256 Cerebellum (2012) 11:246–258 Fig. 7 Changes in volume and neuronal density in cerebellar nuclei of P200–250 PCα1KO and WT mice. a–c Quantification of the volume of the cerebellar nuclei in WT (blue; n=3) and PCα1KO (green; n =3) mice. a Example of a bilateral 3D reconstruction of the cerebellar nuclei of one WT (top) and one PCα1KO mouse (bottom). Light blue lateral cerebellar nucleus (LCN), dark blue anterior interposed nucleus (AIN), purple posterior interposed nucleus (PIN) and gray medial cerebellar nucleus (MCN). b An average decrease of 54% in the total At this time, however, we cannot rule out the possibility that other high-voltage-gated calcium channels, such as CaV2.2 (N-type) and CaV2.3 (R-type), are upregulated during later stages in PCα1KO mice and thereby rescue partly the detrimental effects of CaV2.1 absence. Similar compensatory mechanisms involving CaV2.2, CaV2.3, and CaV1 have been described in other Cacna1a mutant mice at the level of neurotransmission [15, 17, 32, 35]. The first signs of neurodegenerative changes in PCα1KO mice were observed around P45. At this stage, silver impregnation revealed clear argyrophylic staining in the Purkinje cell and molecular layers. From P60 on, Purkinje cell loss was clearly visible and many of the remaining Purkinje cells showed abnormalities such as torpedo’s or axonal swellings. At older ages (P100 and P200–250), Purkinje cell loss became progressively worse and ultimately also affected the survival of neurons in the granular layer and molecular layer. In lurcher and Purkinje cell degeneration (Pcd) mice, which both show near- complete Purkinje cell loss in adulthood, a progressive postnatal Purkinje cell degeneration is also followed by large scale death of granule cells after the loss of Purkinje volume of the cerebellar nuclei in PCα1KO mice is shown. c Quantification of the volume of individual cerebellar nuclei reveals a pronounced volume reduction in all four nuclei. d Overall neuronal surface density of CN neurons per individual CN. e Surface density of small cells (<8.5 μm in diameter). f Surface density of big cells (>8.5 μm in diameter). *p<0.05; **p <0.001 (significant differences among groups) cells [36–38]. Thus, the fact that three completely different mutations lead to the same sequence of cerebellar events (for lurcher see Ref. [39]; for Pcd see Ref. [40]) indicates that the degeneration of granule cells and molecular layer interneurons is probably a common, secondary effect to the loss of Purkinje cells. Downstream Effects of Widespread Purkinje Cell Loss The loss of Purkinje cells also affected the cerebellar nuclei in PCα1KO mice. The extent of volume reduction in PCα1KO mice was similar to that reported in lurcher and Pcd mouse mutants [27, 41]. In lurcher mice deafferenta- tion of the CN resulted in a ∼60% reduction in the volume of all individual CN [27]. We also found a widespread increase in neuronal surface densities in all CN. However, it appeared that the increase in neuronal density is more pronounced in small cells than in large cells. Despite the fact that our results do not allow a firm statement about the total number of cells per CN, our data seems to indicate a possible reduction in the number of large neurons. The data presented here shows a somewhat different pattern from