Diseases of the cerebellum

Early morphological changes of hereditary cerebellar cortical abiotrophy in rabbits

We previously investigated the hereditary cerebellar cortical abiotrophy in littermates at postnatal day (PD) 25-31 delivered from a pair of rabbits. To estimate the onset time and incipient lesions associated with the cerebellar cortical abiotrophy of the cases, we mated the same pair again and examined early stages of the disease in F1 rabbit showing ataxia (PD 15), finding evidence that the ataxia is passed to subsequent generations via autosomal recessive inheritance. Clinical signs of the affected rabbit showed early-onset dysstasia and ataxia. The affected rabbit showed apoptotic granular cells before and after migration completion, degeneration (swelling) of parallel fiber terminals, abnormal junction (invaginated junction) of the parallel fiber-Purkinje cell synapses and irregular orientation of the Purkinje dendritic arbor in the molecular layer. Additionally, a reduced number of synaptic junctions between parallel fibers and Purkinje cells were detected, as well as at PD 25-31. Secondary changes, such as reduction or degeneration of Purkinje cells and granular cells were not yet observed at early stages. As synapse abnormality preceded the degeneration or reduction of Purkinje and granular cells at early stages, we concluded that the pathogenesis of the present cerebellar lesion was caused by failed synaptogenesis during postnatal cerebellar development.

Hereditary cerebellar degenerative disease (cerebellar cortical abiotrophy) in rabbits

A pair of rabbits gave birth to a set of littermates (F1) with symptoms of early-onset ataxia. Microscopic examination revealed cerebellar degenerative disease in 5 of 6 littermates. Light microscopy was used to compare the thickness of each cerebellar layer in affected animals in contrast to a normal control. Affected animals showed narrowing of the molecular layer of the vermis, reduced density of Purkinje cell dendrites and irregular thickness in their branchlets, and reduced density of granular cells and scattered pyknotic cells in the granular layer. Pyknotic cells were apoptotic granular cells, confirmed by positive staining using the TUNEL method. Electron microscopy confirmed the thinning of the molecular layer seen by light microscopy and also showed a reduced number of parallel fibers, which indicate granular cells axons, and a reduced number of synaptic junctions between Purkinje and granular cells. Purkinje cells had electron-dense, irregularly shaped cytoplasm with irregularly shaped nuclei, and some of these cells had a central chromatolysis-like region. These findings support a diagnosis of cerebellar cortical abiotrophy, a hereditary condition that causes nerve function impairment leading to early-onset progressive degeneration of the cerebellar cortex.

Naturally occurring parvovirus-associated feline hypogranular cerebellar hypoplasia-- A comparison to experimentally-induced lesions using immunohistology

Three cases of feline cerebellar hypoplasia are presented. At the time of examination, the ages of the cats ranged from 2 months to 1 year. Necropsy revealed cerebellar and pons hypoplasia. Polymerase chain reaction for parvoviral deoxyribonucleic acid was positive in cerebellar tissue. Cell-specific immunolabeling was used to characterize the lesions, which were characterized into 2 types. In type 1 lesions, the cortex was nearly agranular, with an extremely thin molecular layer; the Purkinje cells were randomly placed and oriented, and their stunted main dendrite produced a thorn-covered atrophic dendritic tree; the basket cell axons ran randomly and had dysmorphic endings; and myelinated fibers were severely reduced in folia axes. In type 2 lesions, the cortex was hypogranular; the Purkinje cells were linearly organized, but their main dendrite extended too far in the molecular layer before giving up smooth, bent secondary dendrites; many basket cells were located along the cerebellar surface, and their axons ran at right angle to the surface; myelinated fibers were moderately reduced. Defects in climbing fiber synapse translocation and elimination were evident in both types of lesion. This immunohistologic study allowed a comparison between lesions in these spontaneous cerebellar hypoplasia cases with those documented when using silver impregnation studies after perinatal experimental cerebellar damage. Such a comparison is consistent with viral infection that occurs before birth in all 3 cases. Progress in parvovirus biology knowledge suggests that viral NS1 protein cytotoxicity might explain degenerative changes in the Purkinje cells that were present, in addition to the development defect.