On the replication and spread of rabies virus in the human central nervous system

Ultrastructural and immunohistochemical studies on the brains of two autopsy cases of human rabies revealed: By the peroxidase-antiperoxidase method, viral antigens were present in all eosinophilic inclusions detected in formalin fixed paraffin sections. Numerous antigenic masses, which apparently corresponded to the matrices and cylindrical particles in neurites revealed by electron microscopy, were present in the neuropil remote from neuronal perikarya. There were virions in the intercellular spaces and virus-budding from the plasma membrane into the extracellular space in the absence of a matrix, strongly indicating that rabies virus in the human central nervous system could spread through the intercellular spaces and that the replication of the virus was not necessarily accompanied by the formation of inclusion bodies. The synapse was involved in rabies as indicated by virions in the synaptic terminals. The implications of these observations are discussed in conjunction with the results of previous in vitro and animal experiments.     

Inhibition of the transport of rabies virus in the central nervous system

The effect of colchicine, an inhibitor of axonal transport, on the spread of rabies virus in the central nervous system was investigated using Wistar rats. Colchicine was inoculated into the striatum at various times before and after inoculation of rabies virus into the same site. Rats were killed at various times after viral inoculation and the spread of rabies virus was monitored by rabies immunofluorescence of selected areas of brain. The most effective inhibitory effect was obtained by colchicine treatment applied two days before virus inoculation. Under these conditions, no fluorescent foci could be detected until day 3 post-infection whereas control rats exhibited infected cells as soon as two days post-infection. This inhibitory effect is reversible and the general consequence seems to be a delay in the rate of viral spread. However, five days after the virus challenge, some major brain areas were still partially preserved from infection (striatum, frontal cortex, pyriform cortex). Ten days after colchicine treatment, the microtubules have recovered their capacity to transport the virus. At the onset of paralysis, the general pattern of infection in brain sections from colchicine-treated rats was not significantly different from that of control rats. This inhibitory effect on the transport of rabies virus can be prolonged by administration of additional colchicine.     

Axonal transport of rabies virus in the central nervous system of the rat

Stereotaxic inoculation of rabies virus into specific nuclei in the central nervous system has been used for the investigation of the central neural transport mechanisms of viral information. The infection was monitored by specific fluorescence and peroxidase studies and the titration of viral infectivity in dissected brain areas. Twenty-four hours after inoculation into the striatum, cortex, or substantia nigra, infected neurons were detected only in cells from areas and nuclei which were related to the site of inoculation. The distribution of infected neurons showed that retrograde axoplasmic flow plays a determining role in the transport of rabies virus 24 hours after delivery of virus to specific target nuclei. Local destruction of neurons by kainic acid at the site of viral inoculation did not prevent the uptake and subsequent retrograde axonal transport of virus. There was an overall correlation between the major neural connections of the inoculated areas (e.g. the striatum) and the infected areas 24 hours later (e.g. the substantia nigra).     

Regional distribution of rabies viral antigen in central nervous system of human encephalitic and paralytic rabies

We studied the distribution of rabies viral antigen in the brain and spinal cord of 7 patients with rabies by immunohistochemical techniques. Four patients presented with encephalitis, the remaining 3 had paralysis. Neither the rabies viral antigen distribution nor inflammation paralleled clinical presentations. Patients who had survival times of 7 days or less (4/7) had a greater amount of antigen-positive neurons in brainstem and spinal cord regardless of the clinical type. Neuroglial cells were also found to contain rabies antigen. Our findings suggest that virus localization may not account for the difference in clinical manifestations.     

Histochemical demonstration of cytoplasmic glycosaminoglycans in the macroneurons of the human central nervous system

The presence of glycosaminoglycans (GAG) has been histochemically demonstrated in the CNS of various mammalian species. They have been related with some nerve functions as neurotransmitters storage and synaptic transmission. In the present paper, the histochemical properties of nerve cell cytoplasmic GAG were studied in several regions of adult human CNS. Samples of brain cortex, pons, upper medulla, and cerebellar cortex obtained by autopsy from subjects not dying after neurological diseases were fixed by immersion in glutaraldehyde, dehydrated with ethanol, and embedded in paraffin. The sections were stained with Alcian blue solutions adjusted to pH 2.5, 4.0, and 5.7. To the latter solution MgCl₂ was added in increasing concentration from 0.05 to 1.2 M. Testicular hyaluronidase, neuraminidase, and ribonuclease were applied on simultaneous sections with their respective controls. The sequence of these reactions allowed us to demonstrate the presence of hyaluronic acid along chondroitin-4- and/or 6-sulphate in the cytoplasm of most nerve cells. The sulphated GAG showed certain variability in the various regions studied related specially with their grade of sulphation.     

Early events in rabies virus infection of the central nervous system in skunks (Mephitis mephitis)

Twenty-four striped skunks were inoculated intramuscularly (long digital extensor muscle of right pelvic limb) with street rabies virus. Groups of two clinically normal skunks were killed at various times after inoculation; skunks that developed rabies were killed in early stages of the clinical signs. Four clinically normal skunks (numbered 1–4) had slight infection in lumbar spinal ganglia, spinal cord and brain. These four skunks were used for detailed immunohistochemical (rabies antigen) studies that included examination of sections from every segment of the spinal cord, most of the spinal ganglia from the 2nd cervical to the 2nd coccygeal (sections at 25-μm intervals of lumbar, sacral and coccygeal ganglia) and brain (sections at 50-μm intervals). In skunks 1–4, there was increasing distribution of antigen-containing neurons that was not correlated with the time elapsed since inoculation. In three skunks (nos. 1, 2 and 3), antigen-containing neurons were predominantly in caudal regions of the spinal cord, caudal right lumbar and sacral spinal ganglia and certain nuclei/regions of the brain (medial reticular formation, right interpositus and lateral vestibular nuclei, left red nucleus, left motor cortex, and left reticular nucleus of the thalamus). Skunk 4 had more extensive infection than skunks 1–3, but the previous pattern was still evident. The results are consistent with viral entrance into the lumbar spinal cord, initial replication mainly at the L2 and L3 levels, local spread in the cord by propriospinal neurons and early transit to the brain via long ascending and descending fiber tracts (bypassing the grey matter of the rostral spinal cord). These mechanisms could provide for early and rapid dissemination in the brain before a significant immune response develops and could induce behavioral changes before the animal is incapacitated by extensive spinal cord infection. Based on the distribution of antigen-containing neurons, the tracts considered most likely to serve as viral transitways from spinal cord to brain include: rubrospinal, corticospinal, spinothalamic, spino-olivary, vestibulospinal and/or spinovestibular, reticulospinal and/or spinoreticular, cerebellospinal and/or spinocerebellar, and dorsal column pathways. Received: 21 April 1995 / Revised: 24 July 1995 / Accepted: 2 August 1995     

Morphological demonstration of the virus of tick-borne encephalitis in the human brain

Summary A case is presented in which the fourfold increase of the HI titer during the progression of the disease, and an increase in IgM content found at the beginning of the second week of the disease confirmed the diagnosis of tick-borne encephalitis. The light microscopic changes corresponded to the findings accepted as characteristic to tick-borne encephalitis.Viruses, morphologically belonging to the Havivirus genus, were found by electron microscopy in the thalamus, substantia nigra, and cerebellum of the dissected brain. This paper presents the first demonstration of the virus in a case of human tick-borne encephalitis.     

Remyelination in the human central nervous system

Remyelination, albeit incomplete, has been demonstrated in human central nervous system (CNS). However, information about the initial stage and the final extent of such remyelination is not available. We describe the morphologic findings of a demyelinating lesion with evidence of early remyelination in a biopsy obtained from a 15-year-old boy about two weeks after the onset of neurologic symptoms. The demyelinated area appeared hypercellular with a relatively large number of oligodendrocytes frequently seen in the process of new myelin formation. In addition to the usual reactive changes, the astrocytes were often seen to contain otherwise normal-looking oligodendrocytes within their cytoplasm. In the ensuing months, the patient made apparently total functional recovery accompanied by nearly complete resolution of the white matter lesions demonstrated by the subsequent magnetic resonance studies. These observations suggested that the initial remyelination seen in the biopsy eventually succeeded in producing extensive remyelination in the lesion. Although the exact nature of the demyelinating disorder in our patient remains undetermined, this study indicates that clinically significant remyelination is possible in human CNS. Also, our findings appeared strikingly similar to those described in certain experimental animal models in which widespread remyelination is known to occur.     

Immunolocalization of cathepsin D in the human central nervous system and central nervous system neoplasms

The cellular distribution of the lysosomal proteinase cathepsin D was studied in a series of 76 neoplasms and 18 non-neoplastic tissues from the human central nervous system, using a well-characterized polyclonal antibody in a peroxidase-antiperoxidase technique. In the normal and developing brain, cathepsin D is confined to neurons and choroid plexus epithelium. Strong granular cytoplasmic staining was present in neuronal and choroid plexus neoplasms, and in reactive macrophages. A large variety of other neoplasms also exhibited positive cytoplasmic staining, albeit usually of a weaker diffuse type. Cathepsin D cannot be considered a specific marker for neuronal or choroid plexus neoplasms, but the antiserum used in this study may be of value in antibody panels for the investigation of these tumours. Its localization may also be of value in embryological studies, particularly in the cerebellum, and in investigations of steroid hormone receptor-associated proteins in meningiomas and Schwannomas.     

Observations on the distribution of canine distemper virus in the central nervous system of dogs with demyelinating encephalitis

Summary The distribution of canine distemper virus in the central nervous system was examined in 11 dogs with demyelinating encephalitis by the direct fluorescent antibody technique on paraffin sections of brain and spinal cord. In the grey matter there was a good correlation between the presence and severity of lesions and presence and amount of viral antigen. Large concentrations of virus were found in neurons and their processes. In most demyelinating lesions only small amounts of viral antigen were found, mostly located in astrocytes. The potential importance of the role of the astrocyte in demyelination in canine distemper virus infection is stressed.     

Up-regulation of Fas ligand (FasL) in the central nervous system: A mechanism of immune evasion by rabies virus

Following its injection into the hindlimbs of mice, CVS, a highly pathogenic strain of rabies virus, invades the spinal cord and brain resulting in the death of the animal. In contrast, central nervous system (CNS) invasion by PV, a strain of attenuated pathogenicity, is restricted to the spinal cord and mice infected with this virus survive. Lymphocytes display transient migration into the infected CNS in fatal rabies and sustained migration in nonfatal rabies. The transient migration of T cells in fatal rabies is associated with an increase in T-cell apoptosis. We found that the early production of Fas ligand (FasL) mRNAs was up-regulated only in fatal rabies. FasL is produced by several neuronal cells and mainly in infected neurons. In mice lacking FasL (gld), infection with the neuroinvasive rabies virus strain was less severe, and the number of CD3 T cells undergoing apoptosis was smaller than that in normal mice. These data provide strong evidence that fatal rabies virus infection involves the early triggering of FasL production leading to the destruction of migratory T cells by the Fas/FasL apoptosis pathway. This mechanism could be in part responsible for the fact that T cells cannot control neuroinvasive rabies infection. Thus, rabies virus seems to use an immunosubversive strategy that takes advantage of the immune privilege status of the CNS.     

Histopathology and immunohistochemistry of tissues outside central nervous system in bovine rabies

We performed a histopathological and immunohistochemical study of tissues outside the central nervous system in 48 cases of bovine rabies confirmed by direct immunofluorescence and/or immunohistochemistry (IHC) of the central nervous system. In the bovines of this study, mononuclear inflammation in all ganglia (trigeminal, spinal, stellate, and celiac) and adrenal medulla was observed. This injury also occurred in 85 % of neuro-pituitaries in 55 % of pars intermediate and 15 % of the pars distalis of pituitary evaluated. IHC was positive in 92.31 % of lumbar spinal ganglia, 90.9 % of trigeminal ganglia, stellate ganglia of 41.67 and 16.67 % of the celiac ganglia. One of the evaluated adrenal (1/17) showed strong immunohistochemical labeling in the cytoplasm of pheochromocytes. The pituitary IHC was positive in one case in the neurohypophysis (1/20) and in one case in the pars intermedia of the adenohypophysis (1/20). Data from this study indicate that in suspected cases of rabies, besides the complex pituitary rete mirabile and trigeminal ganglion, the evaluation of other ganglia, particularly the lumbar spinal, and adrenal may also contribute to the diagnosis and understanding of the clinical presentation and pathogenesis of the disease in bovines.     

Virus receptors in the human central nervous system

The initial event in the life cycle of a virus is its interaction with receptors present on the surface of a cell. Understanding these interactions is important to our understanding of viral tropism, spread, and pathogenesis. This is particularly true of viruses that target the central nervous system as these viruses must maintain a tropism for both the nervous system and for peripheral organs that allow for viral replication and spread to new susceptible hosts. These viruses therefore interact with a diverse set of cells and tissues, interactions that are likely mediated by both common and unique receptors present on each target tissue. In addition, physiological changes in the host can lead to increased or decreased expression of virus receptors, which influence virus trafficking, spread, and tissue specific pathology. This review will focus on the relatively few virus receptor systems that have been described in some level of detail for viruses that target the human central nervous system.     

Human immunodeficiency virus and the central nervous system

Human immunodeficiency virus (HIV) continues to infect large numbers of people, including children, worldwide. The virus produces much of its clinical impact by infecting cellular components of the immune system. However, HIV also has the propensity to infect the brain, where it can induce substantial pathology and impair brain function. Highly active antiretroviral therapy has reduced the severity and prevalence of HIV-associated neurocognitive disorders. Nevertheless, substantial morbidity and mortality continue to stem from HIV infection of the nervous system. This article reviews the pathogenesis of HIV-induced central nervous system disease, the pathological and clinical effects of HIV infection within the brain, and the controversies and challenges of the use of highly active antiretroviral therapy for prevention and treatment of HIV-induced central nervous system dysfunction.     

D-serine in the developing human central nervous system

To elucidate the role of D-serine in human central nervous system, we analyzed D-serine, L-serine, and glycine concentrations in cerebrospinal fluid of healthy children and children with a defective L-serine biosynthesis (3-phosphoglycerate dehydrogenase deficiency). Healthy children showed high D-serine concentrations immediately after birth, both absolutely and relative to glycine and L-serine, declining to low values at infancy. D-Serine concentrations were almost undetectable in untreated 3-phosphoglycerate dehydrogenase-deficient patients. In one patient treated prenatally, D-serine concentration was nearly normal at birth and the clinical phenotype was normal. These observations suggest a pivotal role for D-serine in normal and aberrant human brain development.     

Distribution of metallothionein in the human central nervous system

The distribution of metallothionein (MT), a metal-binding protein, was examined immunohistochemically in the normal human brain and spinal cord. Paraffinembedded brain tissue from three patients who had died from a non-neurological disease and were free of histopathological central nervous system alterations were processed. The results of the present study demonstrate that MT is readily detectable in a subgroup of astrocytes in the normal human brain. MT staining is most intense on grey matter astrocytes that bear short stout processes and which probably represent protoplasmic astrocytes. Using anti-MT and anti-glial fibrillary acidic protein immunostaining, we could demonstrate two subpopulations of astrocytes that were mutually exclusive. The functional significance of MT-expression in protoplasmic astrocytes is not entirely clear. Metal detoxification is only one of the many postulated functions of MT. The finding that staining for MT permits subtyping of astrocytes may be of great importance in glia research and surgical pathology of the human brain. © 1993 Wiley-Liss, Inc.