Unipolar Brush Cells

Abstract

The unipolar brush cells (UBCs) are excitatory interneurons in the granule cell layer of the cerebellar cortex. They amplify extra-cerebellar inputs from vestibular origin as well as other inputs whose origin is the focus of ongoing research. The UBCs are classified in two functionally and chemically distinct subclasses. Type I UBCs express calretinin, are regularly firing, and are located in lobules IX and X. Type II UBCs are characterized by expression of mGluR1α, are burst firing and are present throughout the cerebellum, although they are enriched in the vestibulo-cerebellum. Both UBC types show peculiarly slow glutamatergic currents in response to synaptic activation. This electrophysiological property suggests a critical role for these cells in determining the timing of the response of the cerebellar cortex to the peripheral inputs. Recent data also suggest that cerebellar UBCs may be involved in cerebellar ataxias and represent a potential cellular substrate for the generation of tinnitus.