Metabotrop glutamate receptor type 1a expressing unipolar brush cells in the cerebellar cortex of different species: A comparative quantitative study

Morphology, distribution and number of unipolar brush cells (UBCs) was stud ied in the cerebellar vermal lobules I-X of the chicken, rat, guinea pig, c at, and monkey using monoclonal mGluR1a antibody as a marker to visualise t hese recently described nerve cells (Mugnaini and Floris [1994] J. Comp. Ne ural. 339:174-180; Mugnaini et al. [1994] Synapse 16:284-311). The morpholo gical appearance of mGluR1a immunopositive UBCs is similar in all species i nvestigated: they are small cells, having a single, relatively short and th ick dendrite, terminating in brush-like dendrioles. Although this, probably excitatory, cell type can be found all over the cerebellar cortex, highest density of UBCs can be seen in the vermal cortex. The present study, there fore, was focused on the quantitative morphology and distribution of UBCs i n the 10 lobules of the vermis. Calculating the number of UBCs/1 Purkinje c ell (PC), we have found differences in this value (average in vermal lobule s I-X) from 1.04 in rat, 1.10 in chicken, 1.16 in guinea pig, 2.27 in monke y, and up to 2.44 in cat. The highest density of UBCs was observed in lobul es I, IX, and X, whereas the lowest number of UBCs/1 PC was found in lobule s IV-VI (in the mammals) and in lobules VII-VIII (in the chicken). In mamma ls, particularly the monkey and cat, an increased presence of UBCs was obse rved in vermal sub-lobules VIc-VIIb,c, a region defined as the oculomotor v ermis because of its role in the control of saccadic eye movement. There is also a basic difference between chicken and mammals in the distribution of UBCs within the lobules: in mammals, the lowest density of these nerve cel ls was found in the peripheral portion of the lobules, near to the pia, whi le in the chicken, in contrast, the density of UBCs was the highest subpial ly with fewer UBCs located in the deepest curvature of the lobules. Finally , the functional significance of the differences in the density and in the distribution pattern of UBCs in the cerebellar vermis between the phylogene tically different species; investigated is briefly discussed. (C) 1999 Wile y-Liss, Inc.