Unipolar brush cells (UBCs) are a class of

excitatory In neuroscience, an excitatory postsynaptic potential (EPSP) is a postsynaptic potential that makes the postsynaptic neuron more likely to fire an action potential. This temporary depolarization of postsynaptic membrane potential, caused by the ...

glutamatergic Glutamatergic means "related to glutamate". A glutamatergic agent (or drug) is a chemical that directly modulates the excitatory amino acid (glutamate/aspartate) system in the body or brain. Examples include excitatory amino acid receptor agonis ...

interneuron found in the granular layer of the

cerebellar cortex The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebe ...

and also in the granule cell domain of the

cochlear nucleus The cochlear nuclear (CN) complex comprises two cranial nerve nuclei in the human brainstem, the ventral cochlear nucleus (VCN) and the dorsal cochlear nucleus (DCN). The ventral cochlear nucleus is unlayered whereas the dorsal cochlear nucle ...

Structure

The UBC has a round or oval cell body with usually a single short

dendrite Dendrites (from Greek δένδρον ''déndron'', "tree"), also dendrons, are branched protoplasmic extensions of a nerve cell that propagate the electrochemical stimulation received from other neural cells to the cell body, or soma, of the ...

that ends in a brush-like tuft of short dendrioles (dendrites unique to UBCs). These brush dendrioles form very large synaptic junctions. The dendritic brush and the large endings of the axonal branches are involved in the formation of cerebellar glomeruli. The UBC has one short dendrite where the granule cell has four or five. The brush dendrioles emit numerous, thin

evagination Endodermic evagination relates to the inner germ layers of cells of the very early embryo, from which is formed the lining of the digestive tract, of other internal organs, and of certain glands, implies the extension of a layer of body tissue to ...

s called

filopodia Filopodia (singular filopodium) are slender cytoplasmic projections that extend beyond the leading edge of lamellipodia in migrating cells. Within the lamellipodium, actin ribs are known as ''microspikes'', and when they extend beyond the lame ...

, unique to UBCs. The filopodia emanate from all over the neuron, even including the dendritic stem and the cell body in some cells. Although UBC filopodia do not bear synaptic junctions, they are nevertheless involved in cell signaling.

Function

UBCs are intrinsically firing neurons and considered as a class of excitatory “local circuit neurons”. They work together with vestibular fibres to integrate signals involving the orientation of the head that modulates reflex behaviour. UBCs function to amplify inputs from the vestibular ganglia and nuclei by spreading and prolonging excitation within the granular layer. They receive glutamatergic inputs on its dendritic brush from a single mossy fibre terminal in the form of a giant glutamatergic synapse and make glutamatergic synapses with granule cells and other UBCs.

Location

UBCs are plentiful in those regions linked to vestibular functions. In mammals, UBCs show an uneven distribution within the granule cell domains of the

hindbrain The hindbrain or rhombencephalon or lower brain is a developmental categorization of portions of the central nervous system in vertebrates. It includes the medulla, pons, and cerebellum. Together they support vital bodily processes. Metencephal ...

, being the most dense in the

vermis The cerebellar vermis (from Latin ''vermis,'' "worm") is located in the medial, cortico-nuclear zone of the cerebellum, which is in the posterior fossa of the cranium. The primary fissure in the vermis curves ventrolaterally to the superior s ...

, part of the flocculus/paraflocculus complex, and layers 2–4 of the

dorsal cochlear nucleus The dorsal cochlear nucleus (DCN, also known as the "tuberculum acusticum"), is a cortex-like structure on the dorso-lateral surface of the brainstem. Along with the ventral cochlear nucleus (VCN), it forms the cochlear nucleus (CN), where all a ...

. In the rat cerebellum, UBCs outnumber

Golgi cells In neuroscience, Golgi cells are inhibitory interneurons found within the granular layer of the cerebellum. They were first identified as inhibitory in 1964. It was also the first example of an inhibitory feedback network, where the inhibitory ...

by a factor of 3 and approximately equal the number of

Purkinje cells Purkinje cells, or Purkinje neurons, are a class of GABAergic inhibitory neurons located in the cerebellum. They are named after their discoverer, Czech anatomist Jan Evangelista Purkyně, who characterized the cells in 1839. Structure T ...

. Like other glutamatergic cells of the cerebellum, UBCs originate in the

rhombic lip The rhombic lip is a posterior section of the developing metencephalon which can be recognized transiently within the vertebrate embryo. It extends posteriorly from the roof of the fourth ventricle to dorsal neuroepithelial cells. The rhombic lip ...

History

UBCs were first described in 1977 by Altman and Bayer, who called them "pale cells". The term "unipolar brush cell" was first introduced in the early 1990s, reclassifying pale cells, Rat-302 cells, monodendritic cells, chestnut cells and mitt cells under the same name. The Federative International Committee on Anatomical Terminology (FICAT), which is a subcommittee of the

International Federation of Associations of Anatomists The International Federation of Associations of Anatomists (IFAA) is an umbrella scientific organization of national and multinational Anatomy Associations, dedicated to anatomy and biomorphological sciences. Origins and objectives In 1903, Prof. N ...

(IFAA), officially recognized the “unipolar brush cell” as a new cell type of the cerebellar cortex in 2008.

Pathological significance

UBCs situated in cerebellar lobule VII are affected in some cases of

Pick's disease Frontotemporal dementia (FTD), or frontotemporal degeneration disease, or frontotemporal neurocognitive disorder, encompasses several types of dementia involving the progressive degeneration of frontal and temporal lobes. FTDs broadly present as ...

, where they develop cytoskeletal anomalies and are recognized by antibodies to abnormally hyperphosphorylated

tau protein The tau proteins (abbreviated from tubulin associated unit) are a group of six highly soluble protein isoforms produced by alternative splicing from the gene ''MAPT'' (microtubule-associated protein tau). They have roles primarily in maintaining ...

s. UBCs have also been implicated in the dysfunction of balance and motor coordination present in

Down syndrome Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual dis ...

.Harashima C, Jacobowitz DM, Stoffel M, et al
Elevated expression of the G-protein-activated inwardly rectifying potassium channel 2 (GIRK2) in cerebellar unipolar brush cells of a Down syndrome mouse model
Cell Mol Neurobiol. 2006;26(4-6):719-34.

Structure

Function

Location

History

Pathological significance

References

Further reading