FURTHER EVIDENCE FOR A UNIQUE DEVELOPMENTAL COMPARTMENT IN THE CEREBELLUM OF THE MEANDER TAIL MUTANT MOUSE AS REVEALED BY THE QUANTITATIVE-ANALYSIS OF PURKINJE-CELLS

The cerebellum of the meander tail mutant mouse (mea/mea) is character ized by a relatively normal cytoarchitecture posteriorly with an abrup t transition to an anterior region in which there is abnormal foliatio n, agranularity, and Purkinje cell (PC) ectopia. This study presents t he results of a qualitative and quantitative analysis of the PC in the mea/mea cerebellum. Developmental and morphological analyses reveal t hat the PC in the anterior region of the mea/mea cerebellum do not for m a monolayer during the first week of postnatal development as they d o in the wild type mouse. In the adult mea/mea, the dendrites of these ectopic cells are atrophic and disoriented. Quantitative studies in a dult animals reveal that while the total number of PC is normal, the n umber of PC in the affected anterior region of the mea/mea cerebellum is greater than the number of PC in the anterior lobe, as classically defined by the primary fissure, of the normal animal. These data sugge st that 1) the developmental morphology of the PC in the anterior regi on is abnormal, probably due to the lack of granule cells at early pos tnatal times; 2) the total number of PC in the cerebellum is normal, a nd 3) the defect is not restricted to the anterior lobe but involves a portion of the posterior lobe. The latter supports the notion that th e mutant gene affects a unique developmental compartment in the cerebe llum which does not coincide with the classic adult boundary, the prim ary fissure, between the anterior and posterior lobes. (C) 1996 Wiley- Liss, Inc.