Basal ganglia: From the bench to the bed

The basal ganglia (BG) encompass a set of archaic structures of the vertebrate brain that have evolved relatively little during the phylogenetic process. From an anatomic point of view, they are widely distributed throughout brain from the telencephalon to the mesencephalon. The fact that they have been preserved through evolution suggests that they may play a critical role in behavioral monitoring. Indeed, a line of evidence suggests that they are involved in the building of behavioral routines and habits that drive most of our activities in everyday life. In this article, we first examine the organization and physiology of the basal ganglia to explain their function in the control of behavior. Then, we show how disruption of the putamen, and to a lesser extent of the cerebellum, might lead to various dystonic syndromes that frequently arise during childhood.

The Cortical Processing of Sensorimotor Sequences is Disrupted in Writer's Cramp

Evidence for pre-existing abnormalities in the sensory and motor systems has been previously reported in writer's cramp (WC). However, the processing of somatosensory information during motor planning has received little attention. We hypothesized that sensorimotor integration processes might be impaired partly due to a disruption in the parieto-premotor network. To test this assumption, we designed 2 nonwriting motor tasks in which subjects had to perform a 4-finger motor sequence either on the basis of sensory stimuli previously memorized (SM task) or freely generated (SG task). Brain activity was measured by combining event-related functional magnetic resonance imaging and coherency electroencephalography in 15 WC patients and 15 normal controls. The bold signal was decreased in patients in both tasks during sensory stimulation but not during movement execution. However, the EEG study showed that coherency was decreased in patients compared with controls, during the delay of the SM task and during the execution of the SG task, on both the whole network and for specific couples of electrodes. Overall, these results demonstrate an endophenotypic impairment in the synchronization of cortical areas within the parieto-premotor network during somatosensory processing and motor planning in WC patients.

Differential role of visuospatial working memory in the propensity toward uncertainty in patients with obsessive-compulsive disorder and in healthy subjects

BACKGROUND

Obsessive-compulsive disorder (OCD) is associated with visuospatial working memory deficits. Intolerance of uncertainty is thought to be a core component of OCD symptoms. Recent findings argue for a possible relationship between abilities in visuospatial memory and uncertainty. However, this relationship remains unclear in both OCD patients and healthy subjects. To address this issue, we measured performance in visuospatial working memory and the propensity to express uncertainty during decision making. We assessed their relationship and the temporal direction of this relationship in both OCD patients and healthy subjects.

METHOD

Baseline abilities in visuospatial working memory were measured with the Corsi block-tapping test. A delayed matching-to-sample task was used to identify explicit situations of certainty, uncertainty and ignorance and to assess continuous performance in visuospatial working memory. Behavioural variables were recorded over 360 consecutive trials in both groups.

RESULTS

Baseline scores of visuospatial working memory did not predict the number of uncertain situations in OCD patients whereas they did in healthy subjects. Uncertain trials led to reduced abilities in visuospatial working memory to 65% of usual performance in OCD patients whereas they remained stable in healthy subjects.

CONCLUSIONS

The present findings show an opposite temporal direction in the relationship between abilities in working memory and uncertainty in OCD patients and healthy subjects. Poor working memory performance contributes to the propensity to feel uncertainty in healthy subjects whereas uncertainty contributes to decreased continuous performance in working memory in OCD patients.

The associative and limbic thalamus in the pathophysiology of obsessive-compulsive disorder: an experimental study in the monkey

Obsessive-compulsive disorder (OCD) is a frequent psychiatric disorder characterized by repetitive intrusive thoughts and severe anxiety, leading to compulsive behaviors. Although medical treatment is effective in most cases, resistance is observed in about 30% of patients. In this context, deep brain stimulation (DBS) of the caudate or subthalamic nuclei has been recently proposed with encouraging results. However, some patients were unimproved or exhibited awkward side effects. Therefore, exploration of new targets for DBS remains critical in OCD. In the latter, functional imaging studies revealed overactivity in the limbic and associative cortico-subcortical loops encompassing the thalamus. However, the role of the thalamus in the genesis of repetitive behaviors and related anxiety is unknown. Here, we tested the hypothesis that pharmacological-induced overactivity of the medial thalamus could give rise to abnormal behaviors close to that observed in OCD. We modulated the ventral anterior (VA) and medial dorsal (MD) nuclei activity by in situ bicuculline (GABA(A) antagonist) microinjections in subhuman primates and assessed their pharmacological-induced behavior. Bicuculline injections within the VA caused significant repetitive and time-consuming motor acts whereas those performed within the MD induced symptoms of dysautonomic dysregulation along with abnormal vocalizations and marked motor hypoactivity. These findings suggest that overactivation of the VA and MD nuclei of the thalamus provokes compulsive-like behaviors and neurovegetative manifestations usually associated with the feeling of anxiety in OCD patients. In further research, this translational approach should allow us to test the effectiveness and side effects of these thalamic nuclei DBS in monkey and perhaps, in a second step, to propose a transfer of this technique to severely disabled OCD patients.

Evolution of brain gray matter loss in Huntington's disease: a meta-analysis

BACKGROUND

Huntington's disease is characterized by neuronal loss throughout the disease course. Voxel-based morphometry studies have reported reductions in gray matter concentration (GMC) in many brain regions in patients with Huntington. The description of the time course of gray matter loss may help to identify some evolution markers. Here, we conducted a meta-analysis of voxel-based morphometry studies of Huntington's disease to describe the evolution of brain gray matter loss.

METHODS

A systematic search led to the inclusion of 11 articles on Huntington's disease (297 patients and 205 controls). We extracted data from patients with preclinical Huntington, patients with clinical Huntington, and controls. Finally, anatomical likelihood estimation analyses were conducted to identify GMC changes between preclinical patients and controls, between clinical patients and controls, and between preclinical and clinical patients.

RESULTS

Preclinical patients exhibited gray matter loss in the left basal ganglia and the prefrontal cortex. Clinical patients had bilateral gray matter loss in the basal ganglia, the prefrontal cortex, and the insula. The left striatum was smaller in clinical patients than in preclinical patients.

CONCLUSIONS

Neurodegenerative processes associated with Huntington's disease, as assessed by GMC reduction, begin in the left hemisphere and extend to the contralateral hemisphere throughout the inexorable course of the disease. Changes in gray matter, especially the volumetric side ratio of the striatum, could represent a relevant biomarker for characterizing the different progression stages of the disease.

Forgetting what you have checked: a link between working memory impairment and checking behaviors in obsessive-compulsive disorder

BACKGROUND

Compulsive checking behaviors are common in obsessive-compulsive disorder (OCD). Several authors have suggested that these checking rituals could be related to memory deficits. Our aim was to test whether patients with OCD show working memory impairment in relation to their checking behavior.

METHODS

We evaluated the verbal and visuospatial components of patients' and controls' working memory using the reading span and backward location span tests. Checking behaviors were measured by recording participants' eye movements during an image comparison task using a non-invasive, infra-red TOBII 1750 eyetracker. Participants were seated, head-free, in a natural position in front of the eyetracker screen where the images were displayed.

RESULTS

Patients with OCD made more gaze moves to compare images than controls. Both patients' working memory spans were reduced, and the patients' deficit in the comparison task was negatively related to their working memory spans.

CONCLUSIONS

This work demonstrates that checking behavior in OCD is linked to a general reduction of the patients' verbal and visuospatial working memory span.

The glutamate-based genetic immune hypothesis in obsessive-compulsive disorder. An integrative approach from genes to symptoms

Recent advances in multiple areas of research have contributed to the identification of several pathophysiological factors underlying obsessive-compulsive disorder (OCD). In particular, the glutamate transporter gene SLC1A1 has been associated with the diagnosis of OCD. Immunological and infectious studies have reported alterations of the immune system and the presence of immune complexes directed against the Borna disease virus in OCD patients. In addition, neuroimaging of OCD patients has demonstrated abnormalities in the anterior cingulate cortex, orbitofrontal cortex, thalamus, and the basal ganglia. Neuropsychological assessments have found several cognitive disruptions that have been identified in OCD, especially impairments in cognitive flexibility. Here, we attempt to bridge the gap between these remarkable findings through several previously unpredicted pathophysiological mechanisms. We propose an integrative hypothesis that indicates how genetic and environmental factors may contribute to the structural and functional alterations of cortico-subcortical circuits, leading to the characteristic cognitive disruptions underlying OCD symptoms.

A challenging task for assessment of checking behaviors in obsessive-compulsive disorder

OBJECTIVE

The present study concerns the objective and quantitative measurement of checking activity, which represents the most frequently observed compulsions in obsessive-compulsive disorder (OCD). To address this issue, we developed an instrumental task producing repetitive checking in OCD subjects.

METHOD

Fifty OCD subjects and 50 normal volunteers (NV) were administered a delayed matching-to-sample task that offered the unrestricted opportunity to verify the choice made. Response accuracy, number of verifications, and response time for choice taken to reflect the degree of uncertainty and doubt were recorded over 50 consecutive trials.

RESULTS

Despite similar levels of performance, patients with OCD demonstrated a greater number of verifications and a longer response time for choice before checking than NV. Such behavioral patterns were more pronounced in OCD subjects currently experiencing checking compulsions.

CONCLUSION

The present task might be of special relevance for the quantitative assessment of checking behaviors and for determining relationships with cognitive processes.

Side-effects of subthalamic stimulation in Parkinson's disease: clinical evolution and predictive factors

Chronic bilateral high-frequency stimulation of the subthalamic nucleus (STN) is an alternative treatment for disabling forms of Parkinson's disease when on-off fluctuations and levodopa-induced dyskinesias compromise patients' quality of life. The aim of this study was to assess the evolution of side-effects during the first year of follow-up and search for clinical predictive factors accounting for their occurrence. We compared the frequency of side-effects at 3 and 12 months after surgery in a cohort of 44 patients. The off-medication scores of Unified Parkinson's Disease Rating Scale (UPDRS) II, III, axial symptoms, disease duration and age at surgery were retained for correlation analysis. Dysarthria/hypophonia, weight gain and postural instability were the most frequent chronic side-effects. Whereas dysarthria/hypophonia remained stable over time, weight gain and postural instability increased during the first year post-op. High axial and UPDRS II scores at surgery were predictive of dysarthria/hypophonia. Age and axial score at surgery were positively correlated with postural instability. Despite the occurrence of side-effects, the benefit/side-effects ratio of STN stimulation was largely positive during the first year of follow-up. Age, intensity of axial symptoms and UDPRS II off-medication score before surgery are predictive factors of dysarthria/hypophonia and postural instability after surgery.

Clinical and economic results of bilateral subthalamic nucleus stimulation in Parkinson's disease

BACKGROUND

High frequency stimulation of the subthalamic nucleus (STN) is an alternative but expensive neurosurgical treatment for parkinsonian patients with levodopa induced motor complications.

OBJECTIVE

To assess the safety, clinical effects, quality of life, and economic cost of STN stimulation.

METHODS

We conducted a prospective multicentre study in 95 consecutive Parkinson's disease (PD) patients receiving bilateral STN stimulation and assessed its effects over 12 months. A double blind randomised motor evaluation was carried out at 3 month follow up, and quality of life, self care ability, and predictive factors of outcome following surgery were assessed. The cost of PD was estimated over 6 months before and after surgery.

RESULTS

The Unified Parkinson's Disease Rating Scale (UPDRS) motor score improved by 57% (p<0.0001) and activities of daily living improved by 48% (p<0.0001) at 12 month follow up. Double blind motor scoring improved by 51% at 3 month follow up (p<0.0001). The total PD Quality of Life Questionnaire (PDQL-37) score improved by 28% (p<0.001). The better the preoperative motor score after a levodopa challenge, the better the outcome after STN stimulation. Five patients developed an intracerebral haematoma during electrode implantation with permanent after effects in two. The 6 month costs of PD decreased from 10,087 euros before surgery to 1673 euros after surgery (p<0.0001) mainly because of the decrease in medication. These savings allowed a return on the procedure investment, estimated at 36,904 euros over 2.2 years.

CONCLUSIONS

STN stimulation has good outcomes with relatively low risk and little cost burden in PD patients with levodopa induced motor complications.

Evolution of postural stability after subthalamic nucleus stimulation in Parkinson’s disease: a combined clinical and posturometric study

OBJECTIVES

The occurrence of postural and balance disorders is a frequent feature in advanced forms of Parkinson's disease (PD). However, the pathological substrate of these disturbances is poorly understood.

METHODS

In the present work, we investigated the evolution of posturometric parameters [center of pressure (CoP) displacement and CoP area] and axial scores between the pre-operative period and 3 months post-operative in seven PD patients who underwent bilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN).

RESULTS

After surgery, the patients leaned backwards much more regardless of the STN stimulation, suggesting that surgery could have a deleterious effect on postural adaptation. During the post-operative period, the improvement in axial and postural scores was similar under levodopatherapy and DBS. On the other hand, DBS of the STN significantly reduced the CoP displacement and the CoP area, whereas levodopatherapy tended only to reduce the CoP displacement and to increase the CoP area significantly.

CONCLUSIONS

These data suggest that DBS of the STN and levodopa do not act on the same neurological systems involved in posture regulation. DBS of the STN could improve posture via a direct effect on the pedunculopontine nucleus, which is known to be involved in posture regulation.

Time predictability modulates pre-supplementary motor area neuronal activity

Two monkeys were trained in a delayed sequential motor task in which the time interval between events and the delay duration were either fixed or variable. Single-unit neuronal activity was recorded in the pre-supplementary motor area (pre-SMA). During the delay, we observed a gradual increase in activity (build-up pattern) in the fixed but not in the variable condition. In the former but not in the latter, the monkey had the opportunity to estimate time duration. Consequently, the build-up pattern observed in the pre-SMA might represent the neuronal substrate of a time accumulator system proposed by previous authors on the basis of functional imaging data. Such a system could play a critical role in the working memory of temporal information.

Disruption of information processing in the supplementary motor area of the MPTP-treated monkey: a clue to the pathophysiology of akinesia?

It has been suggested that the underactivity of mesial frontal structures induced by dopamine depletion could constitute one of the main substrates underlying akinesia in Parkinson's disease. Functional imaging and movement-related potential recordings indicate an implication of the frontal lobes in this pathological process, but the question has not yet been investigated at a cellular level using single unit recording. We therefore compared neuronal activity in both the presupplementary motor area (pre-SMA) and the supplementary motor area proper (SMAp) of the Macaca mulatta monkey during a delayed motor task, before and after MPTP treatment. In the pre-SMA, which receives strong inputs from the prefrontal cortex, the baseline firing frequency and the percentage of neurons responding to visual instruction cues decreased in lesioned monkeys. In the SMAp, which sends direct outputs to the primary motor cortex, not only was the response to visual cues impaired, but the percentage of SMAp neurons responding to intracortical microstimulation fell and the threshold of response rose. Neuronal activity after the Go signal diminished sharply in both structures in the symptomatic animal and the discharge pattern became more irregular; in the SMAp neuronal activity remained modified longer. Most of these changes could already be observed in the presymptomatic animal presenting no clinical signs of parkinsonism. These data would indicate that, at the moment when dopamine depletion has impaired the ability of cortical neurons to operate the focused selection of incoming information giving instructions for movement, pre-SMA and SMAp neurons are also in a state of severe hypoactivity. The conjunction of these phenomena could play a critical role in the genesis of akinesia.

Minimal tissue damage after stimulation of the motor thalamus in a case of chorea-acanthocytosis

Autopsy findings are reported from a patient with chorea-acanthocytosis treated for 2 years by deep brain stimulation (DBS) of the motor thalamus. Postoperative testing showed a progressive improvement in axial truncal spasms. Although relatively high currents were used for 2 years in this patient, postmortem analysis showed minimal tissue damage in the vicinity of the electrode tip. It is concluded that DBS has little impact on the surrounding tissues.

Neuronal activity in the monkey motor thalamus during bicuculline-induced dystonia

Recent data suggest that a decreased basal ganglia output may occur in dystonia, resulting in an increased thalamic drive to the mesial premotor cortex. In a previous work we found that injection of the GABAA antagonist bicuculline into the rostral motor thalamus induced contralateral dystonic postures, whereas myoclonic jerks were frequent after injection into the caudal motor thalamus. In the present study, we performed electrophysiological recordings in the rostral and caudal parts of the ventrolateral thalamus of two cynomolgus monkeys before and after bicuculline injections or saline injections. Discharge frequencies of thalamic neurons were increased after bicuculline injections vs. controls. Their discharge pattern was more bursty in the caudal part in which bursts of neuronal activity were correlated with myoclonic jerks. After bicuculline injection, neurons responded more frequently and less selectively to passive limb movements in both parts of the motor thalamus. Conversely, the response to microstimulation increased after bicuculline injection, particularly in the caudal part. Our data show that acute bicuculline-induced dystonia is associated with a reversible overactivity and disorganization of neuronal activity in the motor thalamus. Such a phenomenon might induce an overspreading of cortical activity leading to dystonia. We postulate that the distinct clinical syndromes observed after bicuculline injections into the rostral and caudal motor thalamus are due to differences both in the neuronal circuitry within each thalamic nucleus and in segregated cortical projections.

Comparison of neuronal activity in the rostral supplementary and cingulate motor areas during a task with cognitive and motor demands

A number of cortical motor areas have been identified on the medial wall of the hemisphere in monkeys. However, their specific role in motor control remains unclear. In this study, we sought to describe and compare the functional properties of the presupplementary (pre-SMA) and rostral cingulate (CMAr) motor areas in two monkeys performing a visually instructed, delayed, sequential movement. We recorded 134 task-related neurons in the pre-SMA and 149 in the CMAr. The main difference between the two areas was the abundance of responses to targets (46%) in the pre-SMA, while CMAr activity was more related to reward (28%). Neuronal responses to targets were more phasic and higher in frequency in the pre-SMA than in the CMAr. During the delay, the percentage of neuronal responses was similar in the two areas. The discharge pattern was different depending upon whether the delay duration was fixed or variable but in most neurons was the same regardless of the sequence performed. Movement-related changes were common in the pre-SMA (75%) and in the CMAr (81%) but they occurred earlier in the former. Neurons activated exclusively during movement were more numerous in the CMAr. Finally, neuronal activity in the pre-SMA was more related to the sequential aspect of the task compared to the CMAr. Our results suggest that although the two areas share functional properties, they also participate in different aspects of motor behaviour. Their functional properties reflect their anatomical positions, which give them the potential to integrate external stimuli (pre-SMA) and internal states (CMAr) during motor planning.

Chorea-acanthocytosis: neuropathology of brain and peripheral nerve

We report the neuropathological data from a familial case of chorea-acanthocytosis with central and peripheral nervous system involvement. At the age of 34, the patient underwent a peripheral nerve biopsy which was analyzed by light- and electron microscopy. These studies showed a selective reduction in the large diameter myelinated fibre population, with several clusters of regeneration. Remyelinating fibers surrounded by flattened Schwann cell processes were also present. The patient died at the age of 44, and post-mortem macroscopic examination of the brain showed marked atrophy of the caudate. Histological examination of paraffin sections showed almost complete depletion of neurons in the caudate, with severe astrocytic gliosis. The putamen and pallidum were slightly less severely depleted of neurons, but with marked astrocytic gliosis. Diffuse mild gliosis was also evidenced, by immunohistochemistry with anti-GFAP, in the thalamus and subcortical white matter.

Influence of cognitive strategies on the pattern of cortical activation during mental subtraction. A functional imaging study in human subjects

Functional magnetic resonance imaging (fMRI) at 1.5 T was used to investigate the influence of cognitive strategies on cortical activation during mental calculation. Twenty-nine right-handed subjects performed a serial subtraction of prime numbers. Even though a common corpus of brain areas was activated during this mental calculation, differences appeared between subjects in function of their spontaneous cognitive strategy. In subjects using a so called verbal strategy (n=15), the main activation was located in the whole left dorsolateral frontal cortex with a little activation of the inferior parietal cortex. In subjects using a so called visual strategy (n=14), a bilateral activation in the prefrontal cortex and a high activation in the left inferior parietal cortex were observed. These results demonstrate that numbers are processed through a distributed network of cortical areas, the lateralization of which is clearly influenced by subject strategy.

Bicuculline injections into the rostral and caudal motor thalamus of the monkey induce different types of dystonia

The pathophysiology of dystonia remains unclear in comparison with other movement disorders. Recent data suggest that there may exist in dystonia an increased thalamic drive to the mesial premotor cortex. To test this hypothesis, we induced overactivity of the motor thalamus by injecting a GABA-A (gamma-aminobutyric acid) antagonist (bicuculline) into the rostral (pallidal) and caudal (cerebellar) ventrolateral nuclei of the thalamus in both hemispheres of one monkey. Dystonic postures were observed in the contralateral limbs and axis. Electromyographic recordings revealed bursts of muscular activation with co-contractions during spontaneous dystonic movements and alterations in muscular patterns during sequential visually guided arm movements. The type of dystonia depended on the site of injections. Rostral thalamic injections induced more severe dystonic postures, whereas myoclonic jerks predominated following caudal injections. We conclude that these two distinct clinical patterns, which are frequently associated in humans, are probably due to a dysfunctioning of segregated thalamic projections to the supplementary motor area (from the rostral part) and to the primary motor cortex (from the caudal part).

A functional magnetic resonance imaging study of mental subtraction in human subjects

The neuronal network involved in a precise type of calculation procedure, mental subtraction, was investigated by means of functional magnetic resonance imaging. Two tasks were used requiring covert production of numbers: (1) with calculation; (2) without calculation. During the first task, activation was observed in the left dorsolateral prefrontal and premotor cortices, in Broca's area and bilaterally in the inferior parietal cortex. During the second task, activation was mainly observed in Broca's area and to a less extent in the left prefrontal and premotor cortices. Statistical comparison of data in the two situations revealed that the procedure of mental subtraction is mediated by a distributed system which includes predominantly the left dorsolateral prefrontal cortex and the inferior parietal cortex bilaterally.

Reorganization of area 5 neuron activity in trained deafferented monkeys

A command function is attributable to certain area 5 neurons which clearly fire before movement in trained monkey. Statistical analysis allowed us to define two categories of spontaneous firing mode for these cells: type I which exhibits a random pattern of discharge (14%), and type II displaying markedly "bursty firing". After deafferentation, both categories were still observed in the same proportion. However, the discharge pattern and frequency in type II cells remained altered for 5 months. This paralleled rises in neural latency response (RS) and reaction time (RT). Beginning the 6th month, there was a progressive reorganization of the spontaneous activity along with normalization of RS and RT. Our results support the idea that an enhancement of the excitability of these area 5 neurons, initially depressed by the suppression of sensory inputs, occurs over time. This sensitivity gain could be due to neural network rearrangements induced by repetitive operant solicitation.

[Influence of individual strategies on brain activation patterns during cognitive tasks]

Functional magnetic resonance imaging (fMRI) at 1.5 T was used to investigate the influence of cognitive strategies on cortical activation during mental calculation. Twenty-nine right-handed subjects performed a serial subtraction of prime numbers. Data were analyzed taking into account whether the spontaneous strategy of subjects was verbal (n = 15) or visual (n = 14). Even thought a common corpus of brain areas was activated during this mental calculation task, i.e. the dorsolateral prefrontal, premotor and parietal cortices, and Broca's area, differences appeared between the two groups of subjects. In subjects using a verbal strategy, the main activation was located in the whole left dorsolateral frontal cortex with a little activation of the inferior parietal cortices. In subjects using a visual strategy, a bilateral activation in the prefrontal cortex and a high activation in the left inferior parietal cortex were observed. These results demonstrate that numbers are processed through a distributed network of cortical areas, the lateralization of which is clearly influenced by subject strategy. Taken together this data reveals a functional interaction between the left inferior parietal cortex and the right prefrontal cortex in the visuo-spatial sketchpad for number processing. This network could be involved in sustained selective attention to mental numerical images generated in the left inferior parietal cortex.

Cellular distribution of adenosine A2A receptor mRNA in the primate striatum

The cellular expression of adenosine A2A receptor mRNA in the adult monkey and human striatum was examined by using single and double in situ hybridization with ribonucleotide probes. Analysis on adjacent sections demonstrated a homogeneous overlapping expression of adenosine A2A receptor and preproenkephalin A mRNAs throughout nucleus caudatus, putamen, and nucleus accumbens. By contrast, high expression of preproenkephalin A mRNA but no expression of adenosine A2A receptor mRNA was found in the nucleus basalis of Meynert. Double in situ hybridization demonstrated an extensive colocalization of adenosine A2A receptor and preproenkephalin A mRNAs in approximately 50% of the medium-sized spiny neurons of the monkey nucleus caudatus, putamen, and nucleus accumbens. A small number of neurons (4-12%) that contained adenosine A2A receptor mRNA but not preproenkephalin A mRNA was found along the ventral borders of the striatum. Virtually all adenosine A2A receptor mRNA-containing neurons co-expressed dopamine D2 receptor mRNA, whereas only very few adenosine A2A receptor mRNA containing neurons co-expressed dopamine D1 receptor or substance P mRNAs. In addition, a sub-population of adenosine A2A receptor mRNA-expressing neurons that also contained preproenkephalin A mRNA was found in the septum in monkeys. These results demonstrate that there is a high expression of adenosine A2A receptor mRNA in the primate striatum that is extensively co-localized with dopamine D2 receptor and preproenkephalin A mRNAs. It is concluded that adenosine A2A receptors are likely to be important for the parallel organization of primate striatal neurotransmission and that these receptors could be a target for drug therapy in Parkinson's disease.

Study of central and peripheral conductions to the diaphragm in 22 patients with definite multiple sclerosis

Involvement of the diaphragm was evaluated electrophysiologically in 22 patients with definite multiple sclerosis. Magnetic transcranial stimulation (MTS), magnetic cervical stimulation at C4 level (MCS) and electric stimulation of the phrenic nerve at the neck (EPS) were performed for measuring latencies, motor conduction times and amplitudes of the responses recorded with a pair of surface or subcutaneous electrodes located at the xiphoid and the 8th costal interspace on the anterior axillary line. Latency of the motor evoked potentials (MEPs) was abnormal: in 9 patients following MTS, in 6 following MCS, in 2 following EPS. The motor conduction time between the cortex and the cervical spine, we called CMCT1, was abnormal in 11 patients and the motor conduction time between the cortex and the neck, we called CMCT2, was abnormal in 8 patients. However CMCT1 was more often unmeasurable than CMCT2 because the MEPs following MCS were unreliable in 4 patients. The conduction time between the cervical spine and the neck was abnormally long in 2 patients but it was paradoxically abnormally short in 3, probably because of the difficulties in locating exactly the place of the stimulation at the cervical C4 level. The MEP amplitude was not considered a reliable parameter because of the large range of the values in our controls, although the mean amplitude was significantly lower in the patients than in the controls. The amplitude of the compound muscle action potential (CMAP) following EPS was below the lower limit of the normal in 9 patients. The percentage of abnormal MEP latencies and CMCTs when both sides were combined was higher for the hemidiaphragms than for the upper limbs and was roughly the same for the hemidiaphragms and the lower limbs. Moreover electrophysiological study of the diaphragm was abnormal in 5 patients without pulmonary symptoms and with normal pulmonary function tests, demonstrating that this study is useful for revealing infraclinical demyelinating lesions on the central motor pathways down to diaphragm. In addition, alterations of the CMAPs in some patients suggest a possible extension of the lesions towards the anterior horns and anterior roots.

Movement disorders induced by gamma-aminobutyric agonist and antagonist injections into the internal globus pallidus and substantia nigra pars reticulata of the monkey

Injections of bicuculline into the medial segment of the globus pallidus (GPi) of the monkey induced dose-dependent hypokinesia with dystonic attitudes in contralateral limbs whereas muscimol injections elicited choreiform movements. Injections of the same drugs in substantia nigra pars reticulata (SNr) provoked severe axial postural anomalies with rotational behavior. Conversely, contralateral hypertonia after bicuculline and contralateral hypotonia after muscimol injections were observed. These data suggest that GABA inputs into GPi and SNr play different roles in terms of motor and postural control and add new insights into the pathophysiology of dystonias.

Chronic administration of DL-allyl-glycine into the neostriatum, disorganises the firing modes of the nigral dopaminergic neurons in the rat

Nigral dopaminergic (DA) neurons have been reported to fire according to three modes: very regular (pacemaker 42%) irregular (random 46%) and bursty (12%). The switch from simple spiking mode (pacemaker or random) to bursty firing would correspond to an increase in DA release necessary for the performance of a new motor act. As nigral DA cells are impinged upon by a high percentage of GABAergic afferents we blocked striatal GABAergic output neurons by chronic administration into the neostriatum of allyl-glycine, a glutamic acid decarboxylase (GAD) inhibitor. After treatment, rats presented hyperkinesia and hypertonia on the injected side and recordings showed a drastic change in the percentage distribution of nigral DA cell discharge patterns; 85% were 'random', 12% 'pacemaker' and 3% bursty. Such a disturbance, by impeding adapted DA release, may account for the hyperkinetic and dystonic disorders observed.

Alleviation of experimental hemiparkinsonism by high-frequency stimulation of the subthalamic nucleus in primates: a comparison with L-Dopa treatment

Experimental studies in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys have shown that akinesia and rigidity are linked to a hyperactivity of glutamatergic subthalamic nucleus neurons and that the lesion of this nucleus can ameliorate parkinsonian motor signs. In our study, high-frequency stimulation applied at the subthalamic level was performed on two Macaca mulatta monkeys rendered hemiparkinsonian by unilateral infusion of MPTP. Its effects on rigidity and bradykinesia have been quantified. The results exhibit an important alleviation of both symptoms during the application of subthalamic stimulation comparable to that obtained during L-Dopa treatment, but without the appearance of abnormal movements such hemiballism or dyskinesia. Our data show that subthalamic stimulation has a beneficial effect on experimental parkinsonian rigidity and bradykinesia and suggests a new therapy approach for the treatment of Parkinson's disease by using subthalamic high-frequency stimulation instead of L-Dopa treatment.

[Mechanism of action, clinical indication and results of treatment of botulinum toxin]

Botulinum toxin, the most potent of the neurotoxins, produces paralysis by blocking presynaptic release of the neurotransmitter (acetylcholine) at the neuromuscular junction, with reversible chemical denervation of the muscle fibre, thereby inducing partial paralysis and atrophy. Because chemical denervation is reversible, botulinum toxin has temporary effects, the muscle being progressively reinnervated by nerve sproutings. Type A botulinum toxin (Bix-A) is available under two dosage forms: Botox and Dysport. Although the initial clinical indication was strabismus, subsequent studies have demonstrated the efficacy of Btx-A, mainly in dystonia, hemifacial spasm and spasticity. However, botulinum toxin has been successfully used in various other clinical indications. In regard to spasticity associated with cerebral palsy, Btx-A is a promising treatment requiring a multidisciplinary approach. Btx-A injections lead to effective reduction of muscle hyperactivity with minor side-effects. They are painless, even though electromyographic guidance may be required for the injection of deep muscles. However, the production of antibodies to Btx-A may compromise the effect of long-term treatment.

A randomised, double blind, placebo controlled trial of botulinum toxin in the treatment of spastic foot in hemiparetic patients

OBJECTIVE

To confirm the apparent effectiveness of botulinum toxin (BTX) in hemiparetic patients with ankle plantar flexors and foot invertor spasticity.

METHODS

Twenty three hemiparetic patients with spasticity of the ankle plantar flexors and foot invertors were included in a randomised double blind, placebo controlled study with BTX. Patients were examined on days 0, 30, 90, and 120 and received one injection of BTX and one of placebo in a random order at day 0 and day 90.

RESULTS

Patients reported a clear subjective improvement in foot spasticity after BTX (P = 0.0014) but not after placebo. Significant changes were noted in Ashworth scale values for ankle extensors (P < 0.0001) and invertors (P = 0.0002), and for active ankle dorsiflexion (P = 0.0001). Gait velocity was slightly but not significantly (P = 0.0731) improved after BTX injections. The severity of spasticity did not modify treatment efficacy, but BTX was less effective in patients with longer duration of spasticity (P = 0.0081).

CONCLUSION

The efficacy of BTX injections in the treatment of spastic foot suggests that BTX may be particularly useful during the first year after a stroke.

Responses of substantia nigra pars reticulata neurons to intrastriatal D1 and D2 dopaminergic agonist injections in the rat

Extracellular neuronal recordings were performed in the substantia nigra pars reticulata (SNr) of normal and 6-hydroxydopamine (6-OHDA)-lesioned rats during intrastriatal D1 and D2 dopaminergic-agonist injections. Three types of responses were observed, inhibition, excitation and/or regularization of neuronal discharge patterns. In normal rats, variable responses were observed after D2 injections and a predominance of inhibition after D1 injections. In lesioned rats, the percentage of neurons inhibited and that of neurons regularized increased following D2 injections. During sequential intrastriatal D1 and D2 agonist injections, a response to both dopaminergic agents was observed in 22.5% and 55.5% of SNr neurons in normal and lesioned rats, respectively. Our data suggests that the physiological relevance of direct and indirect pathways convergence upon a given SNr target neuron depends on their respective synaptic weight, the influence of surrounding SNr neurons and the state of dopamine depletion.