Short-term effects of an endotoxin on substantia nigra dopamine neurons

Aging, Parkinson's Disease, and Models: What Are the Challenges?

Parkinson's disease (PD) is a chronic, neurodegenerative condition characterized by motor symptoms such as bradykinesia, rigidity, and tremor, alongside multiple nonmotor symptoms. The appearance of motor symptoms is linked to progressive dopaminergic neuron loss within the substantia nigra. PD incidence increases sharply with age, suggesting a strong association between mechanisms driving biological aging and the development and progression of PD. However, the role of aging in the pathogenesis of PD remains understudied. Numerous models of PD, including cell models, toxin-induced models, and genetic models in rodents and nonhuman primates (NHPs), reproduce different aspects of PD, but preclinical studies of PD rarely incorporate age as a factor. Studies using patient neurons derived from stem cells via reprogramming methods retain some aging features, but their characterization, particularly of aging markers and reproducibility of neuron type, is suboptimal. Investigation of age-related changes in PD using animal models indicates an association, but this is likely in conjunction with other disease drivers. The biggest barrier to drawing firm conclusions is that each model lacks full characterization and appropriate time-course assessments. There is a need to systematically investigate whether aging increases the susceptibility of mouse, rat, and NHP models to develop PD and understand the role of cell models. We propose that a significant investment in time and resources, together with the coordination and sharing of resources, knowledge, and data, is required to accelerate progress in understanding the role of biological aging in PD development and improve the reliability of models to test interventions.

Inflammatory Animal Models of Parkinson’s Disease

Accumulating evidence suggests that microglia and peripheral immune cells may play determinant roles in the pathogenesis of Parkinson’s disease (PD). Consequently, there is a need to take advantage of immune-related models of PD to study the potential contribution of microglia and peripheral immune cells to the degeneration of the nigrostriatal system and help develop potential therapies for PD. In this review, we have summarised the main PD immune models. From a historical perspective, we highlight first the main features of intranigral injections of different pro-inflammogens, including lipopolysaccharide (LPS), thrombin, neuromelanin, etc. The use of adenoviral vectors to promote microglia-specific overexpression of different molecules in the ventral mesencephalon, including α-synuclein, IL-1β, and TNF, are also presented and briefly discussed. Finally, we summarise different models associated with peripheral inflammation whose contribution to the pathogenesis of neurodegenerative diseases is now an outstanding question. Illustrative examples included systemic LPS administration and dextran sulfate sodium-induced colitis in rodents.

Effects of a Short-Term Lipopolysaccharides Challenge on Mouse Brain and Liver Peroxisomal Antioxidant and β-oxidative Functions: Protective Action of Argan Oil

During sepsis, the imbalance between oxidative insult and body antioxidant response causes the dysfunction of organs, including the brain and liver. Exposing mice to bacterial lipopolysaccharides (LPS) results in a similar pathophysiological outcome. The protection offered by argan oil was studied against LPS-induced oxidative stress, dysregulation of peroxisomal antioxidants, and β-oxidation activities in the brain and liver. In a short-term LPS treatment, lipid peroxidation (malonaldehyde assay) increased in the brain and liver with upregulations of proinflammatory tumor necrosis factor (Tnf)-α and anti-inflammatory interleukin (Il)-10 genes, especially in the liver. Although exposure to olive oil (OO), colza oil (CO), and argan oil (AO) prevented LPS-induced lipid peroxidation in the brain and liver, only AO exposure protected against liver inflammation. Remarkably, only exposure to AO prevented LPS-dependent glutathione (GSH) dysregulation in the brain and liver. Furthermore, exposure to AO increased more efficiently than OO and CO in both organs, peroxisomal antioxidant capacity via induction of catalase (Cat) gene, protein and activity expression levels, and superoxide dismutase (Sod1) mRNA and activity levels. Interestingly, LPS decreased protein levels of the peroxisomal fatty acid-ATP binding cassette (ABC) transporters, ABCD1 and ABCD2, and increased acyl-CoA oxidase 1 (ACOX1) protein expression. Moreover, these LPS effects were attenuated for ABCD1 and ACOX1 in the brain of mice pretreated with AO. Our data collectively highlight the protective effects of AO against early oxidative stress caused by LPS in the brain and liver and their reliance on the preservation of peroxisomal functions, including antioxidant and β-oxidation activities, making AO a promising candidate for the prevention and management of sepsis.

Profiling Inflammatory Extracellular Vesicles in Plasma and Cerebrospinal Fluid: An Optimized Diagnostic Model for Parkinson's Disease

Extracellular vesicles (EVs) play a central role in intercellular communication, which is relevant for inflammatory and immune processes implicated in neurodegenerative disorders, such as Parkinson's Disease (PD). We characterized and compared distinctive cerebrospinal fluid (CSF)-derived EVs in PD and atypical parkinsonisms (AP), aiming to integrate a diagnostic model based on immune profiling of plasma-derived EVs via artificial intelligence. Plasma- and CSF-derived EVs were isolated from patients with PD, multiple system atrophy (MSA), AP with tauopathies (AP-Tau), and healthy controls. Expression levels of 37 EV surface markers were measured by a flow cytometric bead-based platform and a diagnostic model based on expression of EV surface markers was built by supervised learning algorithms. The PD group showed higher amount of CSF-derived EVs than other groups. Among the 17 EV surface markers differentially expressed in plasma, eight were expressed also in CSF of a subgroup of PD, 10 in MSA, and 6 in AP-Tau. A two-level random forest model was built using EV markers co-expressed in plasma and CSF. The model discriminated PD from non-PD patients with high sensitivity (96.6%) and accuracy (92.6%). EV surface marker characterization bolsters the relevance of inflammation in PD and it underscores the role of EVs as pathways/biomarkers for protein aggregation-related neurodegenerative diseases.

Indomethacin augments lipopolysaccharide-induced expression of inflammatory molecules in the mouse brain

Indomethacin and other non-steroidal anti-inflammatory drugs (NSAIDs) are used to relieve pain and fever including during infections. However, some studies suggest that NSAIDs protect against neuroinflammation, while some find no effects or worsening of neuroinflammation. We evaluated the effect of indomethacin alone on in combination with minocycline, a drug that inhibits neuroinflammation, on the expression of transcripts of neuroinflammatory molecules-induced by lipopolysaccharide (LPS) in the brain of mice. Inoculation of male BALB/c mice with LPS induced the expression of the microglia marker ionized calcium binding adaptor molecule protein, mRNA expression of the genes for cytokines interleukin-1beta (Il1b) and tumor necrosis factor-alpha (Tnf) and inducible nitric oxide synthase gene (Nos2), but not Il10, in the brain. Treatment with indomethacin had no significant effect on the cytokines or Nos2 mRNA expression in naïve animals. However, pretreatment with indomethacin increased LPS-induced Nos2 mRNA and inducible nitric oxide (iNOS) protein expression, but had no significant effect on LPS-induced mRNA expression of the cytokines. Minocycline reduced LPS-induced Il1b and Tnf, but not Nos2, mRNA expression. Treatment with indomethacin plus minocycline had no effect on LPS-induced Il1b, Tnf and Nos2 mRNA expression. In conclusion these results show that indomethacin significantly augments LPS-induced Nos2 mRNA and iNOS protein expression in the brain. In the presence of indomethacin, minocycline could not inhibit LPS-induced pro-inflammatory cytokine expression. Thus, indomethacin could exacerbate neuroinflammation by increasing the expression of iNOS and also block the anti-inflammatory effects of minocycline.

Lipopolysaccharide animal models of Parkinson's disease: Recent progress and relevance to clinical disease

Parkinson's disease (PD) is one of the most common neurodegenerative movement disorders which is characterised neuropathologically by progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the presence of Lewy bodies (made predominately of α-synuclein) in the surviving neurons. Animal models of PD have improved our understanding of the disease and have played a critical role in the development of neuroprotective agents. Neuroinflammation has been strongly implicated in the pathogenesis of PD, and recent studies have used lipopolysaccharide (LPS), a component of gram-negative bacteria and a potent activator of microglia cells, to mimic the inflammatory events in clinical PD. Modulating the inflammatory response could ameliorate PD associated complications and thus, it is essential to understand the extent to which LPS models reflect human PD. This review will outline the routes of administration of LPS such as stereotaxic, systemic and intranasal, their ability to recapitulate neuropathological markers of PD, and mechanisms of LPS induced toxicity. We will also discuss the ability of the models to replicate motor symptoms and non-motor symptoms of PD such as gastrointestinal dysfunction, olfactory dysfunction, anxiety, depression and cognitive dysfunction.

Pioglitazone Attenuates Lipopolysaccharide-Induced Oxidative Stress, Dopaminergic Neuronal Loss and Neurobehavioral Impairment by Activating Nrf2/ARE/HO-1

The aim of the present study was to examine the neuroprotective potential of pioglitazone via activation of Nrf2/ARE-dependent HO-1 signaling pathway in chronic neuroinflammation and progressive neurodegeneration mouse model induced by lipopolysaccharide (LPS). After assessing spatial memory, anxiety and motor-coordination, TH+ neurons in substantia nigra (SN) were counted. The oxidative stress marker carbonyl protein levels and HO-1 enzyme activity were also evaluated. RT-qPCR was conducted to detect HO-1, Nrf2 and NF-κp65 mRNA expression levels and Nrf2 transcriptional activation of antioxidant response element (ARE) of HO-1 was investigated. Pioglitazone ameliorated LPS-induced dopaminergic neuronal loss, as well as mitigated neurobehavioral impairments. It enhanced Nrf2 mRNA expression, and augmented Nrf2/ARE-dependent HO-1 pathway activation by amplifying HO-1 mRNA expression. Moreover, it induced a significant decrease in NF-κB p65 mRNA expression, while reducing carbonyl protein levels and restoring the HO-1 enzyme activity. Interestingly, LPS induced Nrf2/antioxidant response element (ARE) of HO-1 activation, ultimately resulting in slight enhanced HO-1 mRNA expression. However, LPS elicited decrease in HO-1 enzyme activity. Zinc protoporphyrin-IX (ZnPPIX) administrated with pioglitazone abolished its effects in the LPS mouse model. The study results demonstrate that coordinated activation of Nrf2/ARE-dependent HO-1 pathway defense mechanism by the PPARγ agonist pioglitazone mediated its neuroprotective effects.

Intranigral Injection of Endotoxin Suppresses Proliferation of Hippocampal Progenitor Cells

Brain inflammation can result in functional disorders observed in several neurodegenerative diseases and that can be also associated with reduced neurogenesis. In this study, we investigate the effect of mild inflammation, induced by unilateral injection of Endotoxin (ET) in the substantia nigra (SN)/Ventral Tegmental Area, on the proliferation and survival of stem/progenitor cells in the dentate gyrus (DG) of the hippocampus. Adult female rats received unilateral injection of ET (2 μg/2 μl saline) or sterile saline (2 μl) in the right SN followed by 5′-Bromo-2′-deoxyuridine (BrdU) injections (66 mg/kg/injection). Intranigral ET injection induced bilateral decrease in the number of newly born BrdU positive cells in the DG. This effect was paralleled by a significant decrease in the exploratory behavior of rats, as assessed by the Y-maze novel arm exploration task. ET also induced a transient decrease in the number of tyrosine hydroxylase-positive cells in the injected SN, impaired motor behavior, and caused microglial activation in the SN. This study provides an experimental simulation of the remote effects of moderate and reversible neuroinflammation resulting in impaired communication between midbrain dopaminergic neurons and the hippocampus.

SCI and depression: Does inflammation commandeer the brain?

The incidence of depression is almost twice as high in the spinally injured population compared to the general population. While this incidence has long been attributed to the psychological, economic, and social burdens that accompany spinal cord injury (SCI), data from animal studies indicate that the biology of SCI may play an important role in the development of depression. Inflammation has been shown to impact stress response in rodents and humans, and inflammatory cytokines have been associated with depression for decades. The inflammation inherent to SCI may disrupt necessary mechanisms of mental homeostasis, such as serotonin production, dopamine production, and the hypothalamic pituitary adrenal axis. Additionally, gut dysbiosis that occurs after SCI can exacerbate inflammation and may cause further mood and behavior changes. These mediators combined may significantly contribute to the rise in depression seen after SCI. Currently, there are no therapies specific to depression after SCI. Elucidation of the molecular pathways that contribute to SCI-specific depression is crucial for the understanding of this disease and its potential treatments.

The role of inflammation in core features of depression: Insights from paradigms using exogenously-induced inflammation

A wealth of evidence has implicated inflammation in the development of depression. Yet, the heterogeneous nature of depression has impeded efforts to understand, prevent, and treat the disease. The purpose of this integrative review is to summarize the connections between inflammation and established core features of depression that exhibit more homogeneity than the syndrome itself: exaggerated reactivity to negative information, altered reward processing, decreased cognitive control, and somatic syndrome. For each core feature, we first provide a brief overview of its relevance to depression and neurobiological underpinnings, and then review evidence investigating a potential role of inflammation. We focus primarily on findings from experimental paradigms of exogenously-induced inflammation. We conclude that inflammation likely plays a role in exaggerated reactivity to negative information, altered reward reactivity, and somatic symptoms. There is less evidence supporting an effect of inflammation on cognitive control as assessed by standard neuropsychological measures. Finally, we discuss implications for future research and recommendationsfor how to test the role of inflammation in the pathogenesis of heterogeneous psychiatric disorders.

Imaging the Role of Inflammation in Mood and Anxiety-related Disorders

Background

Studies investigating the impact of a variety of inflammatory stimuli on the brain and behavior have reported evidence that inflammation and release of inflammatory cytokines affect circuitry relevant to both reward and threat sensitivity to contribute to behavioral change. Of relevance to mood and anxiety-related disorders, biomarkers of inflammation such as inflammatory cytokines and acute-phase proteins are reliably elevated in a significant proportion of patients with major depressive disorder (MDD), bipolar disorder, anxiety disorders and post-traumatic stress disorder (PTSD).

Methods

This review summarized clinical and translational work demonstrating the impact of peripheral inflammation on brain regions and neurotransmitter systems relevant to both reward and threat sensitivity, with a focus on neuroimaging studies involving administration of inflammatory stimuli. Recent translation of these findings to further understand the role of inflammation in mood and anxiety-related disorders is also discussed.

Results

Inflammation was consistently found to affect basal ganglia and cortical reward and motor circuits to drive reduced motivation and motor activity, as well as anxiety-related brain regions including amygdala, insula and anterior cingulate cortex, which may result from cytokine effects on monoamines and glutamate. Similar relationships between inflammation and altered neurocircuitry have been observed in MDD patients with increased peripheral inflammatory markers, and such work is on the horizon for anxiety disorders and PTSD.

Conclusion

Neuroimaging effects of inflammation on reward and threat circuitry may be used as biomarkers of inflammation for future development of novel therapeutic strategies to better treat mood and anxiety-related disorders in patients with high inflammation.

Chronic social stress induces peripheral and central immune activation, blunted mesolimbic dopamine function, and reduced reward-directed behaviour in mice

Psychosocial stress is a major risk factor for depression, stress leads to peripheral and central immune activation, immune activation is associated with blunted dopamine (DA) neural function, DA function underlies reward interest, and reduced reward interest is a core symptom of depression. These states might be inter-independent in a complex causal pathway. Whilst animal-model evidence exists for some specific steps in the pathway, there is currently no animal model in which it has been demonstrated that social stress leads to each of these immune, neural and behavioural states. Such a model would provide important existential evidence for the complex pathway and would enable the study of causality and mediating mechanisms at specific steps in the pathway. Therefore, in the present mouse study we investigated for effects of 15-day resident-intruder chronic social stress (CSS) on each of these states. Relative to controls, CSS mice exhibited higher spleen levels of granulocytes, inflammatory monocytes and T helper 17 cells; plasma levels of inducible nitric oxide synthase; and liver expression of genes encoding kynurenine pathway enzymes. CSS led in the ventral tegmental area to higher levels of kynurenine and the microglia markers Iba1 and Cd11b and higher binding activity of DA D1 receptor; and in the nucleus accumbens (NAcc) to higher kynurenine, lower DA turnover and lower c-fos expression. Pharmacological challenge with DA reuptake inhibitor identified attenuation of DA stimulatory effects on locomotor activity and NAcc c-fos expression in CSS mice. In behavioural tests of operant responding for sucrose reward validated as sensitive assays for NAcc DA function, CSS mice exhibited less reward-directed behaviour. Therefore, this mouse study demonstrates that a chronic social stressor leads to changes in each of the immune, neural and behavioural states proposed to mediate between stress and disruption of DA-dependent reward processing. The model can now be applied to investigate causality and, if demonstrated, underlying mechanisms in specific steps of this immune-neural-behavioural pathway, and thereby to identify potential therapeutic targets.

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Mouse chronic social stress (CSS) leads to spleen and liver immune activation.

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Mouse CSS leads to mesolimbic immune activation and blunted dopamine function.

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Mouse CSS leads to reduced reward-directed behaviour in operant tests.

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This constitutes an important model for the study of pathophysiological mechanisms.

Vagus nerve stimulation improves locomotion and neuronal populations in a model of Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a progressive, neurodegenerative disorder with no disease-modifying therapies, and symptomatic treatments are often limited by debilitating side effects. In PD, locus coeruleus noradrenergic (LC-NE) neurons degenerate prior to substantia nigra dopaminergic (SN-DA) neurons. Vagus nerve stimulation (VNS) activates LC neurons, and decreases pro-inflammatory markers, allowing improvement of LC targets, making it a potential PD therapeutic.

OBJECTIVE

To assess therapeutic potential of VNS in a PD model.

METHODS

To mimic the progression of PD degeneration, rats received a systemic injection of noradrenergic neurotoxin DSP-4, followed one week later by bilateral intrastriatal injection of dopaminergic neurotoxin 6-hydroxydopamine. At this time, a subset of rats also had vagus cuffs implanted. After eleven days, rats received a precise VNS regimen twice a day for ten days, and locomotion was measured during each afternoon session. Immediately following final stimulation, rats were euthanized, and left dorsal striatum, bilateral SN and LC were sectioned for immunohistochemical detection of monoaminergic neurons (tyrosine hydroxylase, TH), α-synuclein, astrocytes (GFAP) and microglia (Iba-1).

RESULTS

VNS significantly increased locomotion of lesioned rats. VNS also resulted in increased expression of TH in striatum, SN, and LC; decreased SN α-synuclein expression; and decreased expression of glial markers in the SN and LC of lesioned rats. Additionally, saline-treated rats after VNS, had higher LC TH and lower SN Iba-1.

CONCLUSIONS

Our findings of increased locomotion, beneficial effects on LC-NE and SN-DA neurons, decreased α-synuclein density in SN TH-positive neurons, and neuroinflammation suggest VNS has potential as a novel PD therapeutic.

Inhibition of semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 reduces lipopolysaccharide-induced neuroinflammation

BACKGROUND AND PURPOSE

Neuroinflammation is initiated by a variety of stimuli including infections, sepsis, neurodegenerative diseases or traumatic brain injury and, if not adequately controlled, can lead to various degrees of neuronal damage and behavioural impairment. A critical event in the initial steps of inflammation is neutrophil extravasation. Semicarbazide-sensitive amine oxidase (SSAO, also known as vascular adhesion protein 1 or VAP-1) regulates neutrophil adhesion and extravasation. Here, we elucidate the role of SSAO/VAP-1 in the early stage inflammatory response after LPS insult in the brain.

EXPERIMENTAL APPROACH

PXS-4681A, a selective and irreversible SSAO/VAP-1 inhibitor, was tested in two rat models of neuroinflammation, following systemic or i.c.v. LPS. Immunohistochemical and immunofluorescence techniques were used to measure neutrophils and microglia. VAP-1 was quantitated by Western blotting.

KEY RESULTS

Both systemic and i.c.v. administration of LPS induced an increase in neutrophil recruitment and microglial response in various brain areas including the substantia nigra and striatum. PXS-4681A produced a significant inhibition of neutrophil recruitment and extravasation after i.c.v. LPS injection and also reversed microglial cell recruitment and morphological changes to the level of the sham controls in both LPS models.

CONCLUSIONS AND IMPLICATIONS

PXS-4681A acted as an effective anti-inflammatory agent after both systemic and i.c.v. LPS injections suggesting that SSAO/VAP-1 inhibition could be beneficial in the treatment of brain inflammation.

Inflammation Effects on Motivation and Motor Activity: Role of Dopamine

Motivational and motor deficits are common in patients with depression and other psychiatric disorders, and are related to symptoms of anhedonia and motor retardation. These deficits in motivation and motor function are associated with alterations in corticostriatal neurocircuitry, which may reflect abnormalities in mesolimbic and mesostriatal dopamine (DA). One pathophysiologic pathway that may drive changes in DAergic corticostriatal circuitry is inflammation. Biomarkers of inflammation such as inflammatory cytokines and acute-phase proteins are reliably elevated in a significant proportion of psychiatric patients. A variety of inflammatory stimuli have been found to preferentially target basal ganglia function to lead to impaired motivation and motor activity. Findings have included inflammation-associated reductions in ventral striatal neural responses to reward anticipation, decreased DA and DA metabolites in cerebrospinal fluid, and decreased availability, and release of striatal DA, all of which correlated with symptoms of reduced motivation and/or motor retardation. Importantly, inflammation-associated symptoms are often difficult to treat, and evidence suggests that inflammation may decrease DA synthesis and availability, thus circumventing the efficacy of standard pharmacotherapies. This review will highlight the impact of administration of inflammatory stimuli on the brain in relation to motivation and motor function. Recent data demonstrating similar relationships between increased inflammation and altered DAergic corticostriatal circuitry and behavior in patients with major depressive disorder will also be presented. Finally, we will discuss the mechanisms by which inflammation affects DA neurotransmission and relevance to novel therapeutic strategies to treat reduced motivation and motor symptoms in patients with high inflammation.

Characterization of 11C-GSK1482160 for Targeting the P2X7 Receptor as a Biomarker for Neuroinflammation

The purinergic receptor subtype 7 (P2X7R) represents a novel molecular target for imaging neuroinflammation via PET. GSK1482160, a potent P2X7R antagonist, has high receptor affinity, high blood-brain barrier penetration, and the ability to be radiolabeled with ¹¹C. We report the initial physical and biologic characterization of this novel ligand. Methods:¹¹C-GSK1482160 was synthesized according to published methods. Cell density studies were performed on human embryonic kidney cell lines expressing human P2X7R (HEK293-hP2X7R) and underwent Western blotting, an immunofluorescence assay, and radioimmunohistochemistry analysis using P2X7R polyclonal antibodies. Receptor density and binding potential were determined by saturation and association-disassociation kinetics, respectively. Peak immune response to lipopolysaccharide treatment in mice was determined in time course studies and analyzed via Iba1 and P2X7R Western blotting and Iba1 immunohistochemistry. Whole-animal biodistribution studies were performed on saline- or lipopolysaccharide-treated mice at 15, 30, and 60 min after radiotracer administration. Dynamic in vivo PET/CT was performed on the mice at 72 h after administration of saline, lipopolysaccharide, or lipopolysaccharide + blocking, and 2-compartment, 5-parameter tracer kinetic modeling of brain regions was performed. Results: P2X7R changed linearly with concentrations or cell numbers. For high-specific-activity ¹¹C-GSK1482160, receptor density and K_d were 1.15 ± 0.12 nM and 3.03 ± 0.10 pmol/mg, respectively, in HEK293-hP2X7R membranes. Association constant k_on, dissociation constant k_off, and binding potential (k_on/k_off) in HEK293-hP2X7R cells were 0.2312 ± 0.01542 min^-1⋅nM^-1, 0.2547 ± 0.0155 min^-1, and 1.0277 ± 0.207, respectively. Whole-brain Iba1 expression in lipopolysaccharide-treated mice peaked by 72 h on immunohistochemistry, and Western blot analysis of P2X7R for saline- and lipopolysaccharide-treated brain sections showed a respective 1.8- and 1.7-fold increase in signal enhancement at 72 h. Biodistribution of ¹¹C-GSK1482160 in saline- and lipopolysaccharide-treated mice at 72 h was statistically significant across all tissues studied. In vivo dynamic ¹¹C-GSK1482160 PET/CT of mice at 72 h after administration of saline, lipopolysaccharide, or lipopolysaccharide + blocking showed a 3.2-fold increase and 97% blocking by 30 min. The total distribution volumes for multiple cortical regions and the hippocampus showed statistically significant increases and were blocked by an excess of authentic standard GSK1482160. Conclusion: The current study provides compelling data that support the suitability of ¹¹C-GSK1482160 as a radioligand targeting P2X7R, a biomarker of neuroinflammation.

Are Temporal Differences in GDNF and NOS Isoform Induction Contributors to Neurodegeneration? A Fluorescence Microscopy-Based Study

BACKGROUND

Specific factors in Parkinson's disease have become targets as to their protective and degenerative effects. We have demonstrated that cytokines and PD-CSF detrimentally affect microglia and astrocyte growth. While glial cell-derived neurotrophic factor (GDNF) has been recognized as a possible neuron-rescue agent, nitric oxide synthase (NOS) has been implicated in neurodegenerative processes.

OBJECTIVE

To demonstrate that glial cell activation, cytokine production, and NOS induction, play an intimate role in the loss of dopaminergic signaling, via mechanisms that are a result of inflammation and inflammatory stimuli.

METHODS

Study animals were sacrificed following endotoxin treatment and tissue sections were harvested and probed for GDNF and NOS isomers by fluorescence deconvolution microscopy. Fluorescence was mapped and quantified for each probe.

RESULTS

An immune cell influx into 'vulnerable' areas of the brain was seen, and three NOS isomers, inducible (iNOS), neuronal (nNOS) and endothelial (eNOS), were synthesized in the brains, a finding which suggests that each isomer has a role in neurodegeneration. eNOS was found associated with blood vessels, while iNOS was associated with glial and matrix cells and nNOS was located with both glia and neurons. Following endotoxin treatment, serum levels of nitric oxide were higher at 6-8 hours, while tissue levels of NOS were elevated for much longer. Thus, induction of NOS occurred earlier than the induction of GDNF.

CONCLUSION

Our findings suggest that the protective abilities of GDNF to combat neural destruction are not available rapidly enough, and do not remain at sufficiently high levels long enough to assert its protective effects. (250).

The Role of Dopamine in Inflammation-Associated Depression: Mechanisms and Therapeutic Implications

Studies investigating the impact of a variety of inflammatory stimuli on the brain and behavior have consistently reported evidence that inflammatory cytokines affect the basal ganglia and dopamine to mediate depressive symptoms related to motivation and motor activity. Findings have included inflammation-associated reductions in ventral striatal responses to hedonic reward, decreased dopamine and dopamine metabolites in cerebrospinal fluid, and decreased availability of striatal dopamine, all of which correlate with symptoms of anhedonia, fatigue, and psychomotor retardation. Similar relationships between alterations in dopamine-relevant corticostriatal reward circuitry and symptoms of anhedonia and psychomotor slowing have also been observed in patients with major depression who exhibit increased peripheral cytokines and other inflammatory markers, such as C-reactive protein. Of note, these inflammation-associated depressive symptoms are often difficult to treat in patients with medical illnesses or major depression. Furthermore, a wealth of literature suggests that inflammation can decrease dopamine synthesis, packaging, and release, thus sabotaging or circumventing the efficacy of standard antidepressant treatments. Herein, the mechanisms by which inflammation and cytokines affect dopamine neurotransmission are discussed, which may provide novel insights into treatment of inflammation-related behavioral symptoms that contribute to an inflammatory malaise.

Systemic inflammation and the brain: novel roles of genetic, molecular, and environmental cues as drivers of neurodegeneration

The nervous and immune systems have evolved in parallel from the early bilaterians, in which innate immunity and a central nervous system (CNS) coexisted for the first time, to jawed vertebrates and the appearance of adaptive immunity. The CNS feeds from, and integrates efferent signals in response to, somatic and autonomic sensory information. The CNS receives input also from the periphery about inflammation and infection. Cytokines, chemokines, and damage-associated soluble mediators of systemic inflammation can also gain access to the CNS via blood flow. In response to systemic inflammation, those soluble mediators can access directly through the circumventricular organs, as well as open the blood–brain barrier. The resulting translocation of inflammatory mediators can interfere with neuronal and glial well-being, leading to a break of balance in brain homeostasis. This in turn results in cognitive and behavioral manifestations commonly present during acute infections – including anorexia, malaise, depression, and decreased physical activity – collectively known as the sickness behavior (SB). While SB manifestations are transient and self-limited, under states of persistent systemic inflammatory response the cognitive and behavioral changes can become permanent. For example, cognitive decline is almost universal in sepsis survivors, and a common finding in patients with systemic lupus erythematosus. Here, we review recent genetic evidence suggesting an association between neurodegenerative disorders and persistent immune activation; clinical and experimental evidence indicating previously unidentified immune-mediated pathways of neurodegeneration; and novel immunomodulatory targets and their potential relevance for neurodegenerative disorders.