Purkinje cell degeneration in pcd mice is characterized by dendrite retraction and shrinkage. (A-D) Toluidine blue staining of cerebellar sections. At 14 days of age, Purkinje cells of normal size and morphology (red arrows) are apparent in both wild-type control littermate mice (A) and in pcd5Jhomozygous mice (B). (C) At 21 days of age, Purkinje cells (red arrows) remain regularly spaced, retain normal size and morphology, and exhibit uniformly oriented dendritic processes (yellow arrowheads) in wild-type control mice. (D) However, by 21 days of age, dramatic histopathology becomes obvious in pcd5Jhomozygous mice, as significant drop-out of Purkinje cells has begun to occur. Many of the remaining Purkinje cells have aberrantly small and misshapen soma (red arrows), and display shortened and tortuous dendrites (yellow arrowheads). GCL = granule cell layer; PCL = Purkinje cell layer; ML = molecular layer. Scale bar corresponds to 20 μM.