Striatum

Anatomical terms of neuroanatomy

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The?striatum, or?corpus striatum[5]?(also called the?striate nucleus), is a?nucleus?(a cluster of?neurons) in the?subcortical?basal ganglia?of the?forebrain. The striatum?is a critical component of the?motor?and?reward?systems; receives?glutamatergic?and?dopaminergic?inputs from different sources; and serves as the primary input to the rest of the basal ganglia.

Functionally, the striatum coordinates multiple aspects of?cognition, including both motor and action?planning,?decision-making,?motivation,?reinforcement, and?reward?perception.[2][3][4]?The striatum is made up of the?caudate nucleus?and the?lentiform nucleus.[6][7]?The lentiform nucleus is made up of the larger?putamen, and the smaller?globus pallidus.[8]?Strictly speaking the globus pallidus is part of the striatum. It is common practice, however, to implicitly exclude the globus pallidus when referring to striatal structures.

In?primates, the striatum is divided into a?ventral striatum, and a?dorsal striatum,subdivisions that are based upon function and connections. The?ventral?striatum consists of the?nucleus accumbens?and the?olfactory tubercle.?The?dorsal?striatum consists of the?caudate nucleus?and the?putamen.?A?white matter,?nerve tract?(the?internal capsule) in the dorsal striatum separates the?caudate nucleus?and the?putamen.[4]?Anatomically, the term?striatum?describes its striped (striated) appearance of grey-and-white matter.[9]

The striatum in red as seen on?MRI. The striatum includes the?caudate nucleus?(top), and the?lentiform nucleus?(putamen?(right) and lower left the?globus pallidus)

The striatum is the largest structure of the?basal ganglia. The striatum is divided into a ventral and a dorsal subdivision, based upon function and connections.

The ventral striatum is composed of the?nucleus accumbens?and the?olfactory tubercle.[4][10]?The nucleus accumbens is made up of the?nucleus accumbens core?and the?nucleus accumbens shell, which differ by neural populations. The olfactory tubercle receives input from the?olfactory bulb?but has not been shown to play a role in?processing smell.[10]?In non-primate species, the?islands of Calleja?are included.[11]?The ventral striatum is associated with the limbic system and has been implicated as a vital part of the?circuitry?for decision making and reward-related behavior.[12][13]

The dorsal striatum is composed of the?caudate nucleus?and the?putamen.

Staining?can differentiate the striatum into two distinct compartments of?striosomes?or?patches, and a surrounding?matrix; this is particularly evident on the components of?acetylcholinesterase?and?calbindin. More studies have been carried out on the dorsal striatum but the compartments have also been identified in the ventral striatum. In the dorsal striatum striosomes make up 10-15 per cent of the striatal volume.[14]

Cell types[edit]

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Dendritic spines?on?medium spiny neuron?of striatum

Types of cells in the striatum include:（這里說了這么多關(guān)于neuron細節(jié)的內(nèi)容，但是并沒有提示是否具備去甲腎上腺素遞質(zhì)受體。）

·?Medium spiny neurons?(MSNs), which are the principal neurons of the striatum.[2]?They are?GABAergic?and, thus, are classified as inhibitory neurons. Medium spiny projection neurons comprise 95% of the total neuronal population of the human striatum.[2]?Medium spiny neurons have two?characteristic types:?D1-type?MSNs and?D2-type?MSNs.[2][4][15]?A subpopulation of MSNs contain both D1-type and D2-type receptors, with approximately?40% of striatal MSNs expressing both?DRD1?and?DRD2?mRNA.[2][4][15]

·?Cholinergic?interneurons?release acetylcholine, which has a variety of important effects in the striatum. In humans, other primates, and rodents, these interneurons respond to salient environmental stimuli with stereotyped responses that are temporally aligned with the responses of dopaminergic neurons of the?substantia nigra.[16][17]?The large aspiny cholinergic interneurons themselves are affected by dopamine through?D5 dopamine receptors.[18]?Dopamine also directly controls communication between cholinergic interneurons.[19][20]

·?There are many types of GABAergic interneurons.[21]?The best known are?parvalbumin?expressing interneurons, also known as?fast-spiking?interneurons, which participate in powerful?feedforward?inhibition of principal neurons.[22]?Also, there are GABAergic interneurons that express?tyrosine hydroxylase,[23]?somatostatin,?nitric oxide synthase?and?neuropeptide-y. Recently, two types of neuropeptide-y expressing GABAergic interneurons have been described in detail,[24]?one of which translates synchronous activity of cholinergic interneurons into inhibition of principal neurons.[25]?These?neurons?of the striatum are not distributed evenly.[21]

There are two regions of?neurogenesis?in the brain – the?subventricular zone?in the?lateral ventricles, and the?dentate gyrus?in the?hippocampal formation.?Neuroblasts?that form in the lateral ventricle adjacent to the striatum, integrate in the striatum.[26][27]?This has been noted in the human striatum following an?ischemic stroke. Injury caused to the striatum stimulates the migration of neuroblasts from the subventricular zone, to the striatum, where they differentiate into adult neurons.[28]?The normal passage of SVZ neuroblasts is to the?olfactory bulb?but this traffic is diverted to the striatum after an ischemic stroke. However, few of the new developed neurons survive.[29]

Inputs[edit]

Overview of the main circuits of the basal ganglia. The striatum is shown in blue. Picture shows 2 coronal slices that have been superimposed to include the involved basal ganglia structures.?+?and?–?signs at the point of the arrows indicate respectively whether the pathway is excitatory or inhibitory in effect.?Green arrows?refer to excitatory?glutamatergic?pathways,?red arrows?refer to inhibitory?GABAergic?pathways and?turquoise arrows?refer to?dopaminergic?pathways that are excitatory on the?direct pathway?and inhibitory on the?indirect pathway.

[30]?The largest connection is from the?cortex, in terms of cell axons.?Many parts of the?neocortex?innervate?the dorsal striatum.?The cortical?pyramidal neurons?projecting to the striatum are located in layers II-VI, with the most dense projections come from layer V.[31]?They end mainly on the?dendritic spines?of the spiny neurons.?They are?glutamatergic, exciting striatal neurons.

(難道neuron上的spine只與谷氨酸遞質(zhì)結(jié)合？Aspiny neuron就不與谷氨酸遞質(zhì)結(jié)合？從這一點，就可以通過spine這個結(jié)構(gòu)特點來判斷軸突是否與apiny stellate cell建立聯(lián)系。)

The striatum is seen as having its own internal microcircuitry.[32]?The ventral striatum receives direct input from multiple regions in the?cerebral cortex?and limbic structures such as the?amygdala,?thalamus, and?hippocampus, as well as the?entorhinal cortex?and the?inferior temporal gyrus（舉得例子數(shù)量不夠啊，鑒于，ventral striatum有兩個結(jié)構(gòu)，文中也沒指出具體連接的細節(jié)。）.[33]?Its primary input is to the?basal ganglia?system（這句話的意思是ventral striatum的主要輸出對象是basal ganglia system。）. Additionally, the?mesolimbic pathway?projects from the?ventral tegmental area?to the?nucleus accumbens?of the ventral striatum.

（寫這句話的author是不是忘了mesolimbic pathway?also projects?to olfactory tubercle.換句話說，就是投射到整個ventral striatum。）

[34]

Another well-known afferent is the?nigrostriatal?connection arising from the neurons of the?substantia nigra?pars compacta. While cortical axons synapse mainly on spine heads of spiny neurons, nigral axons synapse mainly on spine shafts. In primates, the thalamostriatal afferent comes from the central median-parafascicular complex of the?thalamus?（來自丘腦的疼痛核團。）(see?primate basal ganglia system). This afferent is glutamatergic. The participation of truly intralaminar neurons is much more limited. The striatum also receives afferents from other elements of the basal ganglia such as the?subthalamic nucleus?(glutamatergic) or the?external globus pallidus?(GABAergic).

Targets[edit]

Further information:?Medium spiny neuron

The primary outputs of the ventral striatum project to the?ventral pallidum,?then the?medial dorsal nucleus?of the?thalamus, which is part of the?frontostriatal circuit. Additionally, the ventral striatum projects to the?globus pallidus, and substantia nigra pars reticulata. Some of its other outputs include projections to the?extended amygdala,?lateral hypothalamus, and?pedunculopontine nucleus.（這些內(nèi)容講的不詳細，不知道是故意隱瞞還是就是不知道，但是確實能夠印證其他詞條中的一些內(nèi)容。）[35]

Striatal outputs from both the dorsal and ventral components are primarily composed of?medium spiny neurons?(MSNs), a type of?projection neuron, which have two primary?phenotypes: "indirect" MSNs that express?D2-like receptors?and "direct" MSNs that express?D1-like receptors.[2][4]

The main nucleus of the basal ganglia is the striatum which projects directly to the globus pallidus via a pathway of?striatopallidal fibers.[36]?The striato-pallidal pathway has a whitish appearance due to the myelinated fibers. This projection comprises successively the external globus pallidus (GPe), the internal globus pallidus (GPi), the?pars compacta?of the?substantia nigra?(SNc), and the?pars reticulata?of substantia nigra (SNr). The neurons of this projection are inhibited by GABAergic synapses from the dorsal striatum. Among these targets, the GPe does not send axons outside the system.?Others send axons to the?superior colliculus. Two others comprise the output to the thalamus, forming two separate channels: one through the internal segment of the globus pallidus to the ventral oralis nuclei of the thalamus?and from there to the cortical?supplementary motor area?and another through the substantia nigra to the ventral anterior nuclei of the thalamus and from there to the?frontal cortex?and the occulomotor cortex.

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Blood supply[edit]

Deep penetrating?striate arteries?supply blood to the striatum. These arteries include the?recurrent artery of Heubner?arising from the?anterior cerebral artery, and the?lenticulostriate arteries?arising from the?middle cerebral artery.[37]

Function[edit]

The ventral striatum, and the?nucleus accumbens?in particular, primarily mediates?reward, cognition,?reinforcement, and?motivational salience, whereas the dorsal striatum primarily mediates cognition involving?motor function, certain?executive functions?(e.g.,?inhibitory control?and?impulsivity), and?stimulus-response learning;[2][3][4][38][39]?there is a small degree of overlap, as the dorsal striatum is also a component of the?reward system?that, along with the?nucleus accumbens core, mediates the encoding of new motor programs associated with future reward acquisition (e.g., the?conditioned motor response?to a reward cue).[3][38]

Metabotropic?dopamine receptors?are present both on spiny neurons and on cortical axon terminals.?Second messenger?cascades triggered by activation of these dopamine receptors can modulate pre- and postsynaptic function, both in the short term and in the long term.[40][41]?In humans, the striatum is activated by stimuli associated with reward, but also by?aversive,?novel,[42]?unexpected, or intense?stimuli, and cues associated with such events.[43]?fMRI?evidence suggests that the common property linking these stimuli, to which the striatum is reacting, is?salience?under the conditions of presentation.[44][45]?A number of other brain areas and circuits are also related to reward, such as frontal areas. Functional maps of the striatum reveal interactions with widely distributed regions of the cerebral cortex important to a diverse range of functions.[46]

The interplay between the striatum and the?prefrontal cortex?is relevant for behavior, particularly adolescent development as proposed by the?dual systems model.[47]

Clinical significance[edit]

Parkinson's disease and other movement disorders[edit]

Parkinson's disease?results in loss of dopaminergic innervation to the dorsal striatum (and other basal ganglia) and a cascade of consequences.?Atrophy?of the striatum is also involved in?Huntington's disease, and?movement disorders?such as?chorea,?choreoathetosis, and?dyskinesias.[48]?These have also been described as?circuit disorders?of the basal ganglia.[49]

Addiction[edit]

Addiction, a disorder of the brain's?reward system, arises through the?overexpression?of?DeltaFosB?(ΔFosB), a?transcription factor, in the?D1-type?medium spiny neurons?of the?ventral striatum. ΔFosB is an?inducible gene?which is increasingly expressed in the?nucleus accumbens?as a result of repeatedly?overdosing?on an addictive drug or overexposure to other addictive stimuli.[50][51]

Bipolar disorder[edit]

An association has been observed between striatal expression of variants of the?PDE10A?gene and some?bipolar I disorder?patients. Variants of other genes,?DISC1?and?GNAS, have been associated with?bipolar II disorder.[52]

Autism spectrum disorder[edit]

Autism spectrum disorder?(ASD) is characterized by cognitive inflexibility and poor understanding of social systems. This inflexible behavior originates in defects in the pre-frontal cortex as well as the striatal circuits.[53]?The defects in the striatum seem to specifically contribute to the motor, social and communication impairments seen in ASD patients. In mice which have an ASD-like phenotype induced via the overexpression of the?eukaryotic initiation of translation factor 4E, it has been shown that these defects seem to stem from the reduced ability to store and process information in the striatum, which leads to the difficulty seen in forming new motor patterns, as well as disengaging from existing ones.[54]

Dysfunction[edit]

Dysfunction in the ventral striatum can lead to a variety of disorders, most notably,?depression?and?obsessive-compulsive disorder. Because of its involvement in reward pathways, the ventral striatum has also been implicated in playing a critical role in addiction. It has been well established that the ventral striatum is strongly involved in mediating the reinforcing effects of drugs, especially stimulants, through dopaminergic stimulation.[55]

History[edit]

In the seventeenth and eighteenth centuries, the term "corpus striatum" was used to designate many distinct, deep, infracortical elements of the hemisphere.[56]?Etymologically it is derived from (Latin) "striatus"?[57]?= "grooved, striated" and the English "striated" = having parallel lines or grooves on the surface.[58]?In 1941,?Cécile?and?Oskar Vogt?simplified the nomenclature by proposing the term?striatum?for all elements in the?basal ganglia?built with striatal elements: the?caudate nucleus, the?putamen, and the?fundus striati,[59]?which is the ventral part linking the two preceding together ventrally to the inferior part of the?internal capsule.

The term?neostriatum?was forged by comparative anatomists comparing the subcortical structures between vertebrates, because it was thought to be a phylogenetically newer section of the corpus striatum. The term is still used by some sources, including?Medical Subject Headings.[60]

Other animals[edit]

In?birds?the term used was the?paleostriatum augmentatum, and in the new avian terminology listing (as of 2002) for?neostriatum?this has been changed to the?nidopallium.[61]

In non-primate species, the?islands of Calleja?are included in the ventral striatum.[11]