Primate Model Of Parkinson's Disease Research Articles

Autotransplantation for Parkinson's disease goes a step further.

Autotransplantation for Parkinson's disease goes a step further.

Frontal cognitive impairments and saccadic deficits in low-dose MPTP-treated monkeys.

There is considerable overlap between the cognitive deficits observed in humans with frontal lobe damage and those described in patients with Parkinson's disease. Similar frontal impairments have been found in the 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP) primate model of Parkinsonism. Here we provide quantitative documentation of the cognitive, oculomotor, and skeletomotor dysfunctions of monkeys trained on a frontal task and treated with low-doses (LD) of MPTP. Two rhesus monkeys were trained to perform a spatial delayed-response task with frequent alternations between two behavioral modes (GO and NO-GO). After control recordings, the monkeys were treated with one placebo and successive LD MPTP courses. Monkey C developed motor Parkinsonian signs after a fourth course of medium-dose (MD) MPTP and later was treated with combined dopaminergic therapy (CDoT). There were no gross motor changes after the LD MPTP courses, and the average movement time (MT) did not increase. However, reaction time (RT) increased significantly. Both RT and MT were further increased in the symptomatic state, under CDoT. Self-initiated saccades became hypometric after LD MPTP treatments and their frequency decreased. Visually triggered saccades were affected to a lesser extent by the LD MPTP treatments. All saccadic parameters declined further in the symptomatic state and improved partially during CDoT. The number of GO mode (no-response, location, and early release) errors increased after MPTP treatment. The monkeys made more perseverative errors while switching from the GO to the NO-GO mode. Saccadic eye movement patterns suggest that frontal deficits were involved in most observed errors. CDoT had a differential effect on the behavioral errors. It decreased omission errors but did not improve location errors or perseverative errors. Tyrosine hydroxylase immunohistochemistry showed moderate ( approximately 70-80%) reduction in the number of dopaminergic neurons in the substantia nigra pars compacta after MPTP treatment. These results show that cognitive and motor disorders can be dissociated in the LD MPTP model and that cognitive and oculomotor impairments develop before the onset of skeletal motor symptoms. The behavioral and saccadic deficits probably result from the marked reduction of dopaminergic neurons in the midbrain. We suggest that these behavioral changes result from modified neuronal activity in the frontal cortex.

Combined PET/MRS brain studies show dynamic and long-term physiological changes in a primate model of Parkinson disease.

We used brain imaging to study long-term neurodegenerative and bioadaptive neurochemical changes in a primate model of Parkinson disease. We gradually induced a selective loss of nigrostriatal dopamine neurons, similar to that of Parkinson disease, by creating oxidative stress through infusion of the mitochondrial complex 1 inhibitor MPTP for 14+/-5 months. Repeated evaluations over 3 years by positron emission tomography (PET) demonstrated progressive and persistent loss of neuronal dopamine pre-synaptic re-uptake sites; repeated magnetic resonance spectroscopy (MRS) studies indicated a 23-fold increase in lactate and macromolecules in the striatum region of the brain for up to 10 months after the last administration of MPTP. By 2 years after the MPTP infusions, these MRS striatal lactate and macromolecule values had returned to normal levels. In contrast, there were persistent increases in striatal choline and decreases in N-acetylaspartate. Thus, these combined PET/MRS studies demonstrate patterns of neurochemical changes that are both dynamic and persistent long after selective dopaminergic degeneration.

In vivo expression of therapeutic human genes for dopamine production in the caudates of MPTP-treated monkeys using an AAV vector.

An adeno-associated virus (AAV) vector, expressing genes for human tyrosine hydroxylase (TH) and aromatic amino acid decarboxylase (AADC), demonstrated significantly increased production of dopamine in 293 (human embryonic kidney) cells. This bicistronic vector was used to transduce striatal cells of six asymptomatic but dopamine-depleted monkeys which had been treated with the neurotoxin MPTP. Striatal cells were immunoreactive for the vector-encoded TH after stereotactic injection for periods up to 134 days, with biochemical effects consistent with dopamine biosynthetic enzyme expression. A subsequent experiment was carried out in six more severely depleted and parkinsonian monkeys. Several TH/aadc-treated monkeys showed elevated levels of dopamine near injection tracts after 2.5 months. Two monkeys that received a beta-galactosidase expressing vector showed no change in striatal dopamine. Behavioral changes could not be statistically related to the vector treatment groups. Toxicity was limited to transient fever in several animals and severe hyperactivity in one animal in the first days after injection with no associated histological evidence of inflammation. This study shows the successful transfection of primate neurons over a period up to 2.5 months with suggestive evidence of biochemical phenotypic effects and without significant toxicity. While supporting the idea of an in vivo gene therapy for Parkinson's disease, more consistent and longer lasting biochemical and behavioral effects will be necessary to establish the feasibility of this appraoch in a primate model of parkinsonism.

CNS immunological modulation of neural graft rejection and survival

Neural transplantation therapy as a possible alternative treatment for neurological movement disorders, such as in Parkinson's disease (PD), has accentuated research interest on the immune status of the central nervous system (CNS). Most animal studies concerned with neural transplantation for the treatment of PD have utilized dopamine (DA) neurons from tissues of the embryonic ventral mesencephalon. Rat embryonic DA neurons, grafted either as solid blocks or dissociated into a cell suspension and stereotaxically injected intraparenchymally into a rat lesion model of PD, have been shown to survive and form connections with the host brain, and ameliorate the behavioral deficits of PD. Similarly, studies on nonhuman primate models of PD provide considerable support for neural transplantation of DA neurons as an experimental clinical procedure for the treatment of PD. To this end, experimental clinical trials have been centered upon transplantation of the embryonic ventral mesencephalic cells for PD patients. Although not conclusive, the findings from clinical studies have provided some evidence that most patients with marked increases in fluorodopa uptake (indicating graft survival) have been immunosuppressed. Furthermore, immune reactions have been observed in rats xenografted with human embryonic tissue. Of note, embryonic ventral mesencephalic tissues compared to adult tissues produce better morphological and long-lasting behavioral amelioration of the neurobehavioral deficits of PD, thus advocating the use of grafts from young donors (embryo) to circumvent the CNS immune rejection. The possible graft rejection due to CNS immune reactions, coupled with the social and ethical problems surrounding the use of embryonic neural tissue, and the logistical problems concerning tissue availability have prompted the development of alternative sources of DA-secreting cells. To circumvent these obstacles, several methods have been suggested including the use of immunosuppressants such as Cyclosporine-A, transplantation of autografts, polymer-encapsulated DA-secreting cells, co-culturing and co-transplantation of DA-secreting cells with microcarrier beads, with Sertoli cells, or with fragments of a monoclonal antibody that can mask the MHC class I antigens, and genetically modifying cells that can withstand CNS immune reactions. Some of these techniques allow transplantation of allograft (same species transplantation), or even xenograft (cross species transplantation) without immunosuppression of the recipient. We discuss recent CNS immunosuppression techniques that pose some promise for enhanced survival of neural grafts. When possible, advantages and disadvantages of each method are presented. Hopefully, such critical analysis of different immunosuppression techniques will produce innovated ideas that will lead to a better understanding of CNS immune response and its modulatory function on graft rejection and survival.

Reversal of parkinsonian symptoms by intrastriatal and systemic manipulations of excitatory amino acid and dopamine transmission in the bilateral 6-OHDA lesioned marmoset

We have investigated the potential of alleviating parkinsonian symptoms by manipulating excitatory amino acid (EAA) transmission, by several different pharmacological means, in a novel primate model of parkinsonism. The model is based on a two-stage bilateral 6-hydroxydopamine lesion procedure in marmosets, which produces a stable but marked parkinsonian condition. Parkinsonian symptoms were reversed in a dose-dependent manner by systemic administration of levodopa and intrastriatal injections of apomorphine administered into either the caudate nucleus or the putamen. (R)-HA-966, a partial agonist for the NMDA receptor associated glycine site, also alleviated parkinsonian symptoms when injected intrastriatally but not when injected systemically. Systemic injection of enadoline, a kappa opiate which blocks release of EAAs, reduced parkinsonian symptoms when injected systemically, though it did not restore completely normal motor behaviour. In contrast, ifenprodil, an antagonist for the NMDA receptor-associated polyamine modulatory site, when injected systemically at an optimal dose, resulted in apparently normal motor behaviour. These data suggest that attenuation of EAA transmission could be used to treat parkinsonism.

MRI and PET studies of manganese‐intoxicated monkeys

Using MRI and PET, we investigated the consequences of manganese intoxication in a primate model of parkinsonism and dystonia. Three rhesus monkeys were injected intravenously with doses of 10 to 14 mg/kg of MnCl2 on seven occasions, each a week apart. Two animals became hypoactive with abnormal extended posturing in the hind limbs. These motor disturbances did not improve with administration of levodopa. In all three monkeys, T1-weighted MRI demonstrated high signal intensities in the regions of the striatum, globus pallidus, and substantia nigra. No significant changes were found on [18F]6-fluoro-L-dopa, [11C]raclopride, or [18F]fluorodeoxyglucose PET. These results are consistent with the pathologic findings, which were primarily confined to the globus pallidus, and indicate that manganese intoxication is associated with preservation of the nigrostriatal dopaminergic pathway, despite clinical evidence of parkinsonian deficits. Chronic manganese intoxication may cause parkinsonism by damaging output pathways downstream to the nigrostriatal dopaminergic pathway. This is consistent with the demonstrated lack of therapeutic response to levodopa.

Glutamate/dopamine D1/D2 balance in the basal ganglia and its relevance to Parkinson's disease.

The recent availability of selective ligands for NMDA and AMPA receptors has enabled neuroscientists to test the hypothesis that Parkinson's disease is a glutamate hyperactivity disorder and hence treatable with glutamate antagonists. This review takes a critical look at the motor characteristics of this new class of drugs in rodent and primate models of parkinsonism and assesses the clinical potential and pitfalls of this radical new approach. Monotherapy of Parkinson's disease with glutamate antagonists appears impractical at the present time, due to their low efficacy and unacceptable side effects, but polypharmacy with L-DOPA and a glutamate antagonist as adjuvant is a more realistic prospect. This review will focus on the ways in which glutamate receptor blockade facilitates motor recovery with L-DOPA and will examine whether the basis for this beneficial effect can be traced to a specific interaction with dopamine at D1 or D2 receptors, and therefore to discrete motor pathways within the basal ganglia.

Morphine and naltrexone modulate D2 but not D1 receptor induced motor behavior in MPTP-lesioned monkeys.

Interactions at the behavioral level between dopamine (DA) and opioid receptors in the mammalian brain have been amply demonstrated. Considering the pivotal role for DA receptors in the pharmacotherapy of Parkinson's disease (PD), these interactions might be clinically relevant. Therefore, in the present study the effects of the opioid antagonist naltrexone and agonist morphine on D1 and D2 receptor induced stimulation of motor behavior in the unilateral MPTP monkey model (n = 5) of PD were investigated. The results show that both naltrexone and morphine [0.1-1.0 mg/kg; intramuscular injection (IM)] inhibited D2 receptor stimulated contralateral rotational behavior and hand use induced by administration of quinpirole (LY 171555; 0.01 mg/kg, IM) in a dose-related way. However, no effects of these opioid drugs were observed on D1 receptor stimulated contralateral rotational behavior and hand use induced by administration of SKF 81297 (0.3 mg/kg, IM). Interestingly, the action of the alleged preferential mu-receptor antagonist naltrexone was mimicked by the selective delta-opioid antagonist naltrindole (0.5 mg/kg, IM). From this study it is concluded that in a non-human primate model of PD, alteration of opioid tonus leads to modulation of D2 receptor but not D1 receptor controlled motor behavior. The possible underlying mechanisms and clinical relevance of these findings are discussed.

Differential recovery of volitional motor function, lateralized cognitive function, dopamine agonist-induced rotation and dopaminergic parameters in monkeys made hemi-parkinsonian by intracarotid MPTP infusion

There is still controversy regarding the fequency and extent of spontaneous functional recovery in primate models of parkinsonism, perhaps in part stemming from the variety of ways in which recovery has been assessed. The present study examined functional recovery in monkeys made unilaterally parkinsonian by intracarotid infusion of MPTP. Monkeys were evaluated prior to lesioning and for at least 1 year after lesioning on a battery of tests including a rating of spontaneous behaviors, a learned reaction time/movement time task, tests of lateralized neglect or inattention (i.e. lateralized reward retrieval task, extinction with double simultaneous stimulation, and response to a target moving from one hemispace to the other), and rotational asymmetry in response to a dopamine agonist. Some animals also received 6-[ 18F]Fluoro-L-Dopa (F-DOPA) positron emission tomography (PET) scans before MPTP, when symptomatic, and when showing signs of functional recovery. These animals were sacrificed for post mortem neurochemical assessment following the last PET scan. Results showed that estimates of functional recovery in hemi-parkinsonian monkeys may depend upon the behavioral assay used. Even in behavioral tasks that were sensitive to recovery effects, the degree of functional recovery shown by an animal on one such task did not predict recovery on another. This may in part be due to the inherent difficulty in designing behavioral tests to assess basal ganglia functioning, when there is no consensus concerning which aspects of behavior the normal basal ganglia actually control. The results also suggest that the relationship of post-mortem striatal dopamine levels or in vivo estimates of pre-synaptic dopaminergic function to functional recovery are also tenuous. The hemi-parkinsonian monkey is a valuable but complex behavioral model and care needs to be taken in assessing functional impairment and functional recovery in such animals.

Reversal of hemiparkinsonian syndrome in nonhuman primates by amnion implantation into caudate nucleus.

Although recent animal and human experiments suggest that tissue implantation can ameliorate parkinsonism, there is controversy about what mechanism underlies recovery. Secretion of dopamine from the graft seems unlikely to be the sole restorative factor. Regenerative sprouting by the host brain may also underlie behavioral recovery. Fetal amnion and term amnion, which were shown to produce and secrete a factor that supports the outgrowth of neurite processes in vitro, were implanted in hemiparkinsonian monkeys. Fetal amnion implants induced sprouting of dopaminergic fibers from the host brain and behavioral improvement, despite failure of the grafts to survive. Animals implanted with term amnion also had some sprouted dopaminergic fibers and behavioral improvement, but these were limited and were similar to the recovery, in prior experiments using the same primate model of parkinsonism, of animals that received surgical cavitation only. Recovery after central nervous system grafting with fetal amnion, a fetal accessory tissue, does not require secretion of a deficient neurotransmitter(s) from the graft and occurs despite the failure of graft survival. Recovery after cerebral implantation of fetal tissues appears to depend more on the regenerative and recuperative processes of the host brain than on graft replacement of deficient neurotransmitters or development of functional synaptic connections between the graft and the host brain.

Glutamate-dopamine interactions in the basal ganglia: relationship to Parkinson's disease.

Current antiparkinsonian therapies focus on either replacing dopamine via precursor (L-DOPA) administration, or directly stimulating post-synaptic dopamine receptors with dopamine agonists. Unfortunately, this approach is associated with numerous side effects and these drugs lose efficacy with disease progression. This article reviews recent evidence which suggests that negative modulation of glutamatergic neurotransmission has antiparkinsonian effects in a variety of rodent and primate models of parkinsonism. The pronounced synergism between dopaminergic agents and glutamate receptor antagonists may provide a means of using very low doses of the two drug classes in concert to treat Parkinson's disease effectively and minimize dose-related drug side effects.

The use of thalamotomy in the treatment of levodopa-induced dyskinesia.

Peak dose dyskinesia is a major problem in the treatment of parkinsonian patients with levodopa and yet this remains the best pharmacological agent for treating the condition. The hypothesis which this research set out to test was that thalamotomy in the area of the thalamus which receives the input from the medial segment of the globus pallidus would decrease or prevent the dyskinesia. A well established primate model of parkinsonism was used. Eight monkeys (Macaca fascicularis) were rendered parkinsonian with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Regular dosing with levodopa or apomorphine reliably resulted in peak dose dyskinesia. Thalamotomy was carried out using a radiofrequency electrode. To ensure that the appropriate area of the thalamus was targeted, that is the area receiving the pallidal input, an anatomical tracing study was carried out. The anterograde anatomical tracer horseradish peroxidase, covalently bound to wheatgerm agglutinin, was injected into the medial segment of the globus pallidus bilaterally in three monkeys. The target site for thalamotomy was accurately worked out from the tracings obtained. Chorea was usually abolished and always reduced by a thalamotomy in the pallidal terminal territory. This result was obtained after 10 thalamotomies: 4 animals receiving bilateral lesions, with an interval between operations, and 2 animals undergoing unilateral surgery. Lesions in three control sites were carried out and had no permanent effect on chorea. The effect of lesions in other areas was also assessed. Dystonia was not relieved by any thalamic lesion. Thalamotomy is a long established procedure used to help parkinsonian tremor. Appropriately placed thalamotomy should be considered for the relief of disabling peak dose dyskinesia, which is predominantly choreic, in parkinsonian patients on otherwise successful levodopa therapy.

Dopamine fiber detection by [11C]-CFT and PET in a primate model of parkinsonism.

Monkeys were treated on two regimens of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) injections to achieve dopamine fiber degeneration of differing severities. A rapid treatment regimen produced a severe parkinsonian syndrome, whereas an intermittent regimen did not cause locomotor symptoms to appear up to 25 weeks. High resolution PET scanning of dopamine nerve terminals revealed that the specific binding of the dopamine transporter [11C]-WIN 35,428 ([11C]-CFT) was diminished by 94% (caudate nucleus) and by 93% (putamen) in the symptomatic monkey. Decreases of 65 and 67% were detected in these regions in the non-symptomatic monkey. Post-mortem immunocytochemical evaluation of presumed dopamine fibers by tyrosine-hydroxylase showed similar reductions in the symptomatic animal.

A novel approach to neural transplantation in Parkinson's disease: Use of polymer-encapsulated cell therapy

Transplantation of dopaminergic neurons derived from fetal or adrenal tissue into the striatum is a potentially useful treatment for Parkinson's disease (PD). Although initially promising, recent clinical studies using adrenal autografts have demonstrated limited efficacy. The use of human fetal cells, despite promising preliminary results, is complicated by tissue availability and ethical concerns. An attractive alternative is based on encapsulating dopamine-producing cells into polymer capsules prior to transplantation. Polymer capsules can be fabricated to surround the cells with a semi-permeable and immunoprotective barrier. The semi-permeable membrane allows nutrients to enter the capsule, so the encapsulated cells will survive and function, and dopamine and other low molecular weight constituents to diffuse out into the host tissue. Thus, the technique allows use of unmatched human tissue (allografts), or even animal tissue (xenografts) without immunosuppression of the recipient. Cell-loaded polymer capsules can also be retrieved if necessary or desired. The demonstration that striatal implants of encapsulated dopamine-producing cells promote behavioral recovery in rodent and primate models of PD further suggests that cellular encapsulation may be a useful strategy for ameliorating the behavioral consequences of PD.

Alleviation of parkinsonism by antagonism of excitatory amino acid transmission in the medial segment of the globus pallidus in rat and primate.

Recent experimental data has made possible the description of the pathophysiological circuitry that mediates parkinsonism. This work has shown that dopamine-denervated striatal cells discharge abnormally and that this ultimately causes cells in the medial segment of the globus pallidus to become abnormally overactive. The main driving force behind the overactive cells in the medial pallidal segment appears to be excess activity in the afferent pathway to it from the subthalamic nucleus. This pathway is known to use an excitatory amino acid (EAA) as its transmitter. It was therefore hypothesized that local blockade of EAA transmission in the medial segment of the globus pallidus should reverse parkinsonism. This hypothesis was tested in rat and primate models of parkinsonism by the direct injection of the EAA antagonist, kynurenic acid, into the medial segment of the globus pallidus. The results demonstrate that this procedure can reverse parkinsonism in a dose-dependent manner, and suggest that manipulation of EAA transmission in the medial segment of the globus pallidus may have therapeutic potential for treating parkinsonism.

III. Primate model of parkinsonism: Selective lesion of nigrostriatal neurons by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine produces an extrapyramidal syndrome in rhesus monkeys

Systemic administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to rhesus monkeys (1.0–2.5 mg/kg i.v.) produces irreversible damage to nigrostriatal neurons. Dopaminergic neurons in the dorsolateral part of striatum were the most vulnerable. The major clinical signs of an extrapyramidal syndrome, but not resting tremor, appeared only in MPTP-treated monkeys suffering from more than 80% reduction in striatal dopamine. No chronic changes in the mesolimbic dopaminergic system were observed. Immunocytochemical staining of the mid-brain with a tyrosine hydroxylase antiserum indicated that MPTP produced a significant decrease of dopaminergic cell bodies in the A9, but not in the A10 ventrotegmental area. Despite greater than 80% decrease in A9 nigral cell bodies, the dopamine content decreased only by 50%. Sprouting of the surviving nigral A9 neurons was observed histologically and neurochemically in the area above substantia nigra. The present behavioral, neurochemical and histological results indicate that MPTP produces an ideal primate model for studying parkinsonism. Selective lesion of more than 80% of the nigrostrial neurons by MPTP is sufficient to produce the major clinical signs of the extrapyramidal syndrome in idiopathic parkinsonism.

A primate model of parkinsonism: selective destruction of dopaminergic neurons in the pars compacta of the substantia nigra by N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.

A syndrome similar to idiopathic parkinsonism developed after intravenous self-administration of an illicit drug preparation in which N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (NMPTP) might have been responsible for the toxicity. In the present study we show that intravenous administration of NMPTP to the rhesus monkey produces a disorder like parkinsonism (akinesia, rigidity, postural tremor, flexed posture, eyelid closure, drooling) that is reversed by the administration of L-dopa. NMPTP treatment decreases the release of dopamine and dopamine accumulates in swollen, distorted axons in the nigrostriatal pathway just above the substantia nigra, followed by severe nerve cell loss in the pars compacta of the substantia nigra and a marked reduction in the dopamine content of the striatum. The pathological and biochemical changes produced by NMPTP are similar to the well-established changes in patients with parkinsonism. Thus, the NMPTP-treated monkey provides a model that can be used to examine mechanisms and explore therapies of parkinsonism.

Street drugs yield primate Parkinson's model

Street drugs yield primate Parkinson's model

Street drugs yield primate Parkinson's model

The tragic mistake of several young drug abusers has led scientists at the National Institute of Mental Health (NIMH) to develop a unique animal model of Parkinson's disease. The animals are rhesus monkeys, and their parkinsonism is produced with 1-methyl4-phenyl-1,2,5,6-tetrahydropyridine (MPTP), a byproduct of the synthesis of a meperidine (Demerol) analogue, MPPP. The story began in November 1976, when a 23-year-old chemistry graduate student became severely rigid, mute, weak, and tremorous. He had injected himself during the course of several days with doses of a sloppy homemade batch of MPPP. He was admitted to the psychiatric ward of a general hospital with an initial diagnosis of catatonic schizophrenia but later was successfully treated with anti-parkinson medications and referred to NIMH for further evaluation. While receiving treatment for his parkinsonian symptoms, the student persisted in abusing drugs and finally died of an overdose in September 1978. Autopsy revealed severe loss of