Assessment of motor behavior using a video system and a clinical rating scale in parkinsonian monkeys lesioned by MPTP

Spatiotemporal scaling changes in gait in a progressive model of Parkinson's disease

Objective

Gait dysfunction is one of the most difficult motor signs to treat in patients with Parkinson's disease (PD). Understanding its pathophysiology and developing more effective therapies for parkinsonian gait dysfunction will require preclinical studies that can quantitatively and objectively assess the spatial and temporal features of gait.

Design

We developed a novel system for measuring volitional, naturalistic gait patterns in non-human primates, and then applied the approach to characterize the progression of parkinsonian gait dysfunction across a sequence of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatments that allowed for intrasubject comparisons across mild, moderate, and severe stages.

Results

Parkinsonian gait dysfunction was characterized across treatment levels by a slower stride speed, increased time in both the stance and swing phase of the stride cycle, and decreased cadence that progressively worsened with overall parkinsonian severity. In contrast, decreased stride length occurred most notably in the moderate to severe parkinsonian state.

Conclusion

The results suggest that mild parkinsonism in the primate model of PD starts with temporal gait deficits, whereas spatial gait deficits manifest after reaching a more severe parkinsonian state overall. This study provides important context for preclinical studies in non-human primates studying the neurophysiology of and treatments for parkinsonian gait.

Use of adeno-associated virus-mediated delivery of mutant huntingtin to study the spreading capacity of the protein in mice and non-human primates

In order to model various aspects of Huntington's disease (HD) pathology, in particular protein spread, we administered adeno-associated virus (AAV) expressing green fluorescent protein (GFP) or GFP coupled to HTT-Exon1 (19Q or 103Q) to the central nervous system of adult wild-type (WT) mice and non-human primates. All animals underwent behavioral testing and post-mortem analyses to determine the long-term consequences of AAV injection. Both mice and non-human primates demonstrated behavioral changes at 2-3 weeks post-surgery. In mice, these changes were absent after 3 months while in non-human primates, they persisted in the majority of tested animals. Post-mortem analysis revealed that spreading of the aggregates was limited, although the virus did spread between synaptically-connected brain regions. Despite circumscribed spreading, the presence of mHTT generated changes in endogenous huntingtin (HTT) levels in both models. Together, these results suggest that viral expression of mHTTExon1 can induce spreading and seeding of HTT in both mice and non-human primates.

Evidence for the spread of human-derived mutant huntingtin protein in mice and non-human primates

In recent years, substantial evidence has emerged to suggest that spreading of pathological proteins contributes to disease pathology in numerous neurodegenerative disorders. Work from our laboratory and others have shown that, despite its strictly genetic nature, Huntington's disease (HD) may be another condition in which this mechanism contributes to pathology. In this study, we set out to determine if the mutant huntingtin protein (mHTT) present in post-mortem brain tissue derived from HD patients can induce pathology in mice and/or non-human primates. For this, we performed three distinct sets of experiments where homogenates were injected into the brains of adult a) Wild-type (WT) and b) BACHD mice or c) non-human primates. Neuropathological assessments revealed that, while changes in the endogenous huntingtin were not apparent, mHTT could spread between cellular elements and brain structures. Furthermore, behavioural differences only occurred in the animal model of HD which already overexpressed mHTT. Taken together, our results indicate that mHTT derived from human brains has only a limited capacity to propagate between cells and does not depict prion-like characteristics. This contrasts with recent work demonstrating that other forms of mHTT - such as fibrils of a pathological polyQ length or fibroblasts and induced pluripotent stem cells derived from HD cases - can indeed disseminate disease throughout the brain in a prion-like fashion.

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.

Quantification of movement in normal and parkinsonian macaques using video analysis

BACKGROUND

Quantification of spontaneous animal movement can be achieved using analysis of video recordings of the animals. Previous reports of video-based methods are based on outdated computer platforms or require the use of specialized equipment.

NEW METHOD

We developed a video analysis algorithm to quantify movement based on the commonly used MATLAB programming language. The algorithm is based on pixel differences between frames of video footage acquired with a standard video camera.

RESULTS

The new algorithm was validated, analyzing the amount of movements made by monkeys undergoing treatment with the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to induce parkinsonism. We compared the movement quantification generated by the new system of analysis with results obtained with a conventional infrared beam break counting system, a parkinsonism rating scale, and accelerometry-based motion quantification in three rhesus macaques. The information provided by our video analysis method was consistent with that obtained with the first two methods, and more detailed than the third.

COMPARISON WITH EXISTING METHODS

The new method can replace other methods to quantify movement. Although other video analysis methods have been described, some have since been deprecated, or involve the use of specialized hardware. The new method provides a straightforward and fast approach of analyzing the amount of movement in caged experimental animals, using conventional off-the-shelf equipment and moderate computing resources.

CONCLUSIONS

This video analysis method provides an affordable, open access platform to quantify animal movement.

MarmoDetector: A novel 3D automated system for the quantitative assessment of marmoset behavior

BACKGROUND

Callithrix jacchus, generally known as the common marmoset, has recently garnered interest as an experimental primate model for better understanding the basis of human social behavior, architecture and function. Modelling human neurological and psychological diseases in marmosets can enhance the knowledge obtained from rodent research for future pre-clinical studies. Hence, comprehensive and quantitative assessments of marmoset behaviors are crucial. However, systems for monitoring and analyzing marmoset behaviors have yet to be established.

NEW METHOD

In this paper, we present a novel multimodal system, MarmoDetector, for the automated 3D analysis of marmoset behavior under freely moving conditions. MarmoDetector allows the quantitative assessment of marmoset behaviors using computerised tracking analysis techniques that are based on a Kinect system equipped with video recordings, infrared images and depth analysis.

RESULTS

Using MarmoDetector, we assessed behavioral circadian rhythms continuously over several days in home cages. In addition, MarmoDetector detected acute, transient complex behaviors of alcohol injected marmosets.

COMPARISON TO EXISTING METHOD

Compared to 2D recording, MarmoDetector detects activities more precisely and is very sensitive as we could detect behavioral defects specifically induced by alcohol administration.

CONCLUSION

MarmoDetector facilitates the rapid and accurate analysis of marmoset behavior and will enhance research on the neural basis of brain disorders.

Social behavioral changes in MPTP-treated monkey model of Parkinson's disease

Parkinsonian patients experience not only the physical discomfort of motor disorders but also the considerable psychological distress caused by cognitive deficits and behavioral disorders. These two factors can result in a disruption of social relationships during the symptomatic and even the presymptomatic motor states of the disease. However, it remains difficult, if not impossible, to evaluate social relationships in presymptomatic patients. The present study focused on the evaluation of social relationships within a group of female long-tailed macaques during presymptomatic and symptomatic motor states induced by Chronic Low-Dose (CLD) and then Chronic High-Dose (CHD) systemic administration of 1-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (MPTP). Dopaminergic denervation within basal ganglia and cortical areas was evaluated using Positron Emission Tomography (PET) scans with (18)F-DOPA (6-[18F]-fluoro-L-3,4-dihydroxyphenylalanine) radiotracer. Interestingly, social behavioral changes could be identified in the presymptomatic motor state before any motor and/or cognitive impairment occurred. Stronger effects were observed in subordinate animals compared to dominant animals. From baseline state to CLD-presymptomatic motor state, the frequency of emitted affiliative and aggressive behaviors increased. From CLD-presymptomatic to CHD-presymptomatic motor states, the frequency of the three categories of social behaviors (aggressive, submissive and affiliative) decreased. At this time, quantitative data analysis in PET scans highlighted a dopaminergic denervation in the insula and the posterior caudate nucleus. Finally, the frequency of the three categories of social behaviors decreased during the stable-symptomatic motor state compared to baseline and presymptomatic motor states; this was also associated with motor and cognitive disorders and a dopaminergic denervation in all the evaluated cortical and subcortical structures.

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.

Systematic identification and characterization of novel human skin-associated genes encoding membrane and secreted proteins

Through bioinformatics analyses of a human gene expression database representing 105 different tissues and cell types, we identified 687 skin-associated genes that are selectively and highly expressed in human skin. Over 50 of these represent uncharacterized genes not previously associated with skin and include a subset that encode novel secreted and plasma membrane proteins. The high levels of skin-associated expression for eight of these novel therapeutic target genes were confirmed by semi-quantitative real time PCR, western blot and immunohistochemical analyses of normal skin and skin-derived cell lines. Four of these are expressed specifically by epidermal keratinocytes; two that encode G-protein-coupled receptors (GPR87 and GPR115), and two that encode secreted proteins (WFDC5 and SERPINB7). Further analyses using cytokine-activated and terminally differentiated human primary keratinocytes or a panel of common inflammatory, autoimmune or malignant skin diseases revealed distinct patterns of regulation as well as disease associations that point to important roles in cutaneous homeostasis and disease. Some of these novel uncharacterized skin genes may represent potential biomarkers or drug targets for the development of future diagnostics or therapeutics.

Modeling a sensitization stage and a precipitation stage for Parkinson's disease using prenatal and postnatal 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine administration

Idiopathic Parkinson's disease (PD) is a neurodegenerative disorder of mature and older individuals. Since all aged individuals do not develop PD, predisposing conditions may exist that pair with the stress placed on the basal ganglia during aging to produce the symptoms of PD. In this project we used 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to test the hypothesis that a sensitization stage and a precipitating stage underlie idiopathic PD. To induce the sensitization stage, pregnant C57BL/6J mice were treated with MPTP (10 mg/kg/day) during gestation days 8-12 to target the emerging fetal nigrostriatal dopamine neurons. For the precipitating stage, the 3-months old offspring were administered MPTP for 7 days, to simulate the changes that occur during aging. The weights and motor activity of the offspring, high performance liquid chromatography (HPLC) striatal dopamine and its metabolites and Western blot for tyrosine hydroxylase (TH) were determined. Offspring exposed to prenatal MPTP showed lower birth weights that eventually recovered. Prenatal MPTP also reduced motor activity by 10-30%, striatal TH by 38%, dopamine by 14%, homovanillic acid by 16.5% and 3-methoxytyramine by 66%. The postnatal MPTP was more potent in the prenatal MPTP-exposed offspring. MPTP at 10, 20 and 30 mg/kg, dose-relatedly, reduced striatal TH by 9.4%, 48.6% and 82.4% in the prenatal-phosphate buffered saline (PBS) mice and by 48%, 78.7% and 92.7% in the prenatal-MPTP groups. More importantly, postnatal MPTP at 10 mg/kg that showed slight effects on DA, DOPAC, HVA and 3-MT in the prenatal-PBS offspring, showed 69.9%, 80.0%, 48.4% and 65.4% reductions in the prenatal-MPTP mice. The study may identify a new model for PD, and the outcome suggests that some cases of idiopathic PD may have a fetal basis in which early subtle nigrostriatal impairments occurred and PD symptoms are precipitated later by deteriorating changes in the nigrostriatum, that would not caused symptoms in individuals with normal nigrostriatal system.

An objective measurement of locomotion behavior for hemiparkinsonian cynomolgus monkeys

Both clinical rating scales and objective locomotion measurement are critical evaluation for primate models of Parkinson's disease. Video image analysis system which has been widely used for objective measurement of locomotion behavior for systemic models has rarely been applied to hemiparkinsonian primate model. In this study, a video image analysis system provided by Vigie Primates software was used to assess the locomotion behavior of MPTP hemi-lesioned parkinsonian cynomolgus monkeys by intracarotid infusion. Regardless the presence of only hemilateral abnormal movement, this video image analysis system was sensitive enough to demonstrate a significant difference between normal and MPTP hemi-lesioned animal on several aspects of motor behavior depicted by this software, including quantity of movement, duration spent in activity and count of burst activity. Specifically, a newly introduced ratio of duration/count for every type of movements was a sensitive parameter to objectively measure the changes of locomotion behavior in MPTP hemi-lesioned parkinsonian primates. As a result, the ratio of duration/count for the middle activity was decreased and the ratio of duration/count for the freezing activity was increased in MPTP hemi-lesioned animals, which correlated well with clinical rating scores. Our results support that video image analysis system would be a sensitive objective measurement of locomotion behavior for hemi-lesioned parkinsonian monkeys.

Objective quantification of arm rigidity in MPTP-treated primates

Rigidity is a cardinal symptom of Parkinson's disease and is frequently used as an outcome measure in clinical and non-human primate studies examining the effects of medication or surgical intervention. A limitation of current rigidity assessment methods is that they are inherently subjective. To better understand the physiological mechanisms of rigidity and how various therapeutic approaches work, a more objective and quantitative method is needed. In this study, an automated arm rigidity testing (ART) system was developed to objectively quantify rigidity while the primate's limb was moved between two user-specified angles. Recordings of normal force versus elbow-angle were categorized according to area and slope. These quantitative measures of rigidity were investigated in three rhesus macaque monkeys treated with 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine and compared with clinical assessment methods. The ART system incorporates electromyographical recordings that can detect and differentiate active from actual resistance. The ART system detected significant changes in rigidity measures following administration of apomorphine or deep brain stimulation of the globus pallidus internus. The most sensitive measures were total area, extension slope, and flexion slope. The ART system provides precise and reliable measures of rigidity that are objective and quantitative.

The 3R principle and the use of non-human primates in the study of neurodegenerative diseases: the case of Parkinson's disease

The aim of this paper is to offer an ethical perspective on the use of non-human primates in neurobiological studies, using the Parkinson's disease (PD) as an important case study. We refer, as theoretical framework, to the 3R principle, originally proposed by Russell and Burch [Russell, W.M.S., Burch, R.L., 1959. The Principles of Humane Experimental Technique. Universities Federation for Animal Welfare Wheathampstead, England (reprinted in 1992)]. Then, the use of non-human primates in the study of PD will be discussed in relation to the concepts of Replacement, Reduction, and Refinement. Replacement and Reduction result to be the more problematic concept to be applied, whereas Refinement offers relatively more opportunities of improvement. However, although in some cases the 3R principle shows its applicative limits, its value, as conceptual and inspirational tool remains extremely valuable. It suggests to the researchers a series of questions, both theoretical and methodological, which can have the results of improving the quality of life on the experimental models, the quality of the scientific data, and the public perception from the non-scientist community.

Mapping the contribution of single muscles to facial movements in the rhesus macaque

The rhesus macaque (Macaca mulatta) is the most utilized primate model in the biomedical and psychological sciences. Expressive behavior is of interest to scientists studying these animals, both as a direct variable (modeling neuropsychiatric disease, where expressivity is a primary deficit), as an indirect measure of health and welfare, and also in order to understand the evolution of communication. Here, intramuscular electrical stimulation of facial muscles was conducted in the rhesus macaque in order to document the relative contribution of each muscle to the range of facial movements and to compare the expressive function of homologous muscles in humans, chimpanzees and macaques. Despite published accounts that monkeys possess less differentiated and less complex facial musculature, the majority of muscles previously identified in humans and chimpanzees were stimulated successfully in the rhesus macaque and caused similar appearance changes. These observations suggest that the facial muscular apparatus of the monkey has extensive homology to the human face. The muscles of the human face, therefore, do not represent a significant evolutionary departure from those of a monkey species. Thus, facial expressions can be compared between humans and rhesus macaques at the level of the facial musculature, facilitating the systematic investigation of comparative facial communication.

Progressive changes of pre- and post-synaptic dopaminergic biomarkers in conscious MPTP-treated cynomolgus monkeys measured by positronemission tomography

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

The Webcam system: a simple, automated, computer-based video system for quantitative measurement of movement in nonhuman primates

Investigations using models of neurologic disease frequently involve quantifying animal motor activity. We developed a simple method for measuring motor activity using a computer-based video system (the Webcam system) consisting of an inexpensive video camera connected to a personal computer running customized software. Images of the animals are captured at half-second intervals and movement is quantified as the number of pixel changes between consecutive images. The Webcam system allows measurement of motor activity of the animals in their home cages, without devices affixed to their bodies. Webcam quantification of movement was validated by correlation with measures simultaneously obtained by two other methods: measurement of locomotion by interruption of infrared beams; and measurement of general motor activity using portable accelerometers. In untreated squirrel monkeys, correlations of Webcam and locomotor activity exceeded 0.79, and correlations with general activity counts exceeded 0.65. Webcam activity decreased after the monkeys were rendered parkinsonian by treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), but the correlations with the other measures of motor activity were maintained. Webcam activity also correlated with clinical ratings of parkinsonism. These results indicate that the Webcam system is reliable under both untreated and experimental conditions and is an excellent method for quantifying motor activity in animals.

Temporal evolution of mouse striatal gene expression following MPTP injury

The gradual loss of striatal dopamine and dopaminergic neurons residing in the substantia nigra (SN) causes parkinsonism characterized by slow, halting movements, rigidity, and resting tremor when neuronal loss exceeds a threshold of approximately 80%. It is estimated that there is extensive compensation for several years prior to symptom onset, during which vulnerable neurons asynchronously die. Recent evidence would argue that much of the compensatory response of the nigrostriatal system is multimodal including both pre-synaptic and striatal mechanisms. Although parkinsonism may have multiple causes, the classic syndrome, Parkinson's disease (PD), is frequently modeled in small animals by repeated administration of the selective neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Because the MPTP model of PD recapitulates many of the known behavioral and pathological features of human PD, we asked whether the striatal cells of mice treated with MPTP in a semi-chronic paradigm enact a transcriptional program that would help elucidate the response to dopamine denervation. Our findings reveal a time-dependent dysregulation in the striatum of a set of genes whose products may impact both the viability and ability to communicate of dopamine neurons in the SN.

Dysregulation of gene expression in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned mouse substantia nigra

Parkinson's disease pathogenesis proceeds through several phases, culminating in the loss of dopaminergic neurons of the substantia nigra (SN). Although the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of oxidative SN injury is frequently used to study degeneration of dopaminergic neurons in mice and non-human primates, an understanding of the temporal sequence of molecular events from inhibition of mitochondrial complex 1 to neuronal cell death is limited. Here, microarray analysis and integrative data mining were used to uncover pathways implicated in the progression of changes in dopaminergic neurons after MPTP administration. This approach enabled the identification of small, yet consistently significant, changes in gene expression within the SN of MPTP-treated animals. Such an analysis disclosed dysregulation of genes in three main areas related to neuronal function: cytoskeletal stability and maintenance, synaptic integrity, and cell cycle and apoptosis. The discovery and validation of these alterations provide molecular evidence for an evolving cascade of injury, dysfunction, and cell death.

Measurement of motor disability in MPTP-treated macaques using a telemetry system for estimating circadian motor activity

The parkinsonian symptoms of primates after MPTP exposure can be measured by several visual methods (classical motor scores). However, these methods have a subjective bias, especially as regards the evaluation of the motor activity. Computerized monitoring systems represent an unbiased method for measuring the motor disability of monkeys after MPTP administration. In this work the motor activity of monkeys before and after MPTP administration is measured and compared with the activity of a control intact group by means of a telemetry system. A pronounced decrease in motor activity was observed after MPTP administration. These results suggest the monitoring method used is suited for characterizing the motor incapacity and possible improvements following treatments to test different therapies to control Parkinson's disease in MPTP models involving primates.

Antidyskinetic effect of magnesium sulfate in MPTP-lesioned monkeys

The antiparkinsonian action of an NMDA receptor antagonist, magnesium sulfate (50, 100, and 200 mg/kg), alone and in association with levodopa was explored in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned parkinsonian and control rhesus monkeys. At the three doses tested, magnesium sulfate decreased levodopa-induced dyskinesia [cumulative dyskinetic scores after levodopa: 129 +/- 13; after levodopa and magnesium sulfate: 65 +/- 14 (50 mg/kg), P < 0.001; 64 +/- 10 (100 mg/kg), P < 0.001; 66 +/- 21 (200 mg/kg), P < 0.001, compared to levodopa administration alone]. These results show that magnesium sulfate importantly reduces levodopa-induced dyskinesia.

The contribution of the MPTP-treated primate model to the development of new treatment strategies for Parkinson's disease

Current research into Parkinson's disease (PD) is directed at developing novel agents and strategies for improved symptomatic management. The aim of this research is to provide effective and maintained symptom control throughout the course of the disease without loss of efficacy and without priming the basal ganglia for the onset of dyskinesia. To achieve these objectives, it is important to have relevant animal models of PD in which new pharmacological agents and treatment strategies can be assessed prior to clinical assessment. At present, the most effective experimental model of PD is the methyl phenyl tetrahydropyridine (MPTP)-treated primate. Primates treated with MPTP develop motor disturbances resembling those seen in idiopathic PD, including bradykinesia, rigidity and postural abnormalities. In addition, MPTP-treated primates are responsive to all commonly used antiparkinsonian agents and display treatment-associated motor complications such as dyskinesia, wearing-off and on-off, which occur during the long-term treatment of the illness. This review examines how studies conducted in MPTP-treated primates have contributed to the development of dopaminergic therapies. There is now accumulating evidence that the pulsatile manner in which short-acting agents stimulate striatal dopamine receptors is a key contributing factor to the priming of the basal ganglia for dyskinesia induction. It has been suggested that providing more continuous stimulation of dopamine receptors will avoid the development of motor complications, particularly dyskinesia. So far, the actions of all commonly used antiparkinsonian drugs assessed in MPTP-treated primates have proved to be highly predictive of drug action in PD. These primate studies have demonstrated that long-acting dopamine agonists and levodopa given in combination with a catechol-O-methyl transferase (COMT) inhibitor (to increase its relatively short half-life), induce significantly less dyskinesia than occurs with standard levodopa therapy.

Effects of prior apparatus experience and novelty of testing environment on locomotor activity following MK-801

Robust increases in locomotor activity are observed following administration of dizocilpine maleate (MK-801). The present study investigated the effects of prior apparatus experience and manipulation of the testing environment on locomotor activity following peripheral MK-801. Gerbils were given zero or nine sessions of apparatus exposure prior to testing with MK-801 (0.1 mg/kg ip) or saline. Sessions were 10 min in duration and separated by 24 h. As previously reported, naive animals treated with MK-801 were significantly more active relative to controls. Exposure to the apparatus for nine sessions resulted in a significant reduction in MK-801-induced activity, but did not alter the activity levels of control animals. To evaluate the effect of changes to the testing environment, animals previously evaluated in the familiar condition were retested in the identical apparatus relocated to a novel experimental room. MK-801-treated animals exhibited a significant increase in activity when tested in this novel environment while the locomotor activity of control gerbils was not significantly altered. The results illustrate the importance of repetitive testing and environmental changes as moderating variables in studies that evaluate locomotor activity. These data also indicate that the effects of MK-801 on activity are sensitive to prior experience with the apparatus and the novelty of the testing environment.