Unipolar brush cells

Cozzi et al. (1989) and Munoz (1990) identified unipolar brush cells in the rat and human cerebellum, respectively, on the basis of their immunoreactivity to antisera against proteins of the secretogranin (or chromogranin) family. Unipolar brush have a relatively high density of large dense core vesicles, which in conjunction with the 

Rogers, 1992 Braak and Braak, 1993 Floris et al., 1994). Calretinin-immunoreactivity in unipolar brush cells was used for a detailed characterization of this cell type, and to 

---

Fig. 2. Diagrams of the cerebellar circuit. Inhibitory neurons are indicated in black. A. Main circuit. B. Cortical interneurons and recurrent pathways. Abbreviations B = basket cell cf = climbing fiber G = Golgi cell GR = granule cell 10 = inferior olive mf = mossy fiber nc = nucleocortical axons no = nucleo-olivary axons pcc = recurrent Purkinje cell axon collaterals P cell = Purkinje cell PCN = precerebellar nuclei pf = parallel fiber pi = pinceau of basket cell axons S = stellate cell UBC = unipolar brush cell I = extracerebellar mossy fiber 2 = nucleo-cortical mossy fiber 3 = mossy fiber collateral of uni-polar brush cell.

Fig. 68. Immuno-electron micrograph of an unipolar brush cell stained with antiserum to calretinin. The micrograph was obtained near the surface of the immunoreacted slice, as indicated by open areas in the tissue and over the cell nucleus (stars). The unipolar cell body has an irregular contour. The nucleus (N) shows a deep indentation (T) and the cytoplasm contains an array of ringlet subunits (R). The short dendrite forms an extensive synapse (arrows) with a calretinin-negative mossy fiber ending (mO. At tbe aspect opposite the synapse the dendrite contains numerous mitochondria. Granule cells (CG) are immunonegative. Bar = 1 fim. Floris et al. (1994).

Fig. 69. A. Monoclonal antibody Rat-302 recognizes a subset of neurons, later identified as unipolar brush cells, restricted to the granular layer of the flocculus and the vermis of rat cerebellum (arrows), whereas in other areas of the cerebellum no positive cells are found. B. In contrast, antibody Rat-303 recognizes Golgi-II cells in the granular layer (g) in the entire cerebellum. C. Rat-302 also recognizes Purkinje cells outside the caudal vermis and the flocculus. D. Rat-302 positive cells in the vermis. E and F. Unipolar brush cells recognized by Rat-302 have a round cell body and short dendrites ending in a spray of appendages (arrows), g, granular layer m, molecular layer p, Purkinje cell layer. Scale bars 500 fim in A and B, 50 /rm in C and D. 10 /rm in E and F. Hockfield (1987).

The distribution of ChAT-positive mossy fibers roughly corresponds to that of unipolar brush cells (see Section 3.6.3.), which raises the question whether these mossy fibers innervate these cells. Electron microscopic analysis of ChAT-immunoreactivity in the nodulus showed that a minority (10-20%) of ChAT-immunoreactive mossy fiber terminals synapse on brush cell profiles, and that a minority (10-30%) of the mossy fiber terminals contact unipolar brush cells that are immunoreactive for ChAT (Jaarsma, 1995c). 

Fig. 146. Parasagittal section of the rat cerebellar vermis immunostained with antiserum to calretinin. Folia are labelled with roman numerals according to Larsell. The pattern of immunoreactivity in the nodulus (lobule X) and portion of the ventral uvula (lobule IXd) differs from that in the other vermal folia. While in most of the vermis weak immunoreactivity is present in granule cell bodies within the granular layer and in parallel fibers within the molecular layer, in the folia X and IXd of the vestibulo-cerebellum the immunoreaction product is largely localized in unipolar brush cells and mossy fibers, MN, medial cerebellar nucleus. Bar = 1 mm. Floris et al. (1994).

The processes responsible for the selection of the appropriate output for a particular mossy fiber-parallel fiber input may function at the level of the synapses of the mossy fibers with granule cells, unipolar brush cells, or Golgi cells and at the level of the parallel fiber-Purkinje cell synapse. Several systems may be involved in this selection process. Nitric oxide, that is synthetized by subsets of granule cells (Schilling et ah, 1994 Hawkes and Turner, 1994) and in stellate and basket cells (Bredt et ah, 1990) (Section... 

Berthie B, Axelrad H (1994) Granular layer collaterals of the unipolar brush cell axon display rosette-like excrescences. A Golgi study in the rat cerebellar cortex. Neurosci Lett., 167, 161-165. 

Floris A, Dino M, Jacobowitz DM, Mugnaini E (1994) The unipolar brush cells of the rat cerebellar cortex and cochlear nucleus are calretinin-positive a study by light and electron microscopic immunocytochem-istry. Anat. Embryol., 189, 495-520. 

Jaarsma D, Wenthold R, Mugnaini E (1995b) Glutamate receptor subunuits at mossy fiber-unipolar brush cell synapses Light and electron microscopic immunocytochemical study in cerebellar cortex of rat and cat. J. Comp. Neurol, 357, 145-160. 

Jaarsma D, Cozzari L, Mugnaini E (1995c) Cholinergic mossy fibers innervate granule cells and unipolar brush cells in the rat cerebellum. Eur. J. Neurosci. (Suppl. 8, 35.1. 

Mugnaini E, Floris A (1994) The unipolar brush cell A neglected neuron of the mammalian cerebellar cortex. J. Comp. Neurol. 339, 174-180. 

Mugnaini E, Floris E, Wright-Goss M (1994) Extraordinary synapses of the unipolar brush cell an electron microscopic study in the rat cerebellum. Synapse, 16, 284-311. 

Rossi RJ, Alford S, Mugnaini E, Slater NY (1995) Properties of transmission at a giant glutamanergic synapse in the cerebellum the mossy fiber-unipolar brush cell synapse. J. Neurophysiol. 74, 24-42. 

---