A quantitative morphological analysis of the cerebellar nuclei in normal and lurcher mutant mice. II. Volumetric changes in cytological components.

In the present study the stereological point counting method has been used to determine volumetric changes in the cytological components of the lurcher cerebellar nuclei. The volume fraction of neuronal somata was estimated, using semithin toludine blue stained sections. Seven categories of profiles were analyzed in electron micrographs: 1) dendrites, 2) boutons on dendrites, 3) boutons on somata, 4) myelinated fibers, 5) glial perikarya, 6) vascular elements, and 7) unclassified components. Volume fraction data indicate that the volumetric composition of the wild-type murine cerebellar nuclei is: 38% myelinated fibers, 8% neuronal somata, 11% dendrites, 10% boutons on dendrites, less than 1% boutons on somata, 2.5% glial somata, and 6% vascular elements. Unclassified elements, consisting primarily of glial processes and intercellular space, comprised 23% of the volume of the wild-type cerebellar nuclei. In lurcher, the loss of myelinated axons and boutons accounts for 59% of the atrophy of the cerebellar nuclei. Loss of nuclear neurons accounts for 2%, and a reduction in dendritic arbors for another 8.3% of this atrophy. The remaining 30.7% of the lost nuclear volume results from reduced volume of glial processes, vascular elements, and intercellular space.