Herpes simplex virus encephalitis: chronic progressive cerebral MRI changes despite good clinical recovery and low viral load - an experimental mouse study

Vulnerability of the Hippocampus to Insults: Links to Blood-Brain Barrier Dysfunction

The hippocampus is a critical brain substrate for learning and memory; events that harm the hippocampus can seriously impair mental and behavioral functioning. Hippocampal pathophysiologies have been identified as potential causes and effects of a remarkably diverse array of medical diseases, psychological disorders, and environmental sources of damage. It may be that the hippocampus is more vulnerable than other brain areas to insults that are related to these conditions. One purpose of this review is to assess the vulnerability of the hippocampus to the most prevalent types of insults in multiple biomedical domains (i.e., neuroactive pathogens, neurotoxins, neurological conditions, trauma, aging, neurodegenerative disease, acquired brain injury, mental health conditions, endocrine disorders, developmental disabilities, nutrition) and to evaluate whether these insults affect the hippocampus first and more prominently compared to other brain loci. A second purpose is to consider the role of hippocampal blood-brain barrier (BBB) breakdown in either causing or worsening the harmful effects of each insult. Recent research suggests that the hippocampal BBB is more fragile compared to other brain areas and may also be more prone to the disruption of the transport mechanisms that act to maintain the internal milieu. Moreover, a compromised BBB could be a factor that is common to many different types of insults. Our analysis indicates that the hippocampus is more vulnerable to insults compared to other parts of the brain, and that developing interventions that protect the hippocampal BBB may help to prevent or ameliorate the harmful effects of many insults on memory and cognition.

The Hippocampal Vulnerability to Herpes Simplex Virus Type I Infection: Relevance to Alzheimer's Disease and Memory Impairment

Herpes simplex virus type 1 (HSV-1) as a possible infectious etiology in Alzheimer’s disease (AD) has been proposed since the 1980s. The accumulating research thus far continues to support the association and a possible causal role of HSV-1 in the development of AD. HSV-1 has been shown to induce neuropathological and behavioral changes of AD, such as amyloid-beta accumulation, tau hyperphosphorylation, as well as memory and learning impairments in experimental settings. However, a neuroanatomical standpoint of HSV-1 tropism in the brain has not been emphasized in detail. In this review, we propose that the hippocampal vulnerability to HSV-1 infection plays a part in the development of AD and amnestic mild cognitive impairment (aMCI). Henceforth, this review draws on human studies to bridge HSV-1 to hippocampal-related brain disorders, namely AD and aMCI/MCI. Next, experimental models and clinical observations supporting the neurotropism or predilection of HSV-1 to infect the hippocampus are examined. Following this, factors and mechanisms predisposing the hippocampus to HSV-1 infection are discussed. In brief, the hippocampus has high levels of viral cellular receptors, neural stem or progenitor cells (NSCs/NPCs), glucocorticoid receptors (GRs) and amyloid precursor protein (APP) that support HSV-1 infectivity, as well as inadequate antiviral immunity against HSV-1. Currently, the established diseases HSV-1 causes are mucocutaneous lesions and encephalitis; however, this review revises that HSV-1 may also induce and/or contribute to hippocampal-related brain disorders, especially AD and aMCI/MCI.

Long-term sequelae of herpes simplex virus encephalitis-related white matter injury: correlation of neuropsychological outcome and diffusion tensor imaging

The pathophysiology of the memory impairment following Herpes Simplex virus encephalitis is not yet established and understood. This study attempts to elucidate the role of white matter injury and its impact on neuropsychological outcome in patients with history of Herpes Simplex virus encephalitis. This is a single-institution prospective study assessing 9 patients and 15 matched controls utilizing a combination of MRI with diffusion tensor imaging and neuropsychological testing. Tract-based spatial statistics analysis was performed and correlated with neuropsychological outcomes. Significantly decreased fractional anisotropy (FA) values were noted in corpus callosum, corona radiata, left posterior thalamic radiation, cingulum, superior longitudinal fasciculus, fornix, inferior longitudinal fasciculus, inferior fronto-occipital fasciculus, and uncinated fasciculus. Impaired facial recognition significantly correlated with reduction in FA of right uncinate fasciculus, right inferior longitudinal fasciculus, and splenium genu of corpus callosum. FA value of left cingulum significantly correlated with logical memory, auditory verbal learning. FA value of fornix correlated with visual recognition; FA value of left uncinate fasciculus with auditory verbal learning and delayed recall. In conclusion, this study demonstrates microstructural abnormalities involving several white matter tracts corresponding to neuropsychological deficits.

The German trial on Aciclovir and Corticosteroids in Herpes-simplex-virus-Encephalitis (GACHE): a multicenter, randomized, double-blind, placebo-controlled trial

INTRODUCTION

Comprehensive treatment of Herpes-simplex-virus-encephalitis (HSVE) remains a major clinical challenge. The current therapy gold standard is aciclovir, a drug that inhibits viral replication. Despite antiviral treatment, mortality remains around 20% and a majority of survivors suffer from severe disability. Experimental research and recent retrospective clinical observations suggest a favourable therapy response to adjuvant dexamethasone. Currently there is no randomized clinical trial evidence, however, to support the routine use of adjuvant corticosteroid treatment in HSVE.

METHODS

The German trial of Aciclovir and Corticosteroids in Herpes-simplex-virus-Encephalitis (GACHE) studied the effect of adjuvant dexamethasone versus placebo on top of standard aciclovir treatment in adult patients aged 18 up to 85 years with proven HSVE in German academic centers of Neurology in a randomized and double blind fashion. The trial was open from November 2007 to December 2012. The initially planned sample size was 372 patients with the option to increase to up to 450 patients after the second interim analysis. The primary endpoint was a binary functional outcome after 6 months assessed using the modified Rankin scale (mRS 0-2 vs. 3-6). Secondary endpoints included mortality after 6 and 12 months, functional outcome after 6 months measured with the Glasgow outcome scale (GOS), functional outcome after 12 months measured with mRS and GOS, quality of life as measured with the EuroQol 5D instrument after 6 and 12 months, neuropsychological testing after 6 months, cranial magnetic resonance imaging findings after 6 months, seizures up to day of discharge or at the latest at day 30, and after 6 and 12 months.

RESULTS

The trial was stopped prematurely for slow recruitment after 41 patients had been randomized, 21 of them treated with dexamethasone and 20 with placebo. No difference was observed in the primary endpoint. In the full analysis set (n = 19 in each group), 12 patients in each treatment arm achieved a mRS of 0-2. Similarly, we did not observe significant differences in the secondary endpoints (GOS, mRS, quality of life, neuropsychological testing).

CONCLUSION

GACHE being prematurely terminated demonstrated challenges encountered performing randomized, placebo-controlled trials in rare life threatening neurological diseases. Based upon our trial results the use of adjuvant steroids in addition to antiviral treatment remains experimental and is at the decision of the individual treating physician. Unfortunately, the small number of study participants does not allow firm conclusions.

TRIAL REGISTRATION

EudraCT-Nr. 2005-003201-81.

Mechanisms of Blood-Brain Barrier Disruption in Herpes Simplex Encephalitis

Herpes simplex encephalitis (HSE) is often caused by infection with herpes simplex virus 1 (HSV-1), a neurotropic double-stranded DNA virus. HSE infection always impacts the temporal and frontal lobes or limbic system, leading to edema, hemorrhage, and necrotic changes in the brain parenchyma. Additionally, patients often exhibit severe complications following antiviral treatment, including dementia and epilepsy. HSE is further associated with disruptions to the blood-brain barrier (BBB), which consists of microvascular endothelial cells, tight junctions, astrocytes, pericytes, and basement membranes. Following an HSV-1 infection, changes in BBB integrity and permeability can result in increased movement of viruses, immune cells, and/or cytokines into the brain parenchyma. This leads to an enhanced inflammatory response in the central nervous system and further damage to the brain. Thus, it is important to protect the BBB from pathogens to reduce brain damage from HSE. Here, we discuss HSE and the normal structure and function of the BBB. We also discuss growing evidence indicating an association between BBB breakdown and the pathogenesis of HSE, as well as future research directions and potential new therapeutic targets. Graphical Abstract During herpes simplex encephalitis, the functions and structures of each composition of BBB have been altered by different factors, thus the permeability and integrity of BBB have been broken. The review aim to explore the potential mechanisms and factors in the process, probe the next research targets and new therapeutic targets.

The case for immunomodulatory approaches in treating HSV encephalitis

HSV encephalitis (HSE) is the most prevalent sporadic viral encephalitis. Although safe and effective antiviral therapies and greatly improved noninvasive diagnostic procedures have significantly improved outcomes, mortality (~20%) and debilitating neurological sequelae in survivors remain unacceptably high. An encouraging new development is that the focus is now shifting away from the virus exclusively, to include consideration of the host immune response to infection in the pathology underlying development of HSE. In this article, the authors discuss results from recent studies in experimental mouse models, as well as clinical reports that demonstrate a role for exaggerated host inflammatory responses in the brain in the development of HSE that is motivating researchers and clinicians to consider new therapeutic approaches for treating HSE. The authors also discuss results from a few studies that have shown that immunomodulatory drugs can be highly protective against HSE, which supports a role for deleterious host inflammatory responses in HSE. The impressive outcomes of some immunomodulatory approaches in mouse models of HSE emphasize the urgent need for clinical trials to rigorously evaluate combination antiviral and immunomodulatory therapy in comparison with standard antiviral therapy for treatment of HSE, and support for such an initiative is gaining momentum.

Amnesia following herpes simplex encephalitis: diffusion-tensor imaging uncovers reduced integrity of normal-appearing white matter

PURPOSE

To explore white matter (WM) and gray matter tissue integrity in the apparently unaffected hemisphere of patients with herpes simplex encephalitis (HSE) who have gross unilateral medial temporal lobe (MTL) lesions and both verbal and visuospatial memory deficits.

MATERIALS AND METHODS

This study had institutional ethics committee approval and included written informed consent. Magnetic resonance (MR) imaging was performed in five patients who had recovered from HSE (one woman, four men; median age, 32 years; interquartile range, 28.5-37 years) and 51 age-matched controls (30 women, 21 men; median age, 32 years; interquartile range, 28-37 years). As markers of microstructural WM integrity, fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity, and radial diffusivity (RD) derived from diffusion-tensor (DT) imaging were used. An automated regional brain segmentation approach yielded estimates of subcortical volumes, including hippocampus, and cortical thickness. Group differences were evaluated by using permutation tests.

RESULTS

Examination of standard MR images found unilateral lesions in all patients. The patients with HSE showed reduced FA and increased MD and RD in several WM tracts contralateral to lesions (P < .05, corrected for multiple comparisons). Affected tracts included connections between the MTLs and other parts of the brain. No significant group differences were observed in subcortical volume or cortical thickness.

CONCLUSION

These results suggest that patients with HSE have reduced microstructural integrity of normal-appearing WM contralateral to grossly visible lesions. These subtle lesions, detectable at DT imaging, probably contribute to the memory impairment manifested by these patients.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.10100179/-/DC1.

Favorable effects of MMP-9 knockdown in murine herpes simplex encephalitis using small interfering RNA

BACKGROUND AND PURPOSE

The prognosis of herpes simplex encephalitis (HSE) remains poor despite available antiviral treatment. Matrix metalloproteinase-9 (MMP-9) is currently considered to play a major role in promoting cerebrovascular complications which contribute to the high mortality and morbidity of HSE. We hypothesize that temporally knockdown MMP-9 expression in early phase of HSE might be an effective treatment strategy.

METHODS

The animal models of herpes simplex encephalitis were established by intracerebrally inoculated herpes simplex virus type 1 (HSV-1) in mice. Mice were inoculated intracerebrally with MMP-9 targeting siRNA (MMP-9 siRNA). MMP-9 expression was assessed by RT-PCR and western blot analysis at 3 and 7 days after HSV-1 infected. The blood-brain barrier (BBB) permeability was quantitated by Evans blue dye extravasations and brain water content. Immunohistochemistry method was adopted to analyse the expression of AQP4 protein. Quantitative real-time PCR analysis was used to detect cytokines expression. Neurological score was quantified using an established neurological scale at 7 days after HSE.

RESULTS

Using synthetic small interfering RNA, we found a single intracerebral injection of siRNA targeting murine MMP-9 mRNA (MMP-9 siRNA) silenced MMP-9 expression and reduced it to normal level at day 7 post-infection. The improvement in neurological function and increased cumulative survival reflected the functional consequence of this therapy. MMP-9 knockdown mice also displayed less uptake of Evans blue and reduced brain water content compared with control siRNA-treated group. Also the HSV-1-induced upregulation of proinflammatory cytokines was significantly diminished in MMP-9 siRNA-treated mice. In addition, aquaporin-4 expression in perivascular decreased in MMP-9 siRNA-treated mice and might contribute to the protection of blood-brain barrier.

DISCUSSION

This compelling evidence suggests that MMP-9 is a key pathogenic factor within HSE, and local injection of synthetic siRNA in the brain could knock down MMP-9 expression in acute phase of HSE, reduce brain edema and improves mice neurological function and increase cumulative survival.

Chronic cortical and subcortical pathology with associated neurological deficits ensuing experimental herpes encephalitis

Long-term neurological sequela is common among herpes simplex encephalitis (HSE) survivors. Animal models for HSE are used to investigate mechanisms of acute disease, but little has been done to model chronic manifestations of HSE. The current study presents a detailed, systematic analysis of chronic neuropathology, including characterization of topography and sequential progression of degenerative lesions and inflammation. Subsequent to intranasal HSV-1 infection, inflammatory responses that were temporally and spatially distinct persisted in infected cortical and brain stem regions. Neutrophils were present exclusively within the olfactory bulb and brain stem regions during the acute phase of infection, while the chronic inflammation was marked by plasma cells, lymphocytes and activated microglia. The chronic lymphocytic infiltrate, cytokine production, and activated microglia were associated with the loss of cortical neuropile in the entorhinal cortex and hippocampus. Animals surviving the acute infection showed a spectrum of chronic lesions from decreased brain volume, neuronal loss, activated astrocytes, and glial scar formation to severe atrophy and cavitations of the cortex. These lesions were also associated with severe spatial memory deficits in surviving animals. Taken together, this model can be utilized to further investigate the mechanisms of neurological defects that follow in the wake of HSE.

MRI deterioration in herpes simplex encephalitis despite clinical recovery

OBJECTIVES

Herpes simplex virus type 1 is a sporadic cause of viral encephalitis. Relapse of encephalitis occurs in up to 10% of patients, manifested by recurrent symptoms, clinical and MRI findings, and the presence of herpes simplex virus type 1 DNA in the cerebrospinal fluid (CSF).

METHODS

We describe the clinical features, MRI findings and outcome in 2 patients with herpes simplex encephalitis during the acute phase and 6 months after the onset of encephalitis.

RESULTS

Both patients had a good response to treatment and an excellent recovery. Despite clinical recovery, in a 6-month follow-up MRI lesions consistent with recurrence were disclosed, without any clinical findings or CSF abnormalities.

CONCLUSIONS

The mechanism underlying this MRI deterioration is unclear and an immune-mediated mechanism may be involved. Thus, MRI deterioration after herpes simplex encephalitis should be interpreted with caution and it does not always represent a relapse, especially when the imaging studies do not correlate with the clinical and CSF findings.

Protocol for German trial of Acyclovir and corticosteroids in Herpes-simplex-virus-encephalitis (GACHE): a multicenter, multinational, randomized, double-blind, placebo-controlled German, Austrian and Dutch trial [ISRCTN45122933]

BACKGROUND

The treatment of Herpes-simplex-virus-encephalitis (HSVE) remains a major unsolved problem in Neurology. Current gold standard for therapy is acyclovir, a drug that inhibits viral replication. Despite antiviral treatment, mortality remains up to 15%, less than 20% of patients are able to go back to work, and the majority of patients suffer from severe disability. This is a discouraging, unsatisfactory situation for treating physicians, the disabled patients and their families, and constitutes an enormous burden to the public health services. The information obtained from experimental animal research and from recent retrospective clinical observations, indicates that a substantial benefit in outcome can be expected in patients with HSVE who are treated with adjuvant dexamethasone. But currently there is no available evidence to support the routine use of adjuvant corticosteroid treatment in HSVE. A randomized multicenter trial is the only useful instrument to address this question.

DESIGN

GACHE is a multicenter, randomized, double-blind, placebo-controlled, parallel group clinical trial of treatment with acyclovir and adjuvant dexamethasone, as compared with acyclovir and placebo in adults with HSVE. The statistical design will be that of a 3-stage-group sequential trial with potential sample size adaptation in the last stage.

CONCLUSION

372 patients with proven HSVE (positive HSV-DNA-PCR), aged 18 up to 85 years; with focal neurological signs no longer than 5 days prior to admission, and who give informed consent will be recruited from Departments of Neurology of academic medical centers in Germany, Austria and The Netherlands. Sample size will potentially be extended after the second interim analysis up to a maximum of 450 patients.

TRIAL REGISTRATION

Current Controlled TrialsISRCTN45122933.

Asymptomatic self-limiting diffuse white matter lesions in subacute to chronic stage of herpes simplex encephalitis

This study evaluated white matter changes in the subacute and chronic stages of herpes simplex encephalitis (HSE). Subjects comprised 15 patients with HSE. All patients were examined using MRI at onset, and then at seven to ten days, three to five weeks and two to three months after onset. In addition, the six patients who displayed white matter signal abnormalities were examined at six months and <one year after onset. Cell count, protein levels, polymerase chain reaction (PCR) of herpes simplex virus in cerebrospinal fluid (CSF), and exacerbation of neurological symptoms as well as dose of acyclovir were compared between patients with and without white matter abnormalities. Diffuse white matter signal changes were identified at the subacute stage (3-5 weeks after onset) of HSE in six patients (6/15, 40%). No significant relationship was observed between the presence of white matter signal abnormalities and laboratory data, acyclovir dose or clinical symptoms. These signal abnormalities disappeared or improved by two years without any clinical treatment. Diffuse white matter signal abnormalities occur frequently in the subacute stage of HSE. Although the mechanisms underlying these white matter lesions have not been elucidated, subclinical immune-mediated processes may be considered. Repeat MRI studies over a long period are necessary for evaluating the clinical process of patients with HSE.

The spectrum of herpes simplex encephalitis in children

Clinical and basic science research carried out in recent years into herpes simplex encephalitis (HSE) have shown that the concept of a "classical" picture of HSE in children is now outdated and that our current knowledge of the disease is probably only the tip of an iceberg. Indeed, increasing evidence supports the existence of a wider range of pathophysiological mechanisms, clinical presentations and disease progressions in paediatric HSE. This paper reviews the clinical, biological and radiological data available and redefines the spectrum of HSE in children. Full understanding of the condition should improve the management of suspected cases and decrease the morbidity and the mortality associated with this disease.

Deterioration on magnetic resonance imaging despite good clinical recovery after viral encephalitis

We present a 2-year-old patient who showed progressive widespread white-matter abnormalities on magnetic resonance imaging 1 month after viral encephalitis, despite her good clinical recovery. These lesions on magnetic resonance imaging had not responded to therapies commonly used to treat secondary immune-mediated demyelinating lesions, as observed in acute disseminated encephalomyelitis. Acute viral encephalitis caused cortical blindness, but no other clinical signs developed during her clinical course. The progressive white-matter lesion in our case was different from the exacerbation of viral encephalitis or secondary immune-mediated encephalitis. A year later, magnetic resonance imaging-demonstrated brain atrophy with cystic changes in the bilateral occipital area, with remarkably reduced white-matter lesions. We hypothesize that the progressive white-matter changes resulted from the process of atrophy, degeneration, and cystic formation after viral encephalitis, rather than from the immune-mediated demyelinating process.

Current issues and perspectives in small rodent magnetic resonance imaging using clinical MRI scanners

Small rodents such as mice and rats are frequently used in animal experiments for several reasons. In the past, animal experiments were frequently associated with invasive methods and groups of animals had to be killed to perform longitudinal studies. Today's modern imaging techniques such as magnetic resonance imaging (MRI) allow non-invasive longitudinal monitoring of multiple parameters. Although only a few institutions have access to dedicated small animal MR scanners, most institutions carrying out animal experiments have access to clinical MR scanners. Technological advances and the increasing field strength of clinical scanners make MRI a broadly available and viable technique in preclinical in vivo research. This review provides an overview of current concepts, limitations, and recent studies dealing with small animal imaging using clinical MR scanners.

Aquaporin 4 regulation during acute and long-term experimental Herpes simplex virus encephalitis

Structural damage of the central nervous system (CNS) often leads to severely disabling residual symptoms despite effective antiviral therapy during Herpes simplex virus encephalitis (HSVE). Edematous space-occupying lesions are pathological and neuroradiological well-known phenomena for this disease. The molecular mechanisms of brain edema development in HSVE are poorly understood, the regulation of water brain-blood barrier (BBB) permeability might be disturbed. Aquaporin 4 (AQP4) is the predominant aquaporin expressed in the brain. Aquaporin 1 (AQP1) plays a role in cerebrospinal fluid modulation. Previous studies suggest that alterations of AQP expression play an important role in the development of brain edema. The mRNA expression of AQP4, AQP1, of their physiologically associated proteins Alpha-syntrophin and KIR 4.1 and of the structural glial protein glial fibrillary acid protein (GFAP) was analyzed in a well-established mice model simulating the human disease. Our data demonstrate a significant down-regulation of AQP4 in the acute phase of disease and an up-regulation of AQP4 and AQP1 in the long term. These results reveal the complex transcription pattern of AQP4, AQP1, KIR 4.1, alpha-syntrophin, and GFAP during HSVE and suggest a role for AQP4 regulation in the pathophysiology of acute and long-term HSVE. AQP4 modulation could be a potential target for brain edema treatment during HSVE.

Spatiotemporal changes of the herpes simplex virus entry receptor nectin-1 in murine brain during postnatal development

Herpes simplex virus (HSV) is known to replicate within the limbic system and to alter behavior in both humans and experimental animals. However, the reason why the virus selectively damages this anatomical, developmental, and functional neural unit remains a mystery. Nor is it known why herpes simplex encephalitis fails to respect these neuroanatomical boundaries in newborns. In the present study, the authors determined the spatiotemporal changes in the distribution of the major neural entry receptor for HSV (nectin-1) in postnatal mouse and rat brains. Discrete nectin-1 immunopositivity was observed in regions susceptible to HSV infection in specific developmental phases of central nervous system. The authors also describe nectin-1-related pathways controlling neuronal cell migration/brain morphogenesis, the disruption of which might lead to the emergence of mental disorders with a rapid cognitive decline.

Apparent diffusion coefficient in the aging mouse brain: A magnetic resonance imaging study

Novel magnetic resonance imaging sequences have and still continue to play an increasing role in neuroimaging and neuroscience. Among these techniques, diffusion-weighted imaging (DWI) has revolutionized the diagnosis and management of diseases such as stroke, neoplastic disease and inflammation. However, the effects of aging on diffusion are yet to be determined. To establish reference values for future experimental mouse studies we tested the hypothesis that absolute apparent diffusion coefficients (ADC) of the normal brain change with age. A total of 41 healthy mice were examined by T2-weighted imaging and DWI. For each animal ADC frequency histograms (i) of the whole brain were calculated on a voxel-by-voxel basis and region-of-interest (ROI) measurements (ii) performed and related to the animals' age. The mean entire brain ADC of mice <3 months was 0.715(+/-0.016) x 10(-3) mm2/s, no significant difference to mice aged 4 to 5 months (0.736(+/-0.040) x 10(-3) mm2/s) or animals older than 9 months 0.736(+/-0.020) x 10(-3) mm2/s. Mean whole brain ADCs showed a trend towards lower values with aging but both methods (i + ii) did not reveal a significant correlation with age. ROI measurements in predefined areas: 0.723(+/-0.057) x 10(-3) mm2/s in the parietal lobe, 0.659(+/-0.037) x 10(-3) mm2/s in the striatum and 0.679(+/-0.056) x 10(-3) mm2/s in the temporal lobe. With advancing age, we observed minimal diffusion changes in the whole mouse brain as well as in three ROIs by determination of ADCs. According to our data ADCs remain nearly constant during the aging process of the brain with a small but statistically non-significant trend towards a decreased diffusion in older animals.

Postinfectious immune-mediated encephalitis after pediatric herpes simplex encephalitis

We report a 3-year-old patient who presented a secondary acute neurological deterioration clinically characterized by a partial Kluver-Bucy syndrome, 1 month after the onset of herpes simplex encephalitis. This episode is unlikely due to continuation or resumption of cerebral viral replication but might be related to an immune-inflammatory process. In children, postinfectious immune-mediated encephalitis occurring after HSE are usually clinically characterized by choreoathetoid movements. This type of movement disorder was, however, not observed in this patient. On the basis of this case and a review of the literature, we hypothesize the existence of a spectrum of secondary immune-mediated process triggered by herpes simplex virus cerebral infection ranging from asymptomatic cases with diffuse white matter involvement to secondary acute neurological deteriorations with or without extrapyramidal features.

Early inhibition of nitric oxide production increases HSV-1 intranasal infection

Here, we studied the role of nitric oxide (NO) production during the first steps of the respiratory infection of BALB/c mice with herpes simplex virus type 1 (HSV-1), strain F. Nitric oxide synthase II (NOS-II) mRNA and protein were detected by reverse transcription (RT)-PCR and dot blot, respectively in samples of lungs and turbinates early post-infection (p.i.). Immunohistochemical analysis revealed pulmonar macrophages and PMN expressing NOS-II in the lungs of infected animals. Animals intranasally treated with aminoguanidine (AG), a NOS inhibitor, during the first steps of infection, showed a dose-dependent increase in pneumonitis compared to controls. Viral titres in turbinates, lungs, and brains were higher in AG treated mice. Finally, histopathology studies revealed a stronger inflammation in eyes, and lungs of these animals. Taken together, these results suggest a role of NO in controlling primary HSV intranasal infection.

Experimental herpes simplex virus encephalitis: a combination therapy of acyclovir and glucocorticoids reduces long-term magnetic resonance imaging abnormalities

Despite early antiviral treatment, herpes simples virus encephalitis (HSVE) still remains a life-threatening sporadic disease with high mortality and morbidity. In patients and in experimental disease, chronic progressive magnetic resonance imaging (MRI) abnormalities have been found even after antiviral therapy. Secondary autoimmune-mediated and not directly virus-mediated mechanisms might play a key role for the outcome of disease. This study aimed to evaluate a possible beneficial effect of a therapy of acyclovir and corticosteroids versus acyclovir only. In a mouse model of HSVE (intranasal inoculation with 10(5) pfu [plaque-forming units] of HSV-1 strain F), a long-term MRI study was realized. Cranial MRI was performed serially at days 2, 7, 14, 21, 60, and 180 in different therapy groups: 1, saline; 2, acyclovir; 3, acyclovir, subsequently methylprednisolone; 4, sham-infected with saline. Brain viral load peaked at day 7 to decline thereafter to a low baseline value. Viral load in group 1 was significantly higher than in animals with antiviral therapy. In group 4, no viral DNA was detectable. Viral load did not differ significantly between acyclovir and acyclovir/corticosteroid-treated groups, suggesting that the use of corticosteroids in addition to acyclovir does not increase viral burden. MRI findings in untreated and acyclovir-treated animals revealed chronic progressive changes. In contrast, there was a significant reduction of the severity of long-term MRI abnormalities in acyclovir/corticosteroid-treated animals. With respect to abnormal MRI findings, this study demonstrates a clear beneficial effect of an acyclovir and corticosteroid therapy without influencing brain viral load.

Technical parameters affecting image characteristics in in vivo MR microscopy of the mouse

The aim of the study was to assess the effects of changing acquisition parameters used for high-resolution in vivo magnetic resonance (MR) microscopy on image quality and scan time. The head or abdomen of 11 normal and 1 glioblastoma-bearing anesthetized BALB/c mice were imaged using a high-resolution 7.0-Tesla magnet. Scan parameters such as matrix size (MTX), slice thickness (ST), number of excitations (NEX), pulse sequence type including repetition time (TR) and echo time (TE), respiratory gating, and intraperitoneal contrast medium administration were altered to assess their actual effect on signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) as compared to calculated effects. As expected, SNR increased with increasing ST or NEX and with decreasing MTX. However, although the empirical increase in SNR was similar to that expected for increased ST, it was less than that anticipated for increasing NEX or decreasing MTX. Increasing NEX and applying respiratory gating both increased SNR and reduced the image degradation associated with respiratory motion in images of the abdomen. Intraperitoneal contrast medium administration produced a marked increase in CNR in the subject with the implanted glioblastoma, suggesting that this route is satisfactory for the enhancement of lesions disrupting the blood-brain barrier. The consequence of improving image quality in terms of spatial and contrast resolution is increased scan time. However, the actual increase in SNR when altering acquisition parameters may not be as much as predicted by theory.

Asymptomatic self-limiting white matter lesions in the chronic phase of herpes simplex encephalitis

We report a 9-month-old girl with herpes simplex encephalitis. T(2)-weighted magnetic resonance imaging (MRI) on the 8th day of illness showed increased signal intensity in the gray and white matter of the bilateral lobes, especially the right temporo-parietal lobe. High voltage slow waves were recorded in the right parieto-occipital region on electroencephalography. She was discharged on the 34th day of illness without sequelae. On discharge, the high signal intensity on MRI had improved and the abnormal slow waves on electroencephalography had disappeared. At 4 months after the onset of illness, MRI revealed decreased signal intensities in T(1)-weighted images and increased signal intensities in T(2)-weighted images in the periventricular white matter adjacent to the posterior horns of the lateral ventricles. The white matter lesions had expanded at 9 months after the onset of illness. At 14 months after the onset of illness, the white matter lesions were reduced in size, and at 2 years after the onset of illness, they had completely disappeared. During 2 years follow-up after discharge, however, there were no neurological abnormalities corresponding to the lesions and her psychomotor development was normal. Although the mechanism underlying these white matter lesions had not been elucidated, an immune-mediated complication such as edema or demyelination is suspected. Repeat MRI studies over a long period are necessary to follow up a patient with herpes simplex encephalitis.

Experimental herpes simplex virus encephalitis: inhibition of the expression of inducible nitric oxide synthase in mouse brain tissue

In the brain tissue of 36 mice infected with herpes simplex virus type 1, strain F, we determined the expression of inducible nitric oxide synthase (iNOS) with semiquantitative reverse transcription polymerase chain reaction. The viral burden was quantitated by polymerase chain reaction. Nitric oxide, induced by iNOS, may contribute to neuronal cell damage following virus infection. As the experimental therapeutic strategy in herpes simplex virus encephalitis (HSVE), we used: N-nitro-L-arginin (L-NA), a selective inhibitor of iNOS; and combination therapies of either methylprednisolone/acyclovir or L-NA/acyclovir. The viral burden peaked in acute disease, and then returned to a low baseline value, except in untreated controls. The expression of iNOS mRNA was suppressed by L-NA and by acyclovir/corticosteroids. INOS inhibition may provide an additional therapeutic strategy targeted specifically to suppress iNOS expression as a potential secondary mechanism of tissue damage in acute and chronic HSVE.

Effects of UV irradiation on skin and nonskin-associated herpes simplex virus infections in rats

Herpes simplex virus (HSV) normally causes vescular lesions on mucocutaneous surfaces but can also cause encephalitis. The virus can reactivate from the latent state in neurons to form recrudescent lesions. One common stimulus for reactivation is exposure to sunlight. In the present study, the effects of irradiating rats with suberythemal ultraviolet (UV) before or after infecting them epidermally with HSV was investigated. Preexposure to UV impaired HSV-specific cellular immune responses, as indicated by delayed type hypersensitivity (DTH) and in vitro lymphoproliferation assays. However, the number and severity of the skin lesions were not altered. In contrast, exposure after infection did not affect cellular immunity but resulted in a large increase in the severity and number of lesions. In a second series of experiments, the effects of preirradiating with UV on HSV infection was examined using a route of inoculation which was not skin-associated, namely intranasal, allowing direct non-invasive access to the nervous system. It was found that suppressed DTH resulted, together with an increase in the incidence and severity of neurological symptoms and an increased viral load in the brain. Therefore, unlike the situation in the skin, irradiation of rats before intranasal inoculation led to a suppressed immune response to HSV which correlated with increased viral load and symptoms. These results indicate that the effects of UV may be dependent on whether the animal is exposed before or after the infection, and whether the infection is skin-associated or systemic.