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Nitric oxide synthase (NOS) inhibitors possess antidepressant-like properties in preclinical tests and in the current investigation the brain penetrant NOS inhibitor N ω -nitro- l -arginine ( l -NA) and the preferential inhibitor of neuronal NOS (nNOS) 1-(2-trifluoromethylphenyl) imidazole (TRIM) were assessed in the olfactory bulbectomised (OB) rat, a well-established animal model of depression. Magnetic resonance imaging (MRI) was employed to assess regional brain volumes, blood perfusion and T1 and T2 relaxometry times both with and without drug treatment. l -NA (10 mg/kg, once daily p.o. for 10 days) attenuated OB-related hyperactivity in the “open field” test in a comparable fashion to the tricyclic antidepressant imipramine (20 mg/kg, once daily p.o. for 14 days) indicative of an antidepressant-like response in the model. Treatment with TRIM (50 mg/kg, once daily s.c.) attenuated OB-related hyperactivity following 7 days of treatment when compared to vehicle treated controls. OB is associated with enlarged ventricular volume, increased periventicular perfusion and a decrease in T2 relaxation times in cortical and hippocampal regions, with enhanced perfusion and reduced T2 times attenuated by l -NA treatment. l -NA treatment was also associated with an increase in T1 relaxation times in limbic and cortical regions and found to reduce resting state hippocampal blood perfusion in OB animals. Behavioural observations are consistent with an antidepressant action of NOS inhibitors where associated changes in perfusion and T2 relaxation times may be related to the antidepressant action of l -NA in the model.

Visceral hypersensitivity is a hallmark of many clinical conditions and remains an ongoing medical challenge. Although the central neural mechanisms that regulate visceral hypersensitivity are incompletely understood, it has been suggested that stress and anxiety often act as initiating or exacerbating factors. Dysfunctional corticolimbic structures have been implicated in disorders of visceral hypersensitivity such as irritable bowel syndrome (IBS). Moreover, the pattern of altered physiological responses to psychological and visceral stressors reported in IBS patients is also observed in the maternally separated (MS) rat model of IBS. However, the relative contribution of various divisions within the cortex to the altered stress responsivity of MS rats remains unknown. The aim of this study was to analyze the cellular activation pattern of the prefrontal cortex and amygdala in response to an acute psychological stressor (open field) and colorectal distension (CRD) using c-fos immunohistochemistry. Several corticoamygdalar structures were analyzed for the presence of c-fos-positive immunoreactivity including the prelimbic cortex, infralimbic cortex, the anterior cingulate cortex (both rostral and caudal) and the amygdala. Our data demonstrate distinct activation patterns within these corticoamygdalar regions including differential activation in basolateral versus central amygdala following exposure to CRD but not the open field stress. The identification of this neuronal activation pattern may provide further insight into the neurochemical pathways through which therapeutic strategies for IBS could be derived.

Accumulating evidence supports the view that deregulation of the immune system represents an important vulnerability factor for psychosis. In a subgroup of psychotic patients, the high comorbidity with autoimmune and chronic inflammatory conditions suggests a common underlying immune abnormality leading to both conditions. The reviewed data of affective and nonaffective psychosis show that if immune biomarkers exist for such immune abnormality, they may be found in raised macrophage/monocyte inflammatory activation patterns (monocytosis, high-inflammatory gene expression, raised glucocorticoid receptor beta/glucocorticoid receptor a ratio, and high levels of proinflammatory and anti-inflammatory monocyte/macrophage derived cytokines in serum/plasma), reduced T cell numbers/proliferation, and TH1 skewing. This activation of the inflammatory response system may be suggestive for microglia activation, as these cells are the macrophages of the brain. Indeed, there is some evidence of activation of the microglia as detected in positron emission tomography scans and in histopathology, and it is assumed that this activation disturbs the development and function of neuronal circuits in the brain. Further, animal models of psychotic conditions (maternal stress and inflammation paradigms) suggest that such monocyte/microglia activation could be seen as the result of a combination of genetic predisposition and an immune-mediated two-hit model. Infection but also environmental stressors during gestation/early life activate microglia, perturbing neuronal development, thereby setting the stage for vulnerability for later psychotic disorders. A second hit, such as endocrine changes, stress, or infection, could further activate microglia, leading to functional abnormalities of the neuronal circuitry in the brain and psychosis.

The neurotransmitter noradrenaline (NA) has anti-inflammatory properties and promotes expression of neurotrophic factors in the central nervous system (CNS) via activation of glial adrenoceptors. Here we examined the ability of conditioned media (CM) from NA-treated glial cells to impact upon neuronal complexity. Primary rat cortical neurons were treated either directly with NA (1-10 μM), or treated with CM from NA-stimulated primary mixed glial cells. Neuronal complexity was assessed using Sholl analysis. Exposure of neurons to CM from NA-stimulated glial cells increased all indices of neuronal complexity, whereas direct exposure of neurons to NA did not. CM from NA-stimulated astrocytes, but not microglia, also increased neuronal complexity indicating a key role for astrocytes. The β-adrenergic subtype was implicated in this response as the increase was blocked by the β-adrenoceptor antagonist propanolol, but not by the α-adrenoceptor antagonist phentolamine. CM from glial cells treated with the β₂-adrenoceptor agonists salmeterol and clenbuterol, but not the β₁-adrenoceptor agonist xamoterol, mimicked the ability of NA to increase neuronal complexity. NA induced expression of a range of growth factors (BDNF, NGF-β, GDNF, FGF-2 and IL-6) in glial cells. In addition to this, the phosphatidylinositol 3-kinase (PI3K), mitogen activated protein kinase (MAPK) and JAK-STAT signalling pathways are implicated in NA CM-induced neuritic growth as inhibition of these pathways attenuated NA CM-induced neuritic growth. In conclusion, this study indicates a novel role for NA acting at glial β₂-adrenoceptors to induce neuritic growth through the expression of soluble factors that elicit a neurotrophic action and increase neuronal complexity.

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.

In this study we characterised the ability of the viral mimetic poly I:C to induce a neuroinflammatory response and induce symptoms of depression and anxiety in rats. Furthermore, the ability of poly I:C to deplete central tryptophan and serotonin via induction of indolamine 2,3 dioxygenase (IDO), and also the ability of poly I:C to impact upon expression of the neurotrophin BDNF and its receptor TrkB were examined as potential mechanisms to link inflammation to depression. Poly I:C induced a neuroinflammatory response characterised by increased expression of IL-1β, IL-6, TNF-α and CD11b in frontal cortex and hippocampus. In the first 24 h following poly I:C administration rats displayed sickness behaviour characterised by reduced locomotor activity and weight gain. Anhedonia measured using the saccharin preference test was used as an indicator of depressive behaviour, and poly I:C induced depressive behaviour that persisted for up to 72 h following administration. Anxiety was measured using the open field test and anxious behaviour was observed 24 h following poly I:C, a time-point when sickness behaviour had resolved. These behavioural changes were accompanied by decreased expression of BDNF and TrkB in hippocampus and frontal cortex. In addition, poly I:C increased central IDO expression and increased concentrations of tryptophan, and its metabolite kynurenine. However this activation of the kynurenine pathway did not result in reduced central serotonin concentrations. These findings suggest that depressive and anxiety-like behaviours elicited by poly I:C are associated with a reduction in BDNF signalling, and activation of the kynurenine pathway, but not a reduction in serotonin.

There is extensive bi-directional communication between the brain and the immune system in both health and disease. In recent years, the role of an altered immune system in the etiology of major psychiatric disorders has become more apparent. Studies have demonstrated that some patients with major psychiatric disorders exhibit characteristic signs of immune dysregulation and that this may be a common pathophysiological mechanism that underlies the development and progression of these disorders. Furthermore, many psychiatric disorders are also often accompanied by chronic medical conditions related to immune dysfunction such as autoimmune diseases, diabetes and atherosclerosis. One of the major psychiatric disorders that has been associated with an altered immune system is schizophrenia, with approximately one third of patients with this disorder showing immunological abnormalities such as an altered cytokine profile in serum and cerebrospinal fluid. An altered cytokine profile is also found in a proportion of patients with major depressive disorder and is thought to be potentially related to the pathophysiology of this disorder. Emerging evidence suggests that altered immune parameters may also be implicated in the neurobiological etiology of autism spectrum disorders. Further support for a role of immune dysregulation in the pathophysiology of these psychiatric disorders comes from studies showing the immunomodulating effects of antipsychotics and antidepressants, and the mood altering effects of anti-inflammatory therapies. This review will not attempt to discuss all of the psychiatric disorders that have been associated with an augmented immune system, but will instead focus on several key disorders where dysregulation of this system has been implicated in their pathophysiology including depression, schizophrenia and autism spectrum disorder.

Review on the key role for activated microglia and monocytes in the pathogenesis of bipolar disorder and schizophrenia. This review describes a key role for mononuclear phagocytes in the pathogenesis of major psychiatric disorders. There is accumulating evidence for activation of microglia (histopathology and PET scans) and circulating monocytes (enhanced gene expression of immune genes, an overproduction of monocyte/macrophage-related cytokines) in patients with bipolar disorder, major depressive disorder, and schizophrenia. These data are strengthened by observations in animal models, such as the MIA models, the chronic stress models, and the NOD mouse model. In these animal models of depressive-, anxiety-, and schizophrenia-like behavior, similar activations of microglia and circulating monocytes can be found. These animal models also make in-depth pathogenic studies possible and show that microglia activation impacts neuronal development and function in brain areas congruent with the altered depressive and schizophrenia-like behaviors.

The neurochemical basis of depression focuses on alterations in the monoaminergic and amino acid neurotransmitter systems. Moreover, decreases in serum levels of the neurotrophin brain-derived neurotrophic factor (BDNF) have led to the more recent neurotrophic hypothesis of depression. Chronic stress is one of the major predisposing factors to developing the disorder and thus we investigated the impact of chronic restraint stress on the levels of several neurotransmitters and their metabolites in a genetic animal model of depression, the Wistar Kyoto (WKY) rat. Behavioural analysis of WKY rats indicated both a depressive and anxiety-like phenotype compared to their Sprague Dawley (SD) controls. WKY animals showed similar stress-induced decreases in hippocampal GABA, noradrenaline and dopamine as their SD counterparts while exhibiting a divergent decrease in 5-HT, 5-HIAA and DOPAC. WKY rats also showed a stress-dependent increase in GABA concentrations in the amygdala compared to the SD animals. Moreover, WKY but not SD rats had a chronic stress-induced decrease in serum BDNF levels. Together these data show that there are specific strain-dependent changes in neurotransmitter and neurotrophin levels in response to chronic stress which may predispose WKY animals to a depressive-like phenotype.

Background A growing body of data implicates increased life stresses with the initiation, persistence and severity of symptoms associated with functional gut disorders such as irritable bowel syndrome (IBS). Activation of central and peripheral corticotropin-releasing factor (CRF) receptors is key to stress-induced changes in gastrointestinal (GI) function. Methods This study utilised immunofluorescent and Western blotting techniques to investigate colonic expression of CRF receptors in stress-sensitive Wistar Kyoto (WKY) and control Sprague Dawley (SD) rats. Key Results No intra-strain differences were observed in the numbers of colonic CRFR1 and CRFR2 positive cells. Protein expression of functional CRFR1 was found to be comparable in control proximal and distal colon samples. Sham levels of CRFR1 were also similar in the proximal colon but significantly higher in WKY distal colons (SD: 0.38 ± 0.14, WKY: 2.06 ± 0.52, P

The prefrontal cortex plays a key role in the perception of painful stimuli, including those emerging from the viscera. Colorectal distension is a non-invasive stimulus used to study visceral pain processing in the nervous system. Visceral hypersensitivity is one of the main characteristics of the functional bowel disorder irritable bowel syndrome (IBS). Moreover, recent human neuroimaging studies have emphasized the importance of altered brain activity and circuitry in the manifestation of IBS symptom severity and reaction to visceral stimuli. It is unclear whether animal models of visceral hypersensitivity display a similar response. Therefore, in the present study, we have used c-Fos protein immunoreactivity as an indicator of cell activation, to compare the response of the viscerally hypersensitive Wistar-Kyoto (WKY) rat and control Sprague-Dawley (SD) rat strains to colorectal distension (CRD), a noxious visceral stimulus. Several corticolimbic structures were analysed including the prelimbic cortex, infralimbic cortex and the rostral and caudal anterior cingulate cortices. Moreover, visceral hypersensitivity was also assessed behaviourally in both strains. As previously described WKY rats had a lower pain threshold than SD controls in response to CRD. In all brain regions analysed, exposure to CRD induced an increase in c-Fos activation in both the WKY and SD rats. However, an exaggerated cell activation was found in the prelimbic, infralimbic and rostral anterior cingulate cortices of the WKY rat compared to SD animals. No significant difference was found in caudal anterior cingulate cortex activation when the strains were compared. These results demonstrate, to our knowledge, for the first time an augmented colorectal distension-induced prefrontal cortex activity in WKY rats similar to that seen in IBS patients, further supporting the use of this strain as a model in which to study brain-gut axis dysregulation observed in IBS.

A growing body of evidence from human postmortem and animal studies suggests that deficits in glial cell (particularly astrocytes) density and function, in limbic regions of the brain contribute to the etiology of depressive disorders. Despite the widespread use of Wistar-Kyoto (WKY) rat strain as a model of depression and stress susceptibility, there is a paucity of data examining whether alterations in brain astrocytic population are present in the model. In the present study, we investigated the expression of the astrocytic markers glial fibrillary acidic protein (GFAP) in various brain regions in WKY rats in comparison to Sprague-Dawley rats. A significant deficit in GFAP-immunoreactive cells was found in the prefrontal cortex region (infralimbic, prelimbic and anterior cingulate cortex), in the basolateral amygdala as well as in the hippocampus (CA3 and dentate gyrus) in WKY rat brain. No statistical difference was found in the other brain regions analyzed (insular cortex, somatosensory cortex, CA1 and callosal white matter). No difference was found in the total density of astrocytes (assessed by s-100beta immunoreactivity), neurons (determined by NeuN expression) or in the total number of cells in the regions of interest. A slight increase in the intensity of s-100beta immunoreactivity was observed. The lower expression of GFAP in WKY rats was further confirmed by Western-blot analysis. These results suggest that specific astrocytic deficits in GFAP expression in corticolimbic circuits may be a general correlate of depressive-like behavior in animal models in addition to human major depression. Moreover, they suggest that glial physiology may become a therapeutic target in depression and other stress-related conditions.

The neurotransmitter noradrenaline (NA) has anti-inflammatory properties and promotes expression of neurotrophic factors in the central nervous system (CNS) via activation of glial adrenoceptors. Here we examined the ability of conditioned media (CM) from NA-treated glial cells to impact upon neuronal complexity. Primary rat cortical neurons were treated either directly with NA (1-10 μM), or treated with CM from NA-stimulated primary mixed glial cells. Neuronal complexity was assessed using Sholl analysis. Exposure of neurons to CM from NA-stimulated glial cells increased all indices of neuronal complexity, whereas direct exposure of neurons to NA did not. CM from NA-stimulated astrocytes, but not microglia, also increased neuronal complexity indicating a key role for astrocytes. The β-adrenergic subtype was implicated in this response as the increase was blocked by the β-adrenoceptor antagonist propanolol, but not by the α-adrenoceptor antagonist phentolamine. CM from glial cells treated with the β₂-adrenoceptor agonists salmeterol and clenbuterol, but not the β₁-adrenoceptor agonist xamoterol, mimicked the ability of NA to increase neuronal complexity. NA induced expression of a range of growth factors (BDNF, NGF-β, GDNF, FGF-2 and IL-6) in glial cells. In addition to this, the phosphatidylinositol 3-kinase (PI3K), mitogen activated protein kinase (MAPK) and JAK-STAT signalling pathways are implicated in NA CM-induced neuritic growth as inhibition of these pathways attenuated NA CM-induced neuritic growth. In conclusion, this study indicates a novel role for NA acting at glial β₂-adrenoceptors to induce neuritic growth through the expression of soluble factors that elicit a neurotrophic action and increase neuronal complexity.

Behavioural antidepressant-like effects of ketamine have been reported in the forced swimming test (FST). The mechanisms mediating such effects are unknown.As serotonin (5-HT) is an important transmitter mediating antidepressant responsiveness in the FST, the influence of 5-HT depletion on the antidepressant-like effect of ketamine was assessed.The effect of ketamine (25 mg/kg, i.p., 1 or 24 h prior to test) was assessed in the FST in naive rats or animals subjected to 5-HT depletion, repeated stress or following a combination of 5-HT depletion and stress. Endogenous 5-HT was depleted using the tryptophan hydroxylase inhibitor para-chlorophenylalanine (3 × 150 mg/kg, i.p.). Stress was induced by physical restraint (2 h/day for 10 days).In naive rats, ketamine administered 24 or 1 h prior to test produced a characteristic antidepressant-like reduction in immobility time in the FST. Depletion of 5-HT blocked this reduction in immobility when ketamine was administered 24 h prior FST, indicative of 5-HT dependency. The increase in immobility provoked by repeated restraint stress (2 h/day for 10 days) was blocked by ketamine when administered 24 h prior to FST, but this effect dissipated when animals were subjected to 5-HT depletion.These observations are consistent with a role for 5-HT in mediating sustained antidepressant activity of ketamine in the FST. Molecular and cellular changes induced by ketamine may produce a rapid adaptation of 5-HT transmission which underlies the antidepressant response.

Stress and anxiety are important causal and exacerbating factors in functional gastro-intestinal (GI) disorders such as irritable bowel syndrome. Stress affects GI motility, faecal transit and visceral pain sensitivity. Additionally, permeability and function of the gut epithelium, which acts as a barrier between the external environment and the body's internal milieu is altered by stress. However, the effects of an enhanced stress response on colonic morphology require further investigation. We have used two animal models of stress and anxiety, the maternally separated (MS) and Wistar Kyoto (WKY) rats to examine colonic morphology. These rats exhibit increased anxiety behaviours, visceral hypersensitivity and increased stress-induced defecation in the open field arena. At a morphological level, increased mucus secretion and an associated elevation in the number of mucosal goblet cells was observed in the high anxiety rats. Additionally, the mucosal layer was flattened in MS and WKY rats, a finding indicative of mild mucosal damage. Furthermore, the muscular layer of the distal colon in these animals was thickened, an observation that may have implications for faecal transit and visceral pain perception. This study provides evidence of altered colonic function and morphology in two animal models with a heightened response to stress.

The generation of large numbers of functionally relevant cells for transplantation remains central to the use of cell replacement as a therapeutic strategy for neurodegenerative diseases. In this study we have analyzed the effect of sonic hedgehog (Shh) pretreatment on the myelinating potential of transplanted oligosphere-derived cells. The retina was chosen as a model for assessing this myelinating capability because 1) there is a lack of endogenous myelin in the normal rodent retina and 2) the retinal ganglion cell (RGC) axons are receptive to myelination, once myelinating cells have access to the retinal nerve fiber layer. Initially, oligospheres were generated in the presence of B104 CM but without the addition of Shh. After transplantation, 60% of the animals developed tumors in the eye that had received the transplant and were not analyzed for the presence of myelin. In the remaining retinas, the transplanted oligosphere-derived cells were not myelin competent, as indicated by the absence of myelin proteins in the retinal nerve fiber layer. In contrast, when B104 CM oligospheres were generated in the presence of Shh, myelin proteins were found in the nerve fiber layer after transplantation. In addition, the amount of myelin proteins synthesized increased with time posttransplantation, with the majority of the nerve fiber layer immunoreactive for these proteins in some retinas after 2 months. This study has demonstrated that growth as oligospheres and endogenously derived growth/differentiation factors alone are not sufficient to induce the differentiation of B104-treated oligosphere-derived cells and that pretreating the oligospheres by growth in the presence of Shh before transplantation is essential to induce their myelinating competence.

Studies on the isolation and propagation of multipotent neural precursors as neurospheres suggest their potential use in the reconstitution of neurons and oligodendrocytes in neurodegenerative diseases. To ensure that an adequate number of functionally relevant cells are present after transplantation, in vitro manipulation of cell fate before transplantation may be necessary to control the terminal phenotype of these cells. Using growth factors known to have a role in oligodendrocyte development such as sonic hedgehog, platelet-derived growth factor (PDGF), and basic fibroblast growth factor (FGF-2), we have tried to increase the number of oligodendroglia derived from E18 cortical neurospheres. We have shown that although all of the growth factor combinations induce the formation of oligodendroglia, they do so in varying proportions, with PDGF favouring the formation of oligodendrocyte progenitor cells and sonic hedgehog favouring the formation of mature oligodendrocytes. To further enhance the generation of oligodendroglia we exposed neurospheres to B104-cell conditioned medium (B104 CM). Long-term growth of the neurospheres in this B104 CM increased markedly the number of cells committed to the oligodendrocyte lineage, specifically oligodendrocyte progenitor cells. These were then referred to as oligospheres. Our results suggest that the oligosphere culture system may provide a valuable source of cells for the reconstitution of oligodendrocytes in neurologic disorders.

Background Patients with primary Sjogren9s syndrome (pSS) often experience disabling fatigue and a depressed mood as their most severe symptom. These symptoms reduce overall health-related quality of life, having an extensive effect on physical and psychological functioning. We previously identified a subgroup (55-60%) of pSS patients, positive for the IFN type I signature, associated with higher EULAR Sjogren9s Syndrome Disease Activity Index (ESSDAI) scores, SSA/anti-SSB antibodies, IgG levels, BAFF levels and lower C3 complement levels [Brkic, Maria et al., 2013]. A role for IFN type I in fatigue and depressive symptoms is supported by induction of these symptoms in subjects undergoing IFN type I therapies. Objectives Previously, indoleamine-2,3-dioxygenase (IDO) expression was related to IFNα-induced depression. IDO degrades tryptophan, a precursor of the neurotransmitter serotonin (5-hydroxytryptamine) to kynurenine. Aberrant tryptophan catabolism has been associated with mood disturbances. We therefore hypothesized that aberrant IDO expression in IFN type I signature positive patients is related to symptoms of fatigue and depression. Methods In a cohort of 110 pSS patients and 70 Healthy controls (HC) the IFNscore, a measure for total IFN type I activation, was calculated using expression values of the IFN type I signature genes –IFI44, IFI44L, IFIT3, LY6E, MX1– thereby stratifying patients in IFN-positive (IFNscore>10) and IFN-negative (IFNscore Results The described cohort had an IFN type I signature prevalence of 60%. Preliminary results shown in Figure 1A indicate a highly elevated tryptophan catabolism, confined to IFNpositive-, compared to both IFNnegative-pSS (p>0.01) and HC (p>0.0001). IDO mRNA levels were significantly increased, restricted to IFNpositive CD14+ monocytes (p>0.0001; Figure 1B). IL-6 (p>0.01), IL-10 (p>0.001) and TNFα (p>0.001) were significantly upregulated in IFNpositive pSS compared to HC, whereas IFNnegative patients showed no significant differences. Furthermore, downstream enzymes suggest an inflammatory-driven neurotoxic reduction in serotonin. Data on fatigue-assessment correlations will be presented. Conclusions Tryptophan catabolism and IDO-related cytokines are highly elevated in pSS, in particular in IFN type I signature positive patients. A disrupted tryptophan catabolism, resulting in reduced serotonin levels, might be the cause of severe fatigue and depression in these patients. Further unraveling this disrupted mechanism, and the possible neurotoxic role of IFN type I, will shed new light on unexplained fatigue in pSS. References Z. Brkic, N.I. Maria et al. 9Prevalence of interferon type I signature in CD14 monocytes of patients with Sjogren9s syndrome and association with disease activity and BAFF gene expression9. Ann Rheum Dis, 2013;72(5). Disclosure of Interest None declared DOI 10.1136/annrheumdis-2014-eular.3725

The kynurenine pathway (KP) is the main pathway by which tryptophan is metabolized. Its rate limiting enzyme indolamine 2, 3-dioxygenase (IDO) catalyses the production of kynurenine, which in turn is metabolised by either kynurenine 3-hydroxylase (KMO) which leads to the production of quinolinic acid (neurotoxic), or by kynurenine aminotransferase (KAT II) which yields kynurenic acid (neuroprotective). These enzymes are localised in microglia and astrocytes respectively. The present studies demonstrated that IFN-γ induces expression of IDO, KMO and kynase along with the production of neurotoxic molecules from BV-2 microglia. This was determined using a cell culture system whereby microglia were activated with IFN-γ and this conditioned medium was then placed on primary cortical neurons. Inhibition of the kynurenine pathway with 1-(D)-methyl-tryptophan (IDO inhibitor) and Ro 61-8048 (KMO inhibitor) completely attenuated this microglial-mediated neurotoxicity, as did the NMDA antagonist MK-801. Furthermore the anti-depressant fluoxetine partially attenuated this neurotoxicity and IFN-γ induced increases in IDO and kynase mRNA expression. Inhibition of classical neurotoxic factors released from microglia i.e. iNOS and the enzyme NADPH oxidase had no effect on this microglial mediated neurotoxicity, and neither did the anti-inflammatory agent dexamethasone. These results propose IFN-γ activated microglia induce neurotoxicity by activating the KP, and this can be attenuated using fluoxetine, suggesting a possible role for anti-depressants in ameliorating neuronal damage and in influencing the KP balance.