Differential glial activation during the degeneration of Purkinje cells and mitral cells in the PCD mutant mice.

Purkinje Cell Degeneration (PCD) mice harbor a nna1 gene mutation which leads to an early and rapid degeneration of Purkinje cells (PC) between the third and fourth week of age. This mutation also underlies the death of mitral cells (MC) in the olfactory bulb (OB), but this process is slower and longer than in PC. No clear interpretations supporting the marked differences in these neurodegenerative processes exist. Growing evidence suggests that either beneficial or detrimental effects of gliosis in damaged regions would underlie these divergences. Here, we examined the gliosis occurring during PC and MC death in the PCD mouse. Our results demonstrated different glial reactions in both affected regions. PC disappearance stimulated a severe gliosis characterized by strong morphological changes, enhanced glial proliferation, as well as the release of pro-inflammatory mediators. By contrast, MC degeneration seems to promote a more attenuated glial response in the PCD OB compared with that of the cerebellum. Strikingly, cerebellar oligodendrocytes died by apoptosis in the PCD, whereas bulbar ones were not affected. Interestingly, the level of nna1 mRNA under normal conditions was higher in the cerebellum than in the OB, probably related to a faster neurodegeneration and stronger glial reaction in its absence. The glial responses may thus influence the neurodegenerative course in the cerebellum and OB of the mutant mouse brain, providing harmful and beneficial microenvironments, respectively.