Multitracer assessment of dopamine function after transplantation of embryonic stem cell‐derived neural stem cells in a primate model of Parkinson's disease

The ability of primate embryonic stem (ES) cells to differentiate into dopamine (DA)‐synthesizing neurons has raised hopes of creating novel cell therapies for Parkinson's disease (PD). As the primary purpose of cell transplantation in PD is restoration of dopaminergic neurotransmission in the striatum, in vivo assessment of DA function after grafting is necessary to achieve better therapeutic effects. A chronic model of PD was produced in two cynomolgus monkeys (M‐1 and M‐2) by systemic administration of neurotoxin. Neural stem cells (NSCs) derived from cynomolgus ES cells were implanted unilaterally in the putamen. To evaluate DA‐specific functions, we used multiple [¹¹C]‐labeled positron emission tomography (PET) tracers, including [β‐¹¹C]L ‐3,4‐dihydroxyphenylalanine (L ‐[β‐¹¹C]DOPA, DA precursor ligand), [¹¹C]‐2β‐carbomethoxy‐3β‐(4‐fluorophenyl)tropane ([¹¹C]β‐CFT, DA transporter ligand) and [¹¹C]raclopride (D₂ receptor ligand). At 12 weeks after grafting NSCs, PET demonstrated significantly increased uptake of L ‐[β‐¹¹C]DOPA (M‐1:41%, M‐2:61%) and [¹¹C]β‐CFT (M‐1:31%, M‐2:36%) uptake in the grafted putamen. In addition, methamphetamine challenge in M‐2 induced reduced [¹¹C]raclopride binding (16%) in the transplanted putamen, suggesting release of DA. These results show that transplantation of NSCs derived from cynomolgus monkey ES cells can restore DA function in the putamen of a primate model of PD. PET with multitracers is useful for functional studies in developing cell‐based therapies against PD. Synapse 63: 541‐548, 2009. © 2009 Wiley‐Liss, Inc.     

The majority of newly generated cells in the adult mouse substantia nigra express low levels of Doublecortin,but their proliferation is unaffected by 6‐OHDA‐induced nigral lesion or Minocycline‐mediated inhibition of neuroinflammation

Parkinson's disease is characterized by a selective loss of dopaminergic neurons in the substantia nigra (SN). However, whether regenerative endogenous neurogenesis is taking place in the mammalian SN of parkinsonian and non‐parkinsonian brains remains of debate. Here, we tested whether proliferating cells in the SN and their neurogenic potential would be affected by anti‐inflammatory treatment under physiological conditions and in the 6‐hydroxy‐dopamine (6‐OHDA) Parkinson's disease mouse model. We report that the majority of newly generated nigral cells are positive for Doublecortin (Dcx), which is an often used marker for neural progenitor cells. Yet, Dcx expression levels in these cells were much lower than in neural progenitor cells of the subventricular zone and the dentate gyrus neural progenitor cells. Furthermore, these newly generated nigral cells are negative for neuronal lineage markers such as TuJ1 and NeuN. Therefore, their neuronal commitment is questionable. Instead, we found evidence for oligodendrogenesis and astrogliosis in the SN. Finally, neither short‐term nor long‐term inhibition of neuroinflammation by Minocycline‐ or 6‐OHDA‐induced lesion affected the numbers of newly generated cells in our disease paradigm. Our findings of adult generated Dcx⁺ cells in the SN add important data for understanding the cellular composition and consequently the regenerative capacity of the SN.     

Functional brain imaging in pure akinesia with gait freezing: [18F] FDG PET and [18F] FP‐CIT PET analyses

Pure akinesia with gait freezing (PAGF) has characteristic features, including freezing of gait and prominent speech disturbance without rigidity or tremor. The purpose of this study was to investigate changes in brain glucose metabolism and presynaptic dopaminergic function in PAGF. By using [¹⁸F] fluorodeoxyglucose (FDG) PET, 11 patients with PAGF were compared with 14 patients with probable progressive supranuclear palsy (PSP), 13 patients with Parkinson's disease (PD), and 11 normal controls. [¹⁸F] N‐(3‐fluoropropyl)‐2β‐carbon ethoxy‐3β‐(4‐iodophenyl) nortropane (FP‐CIT) PET was performed in 11 patients with PAGF and with 10 normal controls. The PAGF patients showed decreased glucose metabolism in the midbrain when compared with normal controls. PSP patients showed a similar topographic distribution of glucose hypometabolism with additional areas, including the frontal cortex, when compared with normal controls. The FP‐CIT PET findings in patients with PAGF revealed severely decreased uptake bilaterally in the basal ganglia. These findings suggest that both PAGF and PSP may be part of the same pathophysiologic spectrum of disease. However, the reason why PAGF manifests clinically in a different manner needs to be further elucidated. © 2008 Movement Disorder Society     

GDNF Contributes to Oestrogen‐Mediated Protection of Midbrain Dopaminergic Neurones

Parkinson’s disease (PD) is characterised by the preferential loss of dopaminergic neurones from the substantia nigra (SN) that leads to the hallmark motor disturbances. Animal and human studies suggest a beneficial effect of oestrogen to the nigrostriatal system, and the regulation of neurotrophic factor expression by oestrogens has been suggested as a possible mechanism contributing to that neuroprotective effect. The present study was designed to investigate whether the neuroprotection exerted by 17β‐oestradiol on nigrostriatal dopaminergic neurones is mediated through the regulation of glial cell line‐derived neurotrophic factor (GDNF) expression. Using an in vivo rat model of PD, we were able to confirm the relevance of 17β‐oestradiol in defending dopaminergic neurones against 6‐hydroxydopamine (6‐OHDA) toxicity. 17β‐oestradiol, released by micro‐osmotic pumps, implanted 10 days before intrastriatal 6‐OHDA injection, prevented the loss of dopaminergic neurones induced by 6‐OHDA. 17β‐oestradiol treatment also promoted an increase in GDNF protein levels both in the SN and striatum. To explore the relevance of GDNF increases to 17β‐oestradiol neuroprotection, we analysed, in SN neurone‐glia cultures, the effect of GDNF antibody neutralisation and RNA interference‐mediated GDNF knockdown. The results showed that both GDNF neutralisation and GDNF silencing abolished the dopaminergic protection provided by 17β‐oestradiol against 6‐OHDA toxicity. Taken together, these results strongly identify GDNF as an important player in 17β‐oestradiol‐mediated dopaminergic neuroprotection.     

Correlation of striatal dopamine transporter imaging with post mortem substantia nigra cell counts

Dopamine transporter imaging is widely used for the differential diagnosis of parkinsonism. Only limited data are available on the relationship between striatal dopamine transporter binding and dopaminergic cell loss in the substantia nigra (SN). We analyzed postmortem SN cell counts in patients who had previously undergone dopamine transporter single‐photon emission computed tomography (SPECT). Pathological diagnoses included Parkinson's disease (n = 1), dementia with Lewy bodies (n = 2), multiple system atrophy (n = 1), corticobasal degeneration (n = 2), atypical parkinsonism with multiple pathological conditions (n = 1), Alzheimer's disease (n = 1), and Creutzfeldt‐Jakob disease (n = 1). [¹²³I]β‐CIT SPECT had been performed in all subjects using a standardized protocol on the same triple‐head gamma camera. The density of neuromelanin‐containing and tyrosine hydroxylase–positive substantia nigra neurons/mm² was evaluated in paraffin‐embedded tissue sections by morphometric methods. Mean disease duration at the time of dopamine transporter imaging was 2.3 years, and the mean interval from imaging to death was 29.3 months (range, 4‐68 months). Visual analysis of dopamine transporter images showed reduced striatal uptake in all seven patients with neurodegenerative parkinsonism, but not in Alzheimer's and Creutzfeldt‐Jakob disease cases. Averaged [(right+left)/2] striatal uptake was highly correlated with averaged SN cell counts (r_s = 0.98, P < 0.0005 for neuromelanin‐ and r_s = 0.96, P < 0.0005 for tyrosine hydroxylase–positive cells). Similar strong correlations were found in separate analyses for the right and left sides. Striatal dopamine transporter binding highly correlated with postmortem SN cell counts, confirming the validity of dopamine transporter imaging as an excellent in vivo marker of nigrostriatal dopaminergic degeneration. © 2014 International Parkinson and Movement Disorder Society     

Alterations in 5‐HT2A receptor binding in various brain regions among 6‐hydroxydopamine‐induced Parkinsonian rats

The serotonergic system has close interactions with the dopaminergic system and is strongly implicated in the pathophysiological mechanisms and therapeutic paradigms of Parkinson's disease (PD). This study aims to investigate regional changes in 5‐hydroxytryptamine (5‐HT) 2A receptors in the rat brain 3 weeks after unilateral medial forebrain bundle lesion by 6‐hydroxydopamine (6‐OHDA). 5‐HT 2A receptor distributions and alterations in the postmortem rat brain were detected by [³H]ketanserin‐binding autoradiography. In the 6‐OHDA‐induced Parkinson's rat model, nigrostriatal dopaminergic neuron loss significantly mediated the decreased [³H]ketanserin binding, predominantly in the agranular insular cortex (17.3%, P = 0.03), cingulate cortex (18.2%, P < 0.001), prefrontal cortex (8%, P = 0.043), primary somatosensory cortex (17.7%, P = 0.002), and caudate putamen (14.5%, P = 0.02) compared to controls while a profound reduction of tyrosine hydroxylase (TH) immunostaining in the striatum was also observed. Alterations in [³H]ketanserin binding in the examined brain areas may represent the specific regions that mediate cognitive dysfunctions via the serotonin system. The downregulation of 5‐HT_2A receptor binding in this study also provides indirect evidence for plasticity in the serotonergic system in the rat brains. This study contributes to a better understanding of the critical roles of 5‐HT_2A receptors in treating neurodegenerative disorders and implicates 5‐HT_2A receptors as a novel therapeutic target in the treatment of PD. Synapse 64:224–230, 2010. © 2009 Wiley‐Liss, Inc.     

A follow‐up study on 6‐[18F]fluoro‐L‐dopa uptake in early Parkinson's disease shows nonlinear progression in the putamen

Sixteen subjects with de novo Parkinson's disease (PD) underwent three 6‐[18F]fluoro‐L‐dopa (Fdopa) positron emission tomography (PET) scans during a follow‐up time of 5 years (mean ± SD 5.5 ± 0.4 years) to study the progression of striatal dopaminergic hypofunction. Throughout the study, the smallest Fdopa uptake values were found in the dorso‐caudal part of the putamen contralateral to the side with dominant motor symptoms. The rate of decline in Fdopa uptake in the contralateral putamen was faster in the beginning of the disease and slowed down as the disease progressed. The annual decline in Fdopa influx constant (Ki, unit × 10^?3 min^?1) was on average 0.5 during the first 2 years and 0.2 during the subsequent 3 years (P = 0.002) in the contralateral putamen. In caudate, the rate of decline in Fdopa values was slower than in the putamen and did not change significantly during the follow‐up time, annual decline in the contralateral caudate being 0.1 between baseline and 2 years and 0.3 between 2 and 5 years (P = 0.4). These results suggest that progression of putaminal dopaminergic hypofuncion in PD follows a nonlinear pattern at least in the contralateral side being faster in the beginning of the disease. © 2009 Movement Disorder Society     

Application of feedback‐controlled bolus plus infusion (FC‐B/I) method for quantitative PET imaging of dopamine transporters with [18F]β‐CFT‐FE in conscious monkey brain

The competitive inhibition of dopamine transporters (DAT) with cocaine, a specific DAT inhibitor, was evaluated with a feedback‐controlled bolus plus infusion (FC‐B/I) method using animal positron emission tomography (PET) in the living brain of conscious monkey. 2β‐Carbomethoxy‐3β‐(4‐fluorophenyl)‐8‐(2‐[¹⁸F]fluoroethyl) nortropane ([¹⁸F]β‐CFT‐FE; Harada et al. [2004] Synapse 54:37–45) was used for this study because it provided specific, fast, and reversible kinetic properties to DAT in the striatum. In FC‐B/I method, the real‐time image reconstruction was started just after intravenous bolus injection of [¹⁸F]β‐CFT‐FE to generate a time‐activity curve in the striatum, and the infusion rate was adjusted to achieve an equilibrium state of the striatal radioactivity concentrations by means of a feedback‐control algorithm. The first equilibrium state in the brain was reached within 20 min after the infusion start. Intravenous administration of cocaine at the doses of 0.02, 0.1, and 0.5 mg/kg shifted the equilibrium radioactivity level to the second equilibrium state in a dose‐dependent manner, while no significant alterations was observed in the cerebellum. The present results demonstrated that the combined use of FC‐B/I method and PET probe with fast kinetics like [¹⁸F]β‐CFT‐FE could be useful to assess the occupancy of drugs in the living brain with PET. Synapse, 2013. © 2012 Wiley Periodicals, Inc.     

Evaluation of N‐benzyl‐N‐[11C]methyl‐2‐ (7‐methyl‐8‐oxo‐2‐phenyl‐7,8‐dihydro‐9H‐purin‐9‐yl)acetamide ([11C]DAC) as a novel translocator protein (18 kDa) radioligand in kainic acid‐lesioned rat

The aim of this study was to evaluate N‐benzyl‐N‐[¹¹C]methyl‐2‐(7‐methyl‐8‐oxo‐2‐phenyl‐7,8‐dihydro‐9H‐purin‐9‐yl)acetamide ([¹¹C]DAC) as a new translocator protein (18 kDa) [TSPO, formerly known as the peripheral‐type benzodiazepine receptor (PBR)] positron emission tomography (PET) ligand in normal mice and unilateral kainic acid (KA)‐lesioned rats. DAC is a derivative of AC‐5216, which is a potent and selective PET ligand for the clinical investigation of TSPO. The binding affinity and selectivity of DAC for TSPO were similar to those of AC‐5216, and DAC was less lipophilic than AC‐5216. The distribution pattern of [¹¹C]DAC was in agreement with TSPO distribution in rodents. No radioactive metabolite of [¹¹C]DAC was found in the mouse brain, although it was metabolized rapidly in mouse plasma. Using small‐animal PET, we examined the in vivo binding of [¹¹C]DAC for TSPO in KA‐lesioned rats. [¹¹C]DAC and [¹¹C]AC‐5216 exhibited similar brain uptake in the lesioned and nonlesioned striatum, respectively. The binding of [¹¹C]DAC to TSPO was increased significantly in the lesioned striatum, and [¹¹C]DAC showed good contrast between the lesioned and nonlesioned striatum (the maximum ratio was about threefold). In displacement experiments, the uptake of [¹¹C]DAC in the lesioned striatum was eventually blocked using an excess of either unlabeled DAC or PK11195 injected. [¹¹C]DAC had high in vivo specific binding to TSPO in the injured rat brain. Therefore, [¹¹C]DAC is a useful PET ligand for TSPO imaging, and its specific binding to TSPO is suitable as a new biomarker for brain injury. Synapse 63:961–971, 2009. © 2009 Wiley‐Liss, Inc.     

Serotonergic markers in Parkinson's disease and levodopa‐induced dyskinesias

Preclinical animal models implicate serotonin neurons in the pathophysiology of levodopa (l ‐dopa)–induced dyskinesias in Parkinson's disease (PD), but effective treatment remains elusive. We examined the relationship between serotonin and l ‐dopa–induced dyskinesias in a pathologically confirmed cohort of PD patients. We obtained brain tissue from 44 PD cases and 17 age‐matched controls and assessed monoamine levels and the serotonin and dopamine transporters in the striatum, and the extent of dopaminergic and serotonergic cell preservation in the substantia nigra (SN) and the dorsal raphe nuclei (DRN), respectively. As expected, PD patients demonstrated a severe loss of all dopaminergic markers, including dopamine (P < 0.0001) and the dopamine transporter (P < 0.0001) in the striatum, and dopaminergic neurons (P < 0.001) in the SN, compared with controls. Marked serotonin loss was observed in the caudate (but not putamen) in PD patients compared with controls (P < 0.001), but no difference was found in the levels of the serotonin transporter in the striatum or density of serotonergic neurons in the DRN between these groups, suggesting a functional but not structural change in the serotonergic system in PD. No difference was seen in levels of serotonergic and dopaminergic markers in the striatum between PD patients with and without dyskinesias, or between cases separated according to the clinical severity of their dyskinesias. The absence of a correlation between striatal serotonin markers and the incidence and severity of l ‐dopa–induced dyskinesias suggests that an intact and functioning serotonergic system is not a risk factor for developing dyskinesias in PD. © 2015 International Parkinson and Movement Disorder Society     

Doxycycline restrains glia and confers neuroprotection in a 6‐OHDA Parkinson model

Neuron–glia interactions play a key role in maintaining and regulating the central nervous system. Glial cells are implicated in the function of dopamine neurons and regulate their survival and resistance to injury. Parkinson's disease is characterized by the loss of dopamine neurons in the substantia nigra pars compacta, decreased striatal dopamine levels and consequent onset of extrapyramidal motor dysfunction. Parkinson's disease is a common chronic, neurodegenerative disorder with no effective protective treatment. In the 6‐OHDA mouse model of Parkinson's disease, doxycycline administered at a dose that both induces/represses conditional transgene expression in the tetracycline system, mitigates the loss of dopaminergic neurons in the substantia nigra compacta and nerve terminals in the striatum. This protective effect was associated with: (1) a reduction of microglia in normal mice as a result of doxycycline administration per se; (2) a decrease in the astrocyte and microglia response to the neurotoxin 6‐OHDA in the globus pallidus and substantia nigra compacta, and (3) the astrocyte reaction in the striatum. Our results suggest that doxycycline blocks 6‐OHDA neurotoxicity in vivo by inhibiting microglial and astrocyte expression. This action of doxycycline in nigrostriatal dopaminergic neuron protection is consistent with a role of glial cells in Parkinson's disease neurodegeneration. The neuroprotective effect of doxycycline may be useful in preventing or slowing the progression of Parkinson's disease and other neurodegenerative diseases linked to glia function.     

A within‐subject comparison of 6‐[18F]fluoro‐m‐tyrosine and 6‐[18F]fluoro‐L‐dopa in Parkinson's disease

Progression of Parkinson's disease symptoms is imperfectly correlated with positron emission tomography biomarkers for dopamine biosynthetic pathways. The radiopharmaceutical 6‐[¹⁸F]fluoro‐m‐tyrosine is not a substrate for catechol‐O‐methyltransferase and therefore has a more favorable uptake‐to‐background ratio than 6‐[¹⁸F]fluoro‐L ‐dopa. The objective of this study was to evaluate 6‐[¹⁸F]fluoro‐m‐tyrosine relative to 6‐[¹⁸F]fluoro‐L ‐dopa with partial catechol‐O‐methyltransferase inhibition as a biomarker for clinical status in Parkinson's disease. Twelve patients with early‐stage Parkinson's disease, off medication, underwent Unified Parkinson Disease Rating Scale scoring, brain magnetic resonance imaging, and 3‐dimensional dynamic positron emission tomography using equivalent doses of 6‐[¹⁸F]fluoro‐m‐tyrosine and 6‐[¹⁸F]fluoro‐L ‐dopa with tolcapone, a catechol‐O‐methyltransferase inhibitor. Images were realigned within subject, after which the tissue‐derived uptake rate constant was generated for volumes of interest encompassing the caudate nucleus, putamen, and subregions of the putamen. We computed both bivariate (Pearson) and partial (covariate of age) correlations between clinical subscores and tissue‐derived uptake rate constant. Tissue‐derived uptake rate constant values were correlated between the radiopharmaceuticals (r = 0.8). Motor subscores were inversely correlated with the contralateral putamen 6‐[¹⁸F]fluoro‐m‐tyrosine tissue‐derived uptake rate constant (|r| > 0.72, P < .005) but not significantly with the 6‐[¹⁸F]fluoro‐L ‐dopa tissue‐derived uptake rate constant. The uptake rate constants for both radiopharmaceuticals were also inversely correlated with activities of daily living subscores, but the magnitude of correlation coefficients was greater for 6‐[¹⁸F]fluoro‐m‐tyrosine. In this design, 6‐[¹⁸F]fluoro‐m‐tyrosine uptake better reflected clinical status than did 6‐[¹⁸F]fluoro‐L ‐dopa uptake. We attribute this finding to 6‐[¹⁸F]fluoro‐m‐tyrosine's higher affinity for the target, L ‐aromatic amino acid decarboxylase, and the absence of other major determinants of the uptake rate constant. These results also imply that L ‐aromatic amino acid decarboxylase activity is a major determinant of clinical status. © 2011 Movement Disorder Society     

Effect of Oestrogen Receptors on Brain NMDA Receptors of 1‐Methyl‐4‐Phenyl‐1,2,3,6‐Tetrahydropyridine Mice

Parkinson’s disease (PD) is characterised by the loss of nigrostriatal dopamine (DA) neurones and glutamate overactivity. There is substantial evidence to suggest that oestrogens prevent or delay the disease. 17β‐oestradiol has neuroprotective effects in the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) mouse model of PD and modulates brain NMDA receptors. In MPTP‐lesioned mice, oestrogen receptor (ER)α and ERβ are important in 17β‐oestradiol‐induced neuroprotection. To evaluate the role of ERs in the response of NMDA receptors to lesion, we compared wild‐type (WT) with ER knockout (KO) C57Bl/6 male mice that received 7, 9 or 11 mg/kg of MPTP. These mice were also treated with MPTP (9 mg/kg) and 17β‐oestradiol. [³H]Ro 25‐6981 specific binding autoradiography was used to label NMDA receptors containing NR2B subunits. In the frontal and cingulate cortex and striatum, vehicle‐treated WT mice had higher [³H]Ro 25‐6981 specific binding compared to ERKO mice. Cortical [³H]Ro 25‐6981 specific binding decreased with increasing doses of MPTP in WT and ERKOα but not ERKOβ mice, whereas a dose‐related decrease was only observed in the striatum of WT mice remaining low in ERKOα and ERKOβ mice. No effect of 17β‐oestradiol treatment in intact or MPTP‐lesioned mice of all three genotypes was observed in the cortex, whereas it increased striatal specific binding of intact ERKOβ and MPTP‐lesioned WT mice. Striatal [³H]Ro 25‐6981 specific binding positively correlated with striatal DA concentrations only in WT mice. MPTP and 17β‐oestradiol treatments had more limited effects in the hippocampus. Only in the CA3 and dentate gyrus did vehicle and 17β‐oestradiol‐treated ERKOα mice have higher [³H]Ro 25‐6981 specific binding than WT and ERKOβ mice, whereas MPTP decreased this specific binding only in the CA1, CA2 and CA3 of ERKOα mice. Hence, brain NMDA receptors were affected by the deletion of ERs, which affect the response to MPTP and 17β‐oestradiol treatments with brain region specificity.     

Gray matter correlates of dopaminergic degeneration in Parkinson's disease: A hybrid PET/MR study using 18F‐FP‐CIT

Dopaminergic degeneration is a hallmark of Parkinson's disease (PD), which causes various symptoms affected by corticostriatal circuits. So far, the relationship between cortical changes and dopamine loss in the striatum is unclear. Here, we evaluate the gray matter (GM) changes in accordance with striatal dopaminergic degeneration in PD using hybrid PET/MR. Sixteen patients with idiopathic PD underwent ¹⁸F‐FP‐CIT PET/MR. To measure dopaminergic degeneration in PD, binding ratio (BR) of dopamine transporter in striatum was evaluated by ¹⁸F‐FP‐CIT. Voxel‐based morphometry (VBM) was used to evaluate GM density. We obtained voxelwise correlation maps of GM density according to the striatal BR. Voxel‐by‐voxel correlation between BR maps and GM density maps was done to evaluate region‐specific correlation of striatal dopaminergic degeneration. There was a trend of positive correlation between striatal BR and GM density in the cerebellum, parahippocampal gyri, and frontal cortex. A trend of negative correlation between striatal BR and GM density in the medial occipital cortex was found. Voxel‐by‐voxel correlation revealed that the positive correlation was mainly dependent on anterior striatal BR, while posterior striatal BR mostly showed negative correlation with GM density in occipital and temporal cortices. Decreased GM density related to anterior striatal dopaminergic degeneration might demonstrate degeneration of dopaminergic nonmotor circuits. Furthermore, the negative correlation could be related to the motor circuits of posterior striatum. Our integrated PET/MR study suggests that the widespread structural progressive changes in PD could denote the cortical functional correlates of the degeneration of striatal dopaminergic circuits. Hum Brain Mapp 37:1710–1721, 2016. © 2016 Wiley Periodicals, Inc .     

Induction of GAP‐43 modulates neuroplasticity in PBSC (CD34+) implanted‐Parkinson's model

As a result of the progressive decrease in efficacy of drugs used to treat Parkinson's disease (PD) and the rapid development of motor complications, effective alternative treatments for PD are required. In a 6‐hydroxydopamine (6‐OHDA)‐induced Parkinson's rat model, intracerebral peripheral blood stem cell (CD34⁺) (PBSC) transplantation significantly protected dopaminergic neurons from 6‐OHDA‐induced neurotoxicity, enhanced neural repair of tyrosine hydroxylase neurons through up‐regulation of Bcl‐2, facilitated stem cell plasticity, and attenuated activation of microglia, in comparison with vehicle‐control rats. The 6‐OHDA‐lesioned hemi‐Parkinsonian rats receiving intrastriatal transplantation of PBSCs also showed: 1) enhanced glucose metabolism in the lesioned striatum and thalamus, demonstrated by [¹⁸F]fluoro‐2‐deoxyglucose positron emission tomography (FDG‐PET), 2) improved neurochemical activity as shown by proton magnetic resonance spectroscopy (¹H‐MRS), and 3) significantly reduced rotational behavior in comparison with control lesioned rats. These observations might be explained by an up‐regulation of growth‐associated protein 43 (GAP‐43) expression because improvements in neurological dysfunction were blocked by injection of MK‐801 in the PBSC‐treated group. In addition, a significant increase in neurotrophic factor expression was found in the ipsilateral hemisphere of the PBSC‐treated group. In summary, this protocol may be a useful strategy for the treatment of clinical PD. © 2009 Wiley‐Liss, Inc.     

β‐amyloid and postural instability and gait difficulty in Parkinson's disease at risk for dementia

Although motor impairments in Parkinson's disease (PD) are attributed to nigrostriatal dopaminergic denervation, postural instability and gait difficulty (PIGD) features are less responsive to dopaminergic medications. PIGD features are a risk factor also for the development of dementia in PD (PDD). These observations suggest that nondopaminergic mechanisms may contribute to axial motor impairments. The aim was to perform a correlative PET study to examine the relationship between neocortical β‐amyloid deposition ([¹¹C]‐Pittsburgh Compound B), nigrostriatal dopaminergic denervation ([¹¹C]‐dihydrotetrabenazine), and PIGD feature severity in PD patients at risk for dementia. This was a cross‐sectional study of 44 PD patients (11 female and 33 male; 69.5 ± 6.6 years of age; 7.0 ± 4.8 years motor disease duration; mean H & Y stage: 2.7 ± 0.5) who underwent PET, motor feature severity assessment using the Movement Disorder Society revised UPDRS, and the Dementia Rating Scale (DRS). Linear regression (R²_adj = 0.147; F_4,39 = 2.85; P = 0.036) showed that increased PIGD feature severity was associated with increased neocortical [¹¹C]‐Pittsburgh Compound B binding (β = 0.346; t₃₉ = 2.13; P = 0.039) while controlling for striatal [¹¹C]‐dihydrotetrabenazine binding, age, and DRS total score. Increased neocortical β‐amyloid deposition, even at low‐range levels, is associated with higher PIGD feature severity in PD patients at risk for dementia. This finding may explain why the PIGD motor phenotype is a risk factor for the development of PDD. © 2012 Movement Disorder Society     

Anti‐inflammatory effects of pioglitazone on iron‐induced oxidative injury in the nigrostriatal dopaminergic system

H. C. Yu, S. F. Feng, P. L. Chao and A. M. Y. Lin (2010) Neuropathology and Applied Neurobiology 36, 612–622
Anti‐inflammatory effects of pioglitazone on iron‐induced oxidative injury in the nigrostriatal dopaminergic system Aims: Transition metals, oxidative stress and neuroinflammation have been proposed as part of a vicious cycle in central nervous system neurodegeneration. Our aim was to study the anti‐inflammatory effect of pioglitazone, a peroxisome proliferative activated receptor‐γ agonist, on iron‐induced oxidative injury in rat brain. Methods: Intranigral infusion of ferrous citrate (iron) was performed on anaesthetized rats. Pioglitazone (20 mg/kg) was orally administered. Oxidative injury was investigated by measuring lipid peroxidation in the substantia nigra (SN) and dopamine content in the striatum. Western blot assay and DNA fragmentation were employed to study the involvement of α‐synuclein aggregation, neuroinflammation as well as activation of endoplasmic reticulum (ER) and mitochondrial pathways in iron‐induced apoptosis. Results: Intranigral infusion of iron time‐dependently increased α‐synuclein aggregation and haem oxygenase‐1 levels. Furthermore, apoptosis was demonstrated by TUNEL‐positive cells and DNA fragmentation in the iron‐infused SN. Systemic pioglitazone was found to potentiate iron‐induced elevation in nuclear peroxisome proliferative activated receptor‐γ levels. However, pioglitazone inhibited iron‐induced α‐synuclein aggregation, elevations in interleukin‐1β and interleukin‐6 mRNA levels as well as increases in oxygenase‐1, cyclo‐oxygenase II, nitric oxide synthase and ED‐1 protein levels, an indicator of activated microglia. Moreover, iron‐induced DNA laddering as well as activation of ER and mitochondrial pathways were attenuated by pioglitazone. In addition, pioglitazone decreased iron‐induced elevation in lipid peroxidation in the infused SN and depletion in striatal dopamine level. Conclusions: Our results suggest that pioglitazone prevents iron‐induced apoptosis via both ER and mitochondrial pathways. Furthermore, inhibition of α‐synuclein aggregation and neuroinflammation may contribute to the pioglitazone‐induced neuroprotection in central nervous system.     

Fluorodopa is a Promising Fluorine‐19 MRI Probe for Evaluating Striatal Dopaminergic Function in a Rat Model of Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra projecting to the striatum. It has been estimated that approximately 80% of the striatal dopamine and 50% of nigral dopaminergic neurons are lost before the onset of typical motor symptoms, indicating that early diagnosis of PD using noninvasive imaging is feasible. Fluorine‐19 (¹⁹F) magnetic resonance imaging (MRI) represents a highly sensitive, easily available, low‐background, and cost‐effective approach to evaluate dopaminergic function using non‐radioactive fluorine‐containing dopaminergic agents. The aim of this study was to find a potent ¹⁹F MRI probe to evaluate dopaminergic presynaptic function in the striatum. To select candidates for ¹⁹F MRI probes, we investigated the following eight non‐radioactive fluorine‐containing dopaminergic agents: fluorodopa (F‐DOPA), F‐tyrosine, haloperidol, GBR13069 duhydrochloride, GBR12909 duhydrochloride, 3‐bis‐(4‐fluorophenyl) methoxytropane hydrochloride, flupenthixol, and fenfluramine. In ¹⁹F nuclear magnetic resonance measurements, F‐tyrosine and F‐DOPA displayed a relatively higher signal‐to‐noise ratio value in brain homogenates than in others. F‐DOPA, but not F‐tyrosine, induced the rotational behavior in a 6‐hydroxydopamine (6‐OHDA)‐induced hemiparkinsonian rat model. In addition, a significantly high amount of F‐DOPA accumulated in the ipsilateral striatum of hemiparkinsonian rats after the injection. We performed ¹⁹F MRI in PC12 cells and isolated rat brain using a 7T MR scanner. Our findings suggest that F‐DOPA is a promising ¹⁹F MRI probe for evaluating dopaminergic presynaptic function in the striatum of hemiparkinsonian rats. © 2016 Wiley Periodicals, Inc.     

Evidence of oligodendrogliosis in 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐induced Parkinsonism

V. Annese, C. Barcia, F. Ros‐Bernal, A. Gómez, C. M. Ros, V. De Pablos, E. Fernández‐Villalba, M.‐E. De Stefano and M. T. Herrero (2013) Neuropathology and Applied Neurobiology 39, 132–143 Evidence of oligodendrogliosis in 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐induced Parkinsonism Aims: Mice and nonhuman primates administered with 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) represent elective experimental models of Parkinsonism, in which degeneration of the nigrostriatal dopaminergic pathway is associated with prominent neuroinflammation, characterized by activated microglia and astrocytes in both substantia nigra (SN) and striatum. To date, it is unknown whether oligodendrocytes play a role in these events. Methods: We performed a detailed qualitative and quantitative analysis of oligodendrocyte‐associated changes induced by acute and chronic MPTP treatment, in the SN and striatum of mice and macaques respectively. Oligodendrocytes were immunolabelled by cell‐specific markers and analysed by confocal microscopy. Results: In both experimental models, MPTP treatment induces an increase in oligodendrocyte cell number and average size, as well as in the total area occupied by this cell type per tissue section, accompanied by evident morphological changes. This multifaceted array of changes, herein referred to as oligodendrogliosis, significantly correlates with the reduction in the level of dopaminergic innervation to the striatum. Conclusions: This event, associated with early damage of the dopaminergic neurone axons and of the complex striatal circuits of which they are part, may result in an important, although neglected, aspect in the onset and progression of Parkinsonism.     

Residual striatal dopaminergic nerve terminals in very long‐standing Parkinson's disease: A single photon emission computed tomography imaging study

Molecular imaging studies of Parkinson's disease (PD) progression mostly focus on the first 5 years after disease onset, demonstrating rapid initial nigrostriatal neuronal loss. The fate of residual functional dopaminergic nerve terminals in patients with long‐standing PD has not yet been specifically explored. Therefore, we performed [¹²³I]‐FP‐CIT single photon emission computed tomography (SPECT) in 15 patients with very long‐standing PD (mean disease duration 20.6 ± 6.3 years). Measurable uptake of [¹²³I]‐FP‐CIT was still detected in the striata of all patients. As seen in early stages, reduction of tracer uptake in the putamen was more prominent than in the caudate nucleus. Asymmetry in tracer uptake between the two putamen and caudate nuclei was preserved. These findings indicate that degeneration of dopaminergic neurons in PD is not total even after many years of illness. Data should be considered in exploring underlying causes of progressive loss of nigrostriatal dopaminergic neurons and development of future novel dopaminergic therapeutic strategies in PD. © 2010 Movement Disorder Society