Chronic Neuroleptic-Induced Parkinsonism Examined With Positron Emission Tomography

BACKGROUND

Neuroleptic drug-induced parkinsonism (NIP) is a leading cause of parkinsonism, particularly in aging. Based on abnormal dopamine transporter scan results, individuals displaying chronic NIP are often diagnosed with Lewy-body Parkinson's disease (PD), but this assumption needs further substantiation.

OBJECTIVE

To quantitate the profile of striatal dopaminergic nerve terminal density in NIP relative to PD.

METHODS

We used the positron emission tomography ligand [¹¹ C](+)-dihydrotetrabenazine targeting vesicular monoamine transporter type 2 (VMAT2) binding sites and collected various clinical parameters (motor ratings, olfaction, polysomnography to document rapid eye movement sleep muscle activity, quantitative sensory testing for pain thresholds) possibly predicting binding results in patients older than age 50 living with schizophrenia spectrum disorders under long-term stable antipsychotic drug treatment, with (N = 11) or without (N = 11) chart documention of chronic NIP, and compared them to healthy volunteers (N = 11) and others medicated for PD (N = 12).

RESULTS

Striatal VMAT2 binding was dichotomous in the NIP group between those with spared (N = 5) or low (N = 6) PD-like values. Striatal binding reduction in the low VMAT2-NIP group was asymmetric without the gradient of maximal involvement in the posterior putamen typical of PD. Anosmia was the only nonmotor parameter measured matching the abnormal striatal VMAT2 binding status.

CONCLUSION

These preliminary observations suggest that striatal VMAT2 binding is abnormal in a fraction of chronic NIP cases and differs in spatial distribution from PD. The possibility of a drug-induced axonopathy and resultant synaptopathy, as well as the evolution of the binding deficit, warrant further longitudinal studies in a large cohort. © 2020 International Parkinson and Movement Disorder Society.

Can We Predict the Motor Performance of Patients With Parkinson's Disease Based on Their Symptomatology?

Introduction: Parkinson's disease hinders the ability of a person to perform daily activities. However, the varying impact of specific symptoms and their interactions on a person's motor repertoire is not understood. The current study investigates the possibility to predict global motor disabilities based on the patient symptomatology and medication.

Methods: A cohort of 115 patients diagnosed with Parkinson's disease (mean age = 67.0 ± 8.7 years old) participated in the study. Participants performed different tasks, including the Timed-Up & Go, eating soup and the Purdue Pegboard test. Performance on these tasks was judged using timing, number of errors committed, and count achieved. K-means method was used to cluster the overall performance and create different motor performance groups. Symptomatology was objectively assessed for each participant from a combination of wearable inertial sensors (bradykinesia, tremor, dyskinesia) and clinical assessment (rigidity, postural instability). A multinomial regression model was derived to predict the performance cluster membership based on the patients' symptomatology, socio-demographics information and medication.

Results: Clustering exposed four distinct performance groups: normal behavior, slightly affected in fine motor tasks, affected only in TUG, and affected in all areas. The statistical model revealed that low to moderate level of dyskinesia increased the likelihood of being in the normal group. A rise in postural instability and rest tremor increase the chance to be affected in TUG. Finally, LEDD did not help distinguishing between groups, but the presence of Amantadine as part of the medication regimen appears to decrease the likelihood of being part of the groups affected in TUG.

Conclusion: The approach allowed to demonstrate the potential of using clinical symptoms to predict the impact of Parkinson's disease on a person's mobility performance.

Cardinal Motor Features of Parkinson's Disease Coexist with Peak-Dose Choreic-Type Drug-Induced Dyskinesia

Background:

Clinical and anecdotal observations propose that patients with Parkinson’s disease (PD) may show drug-induced dyskinesia (DID) concomitantly with cardinal motor features. However, the extent of the concomitant presence of DID and cardinal features remains to be determined.

Objectives:

This cross-sectional study measured peak-dose choreic-type DID in a quantitative manner in patients diagnosed with PD, and determined whether symptoms such as tremor, bradykinesia, rigidity, postural instability or freezing of gait (FoG) were still detectable in these patients.

Methods:

89 patients diagnosed with PD were recruited and assessed using a combination of quantitative measures using inertial measurement units to capture DID, tremor, bradykinesia, and FoG. Clinical evaluations were also used to assess rigidity and postural instability. Motor symptoms of PD were assessed 3 times during the testing period, and a series of activities of daily living were repeated twice, in between clinical tests, during which the level of DID was quantified. Peak-dose was identified as the period during which patients had the highest levels of DID. Levels of tremor, rigidity, bradykinesia, postural instability, and FoG were used to determine the percentage of patients showing these motor symptoms simultaneously with DID.

Results:

72.4% of patients tested presented with measurable DID during the experiment. Rest, postural and kinetic tremor (12.7% , 38.1% , and 15.9% respectively), bradykinesia (28.6% ), rigidity (55.6% ), postural instability (71.4% ) and FoG (9.5% ) were detected simultaneously with DID.

Conclusions:

PD symptomatology remains present in patients showing peak-dose choreic-type DID, illustrating the challenge facing physicians when trying to avoid dyskinesia while attempting to alleviate motor symptoms.

Remnants of Cardinal Symptoms of Parkinson's Disease, Not Dyskinesia, Are Problematic for Dyskinetic Patients Performing Activities of Daily Living

Introduction: The impact of levodopa-induced dyskinesia (LID) on the daily lives of patients with Parkinson's disease (PD) remains to be determined. Furthermore, evidence suggests that cardinal motor symptoms of PD may coexist with LID, but their impact on activities of daily living (ADL) relative to LID is not known. This cross-sectional study aimed at determining the effect of LID and cardinal motor symptoms of PD on ADL in patients who were experiencing peak-dose choreic-type LID.

Method: One hundred and twenty-one patients diagnosed with PD known to experience choreic-type LID were recruited for the study. Patients were asked to perform a set of ADL. Levels of LID, tremor, bradykinesia, and freezing of gait (FoG) were measured using 17 inertial sensors design to capture full body movements, while rigidity, and postural instability were assessed using clinical evaluations. Cognition was also assessed using the mini-mental state examination. Success criteria were set for each ADL using the time needed to perform the task and errors measured in 69 age-gender-matched healthy controls. Binary logistic regressions were used to identify symptoms influencing success or failure for each activity. Receiver operating characteristic curves were computed on each significant symptom, and Youden indexes were calculated to determine the critical level of symptomatology at which the performance significantly changed.

Results: Results show that 97.7% of patients who presented with LID during the experiment also presented with at least one cardinal motor symptom. On average, patients took more time and did more errors during ADL. Multivariate analyses revealed that for the great majority of ADL, LID were not associated with worsening of performance; however, postural instability, tremor, rigidity, and cognitive decline significantly decreased the odds of success.

Conclusions: Residual symptoms of PD, such as tremor, rigidity, and postural instability still present at peak-dose were more problematic than LID in the performance of ADL for patients experiencing slight-to-moderate LID. We also found that cognitive decline was associated with decreased performance in certain tasks. Therefore, a strategy using lower doses of medication to manage LID may be counterproductive since it would not address most of these symptoms already present in patients.

Parkinson's disease patients experiencing peak-dose dyskinesia redistribute involuntary movements throughout their body to improve motor control

INTRODUCTION

In Parkinson's disease (PD), dyskinesia is considered a major side effect of dopamine replacement therapy. Nevertheless, many patients with dyskinesia function adequately.

OBJECTIVE

To study objectively dyskinesia phenomenology in order to understand why or how patients with dyskinesia are still able to perform motor tasks.

METHODS

Patients with and without dyskinesia, as well as healthy older adults, performed a geostationary task during which they attempted to stabilize a glass of water at eye level. Dyskinesia amplitude displayed by each body segment was extracted from accelerometers, and its distribution among the segments, analyzed.

RESULTS

Patients experiencing dyskinesia initially distributed most of their dyskinesia away from the segments directly involved in the task. With time, this distribution shifts back towards the hand.

CONCLUSION

Our results suggest that patients developed a strategy of involuntary movement's redistribution to attenuate their functional impact on voluntary movements. However, this strategy can only be maintained for a certain period before "re-emerging" dyskinesia occurs.

Chronic pain and pain processing in Parkinson's disease

Pain is experienced by the vast majority of patients living with Parkinson's disease. It is most often of nociceptive origin, but may also be ascribed to neuropathic (radicular or central) or miscellaneous sources. The recently validated King's Parkinson's Disease Pain Scale is based on 7 domains including musculoskeletal pain, chronic body pain (central or visceral), fluctuation-related pain, nocturnal pain, oro-facial pain, pain with discolouration/oedema/swelling, and radicular pain. The basal ganglia integrate incoming nociceptive information and contribute to coordinated motor responses in pain avoidance and nocifensive behaviors. In Parkinson's disease, nigral and extra-nigral pathology, involving cortical areas, brainstem nuclei, and spinal cord, may contribute to abnormal central nociceptive processing in patients experiencing pain or not. The dopamine deficit lowers multimodal pain thresholds that are amenable to correction following levodopa dosing. Functional brain imaging with positron emission tomography following administration of H₂¹⁵O revealed abnormalities in the sensory discriminative processing of pain (insula/SII), as well as in the affective motivational processing of pain (anterior cingulate cortex, prefrontal cortex). Pain management is dependent on efforts invested in diagnostic accuracy to distinguish nociceptive from neuropathic pain. Treatment requires an integrated approach including strategies to lessen levodopa-related response fluctuations, in addition to other pharmacological and non-pharmacological options such as deep brain stimulation and rehabilitation.

Electrophysiological predictors of cognitive-behavioral therapy outcome in tic disorders

Cognitive-behavioral therapy (CBT) constitutes an empirically based treatment for tic disorders (TD), but much remains to be learned about its impact at the neural level. Therefore, we examined the electrophysiological correlates of CBT in TD patients, and we evaluated the utility of event-related potentials (ERP) as predictors of CBT outcome. ERPs were recorded during a stimulus-response compatibility (SRC) task in 26 TD patients and 26 healthy controls. Recordings were performed twice, before and after CBT in TD patients, and with a similar time interval in healthy controls. The stimulus- and response-locked lateralized readiness potentials (sLRP & rLRP) were assessed, as well as the N200 and the P300. The results revealed that before CBT, TD patients showed a delayed sLRP onset and larger amplitude of both the sLRP and rLRP peaks, in comparison with healthy controls. The CBT induced an acceleration of the sLRP onset and a reduction of the rLRP peak amplitude. Compared to healthy controls, TD patients showed a more frontal distribution of the No-Go P300, which was however not affected by CBT. Finally, a multiple linear regression analysis including the N200 and the incompatible sLRP onset corroborated a predictive model of therapeutic outcome, which explained 43% of the variance in tic reduction following CBT. The current study provided evidence that CBT can selectively normalize motor processes relative to stimulus-response compatibility in TD patients. Also, ERPs can predict the amount of tic symptoms improvement induced by the CBT and might therefore improve treatment modality allocation among TD patients.

Characterization of Burning Mouth Syndrome in Patients with Parkinson's Disease

AIMS

To determine the prevalence and characteristics of burning mouth syndrome (BMS) in a Parkinson's disease (PD) population through a self-administered, custom-made survey.

METHODS

A total of 218 surveys were collected during regular outpatient visits at two Movement Disorders Clinics in Montreal (Canada) and Toulouse (France) to gather information about pain experience, PD-related symptoms, and oral and general health. A neurologist confirmed the diagnosis of PD, drug treatment, Hoehn-Yahr stage, and Schwab & England Activity of Daily Living score. Data between groups were compared using the independent samples Mann-Whitney U test and two-sided exact Fisher test.

RESULTS

Data from 203 surveys were analyzed. BMS was reported by eight subjects (seven females and one male), resulting in a prevalence of 4.0% (95% confidence interval [CI] = 2.1-7.8). Five participants with chronic nonburning oral pain were excluded. PD severity and levodopa equivalent daily dose did not differ between non-BMS and BMS participants. Mean poor oral health index was higher in BMS compared to non-BMS subjects (49.0 vs 32.2 points, P < .05). BMS manifested after PD onset in seven patients, did not occur on a daily basis in four, and always coexisted with restless legs syndrome.

CONCLUSION

This survey yielded a low prevalence of BMS in PD patients, indicating no strong link between the two conditions. An augmenting effect such as that resulting from drug treatment in restless legs syndrome or sensory neuropathy cannot be excluded.

P300 Source Localization Contrasts in Body-Focused Repetitive Behaviors and Tic Disorders

Tic disorders (TD) and body-focused repetitive behaviors (BFRB) have similar phenotypes that can be challenging to distinguish in clinical settings. Both disorders show high rates of comorbid psychiatric conditions, dysfunctional basal ganglia activity, atypical cortical functioning in the prefrontal and motor cortical regions, and cognitive deficits. Clinicians frequently confound the two disorders and it is important to find reliable objective methods to discriminate TD and BFRB. Neuropsychological tests and event-related potential (ERP) studies have yielded inconsistent results regarding a possible context updating deficit in TD and BFRB patients. However, most previous studies did not control for the presence of comorbid psychiatric condition and medication status, which might have confounded the findings reported to date. Hence, we aimed to investigate the psychophysiology of working memory using ERP in carefully screened TD and BFRB patients excluding those with psychiatric comorbidity and those taking psychoactive medication. The current study compared 12 TD patients, 12 BRFB patients, and 15 healthy control participants using a motor oddball task (button press). The P300 component was analyzed as an index of working memory functioning. Results showed that BFRB patients had decreased P300 oddball effect amplitudes over the right hemisphere compared to the TD and control groups. Clinical groups presented different scalp distributions compared to controls, which could represent a potential endophenotype candidate of BFRB and TD.

The Impact of a Cognitive-Behavioral Therapy on Event-Related Potentials in Patients with Tic Disorders or Body-Focused Repetitive Behaviors

CONTEXT

Tic disorders (TD) are characterized by the presence of non-voluntary contractions of functionally related groups of skeletal muscles in one or multiple body parts. Patients with body-focused repetitive behaviors (BFRB) present frequent and repetitive behaviors, such as nail biting or hair pulling. TD and BFRB can be treated with a cognitive-behavioral therapy (CBT) that regulates the excessive amount of sensorimotor activation and muscular tension. Our CBT, which is called the cognitive-psychophysiological (CoPs) model, targets motor execution and inhibition, and it was reported to modify brain activity in TD. However, psychophysiological effects of therapy are still poorly understood in TD and BFRB patients. Our goals were to compare the event-related potentials (ERP) of TD and BFRB patients to control participants and to investigate the effects of the CoPs therapy on the P200, N200, and P300 components during a motor and a non-motor oddball task.

METHOD

Event-related potential components were compared in 26 TD patients, 27 BFRB patients, and 27 control participants. ERP were obtained from 63 EEG electrodes during two oddball tasks. In the non-motor task, participants had to count rare stimuli. In the motor task, participants had to respond with a left and right button press for rare and frequent stimuli, respectively. ERP measures were recorded before and after therapy in both patient groups.

RESULTS

CoPs therapy improved symptoms similarly in both clinical groups. Before therapy, TD and BFRB patients had reduced P300 oddball effect during the non-motor task, in comparison with controls participants. An increase in the P300 oddball effect was observed posttherapy. This increase was distributed over the whole cortex in BFRB patients, but localized in the parietal area in TD patients.

DISCUSSION

These results suggest a modification of neural processes following CoPs therapy in TD and BFRB patients. CoPs therapy seems to impact patients' attentional processes and context updating capacities in working memory (i.e., P300 component). Our results are consistent with a possible role of the prefrontal cortex and corpus callosum in mediating interhemispheric interference in TD.

Cognitive-behavioral therapy induces sensorimotor and specific electrocortical changes in chronic tic and Tourette's disorder

BACKGROUND

Tic disorders, such as the Gilles de la Tourette syndrome and persistent tic disorder, are neurodevelopmental movement disorders involving impaired motor control. Hence, patients show repetitive unwanted muscular contractions in one or more parts of the body. A cognitive-behavioral therapy, with a particular emphasis on the psychophysiology of tic expression and sensorimotor activation, can reduce the frequency and intensity of tics. However, its impact on motor activation and inhibition is not fully understood.

METHODS

To study the effects of a cognitive-behavioral therapy on electrocortical activation, we recorded the event-related potentials (ERP) and lateralized readiness potentials (LRP), before and after treatment, of 20 patients with tic disorders and 20 healthy control participants (matched on age, sex and intelligence), during a stimulus-response compatibility inhibition task. The cognitive-behavioral therapy included informational, awareness training, relaxation, muscle discrimination, cognitive restructuration and relapse prevention strategies.

RESULTS

Our results revealed that prior to treatment; tic patients had delayed stimulus-locked LRP onset latency, larger response-locked LRP peak amplitude, and a frontal overactivation during stimulus inhibition processing. Both stimulus-locked LRP onset latency and response-locked LRP peak amplitude normalized after the cognitive behavioral therapy completion. However, the frontal overactivation related to inhibition remained unchanged following therapy.

CONCLUSIONS

Our results showed that P300 and reaction times are sensitive to stimulus-response compatibility, but are not related to tic symptoms. Secondly, overactivity of the frontal LPC and impulsivity in TD patients were not affected by treatment. Finally, CBT had normalizing effects on the activation of the pre-motor and motor cortex in TD patients. These results imply specific modifications of motor processes following therapy, while inhibition processes remained unchanged. Given that LRPs are partially generated within the sensorimotor and supplementary motor area, the reported reduction in tic frequency and improvements of LRPs components suggest that CBT induced a physiological change in patients' motor area.

Upregulation of dopamine D3, not D2, receptors correlates with tardive dyskinesia in a primate model

Tardive dyskinesia (TD) is a delayed and potentially irreversible motor complication arising in patients chronically exposed to centrally active dopamine D2 receptor antagonists, including antipsychotic drugs and metoclopramide. The classical dopamine D2 receptor supersensitivity hypothesis in TD, which stemmed from rodent studies, lacks strong support in humans. To investigate the neurochemical basis of TD, we chronically exposed adult capuchin monkeys to haloperidol (median, 18.5 months; n = 11) or clozapine (median, 6 months; n = 6). Six unmedicated animals were used as controls. Five haloperidol-treated animals developed mild TD movements, and no TD was observed in the clozapine group. Using receptor autoradiography, we measured striatal dopamine D1, D2, and D3 receptor levels. We also examined the D3 receptor/preprotachykinin messenger RNA (mRNA) co-expression, and quantified preproenkephalin mRNA levels, in striatal sections. Unlike clozapine, haloperidol strongly induced dopamine D3 receptor binding sites in the anterior caudate-putamen, particularly in TD animals, and binding levels positively correlated with TD intensity. Interestingly, the D3 receptor upregulation was observed in striatonigral neurons. In contrast, D2 receptor binding was comparable to controls, and dopamine D1 receptor binding was reduced in the anterior putamen. Enkephalin mRNA widely increased in all animals, but to a greater extent in TD-free animals. These results suggest for the first time that upregulated striatal D3 receptors correlate with TD in nonhuman primates, adding new insights to the dopamine receptor supersensitivity hypothesis. The D3 receptor could provide a novel target for drug intervention in human TD.

New and emerging treatments for symptomatic tardive dyskinesia

The aim of this review is to assess new, emerging, and experimental treatment options for tardive dyskinesia (TD). The methods to obtain relevant studies for review included a MEDLINE search and a review of studies in English, along with checking reference lists of articles. The leading explanatory models of TD development include dopamine receptor supersensitivity, GABA depletion, cholinergic deficiency, neurotoxicity, oxidative stress, changes in synaptic plasticity, and defective neuroadaptive signaling. As such, a wide range of treatment options are available. To provide a complete summary of choices we review atypical antipsychotics along with resveratrol, botulinum toxin, Ginkgo biloba, tetrabenazine, clonazepam, melatonin, essential fatty acids, zonisamide, levetiracetam, branched-chain amino acids, drug combinations, and invasive surgical treatments. There is currently no US Food and Drug Administration-approved treatment for TD; however, prudent use of atypical antipsychotics with routine monitoring remain the cornerstone of therapy, with experimental treatment options available for further management.

Haloperidol-induced striatal Nur77 expression in a non-human primate model of tardive dyskinesia

Tardive dyskinesia (TD) is a delayed and potentially irreversible motor complication arising in patients chronically exposed to antipsychotic drugs. As several modern (so-called atypical) antipsychotic drugs are common offenders, combined with the widening clinical indications for prescription as well as exposure of vulnerable individuals, TD will remain a significant drug-induced unwanted side effect. In addition, the pathophysiology of TD remains elusive and therapeutics are difficult. Based on rodent experiments, we have previously shown that the transcriptional factor Nur77 (also known as nerve growth factor inducible gene B or Nr4a1) is induced in the striatum following antipsychotic drug exposure as part of a long-term neuroadaptive process. To confirm this, we exposed adult capuchin (Cebus apella) monkeys to prolonged treatments with haloperidol (median 18.5 months, N = 11) or clozapine (median 6 months, N = 6). Six untreated animals were used as controls. Five haloperidol-treated animals developed mild TD movements similar to those found in humans. No TD was observed in the clozapine group. Postmortem analysis of Nur77 expression measured by in situ hybridization revealed a stark contrast between the two drugs, as Nur77 mRNA levels in the caudate-putamen were strongly upregulated in animals exposed to haloperidol but were spared following clozapine treatment. Interestingly, within the haloperidol-treated group, TD-free animals showed higher Nur77 expression in putamen subterritories compared with dyskinetic animals. This suggests that Nur77 expression might be associated with a reduced risk of TD in this experimental model and could provide a novel target for drug intervention.

Comparing three screening tools for drug-induced parkinsonism in patients with advanced schizophrenia: a pilot study

BACKGROUND

Drug-induced parkinsonism (DIP) is seen in one third of patients exposed to antipsychotic drugs and may lead to complications related to dysphagia and falls. Aside from skilled neurological examination, no tool has been validated to facilitate detection and follow-up.

OBJECTIVE

In this pilot study, three validated screening instruments were tested in an age-biased cohort of schizophrenia patients, including four items of the Liverpool University Neuroleptic Side-Effects Rating Scale (LUNSERS) and two brief questionnaires designed for community survey of parkinsonism.

METHOD

Fifty-six subjects living with chronic schizophrenia between 50 and 75 years of age underwent a motor evaluation along the original Unified Parkinson's Disease Rating Scale-section III and answered questions along the selected screening instruments, and results compared to those of 16 patients with Parkinson's disease (PD) and 15 neurologically unimpaired volunteers. Odds ratios, sensitivity, specificity, and their 95% confidence intervals, were calculated.

RESULTS

All three screening instruments correctly identified the PD state and distinguished PD from healthy participants. Eighteen (32%) schizophrenic patients displayed objective motor signs of parkinsonism. A single item of the LUNSERS (shakiness) significantly distinguished DIP from DIP-free patients, with a sensitivity of 61.1% and a specificity of 83.3%. The positive predictive value was 63.5% and the negative predictive value was 81.9%. The two other screening methods showed insufficient predictive value.

CONCLUSION

Apart from a single query on shakiness, none of the tools examined were adequate to screen for DIP in patients treated for schizophrenia. A different instrument is necessary to monitor this important adverse effect in schizophrenia.

Contribution of orodental status to the intensity of orofacial tardive dyskinesia: an interdisciplinary and video-based assessment

BACKGROUND

Tardive dyskinesia (TD) is a neurological motor complication eventually arising in one-third of patients chronically exposed to antipsychotic drugs. Some orodental peripheral factors have been reported to influence TD.

OBJECTIVE

To measure orodental factors such as temporomandibular joint function, static occlusal contacts, and denture condition, and attempt correlations with orofacial TD intensity.

METHODS

In this exploratory cross-sectional pilot study, 31 subjects between 30 and 75 years of age were divided in two groups displaying minimal to mild, or moderate to severe orofacial TD, respectively, and underwent a detailed oral, dental, and prosthetic evaluation to capture various aspects of oral health compared between the two groups. Blinded video-based TD ratings along a validated scale were obtained to compare dentulous and edentulous subjects, and contrast TD intensity in complete denture wearers with and without their own prostheses.

RESULTS

None of the factors examined tightly correlated with orofacial TD intensity. However, edentulism was associated with a higher median orofacial TD rating compared to the dentulous group (p = 0.001). Further, a significant intra-subject difference was observed in the edentulous subjects rated with their own complete dentures in place or not (p = 0.028), the dentures attenuating the mean orofacial ratings by 21.8 ± 7.3%.

CONCLUSION

Of all orodental factors considered, only edentulism and complete denture wearing influenced oral TD expression, calling for the close monitoring of the dental status in antipsychotic drug-exposed patients to prevent tooth loss. Further studies to measure the impact of an adequate prosthodontic rehabilitation in edentulous subjects with orofacial TD seem warranted.

Relevance of animal models to human tardive dyskinesia

Tardive dyskinesia remains an elusive and significant clinical entity that can possibly be understood via experimentation with animal models. We conducted a literature review on tardive dyskinesia modeling. Subchronic antipsychotic drug exposure is a standard approach to model tardive dyskinesia in rodents. Vacuous chewing movements constitute the most common pattern of expression of purposeless oral movements and represent an impermanent response, with individual and strain susceptibility differences. Transgenic mice are also used to address the contribution of adaptive and maladaptive signals induced during antipsychotic drug exposure. An emphasis on non-human primate modeling is proposed, and past experimental observations reviewed in various monkey species. Rodent and primate models are complementary, but the non-human primate model appears more convincingly similar to the human condition and better suited to address therapeutic issues against tardive dyskinesia.

Movement chunking during sequence learning is a dopamine-dependant process: a study conducted in Parkinson's disease

Chunking of single movements into integrated sequences has been described during motor learning, and we have recently demonstrated that this process involves a dopamine-dependant mechanism in animal (Levesque et al. in Exp Brain Res 182:499-508, 2007; Tremblay et al. in Behav Brain Res 198:231-239, 2009). However, there is no such evidence in human. The aim of the present study was to assess this question in Parkinson's disease (PD), a neurological condition known for its dopamine depletion in the striatum. Eleven PD patients were tested under their usual levodopa medication (ON state), and following a 12-h levodopa withdrawal (OFF state). Patients were compared with 12 healthy participants on a motor learning sequencing task, requiring pressing fourteen buttons in the correct order, which was determined by visual stimuli presented on a computer screen. Learning was assessed from three blocks of 20 trials administered successively. Chunks of movements were intrinsically created by each participant during this learning period. Then, the sequence was shuffled according to the participant's own chunks, generating two new sequences, with either preserved or broken chunks. Those new motor sequences had to be performed separately in a fourth and fifth blocks of 20 trials. Results showed that execution time improved in every group during the learning period (from blocks 1 to 3). However, while motor chunking occurred in healthy controls and ON-PD patients, it did not in OFF-PD patients. In the shuffling conditions, a significant difference was seen between the preserved and the broken chunks conditions for both healthy participants and ON-PD patients, but not for OFF-PD patients. These results suggest that movement chunking during motor sequence learning is a dopamine-dependent process in human.

Motor sequence learning in primate: role of the D2 receptor in movement chunking during consolidation

Motor learning disturbances have been shown in diseases involving dopamine insufficiency such as Parkinson's disease and schizophrenic patients under antipsychotic drug treatment. In non-human primates, motor learning deficits have also been observed following systemic administration of raclopride, a selective D2-receptor antagonist. These deficits were characterized by persistent fluctuations of performance from trial to trial, and were described as difficulties in consolidating movements following a learning period. Moreover, it has been suggested that these raclopride-induced fluctuations can result from impediments in grouping separate movements into one fluent sequence. In the present study, we explore the hypothesis that such fluctuations during movement consolidation can be prevented through the use of sumanirole - a highly selective D2 agonist - if administered before raclopride. Two monkeys were trained to execute a well known sequence of movements, which was later recalled under three pharmacological conditions: (1) no drug, (2) raclopride, and (3) sumanirole+raclopride. The same three pharmacological conditions were repeated with the two monkeys, trained this time to learn new sequences of movements. Results show that raclopride has no deleterious effect on the well known sequence, nor the sumanirole+raclopride co-administration. However, results on the new sequence to be learned revealed continuous fluctuations of performances in the raclopride condition, but not in the sumanirole+raclopride condition. These fluctuations occurred concurrently with a difficulty in merging separate movement components, known as a "chunking deficit". D2 receptors seem therefore to be involved in the consolidation of new motor skills, and this might involve the chunking of separate movements into integrated motor sequences.

Sensorimotor adaptation in Parkinson's disease: evidence for a dopamine dependent remapping disturbance

Sensorimotor adaptation is thought to involve a remapping of the kinematic and kinetic parameters associated with movements performed within a changing environment. Patients with Parkinson's disease (PD) are known to be affected on this type of learning process, although the specific role of dopamine depletion in these deficits has not yet been elucidated. The present study was an attempt to clarify whether dopamine depletion in PD may directly affect the capacity to internally reorganize the visuomotor remapping of a distorted environment. Fourteen PD patients were tested twice, while they were treated and while they were withdrawn from their regular levodopa treatment. Fourteen control subjects were also enrolled and tested twice. Two parallel forms of the Computed Mirror Pointing Task (CMPT), requiring making a reaching movement in a visually transformed environment (mirror inversion), were administered to each participant. Each of them had to perform 40 trials at each of the 2 testing sessions. At each trial, sensorimotor adaptation was evaluated by the initial direction angle (IDA), which reflects the direction of movement before any visually guided readjustment. Results revealed no IDA difference at baseline, between control subject and PD patients, whether they were treated or not. In all group, IDA values at that time were large, reflecting a tendency to make movements according to the real life visuomotor mapping (based on the natural direct vision). However, striking differences appeared during sensorimotor learning, in that IDA reduction along trials was poorer in patient not treated with levodopa than both control subjects and the same PD patient treated with levodopa. No difference was observed between the treated PD patients and control subjects. Given that IDA is thought to reflect the internal representation of the visuomotor mapping, it is concluded that dopamine depletion in PD would affects sensorimotor adaptation, in that it facilitates old and poorly adapted movements (real life mapping), instead of new and more adapted ones (mirror transformed mapping).

Raclopride-induced motor consolidation impairment in primates: role of the dopamine type-2 receptor in movement chunking into integrated sequences

Results obtained in patients with schizophrenia have shown that antipsychotic drugs may induce motor learning deficits correlated with the striatal type-2 dopamine receptors (D(2)R) occupancy. Other findings suggest that the role of the striatum in motor learning could be related to a process of "chunking" discrete movements into motor sequences. We therefore hypothesized that a D(2)R blocking substance, such as raclopride, would affect motor learning by specifically disrupting the grouping of movements into sequences. Two monkeys were first trained to perform a baseline-overlearned sequence (Seq. A) drug free. Then, a new sequence was learned (Seq. B) and the overlearned sequence was recalled OFF-drug (Seq. A recall OFF-drug). The effect of raclopride was then assessed on the learning of a third sequence (Seq. C), and on the recall of the overlearned sequence (Seq. A recall ON-drug). Results showed that performance related to the overlearned sequence remained the same in the three experimental conditions (Seq. A, Seq. A recall OFF-drug, Seq. A recall ON-drug), whether the primates received raclopride or not. On the other hand, new sequence learning was significantly affected during raclopride treatment (Seq. C), when compared with new sequence learning without the effect of any drug (Seq. B). Raclopride-induced disturbances consisted in performance fluctuations, which persisted even after many days of trials, and prevented the monkeys from reaching a stable level of performance. Further analyses also showed that these fluctuations appeared to be related to monkeys' inability to group movements into single flowing motor sequences. The results of our study suggest that dopamine is involved in the stabilization or consolidation of motor performances, and that this function would involve a chunking of movements into well-integrated sequences.

Proton magnetic resonance spectroscopy study of dyskinesia patients

Oral dyskinesias may occur spontaneously or be induced by medications such as antipsychotics and antidepressants. In this study, single voxel proton magnetic resonance spectroscopy was used to compare metabolite levels in the striatum for (1) 12 patients with drug-induced tardive dyskinesia (TD), (2) 12 patients with spontaneous oral dyskinesia (SOD), (3) 8 antidepressant-treated patients without TD, and (4) 8 control subjects. Statistically significant reductions in the choline/creatine (Cho/Cr) ratio were measured for the drug-treated patients with TD (-13%, P = 0.020) and SOD patients (-12%, P = 0.034) relative to control subjects. In comparison with antidepressant-treated patients without TD, drug-treated patients with TD showed a non statistically significant reduction in Cho/Cr (-11%, P = 0.079). All other metabolite ratios (N-acetylaspartate (NAA)/Cr, myo-inositol (mI)/Cr, glutamine + glutamate (Glx)/Cr, macromolecule + lipid (MM+Lip)/Cr, NAA/Cho) were unaffected by either type of dyskinesia. The observed Cho/Cr reduction in dyskinesia patients suggests decreased membrane phosphatidylcholine turnover, which provides free choline as precursor of molecules responsible for cellular signal transduction.

Effect of amantadine on motor memory consolidation in humans

Motor skills, once learned, need to be consolidated over time in order to become resistant to disruption or interference. In some instances, the consolidation phase can also include spontaneous gains in performance even in the absence of further rehearsal on a motor task. Clinical and behavioral evidence suggest that N-methyl-D-aspartate (NMDA)-receptor activity is required for motor learning acquisition and behavioral synaptic plasticity. However, the involvement of NMDA receptors in motor consolidation, leading to stabilization of the recently formed motor memory, has not yet been assessed in humans. To address this issue, we used post-training administration of amantadine, a low-affinity NMDA-receptor channel blocker. In a double-blind design, 200 mg of amantadine or a matching placebo was given orally to two different groups of 11 healthy young volunteers each. The subjects were tested twice 24 h apart, using a motor adaptation paradigm consisting of an eight-target-pointing task. Comparison of the mean performance levels on this task revealed that subjects in both groups improved their performance levels significantly on Day 2 compared to Day 1, regardless of the treatment administered. Our data indicate that amantadine failed to block motor learning consolidation in subjects that had already learned the motor adaptation task. Thus, although required in some stages (e.g. acquisition) of motor memory processes, the present results suggest that NMDA-receptor activation may not be essential for consolidation of motor adaptation in humans.

Oral dyskinesia: a clinical overview

PURPOSE

Dentists may be the first health care professionals to recognize unusual and abnormal oral movements collectively termed oral dyskinesias. The aims of this clinical overview are to raise the dental community's awareness about this important and complex topic and describe the clinical features and management of the main entities.

MATERIALS AND METHODS

A MEDLINE search of the different entities reported in the English and French literature was conducted. The main findings of a field study on oral dyskinesia were also reviewed.

RESULTS

Involuntary movement disorders are often drug related. In other cases, excessive oral movements may occur at any age in relation to various neuropsychiatric conditions. Orofacial dystonia apparently triggered by dental procedures has also been reported. Edentulousness has been associated with oral stereotypes. In a survey of 352 edentulous elderly individuals attending daycare centers, only 7% displayed visible oral sterotypes, and ill-fitting dentures were suggested as a possible triggering factor for the majority.

CONCLUSION

A multidisciplinary evaluation is desirable in the care of individuals with oral dyskinesia and in the selection of those who may benefit from a prosthodontic approach. A good knowledge of potentially offending drugs may allow avoidance of unnecessary procedures.

Characterization of subclinical tremor in Parkinson's disease

The physiological or pathological nature of subclinical tremor amplitude in Parkinson's disease (PD) is not well established. We analyzed characteristics of resting and postural tremors of subclinical amplitude in 17 patients with idiopathic PD without visible resting tremor, having a postural tremor in their least-affected hand rated 0 (12 subjects) or 1 (5 subjects) on Item 21 of the Unified Parkinson's Disease Rating Scale, compared to 17 control subjects matched for age, sex, and handedness. Tremor was recorded at the tip of the index finger using a displacement laser transducer. Overall results show that subclinical resting tremor in PD is significantly different from physiological tremor in terms of amplitude fluctuation, frequency dispersion, harmonic index, and proportional power in 4 to 6 Hz. No significant differences were found for postural tremor. These differences appear to originate mainly from patients with the mixed form of the disease. This study also confirms the preservation of physiological tremor likely originating from a distinct central oscillator in PD. The use of this method in the early and detailed characterization of PD tremors when amplitude is still within normal limits is proposed.

Relevance of the MPTP primate model in the study of dyskinesia priming mechanisms

For nearly 20 years, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) primate model has allowed great strides to be made in our understanding of the maladaptive changes underlying the levodopa-related motor response complications occurring in most parkinsonian patients. Studies indicate that sustained dopamine D2 receptor occupancy can prevent and reverse existing dyskinesias. Recent experiments in levodopa-treated MPTP animals, co-administered either a threshold dose of cabergoline or a glutamate NMDA NR2B-selective antagonist (CI-1041), have afforded protection against dyskinesia, perhaps through presynaptic inhibition of glutamate release and blockade of supersensitive postsynaptic NMDA receptors in the striatum, respectively. Some of the biochemical events that have correlated with dyskinesias, namely upregulated GABA(A) receptors in the internal pallidum, rise in pre-proenkephalin-A gene expression in the striatum, and upregulated striatal glutamate ionotropic receptors and adenosine A(2a) receptors, may be counteracted by these preventive strategies.

Prevalence of spontaneous oral dyskinesia in the elderly: A reappraisal

The prevalence and status of spontaneous oral dyskinesia (SOD), clinically defined as the presence of oral stereotypies of no apparent cause, remain controversial in the elderly. The reported high prevalence of SOD in institutionalized demented cases, the apparent similarity between SOD and tardive dyskinesia (TD), and the role of aging in both conditions, are used as arguments to minimise the prevalence of TD and causal role of antipsychotics. We observed 1,018 (69.3% women) noninstitutionalized, frail elderly subjects attending day care centers to document the prevalence and phenomenology of SOD. A total of 38 subjects, including 29 women, were suspected of having SOD, for a prevalence rate of 3.7% (95% confidence interval, 2.6-4.9%), 4.1% for women and 2.9% for men. A survey covering medical and dental issues was filled out by 508 volunteers. Subjects with suspected SOD reported more frequent ill-fitting dental devices (P = 0.002; odds ratio [OR] = 3.5), oral pain (P = 0.01; OR = 3.0), and a lower rate of perception of good oral health (P = 0.04; OR = 0.4) compared to nondyskinetics. Individuals with suspected SOD typically presented with mild stereotyped masticatory or labial movements compared to the more complex phenomenology of probable TD cases. Thus, SOD is comparatively infrequent in the elderly. The relation between its distinct orodental health profile and stereotyped manifestations warrants further attention.

Motor-learning impairment by amantadine in healthy volunteers

NMDA receptor antagonists impair learning and memory in animal models, presumably by inhibiting long-term potentiation in the motor cortex. Human studies are limited and restricted by the paucity of safe NMDA antagonists. Here, we investigated the contribution of glutamatergic neurotransmission to the capacity of acquiring motor-adaptation learning in humans. In a double-blind design, 200 mg of amantadine (a low-affinity NMDA receptor channel blocker) or a matching placebo were given orally to groups of 14 and 13 human healthy young volunteers, respectively. Blood samples were collected 3 h after treatment to assay plasma concentrations, and the subjects were then tested using a motor-adaptation paradigm consisting of an eight-target-pointing task. To rule out drug-related generalized impairments such sedation, tests measuring motor dexterity and attention were also administered pre- and post-treatment. Comparison of the mean performance levels on the motor-adaptation task revealed that subjects in the amantadine group performed at a lower level than those in the placebo group, but this difference did not reach significance. Interestingly, however, despite plasma amantadine concentrations being relatively low, ranging from 2.09 to 4.74 microM (mean=3.3 microM), they nevertheless correlated negatively with motor learning. Furthermore, when the amantadine group was divided into low-performance and high-performance subgroups, subjects in the former subgroup displayed mean amantadine concentrations 36% higher than the latter subgroup, and performed significantly worser than the placebo group. No change in performance was found on the motor-dexterity and attention tests. Altogether, our results lend support to the hypothesis that normal NMDA receptor function is necessary for the acquisition of motor adaptation.

Complications of a trophic xenotransplant approach in parkinsonian monkeys

Various restorative cell transplantation strategies have been investigated to substitute for lost dopamine (DA) neurons or to enhance DA synthesis in Parkinson's disease. Intracerebral implantation of engineered cells encapsulated in a semipermeable polymer membrane constitutes one way to deliver bioactive substances unable to cross the blood-brain barrier while avoiding the need for long-term immunosuppression. Glial cell line-derived neurotrophic factor (GDNF) has shown trophic effects on DA neurons but effective and sustained delivery within the brain parenchyma remains problematic. The long-term efficacy and late complications of a xenotransplant approach utilizing GDNF-expressing encapsulated baby hamster kidney (BHK) cells were examined. Each of five MPTP-lesioned parkinsonian cynomolgus monkeys received five devices containing active or inert cells grafted bilaterally in the striatum in a two-stage procedure 9 months apart and animals were sacrificed 4 months later for analyses. No definite motor benefit was observed, DA levels were comparable between GDNF- and control cell-implanted striata, and tyrosine hydroxylase (TH) immunoreactivity in the substantia nigra showed no consistent recovery. Cell viability and GDNF synthesis in the explanted devices were negligible. The brain tissue surrounding all implants showed an intense immune reaction with prominent "foreign body" inflammatory infiltrates. Membrane biophysics, the cell type used, and the extended period of time the devices remained in situ may have contributed to the negative outcome and should be addressed in future investigations using this approach.

Pitx3 is required for motor activity and for survival of a subset of midbrain dopaminergic neurons

Mesencephalic dopaminergic (MesDA) neurons play crucial roles in motor and behavioral processes; their loss in Parkinson's disease (PD) results in striatal dopamine (DA) deficiency and hypokinetic movement disorder. The Pitx3 homeobox gene is expressed in the MesDA system. We now show that only a subset of MesDA neurons express Pitx3 and that in Pitx3-deficient aphakia mice, this subset is progressively lost by apoptosis during fetal (substantia nigra, SN) and postnatal (ventral tegmental area) development, resulting in very low striatal DA and akinesia. Similar to human PD, dorsal SN neurons (which are Pitx3 negative) are spared in mutant mice. Thus, Pitx3 defines a pathway for survival of neurons that are implicated in PD and that are required for spontaneous locomotor activity.

The fluctuating Parkinsonian patient--clinical and pathophysiological aspects

Although levodopa-related motor response complications remain challenging from a pathophysiological and therapeutic standpoint, major advances have been made in the last decade, supporting the development of several promising drugs. Eventually, these drugs may help us to prevent, alleviate, or even "deprime" these frequent and disabling complications. Knowledge of the basic mechanisms and hypotheses underlying this fascinating conversion in the parkinsonian brain allows neurologists to understand the rationale behind emerging treatment strategies.

Antipsychotic drug-induced movement disorders

Very early in the process of diagnosing abnormal involuntary movement (AIM) disorders, one can be rewarded by keeping a high index of suspicion for possible drug-induced causes, not only through a complete list of current medications, but also identification of the drugs the patient used to take and other possible offending medications that might be available from family members and other sources. Among drug-induced movement disorders, antipsychotic drugs and other dopamine receptor blocking agents occupy a central place. Their various acute and tardive motor complications provide the template of this short review. Movement disorders caused by antidepressants, lithium, antiemetics, antiparkinsonian agents, anticonvulsants, calcium channel blockers, sympathomimetics and others are only briefly covered in table form.

Alteration of glutamate receptors in the striatum of dyskinetic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated monkeys following dopamine agonist treatment

The effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced nigrostriatal lesion and dopaminomimetic treatment on parameters of glutamatergic activity within the basal ganglia of monkeys were studied in relation with the development of dyskinesias. Drug-naive controls, saline-treated MPTP monkeys, as well as MPTP monkeys treated with either a long-acting D2 agonist (cabergoline) or a D1 agonist (SKF-82958) given by intermittent injections or continuous infusion, were included in this study. 3H-L-glutamate, 3H-alpha-amino-3-hydroxy-5-methylisoxasole-4-propionate (AMPA), 3H-glycine, 3H-CGP39653 (an N-methyl-D-aspartate, NMDA, antagonist selective for NR1/NR2A assembly) and 3H-Ro 25-6981 (an NMDA antagonist selective for NR1/NR2B assembly), specific binding to glutamate receptors, the expression of the NR1 subunit of NMDA receptors and glutamate, glutamine and glycine concentrations were studied by autoradiography, in situ hybridization and high-performance liquid chromatography (HPLC), respectively. Pulsatile SKF-82958 and cabergoline treatment relieved parkinsonian symptoms, whereas animals continuously treated with SKF-82958 remained akinetic. Pulsatile SKF-82958 induced dyskinesias in two of the three animals tested, whereas cabergoline did not. MPTP induced no significant changes of striatal specific binding of the radioligands used, NR1 mRNA expression and amino acid concentrations. In the putamen, pulsatile SKF-82958 treatment was associated with decreased content of glycine and glutamate, whereas only glycine was decreased in cabergoline-treated monkeys. Cabergoline and continuous administration of SKF-82958 led to lower levels of NR1 mRNA in the caudate in comparison to pulsatile SKF-82958 administration. The development of dyskinesias following a D1 agonist treatment was associated with an upregulation of 3H-glutamate [+49%], 3H-AMPA [+38%], 3H-CGP39653 [+ 111%], 3H-glycine [+ 26%, nonsignificant] and 3H-Ro 25-6981 [+ 33%] specific binding in the striatum in comparison to nondyskinetic MPTP monkeys. Our data suggest that supersensitivity to glutamatergic input in the striatum might play a role in the pathogenesis of dopaminomimetic-induced dyskinesias and further support the therapeutic potential of glutamate antagonists in Parkinson's disease.

Effect of MPTP-induced denervation on basal ganglia GABA(B) receptors: correlation with dopamine concentrations and dopamine transporter

We investigated the effect of MPTP-induced lesion of the substantia nigra pars compacta (SNpc) dopaminergic neurons on GABA(B) receptors in the basal ganglia of mice and monkeys using receptor autoradiography and in situ hybridization. The extent of the lesion was measured with striatal catecholamine content, striatal binding of (125)I-RTI-121 to dopamine transporter (DAT), and DAT expression in the SNpc. GABA(B) receptors in mice brain were evaluated using (3)H-CGP54626 and its expression was measured with oligonucleotides probes targeting the mRNAs of GABA(B(1a+b)), GABA(B(1a)), GABA(B(1b)), GABA(B(2)) subunits. In monkeys, (125)I-CGP64213 and selective probes for GABA(B(1a+b)) and GABA(B(2)) mRNAs were used. In mice, dopamine content, (125)I-RTI-121 binding, and DAT expression were reduced by 44%, 40%, and 39% after a dose of 40 mg/kg of MPTP and 74%, 70%, and 34% after 120 mg/kg of MPTP, respectively. In monkeys, dopamine content and DAT expression were decreased by more than 90% and 80%, respectively. In the striatum and the subthalamic nucleus, GABA(B) receptors were unchanged following MPTP in both species. In the SNpc of mice, MPTP (120 mg/kg) induced a significant decrease of (3)H-CGP54626 binding (-10%) and of the expression of GABA(B(1a+b)) mRNA (-13%). The decrease of the expression of GABA(B(1a+b)) mRNA was correlated with dopamine content, (125)I-RTI-121 binding and DAT expression. In MPTP-treated monkeys, (125)I-CGP64213 binding (-40%), GABA(B(1a+b)) mRNA (-69%) and GABA(B(2)) mRNA (-66%) were also significantly decreased in the SNpc. Our results suggest that MPTP-induced denervation is associated with a decrease of GABA(B) receptors restricted to the SNpc. These observations may be relevant to the pathophysiology of motor disorders involving dysfunction of the basal ganglia such as Parkinson disease.

Double-blind, crossover, placebo-controlled trial of bromocriptine in patients with sleep bruxism

This study was designed to assess the effects of bromocriptine, a dopamine D2 receptor agonist, on sleep bruxism. Seven otherwise healthy patients with severe and frequent sleep bruxism participated in this randomized, double-blind, placebo-controlled study. The study used a crossover design that included 2 weeks of active treatment or placebo with a washout period of 1 week. To further evaluate whether bromocriptine influences striatal D2 receptor binding, we used iodine-123-iodobenzamide single photon emission computed tomography (SPECT) under both placebo and bromocriptine regimens. Bromocriptine did not reduce the frequency of episodes of bruxism during sleep (mean +/- SEM, 9.0 +/- 1.0 and 9.6 +/- 1.5 bruxism episodes per hour for placebo and bromocriptine, respectively) or the amplitude of masseter muscle contractions (root mean square values, 48.2 +/- 15.5 microV and 46.9 +/- 12.7 microV for placebo and bromocriptine, respectively). SPECT also failed to reveal that either treatment had any influence on striatal D2 binding (values for total binding in counts/pixel, 1.80 [1.72-1.93] and 1.79 [1.56-1.87] for placebo and bromocriptine, respectively). This study shows that a nightly dose of bromocriptine does not exacerbate or reduce sleep bruxism motor activity.

Dopamine-receptor stimulation: biobehavioral and biochemical consequences

The MPTP monkey is a well-characterized animal model of parkinsonism and provides an exceptional tool for the study of dyskinesias induced by dopamine-like agents. Several such agents have been tested during the past 15 years, and it has been found that the duration of action of these compounds is the most reliable variable with which to predict their dyskinesiogenic profile. It is proposed that L-dopa-induced dyskinesias represent a form of pathological learning caused by chronic pulsatile (nonphysiological) stimulation of dopamine receptors, which activates a cascade of molecular and biochemical events. These events include defective regulation of Fos proteins that belong to the deltaFosB family, increased expression of neuropeptides, and defective GABA- and glutamate-mediated neurotransmission in the output structures of the basal ganglia.

125I-CGP 64213 binding to GABA(B) receptors in the brain of monkeys: effect of MPTP and dopaminomimetic treatments

Much evidence indicates that abnormal GABA neurotransmission may be implicated in the pathophysiology of Parkinson's disease (PD) and dopaminomimetic-induced dyskinesias (DID). In this study, autoradiography using (125)I-CGP 64213 was performed to investigate GABA(B) receptor density in the brain of control monkeys as well as monkeys with MPTP-induced nigrostriatal depletion. Three MPTP monkeys received pulsatile administrations of the D1 dopamine (DA) receptor agonist (SKF 82958) whereas a long-acting D2 DA receptor agonist (cabergoline) was given to another three animals. SKF 82958 treatment relieved parkinsonian symptoms but two of three animals developed DID. Cabergoline induced a comparable motor benefit effect without persistent DID. (125)I-CGP 64213 binding to GABA(B) receptors was heterogeneous throughout the brain with the highest levels in the medial habenula of the thalamus. MPTP induced a decrease (-40%) of (125)I-CGP 64213 binding to GABA(B) receptors in the substantia nigra pars compacta (SNpc) and an increase (+29%) in the internal segment of the globus pallidus (GPi). This increase in the GPi was not affected by SKF 82958 but partly reversed by cabergoline. No change was seen in the striatum, the thalamus, the external segment of the globus pallidus, and the substantia nigra pars reticulata following MPTP and dopaminomimetic treatments. The changes of GABA(B) receptors observed in the SNpc and in the GPi suggest that alteration of GABA(B) receptors may play a role in the pathophysiology of PD and DID.

AMPA receptor blockade improves levodopa-induced dyskinesia in MPTP monkeys

OBJECTIVE

To evaluate the contribution of amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) glutamate receptors to the pathogenesis of parkinsonian signs and levodopa-induced dyskinesias.

BACKGROUND

Motor fluctuations and dyskinesias reflect, in part, altered function of glutamate receptors of the NMDA subtype. The possible role of AMPA receptors, however, has not yet been examined.

METHODS

The authors compared the ability of an AMPA agonist (CX516) and a noncompetitive AMPA antagonist (LY300164) to alter parkinsonian symptoms and levodopa-induced dyskinesia in MPTP-lesioned monkeys. Eight levodopa-treated parkinsonian monkeys received rising doses of each drug, first in monotherapy and then in combination with low-, medium-, and high-dose levodopa.

RESULTS

CX516 alone, as well as when combined with low-dose levodopa, did not affect motor activity but induced dyskinesia. Moreover, following injection of the higher doses of levodopa, it increased levodopa-induced dyskinesia by up to 52% (p < 0.05). LY300164 potentiated the motor activating effects of low-dose levodopa, increasing motor activity by as much as 86% (p < 0.05), and that of medium-dose levodopa as much as 54% (p < 0.05). At the same time, LY300164 decreased levodopa-induced dyskinesia by up to 40% (p < 0.05).

CONCLUSIONS

AMPA receptor upregulation may contribute to the expression of levodopa-induced dyskinesia. Conceivably, noncompetitive AMPA receptor antagonists could be useful, alone or in combination with NMDA antagonists, in the treatment of PD, by enhancing the antiparkinsonian effects of levodopa without increasing and possibly even decreasing levodopa-induced dyskinesia.

Molecular basis of levodopa-induced dyskinesias

A series of experiments were performed in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of parkinsonism for the purpose of understanding the mechanism of dopaminergic dyskinesias. Dyskinesias can be induced in this model by de novo treatment with levodopa, or selective D1 or D2 agonists, provided the drugs are short acting and administered in the pulsatile mode. Biochemical analysis of the brains revealed several alterations in dopamine receptor-binding and messenger RNA message following denervation and dopaminergic treatment, but none that clearly correlated with the presence of dyskinesias. On the other hand, gamma-aminobutyric acid (GABA)A binding was increased in the internal segment of the globus pallidus of dyskinetic MPTP monkeys. This was observed consistently and could be associated with an exaggerated response to GABAergic inhibitory inputs in this strategic structure. Increased preproenkephalin message was also found to correlate with dyskinesias and may be linked to changes in GABA receptors. Treatments that caused dyskinesias induced, in the striatum, chronic Fos proteins of the deltaFosB family which, when coupled with Jun-D, form AP-1 complexes that can affect several genes, including enkephalin and N-methyl-D-aspartate receptor. We suggest that levodopa-induced dyskinesias represent a form of pathological learning, which results from deficient gating of glutamatergic inputs to the striatum by dopamine.

Idiopathic myoclonus in the oromandibular region during sleep: a possible source of confusion in sleep bruxism diagnosis

As part of a larger study, polysomnographic and audiovisual data were recorded over 2 nights in 41 subjects with a clinical diagnosis of sleep bruxism (SB). Electromyographic (EMG) events related to SB were scored according to standard criteria (Lavigne et al. J Dent Res 1996;75:546-552). Post hoc analysis revealed that rapid shock-like contractions with the characteristics of myoclonus in the jaw muscles were observed in four subjects. EMG bursts characterized as myoclonus were significantly shorter in duration than bursts classified as SB. None of the subjects had any history of myoclonus while awake. Myoclonic episodes were more frequent in sleep stages 1 and 2 than in REM. Half of the episodes contained one or two contractions whereas the other half had three or more repetitive contractions. SB and myoclonus coexisted in one subject. To rule out sleep epilepsy, full electroencephalogram montage was done in three subjects and no epileptic spikes were noted. Our results suggest that approximately 10% of subjects clinically diagnosed as SB could present oromandibular myoclonus during sleep.