Ventral striatal dopaminergic defect is associated with hallucinations in Parkinson's disease

BACKGROUND AND PURPOSE

Visual hallucinations (VHs) are a common complication of Parkinson's disease (PD). The pathogenesis of VHs in PD is still largely unclear. The aim of this study was to investigate the dopaminergic mechanisms of VHs and specifically whether the degree of striatal dopamine transporter (DAT) function or extrastriatal serotonin transporter (SERT) function can predict the appearance of VHs in patients with PD.

METHODS

Twenty-two PD patients scanned with [¹²³ I]FP-CIT single photon emission computed tomography at an early stage of their disease who later developed VHs were identified and compared with 48 non-hallucinating PD patients. The groups were matched for age, medication, disease duration and motor symptom severity. Clinical follow-up after the scan was a median (range) of 6.9 (3.8-9.6) years. Imaging analyses were performed with both regions-of-interest-based and voxel-based (Statistical Parametric Mapping) methods for the striatal and extrastriatal regions.

RESULTS

The median interval between the scan and the emergence of VHs was 4.8 years. Patients who developed VHs had 18.4% lower DAT binding in the right ventral striatum (P = 0.009), 16.7% lower binding in the left ventral striatum (P = 0.02) and 18.8% lower binding in the right putamen (P = 0.03) compared to patients who did not develop VHs.

CONCLUSIONS

Low striatal DAT function may predispose PD patients to VHs, and the regional distribution of the findings suggests a particular role of the ventral striatum. This is in line with non-PD research that has implicated ventral striatal dysfunction in psychosis.

No relevant midbrain atrophy in Parkinson's disease

AIMS OF THE STUDY

To investigate whether significant midbrain atrophy is present in Parkinson's disease (PD), and if so, whether it can be used as a marker of striatal dopaminergic degeneration.

METHODS

In total, 150 PD patients and 155 controls were scanned with both brain dopamine transporter (DAT) [¹²³ I]FP-CIT SPECT and 1.5T MRI. Midbrain atrophy was measured from sagittal MRIs using the midbrain-to-pons ratios. Both striatal region-of-interest-based (Brass) and striatal and extrastriatal voxel-by-voxel-based DAT binding (SPM8) were investigated in relation to midbrain atrophy.

RESULTS

The midbrain-to-pons ratios in PD patients were slightly lower than those in the controls (mean 0.59 vs 0.61, P < 0.05). The ratios did not significantly correlate with striatal or extrastriatal [¹²³ I]FP-CIT uptake in controls or patients with PD.

CONCLUSIONS

Mild midbrain atrophy is present in PD and can be detected with MRI. However, the midbrain atrophy in PD is not associated with the level of striatal dopaminergic dysfunction, and midbrain measurements therefore cannot be used as a clinically useful predictor of dopamine function.

Pharmacotherapy and generic health-related quality of life in Parkinson's disease

OBJECTIVES

Improvement of health-related quality of life (HRQoL) is one of the primary objectives of symptomatic therapies in Parkinson's disease (PD). The aim of this observational study was to investigate possible changes in generic HRQoL in relation to changed PD pharmacotherapy in the clinical setting.

MATERIALS & METHODS

A total of 219 outpatients with mild to moderate PD (median H&Y score = 2.0), treated with oral antiparkinsonian medications, were investigated twice with a 6-month interval. At baseline, PD medication dose was increased for 82 patients for clinical reasons (median increase of 100 mg levodopa equivalent daily dose or 31.9%), whereas medication remained unchanged for 137 patients. Two generic HRQoL questionnaires, EQ-5D and 15D, were used at baseline and at 6 months, and the baseline and delta HRQoL values were compared between the treatment groups.

RESULTS

In the entire sample, the EQ-VAS score decreased during the study period, indicating a general decline in HRQoL (P = 0.04). There were no differences in the baseline HRQoL values or delta values between the treatment groups as measured with EQ-5D or 15D (levodopa dose elevated vs dopamine agonist/MAO-B inhibitor dose elevated vs no change in medication).

CONCLUSIONS

An approximately 1/3 increase in antiparkinsonian medication dose did not have an impact on generic HRQoL. Disease-specific QoL may be more sensitive to pharmacotherapy-related changes in PD.

Corticostriatal covariance patterns of 6-[18F]fluoro-L-dopa and [18F]fluorodeoxyglucose PET in Parkinson's disease

6-[18F]fluoro-L-dopa (FDOPA) is a common presynaptic dopaminergic tracer used in examinations by positron emission tomography (PET) for patients with Parkinson's disease (PD). The distinct metabolic covariance pattern in the uptake of [18F]fluorodeoxyglucose (FDG) can also be used to investigate PD pathology. Although the two tracers are widely used in PD research and clinical assessment, no thorough comparative studies of the tracers have been made. In this study, 25 PD patients were examined with FDOPA and FDG to investigate relationships and clinical correlates of metabolic and monoaminergic function in the Parkinsonian brain. A VOI (volume-of-interest) analysis was achieved by 3D spatial normalisation and fixed VOI-sets. The hemisphere ipsi- and contralateral to the predominant symptoms of PD was identified in each data set, and data across subjects were related using that laterality, rather than body side. Regional covariance patterns for FDOPA and FDG were derived from principal component analysis (PCA). The results demonstrated hemispheric asymmetries and sex-differences in the striatal FDOPA uptake, which were not seen with FDG. In addition, the PCA analysis identified a positive relationship between a major component in FDOPA uptake (associated with the striatal uptake) and an FDG component, which had positive loadings in the thalamus and the cerebellum. The subject scores for these components correlated positively, and both had a negative association with the clinical severity of the disease. The specific extrastriatal FDG covariance pattern contained the thalamus and the cerebellum, components of the previously reported PD related pattern, but not the striatum. The network correlated with both the severity of clinical symptoms of PD and the severity of nigrostriatal dopaminergic hypofunction. The results indicate that FDG PET, when combined with multivariate network analysis at group-level, can be used as an indicator of PD severity.

Mapping brain structure and personality in late adulthood

Cerebral gray matter (GM) volume decreases in normal aging with a parallel increase in intracranial cerebrospinal fluid (CSF) volume. There is considerable interindividual variation in these changes, and the consequences of age-related GM shrinkage and CSF expansion are unclear. The present study examined whether late adulthood brain structural differences are related to differences in temperament and character. Personality structures of 42 healthy aged adults (mean age 60 years) were examined together with global and regional GM, CSF, and white matter (WM) volumes calculated from structural magnetic resonance images using voxel-based morphometry (VBM). A positive relationship was seen between GM volume at the border of the temporal, parietal, and frontal cortices, and self-transcendence, a character personality trait that reflects mature creativity and spiritualism. The relationship remained significant after a conservative correction for multiple comparisons and it was seen both using uncorrected raw values and after a correction for the effects of age and sex. The results suggest that high self-transcendence, which has adaptive advantages in the later part of life, is associated with relatively greater temporal cortical GM volumes.

Hippocampal and prefrontal atrophy in patients with early non-demented Parkinson's disease is related to cognitive impairment

BACKGROUND

Early stage patients with Parkinson's disease (PD) show cognitive impairment in frontal lobe functions and memory tests. Hippocampal atrophy is seen in medicated patients with advanced PD.

OBJECTIVES

To examine whether prefrontal or hippocampal atrophy are already present in early stage PD, and whether such atrophy is associated with cognitive impairment.

METHODS

Twenty non-medicated, non-demented patients with early stage PD and 22 neurologically healthy age matched controls were studied. All subjects underwent magnetic resonance imaging to study hippocampal and prefrontal atrophy. Atrophy was evaluated by a neuroradiologist using a five point scale. In addition, the patients underwent a neuropsychological test battery sensitive to frontal lobe functions and memory.

RESULTS

Patients with PD had atrophy in the right and the left prefrontal cortex. In the right hippocampus, the mean atrophy score was 1.15 in PD and 0.45 in controls. Corresponding figures for the left hippocampus were 1.05 for PD and 0.64 for controls. In PD, the left hippocampus atrophy correlated with verbal memory and prefrontal atrophy correlated with impaired performance in a test measuring vigilance.

CONCLUSIONS

Non-medicated, non-demented patients with early stage PD show hippocampal and prefrontal atrophy. Impaired memory is related to hippocampal atrophy, whereas sustained attention is related to prefrontal atrophy.

Hippocampal dopamine D2 receptors correlate with memory functions in Alzheimer's disease

Post mortem studies have revealed a loss of dopamine D2 receptors in the temporal lobes in Alzheimer's disease (AD). Moreover, the role of hippocampal D2 receptors on memory performance has been suggested in experimental studies. However, there are no previous in vivo studies on extrastriatal D2 receptors in AD. Our aim was to examine in vivo whether hippocampal or temporal cortical dopamine D2 receptors are affected in AD and whether D2 receptor availability is associated with the memory dysfunction seen in AD. Fourteen patients with probable AD and 11 age- and sex-matched controls were studied with positron emission tomography using a dopamine D2/D3 receptor antagonist [(11)C]FLB 457. The D2 receptor binding potentials (BPs) were measured in extrastriatal brain regions and a neuropsychological investigation was performed on the patients with AD. In AD, the D2 receptor availability was reduced in the hippocampus: by 34% (P = 0.03) in the right hippocampus and by 14% (P = 0.78) in the left hippocampus as compared with controls. Multiple linear regression analysis showed that the BP in the right hippocampus had a significant positive association with verbal memory performance (Wechsler Memory Scale - Revised) (P = 0.001) and picture naming (the Boston Naming Test) (P = 0.002). Our findings suggest a role for temporal lobe D2 receptors in the memory and naming performance in AD, and suggest that studies to evaluate the efficiency of dopaminergic medication on patients with early AD might be warranted.

Extrastriatal dopamine D(2) receptors in Parkinson's disease: a longitudinal study

Most antiparkinsonian drugs are known to act through central dopamine D(2) receptor agonism. A previous longitudinal positron emission tomography (PET) study has indicated that, in the striatum of Parkinson's disease (PD) patients, dopamine D(2) receptor binding declines at a relatively fast annual rate of 2-4% (compared to the rate of <1%/year in healthy individuals). In the present study, the examination of longitudinal changes in D(2) receptors was extended to extrastriatal brain regions in PD. Eight early PD patients were examined twice with PET, approximately 3 years apart, using a high-affinity extrastriatal D(2)/D(3) receptor tracer, [(11)C]FLB 457. Both the MRI-referenced region-of-interest method and the voxel-based statistical analysis method were used independently in the analysis. Regional D(2)-like availabilities (binding potentials) in the left dorsolateral prefrontal cortex, the left temporal cortex and the left and right medial thalami were significantly decreased at the second examination by 20-37% (corresponding to an annual decline of 6-11%). Thus, the annual loss of extrastriatal D(2) availability in PD is up to three times faster than the rate previously reported in the putamen. Our longitudinal study shows first evidence concerning cortical D(2) receptor loss in the progression of PD, although it is not possible to distinguish between the effects of the therapy and the disease.

Brain acetylcholinesterase activity in mild cognitive impairment and early Alzheimer's disease

OBJECTIVE

Brain acetylcholinesterase activity was determined in healthy controls and in patients with mild cognitive impairment and early Alzheimer's disease.

METHODS

A specific acetylcholinesterase tracer, [methyl-(11)C]N-methyl-piperidyl-4-acetate ([(11)C]MP4A), and a three dimensional PET system with magnetic resonance coregistration were used for imaging.

RESULTS

There was a significant difference in the acetylcholinesterase activity in the hippocampus between the groups (p = 0.03), the mean (SD) acetylcholinesterase activity (k(3) values, min(-1)) being 0.114 (0.036) in controls, 0.098 (0.023) in mild cognitive impairment, and 0.085 (0.022) in Alzheimer's disease. The mini-mental state examination score showed no significant relation with acetylcholinesterase activity in any brain area in the combined mild cognitive impairment/Alzheimer group.

CONCLUSIONS

Hippocampal acetylcholinesterase activity is only slightly reduced in mild cognitive impairment and early Alzheimer's disease and so the value of in vivo acetylcholinesterase measurements in detecting the early Alzheimer process is limited.

Striatal dopamine transporter and extrapyramidal symptoms in frontotemporal dementia

OBJECTIVE

To evaluate dopaminergic function in patients with frontotemporal dementia (FTD).

BACKGROUND

Patients with FTD not only show typical behavioral and cognitive deficits but extrapyramidal symptoms, most commonly rigidity and akinesia. The pathophysiologic basis of these symptoms is unclear.

METHODS

The authors investigated 12 patients (mean age = 67.2 +/- 7.2 years, range = 52 to 76 years) with FTD using a cocaine analogue [11C]CFT as a ligand with PET. The results were compared with those of 15 healthy control subjects (mean age = 49.7 years, range = 23 to 70 years) using analysis of covariance to adjust for difference in age. A dynamic 80-minute study was performed, and (region - cerebellum)/cerebellum ratios were calculated for the caudate nucleus and putamen. The severity of extrapyramidal symptoms was evaluated by the motor part of the Unified Parkinson's Disease Rating Scale (UPDRS).

RESULTS

The mean age-adjusted [11C]CFT uptake value in the putamen in patients with FTD was reduced to 82% of the control value (p = 0.017), with the corresponding figure for caudate [11C]CFT uptake being 86% (p = 0.007). The motor UPDRS scores of patients with FTD showed a negative correlation with [11C]CFT uptake in both the putamen (r = -0.76, p = 0.004) and caudate nucleus (r = -0.70, p = 0.01).

CONCLUSIONS

Nigrostriatal dopaminergic function is impaired in FTD, with the projections to the putamen and caudate nucleus being affected to the same degree. The reduction in the binding of the dopamine transporter ligand [11C]CFT is related to the severity of extrapyramidal symptoms of the patients.

Personality traits and brain dopaminergic function in Parkinson's disease

A distinctive personality type, characterized by introversion, inflexibility, and low novelty seeking, has been suggested to be associated with Parkinson's disease. To test the hypothesis that Parkinson's disease is associated with a specific dopamine-related personality type, the personality structures of 61 unmedicated Parkinson's disease patients and 45 healthy controls were examined. Additionally, in 47 Parkinson's disease patients, the dopaminergic function in the brain was directly measured with 6-[(18)F]fluoro-l-dopa ((18)F-dopa) positron emission tomography (PET) with MRI coregistration. The novelty-seeking personality score, supposedly associated with the parkinsonian personality, was slightly lower in the Parkinson's disease group compared with controls, but it did not have a significant relationship with (18)F-dopa uptake in any of the brain regions studied (r = -0.12 to 0.11, P > 0.15). The harm-avoidance personality score, associated with anxiety and depression, was clearly increased in patients with Parkinson's disease and it had a paradoxical, highly significant positive correlation with the (18)F-dopa uptake in the right caudate nucleus (r = 0.53, P = 0.04, Bonferroni corrected for 220 comparisons). Although the results of this study are not in disagreement with the concept of low-novelty-seeking personality type in Parkinson's disease, the personality type does not seem to be dopamine dependent. The correlation between the personality trait of harm avoidance and (18)F-dopa may reflect a specific feedback circuitry of neurotransmitters that is associated with negative emotionality in Parkinson's disease.

Increased frontal [(18)F]fluorodopa uptake in early Parkinson's disease: sex differences in the prefrontal cortex

Previous imaging studies in Parkinson's disease have focused mainly on the striatum, a region with very high dopaminergic activity. Using modern high-sensitivity 3D [(18)F]fluorodopa (Fdopa)-PET, mesocortical monoamine projections can be studied. To study the frontal monoaminergic system in unmedicated early Parkinson's disease in vivo, we examined 20 early Parkinson's disease patients (10 women, 10 men) and 16 healthy subjects (nine women, seven men) with 3D Fdopa-PET, using standard region-of-interest-based analysis with MRI co-registration. Women with Parkinson's disease had 87% higher Fdopa uptake in the right dorsolateral prefrontal cortex (area 46) compared with men with Parkinson's disease, whereas there was no sex difference in the control group (sex x disease interaction, P = 0.03). The uptake in the right dorsolateral prefrontal cortex was 82% higher in men with Parkinson's disease and 219% higher in women with Parkinson's disease compared with control groups (effect of disease, P < 0.0001). Also in the left dorsolateral prefrontal cortex and in the medial frontal cortex, early Parkinson's disease patients had significantly (18-94%) higher Fdopa uptake compared with healthy controls. In the putamen, both men and women with Parkinson's disease had a significantly lower (27-46%) uptake compared with healthy controls. These results indicate that frontal monoaminergic activity is increased and that there is a sex difference in the prefrontal monoaminergic system in early Parkinson's disease. The reported sex difference may be linked to clinical sex differences in the symptoms and treatment response in Parkinson's disease.

Sex differences in extrastriatal dopamine d(2)-like receptors in the human brain

OBJECTIVE

The study examined gender differences in extrastriatal dopamine D2-like receptor levels in the human brain in vivo.

METHOD

[(11)C]FLB 457, a high-affinity radioligand for extrastriatal D(2)-like receptors, and a three-dimensional positron emission tomography system were used to measure D(2)-like receptor binding potentials in frontal cortex, temporal cortex, and thalamus in 12 healthy men and 12 healthy women.

RESULTS

Women had higher D(2)-like receptor binding potentials than men in the three brain regions studied, and the difference in the frontal cortex was statistically significant. In a more detailed regional analysis, the difference between the sexes was most pronounced for the left and right anterior cingulate cortex.

CONCLUSIONS

This study provides in vivo evidence for a gender difference in dopamine D(2)-like receptor levels, which could be reflected in gender-associated differences in clinical disorders linked to the dopamine system.

The translating brain: cerebral activation patterns during simultaneous interpreting

Brain activation was measured in professional interpreters during simultaneous interpreting (SI) vs. repetition (shadowing) of auditorily presented text by positron emission tomography (PET). SI into the native language (Finnish) elicited left frontal activation increases. SI into the non-native language (English) elicited much more extensive left-sided fronto-temporal activation increases. Our results indicate that SI activates predominantly left-hemispheric structures (particularly the left dorsolateral frontal cortex) previously related to lexical search, semantic processing and verbal working memory. Brain activation patterns were clearly modulated by direction of translation, with more extensive activation during translation into the non-native language which is often considered to a be more demanding task.

Age-related dopamine D2/D3 receptor loss in extrastriatal regions of the human brain

Loss of dopamine D2-like receptors in the striatum has been associated with both normal human aging and impairment of cognitive and motor functions in the elderly. To investigate whether there are age-associated changes in dopamine D2 and D3 receptor subtypes (D2/3Rs) outside the striatum, a D2/3R selective high-affinity radioligand [11C]FLB 457 was used in positron emission tomography (PET) examinations for 24 normal healthy male subjects (age range 19-74 years). Significant age-related declines of D2/3Rs were detected in all the brain regions studied: the anterior cingulate cortex (decline of 13% per increase of a decade in age, P < 0.001). the frontal cortex (11%, P < 0.001), the lateral temporal cortex (10%, P < 0.001), the hippocampus (10%, P < 0.01), the medial temporal cortex (9%, P < 0.001), the amygdala (7%, P < 0.01), the medial thalamus (6%, P < 0.001) and the lateral thalamus (5%, P < 0.01). The rate of D2/3R decline was significantly faster in the frontal cortex as compared to the medial temporal cortex (P < 0.05, Bonferroni corrected) and as compared to the medial thalamus (P < 0.05, Bonferroni corrected). These results indicate that the previously demonstrated age-related decline in striatal dopamine D2 receptors extends to several extrastriatal regions in normal human males. Further, the rate of D2/3R decline may be faster in the frontal cortex as compared to the temporal and thalamic regions.

Progression in Parkinson's disease: a positron emission tomography study with a dopamine transporter ligand [18F]CFT

We studied the rate of progression of striatal dopamine transporter function in Parkinson's disease (PD). Eight patients with early PD without antiparkinsonian medication and 7 healthy volunteers were investigated with [18F]CFT positron emission tomography (PET). The PET scan was carried out twice at an approximate 2-year interval. The uptake of [18F]CFT was calculated as a region-cerebellum:cerebellum ratio at 180 to 210 minutes after injection. At the first PET scan, the [18F]CFT uptake in PD patients in the putamen was 1.45 +/- 0.45 (mean +/- SD) (42% of the control mean) and 2.43 +/- 0.59 in the caudate nucleus (76% of the control mean). The ratios declined by the time of the second PET scan, and the rate of annual decline of the baseline mean in PD patients was 13.1% in the putamen and 12.5% in the caudate nucleus. In controls, the corresponding figures were 2.1% for the putamen and 2.9% for the caudate nucleus. The decline in [18F]CFT uptake was significantly higher in PD patients than in controls. Thus, dopamine transporter ligands such as [18F]CFT seem to be sensitive markers for the rate of progression in PD.

Extrastriatal dopamine D2 and D3 receptors in early and advanced Parkinson's disease

OBJECTIVE

To investigate whether dopamine D2 and D3 receptor subtypes (D2/3Rs) outside the caudate-putamen are affected in PD.

BACKGROUND

Alterations in striatal D2-like dopamine receptors in PD have been extensively demonstrated using PET, but there are no studies focusing on extrastriatal D2/3Rs.

METHODS

Fourteen unmedicated patients with idiopathic early PD with predominantly left-sided symptoms, 14 levodopa-medicated patients with advanced PD, and 20 normal age-matched controls were examined using PET. PET scanning was performed with a novel high-affinity D2/3R radioligand ([11C]FLB 457) and a PET scanner in three-dimensional mode.

RESULTS

In advanced PD, the binding potential of [11C]FLB 457 in the dorsolateral prefrontal cortex was decreased by 40% (p < 0.01), in the anterior cingulate cortex by 20% (p < 0.01), and in the medial thalamus by 17% (p < 0.05) compared with healthy controls. In early PD, the extrastriatal [11C]FLB 457 binding potentials were not significantly different compared with the control group. However, the binding potential in the anterior cingulate cortex (29%; p < 0. 05) was higher in early PD compared with advanced PD.

CONCLUSIONS

These results imply that the D2/3 receptor subtypes outside the striatum are affected in advanced PD but not in the early stages of the disease, and that this receptor decline is present in the anterior cingulate cortex, the dorsolateral prefrontal cortex, and the thalamus.

Upregulation of putaminal dopamine D2 receptors in early Parkinson's disease: a comparative PET study with [11C] raclopride and [11C]N-methylspiperone

Dopamine D2 receptor function was assessed in a PET study with 2 dopamine D2 receptor PET ligands, [11C]raclopride (RAC) and [11C]N-methylspiperone (NMSP), in early Parkinson's disease.

METHODS

Seven patients with early Parkinson's disease and 5 healthy volunteers were studied. Each underwent PET both with reversible [11C]RAC and with irreversible [11C]NMSP.

RESULTS

Upregulation of dopamine D2 receptors in the putamen contralateral to the predominant symptoms of Parkinson's disease was confirmed using both [11C]RAC and [11C]NMSP. Uptake of [11C]RAC in the contralateral putamen was 105% of uptake in the opposite putamen (P = 0.020). For [11C]NMSP, uptake in the contralateral putamen was 105% of uptake in the ipsilateral putamen (P = 0.011). No significant differences between Parkinson's disease patients and healthy volunteers were detected in any of the studied brain regions using either [11C]RAC or [11C]NMSP. No significant differences between [11C]RAC and [11C]NMSP uptake were detected in the striatum, whereas in the extrastriatal regions, [11C]NMSP showed significantly higher uptake than [11C]RAC both in healthy volunteers and in Parkinson's disease patients.

CONCLUSION

This study confirms an increase in dopamine D2 receptors in the putamen contralateral to the predominant symptoms, compared with the ipsilateral putamen, in early Parkinson's disease. This increase was seen both with reversible ligand [11C]RAC and with irreversible ligand [11C]NMSP and thus does not seem a consequence of depleted endogenous dopamine.