Increases in GFAP immunoreactive astrocytes in the cerebellar molecular layer of young adult CBA/J mice

Abstract

Background: CBA/J mice are standard experimental animals in auditory studies, and age-related changes in auditory pathways are well documented. However, changes in locomotion-related brain regions have not been systematically explored.

Results: We showed an increase in immunoreactivity for glial fibrillary acidic protein (GFAP) in the cerebellar molecular layer associated with Purkinje cells in mice at 24 weeks of age but not in the younger mice. Increased GFAP immunoreactivity appeared in the form of clusters and distributed multifocally consistent with hyperplasia of astrocytes that were occasionally associated with Purkinje cell degeneration. Three out of 12 animals at 16 and 24 weeks of age exhibited pre-convulsive clinical signs. Two of these 3 animals also showed increased GFAP immunoreactivity in the cerebellum. Rotarod behavioral assessments indicated decreased performance at 24 weeks of age.

Conclusions: These results suggest minimal to mild reactive astrocytosis likely associated with Purkinje cell degeneration in the cerebellum at 24 weeks of age in CBA/J mice. These findings should be taken into consideration prior to using this mouse strain for studying neuroinflammation or aging.

Keywords: Astrocyte; Bergmann glia; CBA/J mice; cerebellum; Glial fibrillary acidic protein.

Fig. 1

Brain sections at the level of mid-cerebellum and medulla oblongata. A representative IHC images of GFAP immunoreactivity in the adult male CBA/J mouse cerebellum. Increased GFAP reactivity was observed in the molecular layer of the cerebellum in mice 24 weeks of age, but not animals 8, 10 or 16 weeks of age. B Magnified IHC images of the corresponding boxed areas in (A). Increased GFAP expression in the Bergmann glia (black arrows) along Purkinje cell spines extending across the molecular layer (M) of the cerebellar cortex and terminating at the pial surface (*). C Representative images of the mouse cerebellum under a confocal fluorescence microscope. The images were from different H&E sections of the same animals as used for (A) and (B). The white arrow points to red eosin fluorescence indicating Purkinje cell (P) soma undergoing degeneration. Note the soma shape change from flask-like (as seen in adjacent neurons, indicated by arrowheads) to an elliptical shape (indicated by the arrow). G: Granular cell layer. Scale bar = 50 μm

Fig. 2

Rotarod performance of CBA/J mice at 10–24 weeks of age. Accelerating rotarod trials at 10, 16 and 24 weeks of age show a decrease in performance at 24 weeks. At 24 weeks, both the time (A) on the rod and the speed at falling (B) were decreased significantly, compared with the first 2 time points (P < 0.01 (**) − 0.05 (*), One-way ANOVA, n = 6). At 24 weeks, the rotarod performance was decreased significantly in those animals with activated GFAP in the cerebellum (C&D, *: P ≤ 0.05, unpaired t-test)