This work is part of the multi-center Alzheimer's Disease Neuroimaging Initiative (ADNI), a large multi-site study of dementia, including patients having mild cognitive impairment (MCI), probable Alzheimer's disease (AD), as well as healthy elderly controls. A major portion of ADNI involves the use of [18F]-fluorodeoxyglucose (FDG) with positron emission tomography (PET). The objective of this paper is reduction of inter-scanner differences in the FDG-PET scans obtained from the 50 participating PET centers having fifteen different scanner models. In spite of a standardized imaging protocol, systematic inter-scanner variability in PET images from various sites is observed primarily due to differences in scanner resolution, reconstruction techniques, and different implementations of scatter and attenuation corrections. Two correction steps were developed by comparison of 3-D Hoffman brain phantom scans with the ‘gold standard’ digital 3-D Hoffman brain phantom: i) high frequency correction; where a smoothing kernel for each scanner model was estimated to smooth all images to a common resolution and ii) low frequency correction; where smooth affine correction factors were obtained to reduce the attenuation and scatter correction errors. For the phantom data, the high frequency correction reduced the variability by 20%-50% and the low frequency correction further reduced the differences by another 20%-25%. Correction factors obtained from phantom studies were applied to 95 scans from normal control subjects obtained from the participating sites. The high frequency correction reduced differences similar to the phantom studies. However, the low frequency correction did not further reduce differences; hence further refinement of the procedure is necessary.
APOE ε4’s role as a modulator of the relationship between soluble plasma beta-amyloid (Aβ) and fibrillar brain Aβ measured by Pittsburgh Compound-B positron emission tomography ([11C]PiB PET) has not been assessed.
Ninety-six Alzheimer’s Disease Neuroimaging Initiative participants with [11C]PiB scans and plasma Aβ1-40 and Aβ1-42 measurements at time of scan were included. Regional and voxel-wise analyses of [11C]PiB data were used to determine the influence of APOE ε4 on association of plasma Aβ1-40, Aβ1-42, and Aβ1-40/Aβ1-42 with [11C]PiB uptake.
In APOE ε4− but not ε4+ participants, positive relationships between plasma Aβ1-40/Aβ1-42 and [11C]PiB uptake were observed. Modeling the interaction of APOE and plasma Aβ1-40/Aβ1-42 improved the explained variance in [11C]PiB binding compared to using APOE and plasma Aβ1-40/Aβ1-42 as separate terms.
The results suggest that plasma Aβ is a potential Alzheimer’s disease biomarker and highlight the importance of genetic variation in interpretation of plasma Aβ levels.
Alzheimer’s disease (AD); mild cognitive impairment (MCI); Alzheimer’s Disease Neuroimaging Initiative (ADNI); beta-amyloid (Aβ); plasma beta-amyloid; positron emission tomography (PET); Pittsburgh Compound-B ([11C]PiB); Apolipoprotein E (APOE)
Autosomal dominant Alzheimer disease (ADAD) is caused by rare genetic
mutations in three specific genes, in contrast to late-onset Alzheimer
Disease (LOAD), which has a more polygenetic risk profile.
Design, Setting, and Participants
We analyzed functional connectivity in multiple brain resting state
networks (RSNs) in a cross-sectional cohort of ADAD (N=79) and LOAD (N=444)
human participants using resting state functional connectivity MRI
(rs-fcMRI) at multiple international academic sites.
Main Outcomes and Measures
For both types of AD, we quantified and compared functional
connectivity changes in RSNs as a function of dementia severity as measured
by clinical dementia rating (CDR). In ADAD, we qualitatively investigated
functional connectivity changes with respect to estimated years from onset
of symptoms within five RSNs.
Functional connectivity decreases with increasing CDR were similar
for both LOAD and ADAD in multiple RSNs. Ordinal logistic regression models
constructed in each type of AD accurately predicted CDR stage in the other,
further demonstrating similarity of functional connectivity loss in each
disease type. Among ADAD participants, functional connectivity in multiple
RSNs appeared qualitatively lower in asymptomatic mutation carriers near
their anticipated age of symptom onset compared to asymptomatic mutation
Conclusions and Relevance
rs-fcMRI changes with progressing AD severity are similar between
ADAD and LOAD. Rs-fcMRI may be a useful endpoint for LOAD and ADAD therapy
trials. ADAD disease process may be an effective model for LOAD disease
Resting-state functional connectivity; autosomal dominant Alzheimer's disease; late-onset Alzheimer's disease; default mode network; apolipoprotein E (APOE)
The pathophysiology of postural instability in Parkinson’s disease remains poorly understood. Normal postural function depends in part on the ability of the postural control system to integrate visual, proprioceptive, and vestibular sensory information. Degeneration of cholinergic neurons in the brainstem pedunculopontine nucleus complex and their thalamic efferent terminals has been implicated in postural control deficits in Parkinson’s disease. Our aim was to investigate the relationship of cholinergic terminal loss in thalamus and cortex, and nigrostriatal dopaminergic denervation, on postural sensory integration function in Parkinson’s disease. We studied 124 subjects with Parkinson’s disease (32 female/92 male; 65.5 ± 7.4 years old; 6.0 ± 4.2 years motor disease duration; modified Hoehn and Yahr mean stage 2.4 ± 0.5) and 25 control subjects (10 female/15 male, 66.8 ± 10.1 years old). All subjects underwent 11C-dihydrotetrabenazine vesicular monoaminergic transporter type 2 and 11C-methylpiperidin-4-yl propionate acetylcholinesterase positron emission tomography and the sensory organization test balance platform protocol. Measures of dopaminergic and cholinergic terminal integrity were obtained, i.e. striatal vesicular monoaminergic transporter type 2 binding (distribution volume ratio) and thalamic and cortical acetylcholinesterase hydrolysis rate per minute (k3), respectively. Total centre of pressure excursion (speed), a measure of total sway, and sway variability were determined for individual sensory organization test conditions. Based on normative data, principal component analysis was performed to reduce postural sensory organization functions to robust factors for regression analysis with the dopaminergic and cholinergic terminal data. Factor analysis demonstrated two factors with eigenvalues >2 that explained 52.2% of the variance, mainly reflecting postural sway during sensory organization test Conditions 1–3 and 5, respectively. Regression analysis of the Conditions 1–3 postural sway-related factor [R2adj = 0.123, F(5,109) = 4.2, P = 0.002] showed that decreased thalamic cholinergic innervation was associated with increased centre of pressure sway speed (β = −0.389, t = −3.4, P = 0.001) while controlling for covariate effects of cognitive capacity and parkinsonian motor impairments. There was no significant effect of cortical cholinergic terminal deficits or striatal dopaminergic terminal deficits. This effect could only be found for the subjects with Parkinson’s disease. We conclude that postural sensory integration function of subjects with Parkinson’s disease is modulated by pedunculopontine nucleus-thalamic but not cortical cholinergic innervation. Impaired integrity of pedunculopontine nucleus cholinergic neurons and their thalamic efferents play a role in postural control in patients with Parkinson’s disease, possibly by participating in integration of multimodal sensory input information.
Parkinson’s disease; pedunculopontine nucleus; postural sensory organization; positron emission tomography; acetylcholine
We investigated dopaminergic and cholinergic correlates of gait speed in Parkinson disease (PD) and non-PD control subjects to test the hypothesis that gait dysfunction in PD may result from multisystem degeneration.
This was a cross-sectional study. Subjects with PD but without dementia (n = 125, age 65.6 ± 7.3 years) and elderly subjects without PD (n = 32, age 66.0 ± 10.6 years) underwent [11C]dihydrotetrabenazine dopaminergic and [11C]methyl-4-piperidinyl propionate acetylcholinesterase PET imaging, and cognitive and clinical testing, including an 8.5-m walk in the dopaminergic “off” state. The fifth percentile of cortical cholinergic activity in the elderly without PD was used to define normal-range activity in the subjects with PD.
Normal-range cortical cholinergic activity was present in 87 subjects with PD (69.6%). Analysis of covariance using gait speed as the dependent variable demonstrated a significant model (F = 6.70, p < 0.0001) with a significant group effect (F = 3.36, p = 0.037) and significant slower gait speed in the low cholinergic PD subgroup (0.97 ± 0.22 m/s) with no significant difference between the normal-range cholinergic PD subgroup (1.12 ± 0.20 m/s) and control subjects (1.17 ± 0.18 m/s). Covariate effects were significant for cognition (F = 6.58, p = 0.011), but not for striatal dopaminergic innervation, sex, or age.
Comorbid cortical cholinergic denervation is a more robust marker of slowing of gait in PD than nigrostriatal denervation alone. Gait speed is not significantly slower than normal in subjects with PD with relatively isolated nigrostriatal denervation.
Background & Methods
As Parkinson disease (PD) may affect men and women differentially, we investigated gender differences in regional projection system integrity in 148 PD subjects (36 women, 112 men) using monoaminergic [11C]dihydrotetrabenazine and acetylcholinesterase [11C]PMP positron emission tomography.
After controlling for age, disease duration, and Hoehn and Yahr score, men showed 5.9% greater caudate dopaminergic denervation (p=0.0018) and 5.8 % greater neocortical cholinergic denervation (p=0.0097). No significant gender differences were seen in putaminal dopaminergic or thalamic cholinergic denervation.
Gender; Women; Acetylcholine; Dopamine; Parkinson disease
Deposition of amyloid-β (Aβ) in the cerebral cortex is thought to be a pivotal event in Alzheimer’s disease (AD) pathogenesis with a significant genetic contribution. Molecular imaging can provide an early noninvasive phenotype but small samples have prohibited genome-wide association studies (GWAS) of cortical Aβ load until now. We employed florbetapir (18F) positron emission tomography (PET) imaging to assess brain Aβ levels in vivo for 555 participants from the Alzheimer’s Disease Neuroimaging Initiative (ADNI). More than six million common genetic variants were tested for association to quantitative global cortical Aβ load controlling for age, gender, and diagnosis. Independent genome-wide significant associations were identified on chromosome 19 within APOE (rs429358, p = 5.5 × 10−14) and on chromosome 3 upstream of BCHE (rs509208, p = 2.7 × 10−8) in a region previously associated with serum butyrylcholinesterase activity. Together, these loci explained 15% of the variance in cortical Aβ levels in this sample (APOE 10.7%, BCHE 4.3%). Suggestive associations were identified within ITGA6, near EFNA5, EDIL3, ITGA1, PIK3R1, NFIB, and ARID1B, and between NUAK1 and C12orf75. These results confirm the association of APOE with Aβ deposition and represent the largest known effect of BCHE on an AD-related phenotype. Butyrylcholinesterase has been found in senile plaques and this new association of genetic variation at the BCHE locus with Aβ burden in humans may have implications for potential disease-modifying effects of butyrylcholinesterase-modulating agents in the AD spectrum.
Alzheimer’s disease (AD); amyloid; apolipoprotein E (APOE); butyrylcholinesterase (BCHE); florbetapir (AV-45); genome-wide association study (GWAS)
Perfluorocarbon (PFC) double emulsions loaded with a water-soluble, therapeutic agent can be triggered by ultrasound in a process known as acoustic droplet vaporization (ADV). Elucidating the stability and biodistribution of these sonosensitive vehicles and encapsulated agents are critical in developing targeted drug delivery strategies using ultrasound. [18F]fluorodeoxyglucose (FDG) was encapsulated in a PFC double emulsion and the in vitro diffusion of FDG was assessed using a Franz diffusion cell. Using dynamic micro positron emission tomography (micro-PET) and direct tissue sampling, the biodistribution of FDG administered as a solution (i.e. non-emulsified) or as an emulsion was studied in Fisher 344 rats (n = 6) bearing subcutaneous 9L gliosarcoma. Standardized uptake values (SUVs) and area under the curve of the SUV (AUCSUV) of FDG were calculated for various tissues. The FDG flux from the emulsion decreased by up to a factor of 6.9 compared to the FDG solution. FDG uptake, calculated from the AUCSUV, decreased by 36% and 44% for brain and tumor, respectively, when comparing FDG solution versus FDG emulsion (p < 0.01). Decreases in AUCSUV in highly metabolic tissues such as brain and tumor demonstrated retention of FDG within the double emulsion. No statistically significant differences in lung AUCSUV were observed, suggesting minimal accumulation of the emulsion in the pulmonary capillary bed. The liver AUCSUV increased by 356% for the FDG emulsion, thus indicating significant hepatic retention of the emulsion.
micro-PET; biodistribution; perfluorocarbon; emulsion; acoustic droplet vaporization; ultrasound; responsive agents
A growing body of research, generated primarily from MRI-based studies, shows that migraine appears to occur, and possibly endure, due to the alteration of specific neural processes in the central nervous system. However, information is lacking on the molecular impact of these changes, especially on the endogenous opioid system during migraine headaches, and neuronavigation through these changes has never been done. This study aimed to investigate, using a novel 3D immersive and interactive neuronavigation (3D-IIN) approach, the endogenous µ-opioid transmission in the brain during a migraine headache attack in vivo. This is arguably one of the most central neuromechanisms associated with pain regulation, affecting multiple elements of the pain experience and analgesia. A 36 year-old female, who has been suffering with migraine for 10 years, was scanned in the typical headache (ictal) and nonheadache (interictal) migraine phases using Positron Emission Tomography (PET) with the selective radiotracer [11C]carfentanil, which allowed us to measure µ-opioid receptor availability in the brain (non-displaceable binding potential - µOR BPND). The short-life radiotracer was produced by a cyclotron and chemical synthesis apparatus on campus located in close proximity to the imaging facility. Both PET scans, interictal and ictal, were scheduled during separate mid-late follicular phases of the patient's menstrual cycle. During the ictal PET session her spontaneous headache attack reached severe intensity levels; progressing to nausea and vomiting at the end of the scan session. There were reductions in µOR BPND in the pain-modulatory regions of the endogenous µ-opioid system during the ictal phase, including the cingulate cortex, nucleus accumbens (NAcc), thalamus (Thal), and periaqueductal gray matter (PAG); indicating that µORs were already occupied by endogenous opioids released in response to the ongoing pain. To our knowledge, this is the first time that changes in µOR BPND during a migraine headache attack have been neuronavigated using a novel 3D approach. This method allows for interactive research and educational exploration of a migraine attack in an actual patient's neuroimaging dataset.
Medicine; Issue 88; μ-opioid; opiate; migraine; headache; pain; Positron Emission Tomography; molecular neuroimaging; 3D; neuronavigation
We evaluated in vivo the μ-opioid system during spontaneous episodic migraine headaches. Seven patients were scanned at different phases of their migraine using positron emission tomography with the selective μ-opioid receptor (μOR) radiotracer [11C]carfentanil. In the ictal phase, there was μOR activation in the medial prefrontal cortex, which was strongly associated with the μOR availability level during the interictal phase. Furthermore, μ-opioid binding changes showed moderate negative correlation with the combined extension and severity of the attacks. These results indicate for the first time that there is high μOR activation in the migraineurs' brains during headache attacks in response to their pain.
We investigated in vivo the allodynic response of the central μ-opioid system during spontaneous migraine headaches, following a sustained pain threshold challenge on the trigeminal ophthalmic region. Six migraineurs were scanned during the ictal and interictal phases using positron emission tomography (PET) with the selective μ-opioid receptor (μOR) radiotracer [11C]carfentanil. Females were scanned during the mid-late follicular phase of two separate cycles. Patients showed ictal trigeminal allodynia during the thermal challenge that was concurrent and positively correlated with μOR activation in the midbrain, extending from red nucleus to ventrolateral periaqueductal gray matter. These findings demonstrate for the first time in vivo the high μOR activation in the migraineurs' brains in response to their allodynic experience.
Comorbid diabetes may be associated with more severe motor impairment in Parkinson disease. In normal elderly individuals, diabetes is associated with parkinsonian features, including gait difficulty and rigidity, though not tremor. Whether diabetes contributes to increased motor dysfunction in Parkinson disease by exacerbating nigrostriatal dopaminergic denervation or through intensification of extranigral pathology is unknown.
We performed a case-control study (n=39) involving 13 Parkinson disease subjects (age 66.4 yrs ± 5.5; duration of disease 6.9 yrs ± 4.4) with diabetes and 26 age, gender, and duration-of-disease-matched Parkinson disease controls without diabetes. All subjects underwent [11C]dihydrotetrabenazine vesicular monoamine transporter type-2 positron emission tomography imaging to assess striatal dihydrotetrabenazine distribution volume ratio and Unified Parkinson disease rating scale motor examination to determine rigidity, bradykinesia, tremor, and postural instability and gait difficulty subscores. Magnetic resonance imaging scans were analyzed to assess leukoaraiosis burden.
After controlling for nigrostriatal dopaminergic denervation, Parkinson disease subjects with diabetes displayed greater postural instability and gait difficulty subscores (t=3.81, p=0.0005). There were no differences in bradykinesia, rigidity, or tremor subscores between cases and controls. The association between diabetes and postural instability and gait difficulty persisted after controlling for comorbid hypertension and body mass index. Leukoaraiosis, distal vibratory sense, and levodopa dose equivalents did not differ significantly between cases and controls.
Diabetes may contribute to postural instability and gait difficulty in Parkinson disease through mechanisms other than nigrostriatal dopaminergic denervation.
Diabetes; Parkinson disease; PET; Dopamine; Postural Instability; Gait Difficulty (PIGD)
The endogenous opioid system, which alleviates physical pain, is also known to regulate social distress and reward in animal models. To test this hypothesis in humans (n = 18), we used a μ-opioid receptor (MOR) radiotracer to measure changes in MOR availability in vivo with positron emission tomography (PET) during social rejection (not being liked by others) and acceptance (being liked by others). Social rejection significantly activated the MOR system (i.e., reduced receptor availability relative to baseline) in the ventral striatum, amygdala, midline thalamus, and periaqueductal gray (PAG). This pattern of activation is consistent with the hypothesis that the endogenous opioids play a role in reducing the experience of social pain. Greater trait resiliency was positively correlated with MOR activation during rejection in the amygdala, PAG, and subgenual anterior cingulate cortex (sgACC), suggesting that MOR activation in these areas is protective or adaptive. In addition, MOR activation in the pregenual ACC was correlated with reduced negative affect during rejection. In contrast, social acceptance resulted in MOR activation in the amygdala and anterior insula, and MOR deactivation in the midline thalamus and sgACC. In the left ventral striatum, MOR activation during acceptance predicted a greater desire for social interaction, suggesting a role for the MOR system in social reward. The ventral striatum, amygdala, midline thalamus, PAG, anterior insula, and ACC are rich in MORs and comprise a pathway by which social cues may influence mood and motivation. MOR regulation of this pathway may preserve and promote emotional well-being in the social environment.
opioid; PET; social; rejection; acceptance; depression; mu; stress
Although motor impairments in Parkinson disease are attributed to nigrostriatal dopaminergic denervation, postural instability and gait difficulty (PIGD) features are less responsive to dopaminergic medications. PIGD features are a risk factor also for development of dementia in Parkinson disease. These observations suggest that non-dopaminergic mechanisms may contribute to axial motor impairments. The objective was to perform a correlative positron emission tomography study to examine the relationship between neocortical β-amyloid deposition ([11C]-Pittsburgh Compound-B), nigrostriatal dopaminergic denervation ([11C]-dihydrotetrabenazine), and PIGD feature severity in Parkinson disease patients at risk for dementia.
Cross-sectional study of 44 Parkinson disease patients (11 Female / 33 Male; 69.5 ± 6.6 years; 7.0 ± 4.8 years motor disease duration; mean Hoehn and Yahr stage 2.7 ± 0.5) who underwent positron emission tomography, motor feature severity assessment using the Movement Disorder Society revised Unified Parkinson's Disease Rating Scale, and the Dementia Rating Scale.
Linear regression (R2adj=0.147, F4,39=2.85, p=0.036) showed that increased PIGD feature severity was associated with increased neocortical [11C]-Pittsburgh Compound-B binding (β=0.346, t39=2.13, p=0.039), while controlling for striatal [11C]-dihydrotetrabenazine binding, age, and Dementia Rating Scale total score.
Increased neocortical β-amyloid deposition, even at low range levels, is associated with higher PIGD feature severity in Parkinson disease patients at risk for dementia. This finding may explain why the PIGD motor phenotype is a risk factor for development of dementia in Parkinson disease.
Parkinson disease; β-amyloid; dopamine; PET; MDS-UPDRS
To investigate default mode network (DMN) functional connectivity MRI (fcMRI) in a large cross-sectional cohort of subjects from families harboring pathogenic presenilin-1 (PSEN1), presenilin-2 (PSEN2), and amyloid precursor protein (APP) mutations participating in the Dominantly Inherited Alzheimer Network.
Eighty-three mutation carriers and 37 asymptomatic noncarriers from the same families underwent fMRI during resting state at 8 centers in the United States, United Kingdom, and Australia. Using group-independent component analysis, fcMRI was compared using mutation status and Clinical Dementia Rating to stratify groups, and related to each participant's estimated years from expected symptom onset (eYO).
We observed significantly decreased DMN fcMRI in mutation carriers with increasing Clinical Dementia Rating, most evident in the precuneus/posterior cingulate and parietal cortices (p < 0.001). Comparison of asymptomatic mutation carriers with noncarriers demonstrated decreased fcMRI in the precuneus/posterior cingulate (p = 0.014) and right parietal cortex (p = 0.0016). We observed a significant interaction between mutation carrier status and eYO, with decreases in DMN fcMRI observed as mutation carriers approached and surpassed their eYO.
Functional disruption of the DMN occurs early in the course of autosomal dominant Alzheimer disease, beginning before clinically evident symptoms, and worsening with increased impairment. These findings suggest that DMN fcMRI may prove useful as a biomarker across a wide spectrum of disease, and support the feasibility of DMN fcMRI as a secondary endpoint in upcoming multicenter clinical trials in Alzheimer disease.
Nicotine has long been recognized as a necessary but insufficient component of tobacco cigarettes to maintain a psychophysiological need to smoke. This study examined venous plasma concentrations effects of nicotine in cigarette smoking after overnight abstinence to release striatal dopamine (DA).
Twenty-two male smokers smoked either denicotinized (denic) or average nicotine (nic) cigarettes under single blind conditions. Each was given [11C]raclopride and scanned in a positron emission tomography (PET) facility.
Smoking either denic or nic cigarettes released striatal DA. Denic cigarette smoking released DA primarily in the right striatum, whereas nic cigarette smoking released DA in both striata, but especially in the left. Increases in venous plasma nicotine concentrations correlated positively with increased DA release in the left caudate nucleus. Smoking denic cigarettes reduced craving as much as smoking nic cigarettes. Craving reduction after nic tobacco smoking correlated with increases in plasma nicotine.
Nonnicotine factors in tobacco smoking produce important right brain effects. Nicotine is a pharmacological factor during tobacco smoking that releases bilateral striatal DA, but more in the left brain.
We evaluated positron emission tomography (PET)-based classification of neurodegenerative pathology in mild cognitive impairment (MCI).
A cross-sectional and prospective evaluation of a cohort of 27 MCI subjects drawn from a university-based Cognitive Disorders clinic. We compared expert clinical consensus classification of MCI at entry, and possible dementia at follow-up, with molecular imaging-based classification employing [11C]DTBZ-PET measurement of striatal dopamine terminal integrity and [11C]PiB-PET measurement of cerebral amyloid burden.
Eleven subjects were initially classified clinically as amnestic MCI, 7 as multidomain MCI, and 9 as nonamnestic MCI. At mean follow-up of 3 years, 18 subjects converted to dementia. PET imaging evidence of significant cerebral amyloid deposition and/or nigrostriatal denervation were strong predictors of conversion to dementia. There was only moderate concordance between expert clinical classifications and PET-based classifications of dementia subtypes.
Combined PET molecular imaging of cerebral amyloid burden and striatal dopamine terminal integrity may be useful identifying subjects at high risk for progression to dementia and in defining neurochemically differentiated subsets of MCI subjects.
Dementia; Alzheimer disease; Lewy Body dementia; Frontotemporal dementia
Using data from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) population, we examined (1) cross-sectional relationships between amyloid deposition, hypometabolism, and cognition, and (2) associations between amyloid and hypometabolism measurements and longitudinal cognitive measurements.
We examined associations between mean cortical florbetapir uptake, mean 18F-fluorodeoxyglucose–positron emission tomography (FDG-PET) within a set of predefined regions, and Alzhiemer’s Disease Assessment Scale (ADAS-cog) performance in 426 ADNI participants (126 normal, 162 early mild cognitive impairment [EMCI], 85 late MCI [LMCI], 53 Alzheimer disease [AD] patients). For a subset of these (76 normal, 81 LMCI) we determined whether florbetapir and FDG-PET were associated with retrospective decline in longitudinal ADAS-cog measurements.
Twenty-nine percent of normal subjects, 43% of EMCI patients, 62% of LMCI patients, and 77% of AD patients were categorized as florbetapir positive. Florbetapir was negatively associated with concurrent FDG and ADAS-cog in both MCI groups. In longitudinal analyses, florbetapir-positive subjects in both normal and LMCI groups had greater ongoing ADAS-cog decline than those who were florbetapir negative. However, in normal subjects, florbetapir positivity was associated with greater ADAS-cog decline than FDG, whereas in LMCI, FDG positivity was associated with greater decline than florbetapir.
Although both hypometabolism and β-amyloid (Aβ) deposition are detectable in normal subjects and all diagnostic groups, Aβ showed greater associations with cognitive decline in normal participants. In view of the minimal cognitive deterioration overall in this group, this suggests that amyloid deposition has an early and subclinical impact on cognition that precedes metabolic changes. At moderate and later stages of disease (LMCI/AD), hypometabolism becomes more pronounced and more closely linked to ongoing cognitive decline.
The aim of our study was to examine the relationship between corticostriatal Aβ-amyloid deposition and cognitive dysfunction in a cohort of patients with Parkinson disease (PD) at risk for dementia.
This was a cross-sectional study of 40 patients with PD with mild cognitive impairment (MCI) or other known dementia risk factors. Subjects underwent dynamic Aβ-amyloid and vesicular monoamine transporter 2 PET imaging using [11C] Pittsburgh compound B (PiB) and [11C]dihydrotetrabenazine (DTBZ), respectively, and neuropsychological assessment. PiB and DTBZ PET data were analyzed using the Logan graphical method to determine cerebral PiB deposition relative to the cerebellar hemispheres and striatal DTBZ binding relative to occipital neocortex. Component z scores were calculated for individual cognitive domains (memory, visuospatial processing, working memory/attention, and executive function) and combined linearly for global estimation of cognition. Correlation of cognitive function and cortical PiB binding was investigated.
Elevated cerebral PiB binding at levels seen in patients with AD was infrequent (6 of 40 subjects). Mean cortical PiB binding in the entire cohort was 1.16 ± 0.16 (distribution volume ratio; range 0.96–1.78). A significant correlation was noted between cortical PiB binding and global composite cognitive function (r = −0.55, p < 0.005) as well as the Wechsler Adult Intelligence Scale score (r = −0.54, p = 0.0004).
Elevated cerebral Aβ-amyloid deposition at levels seen in Alzheimer disease is uncommon in subjects with PD at risk for dementia. In our sample, the prevalence of markedly elevated PiB binding was significantly lower than that found in prior studies of cognitively normal elderly individuals. Neocortical PiB binding correlated robustly with measures of cognitive impairment in our cohort.
Oxytocin, classically involved in social and reproductive activities, is increasingly recognized as an antinociceptive and anxiolytic agent, effects which may be mediated via oxytocin’s interactions with the dopamine system. Thus, genetic variation within the oxytocin gene (OXT) is likely to explain variability in dopamine-related stress responses. As such, we examined how OXT variation is associated with stress-induced dopaminergic neurotransmission in a healthy human sample.
Fifty-five young healthy volunteers were scanned using [11C] raclopride positron emission tomography while they underwent a standardized physical and emotional stressor that consisted of moderate levels of experimental sustained deep muscle pain, and a baseline, control state. Four haplotype tagging single nucleotide polymorphisms located in regions near OXT were genotyped. Measures of pain, affect, anxiety, well-being and interpersonal attachment were also assessed.
Female rs4813625 C allele carriers demonstrated greater stress-induced dopamine release, measured as reductions in receptor availability from baseline to the pain-stress condition relative to female GG homozygotes. No significant differences were detected among males. We also observed that female rs4813625 C allele carriers exhibited higher attachment anxiety, higher trait anxiety and lower emotional well-being scores. In addition, greater stress-induced dopamine release was associated with lower emotional well-being scores in female rs4813625 C allele carriers.
Our results suggest that variability within the oxytocin gene appear to explain interindividual differences in dopaminergic responses to stress, which are shown to be associated with anxiety traits, including those linked to attachment style, as well as emotional well-being in women.
oxytocin; genetics; dopamine; positron emission tomography; humans; sex differences
Parkinson's disease (PD) is a multisystem neurodegenerative disorder. Heterogeneous clinical features may reflect heterogeneous changes in different brain regions. In contrast to the pronounced nigrostriatal denervation characteristic of PD, cholinergic changes are less marked. We investigated cholinergic innervation activity in PD subjects relative to normal subjects. Nondemented PD subjects (n=101, age 65.3±7.2 years) and normal subjects (n=29, age 66.8±10.9 years) underwent clinical assessment and [11C]methyl-4-piperidinyl propionate acetylcholinesterase and [11C]dihydrotetrabenazine monoaminergic positron emission tomography (PET) imaging. Cholinergic projection changes were heterogeneous for 65 out of 101 PD subjects who had neocortical and thalamic acetylcholinesterase activity within the normal range. The remainder had combined neocortical and thalamic (13/101), isolated neocortical (18/101), or isolated thalamic (5/101) acetylcholinesterase activity below the normal range. The low neocortical acetylcholinesterase activity subgroup had significantly lower global cognitive performance compared with the normal range subgroup (F=7.64, P=0.0069) with an independent effect for nigrostriatal denervation (F=7.60, P=0.0074). The low thalamic acetylcholinesterase activity subgroup did not differ from the normal thalamic acetylcholinesterase activity subgroup in cognitive performance or motor impairments except for a history of falls (P=0.0023). Cholinergic denervation is heterogeneous with reduced neocortical and/or thalamic acetylcholinesterase activity in 36% of nondemented PD subjects with corresponding clinical phenotypic variation. Results also show independent cognitive effects for both cholinergic and dopaminergic system changes in nondemented PD subjects.
acetylcholinesterase; cognitive impairment; dopamine; motor; Parkinson's disease; PET
Rapid eye movement sleep behavior disorder (RBD) is common in Parkinson disease (PD), but its relationship to the varied neurotransmitter deficits of PD and prognostic significance remain incompletely understood. RBD and cholinergic system degeneration are identified independently as risk factors for cognitive impairment in PD. We aimed to assess the association between cholinergic denervation and symptoms of RBD in PD patients without dementia.
Eighty subjects with PD without dementia (age, 64.6 ± 7.0 years; range, 50–82 years; 60 males, 20 females; mean Montreal Cognitive Assessment Test [MoCA] score, 26.2 ± 2.1; range 21–30) underwent clinical assessment, neuropsychological testing, and [11C]methylpiperidyl propionate acetylcholinesterase and [11C]dihydrotetrabenazine (DTBZ) vesicular monoamine transporter type 2 positron emission tomography (PET) imaging. 11C3-Amino-4-(2-dimethylaminomethyl-phenylsulfaryl)-benzonitrile (DASB) serotonin transporter PET imaging was performed in a subset of 35 subjects. The presence of RBD symptoms was determined using the Mayo Sleep Questionnaire.
Twenty-seven of 80 subjects (33.8%) indicated a history of RBD symptoms. Subjects with and without RBD symptoms showed no significant differences in age, motor disease duration, MoCA, Unified Parkinson Disease Rating Scale motor scores, or striatal DTBZ binding. Subjects with RBD symptoms, in comparison to those without, exhibited decreased neocortical, limbic cortical, and thalamic cholinergic innervation (0.0213 ± 0.0018 vs 0.0236 ± 0.0022, t = 4.55, p < 0.0001; 0.0388 ± 0.0029 vs 0.0423 ± 0.0058, t = 2.85, p = 0.0056; 0.0388 ± 0.0025 vs 0.0427 ± 0.0042, t = 4.49, p < 0.0001, respectively). Brainstem and striatal DASB binding showed no significant differences between groups.
The presence of RBD symptoms in PD is associated with relative neocortical, limbic cortical, and thalamic cholinergic denervation although not with differential serotoninergic or nigrostriatal dopaminergic denervation. The presence of RBD symptoms may signal cholinergic system degeneration.
Prior studies suggest that serotoninergic neurotransmission reduces β-amyloid (Aβ) production.
To determine whether serotoninergic system degeneration in Parkinson disease promotes Aβ deposition, using in vivo positron emission tomographic probes of serotonin system integrity and Aβ deposition.
Design, Setting, and Patients
Cross-sectional study of 13 subjects with Parkinson disease from the movement disorders clinics at the University of Michigan Health System and Veterans Affairs Ann Arbor Healthcare System, with positron emission tomography using the serotonin transporter ligand carbon 11 ([11C])–labeled 3-amino-4-(2-dimethylaminomethyl-phenylsulfaryl)-benzonitrile (DASB) and the Aβ ligand [11C]Pittsburgh compound B.
Inverse correlations were found between DASB and Pittsburgh compound B distribution volume ratios in the neocortex (ρ=−0.577; P=.04) and striatum (ρ=−0.780; P=.002).
Serotoninergic system degeneration in Parkinson disease may promote the development of cerebral amyloidopathy.
There are two major sources of cholinergic projections in the brain. The nucleus basalis of Meynert provides the principal cholinergic input of the cortical mantle and the pedunculopontine nucleus-laterodorsal tegmental complex (PPN-LDTC; hereafter referred to as PPN) provides the major cholinergic input to the thalamus. Cortical cholinergic denervation has previously been shown to be part of Alzheimer and parkinsonian dementia but there is less information about subcortical thalamic cholinergic denervation. We investigated thalamic cholinergic afferent integrity by measuring PPN-Thalamic (PPN-Thal) acetylcholinesterase (AChE) activity via PET imaging in Alzheimer (AD), Parkinson disease without dementia (PD), Parkinson disease with dementia (PDD) and dementia with Lewy bodies (DLB).
AD (n=13; mean age 75.4±5.5), PD (n=11; age 71.4±6.4), PDD (n=6; age 70.8±4.7), DLB (n=6; age 68.0±8.6) and normal controls (NC; n=14; age 69.0±7.5) subjects underwent AChE [11C]-methyl-4-piperidinyl propionate (PMP) PET imaging. PPN-Thal PET data were analyzed using the Nagatsuka method.
There were no significant differences in mean age between the groups (F=1.86, p=0.134). Kruskal-Wallis testing demonstrated a significant group effect for PPN-Thal AChE hydrolysis rates (F=9.62, P<0.0001). Compared to NC, reduced thalamic k3 hydrolysis rate was noted in subjects with PDD (−19.8%; AChE k3 hydrolysis rates 0.1072±0.0143 min−1), DLB (−17.4%; 0.1103±0.0112 min−1) and PD (−12.8%; 0.1165±0.0114 min−1). Each of these 3 subgroups were statistically different from AD subjects (−0.7%; 0.1326±0.0095 min−1) who showed relatively spared thalamic k3 hydrolysis rates which were comparable to NC (0.1336±0.0142 min−1).
Thalamic cholinergic denervation is present in PD, PDD, and DLB but not in AD. Neurodegenerative involvement of thalamic cholinergic afferent projections may contribute to disease-specific motor and cognitive abnormalities.
Acetylcholine; [11C] PMP PET; Alzheimer disease; Parkinson disease; PPN; Parkinson disease with dementia
Objective: Our goal was to evaluate the association of APOE with amyloid deposition, cerebrospinal fluid levels (CSF) of Aβ, tau, and p-tau, brain atrophy, cognition and cognitive complaints in E-MCI patients and cognitively healthy older adults (HC) in the ADNI-2 cohort.
Methods: Two-hundred and nine E-MCI and 123 HC participants from the ADNI-2 cohort were included. We evaluated the impact of diagnostic status (E-MCI vs. HC) and APOE ε4 status (ε4 positive vs. ε4 negative) on cortical amyloid deposition (AV-45/Florbetapir SUVR PET scans), brain atrophy (structural MRI scans processed using voxel-based morphometry and Freesurfer version 5.1), CSF levels of Aβ, tau, and p-tau, and cognitive performance and complaints.
Results: E-MCI participants showed significantly impaired cognition, higher levels of cognitive complaints, greater levels of tau and p-tau, and subcortical and cortical atrophy relative to HC participants (p < 0.05). Cortical amyloid deposition and CSF levels of Aβ were significantly associated with APOE ε4 status but not E-MCI diagnosis, with ε4 positive participants showing more amyloid deposition and lower levels of CSF Aβ than ε4 negative participants. Other effects of APOE ε4 status on cognition and CSF tau levels were also observed.
APOE ε4 status is associated with amyloid accumulation and lower CSF Aβ, as well as increased CSF tau levels in early prodromal stages of AD (E-MCI) and HC. Alternatively, neurodegeneration, cognitive impairment, and increased complaints are primarily associated with a diagnosis of E-MCI. These findings underscore the importance of considering APOE genotype when evaluating biomarkers in early stages of disease.
apolipoprotein E (APOE); early mild cognitive impairment (E-MCI); Florbetapir/AV-45/Amyvid; positron emission tomography (PET); magnetic resonance imaging (MRI); cerebrospinal fluid (CSF); Alzheimer's disease neuroimaging initiative (ADNI)