Neural–immune interactions in disorders of sleep-wakefulness organization

The Interplay Between Neuroinfections, the Immune System and Neurological Disorders: A Focus on Africa

Neurological disorders related to neuroinfections are highly prevalent in Sub-Saharan Africa (SSA), constituting a major cause of disability and economic burden for patients and society. These include epilepsy, dementia, motor neuron diseases, headache disorders, sleep disorders, and peripheral neuropathy. The highest prevalence of human immunodeficiency virus (HIV) is in SSA. Consequently, there is a high prevalence of neurological disorders associated with HIV infection such as HIV-associated neurocognitive disorders, motor disorders, chronic headaches, and peripheral neuropathy in the region. The pathogenesis of these neurological disorders involves the direct role of the virus, some antiretroviral treatments, and the dysregulated immune system. Furthermore, the high prevalence of epilepsy in SSA (mainly due to perinatal causes) is exacerbated by infections such as toxoplasmosis, neurocysticercosis, onchocerciasis, malaria, bacterial meningitis, tuberculosis, and the immune reactions they elicit. Sleep disorders are another common problem in the region and have been associated with infectious diseases such as human African trypanosomiasis and HIV and involve the activation of the immune system. While most headache disorders are due to benign primary headaches, some secondary headaches are caused by infections (meningitis, encephalitis, brain abscess). HIV and neurosyphilis, both common in SSA, can trigger long-standing immune activation in the central nervous system (CNS) potentially resulting in dementia. Despite the progress achieved in preventing diseases from the poliovirus and retroviruses, these microbes may cause motor neuron diseases in SSA. The immune mechanisms involved in these neurological disorders include increased cytokine levels, immune cells infiltration into the CNS, and autoantibodies. This review focuses on the major neurological disorders relevant to Africa and neuroinfections highly prevalent in SSA, describes the interplay between neuroinfections, immune system, neuroinflammation, and neurological disorders, and how understanding this can be exploited for the development of novel diagnostics and therapeutics for improved patient care.

Sleeping Sickness: A Tale of Two Clocks

Sleeping sickness is caused by a eukaryotic unicellular parasite known to infect wild animals, cattle, and humans. It causes a fatal disease that disrupts many rhythmic physiological processes, including daily rhythms of hormonal secretion, temperature regulation, and sleep, all of which are under circadian (24-h) control. In this review, we summarize research on sleeping sickness parasite biology and the impact it has on host health. We also consider the possible evolutionary advantages of sleep and circadian deregulation for the parasite.

Alterations of orexinergic and melanin-concentrating hormone neurons in experimental sleeping sickness

Human African trypanosomiasis or sleeping sickness is a severe, neglected tropical disease caused by the extracellular parasite Trypanosoma brucei. The disease, which leads to chronic neuroinflammation, is characterized by sleep and wake disturbances, documented also in rodent models. In rats and mice infected with Trypanosoma brucei brucei, we here tested the hypothesis that the disease could target neurons of the lateral hypothalamus (LH) containing orexin (OX)-A or melanin-concentrating hormone (MCH), implicated in sleep/wake regulation. In the cerebrospinal fluid of infected rats, the OX-A level was significantly decreased early after parasite neuroinvasion, and returned to the control level at an advanced disease stage. The number of immunohistochemically characterized OX-A and MCH neurons decreased significantly in infected rats during disease progression and in infected mice at an advanced disease stage. A marked reduction of the complexity of dendritic arborizations of OX-A neurons was documented in infected mice. The evaluation of NeuN-immunoreactive neurons did not reveal significant neuronal loss in the LH of infected mice, thus suggesting a potential selective vulnerability of OX-A and MCH neurons. Immunophenotyping and quantitative analysis showed in infected mice marked activation of microglial cells surrounding OX-A neurons. Day/night oscillation of c-Fos baseline expression was used as marker of OX-A neuron activity in mice. In control animals Fos was expressed in a higher proportion of OX-A neurons in the night (activity) phase than in the day (rest) phase. Interestingly, in infected mice the diurnal spontaneous Fos oscillation was reversed, with a proportion of OX-A/Fos neurons significantly higher at daytime than at nighttime. Altogether the findings reveal a progressive decrease of OX-A and MCH neurons and dysregulation of OX-A neuron diurnal activity in rodent models of sleeping sickness. The data point to the involvement of these peptidergic neurons in the pathogenesis of sleep/wake alterations in the disease and to their vulnerability to inflammatory signaling.

Suprachiasmatic astrocytes modulate the circadian clock in response to TNF-α

The immune and the circadian systems interact in a bidirectional fashion. The master circadian oscillator, located in the suprachiasmatic nuclei (SCN) of the hypothalamus, responds to peripheral and local immune stimuli, such as proinflammatory cytokines and bacterial endotoxin. Astrocytes exert several immune functions in the CNS, and there is growing evidence that points toward a role of these cells in the regulation of circadian rhythms. The aim of this work was to assess the response of SCN astrocytes to immune stimuli, particularly to the proinflammatory cytokine TNF-α. TNF-α applied to cultures of SCN astrocytes from Per2(luc) knockin mice altered both the phase and amplitude of PER2 expression rhythms, in a phase-dependent manner. Furthermore, conditioned media from SCN astrocyte cultures transiently challenged with TNF-α induced an increase in Per1 expression in NIH 3T3 cells, which was blocked by TNF-α antagonism. In addition, these conditioned media could induce phase shifts in SCN PER2 rhythms and, when administered intracerebroventricularly, induced phase delays in behavioral circadian rhythms and SCN activation in control mice, but not in TNFR-1 mutants. In summary, our results show that TNF-α modulates the molecular clock of SCN astrocytes in vitro, and also that, in response to this molecule, SCN astrocytes can modulate clock gene expression in other cells and tissues, and induce phase shifts in a circadian behavioral output in vivo. These findings suggest a role for astroglial cells in the alteration of circadian timing by immune activation.

The sleep-immunity relationship

Research models show a strong interrelationship between sleep quality and immune function. The proinflammatory cytokines, interleukin-1, interleukin-6, and tumor necrosis factor α are classified as official sleep-regulatory substances. However, sleep-promoting properties are also possessed by several other immune and proinflammatory cellular classes. This article reviews the current physiologic evidence for the prominent somnogenic and sleep-regulatory properties inherent to these immune substances. Clinical examples of this relationship are discussed from the perspective of infectious and primarily immune-related conditions associated with significant sleep disruption and from the perspective of immune dysregulation associated with several primary sleep disorders.

Human African trypanosomiasis

Human African trypanosomiasis or sleeping sickness is a neglected tropical disease that affects populations in sub-Saharan Africa. The disease is caused by infection with the gambiense and rhodesiense subspecies of the extracellular parasite Trypanosoma brucei, and is transmitted to humans by bites of infected tsetse flies. The disease evolves in two stages, the hemolymphatic and meningoencephalitic stages, the latter being defined by central nervous system infection after trypanosomal traversal of the blood-brain barrier. African trypanosomiasis, which leads to severe neuroinflammation, is fatal without treatment, but the available drugs are toxic and complicated to administer. The choice of medication is determined by the infecting parasite subspecies and disease stage. Clinical features include a constellation of nonspecific symptoms and signs with evolving neurological and psychiatric alterations and characteristic sleep-wake disturbances. Because of the clinical profile variability and insidiously progressive central nervous system involvement, disease staging is currently based on cerebrospinal fluid examination, which is usually performed after the finding of trypanosomes in blood or other body fluids. No vaccine being available, control of human African trypanosomiasis relies on diagnosis and treatment of infected patients, assisted by vector control. Better diagnostic tools and safer, easy to use drugs are needed to facilitate elimination of the disease.

Parasite-induced alterations of sensorimotor pathways in gammarids: collateral damage of neuroinflammation?

Some larval helminths alter the behavior of their intermediate hosts in ways that favor the predation of infected hosts, thus enhancing trophic transmission. Gammarids (Crustacea: Amphipoda) offer unique advantages for the study of the proximate factors mediating parasite-induced behavioral changes. Indeed, amphipods infected by distantly related worms (acanthocephalans, cestodes and trematodes) encysted in different microhabitats within their hosts (hemocoel, brain) present comparable, chronic, behavioral pathologies. In order to evaluate the potential connection between behavioral disturbances and immune responses in parasitized gammarids, this Review surveys the literature bearing on sensorimotor pathway dysfunctions in infected hosts, on the involvement of the neuromodulator serotonin in altered responses to environmental stimuli, and on systemic and neural innate immunity in arthropods. Hemocyte concentration and phenoloxidase activity associated with melanotic encapsulation are depressed in acanthocephalan-manipulated gammarids. However, other components of the arsenal deployed by crustaceans against pathogens have not yet been investigated in helminth-infected gammarids. Members of the Toll family of receptors, cytokines such as tumor necrosis factors (TNFs), and the free radical nitric oxide are all implicated in neuroimmune responses in crustaceans. Across animal phyla, these molecules and their neuroinflammatory signaling pathways are touted for their dual beneficial and deleterious properties. Thus, it is argued that neuroinflammation might mediate the biochemical events upstream of the serotonergic dysfunction observed in manipulated gammarids – a parsimonious hypothesis that could explain the common behavioral pathology induced by distantly related parasites, both hemocoelian and cerebral.

Post-marketing assessment of neuropsychiatric adverse events in influenza patients treated with oseltamivir: an updated review

A 2008 review by our group concluded that the risk of neuropsychiatric adverse events (NPAEs) in influenza patients was not increased by oseltamivir exposure, and did not identify any mechanism by which oseltamivir or its metabolites could cause or worsen such events. The current article reviews new information on this topic. Between September 16, 2007 and May 15, 2010, 1,805 spontaneously-reported NPAEs were identified in 1,330 patients receiving oseltamivir: 767 (42.5%) from Japan, 296 (16.4%) from the USA, and 742 (41.1%) from other countries. NPAEs were more common in children: 1,072 (59.4%) events were in those aged ≤16 years. NPAEs often occurred within 48 h of treatment initiation (953 events; 52.8%). Nearly half of the events were serious in nature (838; 46.4%). The three largest categories of events were abnormal behavior (457 events, 25.3%), miscellaneous psychiatric events (370; 20.5%), and delusions/perceptual disturbances (316 events, 17.5%). A total of 1,545 events (85.6%) in eight different categories were considered to be delirium or delirium-like. Twenty-eight suicide-related events were reported. A US healthcare claims database analysis showed that the risk of NPAEs in 7,798 oseltamivir-treated patients was no higher than that in 10,411 patients not on antivirals, but a study on oseltamivir and abnormal behavior in Japan was less conclusive. NPAE frequency in oseltamivir-exposed Japanese and Taiwanese children with influenza was the same as in unexposed children. New analysis of the UK General Practice Research Database showed that the relative adjusted risk of NPAEs in influenza patients was 2.18-times higher than in the general population. Other epidemiology studies report frequent occurrence of encephalitis and similar disorders in influenza patients independently of oseltamivir exposure. The new data support the findings of the original assessment. Evidence suggests that influenza-related encephalopathies are caused by influenza-induced inflammatory responses, but more work is needed to confirm the underlying mechanisms.

Actigraphy in human African trypanosomiasis as a tool for objective clinical evaluation and monitoring: a pilot study

Background

Human African trypanosomiasis (HAT) or sleeping sickness leads to a complex neuropsychiatric syndrome with characteristic sleep alterations. Current division into a first, hemolymphatic stage and second, meningoencephalitic stage is primarily based on the detection of white blood cells and/or trypanosomes in the cerebrospinal fluid. The validity of this criterion is, however, debated, and novel laboratory biomarkers are under study. Objective clinical HAT evaluation and monitoring is therefore needed. Polysomnography has effectively documented sleep-wake disturbances during HAT, but could be difficult to apply as routine technology in field work. The non-invasive, cost-effective technique of actigraphy has been widely validated as a tool for the ambulatory evaluation of sleep disturbances. In this pilot study, actigraphy was applied to the clinical assessment of HAT patients.

Methods/Principal Findings

Actigraphy was recorded in patients infected by Trypanosoma brucei gambiense, and age- and sex-matched control subjects. Simultaneous nocturnal polysomnography was also performed in the patients. Nine patients, including one child, were analyzed at admission and two of them also during specific treatment. Parameters, analyzed with user-friendly software, included sleep time evaluated from rest-activity signals, rest-activity rhythm waveform and characteristics. The findings showed sleep-wake alterations of various degrees of severity, which in some patients did not parallel white blood cell counts in the cerebrospinal fluid. Actigraphic recording also showed improvement of the analyzed parameters after treatment initiation. Nocturnal polysomnography showed alterations of sleep time closely corresponding to those derived from actigraphy.

Conclusions/Significance

The data indicate that actigraphy can be an interesting tool for HAT evaluation, providing valuable clinical information through simple technology, well suited also for long-term follow-up. Actigraphy could therefore objectively contribute to the clinical assessment of HAT patients. This method could be incorporated into a clinical scoring system adapted to HAT to be used in the evaluation of novel treatments and laboratory biomarkers.

The clinical picture of the parasitic disease human African trypanosomiasis (HAT, also called sleeping sickness) is dominated by sleep alterations. We here used actigraphy to evaluate patients affected by the Gambiense form of HAT. Actigraphy is based on the use of battery-run, wrist-worn devices similar to watches, widely used in middle-high income countries for ambulatory monitoring of sleep disturbances. This pilot study was motivated by the fact that the use of polysomnography, which is the gold standard technology for the evaluation of sleep disorders and has greatly contributed to the objective identification of signs of disease in HAT, faces tangible challenges in resource-limited countries where the disease is endemic. We here show that actigraphy provides objective data on the severity of sleep-wake disturbances that characterize HAT. This technique, which does not disturb the patient's routine activities and can be applied at home, could therefore represent an interesting, non-invasive tool for objective HAT clinical assessment and long-term monitoring under field conditions. The use of this method could provide an adjunct marker of HAT severity and for treatment follow-up, or be evaluated in combination with other disease biomarkers in body fluids that are currently under investigation in many laboratories.

Evidence for neuroinflammatory and microglial changes in the cerebral response to sleep loss

STUDY OBJECTIVES

Sleep loss has pro-inflammatory effects, but the roles of specific cell populations in mediating these effects have not been delineated. We assessed the modulation of the electroencephalographic and molecular responses to sleep deprivation (S-DEP) by minocycline, a compound that attenuates microglial activation occurring in association with neuroinflammatory events.

DESIGN

Laboratory rodents were subjected to assessment of sleep and wake in baseline and sleep deprived conditions.

PARTICIPANTS

Adult male CD-1 mice (30-35 g) subjected to telemetric electroencephalography.

INTERVENTIONS

Minocycline was administered daily. Mice were subjected to baseline data collection on the first day of minocycline administration and, on subsequent days, 2 S-DEP sessions, 1 and 3 h in duration, followed by recovery sleep. Following EEG studies, mice were euthanized either at the end of a 3 h S-DEP or as time-of day controls for sampling of brain messenger RNAs. Gene expression was measured by real-time polymerase chain reaction.

MEASUREMENTS AND RESULTS

Minocycline-treated mice exhibited a reduction in time spent asleep, relative to saline-treated mice, in the 3-h interval immediately after administration. S-DEP resulted in an increase in EEG slow wave activity relative to baseline in saline-treated mice. This response to S-DEP was abolished in animals subjected to chronic minocycline administration. S-DEP suppressed the expression of the microglial-specific transcript cd11b and the neuroinflammation marker peripheral benzodiazepine receptor, in the brain at the mRNA level. Minocycline attenuated the elevation of c-fos expression by S-DEP. Brain levels of pro-inflammatory cytokine mRNAs interleukin-1β (il-1β), interleukin-6 (il-6), and tumor necrosis factor-α (tnfα) were unaffected by S-DEP, but were elevated in minocycline-treated mice relative to saline-treated mice.

CONCLUSIONS

The anti-neuroinflammatory agent minocycline prevents either the buildup or expression of sleep need in rodents. The molecular mechanism underlying this effect is not known, but it is not mediated by suppression of il-1β, il-6, and tnfα at the transcript level.

Glial transcripts and immune-challenged glia in the suprachiasmatic nucleus of young and aged mice

Biological rhythms are frequently disturbed with advancing age, and aging-related changes of glia in the hypothalamic suprachiasmatic nucleus (SCN), the master circadian pacemaker, require special attention. In particular, astrocytes contribute to SCN function, and aging is associated with increased inflammatory activity in the brain, in which microglia could be especially implicated. On this basis, we investigated in the SCN of young and old mice glial transcripts and cell features, and the glial cell response to a central inflammatory challenge. Quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) was used to analyze the expression of mRNAs encoding the astrocytic glial fibrillary acidic protein and the microglial antigen CD11b. Both these transcripts, here investigated in the SCN for the first time, were significantly increased in the old SCN. Glial cell phenotyping with immunohistochemistry revealed hypertrophic and intensely stained astrocytes and microglia in the aged SCN. In both age groups, microglia were scattered throughout the SCN and astrocytes were prominent in the ventral portion, where retinal fibers are densest; in the aged SCN, astrocytes were also numerous in the dorsal portion. After intracerebroventricular injections of a mixture of interferon-gamma and tumor necrosis factor-alpha, or phosphate-buffered saline as control, immunolabeling was evaluated with stereological cell counts and confocal microscopy. Phenotypic features of astrocyte and microglia activation in response to cytokine injections were markedly enhanced in the aged SCN. Subregional variations in glial cell density were also documented in the aged compared to the young SCN. Altogether, the findings show increases in the expression of glial transcripts and hypertrophy of astrocytes and microglia in the aged SCN, as well as age-dependent variation in the responses of immune-challenged SCN glia. The data thus point out an involvement of glia in aging-related changes of the biological clock.

A direct cross-talk between interferon-gamma and sonic hedgehog signaling that leads to the proliferation of neuronal precursor cells

Interferon-gamma (IFN-gamma) is a pleiotropic cytokine that is critical for innate and adaptive immunity. Recent evidence suggests a connection between IFN-gamma signaling and the sonic hedgehog (Shh) pathway in the developing brain with CNS-targeted expression of IFN-gamma transgene in mice. To determine the relationship between these distinct pathways, we have found that IFN-gamma induces a rapid Shh transcription in cultured primary granular neuron precursor (GNP) cells. The transcriptional induction of Shh by IFN-gamma is resistant to protein synthesis inhibition. Chromatin immunoprecipitation (ChIP) analysis reveals a direct binding of signal transducer and activator of transcription (STAT) 1 to the Shh promoter. Functional analyses, including dual immunofluorescent labeling with 5-bromodeoxyuridine (BrdU) incorporation indicate that IFN-gamma treatment leads to significant GNP proliferation. This mitogenic effect of IFN-gamma is blocked by inhibition of Shh signaling. Therefore, Shh is an IFN-gamma target gene and is responsible for IFN-gamma-induced GNP proliferation. This previously unrecognized cross-talk between IFN-gamma and Shh highlights a potential importance of this immune mediator in the pathogenesis of human developmental and psychiatric disorders.

Trypanosomiasis and the brain

Neurological involvement following trypanosome infection has been recognised for over a century. However, there are still many unanswered questions concerning the mechanisms used by the parasite to gain entry to the CNS and the pathogenesis of the resulting neuroinflammatory reaction. There is a paucity of material from human cases of the disease therefore the majority of current research relies on the use of animal models of trypanosome infection. This review reports contemporary knowledge, from both animal models and human samples, regarding parasite invasion of the CNS and the neuropathological changes that accompany trypanosome infection and disease progression. The effects of trypanosomes on the blood-brain barrier are discussed and possible key molecules in parasite penetration of the barrier highlighted. Changes in the balance of CNS cytokines and chemokines are also described. The article closes by summarising the effects of trypanosome infection on the circadian sleep-wake cycle, and sleep structure, in relation to neuroinflammation and parasite location within the CNS. Although a great deal of progress has been made in recent years, the advent and application of sophisticated analysis techniques, to decipher the complexities of HAT pathogenesis, herald an exciting and rewarding period for advances in trypanosome research.

Neurological practice in the Centuriae of Amatus Lusitanus

Amatus Lusitanus, a Portuguese Jew who gained notoriety as one of the most famous physician-scientists in XVI century Europe published collections of case histories--Centuriae--describing his most interesting patients. The Renaissance was a transitional period for medicine and the neurological sciences, which if still dominated by the humoral and ventricular-pneumatic doctrines, were taking the first steps away from them. We analysed the Centuriae for neurological and psychiatric cases in order to appreciate neurological practice in this period and selected one hundred which fit those diagnostic categories. The Centuriae contain cases of CNS infection and trauma, epilepsy, apoplexy and depressed states of consciousness (including coma, carus, lethargy and cataphora), headache and vertigo, tumours, cranial nerve paralysis, melancholy, anatomical and physiological observations, as well as a short treatise on cranial traumatology. The most relevant observations point to the importance of the brain parenchyma in cognition, provide original observations of epidemic lethargic encephalitis, describe the neurological consequences of syphilis, including the first description of tertiary syphilis, attempt to distinguish mania from melancholy, extensively describe medical and surgical treatment of cranial trauma, document the first use of anatomical dissection to study a case of brain abscess, negate Galen's view of the optic nerves as hollow, and describe the use of new drugs such as guaiac wood for the treatment of headache. The Centuriae not only provide insight into neurological clinical practice in the XVI century, but also emphasize the role of Amatus Lusitanus as an important precursor of this discipline, given his numerous original observations.

The continuing problem of human African trypanosomiasis (sleeping sickness)

Human African trypanosomiasis, also known as sleeping sickness, is a neglected disease, and it continues to pose a major threat to 60 million people in 36 countries in sub-Saharan Africa. Transmitted by the bite of the tsetse fly, the disease is caused by protozoan parasites of the genus Trypanosoma and comes in two types: East African human African trypanosomiasis caused by Trypanosoma brucei rhodesiense and the West African form caused by Trypanosoma brucei gambiense. There is an early or hemolymphatic stage and a late or encephalitic stage, when the parasites cross the blood-brain barrier to invade the central nervous system. Two critical current issues are disease staging and drug therapy, especially for late-stage disease. Lumbar puncture to analyze cerebrospinal fluid will remain the only method of disease staging until reliable noninvasive methods are developed, but there is no widespread consensus as to what exactly defines biologically central nervous system disease or what specific cerebrospinal fluid findings should justify drug therapy for late-stage involvement. All four main drugs used for human African trypanosomiasis are toxic, and melarsoprol, the only drug that is effective for both types of central nervous system disease, is so toxic that it kills 5% of patients who receive it. Eflornithine, alone or combined with nifurtimox, is being used increasingly as first-line therapy for gambiense disease. There is a pressing need for an effective, safe oral drug for both stages of the disease, but this will require a significant increase in investment for new drug discovery from Western governments and the pharmaceutical industry.

Neuroimmunology of the circadian clock

Circadian timekeeping is a ubiquitous feature of all eukaryotes which allows for the imposition of a biologically appropriate temporal architecture on an animal's physiology, behavior and metabolism. There is growing evidence that in mammals the processes of circadian timing are under the influence of the immune system. Such a role for the neuroimmune regulation of the circadian clock has inferences for phenomena such as sickness behavior. Conversely, there is also accumulating evidence for a circadian influence on immune function, raising the likelihood that there is a bidirectional communication between the circadian and immune systems. In this review, we examine the evidence for these interactions, including circadian rhythmicity in models of disease and immune challenge, distribution of cytokines and their receptors in the suprachiasmatic nucleus of the hypothalamus, the site of the master circadian pacemaker, and the evidence for endogenous circadian timekeeping in immune cells.