Mugnaini E, Diño M R, Jaarsma D
Northwestern University Institute for Neuroscience, Chicago, IL 60611-S205, USA.
Prog Brain Res. 1997;114:131-50. doi: 10.1016/s0079-6123(08)63362-2.
The unipolar brush cell (UBC) is a novel type of small neuron that is characterized by sets of morphological and chemical phenotypes. UBCs occur in the granular layer of the mammalian cerebellar cortex, particularly in folia of the vestibulocerebellum, and in the granule cell domains of the dorsal cochlear nucleus. The UBC is characterized by a single dendrite that terminates with a brush-like tip of dendrioles. The soma, the dendritic stem, and especially the dendrioles emit short, non-synaptic appendages. The dendrioles represent the main synaptic apparatus of the UBC and articulate tightly with a single mossy fiber rosette forming a glomerular array characterized by an extraordinarily extensive synaptic contact. Electron microscopic and electrophysiological observations indicate that the unusual synaptic ultrastructure may produce entrapment of neurotransmitter in the synaptic cleft. While ionotropic glutamate receptors are enriched in correspondence of the postsynaptic density, metabotropic glutamate receptors are situated extrasynaptically and are particularly enriched at the appendages, which usually do not bear synaptic junctions. Some of the UBCs receive their input from choline acetyltransferase-positive mossy rosettes originating from the vestibular nuclei, suggesting that ACh and glutamate are co-released at these synapses. The UBC brush occupies a glomerulus where granule cell dendrites are intermixed with the UBC dendrioles, both of which receive synapses from the same mossy fiber rosette and portions of the Golgi axonal plexus. In addition, the dendrioles are presynaptic to granule cell dendrites, forming dendrodendritic contacts that display features of excitatory synapses. Branches of the UBC axon in the granular layer bear large endings resembling mossy fibers. The UBCs may represent an extraordinary device for feedforward, excitatory links along the mossy fiber pathways of cerebellum and dorsal cochlear nucleus.
单极刷状细胞（UBC）是一种新型的小神经元，具有一系列形态和化学表型特征。UBC存在于哺乳动物小脑皮质的颗粒层，特别是在前庭小脑的小叶以及背侧耳蜗核的颗粒细胞区域。UBC的特征是有一个单一的树突，其末端为刷状的小分支尖端。胞体、树突干，尤其是小分支发出短的、非突触性的附属物。小分支是UBC的主要突触装置，并与单个苔藓纤维玫瑰花结紧密相连，形成一种以极其广泛的突触接触为特征的小球状排列。电子显微镜和电生理观察表明，这种不寻常的突触超微结构可能导致神经递质被困在突触间隙中。虽然离子型谷氨酸受体在突触后致密部相对富集，但代谢型谷氨酸受体位于突触外，尤其在通常不具有突触连接的附属物处富集。一些UBC从源自前庭核的胆碱乙酰转移酶阳性苔藓玫瑰花结接收输入，这表明乙酰胆碱和谷氨酸在这些突触处共同释放。UBC刷占据一个小球，其中颗粒细胞树突与UBC小分支相互交织，两者都从同一苔藓纤维玫瑰花结和部分高尔基轴突丛接收突触。此外，小分支对颗粒细胞树突具有突触前作用，形成显示兴奋性突触特征的树突 - 树突接触。颗粒层中UBC轴突的分支带有类似苔藓纤维的大终末。UBC可能是小脑和背侧耳蜗核苔藓纤维通路沿线前馈兴奋性连接的一种特殊装置。
