and rigidity are prominent features. Repletion of deficient DA should at least minimise parkinsonian signs and symptoms. In Section 2, based on extensive pre-clinical and clinical findings, the instability of this approach to Parkinsonism is scrutinised as the existing negative findings challenging the DA deficiency hypothesis are reviewed and reinterpreted. In Section 3 it is suggested that Parkinsonism is due to a DA excess far from the striatum in the area of the posterior lateral hypothalamus (PLH) and the substantia nigra (SN). This unique area, around the diencephalon/mesencephalon border (DCMCB), is packed with many ascending and descending fibres which undergo functional transformation during degeneration, collectively labelled 'orphan neurones'. These malformed cells remain functional resulting in pathological release of transmitter and perpetual neurotoxicity. Orphan neurone formation is commonly observed in the PLH of animals and in man exhibiting Parkinsonism. The mechanism by which orphan neurones impair motor function is analogous to that seen in the diseased human heart. From this perspective, to conceptualise orphan neurones at the DCMCB as 'Time bombs in the brain' is neither fanciful nor unrealistic [E.M. Stricker, M.J. Zigmond, Comments on effects of nigro-striatal dopamine lesions, Appetite 5 (1984) 266-267] as the DA excess phenomenon demands a different therapeutic approach for the management of Parkinsonism. In Section 4 the focus is on this novel concept of treatment strategies by concentrating on non-invasive, pharmacological and surgical modification of functional orphan neurones as they affect adjacent systems. The Orphan neurone/DA excess hypothesis permits a more comprehensive and defendable interpretation of the interrelationship between Parkinsonism and schizophrenia and other related disorders.

PET study of striatal fluorodopa uptake and dopamine D2 receptor binding in a patient with juvenile parkinsonism

We studied pre-synaptic and post-synaptic function in the striatum of a patient with juvenile parkinsonism (JP) using positron emission tomography (PET). [18F]6-fluorodopa (18FDOPA), 11C-YM-09151-2 and [18F]fluoro-2-deoxy-d-glucose (18FDG) were used to measure fluorodopa uptake, dopamine D2 receptor binding and glucose metabolism, respectively. In this patient, 18FDOPA accumulation was decreased markedly in the caudate nucleus and the putamen bilaterally. In the images of 11C-YM-09151-2 and 18FDG, in contrast, no conspicuous changes were observed in the striatum. Thus our PET studies using 18FDOPA, 11C-YM-09151-2 and 18FDG provide a useful approach for assisting the diagnosis of JP, because the present findings are different from the results in patients with dopa-responsive dystonia and hereditary progressive dystonia with marked diurnal fluctuation. Furthermore, our findings are of particular interest in relation to the pathogenesis of JP.Copyright Lippincott-Raven Publishers

Biological imaging and the molecular basis of dopaminergic diseases

The development and validation of preclinical biological probes of nigrostriatal dysfunction are part of the next frontier for battling diseases involving dopamine deficiency. In this work, the quantitative relationship relationship between radiofluorinated L-DOPA, [e.g., L-3,4-dihydroxy-6-[18F]fluorophenylalanine (6-[18F]fluoro-L-DOPA, FDOPA)] kinetics measured with positron emission tomography and central dopamine biochemistry is discussed. A hypothesis of a possible "non-linearity" of FDOPA kinetics with dopaminergic cell losses is presented to explain apparent discrepancies in post-mortem biochemical and histological determinations in Parkinson's disease. Similar observations have been made in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-exposed monkeys and human subjects where the FDOPA uptake constantly fell within normal values unless severe nigral damage had occurred. The limitations of FDOPA, and other biological probes, for examining the asymptomatic phase of dopaminergic diseases and the future direction of research are discussed.

Differentiating between multiple system atrophy and Parkinson's disease by positron emission tomography with 18F-dopa and 18F-FDG

Both the striatal 18F-dopa uptake and brain glucose metabolism were studied by PET with 6-L-[18F]fluorodopa (FD) and [18F]fluorodeoxyglucose (FDG) in 9 patients with multiple system atrophy (MSA) and 15 patients with idiopathic Parkinson's disease (PD). Five of the 9 MSA patients were diagnosed as having olivopontocerebellar atrophy, whereas 2 had striatonigral degeneration and 2 demonstrated Shy-Drager syndrome. The FD uptake ratios to the occipital cortex in the MSA patients at 120 min after the administration of FD were 2.07 +/- 0.31 (mean +/- SD) and 1.96 +/- 0.29 in the caudate and the putamen, respectively, and decreased compared to those in the controls (2.72 +/- 0.11, 2.71 +/- 0.10). The same ratios in the PD patients were 2.07 +/- 0.36 and 1.74 +/- 0.24, respectively, which also decreased, but the decreased uptake in the putamen was more prominent. The caudate-putamen index (CPI)(%), which was calculated by a formula based on the difference in the uptakes in the caudate and putamen divided by the caudate uptake, indicated 5.6 +/- 4.6 in the MSA patients and 14.8 +/- 5.4 in the PD patients. The CPI for all PD patients was more than 7.0, which was the mean + 2SD for the controls, but the CPI for 3 MSA patients was more than 7.0 (accuracy: 88%). The glucose metabolic rates for each region in the PD patients showed no difference from the normal controls. The frontal and the temporal cortical glucose metabolism and the caudate, the putaminal, the cerebellar and the brainstem glucose metabolism in the MSA patients decreased significantly in comparison to those in the controls. But, as the glucose metabolic rates in such regions of each patient overlapped in the two groups, the accuracy of the FDG study for differentiation was lower than that of the FD study. The putaminal glucose metabolic rates, for example, in 3 PD patients were less than 6.8 (mg/min/100 ml), which was the mean-2SD for the controls, while those in 3 MSA patients were more than 6.8 (accuracy: 75%). In addition, the combination of these two methods slightly improved the accuracy. The glucose metabolism is useful for evaluating the regional metabolic activity of the brain, and the FD study, which is specific to the dopamine system, seems to be more useful for differentiating between MSA and PD.

Dopaminergic function in familial Parkinson's disease: a clinical and 18F-dopa positron emission tomography study

There is increasing evidence for familial aggregation in Parkinson's disease (PD). It is possible that some asymptomatic relatives of PD patients have subclinical nigral Lewy body pathology and their identification could help determine the true prevalence of the disease. We used 18F-dopa positron emission tomography to investigate nigrostriatal dopaminergic terminal function in asymptomatic members of 7 unrelated kindreds in which at least 2 members had parkinsonism. Eight (25%) of the 32 asymptomatic relatives showed abnormal putamen 18F-dopa uptake (2.5 standard deviations below the normal mean). When discriminant function analysis was applied, all of these 8 subjects plus another 3 were classified with high probability as having PD. On neurological examination, 5 of the 32 relatives scanned had an isolated mild postural tremor and 2 of these 5 had reduced putamen uptake. Our findings provide further support for a role of inheritance in the etiology of PD and suggest that the penetrance for nigrostriatal dopaminergic dysfunction in familial clusters of PD is higher than the prevalence of clinical parkinsonism reported in epidemiological surveys.

Brain 6-[18F]fluorodopa metabolism in early and late onset of Parkinson's disease studied by positron emission tomography

We measured 6-[18F]fluorodopa (FDOPA) uptake in the caudate nucleus and the putamen of 20 patients with early and late onset of Parkinson's disease (EOPD and LOPD) and 20 normal control subjects using positron emission tomography. The mean influx rate constant values (Ki) were significantly reduced in the caudate nucleus and the putamen of the patients with EOPD and LOPD compared with age-matched control groups (p < 0.01), respectively. There were significant negative correlations between Ki values in the caudate nucleus (r = -0.67, p = 0.0024) and the putamen (r = -0.67, p = 0.0014), and duration of disease in the LOPD group compared with the EOPD group. Similar negative relationships between Ki values and clinical stages by Hoehn and Yahr and degrees of main clinical symptoms (bradykinesia, tremor and rigidity) were more markedly seen in the LOPD group than in the EOPD group. The present results suggest that the function of presynaptic dopaminergic terminals correlates well with clinical disease severity and degrees of main symptoms in the LOPD group, but not in the EOPD group. We speculate that compensatory up-regulatory function in the postsynaptic dopaminergic receptors may modify disease severity and the degrees of main clinical symptoms of EOPD.

Radiofluorinated L-m-tyrosines: new in-vivo probes for central dopamine biochemistry

In this work, we introduce 6-[18F]fluoro-L-m-tyrosine (6-FMT) and compare its in-vivo kinetic and bio-chemical behaviors in monkeys and rodents with those of 4-FMT and 6-[18F]fluoro-L-3, 4-dihydroxyphenylalanine (DOPA) (FDOPA). These radiofluorinated m-tyrosine presynaptic dopaminergic probes, resistant to peripheral 3-O-methylation, offer a nonpharmacological alternative to the use of catechol-O-methyltransferase inhibitors. Like FDOPA, 4-FMT and 6-FMT are analogs that essentially follow the L-DOPA pathway of central metabolism. After i.v. administration in nonhuman primates and rodents, these new radiofluorinated m-tyrosine analogs accumulate selectively in striatal structures and allow for the detection of additional innervation sites (e.g., brain stem) rich in aromatic amino acid decarboxylase. Bio-chemical analyses in rodents and monkeys revealed the specificity of their central and peripheral metabolism. Molecular and enzymatic mechanisms involved in their retention in central brain structures are consistent with involvement of dopaminergic neurons. The high signal-to-noise ratios observed make these radiofluorinated m-tyrosine analogs outstanding candidates for probing the integrity of central dopaminergic mechanisms in humans.

Quantification of dopamine metabolism in man: a mathematically justifiable approach

Model derivation, the proposal of the best model to fit the measured data, is a crucial and often neglected step in compartmental analysis. Since the model which best fits the data in a statistical sense may be simpler than the known physiology of the system, the order (mathematical complexity) of the model that can be accepted must be determined independently of physiological considerations. Although [18F]6-fluoro-L-dopa (F-dopa) has been used as a tracer for the investigation of presynaptic dopamine metabolism for a number of years, a definitive method of quantitative analysis has not yet emerged. Simple graphical analyses have been used predominantly in clinical studies, while compartmental analyses have been used to gain a better understanding of F-dopa kinetics. Over the years quantitative approaches to F-dopa metabolism have grown increasingly complicated, and complex models that rely on the use of parameter constraints, or simplifying assumptions in order to collapse the model to solvable dimensions, have been developed. We propose a simple compartmental model to quantify the metabolism of F-dopa in the striatum. Both compartmental and graphical analyses were performed using this model, and the mathematical expression which relates the results of the two analyses was derived. The ability of our approach to reveal and quantify differences in the dopaminergic metabolism of individuals has been demonstrated in a small number of studies.

Differences in the reduced 18F-Dopa uptakes of the caudate and the putamen in Parkinson's disease: correlations with the three main symptoms

It has been reported that the F-Dopa (FD) uptake in patients with idiopathic Parkinson's disease (PD) decreased significantly in the caudate and putamen when compared to controls. The FD uptake severely decreased in the putamen, while it was relatively spared in the caudate nucleus. We also previously reported that atypical parkinsonism with no or little tremor showed a homogeneously reduced FD uptake in both the caudate and the putamen. In this study we evaluated the caudate and the putaminal FD uptakes in relation to the three main symptoms in PD. The FD uptake was measured by PET with 6-L-[18F]fluorodopa in 17 patients with PD. The caudate and the putaminal FD uptake ratios to the cerebellum at 120 min were evaluated. The caudate and the putaminal FD uptake ratios in the patients with PD decreased as their clinical stages advanced. These decreases also correlated with the degree of rigidity and bradykinesia. However, such decreases did not correlate with the degree of tremor. The caudate-putamen index (CPI)(%), which was calculated by a formula based on the difference in the uptakes of the caudate and putamen divided by the caudate uptake, indicated 11.6 +/- 3.6, 16.5 +/- 5.5 and 18.3 +/- 4.1 in the group of no, mild and moderate tremor, respectively, and increased as the degree of tremor advanced. The CPI in the group of moderate tremor significantly increased from that in the group of no tremor (P < 0.04). However, the CPI did not correlate with the clinical stage, the degree of rigidity or the degree of bradykinesia. The FD/PET study therefore effectively demonstrated the severity of the clinical symptoms of rigidity and bradykinesia in patients with PD in correlation with a decrease in the FD uptakes in the caudate and the putamen, and it also demonstrated that the severity of tremor might have a different mechanism from that of such other symptoms as rigidity and bradykinesia.

Decreased single-photon emission computed tomographic [123I]beta-CIT striatal uptake correlates with symptom severity in Parkinson's disease

Previous studies have utilized single-photon emission computed tomography (SPECT) to demonstrate decreased [123I]beta-CIT striatal uptake in idiopathic Parkinson disease (PD) patients. The present study extends this work by examining SPECT outcome measures in a larger group of PD patients with varying disease severity. Twenty-eight L-dopa-responsive PD patients (Hoehn-Yahr stages 1-4) and 27 healthy controls had SPECT scans at 18 to 24 hours after injection of [123I]beta-CIT. Specific to nondisplaceable striatal uptake ratios (designated V3") were correlated with Hoehn-Yahr stage and Unified Parkinson's Disease Rating Scale (UPDRS) subscores. Linear discriminant function analyses utilizing striatal uptakes, putamen-to-caudate ratios, and ipsilateral-contralateral asymmetry indices were performed. Decreased striatal tracer uptake (V3") was correlated with total UPDRS score for both contralateral and ipsilateral striatum. Putamen uptake was relatively more reduced than caudate with mean putamen:caudate ratios of 0.50 +/- 0.17 and 0.82 +/- 0.09 for PD patients and controls, respectively. Ipsilateral:contralateral asymmetry was significantly greater in PD patients than controls. Discriminant function analysis utilizing V3" for ipsilateral and contralateral caudate and putamen correctly classified all 55 cases. These data demonstrate marked differences in [123I]beta-CIT SPECT measures in healthy controls and PD patients. The significant correlation of SPECT measures with motor severity suggests [123I]beta-CIT may be a useful marker of disease severity in PD.

Memory and skill acquisition in Parkinson's disease and frontal lobe dysfunction

Animal experiments and human neuropsychological studies have provided evidence for the hypothesis that skill acquisition may be regulated by the basal ganglia. In the present studies, perceptual and cognitive skill acquisition as well as a number of explicit verbal memory functions were investigated in patients in early and more advanced stages of Parkinson's disease (PD) and in patients with frontal lobe lesions. Patients in more advanced stages of PD were impaired at cognitive skill acquisition as well as during recall conditions that involved active semantic organisation of the stimulus material. Similar explicit memory deficits were present in frontally lesioned patients. PD patients with unilateral symptoms showed a selective impairment in acquiring a cognitive skill. Perceptual skill acquisition was preserved in all groups. The overall pattern of memory impairment in PD is largely consistent with dysfunction of fronto-striatal circuitry.

Measures and pitfalls for successful preparation of "no carrier added" asymmetric 6-[18F]fluor-L-dopa from 18F-fluoride ion

6-[18F]Fluoro-L-dopa (6FD) has been proposed and used for probing cerebral dopamine metabolism by positron emission tomography. Recently a new method for asymmetric synthesis of 6FD has been reported. This method involves synthesis of 6-[18F]fluoro-3,4-dimethoxybenzylbromide which is reacted with (S)-1-Boc-2-tert-butyl-3-methyl-4-imidazolidinone. The resulting alkylated compound is then hydrolyzed with hydriodic acid to produce 6FD. This method has been used to produce 6FD and several critical steps that required attention found, in addition to some modification for successful 6FD production. 6FD is prepared in 6-13% radiochemical yield (decay not corrected) after HPLC purification with a production time of 85 min.

Associative learning in degenerative neostriatal disorders: contrasts in explicit and implicit remembering between Parkinson's and Huntington's diseases

The performances of 12 patients with Parkinson's disease (PD), 16 with Huntington's disease (HD), and young and old healthy controls were assessed on a number of tests of verbal and nonverbal declarative memory, on a test of nonmotor conditional associative learning (words and colors), and on a number of reaction time (RT) tasks. The RT tasks consisted of cued simple and choice reactions. The relationship between the precue and the imperative stimulus in the S1-S2 paradigm was nonarbitrary in the first series and arbitrary in the second series. The series with arbitrary S1-S2 associations was repeated across two successive blocks of trials. The rationale of the study was to investigate the function of the basal ganglia "complex loop," and it was postulated that HD patients would show greater deficits because of greater involvement of the caudate nucleus. The patients with HD had the slowest RTs. Across the two blocks with arbitrary S1-S2 associations, the patients with HD but not PD nevertheless showed evidence of learning in their precued RTs. In contrast, the patients with PD were better able to remember the associations in free recall than were the HD patients. It is concluded that patients with PD have relatively greater deficits in procedural learning, whereas those with HD have relatively more impairments in declarative memory, and the greater level of cognitive impairment in HD overall is interpreted as being due to more serious damage to the caudate loop.

Assessment of dopamine metabolism in brain of patients with dementia by means of 18F-fluorodopa and PET

By means of positron emission tomography (PET) and 18F-fluorodopa (FDOPA), a study was initiated to analyze the cerebral dopamine (DA) metabolism of 32 subjects including those with AD/SDAT and vascular dementia (VD, multi-infarct type). A semiautomated irregular ROI drawing routine to identify the striatum was developed that interactively defined the PET threshold pixels referring to the count histograms and location of the corresponding pixels. A comparative study by five examiners showed significant improvement in the area size definition and count linearity particularly for low contrast objects. The graphical plot was employed to calculate the FDOPA influx rate (Ki) for the ROI data with cerebellar radioactivity as an input function. The striatal Ki value was found to be relatively stable and did not show signs of a significant age-related change. The vascular patients had smaller Ki to the striatum than the aged control. Although the mean Ki of AD/SDAT was almost compatible with that of age-matched normals, their Ki was more scattered with higher and lower Ki cases. The multiple regression analysis revealed that the Ki could be predicted by age and the mini-mental state (MMS) performance (r2 = 0.590, p < 0.01 for AD/SDAT, r2 = 0.401, and p < 0.05 for VD). MMS was found to be a more dominant factor than age. We conclude that dopamine metabolism became disturbed as dementia became progressively severe.

Radiopharmaceuticals for brain imaging

Brain imaging is performed using radiopharmaceuticals by single photon emission computed tomography (SPECT) and positron emission tomography (PET). SPECT and PET radiopharmaceuticals are classified according to blood-brain-barrier permeability, cerebral perfusion and metabolism receptor-binding, and antigen-antibody binding. The blood-brain-barrier (BBB) SPECT agents, such as 99mTcO4-, [99mTc]DTPA, 201TI and [67Ga]citrate are excluded by normal brain cells, but enter into tumor cells because of altered BBB. These agents were used in the earlier period for the detection of brain tumors. SPECT perfusion agents such as [123I]IMP, [99mTc]HMPAO, [99mTc]ECD are lipophilic agents and therefore, diffuse into the normal brain. These tracers have been successfully used to detect various cerebrovascular diseases such as stroke, Parkinson disease, Huntington's disease, epilepsy, dementia, and psychiatric disorders. Xenon-133 and radiolabeled microspheres have been used for the measurement of cerebral blood flow (CBF). Important receptor-binding SPECT radiopharmaceuticals include [123I]QNE, [123I]IBZM, and [123I]iomazenil. These tracers bind to specific receptors in the brain, thus displaying their distribution in various receptor-related cerebral diseases. Radioiodinated monoclonal antibodies were used for the detection of brain tumors. PET radiopharmaceuticals for brain imaging are commonly labeled with positron-emitters such as 11C, 13N, 15O, and 18F, although other radionuclides such as 82Rb, 62Cu and 68Ga also were used. The brain uptake of [13N]glutamate, [68Ga]EDTA and [82Rb]RbCl depends on the BBB permeability, but these are rarely used for brain imaging. Several cerebral perfusion agents have been introduced, of which [15O]water, [13N]ammonia, and [15O]butanol have been used more frequently. Regional CBF has been quantitated by using these tracers in normal and different cerebral disease states. Other perfusion agents include [15O]O2, [11C]CO, [11C]CO2, [18F]fluoromethane, [15O]O2, [11C]butanol, and [62Cu]PTSM. Among the PET cerebral metabolic agents, [18F]fluorodeoxyglucose (FDG) is most commonly used to detect metabolic abnormalities in the brain. Various brain tumors have been graded by [18F]FDG PET. This technique was used to detect epileptic foci by showing increased uptake in the foci during the ictal period and decreased uptake in the interictal period. Differentiation between recurrent tumors and radiation necrosis and the detection of Alzheimer's disease have been made successfully by [18F]FDG PET. Other PET metabolic agents such as [11C]deoxyglucose, and [11C]methylmethionine have drawn attention in the detection of brain tumors. [18F]fluorodopa is a cerebral neurotransmitter agent, which has been found very useful in the detection of Parkinson disease that shows reduced uptake of the tracer in the striatum of the brain.(ABSTRACT TRUNCATED AT 400 WORDS)

Motor memory and the preselection effect in Huntington's and Parkinson's disease

Patients with Huntington's disease (HD) and Parkinson's disease (PD) show different patterns of preserved and impaired memory performance. This study investigates explicit memory for movements in HD and PD with a linear positioning apparatus using Dick et al.'s procedure (J. Gerontol. 43, 127-135, 1988). In the first experiment, 12 HD patients were compared to 12 matched-controls. HD patients were more impaired than the controls by the delay between criterion and recall movements, whether the delay was filled or unfilled. Switching the limb between criterion and recall movements did not lead to more effects in HD patients and in controls. In the second experiment, 12 non-demented PD patients were compared to matched-controls. PD patients were more impaired than controls when the recall movement was executed with the contralateral hand, but were not more affected by the delay. In both experiments, HD and PD patients, as well as the controls, recalled self-generated preselected movements better than imposed movements. These results suggest the existence of distinct forms of motor memory impairment in some subcortical neurodegenerative diseases.

Differential diagnosis of Parkinson's disease, multiple system atrophy, and Steele-Richardson-Olszewski syndrome: discriminant analysis of striatal 18F-dopa PET data

Clinicopathological series indicate that the clinical diagnosis of Parkinson's disease is correct in only 80% of cases. Multiple system atrophy (MSA) and Steele-Richardson-Olszewski syndrome (SRO) comprise most of the misdiagnoses. By means of 18F-dopa PET the pattern of nigrostriatal dopaminergic dysfunction in 28 patients with clinically probable Parkinson's disease, 25 with MSA, and 10 patients with SRO, was assessed and compared with the pattern in 27 normal subjects. Discriminant function analysis was used to assess the ability of 18F-dopa PET to categorize individual parkinsonian patients on the basis of their caudate and putamen tracer uptake. Discriminant function analysis assigned all control subjects a normal category. One Parkinsonian patient out of 63 was classified as "normal" on the basis of PET findings, although this patient had significantly reduced putamen 18F-dopa uptake. Discriminant function analysis was less effective at distinguishing different categories of akinetic-rigid syndrome on the basis of their striatal 18F-dopa uptake, as judged against clinical criteria. Patients clinically labelled as having typical or atypical Parkinsonian syndromes were assigned the same category on PET criteria 64% and 69% of the time, respectively. When all three categories of Parkinson's disease, MSA, and SRO were considered together, clinical and 18F-dopa PET findings correlated in 64% of patients assigned a diagnosis of Parkinson's disease and 70% of those given a diagnosis of SRO; MSA was less readily discriminated, patients with MSA being assigned to MSA, Parkinson's disease, and SRO groups with equal frequency. The correlation between clinical and discriminant function analysis assignment improved when separate comparisons were made between Parkinson's disease and MSA, or Parkinson's disease and SRO groups. In these analyses, clinical and PET categorisation of MSA and Parkinson's disease agreed in 60% of cases, and of SRO and Parkinson's disease in 90% of cases. In summary, (18)F-dopa PET successfully discriminates normal subjects from parkinsonian patients, and patients with Parkinson's disease from patients with SRO, but is less reliable in distinguishing Parkinson's disease from MSA. The concomitant assessment of striatal neuronal function with additional PET tracers may be necessary to reliably differentiate typical and atypical parkinsonian syndromes.

Neuropsychological correlates of L-deprenyl therapy in idiopathic parkinsonism

1. Monoaminergic neurotransmitter systems are known to play an important role in neuropsychological functions and they are impaired in dementia of DAT and PD. 2. L-deprenyl is a monoamine-enhancing drug which at low doses selectively inhibits MAO-B, an enzyme whose brain activity has been reported to increase in normal aging and neurodegenerative dementing disorders. 3. The authors studied the effects of L-deprenyl, 10 mg/day, on several cognitive domains in idiopathic parkinsonians without dementia. Ten out-patients, treated with levodopa plus DDI, were tested before receiving L-deprenyl and retested six months after they had been treated with the drug. A control group of ten parkinsonian out-patients treated with only levodopa plus DDI, matched for age, educational level, severity and duration of extrapyramidal disease, was tested by the same neuropsychological battery and retested after a comparable time interval. 4. Statistically significant changes were noted in the verbal and visuospatial learning performances of PD patients treated with the combination of L-deprenyl and levodopa.

Positron emission tomographic studies of dopa-responsive dystonia and early-onset idiopathic parkinsonism

There are two major syndromes presenting in the early decades of life with dystonia and parkinsonism: dopa-responsive dystonia (DRD) and early-onset idiopathic parkinsonism (EOIP). DRD presents predominantly in childhood with prominent dystonia and lesser degrees of parkinsonism. EOIP presents before age 40 with parkinsonism (often with associated dystonia). Both disorders are exquisitely sensitive to levodopa, although the long-term prognosis in each appears to be different. Some have suggested, however, that DRD is a form of EOIP. We performed positron emission tomography with 6-fluoro-dopa in 10 patients with DRD and 18 patients with EOIP to study the integrity of their nigrostriatal dopaminergic systems. In DRD, we found normal striatal FD uptake. In contrast, patients with EOIP had reduced striatal FD uptake. We conclude that the patho-physiologies of DRD and EOIP are distinct. Although both disorders presumably represent a deficiency of striatal dopamine, the results suggest that in DRD dopa uptake, decarboxylation, and storage mechanisms are intact. This may explain the sustained response of DRD to low doses of levodopa. 6-Fluoro-dopa positron emission tomography distinguishes DRD from EOIP.

Side of onset of motor symptoms influences cognition in Parkinson's disease

Studies attempting to relate cognitive impairment to asymmetry of motor symptoms in Parkinson's disease (PD) have found contradictory results. We examined 88 patients with unilateral onset of idiopathic PD who underwent a comprehensive neuropsychological assessment, including language, visuospatial abilities, abstraction and reasoning, attention and mental tracking, set shifting, and memory. Patients whose motor signs began on the left side of the body consistently performed more poorly on the battery of cognitive measures than did patients with right-side onset. Significant differences were found on immediate and delayed verbal recall, word retrieval, semantic verbal fluency, visuospatial analysis, abstract reasoning, attention span, and mental tracking. These differences could not be attributed to differences in the overall severity of motor symptoms at the time of cognitive assessment, or the current pattern of motor asymmetry. This finding suggests that damage to right-hemisphere dopamine systems plays a disproportionately greater role in PD-related cognitive decline than a presumably comparable left-hemisphere dopamine depletion.

Correlation of striatal fluorodopa uptake in the MPTP monkey with dopaminergic indices

Striatal 18F-6-fluorodopa (FD) uptake constants were measured by positron emission tomography in (1) normal cynomolgus monkeys and (2) a series of cynomolgus and rhesus monkeys that had received intracarotid infusions of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). After the animals were killed, the number and average size of dopaminergic neurons in the substantia nigra pars compacta were measured. Striatal levels of dopamine and its metabolites, and the striatal activities of the dopaminergic synthetic enzymes, were also determined. The striatal FD uptake constants showed highly significant positive correlations with both number and size of dopaminergic neurons, indicating atrophy of surviving neurons in MPTP-treated animals. The uptake constants also showed significant positive correlations with striatal levels of dopamine, total catecholamines, and the activities of the synthetic enzymes. Both histochemical and biochemical data on tyrosine hydroxylase suggested some contralateral enzyme loss in these MPTP-treated monkeys, as well as decreased enzyme activity in surviving neurons on the lesioned side. However, residual enzyme activities were apparently not rate limiting to striatal FD uptake. It is concluded that PET-FD measurements by positron emission tomography provide a good index of the integrity of the nigrostriatal pathway.

Antisense oligodeoxynucleotide inhibits D2 dopamine receptor-mediated behavior and D2 messenger RNA

There are several subtypes of dopamine receptors in the central nervous system which mediate the actions of dopamine in producing its diverse motor and behavioral effects. In this study we determined whether an antisense oligodeoxynucleotide directed to the mRNA encoding one of the subtypes of the dopamine receptor can inhibit a specific dopamine-mediated behavior. Accordingly, the effects of a phosphorothioate-modified antisense oligodeoxynucleotide targeted toward the D2 dopamine receptor mRNA (D2 antisense) was studied in mice with unilateral 6-hydroxydopamine-induced lesions of the corpus striatum. Rotational behavior in response to different agents, and the levels of D2 and D1 dopamine receptors and D2 and D1 dopamine receptor mRNAs in corpus striatum were then measured. In control mice, lesioning resulted in a contralateral rotational behavior in response to the D1 dopamine receptor agonist SKF 38393, the D2 dopamine agonist quinpirole, and the muscarinic cholinergic agonist oxotremorine. Lesioning also caused an increase in D2 dopamine receptor mRNA levels in the dorsolateral striatum. Intraventricular injections of the D2 antisense inhibited rotational behavior induced by quinpirole but not that induced by SKF 38393 or that induced by oxotremorine. Repeated administration of the D2 antisense significantly reduced the levels of the D2 dopamine receptor and D2 dopamine receptor mRNA in the dorsolateral but not the dorsomedial striatum. Similar treatment failed to significantly alter the levels of the D1 dopamine receptor or D1 receptor mRNA in dorsolateral or dorsomedial striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

The detection of preclinical Parkinson's disease: what is the role of positron emission tomography?

On clinical criteria alone, the diagnosis of early Parkinson's disease can be difficult and, by definition, the prospective recognition of preclinical Parkinson's disease is impossible. Positron emission tomography (PET) using [18F]dopa as tracer has been proposed as a means of identifying patients with preclinical disease. The number of subjects detected to date has been few; most have been identified by serendipity or during the course of family studies. This review examines the significance of a single abnormal scan in an apparently healthy subject in terms of the relationship between normal and abnormal values and the time course of the disease.

6-[18F]fluorodopa metabolism in patients with hemiparkinsonism studied by positron emission tomography

A group of 10 healthy control subjects and 10 patients with hemiparkinsonism (HD) were studied by positron emission tomography (PET) using 6-[18F]fluorodopa (FDOPA). FDOPA metabolism in the caudate nucleus and the putamen was separately estimated by measuring target-to-background ratios (TBRs) using composite images added between 30 and 60 min after FDOPA injection and by TBR-versus-time slopes during PET study. TBRs in the caudate nucleus and the putamen were 1.81 +/- 0.23 (mean +/- SD) and 1.92 +/- 0.28 in the 10 controls, respectively. In HD patients, on the dominantly affected hemisphere related to main clinical symptoms, TBRs were significantly decreased in the caudate nucleus (P < 0.01) and the putamen (P < 0.05) compared with those in the corresponding areas on the contralateral hemisphere, though those TBRs on both hemispheres were significantly decreased compared with the TBRs of normal subjects (P < 0.01). TBRs and TBR slopes in both the caudate nucleus and the putamen were correlated with disease severity according to Hoehn and Yahr. On the dominantly affected hemisphere, TBR and TBR slopes in the putamen were well correlated with individual clinical measures for bradykinesia and rigidity, and those in the caudate nucleus were also correlated with the severity of tremor. Our data suggest that in HD patients, PET study using FDOPA may provide unique and efficient information on the dysfunction of the dominantly affected caudate nucleus and the putamen which are correlated with diseased severity and individual clinical symptoms.

Functional imaging in relation to parkinsonian syndromes

Parkinsonism is a feature not only of Parkinson's disease but also of many other diseases affecting basal ganglia function. Functional imaging (PET and SPECT) can demonstrate the various resting patterns of disruption of regional cerebral blood flow, metabolism, and neuropharmacology associated with different parkinsonian disorders. 18F-dopa PET also has the potential to detect subclinical dysfunction of dopaminergic terminals in at-risk subjects. Finally, functional imaging can help us understand the nature of the networks involved in performing different motor tasks, and can reveal how these networks malfunction in the presence of bradykinesia or parkinsonian tremor.

Survival of implanted fetal dopamine cells and neurologic improvement 12 to 46 months after transplantation for Parkinson's disease

BACKGROUND AND METHODS

Patients with Parkinson's disease tend to have a reduced response to levodopa after 5 to 20 years of therapy, with "on-off" fluctuations consisting of dyskinesia alternating with immobility. In an effort to modify the motor disability of advanced Parkinson's disease, we implanted embryonic mesencephalic tissue containing dopamine cells into the caudate and putamen of seven patients. Two patients received unilateral grafts in the caudate and the putamen on the side opposite the side with worse symptoms. Five patients received bilateral grafts implanted in the putamen only. In six of the seven patients, the fetal tissue was obtained from a single embryo with a gestational age of seven to eight weeks. The tissue was injected by means of 10 to 14 needle passes. There were no surgical complications. Four of the seven patients underwent immunosuppression with cyclosporine and prednisone.

RESULTS

All patients reported improvement according to the Activities of Daily Living Scale when in the on state 3 to 12 months after surgery (P < 0.01). Neurologic examination according to the Unified Disease Rating Scale showed that five of the seven patients improved when in the on state six months after surgery. The mean group Hoehn-Yahr score improved from 3.71 to 2.50 (P < 0.01). Computer and videotape testing in the home supported these findings. Fluctuations in clinical state were moderated, and periods of dyskinesia and off episodes were shorter and less severe than before implantation. Drug doses were reduced by an average of 39 percent (P < 0.01; maximum, 58 percent). The results of clinical evaluation and fluorodopa positron-emission tomography in one patient were compatible with transplant survival for as long as 46 months. Both immunosuppressed and nonimmunosuppressed patients improved.

CONCLUSIONS

Fetal-tissue implants appear to offer long-term clinical benefit to some patients with advanced Parkinson's disease.

Positron emission tomography with 18F-dopa: interpretation and biological correlates in nonhuman primates

Positron emission tomography (PET) was carried out, with 18F-DOPA as a ligand, in normal control monkeys and "parkinsonian" monkeys who had been treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. The following approaches were used in data analysis: ratio of 18F accumulation in specific to nonspecific brain areas and 18F-DOPA influx constant obtained using either the actual plasma 18F-DOPA or the 18F activity in a nonspecific brain area as the input function. The results from these analyses were compared to one another and to biological parameters relevant to dopaminergic function. The striatum/cortex ratio and the rate constant calculated from plasma 18F-DOPA appeared to be the most sensitive analytic techniques.

Increased striatal 18F-dopa uptake and normal glucose metabolism in idiopathic dystonia syndrome

Striatal 18F-Dopa uptake and glucose metabolism were studied by positron emission tomography with 6-L-[18F]fluorodopa and [18F]fluorodeoxyglucose, respectively, in 8 patients with idiopathic dystonia. Patients with abnormal findings on the brain CT and MRI were excluded from this study. The clinical diagnosis consisted of torsion dystonia in 3 patients, focal dystonia limited in the arm in 3 and cervical dystonia (spasmodic torticollis) in 2. The 18F-Dopa uptake, corrected by nonspecific retention in the cerebellum, at 120 min post-administration was evaluated, and increased 18F-Dopa uptake in the putamen and in the caudate head was observed in the patients with idiopathic dystonia compared to the normal controls. The striatal glucose metabolism in the patients with idiopathic dystonia showed no difference with the normal controls. These findings suggest that pathogenetic mechanism of idiopathic dystonia involves increased presynaptic activity of the dopaminergic system in the striatum.

Transplantation of fetal dopamine neurons in Parkinson's disease: PET [18F]6-L-fluorodopa studies in two patients with putaminal implants

Two patients with Parkinson's disease who underwent implantation of fetal mesencephalic tissue into the putamen were serially studied using positron emission tomography and [18F]6-L-fluorodopa ([18F]dopa). The uptake of [18F]dopa is related to the functional integrity of the presynaptic dopaminergic system. Preoperative studies revealed a marked decrease in putamen [18F]dopa uptake, with lesser involvement of the caudate. Two and 4 months, respectively, after operation, both patients demonstrated functional improvement, as described elsewhere. One patient was scanned 5, 8, and 13 months after the operation and the other was scanned 7 and 12 months after the operation. In both patients, [18F]dopa uptake increased within the operated putamen despite a progressive decrease in tracer uptake in the unoperated striatal structures. We believe that this increased uptake of [18F]dopa at the implantation site represents functional integrity within a surviving neural graft. While there has been little further clinical improvement beyond the fifth postoperative month, the uptake of [18F]dopa at the operation site in both patients has progressively increased. The kinetic data provide evidence of disease progression in the unoperated striatum, which, balanced against increasing graft function, may explain why clinical improvement reached a plateau within months after surgery.

Production of 6-[18F]fluoro-L-dopa and its metabolism in vivo--a critical review

This report critically appraises methods for the synthesis of 6-[18F]fluoro-L-3,4-dihydroxyphenylalanine (6-FDOPA) that are based on labelling by non-regioselective electrophilic fluorination, regioselective fluorodemetalation or nucleophilic substitution. Recommendations for the standardization of labelling procedures, the optimization of radiochemical yield and the assurance of product quality and safety are given. Studies of the metabolism of 6-FDOPA in vivo are also reviewed to emphasize the importance of the biochemical component of the development of this tracer for positron emission tomography (PET).

L-6-[18F]fluoro-dopa metabolism in monkeys and humans: biochemical parameters for the formulation of tracer kinetic models with positron emission tomography

Characterization of peripheral and cerebral L-3,4-dihydroxy-6-[18F]fluorophenylalanine (FDOPA) metabolism in humans and monkeys has shown FDOPA to be an analogue of L-DOPA for the study of the dopaminergic system with positron emission tomography (PET). In human studies with carbidopa pretreatment, L-3,4-dihydroxy-6-[18F]fluoro-3-O-methylphenylalanine (3-OMFD) was the only FDOPA metabolite detected in plasma. FDOPA administration in monkeys resulted in selective accumulation of FDOPA metabolites in central dopaminergic regions, whereas 3-OMFD of peripheral origin was uniformly distributed among putamen, caudate, frontal cortex, and cerebellum. At 60 min, 3-OMFD and 6-[18F]fluorodopamine (FDA) each represented approximately 35% of the total activity, the remainder being FDOPA and FDA metabolites. These data on monkey and human FDOPA metabolism provide the basis for the configuration of an FDOPA tracer kinetic model with PET.

Kinetics and modeling of L-6-[18F]fluoro-dopa in human positron emission tomographic studies

Kinetics of L-3,4-dihydroxy-6-[18F]fluorophenylalanine (FDOPA) in striatum and cerebellum were measured in 10 normal human subjects with positron emission tomography (PET) from 0 to 120 min after an intravenous bolus injection of the tracer. The time course of the arterial plasma concentrations of the tracer and its metabolites was also assayed biochemically. FDOPA compartmental models that are based on biochemical information were investigated for their consistency with the measured striatal and cerebellar tissue kinetics. A modeling approach was also developed for separating plasma FDOPA and metabolite time-activity curves from the measured total 18F time-activity curve in plasma. Results showed that a model consisting of three separate compartments for tissue FDOPA, tissue 6-[18F]fluorodopamine (FDA) and its metabolites, and tissue L-3,4-dihydroxy-6-[18F]fluoro-3-O-methylphenylalanine (3-OMFD) could describe adequately the striatal kinetics in humans. Based on this model, the FDOPA transport constant across the blood-brain barrier (BBB) (K1), the FDOPA decarboxylation rate constant (k3), and the turn-over rate constant of FDA and its metabolites (k4) could be estimated by model fitting to the tissue kinetics and were found for the normal subjects to be 0.031 +/- 0.006 ml/min/g (mean +/- SD), 0.041 +/- 0.015/min, and 0.004 +/- 0.002/min, respectively. About 50% of the FDOPA that crossed the BBB from plasma to striatum was decarboxylated. The decarboxylation constant with respect to plasma FDOPA (K3) was 0.015 +/- 0.003 ml/min/g. The BBB transport corresponded to a permeability-surface area product of 0.032 ml/min/g for FDOPA. For 3-OMFD, the BBB transport was 1.7 times faster. The effects of tissue heterogeneity on the FDOPA kinetics and on the estimated model parameters were also investigated. The usefulness and implications of these findings for interpretation of PET FDOPA studies are discussed.

Striatal blood flow, glucose metabolism and 18F-dopa uptake: difference in Parkinson's disease and atypical parkinsonism

Striatal blood flow, glucose metabolism and 18F-Dopa uptake were studied with positron emission tomography (PET) in eight non-demented patients with idiopathic Parkinson's disease and eight with atypical Parkinsonism. Patients with atypical Parkinsonism had no specific cause for the Parkinsonian symptoms and were clinically different from Parkinson's disease with lack of resting tremor and a poor response to dopaminergic drugs. Decreased 18F-Dopa uptake in the putamen was observed in patients with Parkinson's disease and atypical Parkinsonism compared with normal controls. 18F-Dopa uptake in the head of the caudate was also significantly reduced in both conditions but relatively less in Parkinson's disease. Decreased blood flow and glucose metabolism in the striatum associated with a global cerebral decrease were also observed in patients with atypical Parkinsonism compared with controls, while they were preserved in patients with Parkinson's disease, indicating affected neurons not only in the striatum but also in the cerebrum in patients with atypical Parkinsonism compared with patients with Parkinson's disease. The differences in the caudate 18F-Dopa uptake, and blood flow and glucose metabolism in the cerebrum including the striatum between Parkinson's disease and atypical Parkinsonism assessed by PET may be due to the differences in the pathophysiological mechanism between Parkinson's disease and atypical Parkinsonism.

Approaches to the design of biochemical probes for positron emission tomography

Since the development of the 2-deoxy-D-glucose procedure by L. Sokoloff considerable advances have been made in the design of radiotracers for estimation of in-vivo biochemical parameters. Many of these advances are due to the development of positron emission tomography. As a result key biochemical processes can now be evaluated with newly developed positron-emitting labeled enzyme probes in man, in-vivo, allowing the study of a wide range of specific cellular processes in health and disease states.

Distribution and kinetics of 3-O-methyl-6-[18F]fluoro-L-dopa in the rhesus monkey brain

Most attempts to model accurately [18F]-DOPA imaging of the dopamine system are based on the assumptions that its main peripheral metabolite, 3-O-methyl-6-[18F]fluoro-L-DOPA ([18F]3-OM-DOPA), crosses the blood-brain barrier but is present as a homogenous distribution throughout the brain, in part because it is not converted into [18F]DOPA in significant quantities. These assumptions were based mainly on data in rodents. Little information is available in the primate. To verify the accuracy of the above assumptions, we administered 18F-labeled 3-OM-DOPA to normal rhesus monkeys and animals with lesions of the DA nigrostriatal system. No selective 18F regional accumulation in brain was apparent in normal or lesioned animals. The plasma metabolite analysis revealed that only the negatively charged metabolites (e.g., sulfated conjugates) that do not cross the blood-brain barrier were found in significant quantities in the plasma. A one-compartment, three-parameter model was adequate to describe the kinetics of [18F]3-OM-DOPA. In conclusion, assumptions concerning [18F]3-OM-DOPA's behavior in brain appear acceptable for [18F]DOPA modeling purposes.

A method of studying pharmacokinetics in man at picomolar drug concentrations

1. We describe a new method that enables the tissue kinetics of picomolar concentrations of drugs to be measured in man. The method is based on the administration of a drug, labelled with a short-lived positron-emitting radioisotope, such as carbon-11 (t1/2 = 20.4 min, beta + = 99.8%) or fluorine-18 (t1/2 = 109.8 min, beta + = 96.9%), which is then detected in vivo by an array of 10 large uncollimated sodium iodide scintillation detectors, arranged as five opposing pairs, with each pair collecting data over one major organ or region of the body. 2. To illustrate the scope of the new method we report the results of administering [O-methyl-11C]-diprenorphine, an established radioligand for central opiate (mu, kappa, and delta) receptors and L-6-[18F]-fluoro-DOPA, a marker for dopaminergic neurons. 3. Only 2-10 muCi (74-370 kBq) of radioactivity are used and, as a consequence of the high specific activities with which carbon-11 and fluorine-18 labelled compounds can be prepared, the method requires less than a nanomole of drug to be administered. In many cases, this amount of drug might be considered low enough to avoid any adverse biological effect. Furthermore repeat studies are possible in many without delivering unacceptable radiation burdens. 4. The high sensitivity realised for both radioactivity and mass suggests a mean for determining the human biodistribution of a new drug at a very early stage in its development. This has potential benefit to drug discovery programmes and to ensuing drug therapies.

Positron emission tomography suggests that the rate of progression of idiopathic parkinsonism is slow

We performed sequential positron emission tomography scans with 6-[18F]fluoro-L-dopa in 9 patients with idiopathic parkinsonism and 7 age-matched normal control subjects to compare changes in the nigrostriatal dopaminergic pathway over time. The mean interval between the scans was 3.3 years for the group with idiopathic parkinsonism and 3.9 years for the control subjects. The scans were analyzed by calculating the ratio of striatal to background radioactivity. Both groups showed statistically significant reductions of striatal uptake over the interval. The rate of decrease was almost identical in each group (p = 0.6). We infer that the usual rate of loss of integrity of the dopaminergic nigrostriatal pathway in patients with idiopathic parkinsonism is slow and the rate of change between the two groups was comparable.

Evidence for plasticity of the dopaminergic system in parkinsonism

A series of compensatory mechanisms within the dopaminergic system have been shown to maintain clinical function in the presence of dopamine loss. Experimental evidence for increased presynaptic dopamine turnover owing to increased dopamine synthesis, release, and reduced reuptake exists. Direct evidence that these mechanisms maintain extracellular dopamine levels is provided by intracerebral microdialysis techniques. Postsynaptic denervation supersensitivity clearly occurs with D2 dopamine receptors, although this is less evident with D1 receptors. Similarly, mechanisms of plasticity have been shown to be relevant in human postmortem and Positron Emission Tomographic studies of patients with Parkinson's disease. However, although presynaptic increases in dopamine turnover are well documented, postsynaptic D1 and D2 receptor changes have been more difficult to establish, mainly because of methodological difficulties. D2, but not D1, receptor increases have been documented in drug naive Parkinsonian patients with PET techniques. In transplantation of adrenal gland to striatum in animal models and patients with Parkinsonism where clinical improvement occurs, plasticity of host response may be as important as plasticity of the graft. Although some elements of the compensatory mechanism of dopamine plasticity may be deleterious, such as dyskinesias owing to dopamine receptor supersensitivity, the overall effect of delay and minimization of the clinical expression of disease is advantageous. An even greater understanding of the mechanisms involved may assist in developing future therapeutic strategies.

The striatum and motor cortex in motor initiation and execution

The participation of striatal and motor cortex neurons in motor initiation and execution was studied using single neuronal recording in 3 monkeys performing wrist flexion and extension stimulus-initiated reaction time tasks. Observations of 46 striatal neurons whose activity correlated with the tasks were compared to recordings of 59 task-related motor cortex neurons. Neurons were classified as best related to the appearance of the go signal, movement onset, agonist or antagonist electromyographic changes, or the movement reaching target. Timing of neuronal activity changes in both striatum and motor cortex suggested that go signal-related neurons represent input function while most movement onset-related neurons represent output function. In the striatum, those related to reaching target represent output function. Furthermore, go signal-related neurons usually change activity before movement onset-related neurons which change activity prior to target attainment-related neurons. These observations suggest a hierarchical organization within the striatum and motor cortex. Also the striatum participates in programming target acquisition as well as motor initiation.

6-[18F]fluoro-L-dopa metabolism in MPTP-treated monkeys: assessment of tracer methodologies for positron emission tomography

6-[18F]Fluoro-L-DOPA (FDOPA) is an L-DOPA analog that is used to assess the functional integrity of central dopaminergic systems in vivo with positron emission tomography (PET). FDOPA metabolites from putamen of normal and MPTP-treated monkeys were characterized to correlate FDOPA metabolism changes with those of the endogenous dopamine system. In MPTP-lesioned putamen, 6-[18F]fluorodopamine and dopamine levels were less than 2% those of controls. Increases in endogenous dopamine metabolism were reflected by similar increases in 6-[18F]fluorodopamine metabolites. These results suggest that changes in the central dopamine system biochemistry can be monitored in vivo with FDOPA and PET.

Positron emission tomography studies of brain receptors

Probing the regional distribution and affinity of receptors in the brain, in vivo, in human and non human primates has become possible with the use of selective ligands labelled with positron emitting radionuclides and positron emission tomography (PET). After describing the techniques used in positron emission tomography to characterize a ligand receptor binding and discussing the choice of the label and the limitations and complexities of the in vivo approach, the results obtained in the PET studies of various neurotransmission systems: dopaminergic, opiate, benzodiazepine, serotonin and cholinergic systems are reviewed.

The nigrostriatal dopaminergic pathway in Wilson's disease studied with positron emission tomography

Movement disorders, including Parkinsonism, are prominent features of neurological Wilson's disease (WD). This suggests there may be dysfunction of the nigrostriatal dopaminergic pathway. To explore this possibility, five patients were studied using positron emission tomography (PET) with 18F-6-fluorodopa (6FD), and magnetic resonance imaging (MRI). We calculated striatal 6FD uptake rate constants by a graphical method and compared the results with those of 18 normal subjects. It was found that four patients with symptoms all had abnormally low 6FD uptake, and the one asymptomatic patient had normal uptake. PET evidence for nigrostriatal dopaminergic dysfunction was present even after many years of penicillamine treatment. It is concluded that the nigrostriatal dopaminergic pathway is involved in neurological WD.

New rapid analysis method demonstrates differences in 6-[18F] fluoro-L-dopa plasma input curves with and without carbidopa and in hemi-MPTP lesioned monkeys

Kinetic modeling of the PET tracer 6-[18F]fluoro-L-dopa ([18F]Dopa), used to measure presynaptic dopamine function, requires the accurate determination of the plasma input curve. We have developed a new method that uses alumina extraction preceded by cation and anion exchange resins to determine the parent compound, [18F]Dopa and its critical metabolite 3-O-methyl-6-[18F]fluoro-L-dopa. Using this method we found that carbidopa increases the plasma input of [18F]Dopa while decreasing the rate of metabolite formation, and that previous drug treatment can significantly effect [18F]Dopa metabolism.

Positron emission tomography in the differential diagnosis of organic dementias

At present, PET is the only technology affording the quantitative, three-dimensional imaging of various aspects of brain function. Since function and metabolism are coupled, and since glucose is the dominant substrate of the brain's energy metabolism, studies of glucose metabolism by PET of 2(18F)-fluoro-2-deoxy-D-glucose (FDG) are widely applied for investigating the participation of various brain systems in simple or complex stimulations and tasks. In focal or diffuse disorders of the brain, functional impairment of affected or inactivated brain regions is a reproducible finding. While glucose metabolism is decreased slightly with age in a regionally different degree, in most types of dementia severe changes of glucose metabolism are observed. Degenerative dementia of the Alzheimer type is characterized by a metabolic disturbance most prominent in the parieto-occipito-temporal association cortex and later in the frontal lobe, while primary cortical areas, basal ganglia, thalamus, and cerebellum are not affected. By this typical pattern Alzheimer disease can be differentiated from other dementia syndromes, as e.g., Pick's disease (with the metabolic depression most prominent in the frontal and temporal lobe), multi infarct dementia (with multiple focal metabolic defects), and Huntington's chorea (with metabolic disturbance in the neostriatum). In demented patients PET studies can also be applied to the quantification of treatment effects on disturbed metabolism.