1,721,050 research outputs found
The sickness behaviour and CNS inflammatory mediator profile induced by systemic challenge of mice with synthetic double-stranded RNA (poly I:C)
No full textPoly inosinic:poly cytidylic acid (poly I:C) is a synthetic double-stranded RNA and is a ligand for the Toll like receptor-3. This receptor is involved in the innate immune response to viral infection and poly I:C has been used to mimic the acute phase of a viral infection. The effects of TLR3 activation on brain function have not been widely studied. In the current study we investigate the spectrum of sickness behavioural changes induced by poly I:C in C57BL/6 mice and the CNS expression of inflammatory mediators that may underlie this. Poly I:C, at doses of 2, 6 and 12 mg/kg, induced a dose–responsive sickness behaviour, decreasing locomotor activity, burrowing and body weight, and caused a mild hyperthermia at 6 h. The 12 mg/kg dose caused significant hypothermia at later times. The Remo400 remote Telemetry system proved a sensitive measure of this biphasic temperature response. The behavioural responses to poly I:C were not significantly blunted upon a second poly I:C challenge either 1 or 3 weeks later. Plasma concentrations of IL-6, TNF-? and IFN-? were markedly elevated and IL-1? was also detectable. Cytokine synthesis within the CNS, as determined by quantitative PCR, was dominated by IL-6, with lesser inductions of IL-1?, TNF-? and IFN-? and there was a clear activation of cyclooxygenase-2 at the brain endothelium. These findings demonstrate clear CNS effects of peripheral TLR3 stimulation and will be useful in studying aspects of the effects of systemic viral infection on brain function in both normal and pathological situations
Macrophages in the cochlea; an immunological link between risk factors and progressive hearing loss
No full textMacrophages are abundant in the cochlea; however, their role in hearing loss is not well understood. Insults to the cochlea, such as noise or insertion of a cochlear implant, cause an inflammatory response, which includes activation of tissue-resident macrophages. Activation is characterized by changes in macrophage morphology, mediator expression, and distribution. Evidence from other organs shows activated macrophages can become primed, whereby subsequent insults cause an elevated inflammatory response. Primed macrophages in brain pathologies respond to circulating inflammatory mediators by disproportionate synthesis of inflammatory mediators. This signaling occurs behind an intact blood–brain barrier, similar to the blood-labyrinth barrier in the cochlea. Local tissue damage can occur as the result of mediator release by activated macrophages. Damage is typically localized; however, if it is to structures with limited ability to repair, such as neurons or hair cells within the cochlea, it is feasible that this contributes to the progressive loss of function seen in hearing loss. We propose that macrophages in the cochlea link risk factors and hearing loss. Injury to the cochlea causes local macrophage activation that typically resolves. However, in susceptible individuals, some macrophages enter a primed state. Once primed, these macrophages can be further activated, as a consequence of circulating inflammatory molecules associated with common co-morbidities. Hypothetically, this would lead to further cochlear damage and loss of hearing. We review the evidence for the role of tissue-resident macrophages in the cochlea and propose that cochlear macrophages contribute to the trajectory of hearing loss and warrant further study
Maternal low protein diet during oocyte maturation causes increased systolic blood pressure and abnormal behaviour in the mouse [In abstracts special issue]
No full textUnaltered SNARE complex formation in an in vivo model of prion disease
No full textThe ME7 model of prion disease is a chronic slowly evolving model of neurodegeneration in which cell death is preceded by synaptic dysfunction. Previous studies in cell culture show that accumulation of misfolded prion inhibits the formation of the SNARE complexes involving synaptobrevin, syntaxin and SNAP-25 that play an essential role in neurotransmitter release. Such observations suggest that similar phenomenon may contribute to synaptic dysfunction observed in vivo. We have thus used detergent extraction of hippocampal tissue to investigate the status of SNARE complexes in the ME7 model. In the presence of increasing PrPSc deposition we failed to see a change in the amount of SNARE complexes directly extracted into SDS and resolved by SDS-PAGE. Conversely pre-extraction in Triton X-100, a treatment that promotes SNARE complexes ex vivo, demonstrated a modest reduction in hippocampal SNARE complexes when homogenates were made from tissue at late stage disease. This suggests that accumulated PrPSc, or perhaps fibrillar complexes formed of prion only inhibit SNARE complexes that are formed ex vivo following biochemical extraction. Thus the accumulation of PrPSc although deleterious to synaptic function in vivo, does not exert its synaptic effects by disrupting the formation of SNARE complexes that are core to transmitter releas
Central and systemic endotoxin challenges exacerbate the local inflammatory response and increase neuronal death during chronic neurodegeneration
No full textThe contribution of inflammation to the progression of eurodegenerative diseases such as Alzheimer’s, Parkinson’s, and prion diseases is poorly understood. Brain inflammation in animal models of these diseases is dominated by chronic microglial activation with minimal proinflammatory cytokine expression. However, these inflammatory cells are “primed” to produce exaggerated inflammatory responses to subsequent lipopolysaccharide (LPS) challenges. We show that, using the ME7 model of prion disease, intracerebral challenge with LPS results in dramatic interleukin-1 (IL-1) expression, neutrophil infiltration, and inducible nitric oxide synthase expression in the brain parenchyma of prion-diseased mice compared with the same challenge in normal mice. Systemic inflammation evoked by LPS also
produced greater increases in proinflammatory cytokines, pentraxin 3, and inducible nitric oxide synthase transcription in priondiseased mice than in control mice and induced microglial expression of IL-1. These systemic challenges also increased neuronal apoptosis in the brains of ME7 animals. Thus, both central and peripheral inflammation can exacerbate local brain inflammation and neuronal death. The finding that a single acute systemic inflammatory event can induce neuronal death in the CNS has implications for therapy in neurodegenerative diseases
The impact of centrally and systemically administered TNFa on CNS inflamation and function
No full textTHESIS 10941Inflammation has long been recognised as a driver of dementia. However, the pathways by which inflammation alters neuronal function and causes neuronal death remain under investigation. Microglia are primed by chronic neurodegeneration such that toll-like receptor agonists, such as lipopolysaccharide (LPS), drive exaggerated pro-inflammatory cytokine responses on this background. The data presented in this thesis show that endogenous cytokines can also activate primed microglia. Furthermore this thesis describes the novel finding of primed astrocytes in the ME7 prion disease model of neurodegeneration and the APP/PS1 amyloid aggregation model. The astrocyte population showed exaggerated production of the chemokines CXCL1 and CCL2 in response to exogenous LPS or endogenous IL-1? or TNF? challenges in ME7 animals compared to NBH animals. In the ME7 model we examined downstream effects of exaggerated chemokine expression, which resulted in markedly increased neutrophil, T-cell and monocyte infiltration and astrocyte proliferation in the diseased brain. These data have significant implications for acute sterile inflammatory insults such as stroke and traumatic brain injury occurring on a background of aging or neurodegeneration. Systemic infection has been shown to exacerbate progression of neurodegeneration in AD cohorts, this was found to be significantly correlated with levels of systemic circulating TNF?. In mice a single acute dose of systemic TNF? (250?g/kg) exacerbated features of sickness behaviour; including core body temperature changes, open field activity and body weight, in ME7 compared to NBH. A lower dose (50?g/kg) can induce a transient cognitive deficit in a hippocampal dependent task in ME7 animals but not in NBH animals. However these changes are independent of any changes in features of pathology examined. While there was no TNF? effect we discovered a novel feature of pathology; a robust aggregation of APP varicosities in the posterior (PO) and Ventroposteromedial (VPM) nuclei of the thalamus, overlapping with significant neuronal loss in the PO and significant synaptic loss in the VPM. Given systemic TNF? administration did not significantly alter ME7 pathology we utilised systemic administration of XPRO1595 a dominant negative TNF? inhibitor prior to systemic administration of LPS. This showed that the exacerbation of ME7 pathology by LPS was independent of TNF? actions. The timepoint used in the ME7 model is one with severe and widespread pathology, the mild inflammation caused by systemic TNF? in comparison to systemic LPS was not sufficient to alter this severe pathology. It would be of great interest to examine the effects of TNF? on a less severe model of pathology. Elevated systemic TNF? has been shown to be associated with significantly more rapid cognitive decline across 6 months in an AD patient cohort. It is not clear whether this might constitute a causal relationship. A repeated systemic TNF? challenge model was used to examine consequential behaviour and pathology in female APP/PS1 mice. This showed that repeated TNF? did not significantly alter learning of the hippocampal dependent Y maze. Repeated systemic TNF? induced significant deficits in rearing behaviour in W+TNF? but not APP/PS1+TNF? animals. Progressive weight loss was observed in the WT mice but this was not apparent in the APP/PS1 mice. A significant decrease was observed in the hippocampal Amyloid ? burden with a concurrent increase in aggregations of APP in both the hippocampus and thalamus. Microglia were increased in APP/PS1, however there was no alteration following repeated systemic TNF?. There were elevated numbers of T cells in the APP/PS1 animals. Following repeated TNF? there was a further increase in the T cells in APP/PS1s this did not occur in the WT+TNF? group. Repeated TNF? in APP/PS1 animals also diminished the levels of ongoing cell proliferation, a similar decrease did not occur in the WT+TNF? group. These results indicate that repeated systemic TNF? administration has differential effects in aged APP/PS1 and WT animals, suggesting important implications for cognitive and functional decline with systemic inflammation. The data presented here significantly contributes to the study of inflammatory processes in neurodegeneration. The importance of chronic sterile inflammatory co-morbidities is highlighted by this data and perhaps lends evidence to an alternative hypothesis of neurodegeneration, rather than the amyloid beta focused hypothesis that remains prevalent in the field
The role of IL-1 and Type I IFN in CNS function
No full textCytokines including interleukins (ILs) and interferons (IFNs) are induced in response to tissue injury, infection or inflammation. Peripheral cytokines signal to the healthy Central Nervous System (CNS) to produce physiological, behavioural, affective, and cognitive changes collectively known as sickness behaviour. Sickness behaviour is an adaptive response that is beneficial to the organism, but when these inflammatory insults are superimposed upon neurodegeneration, they have deleterious effects such as delirium, an acute cognitive disorder prevalent in elderly and patients with dementia that has significant economic, medical and societal impacts.
There is debate as to whether IL-1 is necessary or detrimental in learning and memory. The role this cytokine plays during systemic inflammation effects on the degenerating brain remains to be investigated in detail. Similarly though type I IFN?s are produced in the periphery during viral infection and in the brain during aging. Research into its effects on brain function is in its infancy.
This thesis aimed to investigate the role of these cytokines on brain function in 3 scenarios, basal, induced and in the vulnerable brain. The effects of these cytokines were first examined at basal levels by using IL-1R1-/- mice and IFNAR1-/- mice to examine the behavioural and cognitive function after deletion of these key receptors. IL-1R1-/-mice and IFNAR1-/- mice displayed intact hippocampal-dependent memory. The IL-1R1-/- mice had a reduction in anxiety as seen with increased time spent in the open arms of the EPM, while IFNAR1-/- mice displayed similar levels of anxiety to WT controls.
WT controls and knockout mice were then challenged systemically with LPS or Poly I:C to examine the effects of induction of these cytokines in cognition and behaviour. There were dissociable effects of LPS on two hippocampal- dependent memory tasks; working memory was intact while consolidation of memory was impaired in the CFC. IL-1RA failed to protect against LPS-induced memory consolidation deficits.
To examine the effect of IL-1 during neurodegeneration, mice were inoculated with NBH or ME7 disease. ME7 mice were vulnerable to the LPS-induced deficits in working memory and both dexamethasone and IL-1RA systemically applied protected against the LPS-induced deficit in the T-maze, independently of CNS cytokine expression. LPS induced hypoglycaemia, and glucose administration to ME7 mice after LPS could ameliorate the LPS-induced deficits in the T-maze. When glycolysis and IL-1 synthesis were inhibited with 2-DG, this lead to decreased activity and increased sickness behaviour and glucose administration once again ameliorated these effects, indicating that systemic inflammation deficits are partially mediated by hypoglycaemia.
The viral mimetic poly I:C triggered robust sickness behaviour and this was significantly diminished in IFNAR1-/-mice. Moreover STAT1 signalling and poly I:C-induced IL-6 were significantly diminished in IFNAR1-/- mice and supplementation with IL-6 reconstituted key aspects of the sickness behaviour response. Despite these suppressive impacts of IFN-I signalling on activity and sickness, IFNAR deletion during aging actually left mice more vulnerable to cognitive decline and decreased expression of microglial transcripts associated with neuronal maintenance.
Together, these data indicate basal IL-1 and IFN-I in the normal brain have no influence on cognitive function but may influence anxiety. In the induced state, IL-1 certainly contributes to acute cognitive dysfunction in the vulnerable brain, and IFN-I contribute to the sickness behaviour response to acute viral mimetics. However, the absence of IFN-I as the brain ages may contribute to age-related cognitive decline. These finding have significant implication for age-related cognitive function and the understanding of the contribution of neuroinflammation to those processes. Considerable further work is required to validate these findings in clinical populations
Microglia in the degenerating brain are capable of phagocytosis of beads and of apoptotic cells, but do not efficiently remove PrPSc, even upon LPS stimulation
No full textDespite the phagocytic machinery available to microglia the aberrant amyloid proteins produced during Alzheimer’s and prion disease, amyloid-b and PrPSc, are inefficiently cleared. We have shown that microglia in the ME7 model of prion disease show morphological evidence of activation, synthesize low levels of pro-inflammatory cytokines and are primed to produce exaggerated responses to subsequent inflammatory challenges. Whether these microglia engage in significant phagocytic activity in the disease per se, or upon subsequent inflammatory challenge is not clear. In the present study we show transcriptional activation of a large number of scavenger receptors (SRs), matrix metallo- proteinases (MMPs), oxidative enzymes, and cathepsins in ME7 animals. Hippocampally-injected inert latex beads (6 µm) are efficiently phagocytosed by microglia of ME7 prion- diseased animals, but not by microglia in normal animals. Stimulation of ME7 animals with systemic bacterial endotoxin (lipopolysaccharide, LPS) induced further increases in SR-A2, MMP3, and urokinase plasminogen activator receptor (uPAR) but decreased, or did not alter, transcription of most phagocytosis-related genes examined and did not enhance clearance of deposited PrPSc. Furthermore, intra-cerebral injection with LPS (0.5 µg) induced marked micro- glial production of IL-1b, robust cellular infiltration and marked apoptosis but also did not induce further clearance of PrPSc. These data indicate that microglia in the prion- diseased brain are capable of phagocytosis per se, but show limited efficacy in removing PrPSc even upon marked escalation of CNS inflammation. Furthermore, microglia/macro- phages remain IL-1b-negative during phagocytosis of apoptotic cells. The data demonstrate that phagocytic activity and pro-inflammatory microglial phenotype do not necessarily correlate
Delineating molecular mechanisms of inflammation-induced delirium using a novel mouse model
No full textTHESIS 10048Delirium is a syndrome of acute and transient confusion with disruption of attention and cognition; it is a common but underdiagnosed neuropsychiatric condition, which is predictive of increased fimctional decline, dementia and mortality. Despite its high incidence and cost, the molecular mechanisms underlying delirium are poorly understood. Prior cognitive impairment is the primary risk factor for delirium and systemic inflammation is a frequent trigger. The objective of the current thesis was to investigate the CNS response to systemic inflammation, particularly where there is underlying neurodegeneration, using a novel animal model of delirium during dementia
Studies on the delirium-dementia continuum : CNS effects of systemic inflammation on hypocholinergia and chronic neurodegeneration
No full textTHESIS 9912Peripheral inflammation can signal to the normal, healthy CNS via multiple routes. During ageing and dementia, however, the brain is particularly susceptible to the deleterious effects of such insults. Delirium is an acute and severe disturbance in cognitive function with particular deficits in attention, memory, orientation and perception and a single episode of delirium is predictive of accelerated long-term decline. There are no licensed treatments for delirium and the pathophysiology of this distressing condition remains poorly understood. Dementia and prior cognitive impairment are the major risk factors for delirium, and
systemic inflammation is a frequent trigger. The overarching aim of this thesis was to study the interaction between peripheral inflammation and neurodegeneration in order to gain a better understanding of how CNS function is affected by inflammatory insults, with particular relevance for the pathophysiology of delirium during dementia
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