Essential Oil Constituents as Anti-Inflammatory and Neuroprotective Agents: An Insight through Microglia Modulation.

Microglia are key players in the brain's innate immune response, contributing to homeostatic and reparative functions but also to inflammatory and underlying mechanisms of neurodegeneration. Targeting microglia and modulating their function may have therapeutic potential for mitigating neuroinflammation and neurodegeneration. The anti-inflammatory properties of essential oils suggest that some of their components may be useful in regulating microglial function and microglial-associated neuroinflammation. This study, starting from the ethnopharmacological premises of the therapeutic benefits of aromatic plants, assessed the evidence for the essential oil modulation of microglia, investigating their potential pharmacological mechanisms. Current knowledge of the phytoconstituents, safety of essential oil components, and anti-inflammatory and potential neuroprotective effects were reviewed. This review encompasses essential oils of Thymus spp., Artemisia spp., Ziziphora clinopodioides, Valeriana jatamansi, Acorus spp., and others as well as some of their components including 1,8-cineole, ß-caryophyllene, ß-patchoulene, carvacrol, ß-ionone, eugenol, geraniol, menthol, linalool, thymol, α-asarone, and α-thujone. Essential oils that target PPAR/PI3K-Akt/MAPK signalling pathways could supplement other approaches to modulate microglial-associated inflammation to treat neurodegenerative diseases, particularly in cases where reactive microglia play a part in the pathophysiological mechanisms underlying neurodegeneration.

Acute neuroinflammation, sickness behavior and working memory responses to acute systemic LPS challenge following noradrenergic lesion in mice.

Locus coeruleus (LC)-derived noradrenaline is important in cognition and decreases with age, but the impact of prior noradrenaline deficiency on vulnerability to inflammation-induced acute cognitive dysfunction is unclear. Here we assessed whether noradrenergic depletion, in female mice, impacted upon inflammation, locomotor activity and working memory directly after acute systemic immune challenge with bacterial lipopolysaccharide (LPS), a paradigm we have previously used to capture delirium-like acute cognitive deficits. Mice received 2 doses of the LC-selective noradrenergic toxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4; 50 mg/kg i.p.) and were challenged, 2 weeks later, with LPS (100 µg/kg i.p.). DSP-4 dramatically reduced noradrenaline concentrations and tyrosine hydroxylase-positive afferents in the frontal cortex and hippocampus. This did not significantly alter numbers of Pu.1-positive microglia, Iba1-positive microglial morphology or mRNA expression of microglia-associated gene transcripts (Tyrobp, Sall1, Cd68, Sra2, Clec7a) in the hippocampus or frontal cortex and produced modest reductions in Cx3cr1 and P2ry12. LPS induced blood and brain cytokine levels, cFOS activation and locomotor responses that were highly similar in DSP-4- and vehicle-treated mice, although LPS-induced plasma TNF-α was significantly reduced in those treated with DSP-4. Importantly, prior noradrenergic depletion did not predispose to LPS-induced T-maze working memory deficits. The data demonstrate that significant depletion of noradrenaline in the hippocampus and frontal cortex does not prompt acutely exaggerated neuroinflammation or leave the brain vulnerable to acute, transient working memory deficits upon low dose LPS challenge. These findings have implications for our understanding of the impact of systemic inflammation on the aging and vulnerable brain during septic encephalopathy and delirium.

PBMC telomerase activity in depression and the response to electroconvulsive therapy.

Telomerase, the DNA polymerase responsible for maintaining telomere length, has previously been implicated in depression and the response to antidepressant drugs. In this study, we aimed to compare telomerase activity in peripheral blood mononuclear cells between patients with severe depression recruited as part of the KEEP-WELL Trial (Ketamine for Depression Relapse Prevention Following ECT; NCT02414932) and age- and sex-matched healthy volunteers both at baseline/pre-ECT and at follow-up 1 month later for controls or in patients after a course of ECT. We found no differences in telomerase activity between patients with depression (n = 20) compared to healthy controls (n = 33) at baseline/pre-ECT, or between patients treated with ECT compared to controls at follow-up. In patients, telomerase activity was not associated with mood, as assessed by the 24-item Hamilton Rating Scale for Depression, or the duration of the current depressive episode. Additionally, we found no significant relationship between telomerase activity and exposure to recent or childhood adversity in either the patient or control groups. Overall, our results suggest that telomerase activity is not associated with depression, the therapeutic response to ECT, or exposure to adversity.

Tryptophan metabolite concentrations in depressed patients before and after electroconvulsive therapy.

Tryptophan and kynurenine pathway (KP) metabolites are implicated in the pathophysiology of depression. We aimed to investigate their plasma concentrations in medicated patients with depression (n = 94) compared to age- and sex-matched healthy controls (n = 57), and in patients with depression after electroconvulsive therapy (ECT) in a real-world clinical setting, taking account of co-variables including ECT modality and heterogenous psychopathology. Depression severity was assessed using the Hamilton Depression Rating Scale (HAM-D24). Tryptophan (TRP) and kynurenine (KYN) metabolite concentrations [anthranilic acid (AA), 3-hydroxyanthranilic acid (3HAA), picolinic acid (PA), kynurenic acid (KYNA), and xanthurenic acid (XA)] and KYNA/KYN and KYNA/quinolinic acid (QUIN) ratios were lower in patients compared to controls. For the total group there was no significant change in KP metabolites post-ECT or correlations with mood ratings. However, improvements in mood score were correlated with increased KYN, 3-hydroxykynurenine (3HK), 3HAA, QUIN, and KYN/TRP in a subgroup of unipolar depressed patients. Additionally, in remitters baseline KYN, 3HK, and QUIN were associated with baseline HAM-D24 scores, and changes in 3HK and 3HAA concentrations post-ECT correlated with improvement in mood. KYN, KYNA, AA, 3HK, XA, PA, and QUIN were increased in a smaller 3-month follow-up group (n = 19) compared to pre-ECT concentrations. Overall, the results indicate that ECT mobilizes the KP, where a moderate association between selected metabolites and treatment response in unipolar depressed patients is evident.

L-alpha-aminoadipic acid restricts dopaminergic neurodegeneration and motor deficits in an inflammatory model of Parkinson's disease in male rats.

Neuroinflammation is a contributory factor underlying the progressive nature of dopaminergic neuronal loss within the substantia nigra (SN) of Parkinson's disease (PD) patients, albeit the role of astrocytes in this process has been relatively unexplored to date. Here, we aimed to investigate the impact of midbrain astrocytic dysfunction in the pathophysiology of intra-nigral lipopolysaccharide (LPS)-induced experimental Parkinsonism in male Wistar rats via simultaneous co-injection of the astrocytic toxin L-alpha-aminoadipic acid (L-AAA). Simultaneous intra-nigral injection of L-AAA attenuated the LPS-induced loss of tyrosine hydroxylase-positive (TH+ ) dopamine neurons in the SNpc and suppressed the affiliated degeneration of TH+ dopaminergic nerve terminals in the striatum. L-AAA also repressed LPS-induced nigrostriatal dopamine depletion and provided partial protection against ensuing motor dysfunction. L-AAA abrogated intra-nigral LPS-induced glial fibrillary acidic protein-positive (GFAP+ ) reactive astrogliosis and attenuated the LPS-mediated increases in nigral S100ß expression levels in a time-dependent manner, findings which were associated with reduced ionized calcium binding adaptor molecule 1-positive (Iba1+ ) microgliosis, thus indicating a role for reactive astrocytes in sustaining microglial activation at the interface of dopaminergic neuronal loss in response to an immune stimulus. These results indicate that midbrain astrocytic dysfunction restricts the development of dopaminergic neuropathology and motor impairments in rats, highlighting reactive astrocytes as key contributors in inflammatory associated degeneration of the nigrostriatal tract.

Persistent central inflammation and region specific cellular activation accompany depression- and anxiety-like behaviours during the resolution phase of experimental colitis.

Depression and anxiety-related psychological symptoms are increasingly recognised as important co-morbidities in patients with inflammatory bowel disease (IBD). Dextran sulfate sodium (DSS) -induced colitis is an animal model of IBD in which afferent activation of the gut-brain axis can be assessed and explored as a source of behavioural change. Exposure of adult male Wistar rats to DSS (5%) in drinking water induced distal colitis. In parallel to local inflammatory responses in the gut wall, increased expression of IL-6 and iNOS was found in the cerebral cortex and an increase in ventricular volume. Immunoreactivity of immediate early gene FosB/ΔFosB activation was measured as an index of cellular activation and was increased in the nucleus accumbens and dorsal raphe nucleus in acutely colitic animals. Following resolution of the acute colitic response, sustained anhedonia in the saccharin preference test, immobility in the forced swim test, reduced burying behaviour in the marble burying test, and mild signs of anxiety in the elevated plus maze and light/dark box were observed. Central increases in iNOS expression persisted during the recovery phase and mapped to reactive microglia, particularly those found in the parenchyma surrounding circumventricular regions. Evidence of associated nitration was also found. Sustained increases in ventricular volume and reduced T2 magnetic resonance relaxometry time in cortical regions were observed during the recovery period. FosB/ΔFosB activation was evident in the dorsal raphe during recovery. Persistent central inflammation and cellular activation may underpin the emergence of symptoms of depression and anxiety in experimental colitis.

Ketamine Versus Midazolam for Depression Relapse Prevention Following Successful Electroconvulsive Therapy: A Randomized Controlled Pilot Trial.

OBJECTIVE: Depression relapse after electroconvulsive therapy (ECT) is common (40% at 6 months). Ketamine has a robust antidepressant effect, but there are no reported studies of ketamine for depression relapse prevention. This pilot trial (NCT02414932) was designed to assess feasibility of the proposed trial protocol, including examining reasons for nonrecruitment, nonrandomization, and dropout. METHODS: Patients with unipolar depression referred for ECT were monitored weekly for therapeutic response, using the 24-item Hamilton Rating Scale for Depression (monitoring phase). Those who met standard response criteria were invited to be randomized to a course of 4 once-weekly infusions of ketamine (0.5 mg/kg) or the active comparator, midazolam (0.045 mg/kg), over 40 minutes to examine trial processes (treatment phase). Participants were followed up for 6 months after ECT to assess for relapse. RESULTS: One hundred seventy-five referrals were screened over 18 months, and 68% of eligible participants (n = 43) were recruited to the monitoring phase; 60.5% of participants met ECT response criteria (n = 26), but only 26% (6) of these consented to take part in the treatment phase. These were randomized (3 to ketamine and 3 to midazolam), and no participant completed the 4-week treatment protocol. Information was gathered on reasons for nonrecruitment, nonrandomization, and dropout, which included practical aspects of infusions and lack of interest in further treatment after response to ECT. CONCLUSIONS: The proposed treatment protocol is not suitable for a definitive trial in our center. Information collected on reasons for dropout may inform future clinical trials of intravenous ketamine. TRIAL REGISTRATION: www.clinicaltrials.gov NCT02414932.

Treatment with the noradrenaline re-uptake inhibitor atomoxetine alone and in combination with the α2-adrenoceptor antagonist idazoxan attenuates loss of dopamine and associated motor deficits in the LPS inflammatory rat model of Parkinson's disease.

The impact of treatment with the noradrenaline (NA) re-uptake inhibitor atomoxetine and the α2-adrenoceptor (AR) antagonist idazoxan in an animal model of Parkinson's disease (PD) was assessed. Concurrent systemic treatment with atomoxetine and idazoxan, a combination which serves to enhance the extra-synaptic availability of NA, exerts anti-inflammatory and neuroprotective effects following delivery of an inflammatory stimulus, the bacterial endotoxin, lipopolysaccharide (LPS) into the substantia nigra. Lesion-induced deficits in motor function (akinesia, forelimb-use asymmetry) and striatal dopamine (DA) loss were rescued to varying degrees depending on the treatment. Treatment with atomoxetine following LPS-induced lesion to the substantia nigra, yielded a robust anti-inflammatory effect, suppressing microglial activation and expression of the pro-inflammatory cytokine TNF-α whilst increasing the expression of neurotrophic factors. Furthermore atomoxetine treatment prevented loss of tyrosine hydroxylase (TH) positive nigral dopaminergic neurons and resulted in functional improvements in motor behaviours. Atomoxetine alone was sufficient to achieve most of the observed effects. In combination with idazoxan, an additional improvement in the impairment of contralateral limb use 7 days post lesion and a reduction in amphetamine-mediated rotational asymmetry 14 days post-lesion was observed, compared to atomoxetine or idazoxan treatments alone. The results indicate that increases in central NA tone has the propensity to regulate the neuroinflammatory phenotype in vivo and may act as an endogenous neuroprotective mechanism where inflammation contributes to the progression of DA loss. In accordance with this, the clinical use of agents such as NA re-uptake inhibitors and α2-AR antagonists may prove useful in enhancing the endogenous neuroimmunomodulatory potential of NA in conditions associated with brain inflammation.

The ß2-adrenoceptor agonist clenbuterol reduces the neuroinflammatory response, neutrophil infiltration and apoptosis following intra-striatal IL-1ß administration to rats.

OBJECTIVES: Clenbuterol is a brain penetrant ß2-adrenoceptor agonist with anti-inflammatory and putative neuroprotective properties. In the present investigation, the effect of clenbuterol was assessed in a rat model of acute brain injury induced by intra-striatal administration of the pro-inflammatory cytokine IL-1ß. METHODS: Clenbuterol (0.5 mg/kg; i.p.) was administered one hour prior to stereotactically delivered IL-1ß (100 ng) into the striatum. Four hours postinjection, rats were anesthetized, blood samples were collected for circulating cytokine and chemokine analysis, and the ipsilateral striatum and liver tissue were harvested for mRNA expression analysis of target genes. RESULTS: Intrastriatal IL-1ß provoked an inflammatory response with increased expression of IL-1ß and the pro-inflammatory cytokine TNF-α. TNF-α expression was also increased in the liver and circulating concentrations of the chemokine cytokine-induced neutrophil chemoattractant 1 (CINC-1) were raised in response to intrastriatal IL-1ß administration. The striatal response was accompanied by NFκB activation and 24 hours postinjection, increased immunoreactivity of the neutrophil marker MBS-2, indicative of cell infiltration and increased TUNEL staining, a cell marker of apoptosis. Treatment with clenbuterol attenuated all IL-1ß-induced changes in the striatum including MBS-2 immunoreactivity and TUNEL + staining. Clenbuterol also attenuated IL-1ß-induced expression of TNF-α in the liver and the increase in circulating CINC-1 concentrations. CONCLUSIONS: The results provide evidence that clenbuterol elicits anti-inflammatory effects, suppresses the peripheral acute phase response and reduces the infiltration of neutrophils and apoptotic response to acute IL-1ß-induced brain injury. Suppression of both the central and peripheral response following clenbuterol administration may contribute to its protective properties following brain injury.

Gut-brain actions underlying comorbid anxiety and depression associated with inflammatory bowel disease.

IntroductionInflammatory bowel disease (IBD) is a chronic relapsing and remitting disorder characterised by inflammation of the gastrointestinal tract. There is a growing consensus that IBD is associated with anxiety- and depression-related symptoms. Psychological symptoms appear to be more prevalent during active disease states with no difference in prevalence between Crohn's disease and ulcerative colitis. Behavioural disturbances including anxiety- and depression-like symptoms have also been observed in animal models of IBD. RESULTS: The likely mechanisms underlying the association are discussed with particular reference to communication between the gut and brain. The close bidirectional relationship known as the gut-brain axis includes neural, hormonal and immune communication links. Evidence is provided for a number of interacting factors including activation of the inflammatory response system in the brain, the hypothalamic-pituitary-adrenal axis, and brain areas implicated in altered behaviours, changes in blood brain barrier integrity, and an emerging role for gut microbiota and response to probiotics in IBD.DiscussionThe impact of psychological stress in models of IBD remains somewhat conflicted, however, it is weighted in favour of stress or early stressful life events as risk factors in the development of IBD, stress-induced exacerbation of inflammation and relapse. CONCLUSION: It is recommended that patients with IBD be screened for psychological disturbance and treated accordingly as intervention can improve quality of life and may reduce relapse rates.

Regional Specific Modulation of Stress-Induced Neuronal Activation Associated with the PSD95/NOS Interaction Inhibitor ZL006 in the Wistar Kyoto Rat.

Background: To determine brain areas involved in the antidepressant-related behavioral effects of the selective neuronal nitric oxide synthase inhibitor 1-(2-Trifluoro-methyl-phenyl) imidazole (TRIM) and experimental test compound 4-((3,5-dichloro-2-hydroxybenzyl)amino)-2-hydroxybenzoic acid (ZL006), an inhibitor of the PSD of 95 kDa/neuronal nitric oxide synthase interaction in the N-methyl-D-aspartic acid receptor signalling pathway, regional specific expression of the neuronal activation marker c-FOS was assessed following exposure to the forced swimming test in the Wistar Kyoto rat. Methods: Wistar Kyoto rats were subjected to a 15-minute swim pretest (pre-forced swimming test) period on day 1. At 24, 5, and 1 hour prior to the 5-minute test, which took place 24 hours following the pre-forced swimming test, animals were treated with TRIM (50 mg/kg; i.p.), ZL006 (10 mg/kg; i.p.), or saline vehicle (1 mL/kg i.p). Behavior was recorded during both pretest and test periods. Results: Both TRIM and ZL006 decreased immobility time in Wistar Kyoto rats in the forced swimming test. Exposure to the forced swimming test increased c-FOS immunoreactivity in the lateral septum, paraventricular nucleus of the hypothalamus, periaqueductal grey, dentate gyrus, and ventral CA1 of the hippocampus compared with non-forced swimming test-exposed controls. Forced swimming test-induced c-FOS immunoreactivity was further increased in the lateral septum, periaqueductal gray, and paraventricular nucleus of the hypothalamus following treatment with TRIM or ZL006. By contrast, forced swimming test-induced c-FOS immunoreactivity was reduced in dorsal dentate gyrus and ventral CA1 following treatment with TRIM or ZL006. Exposure to the forced swimming test resulted in an increase in NADPH diaphorase staining in the paraventricular nucleus of the hypothalamus. This forced swimming test-induced increase was attenuated following treatment with ZL006 and points to the paraventricular nucleus as a brain region where ZL006 acts to attenuate forced swimming test-induced neuronal nitric oxide synthase activity while concomitantly regulating region specific neuronal activation associated with an antidepressant-related response. Conclusions: This study identified a pattern of enhanced and reduced forced swimming test-related c-FOS immunoreactivity indicative of a regulated network where inhibition of nitric oxide coupled to the N-methyl-D-aspartic acid receptor leads to activation of the lateral septum, periaqueductal gray, and paraventricular nucleus of the hypothalamus with concomitant inhibition of the hippocampus.

Diurnal Hypothalamic-Pituitary-Adrenal Axis Measures and Inflammatory Marker Correlates in Major Depressive Disorder.

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and inflammatory systems is a consistent finding in patients with Major Depressive Disorder (MDD). Cortisol is often assessed by measurement of the cortisol awakening response (CAR) and/or diurnal cortisol levels. Some methods of cortisol measurement overestimate cortisol concentration due to detection of other glucocorticoids including the relatively inert cortisone, therefore this study aimed to assess the presence of both cortisol and cortisone, and the cortisol-cortisone catalyzing enzyme 11ß-hydroxysteroiddehydrogenase type 1 (11ß-HSD1), in depressed patients and controls. Because the HPA axis is known to regulate the body's immune system, relationships between measures of cytokines and cortisol were also assessed. Saliva samples were collected from 57 MDD patients and 40 healthy controls at five post-wakening time points (0, +30, +60, +720 and +750 min). Glucocorticoid concentrations were measured by liquid chromatography mass spectrometry. Whole blood mRNA expression of several inflammatory markers was measured by quantitative polymerase chain reaction. This study replicated the common finding of elevated morning cortisol and reduced CAR reactivity in MDD and found no differences in cortisone or 11ß-HSD1 mRNA measures. There was a negative association between interleukin 1-ß (IL-1ß) mRNA and morning cortisol reactivity within the depressed group, indicating that dysregulation of the HPA axis and immune system may be interconnected.

Association between psychological measures with inflammatory anddisease-related markers of inflammatory bowel disease.

OBJECTIVE: This study aimed at investigating the associations between inflammatory mediators, symptoms and psychological disturbances in inflammatory bowel disease (IBD) patients. METHODS: IBD patients and patient controls were examined during a single visit to a gastroenterology clinic. Disease activity was assessed using the Mayo index for ulcerative colitis (UC), inflammatory bowel disease questionnaire (IBDQ), Crohn's disease activity index (CDAI) and Crohn's disease endoscopic index of severity (CDEIS). Gene expression of inflammatory mediators were measured in intestinal biopsies and whole blood samples along with circulating concentrations of interleukin (IL)-6, interferon (IFN)γ, C-reactive protein (CRP), kynurenine and tryptophan. Validated depression, anxiety and quality of life scores were used to assess psychological well-being. RESULTS: Patients who were symptomatic had the highest depression and anxiety scores, together with increased intestinal expression of IL-1ß, IL-6 and matrix metalloproteinase-9, increased circulating IL-6 and CRP, and an increased circulating kynurenine:tryptophan ratio. Increased Hamilton depression (HAM-D) scores in IBD patients were observed independent of the psychological impact of acute symptoms. CONCLUSIONS: Active IBD is associated with symptoms of depression and anxiety and with a raised circulating inflammatory mediator profile. Patients with active IBD exhibiting psychological symptoms should undergo psychological evaluation to ensure the psychological aspects of the condition are considered and addressed.

Stress-Related Immune Markers in Depression: Implications for Treatment.

Major depression is a serious psychiatric disorder; however, the precise biological basis of depression still remains elusive. A large body of evidence implicates a dysregulated endocrine and inflammatory response system in the pathogenesis of depression. Despite this, given the heterogeneity of depression, not all depressed patients exhibit dysregulation of the inflammatory and endocrine systems. Evidence suggests that inflammation is associated with depression in certain subgroups of patients and that those who have experienced stressful life events such as childhood trauma or bereavement may be at greater risk of developing depression. Consequently, prolonged exposure to stress is thought to be a key trigger for the onset of a depressive episode. This review assesses the relationship between stress and the immune system, with a particular interest in the mechanisms by which stress impacts immune function, and how altered immune functioning, in turn, may lead to a feed forward cascade of multiple systems dysregulation and the subsequent manifestation of depressive symptomology. The identification of stress-related immune markers and potential avenues for advances in therapeutic intervention is vital. Changes in specific biological markers may be used to characterize or differentiate depressive subtypes or specific symptoms and may predict treatment response, in turn facilitating a more effective, targeted, and fast-acting approach to treatment.

Clenbuterol activates the central IL-1 system via the ß2-adrenoceptor without provoking inflammatory response related behaviours in rats.

The long-acting, highly lipophilic, ß2-adrenoceptor agonist clenbuterol may represent a suitable therapeutic agent for the treatment of neuroinflammation as it drives an anti-inflammatory response within the CNS. However, clenbuterol is also known to increase the expression of IL-1ß in the brain, a potent neuromodulator that plays a role in provoking sickness related symptoms including anxiety and depression-related behaviours. Here we demonstrate that, compared to the immunological stimulus lipopolysaccharide (LPS, 250µg/kg), clenbuterol (0.5mg/kg) selectively up-regulates expression of the central IL-1 system resulting in a mild stress-like response which is accompanied by a reduction in locomotor activity and food consumption in rats. We provide further evidence that clenbuterol-induced activation of the central IL-1 system occurs in a controlled and selective manner in tandem with its negative regulators IL-1ra and IL-1RII. Furthermore, we demonstrate that peripheral ß2-adrenoceptors mediate the suppression of locomotor activity and food consumption induced by clenbuterol and that these effects are not linked to the central induction of IL-1ß. Moreover, despite increasing central IL-1ß expression, chronic administration of clenbuterol (0.03mg/kg; twice daily for 21days) fails to induce anxiety or depressive-like behaviour in rats in contrast to reports of the ability of exogenously administered IL-1 to induce these symptoms in rodents. Overall, our findings suggest that clenbuterol or other selective ß2-adrenoceptor agonists could have the potential to combat neuroinflammatory or neurodegenerative disorders without inducing unwanted symptoms of depression and anxiety.

Exaggerated Increases in Microglia Proliferation, Brain Inflammatory Response and Sickness Behaviour upon Lipopolysaccharide Stimulation in Non-Obese Diabetic Mice.

The non-obese diabetic (NOD) mouse, an established model for autoimmune diabetes, shows an exaggerated reaction of pancreas macrophages to inflammatory stimuli. NOD mice also display anxiety when immune-stimulated. Chronic mild brain inflammation and a pro-inflammatory microglial activation is critical in psychiatric behaviour. OBJECTIVE: To explore brain/microglial activation and behaviour in NOD mice at steady state and after systemic lipopolysaccharide (LPS) injection. METHODS: Affymetrix analysis on purified microglia of pre-diabetic NOD mice (8-10 weeks) and control mice (C57BL/6 and CD1 mice, the parental non-autoimmune strain) at steady state and after systemic LPS (100 µg/kg) administration. Quantitative PCR was performed on the hypothalamus for immune activation markers (IL-1ß, IFNγ and TNFα) and growth factors (BDNF and PDGF). Behavioural profiling of NOD, CD1, BALB/c and C57BL/6 mice at steady state was conducted and sickness behaviour/anxiety in NOD and CD1 mice was monitored before and after LPS injection. RESULTS: Genome analysis revealed cell cycle/cell death and survival aberrancies of NOD microglia, substantiated as higher proliferation on BrdU staining. Inflammation signs were absent. NOD mice had a hyper-reactive response to novel environments with some signs of anxiety. LPS injection induced a higher expression of microglial activation markers, a higher brain pro-inflammatory set point (IFNγ, IDO) and a reduced expression of BDNF and PDGF after immune stimulation in NOD mice. NOD mice displayed exaggerated and prolonged sickness behaviour after LPS administration. CONCLUSION: After stimulation with LPS, NOD mice display an increased microglial proliferation and an exaggerated inflammatory brain response with reduced BDNF and PDGF expression and increased sickness behaviour as compared to controls.

L-kynurenine/aryl hydrocarbon receptor pathway mediates brain damage after experimental stroke.

BACKGROUND: Aryl hydrocarbon receptor (AhR) is a transcription factor that belongs to the basic helix-loop-helix PAS (Per-Arnt-Sim homology domain) family known to mediate the toxic and carcinogenic effects of xenobiotics. Interestingly, AhR is widely expressed in the central nervous system, but its physiological and pathological roles are still unclear. METHODS AND RESULTS: To define the role of AhR in stroke, we used middle cerebral artery occlusion in mice and oxygen-glucose deprivation in rat cortical neurons. The results presented here show that the ischemic insult increases total and nuclear AhR levels and AhR transcriptional activity in neurons in vivo and in vitro. We also show that AhR has a causal role in acute ischemic damage because pharmacological or genetic loss-of-function approaches result in neuroprotection. Inhibition of cAMP response element-binding protein-dependent signaling may participate in the deleterious actions of AhR. Finally, we have also found that L-kynurenine, a tryptophan metabolite with AhR agonistic properties, is an endogenous ligand that mediates AhR activation in the brain after middle cerebral artery occlusion. CONCLUSIONS: Our data demonstrate that an L-kynurenine/AhR pathway mediates acute brain damage after stroke and open new possibilities for the diagnosis and treatment of this pathology.

Interdependent and independent roles of type I interferons and IL-6 in innate immune, neuroinflammatory and sickness behaviour responses to systemic poly I:C.

Type I interferons (IFN-I) are expressed in the brain during many inflammatory and neurodegenerative conditions and have multiple effects on CNS function. IFN-I is readily induced in the brain by systemic administration of the viral mimetic, poly I:C (synthetic double-stranded RNA). We hypothesised that IFN-I contributes to systemically administered poly I:C-induced sickness behaviour, metabolic and neuroinflammatory changes. IFN-I receptor 1 deficient mice (IFNAR1(-/-)) displayed significantly attenuated poly I:C-induced hypothermia, hypoactivity and weight loss compared to WT C57BL/6 mice. This amelioration of sickness was associated with equivalent IL-1ß and TNF-α responses but much reduced IL-6 responses in plasma, hypothalamus and hippocampus of IFNAR1(-/-) mice. IFN-ß injection induced trivial IL-6 production and limited behavioural change and the poly I:C-induced IFN-ß response did not preceed, and would not appear to mediate, IL-6 induction. Rather, IFNAR1(-/-) mice lack basal IFN-I activity, have lower STAT1 levels and show significantly lower levels of several inflammatory transcripts, including stat1. Basal IFN-I activity appears to play a facilitatory role in the full expression of the IL-6 response and activation of the tryptophan-kynurenine metabolism pathway. The deficient IL-6 response in IFNAR1(-/-) mice partially explains the observed incomplete sickness behaviour response. Reconstitution of circulating IL-6 revealed that the role of IFNAR in burrowing activity is mediated via IL-6, while IFN-I and IL-6 have additive effects on hypoactivity, but the role of IFN-I in anorexia is independent of IL-6. Hence, we have demonstrated both interdependent and independent roles for IFN-I and IL-6 in systemic inflammation-induced changes in brain function.

Effects of brief pulse and ultrabrief pulse electroconvulsive stimulation on rodent brain and behaviour in the corticosterone model of depression.

Brief pulse electroconvulsive therapy (BP ECT; pulse width 0.5-1.5 ms) is the most effective treatment available for severe depression. However, its use is associated with side-effects. The stimulus in ultrabrief pulse ECT (UBP ECT; pulse width 0.25-0.3 ms) is more physiological and has been reported to be associated with less cognitive side-effects, but its antidepressant effectiveness is not yet well established. Using electroconvulsive stimulation (ECS), the animal model of ECT, we previously reported UBP ECS to be significantly less effective than well-established BP ECS in eliciting behavioural, molecular and cellular antidepressant-related effects in naïve rats. We have now compared the effects of BP and UBP ECS in an animal model of depression related to exogenous supplementation with the stress-induced glucocorticoid hormone, corticosterone. Corticosterone administration resulted in an increase in immobility time in the forced swim test (FST) (p < 0.01) and decreases in the expression of brain-derived neurotrophic factor (BDNF) (p < 0.05) and glial fibrillary acidic protein (GFAP) (p < 0.001) in the hippocampus and frontal cortex. There was no significant difference in the duration or type of seizure induced by BP (0.5 ms) or UBP (0.3 ms) ECS. UBP ECS proved to be as effective as BP ECS at inducing a behavioural antidepressant response in the FST with a significant decrease (p < 0.001) in immobility seen following administration of ECS. Both forms of ECS also induced significant increases in BDNF protein (p < 0.01) expression in the hippocampus. BP ECS (p < 0.05) but not UBP ECS induced a significant increase in GFAP levels in the hippocampus and frontal cortex. Overall, UBP ECS effectively induced antidepressant-related behavioural and molecular responses in the corticosterone supplementation model, providing the first preclinical data on the potential role of this form of ECS to treat a depression phenotype related to elevated corticosterone.

Inhibition of stress-induced hepatic tryptophan 2,3-dioxygenase exhibits antidepressant activity in an animal model of depressive behaviour.

The role of hepatic tryptophan 2,3 dioxygenase (TDO) was assessed in the provocation of stress-induced depression-related behaviour in the rat. TDO drives tryptophan metabolism via the kynurenine pathway (KP) and leads to the production of neuroactive metabolites including kynurenine. A single 2 h period of restraint stress in adult male Sprague-Dawley rats provoked an increase in circulating concentrations of the glucocorticoid corticosterone and induction of hepatic TDO expression and activity. Repeated exposure to stress (10 d of 2 h restraint each day) provoked an increase in immobility in the forced swimming test (FST) indicative of depression-related behaviour. Immobility was accompanied by an increase in the circulating corticosterone concentrations, expression and activity of hepatic TDO and increase in the expression of TDO in the cerebral cortex. Increased TDO activity was associated with raised circulating kynurenine concentrations and a reduction in circulating tryptophan concentrations indicative of KP activation. Co-treatment with the TDO inhibitor allopurinol (20 mg/kg, i.p.), attenuated the chronic stress-related increase in immobility in the FST and the accompanying increase in circulating kynurenine concentrations. These findings indicate that stress-induced corticosterone and consequent activation of hepatic TDO, tryptophan metabolism and production of kynurenine provoke a depression-related behavioural phenotype. Inhibition of stress-related hepatic TDO activity promotes antidepressant activity. TDO may therefore represent a promising target for the treatment of depression associated with stress-related disorders in which there is evidence for KP activation.