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.