Spheroids and altered axons in the spinal gray matter of the normal cat. An electron-microscopic study

A Missense Mutation in the Vacuolar Protein Sorting 11 (VPS11) Gene Is Associated with Neuroaxonal Dystrophy in Rottweiler Dogs

Canine neuroaxonal dystrophy (NAD) is a recessive, degenerative neurological disease of young adult Rottweiler dogs (Canis lupus familiaris) characterized pathologically by axonal spheroids primarily targeting sensory axon terminals. A genome-wide association study of seven Rottweilers affected with NAD and 42 controls revealed a significantly associated region on canine chromosome 5 (CFA 5). Homozygosity within the associated region narrowed the critical interval to a 4.46 Mb haplotype (CFA5:11.28 Mb – 15.75 Mb; CanFam3.1) that associated with the phenotype. Whole-genome sequencing of two histopathologically confirmed canine NAD cases and 98 dogs unaffected with NAD revealed a homozygous missense mutation within the Vacuolar Protein Sorting 11 (VPS11) gene (g.14777774T > C; p.H835R) that was associated with the phenotype. These findings present the opportunity for an antemortem test for confirming NAD in Rottweilers where the allele frequency was estimated at 2.3%. VPS11 mutations have been associated with a degenerative leukoencephalopathy in humans, and VSP11 should additionally be included as a candidate gene for unexplained cases of human NAD.

Fine structural alteration in target-deprived axonal terminals in the rat thalamus

Lesioning of thalamic target neurons in the adult rat provokes a resorption of terminal axonal branches of afferent neurons from the dorsal column nuclei. There is, however, no massive neuronal loss in the dorsal column nuclei. In the adult, therefore, the thalamic post synaptic target cells influence primarily the extent of the terminal component of the afferent neurons. The subcellular changes underlying the regression of these adult terminals are unknown. To address this issue, we have looked at the electron microscopic level for the ultrastructural correlates of this retraction of the terminal compartment of target-deprived neurons in the adult rat thalamus. By analysing the fine structure of target-deprived axons and their immunoreactivity for a specific synaptic protein, synaptophysin, we have observed that all the organelles and the protein formed in the cell body, including dense-core vesicles, continue to be transported to the terminal compartment and accumulate at this level. At the terminal level, engorgement of organelles induces the formation of varicosities. An enormous increase in local degradative activity occurs in parallel to this accumulation. In contrast, organelles involved in membrane turnover and degradation (including synaptic and coated vesicles, multivesicular bodies, lysosomes) in the nerve terminals are clearly modified. There is a progressive loss of synaptic vesicles, whereas clathrin-coated vesicles and multivesicular bodies are numerous. We propose that the resorption of terminal axonal branches after thalamic target deprivation in the adult is associated with a bias of the system of membrane recycling at the axonal terminals towards degradation. In the absence of apparent changes in the pathways originating from the cell body in these conditions, it is unlikely that presynaptic neurons in the adult thalamus are dependent upon post synaptic target neurons for the delivery of organelles and proteins to the terminals.

Pericapillary rosettes in the human spinal cord

We have found large eosinophilic bodies in the pericapillary regions of the gray and white matter in the human spinal cord. These are entirely different from the previously reported pericapillary inclusion bodies (PIB). We have designated them pericapillary rosettes (PR), since they consist of clusters of round or ovoid structures of various sizes which form rosettes around the transversely sectioned capillaries. Positive staining with silver impregnation and anti-neurofilament antibody, the presence of the myelin around the bodies and the accumulation of neurofilaments within them indicate that axonal swelling is associated with the formation of PR. These bodies are not observed in individuals aged less than 30 years, and afterwards they increase in proportion to age. Over the age of 80, they are almost always found in the spinal cord, particularly in the gray matter of both the anterior and posterior horns at the thoracic and lumbar levels. Thus, the development of PR is closely related to the aging process.

Polyglucosan bodies in the brain of the cat

Polyglucosan bodies (PGB) were examined by light and electron microscopy in the brain of cats without neurological signs. PGB in the feline brain were round, basophilic, PAS-positive, filamentous structures. Both morphologically and histochemically, PGB in the cat were identical to Lafora bodies and similar structures found in man and other animals. Most of the bodies were situated in the neuronal processes, but were not found in perikarya. PGB were disseminated throughout the brain, especially in the cerebral cortex, midbrain, cerebellum and medulla oblongata. The occurrence of PGB in the feline brain may represent an ageing phenomenon.

Intra-axonal virus in demyelinative lesions of experimental herpes simplex type 2 infection

Three-week-old mice which had been infected intracerebrally with herpes simplex virus type 2 (HSV-2) were examined electron-microscopically for the presence of intra-axonal virus in or near optic nerve and spinal cord demyelinative lesions. Acute lesions and their margins frequently contained a very small proportion of abnormal axons, and in a few of these mature virus particles, nucleocapsids, or other incomplete forms were found. A similar range of particle morphology was present in the cytoplasm of infected and degenerating glia. Axons containing similar particles were not identified in fibers in normal white matter surrounding demyelinative lesions. It is proposed that neuronal infection and axonal transport of virus may lead to foci of oligodendroglial infection, destruction and central nervous system (CNS) demyelination near to or remote from the cell bodies of infected neurons. In some instances, the topography of lesions could reflect a tract association. Anatomical features of nervous tissue could favor amplification of demyelination from a relatively minimal neuronal infection, with little evidence of tract degeneration. This hypothesis is consistent with the great predominance of demyelination relative to gray matter disease seen experimentally in non-fatal CNS infections with HSV-2. It would also explain the marked tendency for demyelinative lesions in at least certain CNS locations to be greatly elongated in the long axis of fiber tracts. This mechanism could be of importance in other animal models of virus-induced demyelination, and perhaps also in multiple sclerosis.