Pathogenesis of viral infections of the nervous system

Mycobacterium tuberculosis combine with EBV infection in severe adult meningoencephalitis: a rare case reports and literature review

Background

Tuberculous meningitis (TBM) with adults Epstein-Barr (EB) virus encephalitis is a very rare infectious disease, with a high mortality and disability. Metagenomic next-generation sequencing (mNGS) of cerebrospinal fluid (CSF) is highly diagnostic. We report on a case of severe meningoencephalitis caused by co-infection with mycobacterium tuberculosis and EB virus. Brain MRI indicated a parenchyma lesion in the brain. mNGS of CSF indicated Mycobacterium tuberculosis and EB virus amplification, positive serum EB virus IgG antibodies, and improved symptoms after anti-tuberculosis and antiviral treatment. A re-examination of the brain MRI revealed that the significantly absorption of the lesions.

Case report

A 49-year-old male patient presented with a chief complaint of headache and fever with consciousness disturbance. The brain magnetic resonance imaging showed a lesions in the right parenchymal brain with uneven enhancement, accompanied by significantly increased intracranial pressure, elevated CSF cell count and protein levels, as well as notably decreased glucose and chloride levels. mNGS of CSF showed the coexistence of Mycobacterium tuberculosis and EBV. The patient was diagnosed as TBM with EBV encephalitis. The patient's symptoms gradually improved with the active administration of anti-tuberculosis combined with antiviral agents, the use of hormones to reduce inflammatory reaction, dehydration to lower intracranial pressure, and intrathecal injection. Subsequent follow-up brain magnetic resonance imaging indicated significant absorption of the lesions, along with a marked decrease in CSF count and protein levels, as well as obvious increase in glucose and chloride levels.

Conclusion

TBM associated with adult EBV encephalitis is extremely rare. The disease's early stages are severe and have a high fatality rate. A prompt and accurate diagnosis is particularly important. NGS of CSF is of great value for early diagnosis.

Innate Immune Signaling and Role of Glial Cells in Herpes Simplex Virus- and Rabies Virus-Induced Encephalitis

The environment of the central nervous system (CNS) represents a double-edged sword in the context of viral infections. On the one hand, the infectious route for viral pathogens is restricted via neuroprotective barriers; on the other hand, viruses benefit from the immunologically quiescent neural environment after CNS entry. Both the herpes simplex virus (HSV) and the rabies virus (RABV) bypass the neuroprotective blood-brain barrier (BBB) and successfully enter the CNS parenchyma via nerve endings. Despite the differences in the molecular nature of both viruses, each virus uses retrograde transport along peripheral nerves to reach the human CNS. Once inside the CNS parenchyma, HSV infection results in severe acute inflammation, necrosis, and hemorrhaging, while RABV preserves the intact neuronal network by inhibiting apoptosis and limiting inflammation. During RABV neuroinvasion, surveilling glial cells fail to generate a sufficient type I interferon (IFN) response, enabling RABV to replicate undetected, ultimately leading to its fatal outcome. To date, we do not fully understand the molecular mechanisms underlying the activation or suppression of the host inflammatory responses of surveilling glial cells, which present important pathways shaping viral pathogenesis and clinical outcome in viral encephalitis. Here, we compare the innate immune responses of glial cells in RABV- and HSV-infected CNS, highlighting different viral strategies of neuroprotection or Neuroinflamm. in the context of viral encephalitis.

Herpes simplex virus encephalitis involving the right thalamus

Herpes simplex virus (HSV) encephalitis is a rare but often fatal disease if left untreated. A 50-year-old woman was admitted with lethargy, confusion, dysphasia and cough. MRI brain demonstrated bilateral temporal and perisylvian hyperintense signal abnormality extending into the cingulate gyrus, typical of HSV encephalitis. However, there was also signal abnormality involving the right thalamus, indicating thalamic involvement. EEG and cerebrospinal fluid PCR confirmed HSV encephalitis. The patient was started on intravenous acyclovir resulting in marked improvement. Adequate assessment and prompt treatment of HSV encephalitis will aid in achieving adequate recovery. Radiological investigation plays a crucial role in diagnosis with typical MR features a useful aid to diagnosis. HSV encephalitis classically involves the medial temporal lobes, insula and cingulated gyri. The basal ganglia and thalami are nearly always spared. We present a very rare case of HSV encephalitis which involved the right thalamus.

Immune responses to West Nile virus infection in the central nervous system

West Nile virus (WNV) continues to cause outbreaks of severe neuroinvasive disease in humans and other vertebrate animals in the United States, Europe, and other regions of the world. This review discusses our understanding of the interactions between virus and host that occur in the central nervous system (CNS), the outcome of which can be protection, viral pathogenesis, or immunopathogenesis. We will focus on defining the current state of knowledge of WNV entry, tropism, and host immune response in the CNS, all of which affect the balance between injury and successful clearance.

Human arboviral encephalitis

Worldwide, arboviral illnesses constitute the most important international infectious threat to human neurological health and welfare. Before the availability of effective immunizations, approximately 50,000 cases of Japanese encephalitis occurred in the world each year, one-fifth of which cases proved lethal and a much larger number were left with severe neurological handicaps. With global climate change and perhaps other factors, the prevalences of some arboviral illnesses appear to be increasing. Arboviral illnesses, including Japanese encephalitis, tick-borne encephalitis, Yellow fever, and others, are emerging as possible global health care threats because of biological warfare. This chapter will review ecology, pathophysiology, diagnosis, management, and outcome of the forms of arboviral encephalitis that are of greatest importance in North America, together with some of the most important arboviral encephalitides prevalent in other parts of the world.

Herpesvirus transport to the nervous system and back again

Herpes simplex virus, varicella zoster virus, and pseudorabies virus are neurotropic pathogens of the Alphaherpesvirinae subfamily of the Herpesviridae. These viruses efficiently invade the peripheral nervous system and establish lifelong latency in neurons resident in peripheral ganglia. Primary and recurrent infections cycle virus particles between neurons and the peripheral tissues they innervate. This remarkable cycle of infection is the topic of this review. In addition, some of the distinguishing hallmarks of the infections caused by these viruses are evaluated in terms of their underlying similarities.

Pervasive olfactory impairment after bilateral limbic system destruction

What pattern of brain damage could completely obliterate the sense of olfaction in humans? We had an opportunity to address this intriguing question in Patient B., who has extensive bilateral damage to most of the limbic system, including the medial and lateral temporal lobes, orbital frontal cortex, insular cortex, anterior cingulate cortex, and basal forebrain, caused by herpes simplex encephalitis. The patient demonstrated profound impairments in odor identification and recognition. Moreover, he could not discriminate between olfactory stimuli, and he had severe impairments in odor detection. Reliable stimulus detection was obtained only for solutions of the organic solvent acetone and highly concentrated solutions of ethanol. In contrast to the more circumscribed olfactory deficits demonstrated in patients with damage confined to either the temporal lobes or orbitofrontal cortex (which tend to involve odor identification but not odor detection), Patient B. demonstrated a strikingly severe and complete anosmia. This contrast in olfactory abilities and deficits as a result of different anatomical pathology affords new insights into the neural substrates of olfactory processing in humans.

Neuroinflammation resulting from covert brain invasion by common viruses - a potential role in local and global neurodegeneration

Neurodegenerative diseases are a horrendous burden for their victims, their families, and society as a whole. For half a century scientists have pursued the hypothesis that these diseases involve a chronic viral infection in the brain. However, efforts to consistently detect a specific virus in brains of patients with such diseases as Alzheimer's or multiple sclerosis have generally failed. Neuropathologists have become increasingly aware that most patients with neurodegenerative diseases demonstrate marked deterioration of the brain olfactory bulb in addition to brain targets that define the specific disease. In fact, the loss of the sense of smell may precede overt neurological symptoms by many years. This realization that the olfactory bulb is a common target in neurodegenerative diseases suggests the possibility that microbes and/or toxins in inhaled air may play a role in their pathogenesis. With regard to inhaled viruses, neuropathologists have focused on those viruses that infect and kill neurons. However, a recent study shows that a respiratory virus with no neurotropic properties can rapidly invade the mouse olfactory bulb from the nasal cavity. Available data suggest that this strain of influenza is passively transported to the bulb via the olfactory nerves (mechanism unknown), and is taken up by glial cells in the outer layers of the bulb. The infected glial cells appear to be activated by the virus, secrete proinflammatory cytokines, and block further spread of virus within the brain. At the time that influenza symptoms become apparent (15 h post-infection), but not prior to symptom onset (10 h post-infection), proinflammatory cytokine-expressing neurons are increased in olfactory cortical pathways and hypothalamus as well as in the olfactory bulb. The mice go on to die of pneumonitis with severe acute phase and respiratory disease symptoms but no classical neurological symptoms. While much remains to be learned about this intranasal influenza-brain invasion model, it suggests the hypothesis that common viruses encountered in our daily life may initiate neuroinflammation via olfactory neural networks. The numerous viruses that we inhale during a lifetime might cause the death of only a few neurons per infection, but this minor damage would accumulate over time and contribute to age-related brain shrinkage and/or neurodegenerative diseases. Elderly individuals with a strong innate inflammatory system, or ongoing systemic inflammation (or both), might be most susceptible to these outcomes. The evidence for the hypothesis that common respiratory viruses may contribute to neurodegenerative processes is developed in the accompanying article.

Potentiating Effect of Freund's Adjuvant on Interferon Production by Endotoxin or Poly rI*Poly rC

Intraperitoneal injection of mice with mineral oil, incomplete (IFA) or complete Freund's adjuvant (CFA) increased the interferon response to endotoxin or (poly rI)*(poly rC) administered intravenously 2 days later. After endotoxin administration, circulating interferon titers were increased at several different times of sampling and with a variety of endotoxin dosages. When injection of endotoxin was delayed until 6 to 8 days after the administration of IFA or CFA, interferon production was markedly decreased. Mice treated with CFA and injected with endotoxin 2 days later became more resistant to intranasal vesicular stomatitis virus challenge than mice injected with endotoxin alone. Hyporeactivity to the interferon-inducing capacity of a second injection of endotoxin 2 days after the first injection could not be overcome by administering CFA simultaneously with the first dose. CFA treatment not only raised the serum interferon titers produced by endotoxin, but also increased the number of interferon-forming cells in the spleen after administration of endotoxin in vivo. In addition, CFA enhanced the intravascular clearance of (poly rI)*(poly rC). The possibility that Freund's adjuvant increased the interferon response to endotoxin and (poly rI)*(poly rC) by stimulating the uptake and processing of the interferon inducer by lymphoreticular cells is discussed.

Progress on the development of therapeutics against West Nile virus

A decade has passed since the appearance of West Nile virus (WNV) in humans in the Western Hemisphere in New York City. During this interval, WNV spread inexorably throughout North and South America and caused millions of infections ranging from a sub-clinical illness, to a self-limiting febrile syndrome or lethal neuroinvasive disease. Its entry into the United States triggered intensive research into the basic biology of WNV and the elements that comprise a protective host immune response. Although no therapy is currently approved for use in humans, several strategies are being pursued to develop effective prophylaxis and treatments. This review describes the current state of knowledge on epidemiology, clinical presentation, pathogenesis, and immunobiology of WNV infection, and highlights progress toward an effective therapy.

Central nervous system infections of herpesvirus family

Herpesviruses are one of the most common groups of pathogens causing central nervous system infections in humans. They mostly cause encephalitis, meningitis, or myelitis in immunocompetent and immunocompromised patients. Children, adults, and the elderly can all be affected. Although contrast-enhanced CT is more widely used for diagnosis, contrast-enhanced MR imaging combined with diffusion-weighted imaging is superior to CT in the detection of early changes and the real extent of the disease, and in assessing prognosis and monitoring response to antiviral treatment. More sophisticated techniques, such as MR spectroscopy and perfusion imaging, can aid in the differential diagnosis of herpesvirus infections from other tumoral, demyelinating, and ischemic processes.

The olfactory vector hypothesis of neurodegenerative disease: is it viable?

Environmental agents, including viruses, prions, and toxins, have been implicated in the cause of a number of neurodegenerative diseases, most notably Alzheimer's and Parkinson's diseases. The presence of smell loss and the pathological involvement of the olfactory pathways in the formative stages of Alzheimer's and Parkinson's diseases, together with evidence that xenobiotics, some epidemiologically linked to these diseases, can readily enter the brain via the olfactory mucosa, have led to the hypothesis that Alzheimer's and Parkinson's diseases may be caused or catalyzed by agents that enter the brain via this route. Evidence for and against this concept, the "olfactory vector hypothesis," is addressed in this review.

Detection of mouse-adapted human influenza virus in the olfactory bulbs of mice within hours after intranasal infection

Influenza pneumonitis causes severe systemic symptoms in mice, including hypothermia and excess sleep. The association of extrapulmonary virus, particularly virus in the brain, with the onset of such disease symptoms has not been investigated. Mature C57BL/6 male mice were infected intranasally with mouse-adapted human influenza viruses (PR8 or X-31) under inhalation, systemic, or no anesthesia. Core body temperatures were monitored continuously by radiotelemetry, and tissues (lung, brain, olfactory bulb, spleen, blood) were harvested at the time of onset of hypothermia (13 to 24 h post infection [PI]) or at 4 or 7 h PI. Whole RNA from all tissues was examined by one or more of three reverse transcriptase-polymerase chain reaction (RT-PCR) procedures using H1N1 nucleoprotein (NP) primers for minus polarity RNA (genomic or vRNA) or plus polarity RNA (replication intermediates). Selected cytokines were assayed at 4, 7, and 15 h in the olfactory bulb (OB). Minus and plus RNA strands were readily detected in OBs as early as 4 h PI by nested RT-PCR. Anesthesia was not required for viral invasion of the OB. Cytokine mRNAs were also significantly elevated in the OB at 7 and 15 h PI in infected mice. Controls receiving boiled virus expressed only input vRNA and that only in lung. Immunohistochemistry demonstrated localization of H1N1 and NP antigens in olfactory nerves and the glomerular layer of the OB. Therefore a mouse-adapted human influenza virus strain, not known to be neurotropic, was detected in the mouse OB within 4 h PI where it appeared to induce replication intermediates and cytokines.

The clinical neurology and epidemiology of Creutzfeldt-Jakob disease, with special reference to iatrogenic cases

The clinical characteristics of Creutzfeldt-Jakob disease (CJD) in a newly analysed group of 223 cases transmitted to primates at the NIH are compared to a recent large series of neuropathologically verified cases in France, and the limited conclusions from worldwide epidemiological studies are briefly summarized. Discussion then focuses on iatrogenic CJD, with special attention to the interplay of clinical, laboratory and epidemiological features of the current outbreak of CJD in hypopituitary dwarfs treated with growth hormone extracted from pools of human pituitary glands.

A preliminary neuropathological study of Japanese encephalitis in humans and a mouse model

Japanese encephalitis virus is a mosquito-borne flavivirus that causes approximately 10000 deaths annually in Asia. After a brief viraemia, the virus enters the central nervous system, but the means of crossing the blood-brain barrier is uncertain. We used routine histological staining, immunohistology and electron microscopy to examine brain material from four fatal human cases, and made comparisons with material from a mouse model. In human material there was oedema, perivascular inflammation, haemorrhage, microglial nodules and acellular necrotic foci, as has been described previously. In addition, there was new evidence suggestive of viral replication in the vascular endothelium, with endothelial cell damage; this included occasional viral antigen staining, uneven binding of the vascular endothelial cells to Ulex europaeus agglutinin I and ultrastructural changes. Viral antigen was also found in neurons. There was an active astrocytic response, as shown by glial fibrillary acidic protein staining, and activation of microglial cells was demonstrated by an increase in major histocompatibility complex class II expression. Similar inflammatory infiltrates and a microglial reaction were observed in mouse brain tissue. In addition, beta-amyloid precursor protein staining indicated impaired axonal transport. Whether these findings are caused by viral replication in the vascular endothelium or the immune response merits further investigation.

Development of effective therapies against West Nile virus infection

Since its entry into North America in 1999, West Nile virus has spread throughout the USA and Canada, and now annually causes a clinical spectrum of human disease ranging from a self-limiting acute febrile illness to potentially lethal encephalitis. Although no therapy is currently approved for use in humans, several strategies are being pursued to develop effective prophylaxis and treatments. This review describes the epidemiology, clinical presentation and pathogenesis of West Nile virus infection, and highlights recent progress towards an effective therapy.

Influenza virus and CNS manifestations

Neurological involvement during influenza infection has been described during epidemics and is often consistent with serious sequelae or death. An increasing incidence of influenza-associated encephalitis/encephalopathy has been reported in Japan, mainly in children. A variety of other clinical CNS manifestations, such as Reye's syndrome, acute necrotising encephalopathy (ANE), and myelitis as well as autoimmune conditions, such as Guillain-Barre's syndrome, may occur during the course of influenza infection. Virological diagnosis is essential and based on virus isolation, antigen detection, RNA detection by PCR, and serological analyses. Neuroimaging with CT and MRI of the brain are of prognostic value. The pathogenic mechanisms behind the influenza CNS complications are unknown. The treatment is symptomatic, with control of vital functions in the intensive care unit, antiepileptic medication and treatment against brain oedema.

Innate and adaptive immune responses determine protection against disseminated infection by West Nile encephalitis virus

WNV continues to spread throughout the Western Hemisphere as virus activity in insects and animals has been reported in the United States, Canada, Mexico, and the Caribbean islands. West Nile virus (WNV) infects the central nervous system and causes severe disease primarily in humans who are immunocompromised or elderly. In this review, we discuss the mechanisms by which the immune system limits dissemination of WNV infection. Recent experimental studies in animals suggest important roles for both the innate and the adaptive immune responses in controlling WNV infection. Interferons, antibody, complement components and CD8+ T cells coordinate protection against severe infection and disease. These findings are analyzed in the context of recent approaches to vaccine development and immunotherapy against WNV.

Evasion of innate and adaptive immunity by flaviviruses

After a virus infects an animal, antiviral responses are generated that attempt to prevent dissemination. Interferons, antibody, complement, T and natural killer cells all contribute to the control and eradication of viral infections. Most flaviviruses, with the exception of some of the encephalitic viruses, cause acute disease and do not establish persistent infection. The outcome of flavivirus infection in an animal is determined by a balance between the speed of viral replication and spread, and the immune system response. Although many of the mechanistic details require further elucidation, flaviviruses have evolved specific tactics to evade the innate and adaptive immune response. A more thorough understanding of these principles could lead to improved models for viral pathogenesis and to strategies for the development of novel antiviral agents.

Viral encephalitis: familiar infections and emerging pathogens

Significant advances have been made in our understanding of the natural history and pathogenesis of viral encephalitides. The development of PCR has greatly increased our ability to diagnose viral infections of the central nervous system, particularly for herpes and enteroviral infections. Advancing knowledge has led to the recognition that some encephalitides can be reliably prevented by vaccination (eg, Japanese encephalitis and rabies). For other pathogens such as the arboviruses, the focus has been on prevention by vector control. Finally, effective therapy has been established for a very limited number of viral infections (eg, acyclovir for herpes simplex encephalitis). Other potentially useful treatments, such as pleconaril for enteroviral meningoencephalitis are under clinical evaluation. We review current understanding of viral encephalitides with particular reference to emerging viral infections and the availability of existing treatment regimens.

High intensity light increases olfactory bulb melatonin in Venezuelan equine encephalitis virus infection

In mice infected with the Venezuelan equine encephalomyelitis (VEE) virus and exposed to high intensity light (2500 lux) with a 12 h light: 12 h dark photoperiod, a significant increase in the levels of melatonin in the olfactory bulb was observed. The significance of these findings deserves further studies to understand the mechanisms involved in this effect since the olfactory bulbs have been proposed as first portal for VEE virus entry into the CNS. The increase in melatonin content could represent one of the mechanisms of defense against the viral attack.

Prodrugs in nasal drug delivery

Prodrugs have been used to overcome poor solubility, insufficient stability, incomplete absorption across biological membranes and premature metabolism to active species. This review examines the importance of various physicochemical factors affecting nasal absorption of drugs. Novel trends in nasal prodrug development in the areas of targeted delivery to the CNS and selective targeting of the nutrient transporter system of the nasal mucosa have received considerable attention.

Neutralizing antiviral antibody responses

Neutralizing antibodies are evolutionarily important effectors of immunity against viruses. Their evaluation has revealed a number of basic insights into specificity, rules of reactivity (tolerance), and memory—namely, (1) Specificity of neutralizing antibodies is defined by their capacity to distinguish between virus serotypes; (2) B cell reactivity is determined by antigen structure, concentration, and time of availability in secondary lymphoid organs; and (3) B cell memory is provided by elevated protective antibody titers in serum that are depending on antigen stimulation. These perhaps slightly overstated rules are simple, correlate with in vivo evidence as well as clinical observations, and appear to largely demystify many speculations about antibodies and B cell physiology. The chapter also considers successful vaccines and compares them with those infectious diseases where efficient protective vaccines are lacking, it is striking to note that all successful vaccines induce high levels of neutralizing antibodies (nAbs) that are both necessary and sufficient to protect the host from disease. Successful vaccination against infectious diseases such as tuberculosis, leprosy, or HIV would require induction of additional long-lasting T cell responses to control infection.

Enhancement of the systemic and CNS specific delivery of L-dopa by the nasal administration of its water soluble prodrugs

PURPOSE

To study the utility of the nasal route for the systemic delivery of L-dopa using water soluble prodrugs of L-dopa and to examine if this delivery method will result in preferential delivery to the CNS.

METHODS

Several alkyl ester prodrugs of L-dopa were prepared and their physicochemical properties were determined. In vitro hydrolysis rate constants in buffer, rat plasma, rat brain homogenate, rat CSF, and rat nasal berfusate were determined by HPLC. In vivo nasal experiments were carried out in rats. Levels of L-dopa and dopamine in plasma, CSF, and olfactory bulb were determined using HPLC method with electrochemical detection.

RESULTS

All the prodrugs showed improved solubility and lipophilicity with relatively fast in vitro conversion in rat plasma. Absorption was fast following nasal delivery of the prodrugs with bioavailability around 90%. Dopamine plasma levels did not change significantly following nasal administration of the butyl ester prodrug. Olfactory bulb and CSF L-dopa concentration were higher following nasal delivery of the butyl ester prodrug compared to an equivalent intravenous dose.

CONCLUSIONS

Utilization of water soluble prodrugs of L-dopa via the nasal route in the treatment of Parkinson's disease may have therapeutic advantages such as improved bioavailability, decreased side effects, and potentially enhanced CNS delivery.

Transnasal delivery of 5-fluorouracil to the brain in the rat

The purpose of this research is to clarify the feasibility and to determine the extent of transnasal drug delivery to the brain through the cerebrospinal fluid (CSF) in the rat, using 3H-5-fluorouracil (5FU) as a model drug. It was confirmed first that the concentration of 5FU in the CSF was significantly higher following nasal administration compared with intravenous injection, indicating direct transport of 5FU from the nasal cavity to the CSF. Concentration-time profiles of 5FU in the plasma and in the cerebral cortex were determined following intravenous infusion, nasal instillation and nasal perfusion. In order to evaluate the extent of drug transport from the nasal cavity to the cerebral cortex by way of the CSF, the apparent brain uptake clearances were calculated. The uptake clearance following nasal perfusion (8.65 microl/min/g tissue) was significantly large (p < 0.001) in comparison with that following intravenous infusion (6.20 microl/min/g tissue), while that following nasal instillation (6.94 microl/min/g tissue) was not. Consequently, significant amount of 5FU is transported from the nasal cavity to the brain through the CSF and thus, the delivery of the hydrophilic drug to the brain is augmented by nasal drug application.

Nasal route for direct delivery of solutes to the central nervous system: fact or fiction?

During this century, several investigators reported that certain viruses, metals, drugs, and other solutes could bypass systemic circulation and enter the brain and/or cerebrospinal fluid directly following nasal administration. Although evidence clearly suggests that the olfactory epithelium and its olfactory cells play a major role, little is known about the mechanisms of direct transport of solutes into the brain. An overview of what is known about these mechanisms may aid in further research in this field, including studies of direct drug delivery to the central nervous system. This review, in addition to summarizing the literature to date, clearly describes the intricate association of the anatomical features involved in direct entry of solutes into the brain following nasal administration. To aid in the understanding of the possible routes a solute can take after nasal administration, the anatomy of the olfactory epithelium and surrounding tissues is described, and a detailed scheme delineating the emerging pathways is presented. Techniques used in delineating these pathways and studies supporting a particular pathway are discussed in greater detail. Finally, some factors influencing the direct transport of solutes to the cerebrospinal fluid and brain are summarized.

Cerebrospinal fluid viral antibodies in obsessive-compulsive disorder in an Indian population

Immunoglobulin G viral antibodies for herpes simplex virus type 1, varicella zoster virus, cytomegalovirus, measles, and mumps were studied in 76 subjects with obsessive-compulsive disorder and compared with a control population. There was a significantly higher titer for herpes simplex virus type 1 antibodies. Sera: cerebrospinal fluid ratios were suggestive of intrathecal synthesis.

Unilateral meningoencephalitis with hemispheric slowing on EEG

We report a 12-year-old boy with unilateral meningoencephalitis due to non-herpes simplex virus. He experienced secondarily generalized partial seizures of the left extremities with loss of consciousness. In contrast with normal neuroimaging findings, interictal electroencephalograms (EEGs) showed prolonged slowing in the right hemisphere. This laterality agreed with the right brain dysfunction verified on neuropsychological examination. Follow-up EEG is important in such a subtle case with normal neuroimaging.

Direct drug transport from the rat nasal cavity to the cerebrospinal fluid: the relation to the molecular weight of drugs

To clarify the relationship between the direct transport from the rat nasal cavity to the cerebrospinal fluid (CSF) and the molecular weight of the drug, the transport of fluorescein isothiocyanate-labelled dextran (FD) with various molecular weights was investigated. FDs (average molecular weights 4,400 (FD4); 9,400 (FD10); 18,900 (FD20); 40,500 Da (FD40)) were administered nasally or intravenously to rats, and the concentrations in the plasma and the CSF were measured and compared. None of the FDs were detected in the CSF after intravenous administration. However, FD4, FD10 and FD20 were observed to appear in the CSF after nasal administration, whereas the concentration in the plasma was much lower than that after intravenous administration. FD40 was not detected even after nasal administration. In addition, the concentration of these FDs in the CSF decreased with the increase in the molecular weight of FDs. These findings show that drugs with a molecular weight up to at least 20,000 Da can be directly transported from the nasal cavity to the CSF and that the transport of FDs to the CSF is dependent on their molecular weights.

In vitro interaction of coronaviruses with primate and human brain microvascular endothelial cells

Primary human and primate brain microvascular endothelial cells were tested for permissiveness to coronaviruses JHM and 229E. While sub-genomic viral RNAs could be detected up to 72 hours post-infection, primate cells were abortively infected and neither virus caused cytopathology. Human cells were non-permissive for JHM but permissive for 229E replication; peak production of progeny 229E and observable cytopathic effects occurred approximately 22 and 32 hour post-infection, respectively. Using the criterion of cytopathology induction in infected endothelial cells, 229E was compared to other human RNA and DNA viruses. In addition, virus induced modulation of intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1) and HLA I was monitored by immunostaining of infected cells.

Herpes simplex virus encephalitis in a mouse model: PCR evidence for CNS latency following acute infection

We have used a mouse model of herpes simplex encephalitis produced by intranasal inoculation of virus to study the expression of viral immediate early, early and late genes and latency associated transcript (LAT) in trigeminal ganglia and brain at various times after inoculation. A PCR technique was used to detect the viral gene transcripts. All viral genes were expressed between post-inoculation days 1 and 13. On post-inoculation day 42 when the acute infection had subsided only the LAT could be detected, most commonly (70%) in the trigeminal ganglion but also, in 50% of mice, in the brain stem, in 40% in olfactory bulbs and in 20% in cerebrum and cerebellum. These findings suggest that latent infection by HSV-1 may be relatively readily established in the CNS as well as in sensory ganglia. The frequency of establishment of latency appears to be related to the neuroanatomical accessibility of each brain region to the site of entry of the virus.

Direct drug transport from the rat nasal cavity to the cerebrospinal fluid: the relation to the dissociation of the drug

We aimed to clarify the relationship between drug dissociation (sulphisomidine) and its direct transport from the nasal cavity to the cerebrospinal fluid (CSF). Rat nasal cavities were perfused in a single pass system with buffers (pH 5.5, 6.5, 7.4, 8.7 and 9.4). Plasma and CSF were collected and the concentration of sulphisomidine was measured. Nasal clearance increased with the increase in the un-ionized fraction of the drug. The ratio of the drug concentration in CSF to that in the nasal perfusion fluid (the index of the degree of the drug transport from the nasal cavity to CSF), was changed in accordance with the un-ionized fraction of drug. These results show that both the nasal absorption and the drug transport conform to the pH partition theory.

Pathogenesis of Venezuelan equine encephalitis virus infection in mice and hamsters

The pathogenesis of Venezuelan equine encephalitis (VEE) virus infection was compared in intraperitoneally inoculated mice (n = 24, 6 to 8 weeks old) and hamsters (n = 9, 90-110 g) using histopathology and immunohistochemical localization of VEE virus antigen. Infected mice developed paralysis, and the majority died by 9 days after inoculation. In contrast, hamsters did not survive beyond 3 days after inoculation, and they did not develop any neurologic signs. VEE virus antigen, demonstrated by immunoperoxidase staining, and pathologic changes were present in extraneural organs of both mice and hamsters. There was more severe involvement in hamsters, particularly in Peyer's patches of the distal small intestine. There was a severe encephalomyelitis in mice, but pathologic changes were not well established in the brains of hamsters before death. VEE virus antigen was widespread in the central nervous system of both mice and hamsters. VEE virus was found to be highly neurotropic in hamsters and had a similar distribution in the brain as in mice, but hamsters died from their extraneural disease before major central nervous system disease developed.

Transport of cephalexin to the cerebrospinal fluid directly from the nasal cavity

The aim of the present study has been to confirm the existence of a transport pathway for a drug (cephalexin) to the cerebrospinal fluid (CSF) directly from the nasal cavity, by comparing the drug's concentrations in CSF after intranasal (i.n.), intravenous (i.v.) and intraduodenal (i.d.) administration. Higher levels of the drug were found in CSF following i.n. administration compared with the i.v. and i.d. routes, even though its plasma concentrations were similar. These findings suggest the existence of a direct transport pathway for cephalexin from the nasal cavity to the CSF. The concentration of drug in CSF at 15 min after i.n. administration was higher than that at 30 min. In contrast, its concentrations in CSF at 15 min after i.v. and i.d. administration were not significantly different from those at 30 min. The results confirm the presence of a direct transport pathway to CSF from the nasal cavity. This pathway may represent a new delivery route to CSF and possibly to brain parenchyma.

Limb paralysis as a manifestation of Coxsackie B virus infection

Forty-four African children (25 girls, 19 boys) are described with single or multiple limb paralysis as a manifestation of infection with Coxsackie B virus. Single limb paralysis involved exclusively the lower extremity, with no nervous system involvement elsewhere and a relatively benign prognosis. Multiple limb paralysis occurred either alone or with other neurological deficits. Only two of 15 patients followed up for five months or longer regained premorbid motor status. Seven patients required assisted ventilation, of whom all but one died. Viral infection remains an important cause of acute limb paralysis in this population, and Coxsackie B is the agent often responsible.

The olfactory system and Alzheimer's disease

Alzheimer's disease (AD) is considered to be the number one health problem and seems to be reaching epidemic proportion in the USA. The cause of AD is not known, a reliable animal model of the disease has not been found and appropriate treatment of this dementia is wanting. The present review focuses on the possibility that a virus or exogenous toxic materials may gain access to the CNS using the olfactory mucosa as a portal of entry. Anterograde and retrograde transport of the virus/zeolites to olfactory forebrain regions, which receive primary and secondary projections from the main olfactory bulb (MOB) and which, in turn, project centrifugal axons to the MOB, may initiate cell degeneration at such loci. Pathological changes may, thus, be initially confined to projecting and intrinsic neurons localized in cortical and subcortical olfactory structures; arguments are advanced which favor the view that excitotoxic phenomena could be mainly responsible for the overall degenerative picture. Neurotoxic activity may follow infection by the virus itself, be facilitated by loss of GABAergic terminals in olfactory cortex, develop following repeated episodes of physiological long term potentiation (which unmasks NMDA receptors) or be due to excessive release, faculty re-uptake or altered glutamate receptor sensitivity. Furthermore, a reduction in central inhibitory inputs to the MOB might then result in disinhibition of mitral/tufted neurons and enhance the excitotoxic phenomena in the MOB projecting field. Within this context, and in line with recent studies, it is believed that pathology begins at cortical (mainly olfactory) regions, basal forebrain neurons being secondarily affected due to retrograde degeneration. In addition, failure to produce a critical level of neurotrophic factors by a damaged MOB and olfactory cortex, could adversely affect survival of basal cholinergic neurons which innervate both regions. Support for these hypothesis is provided, first, by recent reports on pathological findings in AD brains which seem to involve preferentially the olfactory and entorhinal cortices, the olfactory amygdala and the hippocampus, all of which receive primary or secondary projections from the MOB; secondly, by the presence of severe olfactory deficits in the early stages of the disease, mainly of a discriminatory nature, which points to a malfunction of central olfactory structures.

Spread of herpes simplex virus type-1 (Miyama +GC strain) to the central nervous system after intraperitoneal inoculation: the role of the myenteric plexus of the gut

The pathways taken by the HSV-1 virus after intraperitoneal (i.p.) inoculation were studied in 5-week old male C3H/HeN mice injected with 1 x 10(4) PFU (100 LD50) or 5 x 10(5) PFU (5000 LD50) of HSV-1 (Miyama +GC strain). At the higher dosage (5 x 10(5) PFU), HSV-1 began replicating in the adrenal from the first day, then in the gut and thoracic portion of the spinal cord by the third day, and in the brainstem by the fourth day, as shown by the titers of the virus in these organs. By immunoperoxidase staining HSV-1 was localized in a necrotic area of the adrenal, the myenteric plexus of the gut, the intermediolateral columns of the thoracic cord, and the vagus nerve nuclei of the medulla oblongata. In the low dose mice (1 x 10(4) PFU), HSV-1 was not isolated from the adrenal or thoracic segment of the spinal cord from the time of inoculation until the time of death. It was, however, isolated from the gut on days 4-6 and from the brainstem by day 5. HSV-1 was never isolated from the blood of either group at any time. The localizations of viral replication suggest that in the mice inoculated with 1 x 10(4) PFU, HSV-1 spreads to the brainstem via the vagal nerves after replication in the myenteric plexus of the gut. In the mice given the higher dose, localizations suggest not only the above route, but also that the virus spread to the intermediolateral columns of the spinal cord after replicating in the adrenal.

Golgi-like, transneuronal retrograde labelling with CNS injections of herpes simplex virus type 1

The use of HSV1 as a retrograde transneuronal marker for the CNS was assessed in several neuroanatomical systems of the rat brain including the olfactory, visual and somatosensory systems. In all systems, retrograde transneuronal transport was observed; with appropriate survival times transport was evident in third and fourth order neurons in established neuronal circuits. A striking observation was the high frequency of neurons labelled in a Golgi-like manner. The visualization of even the finest dendritic processes provides information about the architecture of neurons several synapses removed from the site of injection. The Golgi-like labelling is so complete that it is possible to identify and process distal parts of dendrites for EM analysis. Thus, it should be feasible to identify synaptic inputs to the dendrites of neurons two or more synapses removed from the site of injection. There was spotty evidence for anterograde transport but the vast majority of the labelling could be accounted for by retrograde transport. With increased survival time, some regions, especially those located one synapse removed from the injection site, became necrotic and the virus spread to glia cells in addition to neurons in those regions. However, in regions more than one synapse removed from the injection there was negligible labelling of glial cells. Taken together, these results suggest that transneuronal retrograde labelling with HSV1 is a useful tool in the analysis of neural circuits.