MPTP-lesioned Animals Research Articles

Spatial lipidomics reveals brain region-specific changes of sulfatides in an experimental MPTP Parkinson’s disease primate model

Metabolism of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) to the neurotoxin MPP+ in the brain causes permanent Parkinson’s disease-like symptoms by destroying dopaminergic neurons in the pars compacta of the substantia nigra in humans and non-human primates. However, the complete molecular pathology underlying MPTP-induced parkinsonism remains poorly understood. We used dual polarity matrix-assisted laser desorption/ionization mass spectrometry imaging to thoroughly image numerous glycerophospholipids and sphingolipids in coronal brain tissue sections of MPTP-lesioned and control non-human primate brains (Macaca mulatta). The results revealed specific distributions of several sulfatide lipid molecules based on chain-length, number of double bonds, and importantly, hydroxylation stage. More specifically, certain long-chain hydroxylated sulfatides with polyunsaturated chains in the molecular structure were depleted within motor-related brain regions in the MPTP-lesioned animals, e.g., external and internal segments of globus pallidus and substantia nigra pars reticulata. In contrast, certain long-chain non-hydroxylated sulfatides were found to be elevated within the same brain regions. These findings demonstrate region-specific dysregulation of sulfatide metabolism within the MPTP-lesioned macaque brain. The depletion of long-chain hydroxylated sulfatides in the MPTP-induced pathology indicates oxidative stress and oligodendrocyte/myelin damage within the pathologically relevant brain regions. Hence, the presented findings improve our current understanding of the molecular pathology of MPTP-induced parkinsonism within primate brains, and provide a basis for further research regarding the role of dysregulated sulfatide metabolism in PD.

Pharmacologic MRI (phMRI) as a tool to differentiate Parkinson's disease–related from age-related changes in basal ganglia function

The prevalence of both parkinsonian signs and Parkinson's disease (PD) per se increases with age. Although the pathophysiology of PD has been studied extensively, less is known about the functional changes taking place in the basal ganglia circuitry with age. To specifically address this issue, 3 groups of rhesus macaques were studied: normal middle-aged animals (used as controls), middle-aged animals with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)–induced parkinsonism, and aged animals (>20 years old) with declines in motor function. All animals underwent the same behavioral and pharmacologic magnetic resonance imaging (phMRI) procedures to measure changes in basal ganglia function in response to dopaminergic drug challenges consisting of apomorphine administration followed by either a D1 (SCH23390) or a D2 (raclopride) receptor antagonist. Significant functional changes were predominantly seen in the external segment of the globus pallidus (GPe) in aged animals and in the striatum (caudate nucleus and putamen) in MPTP-lesioned animals. Despite significant differences seen in the putamen and GPe between MPTP-lesioned versus aged animals, a similar response profile to dopaminergic stimulations was found between these 2 groups in the internal segment of the GP. In contrast, the pharmacologic responses seen in the control animals were much milder compared with the other 2 groups in all the examined areas. Our phMRI findings in MPTP-lesioned parkinsonian and aged animals suggest that changes in basal ganglia function in the elderly may differ from those seen in parkinsonian patients and that phMRI could be used to distinguish PD from other age-associated functional alterations in the brain.

Amphetamine-induced circling behaviour in MPTP-lesioned mice

This study was designed to examine the effect of intrastriatal administration of MPTP on (+)-amphetamine-induced circling behaviour in mice. The results demonstrate that (+)-amphetamine elicits circling behaviour in MPTP-lesioned animals. MPTP produced a 70% depletion of striatal dopamine concentration.

Dopamine Transporter Binding Is Unaffected by L-DOPA Administration in Normal and MPTP-Treated Monkeys

BackgroundRadiotracer imaging of the presynaptic nigrostriatal dopaminergic system is used to assess disease progression in Parkinson's disease (PD) and may provide a useful adjunct to clinical assessment during therapeutic trials of potential neuroprotective agents. Several clinical trials comparing dopamine agonists to L-DOPA or early vs. late L-DOPA have revealed differences between clinical assessment and imaging of the presynaptic dopaminergic system, hence questioning the comparability of these measures as neuroprotection outcome variables. Thus, results of these studies may have been affected by factors other than the primary biological process investigated.Methodology/Principal FindingsWe tested the possibility that L-DOPA might interfere with DAT binding. Post-mortem DAT binding was conducted in normal and MPTP-treated macaque monkeys that were administered L-DOPA, acutely or chronically. In parallel, DAT SPECT was conducted in MPTP-treated animals that were administered chronic L-DOPA. [99mTc]TRODAT-1 SPECT binding was similarly reduced in all MPTP monkeys regardless of L-DOPA treatment. L-DOPA had no significant effect on post-mortem DAT binding either in saline or in MPTP-lesioned animals.Conclusions/SignificanceThese data indicate that L-DOPA does not induce modifications of DAT expression detectable by SPECT of by DAT binding autoradiography, suggesting that differences between clinical assessment and radiotracer imaging in clinical trials may not be specifically related to L-DOPA treatment.

Neurotrophic and neurorescue effects of Echinacoside in the subacute MPTP mouse model of Parkinson's disease

Many experiments support the notion that augmentation of neurotrophic factors' (NTFs) activity, especially glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) could prevent or halt the progress of neurodegeneration in Parkinson's disease (PD). However, application of NTFs as therapeutic agents for PD is hampered by the difficulty in delivering them to specific brain regions safely and effectively. Another potential strategy is to stimulate the endogenous expression of NTFs. In this study, we investigated the effects of Echinacoside (ECH), a monomer extracted from herbs, on rescuing dopaminergic function in 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-lesioned mice. We found that oral administration of ECH (30 mg/kg/day for 14 days) to MPTP-treated mice, commencing after impairment of the nigrstriatal system, suppressed the reduction of nigral dopaminergic neurons, striatal fibers, dopamine and dopamine transporter to 134.24%, 203.17%, 147.25% and 154.72 of MPTP-lesioned animals respectively ( p < 0.05). There was a relative elevation in expression of GDNF and BDNF mRNA (2.94 and 3.75-fold) and protein (184.34% and 185.93%) in ECH treated mice compared with vehicle-treated MPTP-lesioned mice ( p < 0.05). In addition, the apoptosis cells and Bax/Bcl-2 ratio of mRNA and protein in MPTP-lesioned mice significantly increased, and these effects could be prevented by ECH. At the 7th and 14th days of ECH treatment, the gait disorder displayed obvious improvement ( p < 0.05). These findings demonstrate that ECH is probably a novel, orally active, non-peptide inducer of NTFs and inhibitor of apoptosis, and they provide preclinical support for therapeutic potential of this compound in the treatment of PD.

Melatonin attenuates tyrosine hydroxylase loss and hypolocomotion in MPTP-lesioned rats

Parkinson's disease is a chronic neurological disease characterized by dopaminergic neuron degeneration in the substantia nigra pars compacta. Melatonin is a powerful antioxidant agent secreted by the pineal gland which has numerous physiological functions and seems to exert an important neuroprotective effect. The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model has been used to understand the pathophysiology of the disease because of its capacity to mimic biochemical and histological features observed in Parkinson's disease. This study investigated the effect of pretreatment with melatonin (50 mg/kg) on MPTP-lesioned animals 24 h and 7 days after neurotoxin infusion using the open-field test, two-way avoidance task and immunohistochemistry. Twenty-four hours after lesioning, the MPTP + vehicle group exhibited hypolocomotion and significant loss of tyrosine hydroxylase-immunoreactive cells, whereas no differences in these parameters were observed in lesioned animals receiving melatonin. Seven days after surgery, the MPTP-lesioned rats did not show hypolocomotion compared to control animals, while there was a significant dopaminergic neuronal loss. In the two-way avoidance task, MPTP-treated animals presented a cognitive deficit compared to the control groups and melatonin administration did not repair this defect. The present results suggest that melatonin reduces neuronal loss in the MPTP animal model of Parkinson's disease.

Chronic oral nicotine normalizes dopaminergic function and synaptic plasticity in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned primates.

Our recent studies show that chronic oral nicotine partially protects against striatal damage in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated nonhuman primates. To identify the cellular changes associated with this protective action, we investigated the effects of nicotine treatment on stimulus-evoked dopamine release, dopamine turnover, and synaptic plasticity in striatum from lesioned and unlesioned animals. Monkeys were chronically (6 months) treated with nicotine in the drinking water and subsequently lesioned with the dopaminergic neurotoxin MPTP (6 months) while nicotine was continued. Nigrostriatal damage increased nicotinic acetylcholine receptor (nAChR)-mediated fractional dopamine release from residual terminals, primarily through changes in alpha3*/alpha6* nAChRs. In contrast, fractional receptor-evoked dopamine release was similar to control in unlesioned and lesioned animals with chronic oral nicotine. Long-term nicotine administration also attenuated the enhanced K(+)-evoked fractional dopamine release from synaptosomes of MPTP-lesioned animals, suggesting that nicotine treatment had a generalized effect on dopaminergic function. This premise was further supported by experiments showing that nicotine dosing decreased the elevated dopamine turnover that occurs after nigrostriatal damage. We next investigated changes in synaptic plasticity with lesioning and nicotine treatment. Nicotine treatment alone enhanced synaptic plasticity by lowering the threshold for long-term depression (LTD) in the corticostriatal pathway. MPTP lesioning led to a loss of LTD, a measure of short-term synaptic plasticity. In contrast, LTD was preserved in nicotine-treated lesioned animals. Thus, the present data show that the disruptions in striatal dopaminergic function after nigrostriatal damage were attenuated with chronic nicotine administration. These cellular alterations may underlie the ability of nicotine to maintain/restore normal function with nigrostriatal damage.

Immunoautoradiographic analysis of NMDA receptor subunits and associated postsynaptic density proteins in the brain of dyskinetic MPTP‐treated common marmosets

l-3,4-dihydroxyphenylalanine methyl ester (l-DOPA)-induced dyskinesia in Parkinson's disease may result from aberrant glutamatergic stimulation of the striatum due to synaptic plasticity in the motor cortex or striatum as a consequence of adaptation of striatal output pathways. This might result from changes in NMDA receptor subunit or NMDA receptor associated postsynaptic density (PSD) scaffold protein expression. Using immunoautoradiography the expression levels of NR1 and NR2B subunits of the NMDA receptor and the postsynaptic density scaffold proteins, PSD-95, PSD-93, and neurofilament light (NFL) were examined in normal common marmosets (Callithrix jacchus) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned animals that exhibited high or low levels of l-DOPA-induced dyskinesia. Brains from MPTP-lesioned animals that were not primed for l-DOPA-induced dyskinesia were not included in this study. No alterations in the NR1 NMDA receptor subunit were observed. The NR2B NMDA receptor subunit was increased in caudal caudate nucleus and putamen, hippocampus, cingulate motor area (CMA), supplementary motor area (SMA) and dorsal primary motor cortex (dMI) of highly dyskinetic MPTP-lesioned marmosets, but not in animals with low levels of dyskinesia. PSD-93 was decreased in the globus pallidus of marmosets with high and low levels of dyskinesia and increased in the CMA, SMA and dMI of highly dyskinetic marmosets. PSD-95 was increased in the SMA of highly dyskinetic marmosets, but not in animals with low dyskinesia. NFL expression was elevated in the SMA and dorsal and ventral MI of highly dyskinetic marmosets. These results suggest that l-DOPA treatment of MPTP-lesioned marmosets can affect glutamatergic systems and indicate that altered NMDA receptor function may relate to dyskinesia.

A role for endocannabinoids in the generation of parkinsonism and levodopa‐induced dyskinesia in MPTP‐lesioned non‐human primate models of Parkinson's disease

Endocannabinoids and cannabinoid CB1 receptors play a role in the control of movement by modulating GABA, glutamate, and other neurotransmitters throughout the basal ganglia. Roles for abnormalities in endocannabinoid signaling in Parkinson's disease (PD) and the major side effect of current treatments, levodopa-induced dyskinesia (LID), have been suggested by rodent studies. Here we show that signaling by endocannabinoids contributes to the pathophysiology of parkinsonism and LID in MPTP-lesioned, non-human primate models of Parkinson's disease. In MPTP-lesioned marmosets previously treated with levodopa to establish LID, attenuation of CB1 signaling by systemic administration of rimonabant (1 and 3 mg/kg) had anti-parkinsonian actions, equivalent to a 71% increase in motor activity at 3 mg/kg. Rimonabant did not elicit dyskinesia. Co-administration of levodopa (8 mg/kg) and rimonabant (1 and 3 mg/kg) resulted in significantly less dyskinesia than levodopa alone, without significantly affecting the anti-parkinsonian action of levodopa. These data suggest that enhanced endocannabinoid signaling may be involved in the pathophysiology of both parkinsonism and LID. To define potential mechanisms by which such a role might be mediated, we determined the levels of the endocannabinoids anandamide and 2-arachidonyl glycerol (2-AG) throughout the basal ganglia in normal and three groups of MPTP-lesioned cynomolgus monkeys (untreated; acutely treated with L-DOPA, non-dyskinetic; long-term treated, with levodopa-induced dyskinesia). In the untreated, MPTP-lesioned primate, parkinsonism was associated with increases in both 2-AG (+88%) and anandamide (+49%) in the striatum, and of 2-AG (+97%) in the substantia nigra, changes that are consistent with the previously suggested role for endocannabinoids in mechanisms attempting to compensate for loss of dopamine in untreated parkinsonism. Increased levels of anandamide (+34%) in the external globus pallidus of MPTP-lesioned animals were normalized by levodopa treatment and may contribute to the generation of parkinsonian symptoms. However, no clear alteration in endocannabinoid levels could be correlated with the expression of LID. These data highlight the potential roles played by endocannabinoids and CB1 in PD and LID and suggest the need for further research to pursue the multiple therapeutic opportunities for manipulating this system in movement disorders.

Increases in striatal preproenkephalin gene expression are associated with nigrostriatal damage but not L-DOPA-induced dyskinesias in the squirrel monkey

Changes in preproenkephalin expression in the caudate and putamen have been linked to the development of L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesias in primate models of Parkinson’s disease, although not all investigators have been able to confirm this association. Because nigrostriatal damage per se is associated with increases in striatal preproenkephalin mRNA levels, it is difficult to know if changes in transcript levels are a result of lesioning or concurrent L-DOPA treatment and resulting dyskinesias. To circumvent these difficulties, we measured striatal preproenkephalin mRNA levels in monkeys with L-DOPA-induced dyskinesias both with and without lesions of the nigrostriatal system. The latter model is not confounded by morphological and biochemical changes resulting from nigrostriatal damage. Monkeys were gavaged with L-DOPA (15 mg/kg) twice daily for a 2-week period and killed 3 days after treatment. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment alone resulted in an increase in preproenkephalin mRNA levels as previously shown. However, striatal transcript levels were similarly elevated in dyskinetic MPTP-lesioned animals treated with L-DOPA. In unlesioned animals, preproenkephalin mRNA levels were also similar in control and L-DOPA-treated dyskinetic monkeys. Because drug-induced changes in mRNA may not be sustained for a prolonged period after treatment, a second series of experiments were done in which animals were killed 3–4 h after the last dose of L-DOPA, but the results were similar to those obtained after 3 days. These data show that, while elevations in striatal preproenkephalin mRNA levels are associated with nigrostriatal damage, they are not linked to the development of L-DOPA-induced dyskinesias. These results thus question the importance of preproenkephalin mRNA in the pathogenesis of this disabling complication of L-DOPA therapy in Parkinson’s disease.

L-Dopa restores striatal dopamine level but fails to reverse MPTP-induced memory deficits in rats.

The objective of the present investigation was to test the effects of benserazide/L-dopa treatment in a model of learning and memory deficits associated with early Parkinson's disease. Intra-nigral administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) caused a lesion in the substantia nigra, compact part and a specific loss of dopamine (DA) and its metabolites in the striatum of rats and a memory impairment in the two-way active avoidance task. The administration of benserazide/L-dopa (50 and 200 mg/kg) to the MPTP-lesioned rats restored the striatal level of DA, but did not reverse the MPTP-induced learning and memory impairment. As this treatment caused a large increase of DA levels in extrastriatal brain regions of the MPTP-lesioned animals, this study suggests that benserazide/L-dopa therapy was not effective in improving the observed learning impairment because this treatment appears to tilt the balance between DA levels in the striatum and in the extrastriatal regions, such as frontal cortex and limbic structures, resulting in a cognitive deficit.

Opiate receptor avidity is reduced bilaterally in rhesus monkeys unilaterally lesioned with MPTP.

Opiate receptor avidity (unoccupied receptor density / the receptor dissociation constant), was measured in four animals with unilateral parkinsonian symptoms following MPTP (1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine) infusions into the internal carotid of one side, and nine normal controls with positron emission tomography (PET) and 6-deoxy-6-beta-[(18)F]fluoronaltrexone (cyclofoxy, CF), a mu- and kappa-opiate receptor antagonist. PET studies of 6-[(18)F]-L-fluoro-L-3,4-dihydroxyphenylalanine ([(18)F]-DOPA) in these parkinsonian animals, although documenting the primarily unilateral nature of the lesion, also demonstrated a milder loss of dopaminergic on the side opposite the infusion. Opiate receptor avidity was found to be reduced by 20-34% in the caudate, anterior putamen, thalamus, and amygdala of these primarily unilaterally MPTP-exposed animals, bilaterally with no statistically significant differences between the two sides. The affected regions are the same as those previously demonstrated to have a 30-35% loss in clinically recovered bilaterally MPTP-lesioned animals. These findings confirm that the opiate pathway can change in response to modest decreases in basal ganglia dopamine innervation. Thus, opiate pathway adaptation is likely to contribute to the dynamic changes in basal ganglia circuits that forestall the initial clinical manifestations of Parkinson's disease. In addition, opiate pathway(s) may contribute to the treatment responsiveness and progression of the disease either directly through effects on basal ganglia function or indirectly through effects on basal ganglia plasticity.

Opiate receptor avidity is reduced in non-motor impaired MPTP-lesioned rhesus monkeys

Opiate receptor avidity, roughly equivalent to the ratio of unoccupied receptor density to the receptor dissociation constant ( B′ max/ K D), was measured in four MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-lesioned rhesus monkeys and nine normal controls with positron emission tomography (PET) and 6-deoxy-6-β-[ 18 F ]fluoronaltrexone (cyclofoxy, CF), a μ- and κ-opiate receptor antagonist. Although the MPTP-lesioned monkeys were dopamine deficient as measured with [ 18 F ]- l-fluorodopa ([ 18 F ]-DOPA) and PET [Doudet et al., 6-[ 18 F ]- l-DOPA imaging of the dopamine neostriatal system in normal and clinically normal-MPTP-treated rhesus monkeys, Exp. Brain Res. 78 (1989) 69–80], they had clinically recovered from the acute motor effects of MPTP exposure. Opiate receptor avidity was found to be reduced by 30–35% in the opiate-receptor rich areas of caudate, anterior putamen, thalamus, and amygdala of the MPTP-lesioned animals. The results suggest that opiate pathways make a significant contribution to the adjustment of cortico–striatal–thalamic pathway activity and thereby to behavior in rhesus monkeys following dopamine loss.

6-[18F]Fluoro-L-DOPA PET studies of the turnover of dopamine in MPTP-induced parkinsonism in monkeys.

This report describes a method to assess, in vivo, the turnover of dopamine (DA) and describes its application to the evaluation of DA function in normal monkeys and monkeys with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced lesions of the DA nigro-striatal pathway. Using positron emission tomography with the tracer of presynaptic DA function, 6-[18F]fluoro-L-DOPA (FDOPA), and an extension of the graphical method of analysis, we measured the striatal FDOPA uptake rate constant, Ki, and the rate of reversibility of FDOPA trapping k(loss) in normal and MPTP-treated monkeys, either neurologically normal or displaying a parkinsonian symptomatology. An index of effective DA turnover was defined as the ratio of k(loss)/Ki. Compared to normal controls, Ki was decreased and k(loss) was increased in the MPTP-lesioned monkeys. The index of DA turnover was significantly increased in the monkeys displaying a parkinsonian symptomatology as compared to the controls and the neurologically normal MPTP-treated monkeys. The DA turnover index was also significantly increased in the neurologically normal MPTP-lesioned animals compared to normals. This suggests that an increase in DA turnover develops early in the disease process and may be one of the compensatory mechanisms partly responsible for the delay in the development of the clinical manifestations in Parkinson's disease.