Striatum

"Neostriatum" redirects here. For the avian brain region formerly called the neostriatum, see nidopallium.

Striatum
purple=caudate and putamen, orange=thalamus
Details
Latin	neostriatum
Part of	Basal ganglia Reward system
Components	Ventral striatum Dorsal striatum
Identifiers
NeuroLex ID	Striatum
TA
TH	{{#property:P1694}}
TE	{{#property:P1693}}
FMA	{{#property:P1402}}
Anatomical terms of neuroanatomy [[[d:|edit on Wikidata]]]

The striatum, also known as the neostriatum or striate nucleus, is a subcortical part of the forebrain and a critical component of the reward system. It receives glutamatergic and dopaminergic inputs from different sources and serves as the primary input to the basal ganglia system. In all primates, the dorsal striatum is divided by a white matter tract called the internal capsule into two sectors called the caudate nucleus and the putamen. The ventral striatum is composed of the nucleus accumbens and olfactory tubercle in primates. Functionally, the striatum coordinates multiple aspects of cognition, including motor and action planning, decision-making, motivation, reinforcement, and reward perception.

The corpus striatum, a macrostructure which contains the striatum, is composed of the entire striatum and the globus pallidus. The lenticular nucleus refers to the putamen together with the globus pallidus.

Structure

Cell types

The striatum is heterogeneous in terms of its component neurons.

• Spiny projection neurons, commonly referred to as medium spiny neurons, are the principal neurons of the striatum. 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. Medium spiny neurons have two primary phenotypes (i.e., characteristic types): D1-type MSNs of the "direct pathway" and D2-type MSNs of the "indirect pathway". A subpopulation of MSNs contain both D1-type and D2-type receptors, with approximately 40% of striatal MSNs expressing both DRD1 and DRD2 mRNA.
• Cholinergic interneurons release acetylcholine, which has a variety of important effects in the striatum. In humans, non-human 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. The large aspiny cholinergic interneurons themselves are affected by dopamine through dopamine receptors D₅.
• There are many types of GABAergic interneurons. The best known are parvalbumin expressing interneurons, also known as fast-spiking interneurons, which participate in powerful feed-forward inhibition of principal neurons. Also, there are GABAergic interneurons that express tyrosine hydroxylase, somatostatin, nitric oxide synthase and neuropeptide-Y. Recently, two types of neuropeptide-y expressing GABAergic interneurons have been described in detail, one of which translates synchronous activity of cholinergic interneurons into inhibition of principal neurons.

Adult humans continuously produce new neurons in the striatum, and these neurons could play a possible role in new treatments for neurodegenerative disorders.

Anatomical subdivisions

File:Matrix Striosomes mar5.jpg

Matrix and Striosome Compartments: Fluorescence microscopy image of a coronal mouse brain section, cut through the striatum (caudate putamen, CP). The matrix/striosome division is here revealed by dual immunohistochemical (calbindin, CALB; green) and transgenic (red fluorescent protein, RFP; red) labeling of the matrix compartment, using the matrix-specific Cre-mouse line Gpr101-Cre. Unlabeled patches constitute striosomes.

File:Striatum Structural MRI.png

This is a transverse section of the striatum from a structural MR image. The striatum, in red, includes the caudate nucleus (top), the putamen (right), and, when including the term 'corpus' striatum, the globus pallidus (lower left).

The striatum is divided into ventral and dorsal subregions, based upon function and connectivity. The ventral striatum is composed of the nucleus accumbens and olfactory tubercle, whereas the dorsal striatum is composed of the caudate nucleus and putamen.

The dorsal striatum can be differentiated based on immunochemical characteristics—in particular with regard to acetylcholinesterase and calbindin — into "compartments", consisting of "striosomes" and the surrounding "matrix" (See figure "Matrix and Striosome Compartments").

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.

Inputs (afferent connections)

The most important afferent in terms of quantity of axons is the corticostriatal connection. Many parts of the neocortex innervate the dorsal striatum. The cortical pyramidal neurons projecting to the striatum are located in layers II-VI, but the most dense projections come from layer V. They end mainly on the spines of the spiny neurons. They are glutamatergic, exciting striatal neurons. 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 (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 (efferent connections)

Further information: Medium spiny neuron

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-type receptors and "direct" MSNs that express D1-type receptors.

The basal ganglia core is made up of the striatum along with the regions to which it projects directly, via the striato-pallidonigral bundle. The striato-pallidonigral bundle is a very dense bundle of sparsely myelinated axons, giving a whitish appearance. 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 (SMA) and another through the substantia nigra to the ventral anterior nuclei of the thalamus and from there to the frontal cortex and the oculomotor cortex.

Function

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 function, and stimulus-response learning; 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, the conditioned stimulus).

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. In humans, the striatum is activated by stimuli associated with reward, but also by aversive, novel, unexpected, or intense stimuli, and cues associated with such events. fMRI evidence suggests that the common property linking these stimuli, to which the striatum is reacting, is salience under the conditions of presentation. 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.

Clinical significance

Parkinson's disease

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, choreas, choreoathetosis, and dyskinesias.

Addiction

Addiction, a disorder of the brain's reward system, arises through pathological whole cell neuroplasticity in the D1-type medium spiny neurons of the ventral striatum, which are causally mediated through gene transcription by ΔFosB transcription factor. ΔFosB is an inducible gene which is increasingly expressed in the nucleus accumbens following high doses of an addictive drug or overexposure to other addictive stimuli.

Bipolar disorder

There is an association between striatal expression of the PDE10A gene and some bipolar disorder I patients.

History

In the seventeenth and eighteenth centuries, the term "corpus striatum" was used to designate many distinct, deep, infracortical elements of the hemisphere. In 1941, Cécile and Oskar Vogt simplified the nomenclature by proposing the term striatum for all elements built with striatal elements (see primate basal ganglia system): the caudate, the putamen, and the fundus striati, that 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.

See also

• List of regions in the human brain
• Striatopallidal fibres
• Ventral striatum

External links

• Stained brain slice images which include the "striatum" at the BrainMaps project
• hier-207 at NeuroNames
• Corpus Striatum at the US National Library of Medicine Medical Subject Headings (MeSH)