Search

Mounting evidences indicated that elevated iron levels in the substantia nigra (SN) have been concerned as the underlying mechanisms of neurodegenerative diseases, including Parkinson's disease (PD). The present study used the 1-Methyl-4-phenyl-1, 2, 3, 6 -tetrahydropyridine (MPTP)-treated cynomolgus monkeys for PD to evaluate the usability of SWI for assessing iron deposition in the cerebral nuclei of PD. The results showed that susceptibility-weighted imaging (SWI) phase values of the ipsilateral (MPTP-lesion side) SN of MPTP-treated monkeys were lower than those in the contralateral SN of MPTP-treated monkeys and the same side of Control monkeys, suggesting that iron deposition were elevated in the affected side SN of MPTP-treated monkeys. Whereas MPTP has not effects on the SWI phase values in other detected brain regions of monkeys, including red nucleus (RN), putamen (PUT) and caudate nucleus (CA). Furthermore, ICP-MS results showed that MPTP increased the iron levels in MPTP injection side, but no in the ipsilateral striatum. Additionally, MPTP treatment did not affect the calcium and manganese levels in the detected brain regions of monkeys. However, Pearson correlation analysis results indicated that there were not relationship between SWI phase values in MPTP-lesion side of SN with the behavioral score, tyrosine hydroxylase (TH)-positive cells number and iron levels in the MPTP-lesion side of midbrain. Taken together, the results confirm the involvement of SN iron accumulations in the MPTP-treated monkey models for PD, and indirectly verify the usability of SWI for the measurement of iron deposition in the cerebral nuclei of PD., (Copyright © 2019. Published by Elsevier Inc.)

Parkinson's disease (PD) is a basal ganglia movement disorder characterized by progressive degeneration of the nigrostriatal dopaminergic system. Immunohistochemical methods have been widely used for characterization of dopaminergic neuronal injury in animal models of PD, including the MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) mouse model. However, conventional immunohistochemical techniques applied to tissue sections have inherent limitations with respect to loss of 3D resolution, yielding insufficient information on the architecture of the dopaminergic system. To provide a more comprehensive and non-biased map of MPTP-induced changes in central dopaminergic pathways, we used iDISCO immunolabeling, light-sheet fluorescence microscopy (LSFM) and deep-learning computational methods for whole-brain three-dimensional visualization and automated quantitation of tyrosine hydroxylase (TH)-positive neurons in the adult mouse brain. Mice terminated 7 days after acute MPTP administration demonstrated widespread alterations in TH expression. Compared to vehicle controls, MPTP-dosed mice showed a significant loss of TH-positive neurons in the substantia nigra pars compacta and ventral tegmental area. Also, MPTP dosing reduced overall TH signal intensity in basal ganglia nuclei, i.e. the substantia nigra, caudate-putamen, globus pallidus and subthalamic nucleus. In contrast, increased TH signal intensity was predominantly observed in limbic regions, including several subdivisions of the amygdala and hypothalamus. In conclusion, mouse whole-brain 3D imaging is ideal for unbiased automated counting and densitometric analysis of TH-positive cells. The LSFM-deep learning pipeline tracked brain-wide changes in catecholaminergic pathways in the MPTP mouse model of PD, and may be applied for preclinical characterization of compounds targeting dopaminergic neurotransmission., Competing Interests: Competing interestsU.R., C.B.G.S., D.D.T., J.L.S., K.F., P.B., H.H.H. and J.H.-S. are employed by Gubra; L.M.J., V.I.J. and L.B.K. are employed by Novo Nordisk; N.V. and J.J. are owners of Gubra., (© 2019. Published by The Company of Biologists Ltd.)

Background: Dopaminergic and serotonergic degenerations alter pharmacological neurotransmission and structural markers in Parkinson's disease (PD). Alteration of diffusion measures in key brain regions depict MPTP/MDMA lesions in the monkey model of PD. Whether dopatherapy impacts such diffusion measures remains an open question., Objectives: The aim of this study was to investigate the consequences of l-DOPA treatment on diffusion alterations, PET imaging and immunohistochemical markers in MPTP/MDMA-intoxicated monkeys., Methods: We acquired PET imaging and measures of mean diffusivity and fractional anisotropy longitudinally and correlated them with behavior and post-mortem fiber quantification., Results: Severity of l-DOPA-induced dyskinesia was correlated to serotonin transporter radioligand binding increases in the ventral striatum and the anterior cingulate cortex and decreases of mean diffusivity in the ventral striatum. After lesion of serotonergic fibers by MDMA and the second l-DOPA period, diffusion measures were no more altered while the serotonergic binding still increased in all regions of interest, despite abolition of dyskinesia. Interestingly, in the anterior cingulate cortex, the SERT radioligand binding was negatively correlated to the number of SERT fibers., Conclusion: These results show that the increase of SERT radioligand binding is not systematically paralleled by an increase of SERT fibers and does not always reflect the presence of LID. More specifically, our study suggest that SERT increase may be underpinned by an increased density of serotonergic fibers after MPTP and the first l-DOPA period, and by an elevation of SERT itself after MDMA and the second l-DOPA period. This highlights that DTI is complementary to PET imaging to decipher pathophysiological mechanisms underlying l-DOPA-induced dyskinesia in a non-human primate model of PD., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Objective: Interpretation of diffusion MRI in the living brain requires validation against gold standard histological measures. We compared diffusion values of the nigrostriatal tract to PET and histological results in non-human primates (NHPs) with varying degrees of unilateral nigrostriatal injury induced by MPTP, a toxin selective for dopaminergic neurons., Methods: Sixteen NHPs had MRI and PET scans of three different presynaptic radioligands and blinded video-based motor ratings before and after unilateral carotid artery infusion of variable doses of MPTP. Diffusion measures of connections between midbrain and striatum were calculated. Then animals were euthanized to quantify striatal dopamine concentration, stereologic measures of striatal tyrosine hydroxylase (TH) immunostained fiber density and unbiased stereologic counts of TH stained nigral cells., Results: Diffusion measures correlated with MPTP dose, nigral TH-positive cell bodies and striatal TH-positive fiber density but did not correlate with in vitro nigrostriatal terminal field measures or in vivo PET measures of striatal uptake of presynaptic markers. Once nigral TH cell count loss exceeded 50% the stereologic terminal field measures reached a near zero floor effect but the diffusion measures continued to correlate with nigral cell counts., Conclusion: Diffusion measures in the nigrostriatal tract correlate with nigral dopamine neurons and striatal fiber density, but have the same relationship to terminal field measures as a previous report of striatal PET measures of presynaptic neurons. These diffusion measures have the potential to act as non-invasive index of the severity of nigrostriatal injury. Diffusion imaging of the nigrostriatal tract could potentially have diagnostic value in humans with Parkinson disease or related disorders., Competing Interests: The authors have declared that no competing interests exist.

Glutamate chemical exchange saturation transfer (GluCEST) MRI was used to measure metabolic changes in mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) by mapping regional cerebral glutamate. The GluCEST contrast following MPTP treatment was correlated with 1 H-MR spectroscopy, motor function, and immunohistochemical measures. The GluCEST contrast was found to be significantly higher in the striatum and motor cortex of mice treated with MPTP than in controls (p < 0.001), which was confirmed by localized 1 H-MR spectroscopy. Elevated striatal GluCEST was positively associated with local astrogliosis measured by immunohistochemistry for glial fibrillary acidic protein. Additionally, a negative correlation was found between motor function, measured by the four-limb grip strength test, and GluCEST of the striatum (R = -0.705, p < 0.001) and the motor cortex (R = -0.617, p < 0.01), suggesting a role of elevated glutamate in the abnormal cerebral motor function regulation. The GluCEST contrast and glial fibrillary acidic protein immunostaining were unaltered in the thalamus indicating glutamate elevation was localized to the striatum and the motor cortex. These findings suggest that in addition to measuring spatial changes in glutamate, GluCEST may serve as an in vivo biomarker of metabolic and functional changes that may be applied to the assessment of a broad range of neuropathologies. Read the Editorial Highlight for this article on page 346., Competing Interests: The authors declare no conflict of interest, (© 2016 International Society for Neurochemistry.)

Manganese-enhanced magnetic resonance imaging (MEMRI) is a widely used technique for detecting neuronal activity in the brain of a living animal. Ceftriaxone (CEF) has been shown to have neuroprotective effects in neurodegenerative diseases. The present study was aimed at clarifying whether, in an 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson's disease (PD) rat model, the known CEF-induced neuronal protection was accompanied by neurogenesis and decreased loss of neuronal activity. After MPTP lesioning (day 0), the rats were treated with CEF (100mg/kg/day, i.p.) or saline for 15 days. They were then injected with MnCl2 (40mg/kg, i.p.) on day 13 and underwent a brain MRI scan on day 14, then the brain was taken for histological evaluation on day 15. The results showed that MPTP lesioning resulted in decreased neuronal activity and density in the nigrostriatal dopaminergic (DAergic) system and the hippocampal CA1, CA3, and dentate gyrus (DG) areas and reduced neurogenesis in the DG, but in hyperactivity in the subthalamic nucleus (STN). These neuronal changes were prevented by CEF treatment. Positive correlations between MEMRI R1 values and neuronal density in the hippocampus were evidenced. Neuronal densities in the hippocampus and SNc were positively correlated. In addition, the R1 value of the STN showed a positive correlation with its neuronal activity but showed a negative correlation with the density of DAergic neurons in the SNc. Therefore, MEMRI R1 value may serve as a good indicator for PD severity and the effect of treatment. To our knowledge, this is the first study showing that CEF prevents loss of neuronal activity and neurogenesis in the brain of PD rats. CEF may therefore have clinical potential in the treatment of PD., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Unlabelled: We recently developed a novel PET probe, 6-(11)C-methyl-m-tyrosine ((11)C-6MemTyr), for quantitative imaging of presynaptic dopamine synthesis in the living brain. In the present study, (11)C-6MemTyr was compared with β-(11)C-l-DOPA and 6-(18)F-fluoro-l-dopa ((18)F-FDOPA) in the brains of normal and Parkinson disease (PD) model monkeys (Macaca fascicularis)., Methods: PD model monkeys were prepared by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration, and (11)C-β-CFT was applied to assess neuronal damage as dopamine transporter (DAT) availability. (11)C-6MemTyr, β-(11)C-l-DOPA, or (18)F-FDOPA was injected with and without carbidopa, a specific inhibitor of peripheral aromatic L-amino acid decarboxylase. In normal and PD monkeys, the dopamine synthesis rates calculated using PET probes were analyzed by the correlation plot with DAT availability in the striatum., Results: In normal monkeys, whole-brain uptake of β-(11)C-l-DOPA and (18)F-FDOPA were significantly increased by carbidopa at the clinical dose of 5 mg/kg by mouth. In contrast, (11)C-6MemTyr was not affected by carbidopa at this dose, and the metabolic constant value of (11)C-6MemTyr in the striatum was significantly higher than those of the other 2 PET probes. Significant reduction of the presynaptic DAT availability in the striatum was detected in MPTP monkeys, and correlation analyses demonstrated that (11)C-6MemTyr could detect dopaminergic damage in the striatum with much more sensitivity than the other PET probes., Conclusion: (11)C-6MemTyr is a potential PET probe for quantitative imaging of presynaptic dopamine activity in the living brain with PET., (© 2016 by the Society of Nuclear Medicine and Molecular Imaging, Inc.)

We demonstrate that activation-induced manganese-enhanced magnetic resonance imaging with quantitative determination of the longitudinal relaxation time (qAIM-MRI) reveals the severity of Parkinson's disease (PD) in mice. We first show that manganese ion-accumulation depends on neuronal activity. A highly active region was then observed by qAIM-MRI in the caudate-putamen in PD-model mice that was significantly correlated to the severity of PD, suggesting its involvement in the expression of PD symptoms.

Background: We have previously defined a parkinsonism-related metabolic brain network in rhesus macaques using a high-resolution research positron emission tomography camera. This brief article reports a descriptive pilot study to assess the reproducibility of network activity and regional glucose metabolism in independent parkinsonian macaques using a clinical positron emission tomography/CT camera., Methods: [(18)F]fluorodeoxyglucose PET scans were acquired longitudinally over 3 months in three drug-naïve parkinsonian and three healthy control cynomolgus macaques. Group difference and test-retest stability in network activity and regional glucose metabolism were evaluated graphically, using all brain images from these macaques., Results: Comparing the parkinsonian macaques with the controls, network activity was elevated and remained stable over 3 months. Normalized glucose metabolism increased in putamen/globus pallidus and sensorimotor regions but decreased in posterior parietal cortices., Conclusions: Parkinsonism-related network activity can be reliably quantified in different macaques with a clinical positron emission tomography/CT scanner and is reproducible over a period typically employed in preclinical intervention studies. This measure can be a useful biomarker of disease process or drug effects in primate models of Parkinson's disease., (© 2015 International Parkinson and Movement Disorder Society.)

The delayed appearance of motor symptoms in PD poses a crucial challenge for early detection of the disease. We measured the binding potential of the selective dopamine active transporter (DAT) radiotracer [(11)C]PE2I in MPTP-treated macaque monkeys, thus establishing a detailed profile of the nigrostriatal DA status following MPTP intoxication and its relation to induced motor and non-motor symptoms. Clinical score and cognitive performance were followed throughout the study. We measured longitudinally in vivo the non-displaceable binding potential to DAT in premotor, motor-recovered (i.e. both non-symptomatic) and symptomatic MPTP-treated monkeys. Results show an unexpected and pronounced dissociation between clinical scores and [(11)C]PE2I-BP(ND) during the premotor phase i.e. DAT binding in the striatum of premotor animals was increased around 20%. Importantly, this broad increase of DAT binding in the caudate, ventral striatum and anterior putamen was accompanied by i) deteriorated cognitive performance, showing a likely causal role of the observed hyperdopaminergic state (Cools, 2011; Cools and D'Esposito, 2011) and ii) an asymmetric decrease of DAT binding at a focal point of the posterior putamen, suggesting that increased DAT is one of the earliest, intrinsic compensatory mechanisms. Following spontaneous recovery from motor deficits, DAT binding was greatly reduced as recently shown in-vivo with other radiotracers (Blesa et al., 2010, 2012). Finally, high clinical scores were correlated to considerably low levels of DAT only after the induction of a stable parkinsonian state. We additionally show that the only striatal region which was significantly correlated to the degree of motor impairments is the ventral striatum. Further research on this period should allow better understanding of DA compensation at premature stages of PD and potentially identify new diagnosis and therapeutic index., (Copyright © 2014. Published by Elsevier Inc.)

The goal of this study was to describe Parkinson׳s disease (PD)-related modulation of functional connectivity (FC) associated with the striatum in the resting state in a nonhuman primate model of early-stage PD. Weekly intravenous injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (0.5 mg/kg body weight) were performed until parkinsonian motor symptoms developed in four macaques. After 13 weeks of MPTP treatment, all monkeys displayed parkinsonian symptoms. During the course of the experiment, each animal underwent four magnetic resonance imaging scans and four positron emission tomography (PET) scans with the vesicular monoamine transporter 2 (VMAT2)-selective ligand 9-[(18)F] fluoropropyl-(+)-dihydrotetrabenazine, performed prior to the beginning of MPTP administration as well as after 4, 9, and 13 MPTP injections. The FC profile of the striatum was evaluated using a seed voxel correlation approach and post hoc region of interest analysis on resting-state functional magnetic resonance imaging data. The PET images were subjected to region of interest analysis to examine brain regional reductions in VMAT2 density in the PD model. Significant reductions in the connectivity pattern of the striatal regions were observed: limbic striatum and left hippocampus; caudate nucleus/associative and brain regions, including the right pre-supplementary motor area and bilateral dorsolateral prefrontal cortex; putamen/associative region and left inferior temporal gyrus or right orbital and medial prefrontal cortex; and putamen/motor and cortical structures, including the right superior temporal gyrus and bilateral postcentral gyrus. Subsequent PET studies showed the progressive loss of striatal VMAT2 in the striatum with the presentation of parkinsonism. Significant differences between the specific uptake ratio reductions in each striatal subdivision were not found. By using a long-term, low-dose MPTP-lesioned nonhuman primate model, this study demonstrated PD-related decreased corticostriatal FC in a resting state; moreover, altered sensorimotor integration was also found in early-stage PD., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Objective: Development of an effective therapy to slow the inexorable progression of Parkinson disease requires a reliable, objective measurement of disease severity. In the present study, we compare presynaptic positron emission tomography (PET) tracer uptake in the substantia nigra (SN) to cell loss and motor impairment in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated nonhuman primates., Methods: Presynaptic PET tracers 6-[(18)F]-fluorodopa (FD), [(11)C]-2β-methoxy-3β-4-fluorophenyltropane (CFT), and [(11)C]-dihydrotetrabenazine (DTBZ) were used to measure specific uptake in the SN and striatum before and after a variable dose of MPTP in nonhuman primates. These in vivo PET-based measures were compared with motor impairment, as well as postmortem tyrosine hydroxylase-positive cell counts and striatal dopamine concentration., Results: We found the specific uptake of both CFT and DTBZ in the SN had a strong, significant correlation with dopaminergic cell counts in the SN (R(2) = 0.77, 0.53, respectively, p < 0.001), but uptake of FD did not. Additionally, both CFT and DTBZ specific uptake in the SN had a linear relationship with motor impairment (rs = -0.77, -0.71, respectively, p < 0.001), but FD uptake did not., Interpretation: Our findings demonstrate that PET-measured binding potentials for CFT and DTBZ for a midbrain volume of interest targeted at the SN provide faithful correlates of nigral neuronal counts across a full range of lesion severity. Because these measures correlate with both nigral cell counts and parkinsonian ratings, we suggest that these SN PET measures are relevant biomarkers of nigrostriatal function., (© 2013 American Neurological Association.)

Objective: Molecular imaging and clinical endpoints are frequently discordant in Parkinson disease clinical trials, raising questions about validity of these imaging measures to reflect disease severity. We compared striatal uptake for 3 positron emission tomography (PET) tracers with in vitro measures of nigral cell counts and striatal dopamine in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys., Methods: Sixteen macaques had magnetic resonance imaging and baseline PETs using 6-[18F]fluorodopa (FD), [11C]dihydrotetrabenazine (DTBZ), and 2beta-[11 C]carbomethoxy-3beta-(4-fluorophenyl)tropane (CFT). MPTP (0-0.31 mg/kg) infused unilaterally via the internal carotid artery produced stable hemiparkinsonism by 3 weeks. After 8 weeks, PETs were repeated and animals were euthanized for striatal dopamine measurements and unbiased counts of tyrosine hydroxylase-stained nigral cells., Results: Striatal uptake for each radiotracer (FD, DTBZ, CFT) correlated with stereologic nigral cell counts only for nigral loss<50% (r2=0.84, r2=0.86, r2=0.87, p<0.001 respectively; n=10). In contrast, striatal uptake correlated with striatal dopamine over the full range of dopamine depletion (r2=0.95, r2=0.94, r2=0.94, p<0.001; n=16). Interestingly, indices of striatal uptake of FD, DTBZ, and CFT correlated strongly with each other (r2=0.98, p<0.001)., Interpretation: Tracer uptake correlated with nigral neurons only when nigral loss was <50%. This along with previous work demonstrating that nigral cell counts correlate strongly with parkinsonism ratings may explain discordant results between neuroimaging and clinical endpoints. Furthermore, strong correlations among striatal uptake for these tracers support lack of differential regulation of decarboxylase activity (FD), vesicular monoamine transporter type 2 (DTBZ), and dopamine transporter (CFT) within 2 months after nigrostriatal injury., (Copyright © 2013 American Neurological Association.)

We modified an objective behavioral test, namely the food reaching test (FRT), for quantitative assessment of motor performance improved by deep brain stimulation (DBS) of the subthalamic nucleus (STN) in the Parkinsonian monkeys. The symptomatic features and their severity in 3 monkeys treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were evaluated with a subjective monkey Parkinson's disease rating scale (PDRS). We then performed STN-DBS with the minimum current intensity that stopped the tremor. The time required for the monkeys to pick up all 5 pieces of potato (FRT time) was measured as a major index to evaluate bradykinesia. The success rate was adopted as another index for assessing overall motor impairments. Although both FRT time and PDRS score were similarly improved by STN-DBS, change of FRT time appeared more sensitive than that of PDRS scores. FRT is an easily trained behavioral test with high objectivity and sensitivity that can be applied for assessing motor performance in MPTP-treated monkeys during experiments in a restrained condition such as functional imaging of the brain., (Copyright © 2012 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.)

Unlabelled: [¹⁸F]AV-133 is a novel PET tracer for targeting the vesicular monoamine transporter 2 (VMAT2). The aim of this study is to characterize and quantify the loss of monoamine neurons with [¹⁸F]AV-133 in the MPTP-lesioned PD mouse model using animal PET imaging and ex vivo quantitative autoradiography (QARG)., Methods: Optimal imaging time window of [¹⁸F]AV-133 was first determined in normal C57BL/6 mice (n = 3) with a 90-min dynamic scan. The reproducibility of [¹⁸F]AV-133 PET imaging was evaluated by performing a test-retest study within 1 week for the normal group (n = 6). For MPTP-lesioned studies, normal, and MPTP-treated [25 mg mg/kg once (Group A) and twice (Group B), respectively, daily for 5 days, i.p., groups of four normal and MPTP-treated] mice were used. PET imaging studies at baseline and at Day 4 post-MPTP injections were performed at the optimal time window after injection of 11.1 MBq [¹⁸F]AV-133. Specific uptake ratio (SUr) of [¹⁸F]AV-133 was calculated by [(target uptake-cerebellar uptake)/cerebellar uptake] with cerebellum as the reference region. Ex vitro QARG and immunohistochemistry (IHC) studies with tyrosine hydroxylase antibody were carried out to confirm the abundance of dopaminergic neurons., Results: The variability between [¹⁸F]AV-133 test-retest striatal SUr was 6.60 ± 3.61% with less than 5% standard deviation between animals (intervariability). The percentages of MPTP lesions were Group A 0.94 ± 0.29, -42.1% and Group B 0.65 ± 0.09, -60.4%. By QARG, specific binding of [¹⁸F]AV-133 was reduced relative to the control groups by 50.6% and 60.7% in striatum and by 30.6% and 46.4% in substantia nigra (Groups A and B, respectively). Relatively small [¹⁸F]AV-133 SUr decline was noted in the serotonin and norepinephrine-enriched regions (7.9% and 9.4% in mid-brain). Results obtained from IHC consistently confirmed the sensitivity and selectivity of dopaminergic neuron loss after MPTP treatment., Conclusions: [¹⁸F]AV-133 PET SUr displayed a high test-retest stability. The SUr significantly declined in the caudate putamen but not in the hypothalamus and midbrain regions after MPTP treatment in the mouse brain. The results obtained for QARG and IHC were consistent and correlated well with the PET imaging studies. On the basis of these concordant results, we find that [¹⁸F]AV-133 should serve as a useful and reliable PET tracer for evaluating nigrostriatal degeneration., (Copyright © 2012 Wiley Periodicals, Inc.)

Apathy, primarily defined as a lack of motivation, commonly occurs in people with Parkinson disease (PD). Although dysfunction of basal ganglia pathways may contribute to apathy, the role of dopamine remains largely unknown. We investigated the role of dopaminergic pathways in the manifestation of apathetic behaviors by measuring the effects of the selective dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on monkeys' willingness to attempt goal directed behaviors, distinct from their ability to perform tasks. Fifteen macaques received variable doses of MPTP, had PET scans with [(11)C]-dihydrotetrabenazine (DTBZ), [(11)C]-2β-3β-4-fluorophenyltropane (CFT), and [(18)F]-fluorodopa (FD) and performed tasks to assess apathetic behaviors and motor impairment. At 8 weeks post-MPTP, primates were euthanized and stereological cell counts and dopamine measurements were done. Apathy scores were compared to motor scores, in vitro and in vivo dopaminergic measures. Apathy scores increased following MPTP and correlated with DTBZ (r(S) = -0.85), CFT (r(S) = -0.87), and FD (r(S) = -0.85) specific uptake in nucleus accumbens (NAcc,) and dopaminergic cell counts in ventral tegmental area (VTA, r(S) = -0.80). Dopaminergic cell loss in VTA provided significant predictive power for apathy scores after controlling for the influence of cell loss in SN. Additionally, forward step-wise regression analyses indicated that neuropathological changes in the VTA-NAcc pathway predict apathetic behavior better than motor impairment or neuropathological changes in the nigrostriatal network. Our findings suggest that dopaminergic dysfunction within the VTA-NAcc pathway plays a role in the manifestation of apathetic behaviors in MPTP-lesioned primates. Similar changes in people with PD may contribute to apathy., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Background: Electroconvulsive therapy (ECT), an effective treatment for depression, also improves motor symptomatology in Parkinson's disease (PD). We have previously demonstrated that ECT stimulates dopamine (DA) function in the striatum of healthy non-human primates, suggesting that DA may contribute to antidepressant effects., Objective: We investigated the potential role of DA mechanisms in the amelioration of PD symptoms following a clinical course of ECT., Methods: We treated non-human primates rendered mildly bilaterally or unilaterally parkinsonian with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), with a course of 6 ECT treatments. Using positron emission tomography, animals were scanned at baseline and at various time points after ECT with tracers of the DA system. Data were analyzed using the Logan reference tissue model and statistics were performed using orthogonal polynomial contrasts., Results: There was no change in binding of the DA transporter tracer in the lesioned striata after ECT as opposed to what we measured in the striatum of healthy animals. Raclopride binding to the D(2/3) receptors was unaffected in all groups. However, there were increases in vesicular monoamine transporter type 2 and D(1) receptor binding in the MPTP-lesioned striata after ECT, returning towards baseline by 6 weeks., Conclusion: We suggest that the effects of ECT in PD may proceed from a mechanism similar to that in healthy animals but with a blunted dopaminergic response, likely due to the significant loss of striatal DA terminals. The safety of ECT, its mild side effects and its stimulatory effects of the DA system may thus make it an attractive adjunct to antiparkinsonian treatment., (Copyright © 2012 S. Karger AG, Basel.)

Degeneration of the dopaminergic nigrostriatal system and of noradrenergic neurons in the locus coeruleus are important pathological features of Parkinson's disease. There is an urgent need to develop therapies that slow down the progression of neurodegeneration in Parkinson's disease. In the present study, we tested whether the highly specific metabotropic glutamate receptor 5 antagonist, 3-[(2-methyl-1,3-thiazol-4-yl) ethynyl] pyridine, reduces dopaminergic and noradrenergic neuronal loss in monkeys rendered parkinsonian by chronic treatment with low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Weekly intramuscular 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine injections (0.2-0.5 mg/kg body weight), in combination with daily administration of 3-[(2-methyl-1,3-thiazol-4-yl) ethynyl] pyridine or vehicle, were performed until the development of parkinsonian motor symptoms in either of the two experimental groups (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/3-[(2-methyl-1,3-thiazol-4-yl) ethynyl] pyridine versus 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/vehicle). After 21 weeks of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment, all 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/vehicle-treated animals displayed parkinsonian symptoms, whereas none of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/3-[(2-methyl-1,3-thiazol-4-yl) ethynyl] pyridine-treated monkeys were significantly affected. These behavioural observations were consistent with in vivo positron emission tomography dopamine transporter imaging data, and with post-mortem stereological counts of midbrain dopaminergic neurons, as well as striatal intensity measurements of dopamine transporter and tyrosine hydroxylase immunoreactivity, which were all significantly higher in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/3-[(2-methyl-1,3-thiazol-4-yl) ethynyl] pyridine-treated animals than in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/vehicle-treated monkeys. The 3-[(2-methyl-1,3-thiazol-4-yl) ethynyl] pyridine treatment also had a significant effect on the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced loss of norepinephrine neurons in the locus coeruleus and adjoining A5 and A7 noradrenaline cell groups. In 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/vehicle-treated animals, almost 40% loss of tyrosine hydroxylase-positive norepinephrine neurons was found in locus coeruleus/A5/A7 noradrenaline cell groups, whereas the extent of neuronal loss was lower than 15% of control values in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/3-[(2-methyl-1,3-thiazol-4-yl) ethynyl] pyridine-treated monkeys. Our data demonstrate that chronic treatment with the metabotropic glutamate receptor 5 antagonist, 3-[(2-methyl-1,3-thiazol-4-yl) ethynyl] pyridine, significantly reduces 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity towards dopaminergic and noradrenergic cell groups in non-human primates. This suggests that the use of metabotropic glutamate receptor 5 antagonists may be a useful strategy to reduce degeneration of catecholaminergic neurons in Parkinson's disease.

The positron emission tomography (PET) tracer 2β-carbomethoxy-3β-(4-chlorophenyl)-8-(2-[18F]-fluoroethyl)-nortropane ((18)F-FECNT) is a highly specific ligand for dopamine transporter (DAT) that yields higher peak striatum-to-cerebellum ratios and offers more favorable kinetics than most (18)F-radiolabeled DAT ligands currently available. The goal of this study is to validate the use of (18)F-FECNT as a PET radiotracer to assess the degree of striatal dopamine terminals denervation and midbrain dopaminergic cell loss in MPTP-treated parkinsonian monkeys. Three rhesus monkeys received weekly injections of MPTP (0.2-0.5 mg/kg) for 21 weeks, which resulted in the progressive development of a moderate level of parkinsonism. We carried out (18)F-FECNT PET at baseline (twice; 10 weeks apart) and at week 21 post-MPTP injections. Postmortem stereological cell counts of dopaminergic neurons in the ventral midbrain, and intensity measurements of DAT and tyrosine hydroxylase (TH) immunoreactivity in the striatum were performed and correlated with striatal and ventral midbrain PET data. Three additional monkeys were used as controls for midbrain dopaminergic cell counts, and striatal DAT or TH immunoreactivity measurements. The correlation and coefficient of variance between (18)F-FECNT test-retest specific uptake ratios were 0.99 (R²) and 2.65%, respectively. The (18)F-FECNT binding potential of the ventral midbrain and striatal regions was tightly correlated with postmortem stereological cell counts of nigral dopaminergic neurons (R²=0.91), and striatal DAT (R²=0.83) or TH (R²=0.88) immunoreactivity intensity measurements. These findings demonstrate that (18)F-FECNT is a highly sensitive PET imaging ligand to quantify both striatal dopamine denervation and midbrain dopaminergic cell loss associated with parkinsonism., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Positron emission tomography (PET) with [(11)C]raclopride has been used to investigate the density (B(max)) and affinity (K(d)) of dopamine D(2) receptors related to several neurological and psychiatric disorders. However, in assessing the B(max) and K(d), multiple PET scans are necessary under variable specific activities of administered [(11)C]raclopride, resulting in a long study period and unexpected physiological variations. In this paper, we have developed a method of multiple-injection graphical analysis (MI-GA) that provides the B(max) and K(d) values from a single PET scan with three sequential injections of [(11)C]raclopride, and we validated the proposed method by performing numerous simulations and PET studies on monkeys. In the simulations, the three-injection protocol was designed according to prior knowledge of the receptor kinetics, and the errors of B(max) and K(d) estimated by MI-GA were analyzed. Simulations showed that our method could support the calculation of B(max) and K(d), despite a slight overestimation compared with the true magnitudes. In monkey studies, we could calculate the B(max) and K(d) of diseased or normal striatum in a 150 mins scan with the three-injection protocol of [(11)C]raclopride. Estimated B(max) and K(d) values of D(2) receptors in normal or partially dopamine-depleted striatum were comparable to the previously reported values.

Background: In Parkinson's disease (PD) there is increasing evidence to suggest motor function changes of the cerebral cortex occur in addition to the pathological changes in the extrapyramidal system., Aims: To explore the functional changes in the frontal and parietal cortex in PD cat model., Settings and Design: Twenty-four healthy male cats were divided into four animal model groups with the injection of 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP), and one control group., Materials and Methods: Cats in both the animal model and control groups were observed for the behavioral changes. They were also examined by 18 F-fluoro-deoxy glucose positron emission tomography/computed tomography ( 18 F-FDG PET/CT). Region of Interest (ROI) was determined by 18 F-FDG intensity and semi-quantitative analysis was employed after detecting the standard absorption value (SUV). Statistical Analysis : Statistical significance was evaluated by ANOVA., Results: Compared to control group, the 18 F-FDG intensity and SUV were found normal on both the sides of frontal and parietal cortex in the PD models on the second day (P > 0.05), and on the fifth day, they were reduced significantly on both the sides of frontal cortex exclusively (P < 0.05). Moreover on the eighth day, the SUV of both frontal cortexes was reduced, while it was increased in both parietal cortex (P < 0.05). Finally on the eleventh day, the SUV remained stable in both the frontal cortex, and was back to normal level in both the parietal cortex., Conclusions: Functional disorders exist in the frontal cortex of PD animals and aggravate with time. Transient functional enhancement in the parietal cortex of PD cats might be a compensation for the dysfunction of frontal cortex.

Background: Involuntary movements, or dyskinesia, represent a debilitating complication of dopamine replacement therapy for Parkinson disease (PD). The transcription factor DeltaFosB accumulates in the denervated striatum and dimerizes primarily with JunD upon repeated L-3,4-dihydroxyphenylalanine (L-DOPA) administration. Previous studies in rodents have shown that striatal DeltaFosB levels accurately predict dyskinesia severity and indicate that this transcription factor may play a causal role in the dyskinesia sensitization process., Methods: We asked whether the correlation previously established in rodents extends to the best nonhuman primate model of PD, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned macaque. We used western blotting and quantitative polymerase chain reaction (PCR) to compare DeltaFosB protein and messenger RNA (mRNA) levels across two subpopulations of macaques with differential dyskinesia severity. Second, we tested the causal implication of DeltaFosB in this primate model. Serotype 2 adeno-associated virus (AAV2) vectors were used to overexpress, within the motor striatum, either DeltaFosB or DeltaJunD, a truncated variant of JunD lacking a transactivation domain and therefore acting as a dominant negative inhibitor of DeltaFosB., Results: A linear relationship was observed between endogenous striatal levels of DeltaFosB and the severity of dyskinesia in Parkinsonian macaques treated with L-DOPA. Viral overexpression of DeltaFosB did not alter dyskinesia severity in animals previously rendered dyskinetic, whereas the overexpression of DeltaJunD dramatically dropped the severity of this side effect of L-DOPA without altering the antiparkinsonian activity of the treatment., Conclusions: These results establish a mechanism of dyskinesia induction and maintenance by L-DOPA and validate a strategy, with strong translational potential, to deprime the L-DOPA-treated brain.

Positron emission tomography (PET) is a useful technique for the consecutive investigation of the relationship between changes in neurotransmission biomarkers and behavioral signs in animal models of Parkinson's disease (PD). In this study, we aimed to investigate the threshold of dopamine (DA) neuron damage for the appearance of tremor by observing the longitudinal changes of pre- and post-synaptic DA biomarkers in awake monkeys using PET with multiple tracers. Three cynomolgus monkeys were treated with MPTP every 3-6 weeks until tremor was observed. Brain uptake of [11C]PE2I, [beta-11C]DOPA, and [11C]raclopride for DA transporter (DAT), DOPA utilization, and DA D2 receptor were measured using PET as a single set in awake condition. Sets of PET scans were repeated in parallel with continuous behavioral estimation. The pre-synaptic biomarkers of DA neuron in the striatum decreased [11C]PE2I binding and [beta-11C]DOPA uptake in an MPTP dose-dependent manner. Tremor was not observed until striatal [11C]PE2I binding was reduced to about 15% of the pretreatment level and [beta-11C]DOPA uptake was reduced to about 34%. DA D2 receptor measured by [11C]raclopride was not significantly changed throughout the experiment. Our results revealed that it is possible to quantitatively define the threshold of the onset of behavioral PD signs by monitoring spontaneous motor activity, and in vivo PET with DAT marker can be a biomarker for early diagnosis at the presymptomatic stage of PD and for high-risk groups., (Copyright (c) 2007 Wiley-Liss, Inc.)

Clinical DA agonist monotherapy trials, which used in vivo imaging of the DA transporter (DAT) to assess the rate of progression of nigrostriatal degeneration, have failed to demonstrate consistent evidence for neuroprotection. The present study aims at reconciling these experimental and clinical data by testing the protective property of the continuously delivered D3/D2/D1 dopamine receptor agonist rotigotine. Using a progressive 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned (MPTP) macaque model that mimics the progression of Parkinson's disease in vivo ([99mTc]-TRODAT-1 single photon emission computed tomography (SPECT)) and ex vivo ([125I]-nortropane DAT labelling) endpoints were evaluated. After 38 days of treatment followed by two weeks of washout, rotigotine-treated animals were significantly less parkinsonian than the vehicle-treated ones. Such behavioural difference is the consequence of a partial protection of the DA terminals as could be confirmed by ex vivo DAT labelling. However, the protection of nerve terminals was not detected using SPECT. The data suggest that rotigotine exerts partial protection but that conventional imaging would not be able to identify such protection.

The present study investigated the motor response and possible changes in binding to D1 and D2 receptors after intra-nigral 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) infusion on rats. The results indicated that MPTP-lesioned rats exhibited a significant reduction in locomotion and rearing frequencies observed in an open field 24 h after surgery. However, at 7 and 14 days after surgery the MPTP-lesioned rats showed a significant increase in locomotion in comparison to the control groups, as well as a decrease in immobility time. In addition, 21 days after surgery the behavioral measurements were unaltered by these procedures. Moreover, latency in initiating movement and catalepsy were unchanged by this neurotoxin on the same days of observation. An autoradiography approach indicated that there was a reduction in [3H]SCH 23390 binding in substantia nigra pars compacta (SNpc), substantia nigra pars reticulata (SNpr) and ventrolateral striatum in MPTP-treated rats 21 days after the surgery. [3H]raclopride binding remained unaltered by the MPTP treatment. These results suggest that compensatory plastic changes occur in D1 dopamine receptors after partial lesion of nigral dopaminergic neurons. These alterations might be related to the occurrence and recovery of motor impairment observed in MPTP-lesioned rats.

A concept in Parkinson's disease postulates that motor cortex may pattern abnormal rhythmic activities in the basal ganglia, underlying the genesis of observed motor symptoms. We conducted a preclinical study of electrical interference in the primary motor cortex using a chronic MPTP primate model in which dopamine depletion was progressive and regularly documented using 18F-DOPA positron tomography. High-frequency motor cortex stimulation significantly reduced akinesia and bradykinesia. This behavioral benefit was associated with an increased metabolic activity in the supplementary motor area as assessed with 18-F-deoxyglucose PET, a normalization of mean firing rate in the internal globus pallidus (GPi) and the subthalamic nucleus (STN), and a reduction of synchronized oscillatory neuronal activities in these two structures. Motor cortex stimulation is a simple and safe procedure to modulate subthalamo-pallido-cortical loop and alleviate parkinsonian symptoms without requiring deep brain stereotactic surgery.

The functional restoration of the dopamine innervation of striatum in MPTP-poisoned Göttingen minipigs was assessed for 6 months following grafting of fetal pig mesencephalic neurons. Pigs were assigned to a normal control group and a MPTP-poisoned group, members of which received no further treatment, or which received bilateral grafts to the striatum of tissue blocks harvested from E28 fetal pig mesencephalon with and without immunosuppressive treatment after grafting, or with additional co-grafting with immortalized rat neural cells transfected to produce GDNF. In the baseline condition, and again at 3 and 6 months postsurgery, all animals were subjected to quantitative [18F]fluorodopa PET scans and testing for motor impairment. At the end of 6 months, tyrosine hydroxylase (TH)-containing neurons were counted in the grafts by stereological methods. The MPTP poisoning persistently reduced the magnitude of k3(D), the relative activity of DOPA decarboxylase in striatum, by 60%. Grafting restored the rate of [18F]fluorodopa decarboxylation to the normal range, and normalized the scores in motor function. The biochemical and functional recovery was associated with survival of approximately 100,000 TH-positive graft neurons in each hemisphere. Immunosuppression did not impart a greater recovery of [18F]fluorodopa uptake, nor were the number of TH-positive graft neurons or the volumes of the grafts increased in the immunosuppressed group. Contrary to expectation, co-grafting of transfected GDNF-expressing HiB5 cells, a rat-derived neural cell line, tended to impair the survival of the grafts with the lowest values for graft volumes, TH-positive cell numbers, behavioral scores, and relative DOPA decarboxylase activity. From the results we conclude that pig ventral mesencephalic allografts can restore functional dopamine innervation in adult MPTP-lesioned minipigs.