Physiology and Ultrastructure of Unipolar Brush Cells in the Vestibulo-Cerebellum

The vestibulo-cerebellum is unique among the other cerebellar lobules in that it is directly innervated from sensory fibers derived from peripheral ganglia via the dorsal branch of the vestibular nerve, in addition to receiving sensory input already processed in one or more nuclei of the brainstem or spinal cord. Unipolar brush cells (UBCs) generally have a single, relatively thick dendritic stem that terminates in a brush-like formation of branchlets (or dendrioles) provided with nonsynaptic appendages, and shows little interspecies variation. The unusual ultrastructural features of the mossy fibers (MF)-UBC synapse suggest that transmission at this synapse may have some unusual features. Both the fast and slow components of the MF-evoked EPSC in UBCs were evoked in an all-or-none fashion at the same stimulus intensity, a result that is consistent with the ultrastructural observation that most UBCs receive innervation from a single MF.