Abdelhamid Benazzouz

Reversal of Rigidity and Improvement in Motor Performance by Subthalamic High‐frequency Stimulation in MPTP‐treated Monkeys

In Parkinsons disease the loss of dopaminergic neurons in the substantia nigra is associated with global disorganization of basal ganglia activity and, in particular, with increased activity of the excitatory glutamatergic neurons of the subthalamic nucleus. Recent experimental studies have shown that parkinsonian symptoms can be alleviated by selective lesioning of the subthalamic nucleus in monkeys treated with 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP). We measured the effect of high‐frequency stimulation of the subthalamic nucleus in two unilaterally MPTP‐treated monkeys in order to determine whether it was possible to obtain reversible, gradual and controllable functional impairment of this structure. Clinical, mechanographic and electromyographic results demonstrate that this technique can alleviate parkinsonian rigidity and bradykinesia without causing dyskinesia or hemiballismus. This study supports the hypothesis that the subthalamic nucleus and its excitatory projections have an important role in the mechanisms sustaining the expression of parkinsonian motor changes, and suggests that high‐frequency stimulation of the subthalamic nucleus could be included in treatment for parkinsonism.

Riluzole prevents MPTP-induced parkinsonism in the rhesus monkey: a pilot study

Previous studies have shown that riluzole (2-amino-6-trifluoromethoxy-benzothiazole), a drug which interferes with glutamate neurotransmission, has a neuroprotective action in rodent models of global and focal cerebral ischemia. In this pilot study, the protective and palliative effects of riluzole have been examined using an animal model of Parkinsons disease. Two monkeys were rendered hemiparkinsonian by one intracarotid injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and motor signs were evaluated using clinical examination and electromyographic recordings. When riluzole (4 mg/kg) was administered before the injection of MPTP, parkinsonian motor symptoms, in particular bradykinesia and rigidity, were absent. When injected daily in one monkey which presented stable motor symptoms, bradykinesia and rigidity were significantly reduce d. Riluzole pretreatment induced a persistent increase in dopamine turnover when compared to MPTP alone. Thus, a possible neuroprotection and a facilitation of dopamine release may explain the behavioural effects reported with riluzole treatment. These preliminary results suggest that riluzole could possess neuroprotective and palliative effects in a primate model of Parkinsons disease.

Reduction of apomorphine-induced rotational behaviour by subthalamic lesion in 6-OHDA lesioned rats is associated with a normalization of firing rate and discharge pattern of pars reticulata neurons.

The effect of subthalamic nucleus (STh) lesion on apomorphine-induced rotational behaviour and unit activity of substantia nigra pars reticulata (SNr) neurons was studied in normal, sham-control and unilateral 6-OHDA-lesioned rats [SN pars compacta (SNc)-lesioned]. In the latter, contraversive rotational behaviour was greatly reduced by an additional ipsilateral STh lesion. A moderate ipsiversive rotation was observed in rats with a single STh lesion. Concurrently, SN unit extracellular recordings were performed in age-matched normal rats, sham-controls for both lesions, STh-lesioned rats, SNc-lesioned rats, and SNc-lesioned rats with an ipsilateral STh lesion (SNc+STh-lesioned). Pars reticulata neurons had a higher mean firing rate in SNc-lesioned rats than in control rats. Furthermore, 68% of SNr neurons in SNc-lesioned rats had a tonic discharge pattern (against 92.3% in control rats) and 32% a mixed or bursting pattern. After STh lesion, a clear decrease in SNr firing rate was observed in SNc-lesioned rats. Moreover, STh lesion improved interspike interval regularity and decreased the occurrence of bursting patterns. In rats with a single STh lesion, the firing rate was no different from that of the sham-controls but the discharge pattern was more regular. These data show that STh lesion decreased apomorphine-induced rotational behaviour in dopamine-depleted animals. This effect could be related to the suppression of the exitatory effect of STh efferents on the SNr neurons. STh lesion both counterbalanced the increased activity of SNr neurons and regularized their discharge pattern.

MPTP induced hemiparkinsonism in monkeys: behavioral, mechanographic, electromyographic and immunohistochemical studies

SummaryA single infusion of 1-methyl-4-phenyl-1,2,3,6-tetrahydro-pyridine (MPTP) into the right internal carotid artery of Macaca mulatta, monkeys resulted in akinesia and rigidity of the contralateral limb. The immunohistochemical study revealed a dramatic reduction in the number of TH-immunoreactive cells in the substantia nigra of the infused side (70–81%). After unilateral MPTP-treatment movement parameters and EMG activity were altered; the agonist muscle developed increased EMG activity associated with a shift of antagonist muscle activity. These results confirm that hemiparkinsonian monkeys are a valuable model of parkinsonism which can be useful in studies of movement disorder physiology and therapy of Parkinsons disease.

Involvement of Basal Ganglia network in motor disabilities induced by typical antipsychotics.

Background Clinical treatments with typical antipsychotic drugs (APDs) are accompanied by extrapyramidal motor side-effects (EPS) such as hypokinesia and catalepsy. As little is known about electrophysiological substrates of such motor disturbances, we investigated the effects of a typical APD, α-flupentixol, on the motor behavior and the neuronal activity of the whole basal ganglia nuclei in the rat. Methods and Findings The motor behavior was examined by the open field actimeter and the neuronal activity of basal ganglia nuclei was investigated using extracellular single unit recordings on urethane anesthetized rats. We show that α-flupentixol induced EPS paralleled by a decrease in the firing rate and a disorganization of the firing pattern in both substantia nigra pars reticulata (SNr) and subthalamic nucleus (STN). Furthermore, α-flupentixol induced an increase in the firing rate of globus pallidus (GP) neurons. In the striatum, we recorded two populations of medium spiny neurons (MSNs) after their antidromic identification. At basal level, both striato-pallidal and striato-nigral MSNs were found to be unaffected by α-flupentixol. However, during electrical cortico-striatal activation only striato-pallidal, but not striato-nigral, MSNs were found to be inhibited by α-flupentixol. Together, our results suggest that the changes in STN and SNr neuronal activity are a consequence of increased neuronal activity of globus pallidus (GP). Indeed, after selective GP lesion, α-flupentixol failed to induce EPS and to alter STN neuronal activity. Conclusion Our study reports strong evidence to show that hypokinesia and catalepsy induced by α-flupentixol are triggered by dramatic changes occurring in basal ganglia network. We provide new insight into the key role of GP in the pathophysiology of APD-induced EPS suggesting that the GP can be considered as a potential target for the treatment of EPS.

Intrapallidal injection of 6-hydroxydopamine induced changes in dopamine innervation and neuronal activity of globus pallidus

The globus pallidus (GP) plays an important role in basal ganglia circuitry. In contrast to the well-characterized actions of dopamine on striatal neurons, the functional role of the dopamine innervation of GP is still not clearly determined. The present study aimed to investigate the effects of intrapallidal injection of 6-hydroxydopamine (6-OHDA) on rotational behavior induced by apomorphine, on the loss of dopamine cell bodies in the substantia nigra pars compacta (SNc) and fibers in the GP and striatum and on in vivo extracellularly-recorded GP neurons in the rat. Injection of 6-OHDA into GP induced severe loss of tyrosine hydroxylase-immunoreactive (TH-IR) fibers in GP (-85%) with a reduction in the number of TH-IR cell bodies in the SNc (-52%) and fibers in the striatum (-50%). S.c. injection of apomorphine in these rats induced a moderate number of turns (26+/-6 turns/5 min). Electrophysiological recordings show that 6-OHDA injection in GP induced a significant decrease of the firing rate of GP neurons (16.02+/-1.11 versus 24.14+/-1.58 spikes/sec in control animals and 22.83+/-1.28 in sham animals, one-way ANOVA, P<0.0001) without any change in the firing pattern (chi(2)=1.03, df=4, P=0.90). Our results support the premise of the existence of collaterals of SNc dopaminergic axons projecting to the striatum and GP and that dopamine plays a role in the modulation of the firing rate but not the firing pattern of GP neurons. Our data provide important insights into the functional role of the SNc-GP dopaminergic pathway suggesting that dopamine depletion in GP may participate in the development of motor disabilities.

Inhibiting Subthalamic D5 Receptor Constitutive Activity Alleviates Abnormal Electrical Activity and Reverses Motor Impairment in a Rat Model of Parkinson's Disease

Burst firing has been reported as a pathological activity of subthalamic nucleus (STN) neurons in Parkinsons disease. However, the origin of bursts and their causal link with motor deficits remain unknown. Here we tested the hypothesis that dopamine D5 receptors (D5Rs), characterized by a high constitutive activity, may contribute to the emergence of burst firing in STN. We tested whether inhibiting D5R constitutive activity depresses burst firing and alleviates motor impairments in the 6-OHDA rat model of Parkinsons disease. Intrasubthalamic microinjections of either an inverse agonist of D5Rs, flupenthixol, or a D2R antagonist, raclopride, were applied. Behavioral experiments, in vivo and in vitro electrophysiological recordings, and ex vivo functional neuroanatomy studies were performed. Using [5S]GTPγ binding autoradiography, we show that application of flupenthixol inhibits D5R constitutive activity within the STN. Furthermore, flupenthixol reduced evoked burst in brain slices and converted pathological burst firing into physiological tonic, single-spike firing in 6-OHDA rats in vivo. This later action was mimicked by calciseptine, a Cav1 channel blocker. Moreover, the same treatment dramatically attenuated motor impairment in this model and normalized metabolic hyperactivity in both STN and substantia nigra pars reticulata, the main output structure of basal ganglia in rats. In contrast, raclopride as well as saline did not reverse burst firing and motor deficits, confirming the selective action of flupenthixol on D5Rs. These results are the first to demonstrate that subthalamic D5Rs are involved in the pathophysiology of Parkinsons disease and that administering an inverse agonist of these receptors may lessen motor symptoms.

The Subthalamic Nucleus: A More Complex Structure than Expected

Almost all the papers on the subthalamic nucleus, after the usual review of its anatomical connections, summarize the function of this structure with the classical reference to hemiballism. This type of anatomopathological approach is still widely used in neurobiology, despite the fact that it is a little strange to define subthalamic nucleus functions by reference to its dysfunction. The physiological functions have only recently been freed from the impressive and restrictive clinical description of hemiballism. Currently, facts and hypotheses stress the relationship between hypo- or hyperactivity of the subthalamic neurons and two opposite motor dysfunctions, hyperkinesia as in hemiballism and akinesia as in parkinsonism. Moreover, the importance of subthalamic inputs arising from associative or limbic structures should not be overlooked since they are an integral part of this concept of the function of the subthalamic nucleus and suggest that this structure has broader and more complex involvement in a large range of activities which may or may not have a motor component.

An Embedded Deep Brain Stimulator for Biphasic Chronic Experiments in Freely Moving Rodents

This paper describes a Deep Brain Stimulation device, portable, for chronic experiments on rodents in the context of Parkinsons disease. Our goal is to equip the animal with a device that mimics the human therapeutic conditions. It implies to respect a set of properties such as bilateral current-mode and charge-balanced stimulation, as well as programmability, low power consumption and re-usability to finally reach a suitable weight for long-term experiments. After the analysis of the solutions found in the literature, the full design of the device is explained. First, the stimulation front-end circuit driven by a processor unit, then the choice of supply sources which is a critical point for the weight and life-time of our system. Our low cost system has been realized using commercial discrete components and the overall power consumption was minimized. We achieved 6 days of maximal current stimulation with the chosen battery for a weight of 13.8 g. Finally, the device was carried out in vivo on rats during a 3 weeks experiment as the used implantation technique allows battery changing. This experiment also permits to emphasize the mechanical aspects including the packaging and electrodes holding.

Metabolic and electrophysiological changes in the basal ganglia of transgenic Huntington's disease rats.

Huntingtons disease (HD) is characterized by neuronal loss in the striatum, ultimately leading to an imbalance in the electrical activity of the basal ganglia-thalamocortical circuits. To restore this imbalance in HD patients, which is held responsible for (some) of the motor symptoms, different basal ganglia nuclei have been targeted for surgical therapies, such as ablative surgery and deep brain stimulation. However, evidence to target brain nuclei for surgical therapies in HD is lacking. We reasoned that a neuronal and metabolic mapping of the basal ganglia nuclei could identify a functional substrate for therapeutic interventions. Therefore, the aim of the present study was to investigate the metabolic and neuronal activity of basal ganglia nuclei in a transgenic rat model of HD (tgHD). Subjects were 10-12 month old tgHD rats and wildtype littermates. We examined the striatum, globus pallidus, entopeduncular nucleus, the subthalamic nucleus and substantia nigra at different levels. First, we determined the overall neuronal activity at a supracellular level, by cytochrome oxidase histochemistry. Secondly, we determined the subcellular metabolic activity, by immunohistochemistry for peroxisome proliferator-activated receptor-γ transcription co-activator (PGC-1α), a key player in the mitochondrial machinery. Finally, we performed extracellular single unit recordings in the nuclei to determine the cellular activity. In tgHD rats, optical density analysis showed a significantly increased cytochrome oxidase levels in the globus pallidus and subthalamic nucleus when compared to controls. PGC-1α expression was only enhanced in the subthalamic nucleus and electrophysiological recordings revealed decreased firing frequency of the majority of the neurons in the globus pallidus and increased firing frequency of the majority of the neurons in the subthalamic nucleus. Altogether, our results suggest that the globus pallidus and subthalamic nucleus play a role in the neurobiology of HD and can be potential targets for therapeutic interventions.