Neuroimaging in Parkinson's disease

A sporadic Parkinson's disease model via silencing of the ubiquitin-proteasome/E3 ligase component, SKP1A

Our and other's laboratory microarray-derived transcriptomic studies in human PD substantia nigra pars compacta (SNpc) samples have opened an avenue to concentrate on potential gene intersections or cross-talks along the dopaminergic (DAergic) neurodegenerative cascade in sporadic PD (SPD). One emerging gene candidate identified was SKP1A (p19, S-phase kinase-associated protein 1A), found significantly decreased in the SNpc as confirmed later at the protein level. SKP1 is part of the Skp1, Cullin 1, F-box protein (SCF) complex, the largest known class of sophisticated ubiquitin-proteasome/E3-ligases and was found to directly interact with FBXO7, a gene defective in PARK15-linked PD. This finding has led us to the hypothesis that a targeted site-specific reduction of Skp1 levels in DAergic neuronal cell culture and animal systems may result in a progressive loss of DAergic neurons and hopefully recreate motor disabilities in animals. The second premise considers the possibility that both intrinsic and extrinsic factors (e.g., manipulation of selected genes and mitochondria impairing toxins), alleged to play central roles in DAergic neurodegeneration in PD, may act in concert as modifiers of Skp1 deficiency-induced phenotype alterations ('dual-hit' hypothesis of neurodegeneration). To examine a possible role of Skp1 in DAergic phenotype, we have initially knocked down the expression of SKP1A gene in an embryonic mouse SN-derived cell line (SN4741) with short hairpin RNA (shRNA) lentiviruses (LVs). The deficiency of SKP1A closely recapitulated cardinal features of the DAergic pathology of human PD, such as decreased expression of DAergic phenotypic markers and cell cycle aberrations. Furthermore, the knocked down cells displayed a lethal phenotype when induced to differentiate exhibiting proteinaceous round inclusion structures, which were almost identical in composition to human Lewy bodies, a hallmark of PD. These findings support a role for Skp1 in neuronal phenotype, survival, and differentiation. The identification of Skp1 as a key player in DAergic neuron function suggested that a targeted site-specific reduction of Skp1 levels in mice SNpc may result in a progressive loss of DAergic neurons and terminal projections in the striatum. The injected LV SKP1shRNA to mouse SN resulted in decreased expression of Skp1 protein levels within DAergic neurons and loss of tyrosine hydroxylase immunoreactivity (TH-IR) in both SNpc and striatum that was accompanied by time-dependent motor disabilities. The reduction of the vertical movements, that is rearing, may be reminiscent of the early occurrence of hypokinesia and axial, postural instability in PD. According to the 'dual-hit' hypothesis of neurodegenerative diseases, it is predicted that gene-gene and/or gene-environmental factors would act in concert or sequentially to propagate the pathological process of PD. Our findings are compatible with this conjecture showing that the genetic vulnerability caused by knock down of SKP1A renders DAergic SN4741 cells especially sensitive to genetic reduction of Aldh1 and exposure to the external stressors MPP+ and DA, which have been implicated in PD pathology. Future consideration should be given in manipulation SKP1A expression as therapeutic window, via its induction genetically or pharmacological, to prevent degeneration of the nigra striatal dopamine neurons, since UPS is defective.

International Multicenter Analysis of Brain Structure Across Clinical Stages of Parkinson's Disease

BACKGROUND

Brain structure abnormalities throughout the course of Parkinson's disease have yet to be fully elucidated.

OBJECTIVE

Using a multicenter approach and harmonized analysis methods, we aimed to shed light on Parkinson's disease stage-specific profiles of pathology, as suggested by in vivo neuroimaging.

METHODS

Individual brain MRI and clinical data from 2357 Parkinson's disease patients and 1182 healthy controls were collected from 19 sources. We analyzed regional cortical thickness, cortical surface area, and subcortical volume using mixed-effects models. Patients grouped according to Hoehn and Yahr stage were compared with age- and sex-matched controls. Within the patient sample, we investigated associations with Montreal Cognitive Assessment score.

RESULTS

Overall, patients showed a thinner cortex in 38 of 68 regions compared with controls (d_max  = -0.20, d_min  = -0.09). The bilateral putamen (d_left  = -0.14, d_right  = -0.14) and left amygdala (d = -0.13) were smaller in patients, whereas the left thalamus was larger (d = 0.13). Analysis of staging demonstrated an initial presentation of thinner occipital, parietal, and temporal cortices, extending toward rostrally located cortical regions with increased disease severity. From stage 2 and onward, the bilateral putamen and amygdala were consistently smaller with larger differences denoting each increment. Poorer cognition was associated with widespread cortical thinning and lower volumes of core limbic structures.

CONCLUSIONS

Our findings offer robust and novel imaging signatures that are generally incremental across but in certain regions specific to disease stages. Our findings highlight the importance of adequately powered multicenter collaborations.

Pharmacokinetic Modeling of 18F-FDOPA PET in the Human Brain for Early Parkinson's Disease

Objectives:

Early detection is essential for the treatment approaches of Parkinson’s disease (PD). Clinical criteria alone may be insufficient to distinguish early PD from other conditions. This study aimed to investigate the transfer rate constants of 6-¹⁸F-fluoro-L-dopa (¹⁸F-FDOPA) in positron emission tomography (PET) brain images as a sensitive parameter to detect early PD.

Methods:

Retrospective ¹⁸F-FDOPA PET data of five patients with early PD were collected. PET data were acquired for 90 min after intravenous injection of 306-379 MBq ¹⁸F-FDOPA, and reconstructed into a series of 18 five-minute frames. Reoriented PET images were coregistered and normalized with the PET brain template on the statistical parametric mapping. The ¹⁸F-FDOPA activity concentrations were measured in the striatum, caudate, and putamen on both sides: Contralateral (as PD) and ipsilateral (as control) to the main motor symptoms. The pharmacokinetic model was generated using the SAAM II simulation software. The transfer rate constants across the blood-brain barrier (forward, K₁ and reverse, k₂) and decarboxylation rate constants (k₃) were estimated in these regions.

Results:

The activity uptakes in the contralateral striatum (0.0323%±0.0091%) and putamen (0.0169%±0.0054%) were significantly lower than the control (0.0353%±0.0086%, 0.0199%±0.0054%, respectively). The K₁ and k₃ were significantly lower in the contralateral striatum and putamen (p<0.05). There were no significant differences in any transfer rate constants in the caudate.

Conclusion:

The transfer rate constants (K₁ and k₃) of ¹⁸F-FDOPA on the contralateral striatum and putamen were significantly lower than the control. These biokinetic data could be potential indicators for quantitative detection of early PD diagnosis.

Glial activation precedes alpha-synuclein pathology in a mouse model of Parkinson's disease

Neuroinflammation is increasingly recognized as an important feature in the pathogenesis of Parkinson's disease (PD). However, it remains unclear whether neuroinflammation contributes to nigral degeneration in PD or is merely a secondary marker of neurodegeneration. We aimed to investigate the temporal relationship between synucleopathy, neuroinflammation and nigrostriatal degeneration in a mouse model of PD. Mice received unilateral intrastriatal injection of alpha-synuclein pre-formed fibrils, alpha-synuclein monomer or vehicle and were sacrificed at 15, 30 and 90 days post-injection. Intrastriatal inoculation of alpha-synuclein fibrils led to significant alpha-synuclein aggregation in the substantia nigra peaking at 30 days after injection while the significant increase in Iba-1 cells, GFAP cells and IL-1β expression peaked earlier at 15 days. At 90 days, the striatal dopaminergic denervation was associated with astroglial activation. Alpha-synuclein monomer did not result in long-term glia activation or increase in inflammatory markers. The spread of alpha-synuclein aggregates into the cortex was not associated with any changes to neuroinflammatory markers. Our results demonstrate that in the substantia nigra glial activation is an early event that precedes alpha-synuclein inclusion formation, suggesting neuroinflammation could play an important early role in the pathogenesis of PD.

Personalized iPSC-Derived Dopamine Progenitor Cells for Parkinson's Disease

We report the implantation of patient-derived midbrain dopaminergic progenitor cells, differentiated in vitro from autologous induced pluripotent stem cells (iPSCs), in a patient with idiopathic Parkinson's disease. The patient-specific progenitor cells were produced under Good Manufacturing Practice conditions and characterized as having the phenotypic properties of substantia nigra pars compacta neurons; testing in a humanized mouse model (involving peripheral-blood mononuclear cells) indicated an absence of immunogenicity to these cells. The cells were implanted into the putamen (left hemisphere followed by right hemisphere, 6 months apart) of a patient with Parkinson's disease, without the need for immunosuppression. Positron-emission tomography with the use of fluorine-18-L-dihydroxyphenylalanine suggested graft survival. Clinical measures of symptoms of Parkinson's disease after surgery stabilized or improved at 18 to 24 months after implantation. (Funded by the National Institutes of Health and others.).

The cholinergic contribution to the resting-state functional network in non-demented Parkinson's disease

The cholinergic system arising from the basal forebrain plays an important role in cognitive performance in Parkinson's disease (PD). Here, we analyzed cholinergic status-dependent cortical and subcortical resting-state functional connectivity in PD. A total of 61 drug-naïve PD patients were divided into tertiles based on normalized substantia innominata (SI) volumes. We compared the resting-state network from seed region of interest in the caudate, posterior cingulate cortex (PCC), and SI between the lowest (PD-L) and highest tertile (PD-H) groups. Correlation analysis of the functional networks was also performed in all subjects. The functional network analysis showed that PD-L subjects displayed decreased striato-cortical functional connectivity compared with PD-H subjects. Selecting the PCC as a seed, the PD-L patients displayed decreased functional connectivity compared to PD-H patients. Meanwhile, PD-L subjects had significantly increased cortical functional connectivity with the SI compared with PD-H subjects. Correlation analysis revealed that SI volume had a positive correlation with functional connectivity from the right caudate and PCC. The present study demonstrated that PD patients exhibited unique functional connectivity from the caudate and the PCC that may be closely associated with cholinergic status, suggesting an important role for the cholinergic system in PD-associated cognition.

Current understanding of the molecular mechanisms in Parkinson's disease: Targets for potential treatments

Gradual degeneration and loss of dopaminergic neurons in the substantia nigra, pars compacta and subsequent reduction of dopamine levels in striatum are associated with motor deficits that characterize Parkinson’s disease (PD). In addition, half of the PD patients also exhibit frontostriatal-mediated executive dysfunction, including deficits in attention, short-term working memory, speed of mental processing, and impulsivity. The most commonly used treatments for PD are only partially or transiently effective and are available or applicable to a minority of patients. Because, these therapies neither restore the lost or degenerated dopaminergic neurons, nor prevent or delay the disease progression, the need for more effective therapeutics is critical. In this review, we provide a comprehensive overview of the current understanding of the molecular signaling pathways involved in PD, particularly within the context of how genetic and environmental factors contribute to the initiation and progression of this disease. The involvement of molecular chaperones, autophagy-lysosomal pathways, and proteasome systems in PD are also highlighted. In addition, emerging therapies, including pharmacological manipulations, surgical procedures, stem cell transplantation, gene therapy, as well as complementary, supportive and rehabilitation therapies to prevent or delay the progression of this complex disease are reviewed.

Differential Loss of Presynaptic Dopaminergic Markers in Parkinsonian Monkeys

Assessment of dopamine nerve terminal function and integrity is a strategy employed to monitor deficits in Parkinson's disease (PD) patients and in preclinical models of PD. Dopamine replacement therapies effectively replenish the diminished supply of endogenous dopamine and provide symptomatic benefit to patients. Tyrosine hydroxylase (TH), dopamine transporter (DAT), vesicular monoamine transporter 2 (VMAT2), and amino acid decarboxylase (AADC) are widely used markers of dopaminergic neurons and terminals. The present studies were initiated to: (a) assess alterations in all four markers in the MPTP primate model of dopaminergic degeneration and (b) to determine whether L-DOPA treatment may itself modulate the expression of these markers. MPTP treatment induced a significant decline of dopaminergic immunoreactive fiber and terminal density in the basal ganglia. The amount of reduction varied between markers. The rank order of presynaptic marker loss, from most to least profound reduction, was TH > VMAT2 > DAT > AADC. Semiquantitative image analysis of relative dopaminergic presynaptic fiber and terminal density illustrated region-specific reduction of all four markers. Double immunofluorescence colocalization of two presynaptic markers on the same tissue section confirmed there was a more dramatic loss of TH than of VMAT2 or of DAT following MPTP treatment. L-DOPA treatment was associated with a significantly higher level of AADC and VMAT2 immunoreactivity in the caudate nucleus compared to placebo. These results illustrate that neurotoxic injury of the dopamine system in primates leads to altered and differential expression of presynaptic dopaminergic markers in the basal ganglia and that expression of such markers may be modulated by L-DOPA therapy. These findings have implications for the use of biomarkers of disease progression as well as for the assessment of neurorestorative strategies, such as cell replacement, for the treatment of PD.

Combined LRRK2 mutation, aging and chronic low dose oral rotenone as a model of Parkinson's disease

Aging, genetics and environmental toxicity are important etiological factors in Parkinson’s disease (PD). However, its pathogenesis remains unclear. A major obstacle is the lack of an appropriate experimental model which incorporates genetic susceptibility, aging and prolonged environmental toxicity. Here, we explored the interplay amongst these factors using mutant LRRK2^R1441G (leucine-rich-repeat-kinase-2) knockin mice. We found that mutant primary cortical and mesencephalic dopaminergic neurons were more susceptible to rotenone-induced ATP deficiency and cell death. Compared with wild-type controls, striatal synaptosomes isolated from young mutant mice exhibited significantly lower dopamine uptake after rotenone toxicity, due to reduced striatal synaptosomal mitochondria and synaptic vesicular proton pump protein (V-ATPase H) levels. Mutant mice developed greater locomotor deficits in open-field tests than wild-type mice following low oral rotenone doses given twice weekly over 50 weeks (half their lifespan). The increased locomotor deficit was associated with specific reduction in striatal mitochondrial Complex-I (NDUFS4) in rotenone-treated mutant but not in similarly treated wild-type mice. Our unique experimental model which incorporates genetic effect, natural aging and prolonged oral environmental toxicity administered to mutant knockin LRRK2 mice over half their life span, with observable and measurable phenotype, is invaluable in further studies of the pathogenic process and therapeutics of PD.

Long-term treatment of Parkinson's disease with levodopa and other adjunctive drugs

We report a long-term treatment of Parkinson’s disease in out-patient clinics. The patients with Parkinson’s disease were evaluated at the time of clinic visit from September 1st, 2015 to February 29th, 2016. Total number of the patients was 498. The age at the evaluation was 69.9 ± 9.3 years and the age of onset was 60.2 ± 11.3. Hoehn and Yahr severity was 3.28 ± 0.94 in patients who were from 16 to 20 years (n = 53) and 3.00 ± 0.86 in patients from 21 years or more (n = 38) from the onset of the disease to the evaluation. The dose of levodopa was 741 ± 295 mg per day and the number of levodopa dosing was 5.85 ± 2.59 times in 16–20 years from the onset to the evaluation and 703 ± 251 mg/day and 6.03 ± 3.20 times a day in 21 years or more from the onset to the evaluation. Levodopa was given in most cases into an empty stomach. The incidence of wearing off was 73.6% and dyskinesia was 37.7% in the 16–20 years group and 76.3% and 55.3% in 21 years or more group, respectively. The patients who had 15 years or less from the onset to the evaluation had much milder severity of the disease. Hoehn and Yahr severity, the dose of levodopa, and the incidence of wearing off were about the same as in the literature. But the incidence of dyskinesia was much lower than those appeared in the literature. We discussed reasons why the incidence of dyskinesia was lower in our study.

Fluorine-18 Radiolabeled PET Tracers for Imaging Monoamine Transporters: Dopamine, Serotonin, and Norepinephrine

This review focuses on the development of fluorine-18 radiolabeled PET tracers for imaging the dopamine transporter (DAT), serotonin transporter (SERT), and norepinephrine transporter (NET). All successful DAT PET tracers reported to date are members of the 3β-phenyl tropane class and are synthesized from cocaine. Currently available carbon-11 SERT PET tracers come from both the diphenylsulfide and 3β-phenyl nortropane class, but so far only the nortropanes have found success with fluorine-18 derivatives. NET imaging has so far employed carbon-11 and fluorine-18 derivatives of reboxetine but due to defluorination of the fluorine-18 derivatives further research is still necessary.

Multicenter Semiquantitative Evaluation of (123)I-FP-CIT Brain SPECT

AIMS

The aims of this study were: (1) to cross-compare data from semiquantitative, software-assisted, and phantom-corrected evaluations of (123)I-ioflupane [(123)I]N-ω-fluoropropyl-2β-carbomethoxy-3β-{4-iodophenyl}nortropane FP-CIT brain single-photon emission computed tomography (SPECT) acquired in three centers; (2) to assess the accuracy of semiquantitative evaluation; and (3) to identify the threshold with the best accuracy, sensitivity, and specificity in patients with suspected Parkinsonian Syndrome.

MATERIAL AND METHODS

Two-hundred-twenty patients, acquired in three centers, were included. All of them underwent (123)I-FP-CIT brain SPECT. All examinations were analyzed with the freely available software, BasGan, and semiquantitative data were used to predict disease. Analysis was based on the values from the most deteriorated putamen and caudate, normalized for age, and corrected by anthropomorphic phantom data. Receiver operating characteristic (ROC) analysis was performed and areas under the curve (AUC) were estimated.

RESULTS

Analysis showed high AUCs (.880, .866, .920, and .882 for each center and multicenter setting). Best thresholds were 1.53 and 1.56 for putamen and caudate, respectively. Thresholds of putamen data showed sensitivity and specificity of 86% and 89%, respectively, in the multicenter setting. Neither sensibility nor specificity showed significant differences among centers.

CONCLUSION

A unique, accurate threshold for all centers, with high sensitivity and specificity was identified. Semiquantitative assessment of (123)I-FP-CIT brain SPECT among different centers resulted reliable, accurate, and potentially useful in clinical trials.

Central pathways causing fatigue in neuro-inflammatory and autoimmune illnesses

BACKGROUND

The genesis of severe fatigue and disability in people following acute pathogen invasion involves the activation of Toll-like receptors followed by the upregulation of proinflammatory cytokines and the activation of microglia and astrocytes. Many patients suffering from neuroinflammatory and autoimmune diseases, such as multiple sclerosis, Parkinson's disease and systemic lupus erythematosus, also commonly suffer from severe disabling fatigue. Such patients also present with chronic peripheral immune activation and systemic inflammation in the guise of elevated proinflammtory cytokines, oxidative stress and activated Toll-like receptors. This is also true of many patients presenting with severe, apparently idiopathic, fatigue accompanied by profound levels of physical and cognitive disability often afforded the non-specific diagnosis of chronic fatigue syndrome.

DISCUSSION

Multiple lines of evidence demonstrate a positive association between the degree of peripheral immune activation, inflammation and oxidative stress, gray matter atrophy, glucose hypometabolism and cerebral hypoperfusion in illness, such as multiple sclerosis, Parkinson's disease and chronic fatigue syndrome. Most, if not all, of these abnormalities can be explained by a reduction in the numbers and function of astrocytes secondary to peripheral immune activation and inflammation. This is also true of the widespread mitochondrial dysfunction seen in otherwise normal tissue in neuroinflammatory, neurodegenerative and autoimmune diseases and in many patients with disabling, apparently idiopathic, fatigue. Given the strong association between peripheral immune activation and neuroinflammation with the genesis of fatigue the latter group of patients should be examined using FLAIR magnetic resonance imaging (MRI) and tested for the presence of peripheral immune activation.

SUMMARY

It is concluded that peripheral inflammation and immune activation, together with the subsequent activation of glial cells and mitochondrial damage, likely account for the severe levels of intractable fatigue and disability seen in many patients with neuroimmune and autoimmune diseases.This would also appear to be the case for many patients afforded a diagnosis of Chronic Fatigue Syndrome.

Molecular imaging as a guide for the treatment of central nervous system disorders

Molecular imaging techniques have a number of advantages for research into the pathophysiology and treatment of central nervous system (CNS) disorders. Firstly, they provide a noninvasive means of characterizing physiological processes in the living brain, enabling molecular alterations to be linked to clinical changes. Secondly, the pathophysiological target in a given CNS disorder can be measured in animal models and in experimental human models in the same way, which enables translational research. Moreover, as molecular imaging facilitates the detection of functional change which precedes gross pathology, it is particularly useful for the early diagnosis and treatment of CNS disorders.

This review considers the application of molecular imaging to CNS disorders focusing on its potential to inform the development and evaluation of treatments. We focus on schizophrenia, Parkinson's disease, depression, and dementia as major CNS disorders. We also review the potential of molecular imaging to guide new drug development for CNS disorders.

Dopaminergic modulation of resting-state functional connectivity in de novo patients with Parkinson's disease

Parkinson's disease (PD) is characterized by degenerative changes of nigral dopamine neurons, resulting in the dopaminergic denervation of the striatum. Resting state networks studies have demonstrated that dopamine modulates distinct network connectivity patterns in both a linear and a nonlinear fashion, but quantitative analyses of dopamine-dependent functional connectivity secondary to PD pathology were less informative. In the present study, we performed a correlation analysis between striatal dopamine levels assessed quantitatively by FP-CIT positron emission tomography imaging and resting-state functional connectivity in 23 drug naïve de novo patients with PD to elucidate dopamine-dependent functional networks. The major finding is that the patterns of dopamine-dependent positive functional connectivity varied depending on the location of striatal seeds. Dopamine-dependent functional connectivity with the caudate predominantly overlay pericentral cortical areas, whereas dopamine-dependent structures functionally connected with the posterior putamen predominantly involved cerebellar areas. The dorsolateral frontal area overlapped as a dopamine-dependent cortical region that was positively connected with the anterior and posterior putamen. On the other hand, cortical areas where functional connectivity from the posterior cingulate was negatively correlated with dopaminergic status in the posterior putamen were localized in the left anterior prefrontal area and the parietal area. Additionally, functional connectivity between the anterior putamen and mesiofrontal areas was negatively coupled with striatal dopamine levels. The present study demonstrated that dopamine-dependent functional network connectivity secondary to PD pathology mainly exhibits a consistent pattern, albeit with some variation. These patterns may reflect the diverse effects of dopaminergic medication on parkinsonian-related motor and cognitive performance.

Influence of O-methylated metabolite penetrating the blood-brain barrier to estimation of dopamine synthesis capacity in human L-[β-(11)C]DOPA PET

O-methyl metabolite (L-[β-(11)C]OMD) of (11)C-labeled L-3,4-dihydroxyphenylalanine (L-[β-(11)C]DOPA) can penetrate into brain tissue through the blood-brain barrier, and can complicate the estimation of dopamine synthesis capacity by positron emission tomography (PET) study with L-[β-(11)C]DOPA. We evaluated the impact of L-[β-(11)C]OMD on the estimation of the dopamine synthesis capacity in a human L-[β-(11)C]DOPA PET study. The metabolite correction with mathematical modeling of L-[β-(11)C]OMD kinetics in a reference region without decarboxylation and further metabolism, proposed by a previous [(18)F]FDOPA PET study, were implemented to estimate radioactivity of tissue L-[β-(11)C]OMD in 10 normal volunteers. The component of L-[β-(11)C]OMD in tissue time-activity curves (TACs) in 10 regions were subtracted by the estimated radioactivity of L-[β-(11)C]OMD. To evaluate the influence of omitting blood sampling and metabolite correction, relative dopamine synthesis rate (kref) was estimated by Gjedde-Patlak analysis with reference tissue input function, as well as the net dopamine synthesis rate (Ki) by Gjedde-Patlak analysis with the arterial input function and TAC without and with metabolite correction. Overestimation of Ki was observed without metabolite correction. However, the kref and Ki with metabolite correction were significantly correlated. These data suggest that the influence of L-[β-(11)C]OMD is minimal for the estimation of kref as dopamine synthesis capacity.

Nigrostriatal dopamine terminal imaging with dopamine transporter SPECT: an update

This article gives an update on nigrostriatal dopamine terminal imaging, with emphasis on SPECT performed with the presynaptic dopamine transporter (DAT) ligand (123)I-FP-CIT. The paper covers the rational use of this technique in the diagnostic work-up of patients with known or suspected parkinsonian syndromes. In detail, it addresses the impact of the method for the proof or exclusion of neurodegenerative parkinsonism, for its early and preclinical diagnosis, and for the evaluation of disease progression. The importance of normal DAT binding for differentiating symptomatic parkinsonism and relevant tremor syndromes from neurodegeneration is highlighted. Particularly emphasized is the role of DAT SPECT for diagnosing Lewy body dementia and its separation from Alzheimer dementia. Finally, some remarks deal with the economic aspects of the use of these imaging techniques in the clinical setting.

Diagnosis and initiation of treatment in Parkinson's disease

Parkinson's disease (PD) is the most common cause of parkinsonism, yet the diagnosis and management can be a challenge. The United Kingdom Parkinson's Disease Society Brain Bank Clinical Diagnostic Criteria and dopamine transporter/single-photon emission computed tomography (DaT-SPECT) are diagnostic aids that can improve diagnostic accuracy. Even though PD is a progressive disease, for years, physicians and patients have delayed treatment until functional disability occurs. However, studies of monoamine oxidase-type B (MAO-B) inhibitors, dopamine agonists, and levodopa, all of which can be used as initial therapy, have demonstrated that PD patients receiving treatment do better than those who do not receive treatment, and some studies have shown that those receiving treatment earlier do better long term. Therefore, the management strategy for PD has moved toward earlier initiation of treatment. Although treatment for each patient should be individualized and based on their specific symptoms, severity, and lifestyle, in general MAO-B inhibitors may be used initially to treat mild symptoms, adding a dopamine agonist in younger patients or levodopa in older patients, as symptoms become more severe.

Guided delivery of adeno-associated viral vectors into the primate brain

In this review, we discuss recent developments in the delivery of adeno-associated virus-based vectors (AAV), particularly with respect to the role of axonal transport in vector distribution in the brain. The use of MRI-guidance and new stereotactic aiming devices have now established a strong foundation for neurological gene therapy to become an accepted procedure in interventional neurology.

Pathologic lesions in neurodegenerative diseases

This chapter will discuss two of the most widely used approaches to assessing brain structure: neuroimaging and neuropathology. Whereas neuropathologic approaches to studying the central nervous system have been utilized for many decades and have provided insights into morphologic correlates of dementia for over 100 years, accurate structural imaging techniques "blossomed" with the development and refinement of computerized tomographic scanning and magnetic resonance imaging (MRI), beginning in the late 1970s. As Alzheimer disease progresses over time, there is progressive atrophy of the hippocampus and neocortex--this can be quantified and regional accentuation of the atrophy can be evaluated using quantitative MRI scanning. Furthermore, ligands for amyloid proteins have recently been developed--these can be used in positron emission tomography studies to localize amyloid proteins, and (in theory) study the dynamics of their deposition (and clearance) within the brain over time. Neuropathologic studies of the brain, using highly specific antibodies, can demonstrate synapse loss and the deposition of proteins important in AD progression--specifically ABeta and phosphor-tau. Finally, neuropathologic assessment of (autopsy) brain specimens can provide important correlation with sophisticated neuroimaging techniques.

Critical aspects of clinical trial design for novel cell and gene therapies

Neural cell transplantation and gene therapy have attracted considerable interest as promising therapeutic alternatives for patients with Parkinson's disease (PD). Preclinical and open-label studies have suggested that grafted fetal neural tissue or viral vector gene transfer can achieve considerable biochemical and clinical improvements, whereas subsequent double-blind, placebo-controlled protocols have produced rather more modest and variable results. Detailed evaluation of these discordant findings has highlighted several crucial issues such as patient selection criteria, details surrounding transplantation or gene therapy methodologies, as well as the study designs themselves that ought to be carefully considered in the planning phases of future clinical trials. Beyond the provision of symptomatic efficacy and safety data, it also remains to be identified whether the possibilities offered by stem cell and gene therapy technological advances might translate to meaningful neuroprotection and/or disease-modifying effects or alleviate the nonmotor aspects of PD and thus offer additional benefits beyond those achieved through conventional pharmacotherapy or deep brain stimulation (DBS).

Regional alterations of brain microstructure in Parkinson's disease using diffusion tensor imaging

This study tested the hypothesis that diffusion tensor imaging can detect alteration in microscopic integrity of white matter and basal ganglia regions known to be involved in Parkinson's disease (PD) pathology. It was also hypothesized that there is an association between diffusion abnormality and PD severity and subtype. Diffusion tensor imaging at 4 Tesla was obtained in 12 PD and 20 control subjects, and measures of fractional anisotropy and mean diffusivity were evaluated using both region-of-interest and voxel-based methods. Movement deficits and subtypes in PD subjects were assessed using the Motor Subscale (Part III) of the Unified Parkinson's Disease Rating Scale. Reduced fractional anisotropy (P < .05, corrected) was found in PD subjects in regions related to the precentral gyrus, substantia nigra, putamen, posterior striatum, frontal lobe, and the supplementary motor areas. Reduced fractional anisotropy in the substantia nigra correlated (P < .05, corrected) with the increased rating scale motor scores. Significant spatial correlations between fractional anisotropy alterations in the putamen and other PD-affected regions were also found in the context of PD subtypes index analysis. Our data suggest that microstructural alterations detected with diffusion tensor might serve as a potential biomarker for PD.

The role of dopaminergic imaging in patients with symptoms of dopaminergic system neurodegeneration

Diagnosis of neurological and psychiatric conditions associated with disturbances of dopaminergic functioning can be challenging, especially in the early stages, and may be assisted with biomarkers such as dopamine system imaging. Distinguishing between Alzheimer's disease and dementia with Lewy bodies is a major diagnostic challenge. Clinical diagnosis of Parkinson's disease is straightforward with classic presentation, but accurate distinction among Parkinsonian variants may be difficult; non-Parkinson's disease conditions are commonly misdiagnosed as Parkinson's disease, and ~20% of patients with Parkinson's disease are not clinically diagnosed despite coming to medical attention. Early and accurate diagnosis is desirable to improve management. Imaging of the dopamine transporter using single-photon emission computed tomography may be of particular utility in this regard. Abnormal imaging indicates underlying nigrostriatal neurodegeneration, supportive of a diagnosis of Parkinson's disease, atypical parkinsonism or dementia with Lewy bodies, and identifies patient groups in whom dopaminergic therapy may be beneficial. Normal imaging supports diagnosis of a condition not involving nigrostriatal neurodegeneration such as Alzheimer's disease, essential tremor or drug-induced parkinsonism and hence a different therapeutic approach. In patients in whom there was diagnostic uncertainty between degenerative parkinsonism and non-degenerative tremor disorders, baseline imaging with the dopamine transporter ligand [(123)I]ioflupane (DaTscan™) has shown 78% sensitivity and 97% specificity with reference to clinical diagnosis at 3 years, versus 93% and 46%, respectively, for baseline clinical diagnosis. In a Phase III trial of [(123)I]ioflupane in patients with initial clinical diagnosis of probable or possible dementia with Lewy bodies or non-Lewy body dementia, mean specificity for excluding non-Lewy body dementia (predominantly Alzheimer's disease) was 90.4%. Using clinical diagnosis as a reference against which to assess sensitivity and specificity of dopamine transporter imaging is a limitation, but definitive diagnosis via pathological confirmation is generally not feasible. In a series of patients with post-mortem brain examination, imaging using [(123)I]ioflupane has demonstrated higher sensitivity (88%) and specificity (100%) for differentiating dementia with Lewy bodies from non-Lewy body dementia than clinical diagnosis (75% and 42%, respectively). Dopaminergic system imaging may be particularly valuable in patients with clinically inconclusive parkinsonism or a clinical diagnosis of possible dementia with Lewy bodies; it is not helpful in differentiating between Parkinson's disease and atypical parkinsonism, although postsynaptic dopaminergic imaging may be of utility. Other potential uses of dopamine transporter imaging include identification of patients with premotor Parkinson's disease, monitoring disease progression in testing novel therapeutics, and as an inclusion criterion for entry into clinical trials.

Sensitivity of kinetic macro parameters to changes in dopamine synthesis, storage, and metabolism: a simulation study for [¹⁸F]FDOPA PET by a model with detailed dopamine pathway

Quantitative interpretation of brain [¹⁸F]FDOPA PET data has been made possible by several kinetic modeling approaches, which are based on different assumptions about complex [¹⁸F]FDOPA metabolic pathways in brain tissue. Simple kinetic macro parameters are often utilized to quantitatively evaluate metabolic and physiological processes of interest, which may include DDC activity, vesicular storage, and catabolism from (18) F-labeled dopamine to DOPAC and HVA. A macro parameter most sensitive to the changes of these processes would be potentially beneficial to identify impaired processes in a neurodegenerative disorder such as Parkinson's disease. The purpose of this study is a systematic comparison of several [¹⁸F]FDOPA macro parameters in terms of sensitivities to process-specific changes in simulated time-activity curve (TAC) data of [¹⁸F]FDOPA PET. We introduced a multiple-compartment kinetic model to simulate PET TACs with physiological changes in the dopamine pathway. TACs in the alteration of dopamine synthesis, storage, and metabolism were simulated with a plasma input function obtained by a non-human primate [¹⁸F]FDOPA PET study. Kinetic macro parameters were calculated using three conventional linear approaches (Gjedde-Patlak, Logan, and Kumakura methods). For simulated changes in dopamine storage and metabolism, the slow clearance rate (k(loss) ) as calculated by the Kumakura method showed the highest sensitivity to these changes. Although k(loss) performed well at typical ROI noise levels, there was large bias at high noise level. In contrast, for simulated changes in DDC activity it was found that K(i) and V(T), estimated by Gjedde-Patlak and Logan method respectively, have better performance than k(loss).

Use of MRI to monitor Parkinson’s disease

SUMMARY Objective biological markers of Parkinson’s disease (PD) are pivotal for confirming diagnosis, monitoring disease progression, and evaluating therapeutic interventions and disease-modifying agents. Structural and functional MRI provide an in vivo means to investigate the cortical and subcortical regions known to be affected in PD. In this article, we summarize how several MRI techniques, namely conventional MRI, iron-based MRI, volume-based MRI, diffusion tensor imaging, magnetic resonance spectroscopy and functional MRI have been used to assess the neurobiological changes related to the motor features of PD. We also discuss promising new research in which multiple MRI techniques are combined to achieve greater sensitivity and specificity of disease detection. Longitudinal research is necessary to establish MRI techniques as viable disease-state biomarkers of PD.

Anterograde axonal transport of AAV2-GDNF in rat basal ganglia

We elucidated the effects of parkinsonian degeneration on trafficking of AAV2-GDNF in the nigro-striatum (nigro-ST) of unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats. Vector infused into striatum (ST) was transported to substantia nigra (SN), both pars compacta (SNc), and pars reticulata (SNr). In the lesioned hemisphere, glial cell line-derived neurotrophic factor (GDNF) immunoreactivity was only found in SNr consistent with elimination of SNc dopaminergic (DA) neurons by 6-OHDA. Further analysis showed that striatal delivery of AAV2-GDNF resulted in GDNF expression in globus pallidus (GP), entopeduncular nucleus (EPN), and subthalamic nucleus (STN) in both lesioned and unlesioned hemispheres. Injection of vector into SN, covering both SNc and SNr, resulted in striatal expression of GDNF in the unlesioned hemisphere but not in the lesioned hemisphere. No expression was seen in GP or EPN. We conclude that adeno-associated virus serotype 2 (AAV2) is transported throughout the nigro-ST exclusively by anterograde transport. This transport phenomenon directs GDNF expression throughout the basal ganglia in regions that are adversely affected in Parkinson's disease (PD) in addition to SNc. Delivery of vector to SN, however, does not direct expression of GDNF in ST, EPN, or GP. On this basis, we believe that striatal delivery of AAV2-GDNF is the preferred course of action for trophic rescue of DA function.

Biomarkers and imaging: physics and chemistry for noninvasive analyses

The era of ‘modern medicine’ has changed its name to ‘molecular medicine’, and reflects a new age based on personalized medicine utilizing molecular biomarkers in the diagnosis, staging and monitoring of therapy. Alzheimer’s disease has a classical biomarker determined at autopsy with the histologic staining of amyloid accumulation in the brain. Today we can diagnose Alzheimer’s disease using the same classical pathologic biomarker, but now using a noninvasive imaging probe to image the amyloid deposition in a patient and potentially provide treatment strategies and measure their effectiveness. Molecular medicine is the exploitation of biomarkers to detect disease before overt expression of pathology. Physicians can now find, fight and follow disease using imaging, and the need for other disease biomarkers is in high demand. This review will discuss the innovative physical and molecular biomarker probes now being developed for imaging systems and we will introduce the concepts needed for validation and regulatory acceptance of surrogate biomarkers in the detection and treatment of disease.

Metabolomics tools for identifying biomarkers for neuropsychiatric diseases

The repertoire of biochemicals (or small molecules) present in cells, tissue, and body fluids is known as the metabolome. Today, clinicians utilize only a very small part of the information contained in the metabolome, as revealed by the quantification of a limited set of analytes to gain information on human health. Examples include measuring glucose or cholesterol to monitor diabetes and cardiovascular health, respectively. With a focus on comprehensively studying the metabolome, the rapidly growing field of metabolomics captures the metabolic state of organisms at the global or "-omics" level. Given that the overall health status of an individual is captured by his or her metabolic state, which is a reflection of what has been encoded by the genome and modified by environmental factors, metabolomics has the potential to have a great impact upon medical practice by providing a wealth of relevant biochemical data. Metabolomics promises to improve current, single metabolites-based clinical assessments by identifying metabolic signatures (biomarkers) that embody global biochemical changes in disease, predict responses to treatment or medication side effects (pharmachometabolomics). State of the art metabolomic analytical platforms and informatics tools are being used to map potential biomarkers for a multitude of disorders including those of the central nervous system (CNS). Indeed, CNS disorders are linked to disturbances in metabolic pathways related to neurotransmitter systems (dopamine, serotonin, GABA and glutamate); fatty acids such as arachidonic acid-cascade; oxidative stress and mitochondrial function. Metabolomics tools are enabling us to map in greater detail perturbations in many biochemical pathways and links among these pathways this information is key for development of biomarkers that are disease-specific. In this review, we elaborate on some of the concepts and technologies used in metabolomics and its promise for biomarker discovery. We also highlight early findings from metabolomic studies in CNS disorders such as schizophrenia, Major Depressive Disorder (MDD), Bipolar Disorder (BD), Amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD).

Imaging the impact of genes on Parkinson's disease

Although Parkinson's disease (PD) has traditionally been considered to be a non-genetic disorder, recent progress in the neurogenetics of PD provided converging evidence that genetic factors play a relevant role in the etiology of PD. The strongest case for a genetic contribution to PD was made by the discovery of mutations in single genes that can cause autosomal dominant (alpha-synuclein (SNCA)) and leucine rich repeat kinase 2 (LRRK2) gene) or recessive (Parkin, PTEN-induced putative kinase 1 (PINK1), DJ-1, and ATP13A2 gene) forms of PD. Here, we review how structural and functional neuroimaging of individuals carrying a mutation in one of the PD genes has offered a unique avenue of research into the pathogenesis of PD. In symptomatic mutation carriers (i.e. those with overt disease), brain mapping can help to link the molecular pathogenesis of PD more directly with functional and structural changes in the intact human brain. In addition, neuroimaging of presymptomatic (i.e. non-manifesting) mutation carriers has emerged as a valuable tool to identify mechanisms of adaptive motor reorganization at the preclinical stage that may prevent or delay clinical manifestation. In addition to mutations causing monogenic forms of PD, common polymorphisms in genes that influence mono-aminergic signaling or synaptic plasticity may have modifying effects on distinct aspects of PD. We also discuss how functional and structural neuroimaging can be used to better characterize these genotype-phenotype correlations.

In vivo imaging markers of neurodegeneration of the substantia nigra

Non invasive detection and monitoring of substantia nigra degeneration is a long sought aim for neuroscientists, clinicians and pharmaceutical companies with an interest in Parkinson's disease (PD). Functional imaging techniques are established tools to assess the extent of striatal dopaminergic denervation that indirectly reflects nigral degeneration. They allow characterization of the dopaminergic denervation during the premotor phase of PD and have clinical value to establish the diagnosis in parkinsonism, but have proven to be unsatisfactory as surrogate markers in recent treatment trials. There is strong research interest in developing new imaging tests for nigral degeneration using a variety of structural brain imaging techniques. Nigral hyperechogenicity assessed by transcranial sonography emerges as a robust and low cost test to diagnose PD. Additionally, various advanced magnetic resonance imaging contrasts and high field magnetic resonance spectroscopy show promising sensitivity to nigral pathology in PD. Qualification of these emerging imaging tests against defined biomarker criteria is a complex and challenging task ahead. More systematic validation studies analogous to clinical trials are needed to meet the expectations and criteria defined by regulatory bodies before imaging biomarkers can be used as surrogate endpoints for neuroprotective or restorative trials.

Opioid Imaging

Many breakthrough scientific discoveries have been made using opioid imaging. Developments include the application of ever higher resolution whole-brain positron emission tomography (PET) scanners, the availability of several radioligands, the combination of PET with advanced structural imaging, advances in modeling macroparameters of PET ligand binding, and large-scale statistical analysis of imaging datasets. Suitable single-photon emission computed tomography (SPECT) tracers are lacking, but with the increase in the number of available PET (or PET/CT) cameras and cyclotrons thanks to the clinical successes of PET in oncology, PET may become widespread enough to overcome this. In the coming decade, there should be a more widespread application of the available techniques to patients and an impact in clinical medicine.

Design of clinical trials of gene therapy in Parkinson disease

No current therapy for Parkinson disease has been shown to slow or reverse the progressive course of the disease. As a departure from traditional treatments, gene therapy approaches provide a new hope for realizing this long-sought goal; but before they can be widely employed for use in patients, they must first be submitted to the rigorous safety and efficacy standards of the clinical trial. Some of the challenges of gene therapy clinical trial design are similar to those in studies of conventional pharmacological agents and include addressing the heterogeneity of the disease, the need for clinical and surrogate endpoints, and the issue of distinguishing "symptomatic" from "neuroprotective" effects. Gene therapy trials also raise the issues of the risks of viral therapy, issues of dose-response, the need for sham surgery, and the long duration of risks and benefits. We conclude that the most feasible designs are for those treatments that are expected to produce a rapid improvement in directly observable symptoms. Trials of agents which are expected to produce only a slowing of progression and not a reversal of the disease course are likely to take much longer and will require the development of methods to assess quality of life and other non-motor aspects of the disease.

Synthesis and radiopharmacological characterization of 2beta-carbo-2'-[18F]fluoroethoxy-3beta-(4-bromo-phenyl)tropane ([18F]MCL-322) as a PET radiotracer for imaging the dopamine transporter (DAT)

The fluoroalkyl-containing tropane derivative 2beta-carbo-2'-fluoroethoxy-3beta-(4-bromo-phenyl)tropane (MCL-322) is a highly potent and moderately selective ligand for the dopamine transporter (DAT). The compound was labeled with the short-lived positron emitter (18)F in a single step by nucleophilic displacement of the corresponding tosylate precursor MCL-323 with no-carrier-added [(18)F]fluoride. The positron emission tomography (PET) radiotracer 2beta-carbo-2'-[(18)F]fluoroethoxy-3beta-(4-bromo-phenyl)tropane [(18)F]MCL-322 was obtained in decay-corrected radiochemical yields of 30-40% at a specific radioactivity of 1.6-2.4Ci/mumol (60-90GBq/mumol) at the end-of-synthesis (EOS). Small animal PET, ex vivo and in vivo biodistribution experiments in rats demonstrated a high uptake in the striatum (3.2% ID/g) 5min after injection, which increased to 4.2% ID/g after 60min. The uptake in the cerebellum was 1.8% ID/g and 0.6% ID/g after 5min and 60min post-injection, respectively. Specific binding to DAT of [(18)F]MCL-322 was confirmed by blocking experiments using the high affinity DAT ligand GBR 12909. The radiopharmacological characterization was completed with metabolite and autoradiographic studies confirming the selective uptake of [(18)F]MCL-322 in the striatum. It is concluded that the simple single-step radiosynthesis of [(18)F]MCL-322 and the promising radiopharmacological data make [(18)F]MCL-322 an attractive candidate for the further development of a PET radiotracer potentially suitable for clinical DAT imaging in the human brain.

Molecular imaging in hereditary forms of parkinsonism

The development of in vivo molecular imaging to evaluate the dopamine (DA) system with positron-emission tomography and single photon emission computed tomography has been of key importance on monitoring in vivo nigrostriatal neuronal loss in Parkinson's disease (PD), mostly through assessments of pre- and post-synaptic DA receptors. The discoveries of genes related to hereditary forms of parkinsonism (PARK1, PARK2, PARK6, PARK7 and PARK8) have increased our understanding either of distinct subtypes of clinical expression in PD or its etiology. This article revises current data on molecular neuroimaging of genetic forms of parkinsonism comparing and contrasting its main features with the classical sporadic forms. Awareness of the spectrum variance in the genotype and its respective PD phenotype are useful to distinguish different pathophysiological mechanisms of PD.

The role of neuroimaging in elucidating delirium pathophysiology

Understanding of delirium pathogenesis remains limited despite improved diagnosis, and elucidation of risk factors and prognosis. Major advances in neuroimaging offer the possibility of probing the mechanisms and networks involved in delirium and hence improving understanding of this often devastating syndrome. This review describes the current literature of imaging studies in delirium and related conditions, introduces some of the newer capabilities of neuroimaging with magnetic resonance imaging, positron emission tomography, and single photon emission computed tomography, and discusses how these techniques may be applied to the study of delirium. Despite considerable challenges in patient recruitment, study design, intersubject variability, and scanner and contrast agent availability, imaging offers great potential for the identification and clarification of pathogenic mechanisms of delirium and its long-term sequelae.

Exploring the relationship between essential tremor and Parkinson's disease

Although essential tremor (ET) and Parkinson's disease (PD) are considered distinct disorders, there is overlap in some clinical features. In some PD patients, a long-standing postural tremor in the hands may precede the onset of parkinsonian features by several years or decades. Furthermore, large families with both ET and PD phenotypes have been described and autopsy studies have demonstrated Lewy body pathology in brains of ET patients. Functional neuroimaging suggests that some ET patients have dopaminergic deficit. We examine here the evidence for and against an association between ET and PD, and critically review data supporting the notion that a subset of ET patients is predisposed to developing PD.

Chronic epidural motor cortical stimulation for movement disorders

Recent data suggest that epidural chronic motor cortical stimulation could improve movement disorders. Because the procedure is safe, it might be a valuable therapeutic option. Although the therapeutic effects of cortical stimulation still need to be assessed in controlled studies, we discuss its rationale and the possible physiological mechanisms involved. There are several factors that support the use of chronic cortical stimulation in patients with movement disorders, including the strategic position of the motor cortex, the improvement induced in some motor disorders by cortical lesions, the functional imaging findings documenting widespread cortical dysfunction in movement disorders, and the improvement induced in patients with Parkinson's disease and dystonia by repetitive transcranial magnetic stimulation. Among the possible mechanisms of action of chronic motor cortex stimulation, besides modifications in the motor cortex itself, the most probable is that of eliciting distant bilateral changes through efferents and afferents that bilaterally connect the motor cortex with other cortical and subcortical structures.

Opioid Imaging

Many breakthrough scientific discoveries have been made using opioid imaging, particularly in the fields of pain, addiction and epilepsy research. Recent developments include the application of ever higher resolution whole-brain positron emission tomography (PET) scanners, the availability of several radioligands, the combination of PET with advanced structural imaging, advances in modeling macroparameters of PET ligand binding, and large-scale statistical analysis of imaging datasets. Suitable single-photon emission computed tomography (SPECT) tracers are lacking, but with the increase in the number of available PET (or PET/CT) cameras and cyclotrons thanks to the clinical successes of PET in oncology, PET may become widespread enough to overcome this limitation. In the coming decade, we hope to see a more widespread application of the techniques developed in healthy volunteers to patients and more clinical impact of opioid imaging.

Evaluation of treatment effects in Alzheimer's and other neurodegenerative diseases by MRI and MRS

Neurodegeneration refers to a large clinically and pathologically heterogeneous disease entity associated with slowly progressive neuronal loss in different anatomical and functional systems of the brain. Neurodegenerative diseases often affect cognition, e.g. Alzheimer's disease (AD), dementia with Lewy bodies and vascular dementia, or different aspects of the motor system, e.g., amyotrophic lateral sclerosis, Parkinson's disease and ataxic disorders. Owing to increasing knowledge about the mechanisms leading to neurodegeneration, the development of treatments able to modify the neurodegenerative process becomes possible for the first time. Currently, clinical outcome measures are used to assess the efficacy of such treatments. However, most clinical outcome measures have a low test-retest reliability and thus considerable measurement variance. Therefore, large patient populations and long observation times are needed to detect treatment effects. Furthermore, clinical outcome measures cannot distinguish between symptomatic and disease-modifying treatment effects. Therefore, alternative biomarkers including neuroimaging may take on a more important role in this process. Because MR scanners are widely available and allow for non-invasive detection and quantification of changes in brain structure and metabolism, there is increasing interest in the use of MRI/MRS to monitor objectively treatment effects in clinical trials of neurodegenerative diseases. Particularly volumetric MRI has been used to measure atrophy rates in treatment trials of AD because the relationship between atrophic changes and neuron loss is well established and correlates well with clinical measures. More research is needed to determine the value of other MR modalities, i.e. diffusion, perfusion and functional MRI and MR spectroscopy, for clinical trials with neuroprotective drugs.

Quantification of MPTP-induced dopaminergic neurodegeneration in the mouse substantia nigra by laser capture microdissection

The neurotoxin MPTP is widely used to cause damage to the dopaminergic system in rodents and non-human primates to model various aspects of Parkinson's disease. In mice, depletion of striatal dopamine is the commonly used endpoint to assess neuronal damage. However, it has proved technically challenging to quantify dopaminergic cell bodies as an index of neuronal integrity. To meet this challenge, we applied laser pressure catapult microdissection (LCM) of the substantia nigra in combination with quantitative Western blot to provide an index of dopamine neurodegeneration in mice treated with MPTP. Seven days following initiation of MPTP treatment, striatal dopamine depletion was maximal and there was histological evidence of neuronal degeneration in the substantia nigra. To index the integrity of dopamine cell bodies, tyrosine hydroxylase (TH) and beta-actin were quantified by Western blot in LCM extracts. In untreated mice, TH was detected in LCM extracts of substantia nigra but was undetectable in equivalently sized extracts of cortex from the same animals. In MPTP-treated mice, there was a significant 70% reduction in TH relative to beta-actin in LCM extracts as compared to vehicle-injected controls. This reduction corresponded to decreases in striatal dopamine and loss of immunocytochemically detected TH but not beta-actin in the substantia nigra (SN). Thus, this method provides a quantitative means to measure dopamine neuron toxicity in the substantia nigra and, as such has potential application in evaluating regimens that may be neuroprotective or neurorestorative for dopaminergic neurons.