Modeling Parkinson's disease in monkeys for translational studies, a critical analysis

The importance of social behavior in nonhuman primate studies of aging: A mini-review

Social behavior plays an important role in supporting both psychological and physical health across the lifespan. People's social lives change as they age, and the nature of these changes differ based on whether people are on healthy aging trajectories or are experiencing neurodegenerative diseases that cause dementia, such as Alzheimer's disease and Parkinson's disease. Nonhuman primate models of aging have provided a base of knowledge comparing aging trajectories in health and disease, but these studies rarely emphasize social behavior changes as a consequence of the aging process. What data exist hold particular value, as negative effects of disease and aging on social behavior are likely to have disproportionate impacts on quality of life. In this mini review, we examine the literature on nonhuman primate models of aging with a focus on social behavior, in the context of both health and disease. We propose that adopting a greater focus on social behavior outcomes in nonhuman primates will improve our understanding of the intersection of health, aging and sociality in humans.

Remote photobiomodulation targeted at the abdomen or legs provides effective neuroprotection against parkinsonian MPTP insult

Photobiomodulation (PBM)-the irradiation of tissue with low-intensity light-mitigates neuropathology in rodent models of Parkinson's disease (PD) when targeted at the head ('transcranial PBM'). In humans, however, attenuation of light energy by the scalp and skull necessitates a different approach. We have reported that targeting PBM at the body also protects the brain by a mechanism that spreads from the irradiated tissue ('remote PBM'), although the optimal peripheral tissue target for remote PBM is currently unclear. This study compared the neuroprotective efficacy of remote PBM targeting the abdomen or leg with transcranial PBM, in mouse and non-human primate models of PD. In a pilot study, the neurotoxin MPTP was used to induce PD in non-human primates; PBM (670 nm, 50 mW/cm2 , 6 min/day) of the abdomen (n = 1) was associated with fewer clinical signs and more surviving midbrain dopaminergic cells relative to MPTP-injected non-human primates not treated with PBM. Validation studies in MPTP-injected mice (n = 10 per group) revealed a significant rescue of midbrain dopaminergic cells in mice receiving PBM to the abdomen (~80%, p < .0001) or legs (~80%, p < .0001), with comparable rescue of axonal terminals in the striatum. Strikingly, this degree of neuroprotection was at least as, if not more, pronounced than that achieved with transcranial PBM. These findings confirm that remote PBM provides neuroprotection against MPTP-induced destruction of the key circuitry underlying PD, with both the abdomen and legs serving as viable remote targets. This should provide the impetus for a comprehensive investigation of remote PBM-induced neuroprotection in other models of PD and, ultimately, human patients.

Quantification of early gait development: Expanding the application of Catwalk technology to an infant rhesus macaque model

BACKGROUND

Understanding gait development is essential for identifying motor impairments in neurodevelopmental disorders. Defining typical gait development in a rhesus macaque model is critical prior to characterizing abnormal gait. The goal of this study was to 1) explore the feasibility of using the Noldus Catwalk to assess gait in infant rhesus macaques and 2) provide preliminary normative data of gait development during the first month of life.

NEW METHOD

The Noldus Catwalk was used to assess gait speed, dynamic and static paw measurements, and interlimb coordination in twelve infant rhesus macaques at 14, 21, and 28 days of age. All macaque runs were labeled as a diagonal or non-diagonal walking pattern.

RESULTS

Infant rhesus macaques primarily used a diagonal (mature) walking pattern as early as 14 days of life. Ten infant rhesus macaques (83.3%) were able to successfully walk across the Noldus Catwalk at 28 days of life. Limited differences in gait parameters were observed between timepoints because of the variability within the group at 14, 21, and 28 days.

COMPARISON WITH EXISTING METHODS

No prior gait analysis system has been used to provide objective quantification of gait parameters for infant macaques.

CONCLUSIONS

The Catwalk system can be utilized to quantify gait in infant rhesus macaques less than 28 days old. Future applications to infant rhesus macaques could provide a better understanding of gait development and early differences within various neurodevelopmental disorders.

Dyskinesia and Parkinson's disease: animal model, drug targets, and agents in preclinical testing

INTRODUCTION

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease. PD patients exhibit a classic spectrum of motor symptoms, arising when dopamine neurons in the substantia nigra pars compacta are reduced by 60%. The dopamine precursor L-DOPA represents the most effective therapy for improving PD motor dysfunctions, thus far available. Unfortunately, long-term treatment with L-DOPA is associated with the development of severe side effects, resulting in abnormal involuntary movements termed levodopa-induced dyskinesia (LID). Amantadine is the only drug currently approved for the treatment of LID indicating that LID management is still an unmet need in PD and encouraging the search for novel anti-dyskinetic drugs or the assessment of combined therapies with different molecular targets.

AREAS COVERED

This review provides an overview of the main preclinical models used to study LID and of the latest preclinical evidence on experimental and clinically available pharmacological approaches targeting non-dopaminergic systems.

EXPERT OPINION

LIDs are supported by complex molecular and neurobiological mechanisms that are still being studied today. This complexity suggests the need of developing personalized pharmacological approach to obtain an effective amelioration of LID condition and improve the quality of life of PD patients.

Current Knowledge on the Background, Pathophysiology and Treatment of Levodopa-Induced Dyskinesia-Literature Review

Levodopa remains the primary drug for controlling motor symptoms in Parkinson’s disease through the whole course, but over time, complications develop in the form of dyskinesias, which gradually become more frequent and severe. These abnormal, involuntary, hyperkinetic movements are mainly characteristic of the ON phase and are triggered by excess exogenous levodopa. They may also occur during the OFF phase, or in both phases. Over the past 10 years, the issue of levodopa-induced dyskinesia has been the subject of research into both the substrate of this pathology and potential remedial strategies. The purpose of the present study was to review the results of recent research on the background and treatment of dyskinesia. To this end, databases were reviewed using a search strategy that included both relevant keywords related to the topic and appropriate filters to limit results to English language literature published since 2010. Based on the selected papers, the current state of knowledge on the morphological, functional, genetic and clinical features of levodopa-induced dyskinesia, as well as pharmacological, genetic treatment and other therapies such as deep brain stimulation, are described.

Opicapone enhances the reversal of MPTP-induced Parkinson-like syndrome by levodopa in cynomolgus monkeys

Opicapone is a third generation nitrocatechol catechol-O-methyltransferase inhibitor that has received regional market approval for use as adjunctive therapy to levodopa in Parkinson's disease patients with motor fluctuations. This study evaluated the effects of opicapone as adjunct to levodopa in reversing a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced Parkinson's-like syndrome in cynomolgus monkeys in during opicapone preclinical development program. A Parkinson's-like syndrome was induced in cynomolgus monkeys by daily administrations of MPTP. Evaluation of the animals included scoring with the Primate Parkinsonism Motor Rating Scale (PPMRS) and assessment of locomotor activity. MPTP produced a stable Parkinson's-like behavioural syndrome as evidenced by tremor, postural changes, rigidity, impaired movements and balance, (PPMRS scores of 10-15) and decreased locomotor activity (13% of pre-MPTP values). Opicapone treatment alone, for 14 days, did not change Parkinson's-like symptoms nor decreased subject's locomotor behaviour. Ascending combinations of levodopa/benserazide dose-dependently decreased PPMRS and improved locomotor behaviour reaching statistical significance for levodopa/benserazide doses of 18/4.5 mg/kg and those effects were enhanced in opicapone treated subjects. Opicapone treated subjects as compared vehicle-treated, had markedly reduced erythrocyte catechol-O-methyltransferase activity, significantly increased plasma levodopa levels (1.8-fold higher AUC) with no statistically significant changes in C_max and significantly reduced 3-OMD AUC and C_max values (7.8- and 6.8-fold respectively). Opicapone potentiated the improvements in Parkinson's-like symptoms produced by levodopa/benserazide combinations with concomitant increase in plasma levodopa exposure, reduction of plasma 3-O-methyldopa levels and erythrocyte catechol-O-methyltransferase activity, results that were later demonstrated in 2 large Phase 3 studies in Parkinson's disease patients.

Impaired Hand Dexterity Function in a Non-human Primate Model with Chronic Parkinson's Disease

Symptoms of Parkinson’s disease (PD) caused by loss of dopaminergic neurons are accompanied by movement disorders, including tremors, rigidity, bradykinesia, and akinesia. Non-human primate (NHP) models with PD play an essential role in the analysis of PD pathophysiology and behavior symptoms. As impairments of hand dexterity function can affect activities of daily living in patients with PD, research on hand dexterity function in NHP models with chronic PD is essential. Traditional rating scales previously used in the evaluation of animal spontaneous behavior were insufficient due to factors related to subjectivity and passivity. Thus, experimentally designed applications for an appropriate apparatus are necessary. In this study, we aimed to longitudinally assess hand dexterity function using hand dexterity task (HDT) in NHP-PD models. To validate this assessment, we analyzed the alteration in Parkinsonian tremor signs and the functionality of presynaptic dopaminergic neuron using positron emission tomography imaging of dopamine transporters in these models. In addition, a significant inverse correlation between HDT and DAT level was identified, but no local bias was found. The correlation with intention tremor signs was lower than the resting tremor. In conclusion, the evaluation of HDT may reflect behavioral symptoms of NHP-PD models. Furthermore, HDT was effectively used to experimentally distinguish intention tremors from other tremors.

Striatal Oscillations in Parkinsonian Non-Human Primates

Dopamine loss in Parkinson's disease (PD) is associated with abnormal oscillatory activity in the cortico-basal ganglia network. However, the oscillatory pattern of striatal neurons in PD remains poorly defined. Here, we analyzed the local field potentials in one untreated and five MPTP-treated non-human primates (NHP) with chronic, advanced parkinsonism. Oscillatory activities in the alpha (8-13 Hz) and low-beta (13-20 Hz) frequency bands were found in the striatum similarly to the motor cortex and globus pallidus of the NHP model of PD. Both alpha and low-beta frequency band oscillations of the striatum were highly coherent with the cortical and pallidal oscillations, confirming the presence of abnormal 8-20 Hz oscillatory activity in the cortico-basal ganglia network in parkinsonian NHPs. The reversal of parkinsonism induced by acute levodopa administration was associated with reduced 8-20 Hz oscillations in the striatum. These findings indicate that pathological oscillations at alpha and low-beta bands are also present in the striatum concordant with basal ganglia network changes in the primate model of PD.

Chronic Infiltration of T Lymphocytes into the Brain in a Non-human Primate Model of Parkinson's Disease

Study of interactions between the nervous system and immunity offers insights into the pathogenesis of Parkinson's disease (PD) and potential therapeutic strategies for neurodegenerative diseases. Studies on rodents have revealed regulatory mechanisms of microglial activation and T lymphocyte recruitment in PD. However, the mechanisms underlying chronic T lymphocyte infiltration into the brain after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) injection into a non-human primate (NHP) model of PD remain unknown. This study aimed to investigate changes in serum RANTES (regulated on activation, normal T cell expression and secretion) and analyze the chronic infiltration of T lymphocytes into the brain and microglia activation in NHPs at 48 weeks post-MPTP administration. We found selective and local chronic infiltration of CD4+ and CD8+ T lymphocytes, loss of dopaminergic neurons, dopamine transporter expression, chronic normalization of RANTES in the peripheral blood, and altered microglial morphology at 48 weeks after MPTP injection. This study confirms the involvement of CD4+ and CD8+ T lymphocyte infiltration in MPTP-induced NHP models of PD. Additionally, we corroborated previous findings regarding the mechanisms of T lymphocyte-induced neurodegeneration. The findings of chronic infiltration of T lymphocytes in our NHP model of PD provide novel insights into PD pathogenesis and the development of preventive and therapeutic agents.

A pilot study on assessment of locomotor behavior using a video tracking system in minipigs

Pigs are often selected for large animal models including for neuroscience and behavioral research, because their anatomy and biochemistry are similar to those of humans. However, behavioral assessments, in combination with objective long-term monitoring, is difficult. In this study, we introduced an automated video tracking system which was previously used in rodent studies, for use with pig models. Locomotor behaviors (total distance, number of zone transitions, and velocity) were evaluated and their changes were validated by different 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration methods and dosing regimens. Three minipigs (23-29 kg) received subcutaneous or intravenous MPTP, either 1 or 3 times per week. Immediately after MPTP injection, the minipigs remained in a corner and exhibited reduced trajectory. In addition, the total distance travelled, number of zone transitions, and velocity were greatly reduced at every MPTP administration in all the minipigs, accompanying to increased resting time. However, the MPTP-induced symptoms were reversed when MPTP administration was terminated. In conclusion, this automated video-tracking system was able to monitor long-term locomotor activity and differentiate detailed alterations in large animals. It has the advantages of being easy to use, higher resolution, less effort, and more delicate tracking. Additionally, as our method can be applied to the animals' home pen, no habituation is needed.

Advancement in the modelling and therapeutics of Parkinson's disease

Since the discovery of L-dopa in the middle of the 20th century (1960s), there is not any neuroprotective therapy available although significant development has been made in the treatment of symptomatic Parkinson's disease (PD). Neurological disorders like PD can be modelled in animals so as to recapitulates most of the symptoms seen in PD patients. In aging population, PD is the second most common neurodegenerative disease after Alzheimer's disease, even though significant outcomes have been achieved in PD research yet it still is a mystery to solve the treatments for PD. In the last two decades, PD models have provided enhanced precision into the understanding of the process of PD disease, its etiology, pathology, and molecular mechanisms behind it. Furthermore, at the same time as cellular models have helped to recognize specific events, animal models, both toxic and genetic, have replicated almost all of the hallmarks of PD and are very helpful for testing and finding new strategies for neuroprotection. Recently, in both classical and newer models, major advances have been done in the modelling of supplementary PD features have come into the light. In this review, we have try to provide an updated summary of the characteristics of these models related to in vitro and in vivo models, animal models for PD, stem cell model for PD, newer 3D model as well as the strengths and limitations of these most popular PD models.

Quantitative whole-brain 3D imaging of tyrosine hydroxylase-labeled neuron architecture in the mouse MPTP model of Parkinson's disease

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.

Summary: Whole-brain immunolabeling, mapping and absolute quantification of tyrosine hydroxylase neurons in the adult mouse brain provides a useful tool for studying changes in dopaminergic signaling in a mouse model of PD.

The Rodent Models of Dyskinesia and Their Behavioral Assessment

Dyskinesia, a major motor complication resulting from dopamine replacement treatment, manifests as involuntary hyperkinetic or dystonic movements. This condition poses a challenge to the treatment of Parkinson's disease. So far, several behavioral models based on rodent with dyskinesia have been established. These models have provided an important platform for evaluating the curative effect of drugs at the preclinical research level over the past two decades. However, there are differences in the modeling and behavioral testing procedures among various laboratories that adversely affect the rat and mouse models as credible experimental tools in this field. This article systematically reviews the history, the pros and cons, and the controversies surrounding rodent models of dyskinesia as well as their behavioral assessment protocols. A summary of factors that influence the behavioral assessment in the rodent dyskinesia models is also presented, including the degree of dopamine denervation, stereotaxic lesion sites, drug regimen, monitoring styles, priming effect, and individual and strain differences. Besides, recent breakthroughs like the genetic mouse models and the bilateral intoxication models for dyskinesia are also discussed.

Role of striatal ΔFosB in l-Dopa-induced dyskinesias of parkinsonian nonhuman primates

Long-term dopamine (DA) replacement therapy in Parkinson's disease (PD) leads to the development of abnormal involuntary movements known as l-Dopa-induced dyskinesia (LID). The transcription factor ΔFosB that is highly up-regulated in the striatum following chronic l-Dopa exposure may participate in the mechanisms of altered neuronal responses to DA generating LID. To identify intrinsic effects of elevated ΔFosB on l-Dopa responses, we induced transgenic ΔFosB overexpression in the striatum of parkinsonian nonhuman primates kept naïve of l-Dopa treatment. Elevated ΔFosB levels led to consistent appearance of LID since the initial acute l-Dopa tests. In line with this motor response, striatal projection neurons (SPNs) responded to DA with changes in firing frequency that reversed at the peak of the motor response, and these unstable SPN activity changes in response to DA are typically associated with the emergence of LID. Transgenic ΔFosB overexpression also induced up-regulation of other molecular markers of LID. These results support an autonomous role of striatal ΔFosB in the adaptive mechanisms altering motor responses to chronic DA replacement in PD.

Sensory neuropathy and nociception in rodent models of Parkinson's disease

Parkinson's disease (PD) often manifests with prodromal pain and sensory losses whose etiologies are not well understood. Multiple genetic and toxicity-based rodent models of PD partly recapitulate the histopathology and motor function deficits. Although far less studied, there is some evidence that rodents, similar to humans, develop sensory manifestations of the disease, which may precede motor disturbances and help to elucidate the underlying mechanisms of PD-associated pain at the molecular and neuron circuit levels. The present Review summarizes nociception and other sensory functions in frequently used rodent PD models within the context of the complex phenotypes. In terms of mechanisms, it appears that the acute loss of dopaminergic neurons in systemic toxicity models (MPTP, rotenone) primarily causes nociceptive hyperexcitability, presumably owing to a loss of inhibitory control, whereas genetic models primarily result in a progressive loss of heat perception, reflecting sensory fiber neuropathies. At the molecular level, neither α-synuclein deposits alone nor failure of mitophagy alone appear to be strong enough to result in axonal or synaptic pathology of nociceptive neurons that manifest at the behavioral level, and peripheral sensory loss may mask central ‘pain’ in behavioral tests. Hence, allostatic combinations or additional challenges and novel behavioral assessments are needed to better evaluate PD-associated sensory neuropathies and pain in rodents.

Summary: Rodent models of Parkinson's disease partially develop prodromal somatosensory and olfactory dysfunctions reminiscent of sensory neuropathies in patients and reveal mechanistic insight, but data are incomplete and fragmented.

Fine Manual Dexterity Assessment After Autologous Neural Cell Ecosystem (ANCE) Transplantation in a Non-human Primate Model of Parkinson's Disease

Background. Autologous neural cell ecosystem (ANCE) transplantation improves motor recovery in MPTP monkeys. These motor symptoms were assessed using semi-quantitative clinical rating scales, widely used in many studies. However, limitations in terms of sensitivity, combined with relatively subjective assessment of their different items, make inter-study comparisons difficult to achieve. Objective. The aim of this study was to quantify the impact of MPTP intoxication in macaque monkeys on manual dexterity and assess whether ANCE can contribute to functional recovery. Methods. Four animals were trained to perform 2 manual dexterity tasks. After reaching a motor performance plateau, the animals were subjected to an MPTP lesion. After the occurrence of a spontaneous functional recovery plateau, all 4 animals were subjected to ANCE transplantation. Results. Two of 4 animals underwent a full spontaneous recovery before the ANCE transplantation, whereas the 2 other animals (symptomatic) presented moderate to severe Parkinson's disease (PD)-like symptoms affecting manual dexterity. The time to grasp small objects using the precision grip increased in these 2 animals. After ANCE transplantation, the 2 symptomatic animals underwent a significant functional recovery, reflected by a decrease in time to execute the different tasks, as compared with the post-lesion phase. Conclusions. Manual dexterity is affected in symptomatic MPTP monkeys. The 2 manual dexterity tasks reported here as pilot are pertinent to quantify PD symptoms and reliably assess a treatment in MPTP monkeys, such as the present ANCE transplantation, to be confirmed in a larger cohort of animals before future clinical applications.

Abnormal Mitochondria in a Non-human Primate Model of MPTP-induced Parkinson's Disease: Drp1 and CDK5/p25 Signaling

Mitochondria continuously fuse and divide to maintain homeostasis. An impairment in the balance between the fusion and fission processes can trigger mitochondrial dysfunction. Accumulating evidence suggests that mitochondrial dysfunction is related to neurodegenerative diseases such as Parkinson's disease (PD), with excessive mitochondrial fission in dopaminergic neurons being one of the pathological mechanisms of PD. Here, we investigated the balance between mitochondrial fusion and fission in the substantia nigra of a non-human primate model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD. We found that MPTP induced shorter and abnormally distributed mitochondria. This phenomenon was accompanied by the activation of dynamin-related protein 1 (Drp1), a mitochondrial fission protein, through increased phosphorylation at S616. Thereafter, we assessed for activation of the components of the cyclin-dependent kinase 5 (CDK5) and extracellular signal-regulated kinase (ERK) signaling cascades, which are known regulators of Drp1(S616) phosphorylation. MPTP induced an increase in p25 and p35, which are required for CDK5 activation. Together, these findings suggest that the phosphorylation of Drp1(S616) by CDK5 is involved in mitochondrial fission in the substantia nigra of a non-human primate model of MPTP-induced PD.

The Potential of L-Type Calcium Channels as a Drug Target for Neuroprotective Therapy in Parkinson's Disease

The motor symptoms of Parkinson's disease (PD) mainly arise from degeneration of dopamine neurons within the substantia nigra. As no disease-modifying PD therapies are available, and side effects limit long-term benefits of current symptomatic therapies, novel treatment approaches are needed. The ongoing phase III clinical study STEADY-PD is investigating the potential of the dihydropyridine isradipine, an L-type Ca²⁺ channel (LTCC) blocker, for neuroprotective PD therapy. Here we review the clinical and preclinical rationale for this trial and discuss potential reasons for the ambiguous outcomes of in vivo animal model studies that address PD-protective dihydropyridine effects. We summarize current views about the roles of Cav1.2 and Cav1.3 LTCC isoforms for substantia nigra neuron function, and their high vulnerability to degenerative stressors, and for PD pathophysiology. We discuss different dihydropyridine sensitivities of LTCC isoforms in view of their potential as drug targets for PD neuroprotection, and we conclude by considering how these aspects could guide further drug development.

A non-human primate model for stable chronic Parkinson's disease induced by MPTP administration based on individual behavioral quantification

BACKGROUND

The guidelines for applying individual adjustments to macaques according to the severity of behavioral symptoms during 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment were provided to reproduce stable chronic Parkinsonism in a recent study (Potts et al., 2014). But, since there are insufficient guidelines regarding objective severity criteria of individual symptoms for adjustments of MPTP treatment, it is difficult to develop MPTP-induced chronic non-human primate (NHP) models with stable symptoms.

NEW METHOD

The individual adjustments of MPTP administration based on results of automatic quantification of global activity (GA) using a video-based tracking system were applied to develop MPTP-PD model. Low-dose (0.2 mg/kg) intramuscular injection was repeated continuously until GA was lower than 8% of baseline Parkinsonian behavior scores. The positron emission tomography imaging were used to follow the longitudinal course of Parkinson's disease (PD).

RESULTS

Significant reductions in GA and dopamine transporter activity, along with significant increases in Parkinsonian behavior scores were found from 4 to 48 weeks following the first administration. GA was correlated with the Parkinsonian behavior score. The dopamine transporter activity was correlated with GA and the Parkinsonian behavior score. However, it was not correlated with the total dose of MPTP. Damage of dopaminergic neuronal systems in the basal ganglia was confirmed by immunohistochemistry and Western blot.

COMPARISON WITH EXISTING METHOD

This study reinforces previous guidelines regarding production of NHP models with stable Parkinsonian symptoms.

CONCLUSIONS

This novel strategy of MPTP administration based on global activity evaluations provides an important conceptual advance for the development of chronic NHP Parkinsonian models.

Pathophysiology of dyskinesia and behavioral disorders in non-human primates: the role of serotonergic fibers

The MPTP monkey model of Parkinson's disease (PD) has allowed huge advances regarding the understanding of the pathological mechanisms of PD and L-DOPA-induced adverse effects. Among the main findings were the imbalance between the efferent striatal pathways in opposite directions between the hypokinetic and hyperkinetic states of PD. In both normal and parkinsonian monkeys, the combination of behavioral and anatomical studies has allowed the deciphering of the cortico-basal ganglia circuits involved in both movement and behavioral disorders. A major breakthrough has then been made regarding the hypothesis of the involvement of serotonergic fibers in the conversion of L-DOPA to dopamine when dopaminergic neurons are dying and to release it, in an uncontrolled manner, as serotonergic neurons are deprived from the machinery required for buffering dopamine from the synaptic cleft. The crucial involvement of serotonergic fibers underlying L-DOPA-induced dyskinesia (LID) has been demonstrated in both rodent and monkey models of PD, in which dyskinesia induced by L-DOPA is abolished following lesion of the serotonergic system. Moreover, the role of serotonergic fibers goes well beyond dyskinesia, as lesioning of such serotonergic fibers by MDMA in the monkey also decreased other L-DOPA-induced adverse effects such as impulsive compulsive behaviors and visual hallucinations. The same pathological mechanism, i.e., an imbalance between serotonin and dopamine terminals may, therefore, favor L-DOPA-induced adverse effects according to the basal ganglia territory it inhabits. Further non-human primate studies will be needed to demonstrate the role of such a pathological mechanism in both movement and behavioral disorders driven by L-DOPA therapy but also to determine the causal link between serotonin lesions and the expression of non-motor symptoms like apathy, depression and anxiety, frequently observed in PD patients.

Glutamatergic Tuning of Hyperactive Striatal Projection Neurons Controls the Motor Response to Dopamine Replacement in Parkinsonian Primates

Dopamine (DA) loss in Parkinson's disease (PD) alters the function of striatal projection neurons (SPNs) and causes motor deficits, but DA replacement can induce further abnormalities. A key pathological change in animal models and patients is SPN hyperactivity; however, the role of glutamate in altered DA responses remains elusive. We tested the effect of locally applied AMPAR or NMDAR antagonists on glutamatergic signaling in SPNs of parkinsonian primates. Following a reduction in basal hyperactivity by antagonists at either receptor, DA inputs induced SPN firing changes that were stable during the entire motor response, in clear contrast with the typically unstable effects. The SPN activity reduction over an extended putamenal area controlled the release of involuntary movements in the "on" state and therefore improved motor responses to DA replacement. These results demonstrate the pathophysiological role of upregulated SPN activity and support strategies to reduce striatal glutamate signaling for PD therapy.

From Reproducibility to Translation in Neurodegenerative Disease

Despite tremendous investment and preclinical success in neurodegenerative disease, effective disease-altering treatments for patients have remained elusive. One highly cited reason for this discrepancy is flawed animal study design and reporting. If this can be broadly remedied, reproducibility of preclinical studies will improve. However, without concurrent efforts to improve generalizability, these improvements may not translate effectively from animal experiments to more complex human neurodegenerative diseases. Mechanistic and phenotypic variability of neurodegenerative disease is such that most models are only able to interrogate individual aspects of complex phenomena. One approach is to consider animals as models of individual targets rather than as models of individual diseases and to migrate the concept of predictive validity from the individual model to the body of experiments that demonstrate translatability of a target. Both exploratory and therapeutic preclinical studies are dependent upon study design methods that promote rigor and reproducibility. However, the body of evidence that is needed to demonstrate efficacy in therapeutic studies is substantially broader than that needed for exploratory studies. In addition to requiring rigor within individual experiments, convincing evidence for therapeutic potential must assess the relationships between model choice, intended goal of the intervention, pharmacologic criteria, and integration of biomarker data with outcome measures that are clinically relevant to humans. It is conceivable that proof-of-concept studies will migrate to cell-based systems and that animal systems will be increasingly reserved for more distal translational purposes. If this occurs, it is likely to prompt reexamination of what the term "translational" truly means.

Transplantation in the nonhuman primate MPTP model of Parkinson's disease: update and perspectives

In order to calibrate stem cell exploitation for cellular therapy in neurodegenerative diseases, fundamental and preclinical research in NHP (nonhuman primate) models is crucial. Indeed, it is consensually recognized that it is not possible to directly extrapolate results obtained in rodent models to human patients. A large diversity of neurological pathologies should benefit from cellular therapy based on neural differentiation of stem cells. In the context of this special issue of Primate Biology on NHP stem cells, we describe past and recent advances on cell replacement in the NHP model of Parkinson's disease (PD). From the different grafting procedures to the various cell types transplanted, we review here diverse approaches for cell-replacement therapy and their related therapeutic potential on behavior and function in the NHP model of PD.

Chronic MPTP administration regimen in monkeys: a model of dopaminergic and non-dopaminergic cell loss in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder clinically characterized by cardinal motor deficits including bradykinesia, tremor, rigidity and postural instability. Over the past decades, it has become clear that PD symptoms extend far beyond motor signs to include cognitive, autonomic and psychiatric impairments, most likely resulting from cortical and subcortical lesions of non-dopaminergic systems. In addition to nigrostriatal dopaminergic degeneration, pathological examination of PD brains, indeed, reveals widespread distribution of intracytoplasmic inclusions (Lewy bodies) and death of non-dopaminergic neurons in the brainstem and thalamus. For that past three decades, the MPTP-treated monkey has been recognized as the gold standard PD model because it displays some of the key behavioral and pathophysiological changes seen in PD patients. However, a common criticism raised by some authors about this model, and other neurotoxin-based models of PD, is the lack of neuronal loss beyond the nigrostriatal dopaminergic system. In this review, we argue that this assumption is largely incorrect and solely based on data from monkeys intoxicated with acute administration of MPTP. Work achieved in our laboratory and others strongly suggest that long-term chronic administration of MPTP leads to brain pathology beyond the dopaminergic system that displays close similarities to that seen in PD patients. This review critically examines these data and suggests that the chronically MPTP-treated nonhuman primate model may be suitable to study the pathophysiology and therapeutics of some non-motor features of PD.

Improved methods for acrylic-free implants in nonhuman primates for neuroscience research

Traditionally, head fixation devices and recording cylinders have been implanted in nonhuman primates (NHP) using dental acrylic despite several shortcomings associated with acrylic. The use of more biocompatible materials such as titanium and PEEK is becoming more prevalent in NHP research. We describe a cost-effective set of procedures that maximizes the integration of headposts and recording cylinders with the animal's tissues while reducing surgery time. Nine rhesus monkeys were implanted with titanium headposts, and one of these was also implanted with a recording chamber. In each case, a three-dimensional printed replica of the skull was created based on computerized tomography scans. The titanium feet of the headposts were shaped, and the skull thickness was measured preoperatively, reducing surgery time by up to 70%. The recording cylinder was manufactured to conform tightly to the skull, which was fastened to the skull with four screws and remained watertight for 8.5 mo. We quantified the amount of regression of the skin edge at the headpost. We found a large degree of variability in the timing and extent of skin regression that could not be explained by any single recorded factor. However, there was not a single case of bone exposure; although skin retracted from the titanium, skin also remained adhered to the skull adjacent to those regions. The headposts remained fully functional and free of complications for the experimental life of each animal, several of which are still participating in experiments more than 4 yr after implant.NEW & NOTEWORTHY Cranial implants are often necessary for performing neurophysiology research with nonhuman primates. We present methods for using three-dimensional printed monkey skulls to form and fabricate acrylic-free implants preoperatively to decrease surgery times and the risk of complications and increase the functional life of the implant. We focused on reducing costs, creating a feasible timeline, and ensuring compatibility with existing laboratory systems. We discuss the importance of using more biocompatible materials and enhancing osseointegration.

Dysregulation of striatal projection neurons in Parkinson's disease

The loss of nigrostriatal dopamine (DA) is the primary cause of motor dysfunction in Parkinson's disease (PD), but the underlying striatal mechanisms remain unclear. In spite of abundant literature portraying structural, biochemical and plasticity changes of striatal projection neurons (SPNs), in the past there has been a data vacuum from the natural human disease and its close model in non-human primates. Recently, single-cell recordings in advanced parkinsonian primates have generated new insights into the altered function of SPNs. Currently, there are also human data that provide direct evidence of profoundly dysregulated SPN activity in PD. Here, we review primate recordings that are impacting our understanding of the striatal dysfunction after DA loss, particularly through the analysis of physiologic correlates of parkinsonian motor behaviors. In contrast to recordings in rodents, data obtained in primates and patients demonstrate similar major abnormalities of the spontaneous SPN firing in the alert parkinsonian state. Furthermore, these studies also show altered SPN responses to DA replacement in the advanced parkinsonian state. Clearly, there is yet much to learn about the striatal discharges in PD, but studies using primate models are contributing unique information to advance our understanding of pathophysiologic mechanisms.

Loss and remodeling of striatal dendritic spines in Parkinson's disease: from homeostasis to maladaptive plasticity?

In Parkinson's disease (PD) patients and animal models of PD, the progressive degeneration of the nigrostriatal dopamine (DA) projection leads to two major changes in the morphology of striatal projection neurons (SPNs), i.e., a profound loss of dendritic spines and the remodeling of axospinous glutamatergic synapses. Striatal spine loss is an early event tightly associated with the extent of striatal DA denervation, but not the severity of parkinsonian motor symptoms, suggesting that striatal spine pruning might be a form of homeostatic plasticity that compensates for the loss of striatal DA innervation and the resulting dysregulation of corticostriatal glutamatergic transmission. On the other hand, the remodeling of axospinous corticostriatal and thalamostriatal glutamatergic synapses might represent a form of late maladaptive plasticity that underlies changes in the strength and plastic properties of these afferents and the resulting increased firing and bursting activity of striatal SPNs in the parkinsonian state. There is also evidence that these abnormal synaptic connections might contribute to the pathophysiology of L-DOPA-induced dyskinesia. Despite the significant advances made in this field over the last thirty years, many controversial issues remain about the striatal SPN subtypes affected, the role of spine changes in the altered activity of SPNs in the parkinsonisn state, and the importance of striatal spine plasticity in the pathophysiology of L-DOPA-induced dyskinesia. In this review, we will examine the current state of knowledge of these issues, discuss the limitations of the animal models used to address some of these questions, and assess the relevance of data from animal models to the human-diseased condition.

Non-human primate models of PD to test novel therapies

Non-human primate (NHP) models of Parkinson disease show many similarities with the human disease. They are very useful to test novel pharmacotherapies as reviewed here. The various NHP models of this disease are described with their characteristics including the macaque, the marmoset, and the squirrel monkey models. Lesion-induced and genetic models are described. There is no drug to slow, delay, stop, or cure Parkinson disease; available treatments are symptomatic. The dopamine precursor, L-3,4-dihydroxyphenylalanine (L-Dopa) still remains the gold standard symptomatic treatment of Parkinson. However, involuntary movements termed L-Dopa-induced dyskinesias appear in most patients after chronic treatment and may become disabling. Dyskinesias are very difficult to manage and there is only amantadine approved providing only a modest benefit. In this respect, NHP models have been useful to seek new drug targets, since they reproduce motor complications observed in parkinsonian patients. Therapies to treat motor symptoms in NHP models are reviewed with a discussion of their translational value to humans. Disease-modifying treatments tested in NHP are reviewed as well as surgical treatments. Many biochemical changes in the brain of post-mortem Parkinson disease patients with dyskinesias are reviewed and compare well with those observed in NHP models. Non-motor symptoms can be categorized into psychiatric, autonomic, and sensory symptoms. These symptoms are present in most parkinsonian patients and are already installed many years before the pre-motor phase of the disease. The translational usefulness of NHP models of Parkinson is discussed for non-motor symptoms.

Established patterns of animal study design undermine translation of disease-modifying therapies for Parkinson's disease

Translation of disease-modifying therapies in neurodegenerative disease has been disappointing. Parkinson's disease (PD) was used to compare patterns of preclinical study design for symptomatic and potentially disease-modifying interventions. We examined the relationship of model, intervention type and timing, outcomes and outcome measures in 543 animal and human studies (1973-2015) across a contemporary cohort of animal and human interventional studies (n = 445), animal studies for approved interventions (n = 28), animal and human studies for those that failed to translate (n = 70). Detailed study design data were collected for 216 studies in non-human primate (NHP) and rodent toxin-induced models. Species-specific patterns of study design prevailed regardless of whether interventions were symptomatic or potentially disease-modifying. In humans and NHPs, interventions were typically given to both sexes well after the PD phenotype was established, and clinical outcome measures were collected at single (symptomatic) or multiple (disease-modifying) time-points. In rodents, interventions often preceded induction of the model, acute toxic protocols were common, usually given to young males, clinical outcome measures were used less commonly, and outcomes were less commonly assessed at multiple time points. These patterns were more prevalent in mice than rats. In contrast, study design factors such as randomization and blinding did not differ appreciably across symptomatic and disease-modifying intervention categories. The translational gap for potentially disease-modifying interventions in PD in part results from study designs, particularly in mice, that fail to model the progressive nature and relatively late intervention characteristic of PD, or that anchor mechanistic and neuropathologic data to longitudinal clinical outcomes. Even if measures to improve reproducibility are broadly adopted, perpetuation of these norms will continue to impede effective translation.

Effects of a novel phosphodiesterase 10A inhibitor in non-human primates: A therapeutic approach for schizophrenia with improved side effect profile

Schizophrenia symptoms are associated with alterations in basal ganglia-cortical networks that include the cyclic nucleotides (cAMP/cGMP) signaling pathways. Phosphodiesterase 10A (PDE10A) inhibitors have been considered as therapeutic agents for schizophrenia because the regulation of cAMP and cGMP in the striatum by PDE10A plays an important role in the signaling mechanisms of the striatal-cortical network, and thereby in cognitive function. In the present study we assessed in non-human primates (NHPs) the effects of a novel PDE10A inhibitor (FRM-6308) that has demonstrated high potency and selectivity for human recombinant PDE10A in vitro. The behavioral effects of FRM-6308 in a dose range were determined in rhesus monkeys using a standardized motor disability scale for primates, motor tasks, and the "drug effects on the nervous system" (DENS) scale. The neuronal metabolic effects of FRM-6308 were determined with [(18)F]-fluorodeoxyglucose PET imaging. Results showed that FRM-6308 did not have any specific effects on the motor system at s.c. doses up to 0.32 mg/kg in NHPs, which induced a significant increase in the FDG-SUV in striatum (F 16.069, p < 0.05) and cortical (F 15.181, p < 0.05) regions. Higher doses induced sedation and occasional involuntary movements with clear development of tolerance after repeated exposures. These findings suggest that FRM-6308 has the adequate pharmacological profile to advance testing in clinical trials and demonstrate antipsychotic efficacy of PDE10A inhibition for the treatment of schizophrenia patients.

Neuroprotective Effects of 7, 8-dihydroxyflavone on Midbrain Dopaminergic Neurons in MPP+-treated Monkeys

Parkinson’s disease (PD) is one common neurodegenerative disease caused by a significant loss of midbrain dopaminergic neurons. Previous reports showed that 7, 8- dihydroxyflavone (7, 8-DHF) as a potent TrkB agonist can mimic BDNF and play neuroprotective roles for mouse dopaminergic neurons. Nonetheless, the safety and neuroprotective effects are unclear in monkey models of PD. Here, we find that 7, 8-DHF could be absorbed and metabolized into 7-hydroxy-8-methoxyflavone through oral administration in monkeys. The half-life time of 7, 8-DHF in monkey plasma is about 4–8 hrs. Furthermore, these monkeys maintain health state throughout the course of seven-month treatments of 7, 8-DHF (30 mg/kg/day). Importantly, 7, 8-DHF treatments can prevent the progressive degeneration of midbrain dopaminergic neurons by attenuating neurotoxic effects of MPP⁺ and display strong neuroprotective effects in monkeys. Our study demonstrates that this promising small molecule may be transited into a clinical useful pharmacological agent.

Neural substrates and potential treatments for levodopa-induced dyskinesias in Parkinson's disease

Parkinson's disease (PD) is primarily a motor disorder that involves the gradual loss of motor function. Symptoms are observed initially in the extremities, such as hands and arms, while advanced stages of the disease can effect blinking, swallowing, speaking, and breathing. PD is a neurodegenerative disease, with dopaminergic neuronal loss occurring in the substantia nigra pars compacta, thus disrupting basal ganglia functions. This leads to downstream effects on other neurotransmitter systems such as glutamate, γ-aminobutyric acid, and serotonin. To date, one of the main treatments for PD is levodopa. While it is generally very effective, prolonged treatments lead to levodopa-induced dyskinesia (LID). LID encompasses a family of symptoms ranging from uncontrolled repetitive movements to sustained muscle contractions. In many cases, the symptoms of LID can cause more grief than PD itself. The purpose of this review is to discuss the possible clinical features, cognitive correlates, neural substrates, as well as potential psychopharmacological and surgical (including nondopaminergic and deep brain stimulation) treatments of LID.

Advantages of nonhuman primates as preclinical models for evaluating stem cell-based therapies for Parkinson's disease

The derivation of dopaminergic neurons from induced pluripotent stem cells brings new hope for a patient-specific, stem cell-based replacement therapy to treat Parkinson's disease (PD) and related neurodegenerative diseases; and this novel cell-based approach has already proven effective in animal models. However, there are several aspects of this procedure that have yet to be optimized to the extent required for translation to an optimal cell-based transplantation protocol in humans. These challenges include pinpointing the optimal graft location, appropriately scaling up the graft volume, and minimizing the risk of chronic immune rejection, among others. To advance this procedure to the clinic, it is imperative that a model that accurately and fully recapitulates characteristics most pertinent to a cell-based transplantation to the human brain is used to optimize key technical aspects of the procedure. Nonhuman primates mimic humans in multiple ways including similarities in genomics, neuroanatomy, neurophysiology, immunogenetics, and age-related changes in immune function. These characteristics are critical to the establishment of a relevant model in which to conduct preclinical studies to optimize the efficacy and safety of cell-based therapeutic approaches to the treatment of PD. Here we review previous studies in rodent models, and emphasize additional advantages afforded by nonhuman primate models in general, and the baboon model in particular, for preclinical optimization of cell-based therapeutic approaches to the treatment of PD and other neurodegenerative diseases. We outline current unresolved challenges to the successful application of stem cell therapies in humans and propose that the baboon model in particular affords a number of traits that render it most useful for preclinical studies designed to overcome these challenges.

Subthalamic, not striatal, activity correlates with basal ganglia downstream activity in normal and parkinsonian monkeys

The striatum and the subthalamic nucleus (STN) constitute the input stage of the basal ganglia (BG) network and together innervate BG downstream structures using GABA and glutamate, respectively. Comparison of the neuronal activity in BG input and downstream structures reveals that subthalamic, not striatal, activity fluctuations correlate with modulations in the increase/decrease discharge balance of BG downstream neurons during temporal discounting classical condition task. After induction of parkinsonism with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), abnormal low beta (8-15 Hz) spiking and local field potential (LFP) oscillations resonate across the BG network. Nevertheless, LFP beta oscillations entrain spiking activity of STN, striatal cholinergic interneurons and BG downstream structures, but do not entrain spiking activity of striatal projection neurons. Our results highlight the pivotal role of STN divergent projections in BG physiology and pathophysiology and may explain why STN is such an effective site for invasive treatment of advanced Parkinson's disease and other BG-related disorders.

DOI:http://dx.doi.org/10.7554/eLife.16443.001

The symptoms of Parkinson’s disease include tremor and slow movement, as well as loss of balance, depression and problems with sleep and memory. The death of neurons in a region of the brain called the substantia nigra pars compacta is one of the major hallmarks of Parkinson’s disease. These neurons produce a chemical called dopamine, and their death reduces dopamine levels in another area of the brain called the striatum. This structure is one of five brain regions known collectively as the basal ganglia, which form a circuit that helps to control movement.

The most effective treatment currently available for advanced Parkinson’s disease entails lowering electrodes deep into the brain in order to shut down the activity of part of the basal ganglia. However, the target is not the striatum; instead it is a structure called the subthalamic nucleus. The striatum and the subthalamic nucleus are the two input regions of the basal ganglia: each sends signals to the other three structures downstream. So why does targeting the subthalamic nucleus, but not the striatum, reduce the symptoms of Parkinson’s disease?

To shed some light on this issue, Deffains et al. recorded the activity of neurons in the basal ganglia before and after injecting two monkeys with a drug called MPTP. Related to heroin, MPTP produces symptoms in animals that resemble those of Parkinson’s disease. Before the injections, spontaneous fluctuations in the activity of the subthalamic nucleus produced matching changes in the activity of the three downstream basal ganglia structures. Fluctuations in the activity of the striatum, by contrast, had no such effect. Moreover, injecting the monkeys with MPTP caused the basal ganglia to fire in an abnormal highly synchronized rhythm, similar to that seen in Parkinson’s disease. Crucially, the subthalamic nucleus contributed to this abnormal rhythm, whereas the striatum did not.

The results presented by Deffains et al. provide a concrete explanation for why inactivating the subthalamic nucleus, but not the striatum, reduces the symptoms of Parkinson’s disease. Further research is now needed to explore how the striatum controls the activity of downstream regions of the basal ganglia, both in healthy people and in those with Parkinson's disease.

DOI:http://dx.doi.org/10.7554/eLife.16443.002

Human striatal recordings reveal abnormal discharge of projection neurons in Parkinson's disease

Circuitry models of Parkinson's disease (PD) are based on striatal dopamine loss and aberrant striatal inputs into the basal ganglia network. However, extrastriatal mechanisms have increasingly been the focus of attention, whereas the status of striatal discharges in the parkinsonian human brain remains conjectural. We now report the activity pattern of striatal projection neurons (SPNs) in patients with PD undergoing deep brain stimulation surgery, compared with patients with essential tremor (ET) and isolated dystonia (ID). The SPN activity in ET was very low (2.1 ± 0.1 Hz) and reminiscent of that found in normal animals. In contrast, SPNs in PD fired at much higher frequency (30.2 ± 1.2 Hz) and with abundant spike bursts. The difference between PD and ET was reproduced between 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated and normal nonhuman primates. The SPN activity was also increased in ID, but to a lower level compared with the hyperactivity observed in PD. These results provide direct evidence that the striatum contributes significantly altered signals to the network in patients with PD.

Adapting Preclinical Benchmarks for First-in-Human Trials of Human Embryonic Stem Cell-Based Therapies

: As research on human embryonic stem cell (hESC)-based therapies is moving from the laboratory to the clinic, there is an urgent need to assess when it can be ethically justified to make the step from preclinical studies to the first protocols involving human subjects. We examined existing regulatory frameworks stating preclinical requirements relevant to the move to first-in-human (FIH) trials and assessed how they may be applied in the context of hESC-based interventions to best protect research participants. Our findings show that some preclinical benchmarks require rethinking (i.e., identity, purity), while others need to be specified (i.e., potency, viability), owing to the distinctive dynamic heterogeneity of hESC-based products, which increases uncertainty and persistence of safety risks and allows for limited predictions of effects in vivo. Rethinking or adaptation of how to apply preclinical benchmarks in specific cases will be required repeatedly for different hESC-based products. This process would benefit from mutual learning if researchers included these components in the description of their methods in publications.

SIGNIFICANCE

To design translational research with an eye to protecting human participants in early trials, researchers and regulators need to start their efforts at the preclinical stage. Existing regulatory frameworks for preclinical research, however, are not really adapted to this in the case of stem cell translational medicine. This article reviews existing regulatory frameworks for preclinical requirements and assesses how their underlying principles may best be applied in the context of human embryonic stem cell-based interventions for the therapy of Parkinson's disease. This research will help to address the question of when it is ethically justified to start first-in-human trials in stem cell translational medicine.

Repertoire comparison of the B-cell receptor-encoding loci in humans and rhesus macaques by next-generation sequencing

Rhesus macaques (RMs) are a widely used model system for the study of vaccines, infectious diseases and microbial pathogenesis. Their value as a model lies in their close evolutionary relationship to humans, which, in theory, allows them to serve as a close approximation of the human immune system. However, despite their prominence as a human surrogate model system, many aspects of the RM immune system remain ill characterized. In particular, B cell-mediated immunity in macaques has not been sufficiently characterized, and the B-cell receptor-encoding loci have not been thoroughly annotated. To address these gaps, we analyzed the circulating heavy- and light-chain repertoires in humans and RMs by next-generation sequencing. By comparing V gene segment usage, J-segment usage and CDR3 lengths between the two species, we identified several important similarities and differences. These differences were especially notable in the IgM(+) B-cell repertoire. However, the class-switched, antigen-educated B-cell populations converged on a set of similar characteristics, implying similarities in how each species responds to antigen. Our study provides the first comprehensive overview of the circulating repertoires of the heavy- and light-chain sequences in RMs, and provides insight into how they may perform as a model system for B cell-mediated immunity in humans.

Animal behavioral assessments in current research of Parkinson's disease

Parkinson's disease (PD), a neurodegenerative disorder, is traditionally classified as a movement disorder. Patients typically suffer from many motor dysfunctions. Presently, clinicians and scientists recognize that many non-motor symptoms are associated with PD. There is an increasing interest in both motor and non-motor symptoms in clinical studies on PD patients and laboratory research on animal models that imitate the pathophysiologic features and symptoms of PD patients. Therefore, appropriate behavioral assessments are extremely crucial for correctly understanding the mechanisms of PD and accurately evaluating the efficacy and safety of novel therapies. This article systematically reviews the behavioral assessments, for both motor and non-motor symptoms, in various animal models involved in current PD research. We addressed the strengths and weaknesses of these behavioral tests and their appropriate applications. Moreover, we discussed potential mechanisms behind these behavioral tests and cautioned readers against potential experimental bias. Since most of the behavioral assessments currently used for non-motor symptoms are not particularly designed for animals with PD, it is of the utmost importance to greatly improve experimental design and evaluation in PD research with animal models. Indeed, it is essential to develop specific assessments for non-motor symptoms in PD animals based on their characteristics. We concluded with a prospective view for behavioral assessments with real-time assessment with mobile internet and wearable device in future PD research.

Contributions of Nonhuman Primates to Research on Aging

Aging is the biological process of declining physiologic function associated with increasing mortality rate during advancing age. Humans and higher nonhuman primates exhibit unusually longer average life spans as compared with mammals of similar body mass. Furthermore, the population of humans worldwide is growing older as a result of improvements in public health, social services, and health care systems. Comparative studies among a wide range of organisms that include nonhuman primates contribute greatly to our understanding about the basic mechanisms of aging. Based on their genetic and physiologic relatedness to humans, nonhuman primates are especially important for better understanding processes of aging unique to primates, as well as for testing intervention strategies to improve healthy aging and to treat diseases and disabilities in older people. Rhesus and cynomolgus macaques are the predominant monkeys used in studies on aging, but research with lower nonhuman primate species is increasing. One of the priority topics of research about aging in nonhuman primates involves neurologic changes associated with cognitive decline and neurodegenerative diseases. Additional areas of research include osteoporosis, reproductive decline, caloric restriction, and their mimetics, as well as immune senescence and chronic inflammation that affect vaccine efficacy and resistance to infections and cancer. The purpose of this review is to highlight the findings from nonhuman primate research that contribute to our understanding about aging and health span in humans.

Behavior, PET and histology in novel regimen of MPTP marmoset model of Parkinson's disease for long-term stem cell therapy

Stem cell technologies are particularly attractive in Parkinson's disease (PD) research although they occasionally need long-term treatment for anti-parkinsonian activity. Unfortunately, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) widely used as a model for PD has several limitations, including the risk of dose-dependent mortality and the difficulty of maintenance of PD symptoms during the whole experiment period. Therefore, we tested if our novel MPTP regimen protocol (2 mg/kg for 2 consecutive days and 1 mg/kg for next 3 consecutive days) can be maintained stable parkinsonism without mortality for long-term stem cell therapy. For this, we used small-bodied common marmoset monkeys (Callithrix jacchus) among several nonhuman primates showing high anatomical, functional, and behavioral similarities to humans. Along with no mortality, the behavioral changes involved in PD symptoms were maintained for 32 weeks. Also, the loss of jumping ability of the MPTP-treated marmosets in the Tower test was not recovered by 32 weeks. Positron emission tomography (PET) analysis revealed that remarkable decreases of bindings of 18F-FP-CIT were observed at the striatum of the brains of the marmosets received MPTP during the full period of the experiment for 32 weeks. In the substantia nigra of the marmosets, the loss of tyrosine hydroxylase (TH) immunoreactivity was also observed at 32 weeks following the MPTP treatment. In conclusion, our low-dose MPTP regimen protocol was found to be stable parkinsonism without mortality as evidenced by behavior, PET, and TH immunohistochemistry. This result will be useful for evaluation of possible long-term stem cell therapy for anti-parkinsonian activity.

The temporary and accumulated effects of transcranial direct current stimulation for the treatment of advanced Parkinson's disease monkeys

Transcranial direct current stimulation (tDCS) is a useful noninvasive technique of cortical brain stimulation for the treatment of neurological disorders. Clinical research has demonstrated tDCS with anodal stimulation of primary motor cortex (M1) in Parkinson’s disease (PD) patients significantly improved their motor function. However, few studies have been focused on the optimization of parameters which contributed significantly to the treatment effects of tDCS and exploration of the underline neuronal mechanisms. Here, we used different stimulation parameters of anodal tDCS on M1 for the treatment of aged advanced PD monkeys induced with 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) administration, and then analyzed the temporary and accumulated effects of tDCS treatment. The results indicated anodal tDCS on M1 very significantly improved motor ability temporarily; importantly, the treatment effects of anodal tDCS on M1 were quantitatively correlated to the accumulated stimulation instead of the stimuli intensity or duration respectively. In addition, c-fos staining showed tDCS treatment effects activated the neurons both in M1 and substantia nigra (SN). Therefore, we propose that long time and continue anodal tDCS on M1 is a better strategy to improve the motor symptoms of PD than individual manipulation of stimuli intensity or duration.

1-Methyl-4-phenylpyridinium stereotactic infusion completely and specifically ablated the nigrostriatal dopaminergic pathway in rhesus macaque

Introduction

Complete and specific ablation of a single dopaminergic (DA) pathway is a critical step to distinguish the roles of DA pathways in vivo. However, this kind of technique has not been reported in non-human primates. This study aimed to establish a lesioning method with a complete and specific ablation.

Method

A carefully designed infusion route based on a MRI stereotactic technique was developed to deliver the highly selective dopaminergic toxin 1-methyl-4-phenylpyridinium (MPP⁺) unilaterally into multiple sites of compact part of substantia nigra (SNc) and striatum in monkeys. The nigrostriatal DA pathway was selected because lesioning of this pathway may induce symptoms that are suitable for evaluation. The pathological, behavioral, neuropharmacological, and clinical laboratorial data were collected to evaluate the lesioning effects.

Result

Pathological examination revealed a complete ablation of tyrosine hydroxylase positive (TH+) neurons in the SNc, while preserving intact TH+ neurons in the ventral tegmental area (VTA) nearby. TH+ projections in the striatum were also unilaterally lost. The monkeys displayed stable (>28 weeks) rotations and symptoms which were expected with loss of DA neurons in the SNc, with rest tremor being an exception. No item implied the presence of a severe side effect caused by the operation or the intracerebral MPP⁺ infusion. The results suggested that rest tremor may not directly rely on the nigrostriatal pathway.

Conclusion

Taken together, in addition to providing a specific nigrostriatal DA lesioned model, this method, combined with brain stimulation or other techniques, can be applied as a powerful tool for the complete lesion of any desired DA pathway in order to study its specific functions in the brain.

A quantitative approach to developing Parkinsonian monkeys (Macaca fascicularis) with intracerebroventricular 1-methyl-4-phenylpyridinium injections

BACKGROUND

Non-human primate Parkinson's disease (PD) models are essential for PD research. The most extensively used PD monkey models are induced with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). However, the modeling processes of developing PD monkeys cannot be quantitatively controlled with MPTP. Therefore, a new approach to quantitatively develop chronic PD monkey models will help to advance the goals of "reduction, replacement and refinement" in animal experiments.

NEW METHOD

A novel chronic PD monkey models was reported using the intracerebroventricular administration of 1-methyl-4-phenylpyridinium (MPP(+)) in Cynomolgus monkeys (Macaca fascicularis).

RESULTS

This approach successfully produced stable and consistent PD monkeys with typical motor symptoms and pathological changes. More importantly, a sigmoidal relationship (Y=8.15801e(-0.245/x); R=0.73) was discovered between PD score (Y) and cumulative dose of MPP(+) (X). This relationship was then used to develop two additional PD monkeys under a specific time schedule (4 weeks), with planned PD scores (7) by controlling the dose and frequency of the MPP(+) administration as an independent validation of the formula.

COMPARISON WITH EXISTING METHOD(S)

We developed Parkinsonian monkeys within controlled time frames by regulating the accumulated dose of MPP(+) intracerebroventricular administered, while limiting side effects often witnessed in models developed with the peripheral administration of MPTP, makes this model highly suitable for treatment development.

CONCLUSIONS

This novel approach provides an edge in evaluating the mechanisms of PD pathology associated with environmental toxins and novel treatment approaches as the formula developed provides a "map" to control and predict the modeling processes.

A new quantitative rating scale for dyskinesia in nonhuman primates

The aim of this study was to develop a quantitative scale to assess levodopa-induced dyskinesias (LIDs) in nonhuman primates using a video-based scoring system [Quantitative Dyskinesia Scale (QDS)]. Six macaques with stable Parkinsonism and LID were used for tests of the new QDS, in comparison with our current standardized scale (Drug-Related Side effects), which provides a classic subjective measurement of dyskinesia. QDS scoring is based on systematic movement counts in time frames, using videotape recordings. For both scales, body segments scored included each extremity, the trunk, the neck, and the face, and raters were blinded to L-dopa treatments. Comparison of the two scales revealed that their scores are highly correlated with and are parallel to the L-dopa pharmacokinetic profile, although the QDS provided significantly more quantifiable measurements. This remained the case after separating animals into groups of mild and severe dyskinesias. Inter-rater reliability for application of the QDS was confirmed from scores obtained by three examiners. We conclude that the QDS is a quantitative tool for reliably scoring LID in parkinsonian monkeys at all levels of severity of dyskinesia. The application of this new standard for scoring LID in primates will allow for more precise measurements of the effects of experimental treatments and will improve the quality of results obtained in translational studies.

Dopamine regulates distinctively the activity patterns of striatal output neurons in advanced parkinsonian primates

Nigrostriatal dopamine denervation plays a major role in basal ganglia circuitry disarray and motor abnormalities of Parkinson's disease (PD). Studies in rodent and primate models have revealed that striatal projection neurons, namely, medium spiny neurons (MSNs), increase the firing frequency. However, their activity pattern changes and the effects of dopaminergic stimulation in such conditions are unknown. Using single-cell recordings in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated primates with advanced parkinsonism, we studied MSN activity patterns in the transition to different motor states following levodopa administration. In the "off" state (baseline parkinsonian disability), a burst-firing pattern accompanied by prolonged silences (pauses) was found in 34% of MSNs, and 80% of these exhibited a levodopa response compatible with dopamine D1 receptor activation (direct pathway MSNs). This pattern was highly responsive to levodopa given that bursting/pausing almost disappeared in the "on" state (reversal of parkinsonism after levodopa injection), although this led to higher firing rates. Nonbursty MSNs fired irregularly with marked pausing that increased in the on state in the MSN subset with a levodopa response compatible with dopamine D2 receptor activation (indirect pathway MSNs), although the pause increase was not sustained in some units during the appearance of dyskinesias. Data indicate that the MSN firing pattern in the advanced parkinsonian monkey is altered by bursting and pausing changes and that dopamine differentially and inefficiently regulates these behaviorally correlated patterns in MSN subpopulations. These findings may contribute to understand the impact of striatal dysfunction in the basal ganglia network and its role in motor symptoms of PD.

Infinium monkeys: Infinium 450K array for the Cynomolgus macaque (Macaca fascicularis)

The Infinium Human Methylation450 BeadChip Array (Infinium 450K) is a robust and cost-efficient survey of genome-wide DNA methylation patterns. Macaca fascicularis (Cynomolgus macaque) is an important disease model; however, its genome sequence is only recently published, and few tools exist to interrogate the molecular state of Cynomolgus macaque tissues. Although the Infinium 450K is a hybridization array designed to the human genome, the relative conservation between the macaque and human genomes makes its use in macaques feasible. Here, we used the Infinium 450K array to assay DNA methylation in 11 macaque muscle biopsies. We showed that probe hybridization efficiency was related to the degree of sequence identity between the human probes and the macaque genome sequence. Approximately 61% of the Human Infinium 450K probes could be reliably mapped to the Cynomolgus macaque genome and contain a CpG site of interest. We also compared the Infinium 450K data to reduced representation bisulfite sequencing data generated on the same samples and found a high level of concordance between the two independent methodologies, which can be further improved by filtering for probe sequence identity and mismatch location. We conclude that the Infinium 450K array can be used to measure the DNA methylome of Cynomolgus macaque tissues using the provided filters. We also provide a pipeline for validation of the array in other species using a simple BLAST-based sequence identify filter.