In vivo oxygen measurement in cerebrospinal fluid of pigs to determine physiologic and pathophysiologic oxygen values during CNS infections.

During infection and inflammation, a reduced oxygen level clearly affects cellular functions. Oxygen levels during CNS infections are unknown. Here we established and evaluated an in vivo measurement system to characterize the oxygen level in parallel with bacterial numbers (CFU/mL), the cell number and pH level inside the CSF of healthy compared to Streptococcus suis-infected pigs. The animals were anesthetized over a seven-hour period with isoflurane in air/oxygen at physiologic arterial partial pressure of oxygen. Oxygen levels in CSF of anesthetized pigs were compared to euthanized pigs. The detected partial pressure of oxygen in the CSF remained constant in a range of 47-63 mmHg, independent of the infection status (bacterial or cell number). In contrast, the pH value showed a slight drop during infection, which correlated with cell and bacterial number in CSF. We present physiologic oxygen and pH values in CSF during the onset of bacterial meningitis.

Pathophysiology of bacterial infection of the central nervous system and its putative role in the pathogenesis of behavioral changes.

Invasion of the central nervous system (CNS) by microorganisms is a severe and frequently fatal event during the course of many infectious diseases. It may lead to deafness, blindness, cerebral palsy, hydrocephalus, cognitive impairment or permanent neurological dysfunction in survivors. Pathogens can cross the blood-brain barrier by transcellular migration, paracellular migration and in infected macrophages. Pathogens may breach the blood-brain barrier and be recognized by antigen-presenting cells through the binding of Toll-like receptors. This induces the activation of nuclear factor kappa B or mitogen-activated protein kinase pathways and subsequently induces leukocyte infiltration and proliferation and the expression of numerous proteins involved in inflammation and the immune response. Many brain cells can produce cytokines, chemokines and other pro-inflammatory molecules in response to bacteria stimuli; as a consequence, polymorphonuclear cells are attracted and activated, and release large amounts of superoxide anion and nitric oxide, leading to peroxynitrite formation and oxidative stress. This cascade leads to lipid peroxidation, mitochondrial damage and blood-brain barrier breakdown, contributing to cellular injury during neuronal infection. Current evidence suggests that bacterial CNS infections can play a role in the etiopathogenesis of behavioral disorders by increasing pro-inflammatory cytokines and bacterial virulence factors. The aim of this review is to summarize the current knowledge of the relevant pathophysiologic steps in CNS infections.

Neurobrucellosis: clinical and diagnostic features.

BACKGROUND: We describe the neurological involvement in brucellosis and revisited diagnostic criteria for neurobrucellosis. METHODS: Patients with laboratory-confirmed brucellosis who were consequently hospitalized were observed prospectively in a brucellosis-endemic region. The neurobrucellosis was diagnosed by any one of the following criteria: (1) symptoms and signs consistent with neurobrucellosis; (2) isolation of Brucella species from cerebrospinal fluid (CSF) and/or presence of anti-Brucella antibodies in CSF; (3) the presence of lymphocytosis, increased protein, and decreased glucose levels in CSF; or (4) diagnostic findings in cranial magnetic resonance imaging or CT. RESULTS: Lumbar puncture was performed in 128 laboratory-confirmed brucellosis cases who had neurological symptoms and signs, and 48 (37.5%) were diagnosed as neurobrucellosis. The sensitivity of tube agglutination (TA) in CSF was 0.94, specificity 0.96, positive predictive value 0.94, and negative predictive value 0.96. Brucella bacteria were isolated from CSF in 7 of 48 patients (15%). The mean age of 48 neurobrucellosis patients was 42 years (SD, 19 years), and 16 (33%) were female. The most common neurological findings were agitation (25%), behavioral disorders (25%), muscle weakness (23%), disorientation (21%), and neck rigidity (17%). Cranial nerves were involved in 9 of 48 patients (19%). One patient was left with a sequela of peripheral facial paralysis and 2 patients with sensorineural hearing loss. CONCLUSIONS: Patients with severe and persistent headache and other neurologic symptoms and signs should be considered for neurobrucellosis in endemic regions and to possibly receive longer therapy than 6 weeks. Brucella TA with Coombs test in CSF is sensitive and specific by using a cutoff of ≥1:8.

Pathophysiology of bacterial infection of the central nervous system and its putative role in the pathogenesis of behavioral changes

Invasion of the central nervous system (CNS) by microorganisms is a severe and frequently fatal event during the course of many infectious diseases. It may lead to deafness, blindness, cerebral palsy, hydrocephalus, cognitive impairment or permanent neurological dysfunction in survivors. Pathogens can cross the blood-brain barrier by transcellular migration, paracellular migration and in infected macrophages. Pathogens may breach the blood-brain barrier and be recognized by antigen-presenting cells through the binding of Toll-like receptors. This induces the activation of nuclear factor kappa B or mitogen-activated protein kinase pathways and subsequently induces leukocyte infiltration and proliferation and the expression of numerous proteins involved in inflammation and the immune response. Many brain cells can produce cytokines, chemokines and other pro-inflammatory molecules in response to bacteria stimuli; as a consequence, polymorphonuclear cells are attracted and activated, and release large amounts of superoxide anion and nitric oxide, leading to peroxynitrite formation and oxidative stress. This cascade leads to lipid peroxidation, mitochondrial damage and blood-brain barrier breakdown, contributing to cellular injury during neuronal infection. Current evidence suggests that bacterial CNS infections can play a role in the etiopathogenesis of behavioral disorders by increasing pro-inflammatory cytokines and bacterial virulence factors. The aim of this review is to summarize the current knowledge of the relevant pathophysiologic steps in CNS infections.

Infectious etiologies of myelopathy.

Myelopathy refers to a spinal cord disorder that presents with motor and/or sensory deficits. Infectious agents that cause myelopathy do so by either direct infection of neural structures (e.g., polio), a parainfectious mechanism (with a presumed autoimmune pathogenesis), or as a result of involvement of structures adjoining the spinal cord, which may cause a compressive myelopathy. This review of infectious causes of myelopathy focuses on pathogens that are most relevant to clinicians in North America.

Hardware-related infections after deep brain stimulation surgery: review of incidence, severity and management in 212 single-center procedures in the first year after implantation.

BACKGROUND: Device-related infection is a common occurrence after deep brain stimulation (DBS) surgery, and may result in additional interventions and a loss of efficacy of therapy. This retrospective review aimed to evaluate the incidence, severity and management of device-related infections in 212 DBS procedures performed in our institute. METHODS: Data on 106 patients, in whom 212 DBS procedures were performed between 2001 and 2011 at our institute by a single neurosurgeon (M.P.), were reviewed to assess the incidence, severity, management and clinical characteristics of infections in the first year after the implantation of a DBS system. RESULTS: Infections occurred in 8.5% of patients and 4.2% of procedures. Of the nine infections, eight involved the neurostimulator and extensions, and one the whole system. The infections occurred 30.7 days after implantation: 7 within 30 days and 2 within 6 months. Infected and uninfected patients were comparable in terms of age, sex, indication for DBS implantation and neurostimulator location. In eight cases, the system components involved were removed and re-implanted after 3 months, while in one case the complete hardware was removed and not re-implanted. CONCLUSION: The overall incidence of postoperative infections after DBS system implantation was 4.2%; this rate decreased over time. All infections required further surgery. Correct and timely management of partial infections may result in successful salvage of part of the system.

Pathophysiology of septic encephalopathy--an unsolved puzzle.

The exact cellular and molecular mechanisms of sepsis-induced encephalopathy remain elusive. The breakdown of the blood-brain barrier (BBB) is considered a focal point in the development of sepsis-induced brain damage. Contributing factors for the compromise of the BBB include cytokines and chemokines, activation of the complement cascade, phagocyte-derived toxic mediators, and bacterial products. To date, we are far from fully understanding the neuropathology that develops as a secondary remote organ injury as a consequence of sepsis. However, recent studies suggest that bacterial proteins may readily cross the functional BBB and trigger an inflammatory response in the subarachnoid space, in absence of a bacterial invasion. A better understanding of the pathophysiological events leading to septic encephalopathy appears crucial to advance the clinical care for this vulnerable patient population.

Influence of Escherichia coli shiga toxin on the mammalian central nervous system.

In severe cases of the infectious disease by Shiga toxin-producing Escherichia coli (STEC), patients display renal dysfunction known as hemolytic uremic syndrome (HUS) and central nervous system (CNS) failure. Among those severe symptoms, patients with CNS dysfunction with HUS have a greater chance of getting severe sequelae and mortality than with HUS alone. Autopsy of the CNS shows mostly edema and hypoxic-ischemic changes, often with microhemorrhages. Magnetic resonance imaging (MRI) of brains of patients confirms hemorrhagic component involvement. This suggests the weakening of the blood-brain barrier (BBB) during the disease. Also, cerebrospinal fluid (CSF) analysis shows the weakening of the blood-CSF barrier. Although evidence of vascular involvement in CNS exists, the typical observation of microthrombosis in renal pathology is often absent in CNS. Importantly, there are people who develop CNS symptoms before the onset of HUS. This suggests direct involvement of Shiga toxin (Stx) in CNS disease which is in addition to renal involvement. The advantages of animal models are that Stx receptor expression in normal CNS tissue can be determined, and changes in histopathology, hematology, and serum and CSF contents can be analyzed at several different time points, which allow investigation of the nature of the disease. Importantly, in animal models with either STEC oral inoculation or purified Stx injection, paralysis of extremities is commonly observed. This shows the central role of Stx in CNS dysfunction in this disease. It is anticipated that precise mechanisms of Stx influence in the CNS will be delineated, and this information will lead to effective therapeutics in the near future.

Acute encephalopathy of Bacillus cereus mimicking Reye syndrome.

We present an 11-year-old boy diagnosed as having acute encephalopathy and liver failure with the underlying condition of a metabolic dysfunction. He developed convulsions and severe consciousness disturbance following gastroenteritis after the ingestion of some fried rice. He showed excessive elevation of transaminases, non-ketotic hypoglycemia and hyperammonemia, which were presumed to reflect a metabolic dysfunction of the mitochondrial beta-oxidation, and he exhibited severe brain edema throughout the 5th hospital day. He was subjected to mild hypothermia therapy for encephalopathy, and treated with high-dose methylprednisolone, cyclosporine and continuous hemodiafiltration for liver failure, systemic organ damage and hyperammonemia. The patient recovered with the sequela of just mild intelligence impairment. In this case, Bacillus cereus, producing emetic toxin cereulide, was detected in a gastric fluid specimen, a stool specimen and the fried rice. It was suggested that the cereulide had toxicity to mitochondria and induced a dysfunction of the beta-oxidation process. The patient was considered as having an acute encephalopathy mimicking Reye syndrome due to food poisoning caused by cereulide produced by B. cereus.

Alzheimer's disease and infection: do infectious agents contribute to progression of Alzheimer's disease?

Infection with several important pathogens could constitute risk factors for cognitive impairment, dementia, and Alzheimer's disease (AD) in particular. This review summarizes the data related to infectious agents that appear to have a relationship with AD. Infections with herpes simplex virus type 1, picornavirus, Borna disease virus, Chlamydia pneumoniae, Helicobacter pylori, and spirochete were reported to contribute to the pathophysiology of AD or to cognitive changes. Based on these reports, it may be hypothesized that central nervous system or systemic infections may contribute to the pathogenesis or pathophysiology of AD, and chronic infection with several pathogens should be considered a risk factor for sporadic AD. If this hypothesis holds true, early intervention against infection may delay or even prevent the future development of AD.

Overview of neurobrucellosis: a pooled analysis of 187 cases.

Central nervous system involvement is a serious complication of brucellosis; data found in the literature are generally restricted to case reports and case series. In this study we pooled the data from Turkish medical practice in order to gain a thorough understanding of the subject. A search of Turkish publications on chronic neurobrucellosis was made using both Turkish and international databases. A total of 35 publications were analyzed and 187 neurobrucellosis cases were evaluated. Headache, fever, sweating, weight loss, and back pain were the predominant symptoms, while meningeal irritation, confusion, hepatomegaly, hypoesthesia, and splenomegaly were the most frequent findings. The major complications in patients were cranial nerve involvement, polyneuropathy/radiculopathy, depression, paraplegia, stroke, and abscess formation. Antibiotics were used in different combinations and over different intervals. The duration of antibiotic therapy reported ranged from 2 to 15 months (median 5 months). The mortality was 0.5% with suitable antibiotics. Neurobrucellosis may mimic various pathologies. For this reason, a thorough evaluation of the patient with probable disease is crucial for an accurate diagnosis and proper management of the disease.

Pathogenesis of septic encephalopathy.

PURPOSE OF REVIEW: Septic encephalopathy is a frequent complication in severe sepsis, the pathogenesis and mechanisms of which are not fully understood. Here, we review recent advances in our understanding of septic encephalopathy, from molecular mechanisms to behavioral alterations, from diagnostic tools to potential therapeutic agents. RECENT FINDINGS: Recent insights into septic encephalopathy include: microcirculatory failure precedes changes in evoked potential responses; blood-brain barrier alteration is prevented by reducing intercellular adhesion molecule expression and pericyte detachment; reducing infiltration of CD68 macrophages and inhibiting complement activation alleviates neuroinflammation in septic encephalopathy; and reducing mitochondrial dysfunction and inducible nitric oxide synthase expression can restore altered brain function. In addition, other factors such as the circulating levels of growth hormone are independent predictors for mortality and correlate with the severity of sepsis. Similar to humans, septic rats present recognition memory impairment and depressive-like symptoms but not anxiety-like behavior and will serve as efficient models to study the underlying mechanisms of septic encephalopathy. SUMMARY: Septic encephalopathy is a dynamic disease caused by a complex network of systems and pathways going awry. More insights into the pathogenesis of septic encephalopathy are expected to lead to new cellular and molecular targets, which in turn will permit design of specific septic encephalopathy-alleviating drugs and prevent its negative influence on survival.

NOD2 plays an important role in the inflammatory responses of microglia and astrocytes to bacterial CNS pathogens.

While glial cells are recognized for their roles in maintaining neuronal function, there is growing appreciation that resident central nervous system (CNS) cells initiate and/or augment inflammation following trauma or infection. We have recently demonstrated that microglia and astrocytes constitutively express nucleotide-binding oligomerization domain-2 (NOD2), a member of the novel nucleotide-binding domain leucine-rich repeat region containing a family of proteins (NLR) that functions as an intracellular receptor for a minimal motif present in all bacterial peptidoglycans. In this study, we have confirmed the functional nature of NOD2 expression in astrocytes and microglia and begun to determine the relative contribution that this NLR makes in inflammatory CNS responses to clinically relevant bacterial pathogens. We demonstrate the increased association of NOD2 with its downstream effector molecule, Rip2 kinase, in primary cultures of murine microglia and astrocytes following exposure to bacterial antigens. We show that this cytosolic receptor underlies the ability of muramyl dipeptide to augment the production of inflammatory cytokines by glia following exposure to specific ligands for disparate Toll-like receptor homologues. In addition, we demonstrate that NOD2 is an important component in the in vitro inflammatory responses of resident glia to N. meningitidis and B. burgdorferi antigens. Finally, we have established that NOD2 is required, at least in part, for the astrogliosis, demyelination, behavioral changes, and elevated inflammatory cytokine levels observed following in vivo infection with these pathogens. As such, we have identified NOD2 as an important component in the generation of damaging CNS inflammation following bacterial infection.

alpha-Phenyl-n-tert-butyl-nitrone attenuates lipopolysaccharide-induced brain injury and improves neurological reflexes and early sensorimotor behavioral performance in juvenile rats.

Our previous study showed that treatment with alpha-phenyl-n-tert-butyl-nitrone (PBN) after exposure to lipopolysaccharide (LPS) reduced LPS-induced white matter injury in the neonatal rat brain. The object of the current study was to further examine whether PBN has long-lasting protective effects and ameliorates LPS-induced neurological dysfunction. Intracerebral (i.c.) injection of LPS (1 mg/kg) was performed in postnatal day (P) 5 Sprague Dawley rat pups and PBN (100 mg/kg) or saline was administered intraperitoneally 5 min after LPS injection. The control rats were injected (i.c.) with sterile saline. Neurobehavioral tests were carried out from P3 to P21, and brain injury was examined after these tests. LPS exposure resulted in severe brain damage, including enlargement of ventricles bilaterally, loss of mature oligodendrocytes, impaired myelination as indicated by the decrease in myelin basic protein immunostaining, and alterations in dendritic processes in the cortical gray matter of the parietal cortex. Electron microscopic examination showed that LPS exposure caused impaired myelination as indicated by the disintegrated myelin sheaths in the juvenile rat brain. LPS administration also significantly affected neurobehavioral functions such as performance in righting reflex, wire hanging maneuver, cliff avoidance, negative geotaxis, vibrissa-elicited forelimb-placing test, beam walking, and gait test. Treatment with PBN, a free radical scavenger and antioxidant, provided protection against LPS-induced brain injury and associated neurological dysfunction in juvenile rats, suggesting that antioxidation might be an effective approach for therapeutic treatment of neonatal brain injury induced by infection/inflammation.

Risk factors for infections related to external ventricular drainage.

BACKGROUND: External ventricular drainage (EVD) is frequently used in neurosurgery for cerebrospinal fluid (CSF) drainage in patients with raised intracranial pressure. The major complication of this procedure is an EVD-related infection, i.e., meningitis or ventriculitis. The purpose of the present retrospective single centre study is to assess the possible causes of these infections. PATIENTS AND METHODS: Two hundred and twenty-eight patients were included in the period from January 1993 until April 2005. Patient and disease demographics, as well as EVD data, and the occurrence of infection were reviewed, compared, and included in a risk-analysis study. RESULTS: The population's mean age was 56 +/- 15 years and the sexes were equally distributed. Most frequently, the indication for EVD was hydrocephalus due to intraventricular haemorrhage (48.2%). An infection was documented in 23.2% of all patients. Duration of EVD drainage appeared to be a risk factor for infection (>11 days: OR 4.1; 95% CI 1.8-9.2, p = 0.001). CSF sampling frequency was also a significant risk-factor (no sampling: OR 0.2, 95% CI 0.2-0.5, p = 0.003). CONCLUSIONS: We found a relatively high percentage of EVD-related infections. After multivariate analysis there appears to be a relation with duration of drainage and frequent CSF sampling. As a result, a new EVD protocol is proposed in our institution that we believe will decrease the number of EVD-related infections to a minimum.

Activated protein C reduces endotoxin-induced white matter injury in the developing rat brain.

Periventricular leukomalacia (PVL), the dominant form of brain injury in premature infants, is characterized by white matter injury (WMI) and is associated with cerebral palsy. The pathogenesis of PVL is complex and likely involves ischemia/reperfusion, free radical formation, excitotoxicity, impaired regulation of cerebral blood flow, a procoagulant state, and inflammatory mechanisms associated with maternal and/or fetal infection. Using an established animal model of human PVL, we investigated whether activated protein C (APC), an anti-coagulant factor with anti-inflammatory, anti-apoptotic, anti-oxidant, and cytoprotective activities, could reduce endotoxin-induced WMI in the developing rat brain. Intraperitoneal injections of lipopolysaccharide (LPS) (0.5 mg/kg body weight) were given at embryonic days 18 (E18) and 19 (E19) to pregnant Sprague-Dawley rats; control rats were injected with sterile saline. A single intravenous injection of recombinant human (rh) APC (0.2 mg /kg body weight) was given to pregnant rats following the second LPS dose on embryonic day 19 (E19). Reduced cell death in white matter and hypomyelination were shown on TUNEL and myelin basic protein (MBP) staining, respectively, on late postnatal days (P7) in APC-treated groups. There were significantly fewer TUNEL+nuclei in the periventricular WM in the APC+LPS group than in the untreated LPS group. Compared to the APC+LPS and control group, MBP expression was weak in the LPS group on P7, indicating endotoxin-induced hypomyelination in the developing rat brain. APC attenuated the LPS-induced protein expression of inflammatory cytokines, tumor necrosis factor-alpha, and interleukin-6, as evaluated by ELISA in neonatal rat brains. A single intraperitoneal injection of rhAPC (0.2 mg/kg body weight) to neonatal rats on P1 also had similar protective and anti-inflammatory effects against maternally administered LPS. Collectively, these data support the hypothesis that APC may provide protection against an endotoxin-evoked inflammatory response and WMI in the developing rat brain. Moreover, our results suggest that the possible use of APC in treatment of preterm infants and pregnant women with maternal or placental infection may minimize the risk of PVL and cerebral palsy.

Glycoconjugates: roles in neural diseases caused by exogenous pathogens.

Numerous reports indicate that lipid or protein associated carbohydrates are essential for infection of cells by various viruses, bacteria, or bacterial toxins, some of which affect the nervous system. Examples of such pathogens include tetanus and botulinum neurotoxin, Shiga and Shiga-like toxins, Borrelia burgdorferi, Mycobacterium leprae, and human immunodeficiency virus. This review discusses evidence indicating that carbohydrates are essential for these pathogens to induce their deleterious effects, the putative function of the carbohydrates, and how this knowledge might be used to combat the effects of the pathogen.