Experimental spongiform encephalopathy (Creutzfeldt-Jakob disease) in chimpanzees. Electron microscopic studies

Analysis of non-human primate models for evaluating prion disease therapeutic efficacy

Prion disease is a fatal neurodegenerative disease caused by the conformational corruption of the prion protein (PrP), encoded by the prion protein gene (PRNP). While no disease-modifying therapy is currently available, genetic and pharmacological proofs of concept support development of therapies that lower PrP levels in the brain. In light of proposals for clinical testing of such drugs in presymptomatic individuals at risk for genetic prion disease, extensive nonclinical data are likely to be required, with extra attention paid to choice of animal models. Uniquely, the entire prion disease process can be faithfully modeled through transmission of human prions to non-human primates (NHPs), raising the question of whether NHP models should be used to assess therapeutic efficacy. Here we systematically aggregate data from N = 883 prion-inoculated animals spanning six decades of research studies. Using this dataset, we assess prion strain, route of administration, endpoint, and passage number to characterize the relationship of tested models to currently prevalent human subtypes of prion disease. We analyze the incubation times observed across diverse models and perform power calculations to assess the practicability of testing prion disease therapeutic efficacy in NHPs. We find that while some models may theoretically be able to support therapeutic efficacy studies, pilot studies would be required to confirm incubation time and attack rate before pivotal studies could be designed, cumulatively requiring several years. The models with the shortest and most tightly distributed incubation times are those with smaller brains and weaker homology to humans. Our findings indicate that it would be challenging to conduct efficacy studies in NHPs in a paradigm that honors the potential advantages of NHPs over other available models, on a timeframe that would not risk unduly delaying patient access to promising drug candidates.

Molecular pathogenesis of sporadic prion diseases in man

The yeast, fungal and mammalian prions determine heritable and infectious traits that are encoded in alternative conformations of proteins. They cause lethal sporadic, familial and infectious neurodegenerative conditions in man, including Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker syndrome (GSS), kuru, sporadic fatal insomnia (SFI) and likely variable protease-sensitive prionopathy (VPSPr). The most prevalent of human prion diseases is sporadic (s)CJD. Recent advances in amplification and detection of prions led to considerable optimism that early and possibly preclinical diagnosis and therapy might become a reality. Although several drugs have already been tested in small numbers of sCJD patients, there is no clear evidence of any agent’s efficacy. Therefore, it remains crucial to determine the full spectrum of sCJD prion strains and the conformational features in the pathogenic human prion protein governing replication of sCJD prions. Research in this direction is essential for the rational development of diagnostic as well as therapeutic strategies. Moreover, there is growing recognition that fundamental processes involved in human prion propagation – intercellular induction of protein misfolding and seeded aggregation of misfolded host proteins – are of far wider significance. This insight leads to new avenues of research in the ever-widening spectrum of age-related human neurodegenerative diseases that are caused by protein misfolding and that pose a major challenge for healthcare.

A 25 nm virion is the likely cause of transmissible spongiform encephalopathies

The transmissible spongiform encephalopathies (TSEs) such as endemic sheep scrapie, sporadic human Creutzfeldt-Jakob disease (CJD), and epidemic bovine spongiform encephalopathy (BSE) may all be caused by a unique class of "slow" viruses. This concept remains the most parsimonious explanation of the evidence to date, and correctly predicted the spread of the BSE agent to vastly divergent species. With the popularization of the prion (infectious protein) hypothesis, substantial data pointing to a TSE virus have been largely ignored. Yet no form of prion protein (PrP) fulfills Koch's postulates for infection. Pathologic PrP is not proportional to, or necessary for infection, and recombinant and "amplified" prions have failed to produce significant infectivity. Moreover, the "wealth of data" claimed to support the existence of infectious PrP are increasingly contradicted by experimental observations, and cumbersome speculative notions, such as spontaneous PrP mutations and invisible strain-specific forms of "infectious PrP" are proposed to explain the incompatible data. The ability of many "slow" viruses to survive harsh environmental conditions and enzymatic assaults, their stealth invasion through protective host-immune defenses, and their ability to hide in the host and persist for many years, all fit nicely with the characteristics of TSE agents. Highly infectious preparations with negligible PrP contain nucleic acids of 1-5 kb, even after exhaustive nuclease digestion. Sedimentation as well as electron microscopic data also reveal spherical infectious particles of 25-35 nm in diameter. This particle size can accommodate a viral genome of 1-4 kb, sufficient to encode a protective nucleocapsid and/or an enzyme required for its replication. Host PrP acts as a cellular facilitator for infectious particles, and ultimately accrues pathological amyloid features. A most significant advance has been the development of tissue culture models that support the replication of many different strains of agent and can produce high levels of infectivity. These models provide new ways to rapidly identify intrinsic viral and strain-specific molecules so important for diagnosis, prevention, and fundamental understanding.

Cells infected with scrapie and Creutzfeldt-Jakob disease agents produce intracellular 25-nm virus-like particles

We had repeatedly found approximately 25-nm-diameter virus-like particles in highly infectious brain fractions with little prion protein (PrP), and therefore we searched for similar virus-like particles in situ in infected cell lines with high titers. Neuroblastoma cells infected with the 22L strain of scrapie as well as hypothalamic GT cells infected with the FU Creutzfeldt-Jakob disease agent, but not parallel mock controls, displayed dense 25-nm virus-like particles in orthogonal arrays. These particles had no relation to abnormal PrP amyloid in situ, nor were they labeled by PrP antibodies that faithfully recognized rough endoplasmic reticulum membranes and amyloid fibrils, the predicted sites of normal and pathological intracellular PrP. Additionally, phorbol ester stimulated the production of abnormal PrP gel bands by >5-fold in infected N2a + 22L cells, yet this did not increase either the number of virus-like arrays or the infectious titer of these cells. Thus, the 25-nm infection-associated particles could not be prions. Synaptic differentiation and neurodegeneration, as well as retroviruses that populate the rough endoplasmic reticulum of neuroblastoma cells, were not required for particle production. The 25-nm particle arrays in cultured cells strongly resembled those first described in 1968 in synaptic regions of scrapie-infected brain and subsequently identified in many natural and experimental TSEs. The high infectivity of comparable, isolated virus-like particles that show no intrinsic PrP by antibody labeling, combined with their loss of infectivity when nucleic acid-protein complexes are disrupted, make it likely that these 25-nm particles are the causal TSE virions that induce late-stage PrP brain pathology.

Pathologic features of dysplasia and accompanying alterations observed in surgical specimens from patients with intractable epilepsy

Malformations caused by abnormalities of cortical development, or cortical dysplasias, were examined in surgical specimens from 108 patients with medically intractable epilepsy to determine the scope of histopathologic changes. The relevance of the clinical findings was also evaluated. Various types and degrees of dysplastic features were observed in various combinations, including architectural abnormalities, an increased number of neurons in the molecular layer and/or cortical layer II, neuronal clustering, an increased number of satellite oligodendrocytes, abnormal gyration, single and/or aggregates of heterotopic neurons in the white matter, and the appearance of cytologically abnormal cells, such as giant or dysmorphic neurons and balloon cells. In the temporal lobe specimens, microdysgenesis (corresponding to mild malformations caused by abnormalities of cortical development and type IA/B focal cortical dysplasias) was more frequently observed than Taylor-type focal cortical dysplasia (type IIA/B), whereas in the frontal lobe specimens, the frequency of occurrence of both types was even. The ages at seizure onset and surgery of patients with the latter type were significantly lower than those of patients with the former. On the other hand, prominent astrocytosis in the cortex and white matter was evident in all cases, and many corpora amylacea and neurofibrillary tangle-like inclusions were observed in a subset of cases. An ultrastructural investigation revealed dilatation of the postsynaptic dendritic spines and shafts in the cortex and features indicating the occurrence in the white matter of demyelination followed by remyelination. Thus, with regard to the epileptogenic lesions, although dysplastic changes constitute the pathogenetic basis, the overlapping subsequent degenerative processes involving synapses, dendrites, and axons might contribute to the development of epileptogenic processes. Astrocytes might also actively participate in the development of the pathogenesis of epilepsy.

Cerebral lipoma and the underlying cortex of the temporal lobe: pathological features associated with the malformation

Intracranial lipomas are believed to be congenital malformations rather than true neoplasms, resulting from the abnormal differentiation of the meninx primitiva, the undifferentiated mesenchyme. We report here the surgical pathological features of a lipoma that was located on the cerebral surface of an abnormally formed fissure, and the underlying cortex of the middle temporal gyrus of a 20-year-old woman. The mass was composed of typical adipose tissue in which a large number of blood vessels were present. Thick connective tissue associated with the arachnoid membrane covered the cortical surface. The cortex exhibited a polymicrogyric configuration in which the cortical ribbon was abnormally undulated and excessively folded. Reelin-immunolabeled Cajal-Retzius-cell-like cells were observed frequently in the fused molecular layer. The cortical lamination underlying the molecular layer was poorly defined. Along the border between the connective tissue and cortical surface, there was a narrow zone in which the mesenchymal and neuronal tissues were intermingled, and where immunohistochemical and ultrastructural investigations disclosed disruption of the basal lamina, prominent astrocytosis, and abundant axonal and synaptic profiles. These findings suggest that focal disturbances in cerebral cortical development occur in association with the development of lipomas.

Tubulovesicular structures: what are they really?

The tubulovesicular structures (TVS) are the only structures unique at the level of thin-section electron microscopy for all TSEs so far examined. They were first described in NIH Swiss mice infected intracerebrally with the "Chandler" strain of scrapie by David-Ferreira et al. in 1968 [Proc. Soc. Exp. Biol. Med. 127:313-320]. TVS were described as "particles and rods ranging in diameter from 320 to 360 A(o)." The exact topology of TVS is not entirely clear. In most published electron micrographs, TVS appeared as spheres measuring between 20 and 40 nm in diameter. The number of neuritic processes containing TVS increases through the incubation period and has been shown to correlate with the incubation period and titre of infectivity in three longitudinal disease studies of scrapie and CJD. These studies, therefore, suggest that TVS may represent a primary pathogenetic event rather than a pathological product of disease. The predominant theory of the scrapie agent is now the "prion hypothesis" and its derivatives, which implies that a conformationally altered abnormal isoform (PrP(Sc) or PrP*) of a normal cellular membrane glycoprotein (PrP(c)) is the agent and its accumulation merely mimicks replication. If an abnormal fraction of PrP is indeed the infectious agent, (although it is no longer suggested in some quarters that protease resistant fraction of PrP(Sc) is the agent). The absence of stainable PrP in TVS, however, would indicate that they are not the ultrastructural correlate of the agent. However, TVS appear to be specific and unique to the TSEs, appearing before the earliest pathological changes and increasing in line with incubation period or titre. The very existence of TVS and their correlation with infectivity, therefore, urgently needs an explanation.

Close relationship between spongiform change and ubiquitin-positive granular structures in diffuse Lewy body disease

The origin of spongiform change seen in diffuse Lewy body disease (DLBD) cases was elucidated, as compared with Alzheimer-type dementia (ATD) cases. Spongiform change was composed of numerous vacuoles in the neuropil, predominantly in layers II-IIIab of the transentorhinal cortex and in the intermediate area of the accessory basal amygdaloid nucleus. The distribution of spongiform change was identical to that of ubiquitin-positive granular structures (UPG) in non-demented cases. The degree of spongiform change was correlated with loss of the large pyramidal neurons in layers IIIc and V of the transentorhinal cortex and with the disappearance of their ubiquitin-positive granular processes. With electron microscopy, the early vacuoles of spongiform change appeared to arise in the presynaptic terminals as well as in the postsynaptic terminals and dendritic processes. These findings indicate that the vacuoles derive from degeneration of terminal axons of the large pyramidal neurons. The occurrence of spongiform change characteristic to DLBD suggests that the large pyramidal neurons degenerate more rapidly in DLBD than in ATD.

Neuroaxonal dystrophy in experimental Creutzfeldt-Jakob disease: electron microscopical and immunohistochemical demonstration of neurofilament accumulations within affected neurites

Neuroaxonal dystrophy is a feature of neuronal degeneration encountered in all subacute spongiform "virus" encephalopathies, including scrapie and Creutzfeldt-Jakob disease (CJD). By immunohistochemical techniques, the accumulation of 200 kDa neurofilament protein was demonstrated in affected neurites in murine CJD. These neurites exhibited the ultrastructural features of dystrophic neurites encountered in other neurodegenerative disorders, particularly Alzheimer's disease. These findings support the hypothesis that impairment of slow axoplasmic transport is a common pathogenetic mechanism for CJD and many other neurodegenerative conditions.

Transmissible cerebral amyloidoses as a model for Alzheimer's disease. An ultrastructural perspective

Alzheimer's disease, a prototypic nontransmissible cerebral amyloidosis, has no adequate experimental model. Several pathogenetic events, however, may be modeled and accurately studied in the transmissible cerebral amyloidoses of kuru, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker disease, and scrapie. The common neuropathological denominator in both types of cerebral amyloidoses is the presence of stellate kuru plaques, senile plaques, and pure neuritic plaques. These amyloid plaques consist of amyloid fibers, dystrophic neurites, and reactive astrocytes in different proportions. Microglial cells, which are regarded as amyloid producer/processor cells in Alzheimer's disease, may play the same function in the transmissible cerebral amyloidoses. In both transmissible and nontransmissible amyloidoses, the impairment of axonal transport leads to accumulation of abnormally phosphorylated cytoskeleton proteins (such as neurofilament proteins and microtubule-associated protein tau), which eventually produce dystrophic neurites observed as parts of plaque or as isolated pathological structures.

Immunohistochemical study of microglia in the Creutzfeldt-Jakob diseased brain

Immunohistochemical techniques have been used to investigate microglial reaction in Creutzfeldt-Jakob diseased (CJD) brains. Autopsy cases of six patients with CJD and age-matched controls were studied. Formalin-fixed, paraffin-embedded brain tissue samples were stained with antibodies against major histocompatibility complex (MHC) class II antigen (Ag), leukocyte common antigen (LCA), CDw75, CD68 and glial fibrillary acidic protein. Of the patients with CJD, two with a subacute spongiform encephalopathic type and short-survival periods after onset of the disease showed an increased number of reactive microglia labeled with anti-MHC class II Ag or LCA in the affected cerebral cortex. In advanced cases of the panencephalopathic type of CJD, in which both cerebral atrophy and astrocytosis were marked, the increase of reactive microglia was small. Some vacuoles developing in the neuropil of the CJD patients were surrounded by MHC class II Ag- or LCA-immunoreactive microglial cells. The number of ramified microglia in the affected lesions was decreased, although their number in the hippocampus was not affected. These results indicate that microglia can frequently be involved in the process of CJD and may be activated at the early stage of the disease.

Comparative ultrastructural neuropathology of naturally occurring bovine spongiform encephalopathy and experimentally induced scrapie and Creutzfeldt-Jakob disease

We report the ultrastructural neuropathology of bovine spongiform encephalopathy (BSE), a recently described slow virus disease first recognized in Friesian/Holstein cattle, and compare it to that of experimental scrapie and Creutzfeldt-Jakob disease. The spongiform change, which was most pronounced in the central grey matter of the midbrain, consisted of membrane-bound vacuoles within neuronal processes, containing curled membrane fragments, secondary chambers and vesicles. Axons and dendrites accumulated whorls of neurofilaments and other subcellular organelles, such as mitochondria and dense bodies, which were entrapped within the filamentous masses. Other neurites accumulated electron-dense bodies, and still others electron-lucent cisterns and branching tubules. Membrane-bound neuronal inclusions, composed of tubules measuring 10 nm in diameter, were found in axonal terminals. Tubulovesicular structures were loosely packed and were occasionally surrounded by a common membrane, a finding previously described only in natural scrapie in sheep. Except for the intraneuronal inclusions, all of the ultrastructural features of BSE resembled those found in scrapie and Creutzfeldt-Jakob disease.

Scrapie-associated tubulofilamentous particles in human Creutzfeldt-Jakob disease

Scrapie-associated fibrils (SAF) were demonstrated by a simple negative staining method for electron microscopy from fresh and frozen brains with naturally occurring human Creutzfeldt-Jakob disease (CJD). The findings confirm that SAF occur as an internal part of a larger three-layer particle. The two outer coats of SAF can be disrupted by detergent alone or can be digested in two stages by a combination of proteolytic enzymes and subsequent treatment with DNase and mung bean nuclease. Examination of thin sections from the cerebral cortex of brains from patients with CJD revealed the presence of 26-30-nm diameter tubulofilamentous particles, identical to those previously described in natural scrapie of sheep and bovine spongiform encephalopathy and also in experimentally induced scrapie in mice and hamsters and CJD-infected mice and chimpanzees. Thus, it would appear that the particles are not contaminants passaged in experimental animals.

Mechanism of the damage to myelinated axons in experimental Creutzfeldt-Jakob disease in mice: an ultrastructural study

We report the ultrastructural pathology of myelinated axons in mice infected experimentally with the Fujisaki strain of Creutzfeldt-Jakob disease (CJD). Initially the myelin sheath was separated into several concentric bands, and cellular processes penetrated between layers of myelin and lifted away the outermost lamella. Then a complicated labyrinth of the concentric cellular processes, clearly belonging to either astrocytes or macrophages, invested myelinated axons. In terminal stages axons completely denuded of myelin were seen in the center of concentric networks of cellular processes. Myelin remnants were seen within astrocytes and macrophages. We conclude that the mechanism(s) of damage to myelinated axons in CJD may be similar to that operating in immunologically mediated demyelinating disorders.

Tubulovesicular structures in human and experimental Creutzfeldt-Jakob disease

Tubulovesicular structures (TVS) have been consistently observed in brain tissue of animals with transmissible spongiform encephalopathies such as natural and experimental scrapie, bovine spongiform encephalopathy, and experimental Creutzfeldt-Jakob disease (CJD). In this communication we demonstrate for the first time the presence of TVS in natural CJD. TVS were detected in all 3 CJD specimens. However, they were rare and were found only in one or two locations per grid. They were seen in distended pre- and postsynaptic terminals and measured approximately 35 nm in diameter, and they were smaller and of higher electron density than synaptic vesicles. Their occurrence in all types of spongiform encephalopathies irrespective of the affected host and the strain of infectious agent emphasizes their biological significance.

Creutzfeldt-Jakob disease with severe involvement of cerebral white matter and cerebellum

We describe a patient with Creutzfeldt-Jakob disease (CJD) of the ataxic and panencephalopathic type. Postmortem examination revealed the characteristic lesions of CJD in the grey matter and profound white matter involvement was seen with immunocytochemical techniques. Ultrastructural white matter lesions were identical to those described in experimentally transmitted CJD. There was marked loss of cerebellar granule cells with virtual disappearance of parallel fibres, but Purkinje cells were only slightly reduced. Electron microscopic studies revealed extensive degenerative changes including cytoplasmic vacuoles in both cell types. Silver methods disclosed massive impregnation of white matter and striking abnormalities of Purkinje cells consisting of hypertrophy and flattening of thick dendritic branches, reduction in the number of terminal branchlets, segmentary loss of spines and polymorphic spines. These findings show the extensive involvement of all three cerebellar cortical layers and the reactive plasticity of Purkinje cells to deafferentiation. They favour the hypothesis that demyelination represents a primary lesion of the white matter.

Appearance of tubulovesicular structures in experimental Creutzfeldt-Jakob disease and scrapie precedes the onset of clinical disease

We have consistently observed tubulovesicular structures in brain tissues during the terminal stages of naturally occurring and experimentally induced spongiform encephalopathies, irrespective of the host species and virus strain. In NIH Swiss mice inoculated intracerebrally or intraocularly with the Fujisaki strain of Creutzfeldt-Jakob disease (CJD) virus, tubulovesicular structures, measuring 20-50 nm in diameter, were particularly prominent in dilated, pre- and postsynaptic neuronal processes, occasionally being mixed with synaptic vesicles. These structures appeared 13 weeks following intracerebral inoculation, 5 weeks before the onset of clinical signs, when spongiform changes were also detected. The number and density of tubulovesicular structures increased steadily during the course of clinical disease, and were particularly abundant in mice 47 to 51 weeks after intraocular inoculation. In hamsters infected with the 263 K strain of scrapie virus, these structures were initially detected 3 weeks following intracerebral inoculation and increased dramatically at 10 weeks postinoculation. The appearance of tubulovesicular structures before the onset of overt disease in mice inoculated with CJD virus by either the intracerebral or intraocular route, and before the appearance of other neuropathological changes in hamsters infected with scrapie virus, indicate that they represent either a part or aggregate of the infectious virus or a pathological product of the infection.

Serial ultrastructural studies of scrapie in hamsters

We report sequential studies of the ultrastructural neuropathology of the subcortical grey matter of hamsters infected with the 263K strain of scrapie virus. Vacuolation in this model develops relatively late in the incubation period, while tubulovesicular structures appear early. Furthermore, neuroaxonal dystrophy, accumulations of branching tubules, and neuronal change consisting of intracytoplasmic "whorls" of proliferating membranes constitute prominent features of scrapie-related neurodegeneration.

An electron microscopic study of inclusion bodies in synaptic terminals of scrapie-infected animals

Inclusion bodies consisting of vesicles of about 25 nm diameter and occurring in the synaptic terminals of scrapie-infected animals have been described by a number of people. In the present study these inclusion bodies were looked for in the neocortex, hippocampus and corpus callosum in a variety of strains of mice (C3H, LM, RIII, IM, VL) infected with different strains of scrapie agent (22C, 79A, ME7, 87V) after intracerebral inoculation. In plaque-bearing models of scrapie, terminals containing synaptic inclusion bodies were frequently found surrounding the amyloid plaque cores in the neocortex but not in the corpus callosum. In non-plaque-bearing models, terminals containing synaptic inclusion bodies were found in the neuropil of the neocortex and hippocampus. For all models, these bodies were either presynaptic or postsynaptic but were not, as a rule, found on both sides of the same synapse. Fibrillary material was frequently seen in the postsynaptic terminals containing the inclusion bodies in both the plaque- and non-plaque-bearing models. On one occasion fibrillary material was seen, together with the inclusion bodies, in a neuron cell body. Inclusion bodies were also seen in the neocortex of hamsters infected with the 263K strain of scrapie agent and a Cheviot sheep infected with the ME7 strain of agent. The inclusion bodies and the fibrillary material were thought to be derived from the breakdown of neurotubules.

Cerebral glycosidases in experimental Creutzfeldt-Jakob disease

In Creutzfeldt-Jakob disease (CJD), there are prominent ultrastructural alterations of the plasma membrane, which contains many glycolipids and glycoproteins. Glycosidases can degrade glycolipids and glycoproteins. Gangliosides, a subset of glycolipids, are decreased in amount at the terminal stages of CJD, and CJD infectivity is closely associated with membrane rich fractions. We therefore studied 10 glycosidases, and found a statistically significant increase in beta-xylosidase, beta-glucuronidase, N-acetyl-beta-D-glucosaminidase and N-acetyl-beta-D-galactosaminidase activities in CJD. In contrast, alpha-glucosidase, beta-glucosidase, alpha-galactosidase, alpha-mannosidase, alpha-fucosidase, and beta-galactosidase were not significantly changed. The above results are consistent with degenerative membrane changes observed morphologically, and with increased degradation of sugar residues on lipids and/or proteins. These changes may be effected by the accumulation of the CJD agent in cell membranes. We suggest that the higher activities of these enzymes in CJD may be partially responsible for some of the structural and biochemical alterations in CJD infected brains.

A chronological study of experimental scrapie in mice

The development of scrapie-associated particles and lesions in four regions of the brain was studied in mice over a period of 30 weeks. Characteristic tubulovesicular particles, identical to those previously described, were first found about half way through the incubation period in mice inoculated by four different routes. The particles are found in brains with scrapie and other spongiform encephalopathies; they have never been seen in other conditions, and potentially represent the infectious agent.

Impairment of the cortical and thalamic electrical activity in scrapie-infected rats

Cortical and thalamic EEG and somatosensory evoked potential (SEP) induced by stimulation of the somesthetic radiations were studied in scrapie-infected rats. Animals were inoculated intracerebrally with a rat-adapted strain (originating in the C506 M3 mouse scrapie strain). EEG and SEP were recorded from 9 to 17 months after inoculation (ti). Abnormalities (paroxysmal bursts, isolated spikes) first occurred in the cortex (parietal areas) and later in the thalamus, where they were usually less marked. Latencies of the postsynaptic components of the SEP increased at ti + 9 months. This effect became progressively more pronounced and at ti + 15 months, latencies of presynaptic components were also delayed. Nevertheless, marked alteration of the SEP occurred only at the terminal stage of the disease. These findings show that the scrapie-induced disturbances affect more especially the cortex. Decrease of inhibitory processes as well as electronic coupling between cells, resulting from the virus-induced membrane fusion, could produce paroxysmal activity of EEG and SEP impairments.

On the biology of prions

Prions cause scrapie and Creutzfeldt-Jakob disease (CJD); these infectious pathogens are composed largely, if not entirely, of protein molecules. No prion-specific polynucleotide has been identified. Purified preparations of scrapie prions contain high titers (greater than or equal to 10(9.5) ID50/ml), one protein (PrP 27-30) and amyloid rods (10-20 nm in diameter X 100-200 nm in length). Considerable evidence indicates that PrP 27-30 is required for and inseparable from scrapie infectivity. PrP 27-30 is encoded by a cellular gene and is derived from a larger protein, denoted PrPSc or PrP 33-35Sc, by protease digestion. A cellular isoform, designated PrPC or PrP 33-35C, is encoded by the same gene as PrPSc and both proteins appear to be translated from the same 2.1 kb mRNA. Monoclonal antibodies to PrP 27-30, as well as antisera to PrP synthetic peptides, specifically react with both PrPC and PrPSc, establishing their relatedness. PrPC is digested by proteinase K, while PrPSc is converted to PrP 27-30 under the same conditions. Prion proteins are synthesized with signal peptides and are integrated into membranes. Detergent extraction of microsomal membranes isolated from scrapie-infected hamster brains solubilizes PrPC but induces PrPSc to polymerize into amyloid rods. This procedure allows separation of the two prion protein isoforms and the demonstration that PrPSc accumulates during scrapie infection, while the level of PrPC does not change. The prion amyloid rods generated by detergent extraction are identical morphologically, except for length, to extracellular collections of prion amyloid filaments which form plaques in scrapie- and CJD-infected brains. The prion amyloid plaques stain with antibodies to PrP 27-30 and PrP peptides. PrP 33-35C does not accumulate in the extracellular space. Prion rods composed of PrP 27-30 can be dissociated into phospholipid vesicles with full retention of scrapie infectivity. The murine PrP gene (Prn-p) is linked to the Prn-i gene which controls the length of the scrapie incubation period. Prolonged incubation times are a cardinal feature of scrapie and CJD. While the central role of PrPSc in scrapie pathogenesis is well established, the chemical as well as conformational differences between PrPC and PrPSc are unknown but probably arise from post-translational modifications.

Cerebrocortical degeneration in goats inoculated with mink-passaged scrapie virus

Widespread spongiform degeneration of the cerebral cortex occurred in four African pygmy goats that became affected with scrapie after intracerebral inoculation with scrapie virus (Suffolk sheep brain origin) that had been passed three times in ranch mink. The occurrence of such cerebrocortical degeneration was a distinct departure from the topographic pattern of neuropathologic changes that characterizes scrapie in sheep and goats. But the cortical lesion was identical to the one found in goats that became affected with a disease otherwise indistinguishable from scrapie after intracerebral inoculation with transmissible mink encephalopathy (TME) virus that had been passed twice in mink. If TME originated from infection with wild scrapie virus, as is generally thought, then the viruses used in these two instances would be equivalent in their passage history in this aberrant host. Given this similarity, the common occurrence of the cortical lesion is thought to be consistent with the view that TME virus almost certainly is scrapie virus whose biologic properties became altered by chance passage in ranch mink.

Pathology of Creutzfeldt-Jakob disease associated with pituitary-derived human growth hormone administration

This report describes the pathological features in the brain of a 22 year old woman who died with Creutzfeldt-Jakob disease 8 1/2 years after completing a 4 year course of injections of human growth hormone derived from cadaver pituitaries. Spongiform change was seen in the frontal cortex. There was gliosis and neuronal loss throughout the frontal cortex, basal ganglia, thalamus, peri-aqueductal grey matter and tectum of the mid brain, pontine nuclei and dorsal medulla but no evidence of inflammation. Extensive atrophy and gliosis of the cerebellar cortex was present with widespread loss of neurons from the internal granular layer but relative sparing of Purkinje cells. Gliosis and atrophy of the mammillary bodies and gliosis of the hypothalamus may have been related to the previous surgical excision of a craniopharyngioma at the age of 2 1/2 years. The pattern of changes presented is comparable to that in other cases of Creutzfeldt-Jakob disease including those previously reported after human growth hormone administration.

Role of VSV G antigen in the development of experimental spongiform encephalopathy in mice

The ts G31 VSV mutant induced spongiform encephalopathy without any inflammatory response when injected i.c. into the mouse. In electron microscopy, no virions could be detected in spongiform lesions. In contrast, with the wild VSV strain inflammatory lesions were seen, which contained viral particles in great abundance. As previously shown in vitro, when using the ts G 31 mutant at the nonpermissive temperature, the G antigen can spread from membrane to membrane to distant sites, fusing a great number of cells even in the absence of virus multiplication. Therefore, we postulate that a comparable mechanism is responsible for extensive brain lesions originating probably from a relatively small number of G antigen-producing cells. Indeed, the spongious regions seen mainly in the grey matter contained vacuoles, whose walls were clearly stained by peroxidase-labelled immune serum to G antigen, without detectable virions or inflammatory lesions. The vacuoles probably represent altered and swollen dendritic cell membranes. The relationship between spongiosis development and antigen diffusion in the absence of significant virus replication is discussed.

Serial ultrastructural study of experimental Creutzfeldt-Jacob disease in guinea pigs

Guinea pigs inoculated with brain homogenate from serially passaged Creutzfeldt-Jakob disease (CJD) were killed biweekly starting at week 2 until terminal illness (about 200 days following inoculation). A mild swelling of postsynaptic dendrites and an increase in the number of glial filaments in astrocytic processes was seen at week 4, followed by increased swelling and lucency of axons and dendrites by week 6 post inoculation (p.i.). Severe undulation and focal interruptions of synaptic membranes were also observed both at weeks 4 and 6. By week 8, one could see cystically dilated cellular processes. These sometimes showed continuity with adjacent swollen processes through focally disrupted plasma membranes, and most likely represent a progressive enlargement of vacuoles through fusion and subsequent addition of adjoining processes. The spongiform changes increased mildly between week 8 and week 10 and remained essentially the same in subsequent weeks. After week 24 there was a sharp increase in both the number and size of vacuoles. At week 24 severe structural alterations were present both in the neurons and astrocytes, and numerous intranuclear inclusions were demonstrated in many neuronal nuclei. This study shows that morphological changes in the brain occur considerably earlier than the clinical manifestations of the disease. In the early phase of the disease, there were significant alterations on the dendrites and synapses.

Identification of prion amyloid filaments in scrapie-infected brain

Extracellular collections of abnormal filaments composed of prion proteins have been identified in the brains of scrapie-infected hamsters using immunoelectron microscopy. Some of the filaments were 1500 nm in length; generally, they exhibited a uniform diameter of 16 nm. Rarely, the filaments had a twisted appearance, raising the possibility that they are flattened cylinders or are composed of helically wound protofilaments. The prion filaments possess the same diameter and limited twisting as the shorter rod-shaped particles observed in purified preparations of prions. Both the filaments and rods are composed of PrP 27-30 molecules, as determined by immunoelectron microscopy using affinity-purified antibodies. The ultrastructural features of the prion filaments are similar to those reported for amyloid in many tissues including brain. These results provide the first evidence that prion proteins assemble into filaments within the brain and that these filaments accumulate in extracellular spaces to form amyloid plaques.

Differentiation between Crohn's disease and other inflammatory conditions by electron microscopy

The authors previously have demonstrated axonal necrosis of autonomic nerves in the surgically resected ilea of patients with Crohn's disease both in grossly normal ileal resection margins and in diseased areas. The present study of ileal stomal biopsies was carried out to obviate the possibility that the observed axonal damage might be related to the prolonged surgical manipulations required for ileal resection. The authors present studies of biopsies of ileal stomas and of small bowel from patients with Crohn's disease and various control disorders, including ulcerative colitis. Stomal biopsies were fixed immediately after they were obtained. Widespread, severe axonal necrosis of autonomic nerves was present in all Crohn's disease specimens, regardless of the patient's clinical status or the gross or routine microscopic evaluation of the same specimen. Controls either had no necrosis or displayed a minor degree of focal necrosis involving single axons. The authors conclude that Crohn's disease is accompanied by a severe and extensive necrosis of gut axons, and that such electron microscopic findings may serve to differentiate Crohn's disease from other inflammatory disorders.

Rabies: spongiform lesions in the brain

Striped skunks (Mephitis mephitis) experimentally infected with street rabies virus developed spongiform lesions that light- and electron-microscopically were indistinguishable from those found in the transmissible spongiform encephalopathies of man and animals. These previously unreported lesions were also detected in naturally occurring cases of rabies. The spongiform lesions consisted of round or oval vacuoles in the neuropil, rarely in neuronal perikarya. The most severely affected areas were the thalamus and cerebral cortex. The implications of this finding include similarities in the pathogenetic mechanisms of rabies and the traditional spongiform encephalopathies and the possibility of lesion variation due to differences in rabies viral strains. The spongiform lesions of rabies will require consideration in differential diagnosis.

Creutzfeld-Jakob disease: clinical, EEG and neuropathological findings in a cluster of eleven patients

10 of 11 Creutzfeld-Jakob disease patients were seen between February 1975 and November 1979. Whilst the clinical and EEG findings were uniform, the neuropathological changes were not: astrogliosis was always diffuse and widespread but the other typical changes (neuronal loss and spongiosis) varied greatly both in degree and location.

Spongiform-like changes in Alzheimer's disease. An ultrastructural study

THe ultrastructural study of the cortex of four patients with sporadic or familial AD, of two age-matched controls without dementia, and of one normal pressure hydrocephalus, revealed in all the cases in the neuropil only occasional vacuoles which had a morphology similar to those observed in CJD. The degree of spongiform-like changes was, however, far less prominent than in CJD and considered mild in all the cases examined. Moreover, curled fragments of membranes within the vacuoles were not observed. It is suggested that the mild vacuolization of the neuropil occasionally observed in cortical biopsies of AD is a non-specific finding and cannot be considered a neuropathologic link between AD and CJD.

Morphological alterations of Purkinje cell axons and presynaptic terminals in organotypic cerebellar cultures exposed to ionizing irradiation

Ionizing irradiation induced marked morphological alterations in the Purkinje cell axons and axonic terminals in vitro. The myelinated segments demonstrated a very poor development of the myelin sheath. The axoplasm demonstrated various alterations of the mitochondria, and the smooth endoplasmic reticulum and the numerous elongated presynaptic terminals contained large aggregates of tubulovesicular structures and neurofilaments arranged in parallel and reticular array.

Virus-induced electrotonic coupling: hypothesis on the mechanism of periodic EEG discharges in Creutzfeldt-Jakob disease

Experimental evidence and computer modeling indicate that periodic synchronous cellular depolarizing bursts (interictal spikes) arise when the balance recurrent inhibition and local excitatory coupling is altered. Such a mechanism may explain the generalized periodic sharp waves that characterize the electroencephalogram of many patients with Creutzfeldt-Jakob disease. In Creutzfeldt-Jakob disease, fusions of neuronal processes, particularly dendrites, may lead to abnormal electrotonic coupling between cells, providing the basis for powerful excitatory interaction whereby large neuronal aggregates burst in near synchrony. Cortical synchronous discharges would give rise to sharp waves in the electroencephalogram, whereas similar discharges in brainstem, spinal cord, or elsewhere could lead to myoclonic jerks.

A typical presenile dementia. Report of an anatomo-clinical case and review of the literature

A clinico-pathological report is given of a case of dementia of frontal type with EEG changes, associated with a diffuse neuronal loss, subcortical gliosis and laminar spongiosis in the superficial part of the 2nd cortical layer. The authors discuss the cortical biopsy and the post-mortem findings in their case. They draw a comparison between their case an two conditions known as "progressive sub-cortical gliosis" and "Kraepelin's disease" which might be a single entity "atypical presenile dementia".

Spongiform polioencephalomyelopathy caused by a murine retrovirus. II. Ultrastructural localization of virus replication and spongiform changes in the central nervous system

The development of murine retrovirus induced spongiform polioencephalomyelopathy was studied sequentially by electron microscopy. During the initial 30 days, viral infection of the central nervous system, as evidenced by viral budding from membranes, was limited to the endothelial cells and pericytes. Viral particles were observed in the lumen of blood vessels, extracellular spaces and astrocytic endfeet surrounding blood vessels, but no morphological evidence of productive infection was found in astrocytes or neurons during early development of vacuolation. The earliest lesions in the neuropil consisted of swelling of astroglia followed by vacuolation, initially in axons and dendrites and later in neuronal and astrocytic soma, where vacuoles appeared to arise from dilated cisternae of the Golgi apparatus. Vacuoles contained only amorphous debris and fragments of membranes. Virions budding aberrantly into vacuoles were seen only in mice surviving beyond 35 days. Numerous reactive astrocytes were observed, but inflammatory cells were absent. The ultrastructural changes were remarkably similar to those described in scrapie, Kuru, and Creutzfeldt-Jakob disease.

Crohn's disease: transmission electron microscopic studies. III. Target tissues. Proliferation of and injury to smooth muscle and the autonomic nervous system

Transmission electron microscopy was done on surgical specimens from 12 patients with Crohn's disease and three control subjects. Nonulcerated involved areas of ileum as well as proximal, grossly uninvolved resection margins were chosen for study. Specimens for transmission electron microscopy were prepared by a variety of techniques and 112 blocks were examined by electron microscopy. The study was concentrated on two target tissues of the gut: the autonomic nervous system and the smooth muscle. Proliferative and injurious changes were found in each. Proliferation, myofibroblastic transformation, hypercontraction, and necrosis characterized the smooth muscle changes seen in Crohn's disease of the ileum. Autonomic nervous system changes included proliferation of axons containing dense core granules (catecholamines) and axonal necrosis. The possible pathogenetic significance of these changes is discussed here and in the accompanying article beginning on page 606 of this issue.

Further observations on particulate structures in scrapie affected brain

A search procedure at the ultrastructural level revealed characteristic particulate structures in mice of two further laboratory stocks experimentally inoculated with scrapie. The structures represent a specific change related to scrapie disease; their relationship to the scrapie agent is discussed.

Creutzfeldt-Jakob disease with extensive degeneration of white matter

Degeneration of the white matter is uncommon is Creutzfeldt-Jakob disease (CJD), and when it occurs is usually mild, and limited in distribution. In the case of 77-year-old woman with CJD lasting 1 year, there was extensive degeneration of cerebral white matter in addition to severe loss of neurons and hypertrophic astrogliosis in cortex and striatum. The extent and severity of white matter lesions makes the case unusual.

Experimental transmission of human subacute spongiform encephalopathy to small rodents. II. Ultrastructural study of spongy state in the gray and white matter

Light and electron microscopic findings of spongy state in four species of small rodents, viz, mice, rats, Mongolian gerbils, and guinea pigs, are described. The spongy state existed in both gray and white matter; its intensity varied in each species, and in the gray matter corresponded to vacuoles within the neuropil. They were of two types; one was the true vacuoles within neurites, and the other was markedly swollen cell processes, some of which were also identified as neurites. In the white matter, the spongy state corresponded mainly to distension of the myelin sheaths, due to splitting of the major dense line or swelling of the inner loop, and partly to intra-axonal vacuoles. In mice before appearance of clinical symptoms, the vacuolation occurred first in the cerebral white matter 5 weeks after inoculation and in the cerebral cortex at 7 weeks. The occurrence and development of the vacuoles are discussed.

Transmission of chronic spongiform encephalopathy with kuru plaques from humans to small rodents

An unusual case of spongiform encephalopathy was transmitted directly from a human to rats and mice. After serial passages, incubation periods were shortened to about six months in rats and four months in mice. Clinical symptoms were similar in rats and mice, including ruffled fur, arched back, bradykinesia, and hind limb paralysis. Pathologically, a spongy state, proliferation of astrocytes, and neuronal changes were observed. Electron microscopic observation of the parietal cortex of rats and mice disclosed many membrane-bound vacuoles in the neuropil, predominantly in dendrites. In the pons of mice, intramyelinic vacuoles and accumulation of extracellular fluid were prominent. The clinicopathological symptoms of the affected animals resembled those in other experimental spongiform encephalopathies, especially scrapie.

Virus-simulating structures in the optic nerve head in Creutzfeldt-Jakob disease

A 68-year-old man was treated for and died of Creutzfeldt-Jakob disease. At autopsy we found multiple virus-like particles in the optic nerve head, but saw no similar structures in the cornea. Although these particles were morphologically similar to those previously reported in brain, we believe that they are not virions but unrelated cellular structures. We speculate that the causative agents may be naked membrane bound nucleic acids rather than true viruses. We found no optic atrophy or other specific pathologic changes in the eyes; severe occipital cortical degeneration was responsible for the patient's visual loss.

Spongiform alterations in brain biopsies of presenile dementia

Spongiform lesions were observed in close association with typical presenile alterations in three of six frontal lobe biopsies taken in presenile demented patients without any familial relationship. These findings are discussed in relation with recent investigations indicating the production of spongiform lesions after inoculation of nervous tissue from an Alzheimer patient to animals and the effects of saline extract of such material on cultured nerve cells.

Experimental scrapie in mice: ultrastructural observations

Scrapie, kuru, and Creutzfeldt-Jakob disease are characterized by a similar spongiform pathology, prolonged incubation periods, and an agent with unique physical, chemical, and biological properties. Swiss mice were inoculated with the scrapie agent and sacrificed three to five months later for light and electron microscopy. At three months, small vacuoles were seen within the neuropil of the cerebral cortex and basal ganglia. By the fifth month these vacuoles had increased in number and size and were accompanied by moderate astrocytic proliferation. The brainstem, cerebellum, and spinal cord showed variable changes of much less intensity. Many dilated postsynaptic processes contained osmiophilic particles in random or crystalline arrays. The particles, measuring approximately 23 nm in diameter, appeared consistently in postsynaptic processes of brain from scrapie-infected mice, were lacking in controls, and were a size consistent with sedimentation and filtration data for the scrapie agent. Whether these particles represent the scrapie agent must await further studies.