Ultrastructural changes in the optic nerves of rodents with experimental Creutzfeldt-Jakob Disease (CJD), Gerstmann-Sträussler-Scheinker disease (GSS) or scrapie.

This report describes the ultrastructural changes in the optic nerves of (1) hamsters infected with the Echigo-1 strain of Creutzfeldt-Jakob disease (CJD), (2) hamsters infected with the 263K or 22C-H strain of scrapie, and (3) mice infected with the Fujisaki strain of Gerstmann-Sträussler-Scheinker disease (GSS). Vacuolation of myelinated fibres was present in the myelin sheaths, with splitting of myelin lamellae. These vacuoles contained typical secondary vacuoles and curled membrane fragments. Myelinated fibre vacuolation was also accompanied by an exuberant cellular reaction consisting of macrophages containing numerous mitochondria, abundant rough endoplasmic reticulum, and secondary lysosomes filled with digested myelin debris and other electron-dense material. Within macrophages, myelin fragments undergoing active digestion, lyre-like bodies and paracrystalline inclusions were frequently noted. Astrocytes and their processes were prominent; glial filaments and many mitochondria were readily detected. Proliferation of inner mesaxons was observed. Cross-sectional profiles of innumerable myelinated fibres contained membranous organelles continuous with the inner lamellae of the oligodendroglial cells. The proliferations of inner mesaxons formed whorls and loops, and intrusion of the membranous tongue of the inner mesaxon into the axoplasm was occasionally observed; dystrophic neurites were relatively numerous. In mice infected with the Fujisaki strain of GSS, fibres had undergone demyelination with stripping of the myelin lamellae, while others showed vesicular myelin degeneration.

Deposition patterns of disease-associated prion protein in captive mule deer brains with chronic wasting disease.

Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy (TSE) in captive and free-ranging cervids in the USA; its origin is obscure. Archival formalin-fixed and paraffin-embedded specimens of 16 captive mule deer brains with CWD were analyzed using immunocytochemistry for the disease-associated prion protein (PrP). The most prominent pattern of PrP deposition were plaque-like structures, a substantial proportion of which were florid plaques surrounded by a rim of spongiform vacuoles. The percentage of florid plaques was highly variable according to region, ranging from 0% to 52.7%. The highest percentage was observed in the medulla and basal ganglia, the lowest in the cerebral cortex. Only three brains contained no florid plaques. There were also punctate synaptic-type and perivascular deposits, particularly in areas of severe spongiform change, and subpial and subependymal plaque-like deposits, whereas cerebellar involvement was mild. Thus, CWD brain pathology prominently features florid PrP plaques, as does variant Creutzfeldt-Jakob disease (vCJD), but differs in other characteristics from vCJD.

A special report I. Prion protein (PrP)--amyloid plaques in the transmissible spongiform encephalopathies, or prion diseases revisited.

We present a retrospective analysis of PrP-amyloid plaques encountered in CJD and GSS. In human TSEs (kuru, CJD and GSS) several PrP-immunopositive plaques and plaque-like deposits were detected. In kuru, plaques were typical "kuru" plaques--stellate structures deposited mostly in the granular- and Purkinje-cell layer of the cerebellum. Many smaller or larger clusters were visible but, in contrast to GSS, they never merged together to form multicentric plaques. In all cases of GSS, plaques were localised in the granular- and Purkinje-cell layer and the molecular cell layer. There were many different forms of plaques: from kuru plaques (unicentric stellate plaques) to clusters of unicentric plaques, which by merging eventually formed "multicentric plaques". The latter are the hallmark of this disease. By electron microscopy, several types of amyloid plaques, which corresponded to those seen by PrP immunohistochemistry, were observed. The first type, unicentric "kuru" plaque, consisted of stellate arrangements (stars or cores) of amyloid bundles emanating from a densely interwoven centre. Amyloid stars were surrounded by astrocytic processes and invaded by microglial cells but dystrophic neurites were only rarely seen. In contrast, multicentric plaques were often surrounded by dystrophic neurites. The rarest type of plaque were neuritic plaques. In 263K- and 22C-H scrapie-infected hamster brains, by light microscopy and semi-thin (1 microm) sections, discrete PrP-immunopositive plaques were observed in the subependymal region but not in the deep brain neuroparenchyma. These plaques were not discernible by routine H & E staining. Ultrastructurally, plaques were recognised as areas of low electron density containing haphazardly-oriented fibrils and not as stellate compact structures typical of plaques in human cases of CJD and GSS. These plaques were located beneath the basal border of the ependymal cells and adjacent blood vessels. Occasional dystrophic neurites containing electron-dense inclusion bodies were seen within the plaque perimeter, which always remained PrP-negative.

A special report I. Prion protein (Prp)--amyloid plaques in the transmissible spongiform encephalopathies (TSEs) or prion disease revisited.

We present a retrospective analysis of PrP-amyloid plaques encountered in CJD and GSS. In human TSEs (kuru, CJD and GSS) several PrP-immunopositive plaques and plaque-like deposits were detected. In kuru, plaques were typical "kuru" plaques--stellate structures deposited mostly in the granular and Purkinje cell layer of the cerebellum. Many smaller or larger clusters were visible but, in contrast to GSS, they never have merged together to form multicentric plaques. In all cases of GSS, plaques were located in the granular and Purkinje cell layer and in the molecular layer. There were many different forms of plaques: from kuru plaques (unicentric stellate plaques) to clusters of unicentric plaques which by merging eventually formed "multicentric plaques". The latter are the hallmark of this disease. By electron microscopy several types of amyloid plaques, which corresponded to those seen by PrP immunohistochemistry were observed. The first type, unicentric kuru plaque consisted of stellate arrangements (stars or cores) of amyloid bundles emanating from a densely interwoven center. Amyloid stars were surrounded by astrocytic processes and invaded by microglial cells but dystrophic neurites were only rarely seen. In contrast multicentric plaques were often surrounded by dystrophic neurites. The rarest type of plaque, were neuritic plaques. In 263K and 22C-H scrapie-infected hamster brains, on the light microscopy of the semi-thin (1 micron) sections, discrete PrP-immunopositive plaques were observed in the subependymal region but not in the deep brain neuroparenchyma. These plaques were not discernible by routine HE staining. Ultrastructurally, plaques were recognized as areas of low electron density containing haphazardly-oriented fibrils and not as stellate compact structures typical of plaques in human cases of CJD and GSS. These plaques were located beneath the basal border of the ependymal cells and adjacent blood vessels. Occasional dystrophic neurites containing electron-dense inclusion bodies were seen within the plaque perimeter, which always remained PrP-negative.

Echigo-1: a panencephalopathic strain of Creutzfeldt-Jakob disease: ultrastructural studies of the optic nerve.

The Echigo-1 strain of CJD was isolated by Mori and colleagues (1989) from a case of 33-year-old female with a panencephalopathic type of CJD. An incubation period following intracerebral inoculation of hamsters with 10% cleared suspension of the Echigo-1-affected brain was approximately six months. We report here ultrastructural changes which are comparable with those in the white matter of another panencephalopathic type of CJD, the Fujisaki strain of CJD (GSS) passaged in mice. Vacuoles developed within myelinated axons: within axoplasm or within the myelin sheath and these were accompanied by exuberant reaction of macrophages and hypertrophic astrocytes. Axons underwent Wallerian degeneration and dystrophic neurites were also seen. Most important, we observed proliferation of inner mesaxons. Cross-sectional profiles of innumerable myelinated fibers contained membranous organelles which were continuous with the inner lamellae of the oligodendroglial cells. These unusual proliferations of inner mesaxon formed whorls and elaborated loops. In some axons, proliferation was so severe that loops of mesaxon filled the whole cross-section of the axon. Occasionally, we observed intrusion of the membranous tongue of the inner mesaxon into axoplasm. This study presents a second panencephalopathic model of CJD available in small laboratory rodents. It is important because this is the only such model in hamsters and it may be used for comparative studies of different strains of agent in the same host; thus far only mouse and hamster model have been available for comparative studies.

Electron microscopic studies of the optic nerve in experimental scrapie and the panencephalopathic type of Creutzfeldt-Jakob disease.

We report the optic nerve ultrastructural pathology in experimental scrapie and Creutzfeldt-Jakob disease. Vacuoles developed within myelinated axons contained typical secondary vacuoles and curled membranes. These were seen either within the axoplasm or within the myelin sheath which split either at the major dense line or at the intraperiod line. Spongiform changes were accompanied by an exuberant cellular reaction consisting of macrophages and hypertrophic astrocytes. Occasionally, vesicular myelin degeneration and coated vesicles in a close proximity to the myelin were observed.