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[[Image:Gray717.png|thumb|Coupe coronale du cerveau passant par le noyau sous-thalamique.]] |
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Le '''noyau sous-thalamique''' ou '''subthalamique''' ('''''Nucleus subthalamicus'''''), encore appelé '''Corps de [[Jules Bernard Luys|Luys]]''' est l'un des [[ganglions de la base]] du [[diencéphale]]. |
Le '''noyau sous-thalamique''' ou '''subthalamique''' ('''''Nucleus subthalamicus'''''), encore appelé '''Corps de [[Jules Bernard Luys|Luys]]''' est l'un des [[ganglions de la base]] du [[diencéphale]]. Ce noyau de petite taille en forme de lentille se situe ventralement au [[thalamus]], dorsalement au [[locus niger]] et au contact de la [[capsule interne]], médialement à celle-ci. On doit sa description au [[Neurologie|neurologue]] [[Jules Bernard Luys]] en 1865.<ref>{{cite book | last=Luys | first=Jules Bernard | authorlink=Jules Bernard Luys | year=1865 | title=Recherches sur le système cérébro-spinal, sa structure, ses fonctions et ses maladies | publisher=Baillière | location=Paris | language=French}}</ref> |
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Les lésions de ce noyau sont responsables de l'[[hémiballisme]], un mouvement anormal de grande amplitude de la racine des membres, à caractère explosif. |
Les lésions de ce noyau sont responsables de l'[[hémiballisme]], un mouvement anormal de grande amplitude de la racine des membres, à caractère explosif. La cause la plus fréquente d'une telle lésion est un [[accident vasculaire cérébral]] impliquant les petits vaisseaux, comme en cas de [[diabète]] ou d'[[hypertension artérielle]]. |
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== Fonction == |
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Le rôle exact du noyau sous-thalamique est encore inconnu. Les théories actuelles en font un composant du système de contrôle des ganglions de la base permettant la sélection des actions. On a montré qu'un dysfonctionnement du noyau sous-thalamique augmente l'impulsivité de sujets soumis à deux stimuli entraînant la même récompense.<ref>{{cite journal | author=Frank, M.; Samanta, J.; Moustafa, A.; Sherman, S. | title=Hold Your Horses: Impulsivity, Deep Brain Stimulation, and Medication in Parkinsonism | journal=Science | year=2007 | pages=1309–12 | volume=318 | issue=5854 | pmid=17962524 | doi=10.1126/science.1146157}}</ref> |
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== Références== |
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{{reflist|2}} |
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== Voir aussi == |
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* [[Ganglions de la base]] |
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== Lien externe== |
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*{{en}} [http://isc.temple.edu/neuroanatomy/lab/atlas/pdhn/ atlas de neuroanatomie] |
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==Anatomy== |
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===Structure=== |
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The principal type of [[neuron]] found in the subthalamic nucleus has rather long sparsely spiny [[dendrite]]s.<ref name=Afsharpour1985>{{Cite doi|10.1002/cne.902360102}}</ref><ref>{{Cite doi|10.1002/cne.901680105}}</ref> The dendritic arborizations are ellipsoid, replicating in smaller dimension the shape of the nucleus.<ref>{{cite journal | author=Yelnik, J. & Percheron, G. | title=Subthalamic neurons in primates : a quantitative and comparative anatomy | journal=Neuroscience | year=1979 | pages=1717–1743 | volume=4 | issue=11 | pmid=117397 | doi=10.1016/0306-4522(79)90030-7}}</ref> The dimensions of these arborizations (1200,600 and 300 μm) are similar across many species—including rat, cat, monkey and man—which is unusual. However, the number of neurons increases across evolution as well as the external dimensions of the nucleus. Due to the bending of dendrites at the border, the subthalamic nucleus is a close nucleus, able to receive information only in its space. The principal neurons are [[glutamatergic]], which give them a particular functional position in the basal ganglia system. In humans there are also a small number (about 7.5%) of [[GABA]]ergic [[interneuron]]s that participate in the local circuitry.<ref>{{cite journal | author=Levesque J.C. & Parent A. | title=GABAergic interneurons in human subthalamic nucleus | journal=Movement Disorders | year=2005 | pages=574–584 | volume=20 | issue=5 | pmid=15645534 | doi=10.1002/mds.20374}}</ref> |
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===Afferent axons=== |
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The subthalamic nucleus receives its main input from the lateral pallidum (external segment of the [[globus pallidus]]) (84.2% of its axons),<ref name=Sato2000>{{cite journal | author=Sato F.; Parent M.; Levesque M.; & Parent A. | title=Axonal branching pattern of neurons of the subthalamic nucleus in primates | journal=Journal of Comparative Neurology | year=2000 | pages=142–152 | volume=424 | issue=1 | pmid=10888744 | doi=10.1002/1096-9861(20000814)424:1<142::AID-CNE10>3.0.CO;2-8}}</ref> not so much through the ansa lenticularis as often said but by radiating fibers crossing the medial pallidum first and the internal capsule (see figure). This afference is GABAergic, inhibiting the neurons of the subthalamic nucleus. Excitatory, glutamatergic inputs come from the [[cerebral cortex]] (particularly the motor cortex), and from the pars [[parafascicularis]] of the [[central complex]]. The subthalamic nucleus also receives [[neuromodulator]]y inputs, notably [[dopaminergic]] axons from the [[substantia nigra]] pars compacta.<ref>{{cite journal | author=Cragg S.J.; Baufreton J.; Xue Y.; Bolam J.P.; & Bevan M.D. | title=Synaptic release of dopamine in the subthalamic nucleus | journal=European Journal of Neuroscience | year=2004 | pages=1788–1802 | volume=20 | issue=7 | pmid=15380000 | doi=10.1111/j.1460-9568.2004.03629.x}}</ref> |
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===Efferent targets=== |
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The axons of subthalamic nucleus neurons leave the nucleus dorsally. The efferent axons are glutamatergic (excitatory). Except for the connection to the striatum (17.3% in macaques), most of the subthalamic principal neurons are multitargets and directed to the other elements of the core of the basal ganglia.<ref name=Sato2000 /> Some send axons to the substantia nigra medially and to the medial and lateral nuclei of the pallidum laterally (3-target, 21.3%). Some are 2-target with the lateral pallidum and the substantia nigra (2.7%) or the lateral pallidum and the medial (48%). Less are single target for the lateral pallidum. In the pallidum, subthalamic terminals end in bands parallel to the pallidal border.<ref>{{cite journal | author=Nauta, H.J.W. & Cole, M. | title=Efferent projections of the subthalamic nucleus : an autoradiographic study in monkey and cat | journal=Journal of Comparative Neurology | year=1978 | pages=1–16 | volume=180 | issue=1 | pmid=418083 | doi=10.1002/cne.901800102}}</ref><ref name=Smith1990>{{cite journal | author=Smith, Y.; Hazrati, L-N. & Parent, A. | title=Efferent projections of the subthalamic nucleus in the squirrel monkey as studied by the PHA-L anterograde tracing method | journal=Journal of Comparative Neurology | year=1990 | pages=306–323 | volume=294 | issue=2 | pmid=2332533 | doi=10.1002/cne.902940213}}</ref> When all axons reaching this target are added, the main afference of the subthalamic nucleus is, in 82.7% of the cases, clearly the [[medial pallidum]] (internal segment of the globus pallidus). Some researchers have reported internal [[axon]] collaterals.<ref>{{cite journal | author=Kita, H.; Chang, H.T.; & Kitai, S.T. | title=The morphology of intracellularly labeled rat subthalamic neurons: A light microscopic analysis | journal=Neuroscience | year=1983 | pages=245–257 | volume=215 | issue=3 | pmid=6304154}}</ref> However, there is little functional evidence for this. |
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==Physiology== |
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===Subthalamic nucleus=== |
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The first intracellular electrical recordings of subthalamic neurons were performed using sharp electrodes in a rat slice preparation (Nakanishi et al., 1987). In these recordings three key observations were made, all three of which have dominated subsequent reports of subthalamic firing properties. The first observation was that, in the absence of current injection or synaptic stimulation, the majority of cells were spontaneously firing. The second observation is that these cells are capable of transiently firing at very high frequencies. The third observation concerns non-linear behaviors when cells are transiently depolarized after being hyperpolarized below –65mV. They are then able to engage voltage-gated calcium and sodium currents to fire bursts of action potentials. Several recent studies have focused on the autonomous pacemaking ability of subthalamic neurons. These cells are often referred to as "fast-spiking pacemakers",<ref>{{cite journal | author=Surmeier D.J.; Mercer J.N.; & Chan C.S. | title=Autonomous pacemakers in the basal ganglia: who needs excitatory synapses anyway? | journal=Current Opinion in Neurobiology | year=2005 | pages=312–318 | volume=15 | issue=3 | pmid=15916893 | doi=10.1016/j.conb.2005.05.007}}</ref> since they can generate spontaneous [[action potential]]s at rates of 80 to 90Hz in primates. |
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=== Lateropallido-subthalamic system=== |
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Strong reciprocal connections link the subthalamic nucleus and the external segment of the globus pallidus. Both are fast-spiking pacemakers. Together, they are thought to constitute the "central pacemaker of the basal ganglia"<ref>{{cite journal | author=Plenz, D. & Kitai, S.T. | title=A basal ganglia pacemaker formed by the subthalamic nucleus and external globus pallidus | journal=Nature | year=1999 | pages=677–682 | volume=400 | issue=6745 | pmid=10458164 | doi=10.1038/23281}}</ref> with synchronous bursts. The connection of the lateral pallidum with the subthalamic nucleus is also the one in the basal ganglia system where the reduction between emitter/receiving elements is likely the strongest. In terms of volume, in humans, the lateral pallidum mesures 808 mm³, the subthalamic nucleus only 158 mm³.<ref>{{cite journal | author=Yelnik, J. | title=Functional anatomy of the basal ganglia | journal=Movement Disorders | year=2002 | pages=S15–S21 | volume=17 | issue=Suppl. 3 | pmid=11948751 | doi=10.1002/mds.10138}}</ref> This translated in numbers of neurons represents a strong compression with loss of map precision. Some axons from the lateral pallidum go to the striatum.<ref>{{cite journal | author=Sato, F.; Lavallée, P.; Levesque, M. & Parent, A. | title=Single-axon tracing study of neurons of the external segment of the globus pallidus in primate | journal=Journal of Comparative Neurology | year=2000 | pages=17–31 | volume=417 | issue=1 | pmid=10660885 | doi=10.1002/(SICI)1096-9861(20000131)417:1<17::AID-CNE2>3.0.CO;2-I}}</ref> The activity of the medial pallidum is influenced by afferences from the lateral pallidum and from the subthalamic nucleus.<ref>{{cite journal | author=Smith, Y.; Wichmann, T. & DeLong, M.R. | title=Synaptic innervation of neurones in the internal pallidal segment by the subthalamic nucleus and the external pallidum in monkeys | journal=Journal of Comparative Neurology | year=1994 | pages=297–318 | volume=343 | issue=2 | pmid=8027445 | doi=10.1002/cne.903430209}}</ref> The same for the [[nigra reticulata]].<ref name=Smith1990 /> The subthalamic nucleus sends axons to another regulator: the pedunculo-pontine complex (id). The lateropallido-subthalamic system is thought to play a key role in the generation of the patterns of activity seen in [[Parkinson's disease]].<ref>{{cite journal | author=Bevan M.D.; Magill P.J.; Terman D.; Bolam J.P.; & Wilson CJ. | title=Move to the rhythm: oscillations in the subthalamic nucleus-external globus pallidus network | journal=Trends in Neurosciences | year=2002 | pages=525–531 | volume=25 | issue=10 | pmid=12220881 | doi=10.1016/S0166-2236(02)02235-X}}</ref> ==Physiopathology and interventions== Chronic stimulation of the STN, called [[deep brain stimulation]] (DBS), is used to treat patients with [[Parkinson disease]]. The first to be stimulated are the terminal arborisations of afferent axons which modifies the activity of subthalamic neurons. However, it has been shown in thalamic slices from mice<ref>{{cite journal | author=Bekar L., Libionka W., Tian G., Xu Q., Torres A., Wang X., Lovatt D., Williams E., Takano T., Schnermann J., Bakos R., Nedergaard M. | title=Adenosine is crucial for deep brain stimulation–mediated attenuation of tremor| journal=Nature Medicine | year=2008 | pages=75–80 | volume=14 | issue=1 | doi=10.1038/nm1693 }}</ref>, that the stimulus also causes nearby astrocytes to release [[Adenosine Triphosphate]] (ATP), a precursor to [[adenosine]] (through a catabolic process). In turn, adenosine A1 receptor activation depresses excitatory transmission in the thalamus, thus mimicking [[ablation]] of the subthalamic nucleus. |
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Version du 9 février 2009 à 15:54
Le noyau sous-thalamique ou subthalamique (Nucleus subthalamicus), encore appelé Corps de Luys est l'un des ganglions de la base du diencéphale. Ce noyau de petite taille en forme de lentille se situe ventralement au thalamus, dorsalement au locus niger et au contact de la capsule interne, médialement à celle-ci. On doit sa description au neurologue Jules Bernard Luys en 1865.[1] Les lésions de ce noyau sont responsables de l'hémiballisme, un mouvement anormal de grande amplitude de la racine des membres, à caractère explosif. La cause la plus fréquente d'une telle lésion est un accident vasculaire cérébral impliquant les petits vaisseaux, comme en cas de diabète ou d'hypertension artérielle.
Fonction
Le rôle exact du noyau sous-thalamique est encore inconnu. Les théories actuelles en font un composant du système de contrôle des ganglions de la base permettant la sélection des actions. On a montré qu'un dysfonctionnement du noyau sous-thalamique augmente l'impulsivité de sujets soumis à deux stimuli entraînant la même récompense.[2]
Références
- Jules Bernard Luys, Recherches sur le système cérébro-spinal, sa structure, ses fonctions et ses maladies, Paris, Baillière,
- Frank, M.; Samanta, J.; Moustafa, A.; Sherman, S., « Hold Your Horses: Impulsivity, Deep Brain Stimulation, and Medication in Parkinsonism », Science, vol. 318, no 5854, , p. 1309–12 (PMID 17962524, DOI 10.1126/science.1146157)
Voir aussi
Lien externe
