Exposure to forced swim stress does not alter central production of IL-1

Olax subscorpioidea prevented scopolamine-induced memory impairment through the prevention of oxido-inflammatory damage and modulation of cholinergic transmission

ETHNOPHARMACOLOGICAL RELEVANCE

Olax subscorpioidea oliv. is a shrub plant of the Olacaceae family with reported usage in ethnomedicine as a nootropic agent for the management of Alzheimer's-like dementia.

AIM

The aim of this study is to investigate the nootropic potential of methanol extract of Olax subscorpioidea (MEOS) in scopolamine-induced Alzheimer's-like dementia.

MATERIALS AND METHODS

Thirty male mice, assigned into six groups (n = 8), were used for this study. Group, I received distilled water, group II received scopolamine (1 mg/kg, i.p.), groups iii-v received 25, 50, and 100 mg/kg, p.o. of MEOS and scopolamine (1 mg/kg/i.p.), and group vi received donepezil 5 mg/kg, p.o.and scopolamine (1 mg/kg, i.p.). The animals were pre-treated with MEOS and Donepezil for 14 days, and scopolamine from the 8th to 14th day. Followed by cognitive, oxidative stress, neuroinflammation, and histology assessments.

RESULTS

100 mg/kg MEOS significantly reduced transfer latency and increased discrimination index in the elevated plus maze and novel object recognition test cognitive assessments. 100 mg/kg MEOS, significantly reduced oxidative stress, protect endogenous antioxidants, suppressed neuroinflammation, and acetylcholinesterase (ACHE) activity. The histomorphometry study of the hippocampus revealed that MEOS prevented extensive pyknosis, karyolysis, chromatolysis, and loss of hippocampal neurons that accompanied scopolamine treatment.

CONCLUSION

MEOS protected against Alzheimer's-like dementia via the suppression of neuroinflammation and oxidative stress associated with scopolamine-induced amnesic behavior.

Neuropharmacological effects of honey in lipopolysaccharide-induced neuroinflammation, cognitive impairment, anxiety and motor impairment

Objectives: Honey contains phenolic acids and flavonoids, which are significant in developing drugs against neuroinflammation. The study was designed to evaluate the ameliorative potential of honey in lipopolysaccharides-induced neuroinflammation.Methods: Thirty male Wistar rats were divided into six groups, namely: the control group (10 mL/kg vehicle), the LPS only group (250 µg/kg), the honey (0.26, 0.31 and 0.36 g/kg) and the ibuprofen (100 mg/kg). LPS (250 µg/kg i.p) was administered for 7days followed by the treatment with honey and Ibuprofen for another 7days. Animals were assessed for memory impairment and anxiety levels using a Novel object recognition test (NORT), elevated plus maze (EPM), and open field test (OFT). Brain levels of pro-inflammatory cytokine level, acetylcholinesterase activity, and oxidative stress were determined. The neuronal alteration was assessed histologically using cresyl fast violet staining of the hippocampus, prefrontal cortex, and striatum.Results: Honey (0.31 and 0.36 g/kg) significantly ameliorated LPS-induced memory impairment on NORT and increased time spent in the open arm and increased the locomotor activity in the OFT. Honey significantly (p < 0.05) reduced LPS-induced elevation of tumor necrosis factor (TNF-α) and interleukin-6 (IL-6). It significantly reduced malondialdehyde and nitrite levels in mice brains and reversed depletion of reduced glutathione levels. Honey attenuated LPS-induced elevation of acetylcholinesterase activity in rat brains. Cresyl violet staining showed the restoration of neuronal organization and Nissl body distribution in the hippocampus, prefrontal cortex and striatum compared to the LPS only group.Discussion: Honey effectively ameliorated LPS-induced poor cognitive performance, anxiety, motor coordination responses to neuroinflammation, and oxidative stress.

Neuroendocrine and neuroimmune responses in male and female rats: evidence for functional immaturity of the neuroimmune system during early adolescence

Adolescence is a developmental period characterized by rapid behavioral and physiological changes, including enhanced vulnerability to stress. Recent studies using rodent models of adolescence have demonstrated age differences in neuroendocrine responses and blunted neuroimmune responding to pharmacological challenges. The present study was designed to test whether this neuroimmune insensitivity would generalize to a non-pharmacological stress challenge. Male and female adolescent (P29-33) and adult (P70-80) Sprague Dawley rats were exposed to intermittent footshock for one-, two-, or two-hours + recovery. Plasma corticosterone and progesterone levels as well as gene expression of several cytokines and c-Fos gene expression in the paraventricular nucleus of the hypothalamus (PVN), the medial amygdala (MeA), and the ventral hippocampus (vHPC) were analyzed. The results of the present study demonstrated differences in response to footshock, with these differences dependent on age, sex, and brain region of interest. Adult males and females demonstrated time-dependent increases in IL-1β and IL-1R2 in the PVN, with these changes not evident in adolescent males and substantially blunted in adolescent females. TNFα expression was decreased in all regions of interest, with adults demonstrating more suppression relative to adolescents and age differences more apparent in males than in females. IL-6 expression was affected by footshock predominantly in the vHPC of adolescent and adult males and females, with females demonstrating prolonged elevation of IL-6 gene expression. In summary, central cytokine responses to acute stressor exposure are blunted in adolescent rats, with the most pronounced immaturity evident for the brain IL-1 signaling system.

Memantine and Ibuprofen pretreatment exerts anti-inflammatory effect against streptozotocin-induced astroglial inflammation via modulation of NMDA receptor-associated downstream calcium ion signaling

We had previously reported that neuroinflammation and memory impairment associated with intracerebroventricular streptozotocin (ICV STZ) injection in rats was due to glial activation and modulation of the N-methyl-D-aspartate (NMDA) receptor function. However, the exact role of the NMDA receptor and the molecules associated with downstream calcium ion signaling in STZ-induced astroglial activation is not known. Thus, in the present study, Memantine (an NMDA receptor antagonist) and Ibuprofen (an anti-inflammatory drug) were used as the pharmacological tool to investigate the molecular mechanisms involved in STZ-induced astroglial inflammation. We have studied the effect of STZ (100 μM) treatment for 24 h on NMDA receptor subunits (NR1, NR2A, and NR2B) expression and its associated calcium ion regulated molecules calcium/calmodulin-dependent protein kinase II subunit α (CaMKIIα), cyclic AMP-response element-binding (CREB) protein, Calpain, and Caspase 3. We have found a significant increase in the expression of NR1, NR2B, Calpain, and Caspase 3 expression, whereas a decrease in the level of NR2A, CaMKIIα, and CREB protein expression after 24 h of STZ treatment. These results indicate that STZ altered the NMDA receptor subunit expression and its downstream calcium (Ca²⁺) ion signaling molecules. We have also found that both Memantine (5 µM) and Ibuprofen (200 μM) significantly prevented the STZ-induced change in CaMKIIα, CREB, Calpain, and Caspase 3 expressions in C6 astrocytoma cells. Interestingly, only Memantine (and not Ibuprofen) was able to prevent the changes in NMDA receptor subunit expression in STZ-treated astrocytoma cells. STZ treatment also increased the level of glial fibrillary acidic protein (GFAP), tumor necrosis factor-alpha (TNF-α), inducible nitric oxide synthase (iNOS), and decreased the level of interleukin-10 (IL-10), indicating inflammatory condition, which was restored by both Memantine and Ibuprofen. These results suggest that both Memantine and Ibuprofen exert anti-inflammatory effect against STZ-induced astroglial activation and neuroinflammation via modulation of NMDA receptor-associated downstream calcium signaling cascade. However, only Memantine (not Ibuprofen) was able to revert STZ-induced changes in NMDA receptor subunit expression.

Adolescent forced swim stress increases social anxiety-like behaviors and alters kappa opioid receptor function in the basolateral amygdala of male rats

Adolescence is a developmental period marked by robust neural alterations and heightened vulnerability to stress, a factor that is highly associated with increased risk for emotional processing deficits, such as anxiety. Stress-induced upregulation of the dynorphin/kappa opioid receptor (DYN/KOP) system is thought to, in part, underlie the negative affect associated with stress. The basolateral amygdala (BLA) is a key structure involved in anxiety, and neuromodulatory systems, such as the DYN/KOP system, can 1) regulate BLA neural activity in an age-dependent manner in stress-naïve animals and 2) underlie stress-induced anxiety in adults. However, the role of the DYN/KOP system in modulating stress-induced anxiety in adolescents is unknown. To test this, we examined the impact of an acute, 2-day forced swim stress (FSS - 10 min each day) on adolescent (~postnatal day (P) 35) and adult Sprague-Dawley rats (~P70), followed by behavioral, molecular and electrophysiological assessment 24 h following FSS. Adolescent males, but not adult males or females of either age, demonstrated social anxiety-like behavioral alterations indexed via significantly reduced social investigation and preference when tested 24 h following FSS. Conversely, adult males exhibited increased social preference. While there were no FSS-induced changes in expression of genes related to the DYN/KOP system in the BLA, these behavioral alterations were associated with alterations in BLA KOP function. Specifically, while GABA transmission in BLA pyramidal neurons from non-stressed adolescent males responded variably (potentiated, suppressed, or was unchanged) to the KOP agonist, U69593, U69593 significantly inhibited BLA GABA transmission in the majority of neurons from stressed adolescent males, consistent with the observed anxiogenic phenotype in stressed adolescent males. This is the first study to demonstrate stress-induced alterations in BLA KOP function that may contribute to stress-induced social anxiety in adolescent males. Importantly, these findings provide evidence for potential KOP-dependent mechanisms that may contribute to pathophysiological interactions with subsequent stress challenges.

Repeated stress induces a pro-inflammatory state, increases amygdala neuronal and microglial activation, and causes anxiety in adult male rats

A link exists between immune function and psychiatric conditions, particularly depressive and anxiety disorders. Psychological stress is a powerful trigger for these disorders and stress influences immune state. However, the nature of peripheral immune changes after stress conflicts across studies, perhaps due to the focus on few measures of pro-inflammatory or anti-inflammatory processes. The basolateral amygdala (BLA) is critical for emotion, and plays an important role in the effects of stress on anxiety. As such, it may be a primary central nervous system (CNS) mediator for the effects of peripheral immune changes on anxiety after stress. Therefore, this study aimed to delineate the influence of stress on peripheral pro-inflammatory and anti-inflammatory aspects, BLA immune activation, and its impact on BLA neuronal activity. To produce a more encompassing view of peripheral immune changes, this study used a less restrictive approach to categorize and group peripheral immune changes. We found that repeated social defeat stress in adult male Sprague-Dawley rats increased the frequencies of mature T-cells positive for intracellular type 2-like cytokine and serum pro-inflammatory cytokines. Principal component analysis and hierarchical clustering was used to guide grouping of T-cells and cytokines, producing unique profiles. Stress shifted the balance towards a specific set that included mostly type 2-like T-cells and pro-inflammatory cytokines. Within the CNS component, repeated stress caused an increase of activated microglia in the BLA, increased anxiety-like behaviors across several assays, and increased BLA neuronal firing in vivo that was prevented by blockade of microglia activation. Because repeated stress can trigger anxiety states by actions in the BLA, and altered immune function can trigger anxiety, these results suggest that repeated stress may trigger anxiety-like behaviors by inducing a pro-inflammatory state in the periphery and the BLA. These results begin to uncover how stress may recruit the immune system to alter the function of brain regions critical to emotion.

Acute stress imposed during adolescence yields heightened anxiety in Sprague Dawley rats that persists into adulthood: Sex differences and potential involvement of the Medial Amygdala

Stressors experienced during adolescence have been demonstrated to have a long-lasting influence on affective behavior in adulthood. Notably, most studies to date have found these outcomes after chronic stress during adolescence. In the present study we tested how exposure to a single episode of acute footshock during early adolescence would modify subsequent adult anxiety- and depressive-like behaviors in male and female Sprague-Dawley rats. Adolescent rats were exposed to inescapable footshock (80 shocks, 5 s, 1.0 mA, 90 sec variable inter-trial interval (ITI)) at Post-natal day (PND) 29-30 and remained undisturbed until adulthood where they were evaluated with several behavioral assays for anxiety as well as depressive-like behavior via forced swim. In addition, gene expression changes were assessed immediately after a 30 min forced swim challenge in adulthood among several stress-related brain regions including the Central Amygdala (CeA), Medial Amygdala (MeA), ventral Hippocampus (vHPC), and Paraventricular Nucleus (PVN). Studies used real-time RT-PCR to examine the cytokines Interleukin-1β (IL-1β) and Interleukin-6 (IL-6), corticotropin-releasing hormone (CRH), the immediate early genes c-Fos, c-Jun, Egr1 and Arc, and several genes relating to corticosteroid receptor function (glucocorticoid and mineralocorticoid receptor (GR and MR, respectively), Gilz (glucocorticoid-induced leucine zipper), Sgk1 (Serum and Glucocorticoid regulated Kinase 1)). Behaviorally, males displayed signs of increased anxiety, most notably in the light-dark box, whereas females did not. No notable depressive-like behavior was observed in forced swim as a result of adolescent stress history, but adolescent footshock exacerbated the c-Fos response in the MeA produced by swim in both sexes. Forced swim led to increased IL-1β expression in the PVN regardless of adolescent stress history, whereas most HPA (hypothalamic-pituitaryadrenal) axis-related genes were largely unaffected in the vHPC. To determine the potential for β-adrenergic receptors to contribute to the male-specific anxiety-like behavior, two further studies applied a β-adrenergic agonist (isoproterenol) or antagonist (propranolol) in male rats. These studies found that propranolol administered 2 h after footshock led to a reduction in some anxiety-like behaviors as compared to controls. Overall, these findings suggest that exposure to a single, intense stress challenge imposed during adolescence may have sex-specific consequences across the lifespan and may implicate the MeA in developmental plasticity.

Neuroendocrine Regulation of Brain Cytokines After Psychological Stress

There is growing evidence that stress-induced brain cytokines are important in the etiology of depression and anxiety. Here, we review how the neuroendocrine responses to psychological stressors affect the immediate and long-term regulation of inflammatory cytokines within the brain and highlight how the regulation changes across time with repeated stress exposure. In doing so, we report on the percentage of studies in the literature that observed increases in either IL-1β, TNF-α, or IL-6 within the hypothalamus, hippocampus, or prefrontal cortex after either acute or chronic stress exposure. The key takeaway is that catecholamines and glucocorticoids play critical roles in the regulation of brain cytokines after psychological stress exposure. Central catecholamines stimulate the release of IL-1β from microglia, which is a key factor in the further activation of microglia and recruitment of monocytes into the brain. Meanwhile, the acute elevation of glucocorticoids inhibits the production of brain cytokines via two mechanisms: the suppression of noradrenergic locus coeruleus neurons and inhibition of the NFκB signaling pathway. However, glucocorticoids and peripheral catecholamines facilitate inflammatory responses to future stimuli by stimulating monocytes to leave the bone marrow, downregulating inhibitory receptors on microglia, and priming inflammatory responses mediated by peripheral monocytes or macrophages. The activation of microglia and the elevation of peripheral glucocorticoid and catecholamine levels are both necessary during times of stress exposure for the development of psychopathologies.

Sex differences in the regulation of brain IL-1β in response to chronic stress

Elevations in brain interleukin-1 beta (IL-1β) during chronic stress exposure have been implicated in behavioral and cognitive impairments associated with depression and anxiety. Two critical regulators of brain IL-1β production during times of stress are glucocorticoids and catecholamines. These hormones work in opposition to one another to inhibit (via glucocorticoid receptors) or stimulate (via beta-adrenergic receptors: β-AR) IL-1β production. While chronic stress often heightens both corticosterone and catecholamine levels, it remains unknown as to how chronic stress may affect the "yin-yang" balance between adrenergic stimulation and glucocorticoid suppression of brain IL-1β. To investigate this further, male and female rats underwent 4 days of stress exposure or served as non-stressed controls. On day 5, animals were administered propranolol (β-AR antagonist), metyrapone (a glucocorticoid synthesis inhibitor), vehicle, or both drugs and brain IL-1β mRNA was measured by rtPCR in limbic brain areas. In males, administration of propranolol had no effect on IL-1β expression in non-stressed controls but significantly reduced IL-1β in the hippocampus and amygdala of chronically stressed animals. In females, propranolol significantly reduced IL-1β in the amygdala and hypothalamus of both control and stressed rats. In male rats, metyrapone treatment significantly increased IL-1β mRNA regardless of stress treatment in all brain areas, while in female rats metyrapone only increased IL-1β in the hypothalamus. Interestingly, propranolol treatment blocked the metyrapone-induced increase in brain IL-1β indicating the increase in brain IL-1β following metyrapone treatment was due to increase β-AR activation. Additional studies revealed that metyrapone significantly increases norepinephrine turnover in the hypothalamus and medial prefrontal cortex in male rats and that microglia appear to be the cell type contributing to the production of IL-1β. Overall, data reveal that stress exposure in male rats affects the regulation of brain IL-1β by the norepinephrine-β-AR pathway, while stress had no effect in the regulation of brain IL-1β in female rats.

Stress and aging act through common mechanisms to elicit neuroinflammatory priming

Over the course of an animal's lifespan, there is a protracted breakdown in basic homeostatic functions. Stressors (both psychological and physiological) can accelerate this process and compromise multiple homeostatic mechanisms. For example, both stress and aging can modulate neuroinflammatory function and cause a primed phenotype resulting in a heightened neuroinflammatory profile upon immune activation. Microglia, the brain's resident myeloid cell, produce "silent" immune machinery in response to stress and aging that does not cause immediate immune activation; rather, these changes prime the cell for a subsequent immune insult. Primed microglia exhibit a hyperinflammatory response upon immune activation that can exacerbate pathology. In this review, we will explore parallels between stress- and aging-induced neuroinflammatory priming. First, we will provide a background on the basic principles of neuroimmunology. Next, we will discuss evidence that neuroinflammatory responses become primed in the context of both stress and aging. We will also describe cell-specific contributions to neuroinflammatory priming with a focus on microglia. Finally, common mechanisms underlying priming in the context of stress and aging will be discussed: these mechanisms include glucocorticoid signaling; accumulation of danger signals; dis-inhibition of microglia; and breakdown of circadian rhythms. Overall, there are multifarious parallels between stress- and aging-elicited neuroinflammatory priming, suggesting that stress may promote a form of premature aging. Further unravelling mechanisms underlying priming could lead to improved treatments for buffering against stress- and aging-elicited behavioral pathologies.

Neuroendocrine and neuroimmune adaptation to Chronic Escalating Distress (CED): A novel model of chronic stress

Acute and chronic stress challenges have a profound influence on the development and expression of subsequent affective disorders, alcohol use disorders, and natural aging processes. These experiments examined adaptation in neuroimmune and neuroendocrine responses that occurred as a result of exposure to a novel model of chronic stress, termed chronic escalating distress (CED). This model involves exposure to highly predictable daily stress challenges involving a systematic escalation in both the intensity and length of daily stress challenges, and has recently been shown to profoundly alter alcohol sensitivity. Male Sprague-Dawley rats were exposed to an 11 day procedure where days 1-5 consisted of 60  min of restraint, days 6-10 consisted of 60  min of restraint immediately followed by 30  min of forced swim, and on day 11 subjects were exposed to a 2 h session of intermittent footshock. Experiment 1 examined adaptation in the corticosterone (CORT) response at key points in the 11 day procedure, and found that the escalation in stressors disrupted habituation to restraint, whereas the CORT response to daily forced swim exposure increased across days. Experiment 2 investigated the impact of this stress paradigm on the expression of several cytokine (IL-1β, IL-6, TNF-α) and cellular activation marker (c-Fos, CD14, CD200R) genes in key brain regions (PVN, HPC, & PFC) known to be influenced by stress. Interestingly, a history of CED had no effect on footshock-induced neuroimmune changes (increased IL-1 in the PVN; increased IL-6 in the HPC and PFC). In addition, acute footshock and CED produced similar c-fos induction within the PVN whereas CED led to enhanced c-fos induction in both the HPC and PFC. These findings support recent work indicating that neuroimmune responses to acute stress challenges persisted in rats with a recent history of repeated stress exposure, and that these effects occurred contemporaneously with ongoing changes in HPA axis reactivity. Overall, this CED model may serve as a highly tractable model for studying adaptation to chronic stress, and may have implications for understanding stress-induced alterations in alcohol sensitivity and natural aging processes.

Brain Interleukin-1 Facilitates Learning of a Water Maze Spatial Memory Task in Young Mice

The proinflammatory cytokine interleukin-1 (IL-1) is produced by many types of cells, including immune cells in the periphery and glia and neurons in the brain. The type I IL-1 receptor (IL-1r1) is primarily responsible for transmitting the inflammatory effects of IL-1 and mediates several biological functions by binding to either IL-1α or IL-1β. IL-1β activation is associated with hippocampus-dependent memory tasks. Although IL-1β impairs spatial memory under certain pathophysiological conditions, IL-1β may be required for the normal physiological regulation of hippocampal plasticity and memory. In addition, brain IL-1β levels are thought to change in the hippocampus in an age-dependent manner. These findings suggest that IL-1β may have a beneficial, temporary effect on learning and memory in young mice, but the matter remains unclear. Therefore, we hypothesized that hippocampal IL-1β has a beneficial effect on spatial learning and memory in young mice via IL-1r1, which is diminished in adults. We investigated the performance of young (3-month-old) and adult (6-month-old) wild-type mice, IL-1β knockout mice (IL-1βko) and IL-1r1 knockout mice (IL-1r1ko) in learning a spatial memory task with a fixed platform in a water maze (WM) and measured the levels of IL-1β and IL-1α in the hippocampus and cortex of adult and young mice by using homogeneous time-resolved fluorescence (HTRF). Learning was significantly impaired in the training trials of the WM spatial memory task in young IL-1βko and IL-1r1ko mice but not in adult IL-1βko and IL-1r1ko mice. Moreover, young IL-1r1ko mice but not IL-1βko mice showed an impairment in long-term memory extinction, suggesting that IL-1α might facilitate memory extinction. In this study, the cytokine assay using HTRF did not indicate a higher expression of hippocampal IL-1 in young mice but cortical IL-1β and IL-1α were significantly increased in adult mice. We need to investigate the role of cortical IL-1 and the local IL-1 expression in the hippocampal neurons in the future.

A multispecies approach for understanding neuroimmune mechanisms of stress

The relationship between stress challenges and adverse health outcomes, particularly for the development of affective disorders, is now well established. The highly conserved neuroimmune mechanisms through which responses to stressors are transcribed into effects on males and females have recently garnered much attention from researchers and clinicians alike. The use of animal models, from mice to guinea pigs to primates, has greatly increased our understanding of these mechanisms on the molecular, cellular, and behavioral levels, and research in humans has identified particular brain regions and connections of interest, as well as associations between stress-induced inflammation and psychiatric disorders. This review brings together findings from multiple species in order to better understand how the mechanisms of the neuroimmune response to stress contribute to stress-related psychopathologies, such as major depressive disorder, schizophrenia, and bipolar disorder.

Repeated exposure to two stressors in sequence demonstrates that corticosterone and paraventricular nucleus of the hypothalamus interleukin-1β responses habituate independently

A wide range of stress-related pathologies such as post-traumatic stress disorder are considered to arise from aberrant or maladaptive forms of stress adaptation. The hypothalamic-pituitary-adrenal (HPA) axis readily adapts to repeated stressor exposure, yet little is known about adaptation in neuroimmune responses to repeated or sequential stress challenges. In Experiment 1, rats were exposed to 10 days of restraint alone (60 minutes daily), forced swim alone (30 minutes daily) or daily sequential exposure to restraint (60 minutes) followed immediately by forced swim (30 minutes), termed sequential stress exposure. Habituation of the corticosterone (CORT) response occurred to restraint by 5 days and swim at 10 days, whereas rats exposed to sequential stress exposure failed to display habituation to the combined challenge. Experiment 2 compared 1 or 5 days of forced swim with sequential stress exposure and examined how each affected expression of several neuroimmune and cellular activation genes in the paraventricular nucleus of the hypothalamus (PVN), prefrontal cortex (PFC) and hippocampus (HPC). Sequential exposure to restraint and swim increased interleukin (IL)-1β in the PVN, an effect that was attenuated after 5 days. Sequential stress exposure also elicited IL-6 and tumour necrosis factor-α responses in the HPC and PFC, respectively, which did not habituate after 5 days. Experiment 3 tested whether prior habituation to restraint (5 days) would alter the IL-1β response evoked by swim exposure imposed immediately after the sixth day of restraint. Surprisingly, a history of repeated exposure to restraint attenuated the PVN IL-1β response after swim in comparison to acutely-exposed subjects despite an equivalent CORT response. Overall, these findings suggest that habituation of neuroimmune responses to stress proceeds: (i) independent of HPA axis habituation; (ii) likely requires more daily sessions of stress to develop; and (iii) IL-1β displays a greater tendency to habituate after repeated stress challenges compared to other stress-reactive cytokines.

Gastro-protective and Anti-stress Efficacies of Monomethyl Fumarate and a Fumaria indica Extract in Chronically Stressed Rats

Results of the very first experiments conducted to evaluate therapeutic potentials of a fumarate containing Fumaria indica extract and of fairly low daily oral doses of monomethyl fumarate for prevention of chronic unavoidable foot-shock stress-induced gastric ulcers, and possible involvement of diverse neuro-hormonal and oxidative process in their stress response desensitizing effects are reported and discussed in this article. Preventive effects of 21 daily oral 60, 120, and 240 mg/kg doses of a standardized 50 % methanolic F. indica extract (MFI) and 1.25, 2.50, and 5.00 mg/kg/day of pure monomethyl fumarate (MMF) were compared in rats subjected to one hour daily unavoidable foot-shocks. A pharmaceutically well-standardized Withania somnifera (WS) root extract was used as a reference herbal anti-stress agent in all experiments. Effects of the treatments on stress-induced alterations in body weight, adrenal and spleen weights, gastric ulcer and ulcer index, weight of glandular stomach, protective mucosal glycoprotein content, cellular proliferation, oxidative stress on stomach fundus, and brain tissues of male rats were quantified. Other parameters quantified were plasma corticosterone levels, brain monoamine levels, and expressions of the cytokines TNF-α, IL-10, and IL-1β in blood and brain of stressed and treated rats. Most but not every observed stress-induced anomalies were suppressed or completely prevented by both MFI and pure MMF treatments in dose-dependent manner. Qualitatively, the observed activity profiles of both of them were similar to those of WS dose tested. These results reveal that both MFI and MMF are potent gastro-protective agents against chronic unavoidable stress-induced ulcers and strongly suggest that they act as regulators or modulators of monoamine, corticosterone, and cytokine homeostasis.

Stress-induced neuroinflammation is mediated by GSK3-dependent TLR4 signaling that promotes susceptibility to depression-like behavior

Most psychiatric and neurological diseases are exacerbated by stress. Because this may partially result from stress-induced inflammation, we examined factors involved in this stress response. After a paradigm of inescapable foot shock stress that causes learned helplessness depression-like behavior, eighteen cytokines and chemokines increased in mouse hippocampus, peaking 6-12h after stress. A 24h prior pre-conditioning stress accelerated the rate of stress-induced hippocampal cytokine and chemokine increases, with most reaching peak levels after 1-3h, often without altering the maximal levels. Toll-like receptor 4 (TLR4) was involved in this response because most stress-induced hippocampal cytokines and chemokines were attenuated in TLR4 knockout mice. Stress activated glycogen synthase kinase-3 (GSK3) in wild-type mouse hippocampus, but not in TLR4 knockout mice. Administration of the antidepressant fluoxetine or the GSK3 inhibitor TDZD-8 reduced the stress-induced increases of most hippocampal cytokines and chemokines. Stress increased hippocampal levels of the danger-associated molecular pattern (DAMP) protein high mobility group box 1 (HMGB1), activated the inflammatory transcription factor NF-κB, and the NLRP3 inflammasome. Knockdown of HMGB1 blocked the acceleration of cytokine and chemokine increases in the hippocampus caused by two successive stresses. Fluoxetine treatment blocked stress-induced up-regulation of HMGB1 and subsequent NF-κB activation, whereas TDZD-8 administration attenuated NF-κB activation downstream of HMGB1. To test if stress-induced cytokines and chemokines contribute to depression-like behavior, the learned helplessness model was assessed. Antagonism of TNFα modestly reduced susceptibility to learned helplessness induction, whereas TLR4 knockout mice were resistant to learned helplessness. Thus, stress-induces a broad inflammatory response in mouse hippocampus that involves TLR4, GSK3, and downstream inflammatory signaling, and these stress responses contribute to susceptibility to depression-like behavior in mice.

Divergent responses of inflammatory mediators within the amygdala and medial prefrontal cortex to acute psychological stress

There is now a growing body of literature that indicates that stress can initiate inflammatory processes, both in the periphery and brain; however, the spatiotemporal nature of this response is not well characterized. The aim of this study was to examine the effects of an acute psychological stress on changes in mRNA and protein levels of a wide range of inflammatory mediators across a broad temporal range, in key corticolimbic brain regions involved in the regulation of the stress response (amygdala, hippocampus, hypothalamus, medial prefrontal cortex). mRNA levels of inflammatory mediators were analyzed immediately following 30min or 120min of acute restraint stress and protein levels were examined 0h through 24h post-termination of 120min of acute restraint stress using both multiplex and ELISA methods. Our data demonstrate, for the first time, that exposure to acute psychological stress results in an increase in the protein level of several inflammatory mediators in the amygdala while concomitantly producing a decrease in the protein level of multiple inflammatory mediators within the medial prefrontal cortex. This pattern of changes seemed largely restricted to the amygdala and medial prefrontal cortex, with stress producing few changes in the mRNA or protein levels of inflammatory mediators within the hippocampus or hypothalamus. Consistent with previous research, stress resulted in a general elevation in multiple inflammatory mediators within the circulation. These data indicate that neuroinflammatory responses to stress do not appear to be generalized across brain structures and exhibit a high degree of spatiotemporal specificity. Given the impact of inflammatory signaling on neural excitability and emotional behavior, these data may provide a platform with which to explore the importance of inflammatory signaling within the prefrontocortical-amygdala circuit in the regulation of the neurobehavioral responses to stress.

Chronic Physical Stress Does Not Interact with Epstein-Barr Virus (EBV)-Encoded Dutpase to Alter the Sickness Response

Most adult humans have been infected with Epstein-Barr virus (EBV), which is thought to contribute to the development of chronic fatigue syndrome. Stress is known to influence the immune system and can exacerbate the sickness response. Although a role for psychological stress in the sickness response, particularly in combination with EBV-encoded deoxyuridine triphosphate nucleotidohydrolase (dUTPase) has been established, and the role of physical stressors in these interactions remains unspecified. In this study, we seek to determine the interaction of chronic physical (swim) stress and EBV-encoded dUTPase injection. We hypothesize that a chronic physical stressor will exacerbate the sickness response following EBV-encoded dUTPase injection. To test this hypothesis mice receive daily injections of EBV-encoded dUTPase or vehicle and are subjected to 15 min of swim stress each day for 14 days or left unmanipulated. On the final evening of injections mice undergo behavioral testing. EBV-encoded dUTPase injection alone produces some sickness behaviors. The physical swimming stress does not alter the sickness response.

Sulforaphane Ameliorates Okadaic Acid-Induced Memory Impairment in Rats by Activating the Nrf2/HO-1 Antioxidant Pathway

Okadaic acid (OKA) causes memory impairment and attenuates nuclear factor erythroid 2-related factor 2 (Nrf2) along with oxidative stress and neuroinflammation in rats. Sulforaphane (dietary isothiocyanate compound), an activator of Nrf2 signaling, exhibits neuroprotective effects. However, the protective effect of sulforaphane in OKA-induced neurotoxicity remains uninvestigated. Therefore, in the present study, the role of sulforaphane in OKA-induced memory impairment in rats was explored. A significant increased Nrf2 expression in the hippocampus and cerebral cortex was observed in trained (Morris water maze) rats, and a significant decreased Nrf2 expression in memory-impaired (OKA, 200 ng icv) rats indicated its involvement in memory function. Sulforaphane administration (5 and 10 mg/kg, ip, days 1 and 2) ameliorates OKA-induced memory impairment in rats. The treatment also restored Nrf2 and its downstream antioxidant protein expression (GCLC, HO-1) and attenuated oxidative stress (ROS, nitrite, GSH), neuroinflammation (NF-κB, TNF-α, IL-10), and neuronal apoptosis in the cerebral cortex and hippocampus of OKA-treated rats. Further, to determine whether modulation of Nrf2 signaling is responsible for the protective effect of sulforaphane, in vitro, Nrf2 siRNA and its downstream HO-1 inhibition studies were carried out in a rat astrocytoma cell line (C6). The protective effects of sulforaphane were abolished with Nrf2 siRNA and HO-1 inhibition in astrocytes. The results suggest that Nrf2-dependent activation of cellular antioxidant machinery results in sulforaphane-mediated protection against OKA-induced memory impairment in rats. Graphical Abstract ᅟ.

Intoxication- and withdrawal-dependent expression of central and peripheral cytokines following initial ethanol exposure

BACKGROUND

Evidence has emerged demonstrating that ethanol (EtOH) influences cytokine expression within the central nervous system, although most studies have examined long-term exposure. Thus, the cytokine response to an acute EtOH challenge was investigated, in order to characterize profiles of cytokine changes following acute exposure.

METHODS

Rats pups were injected intraperitoneally (i.p.) with 2-g/kg EtOH, and IL-1 mRNA and protein were assessed 0, 60, 120, 180, and 240 minutes post injection (Experiment 1). In Experiments 2 to 5, the expression of several cytokines was examined in adult male rats during acute intoxication (3 hours after 4-g/kg EtOH), as well as withdrawal (18 hours post injection), after i.p. or intragastric (i.g.) EtOH administration.

RESULTS

Early in ontogeny, acute EtOH significantly decreased brain IL-1 mRNA and protein. Subsequently, when adult rats were examined, significant and temporally dynamic alterations in central and peripheral cytokines were observed following acute i.p. EtOH exposure (4 g/kg). Although cytokine- and region-dependent central IL-6 expression was generally increased and tumor necrosis factor alpha decreased during intoxication, IL-1 expression exhibited increases during withdrawal. In the periphery, acute i.p. EtOH elevated expression of all cytokines, with the response growing in magnitude as the time post injection increased. Following acute i.g. EtOH (4 g/kg), intoxication-related increases in IL-6 expression were again observed in the paraventricular nucleus of the hypothalamus (PVN), although to a lesser extent. Long-term, voluntary, intermittent EtOH consumption resulted in tolerance to the effects of an i.g. EtOH challenge (4 g/kg) on PVN IL-6 expression, whereas these same elevations in IL-6 expression were still seen in the amygdala in rats with a history of moderate EtOH intake. Treatment with minocycline did not significantly attenuate i.p. or i.g. EtOH-induced changes in central cytokine expression.

CONCLUSIONS

Together, these studies provide a foundation for understanding fluctuations in central and peripheral cytokines following acute EtOH as potential contributors to the constellation of neural and behavioral alterations observed during EtOH intoxication and withdrawal.

A pre-conditioning stress accelerates increases in mouse plasma inflammatory cytokines induced by stress

Background

Major depressive disorder is a prevalent disease that is inadequately treated with currently available interventions. Stress increases susceptibility to depression in patients and rodent models. Depression is also associated with aberrant activation of inflammation, such as increases in circulating levels of interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNFα). The two main goals of this study were (i) to identify cytokine changes measuring a broad panel of 19 cytokines, and (ii) to test if a pre-conditioning stress altered the inflammatory response to a subsequent stress.

Result

Stress-induced changes in mouse plasma cytokines were measured by multiplex following administration of one or two daily stresses of inescapable foot shocks using the learned helplessness paradigm for modeling depression-like behavior.

Administration of inescapable foot shocks increased plasma levels of IL-1β, IL-6, TNFα, IL-3, IL-10, IL-13, IL-17A, IL-5, GM-CSF, IL-12(p70), IFN-γ, MIP-1α, MIP-1β, IL-1α, IL-2, KC, RANTES and G-CSF, with peak levels occurring in the range of 6 to 12 hr after stress. Pre-conditioning the mice 24 hr before with an equivalent inescapable foot shock stress resulted in similar magnitudes of increases in most cytokines as occurred after a single stress, but accelerated the increase, causing the levels of most cytokines to peak 1 hr after stress. These results demonstrate that a single stress induces the expression of many cytokines, and that sequential, daily stresses accelerates the rate of cytokine production.

Conclusions

Acute stress broadly activates inflammation in mice, and the inflammatory response is more rapid following repeated stress, actions that may contribute to deleterious effects of stress on depression and other stress-linked diseases.

Comparison of stress-induced and LPS-induced depressive-like behaviors and the alterations of central proinflammatory cytokines mRNA in rats

Although proinflammatory cytokine changes in depression have been studied widely, few investigations have searched for specific and common changes in cytokines. In the present study, two animal models of depression were compared: a chronic stress model using forced swim stress and an immune activation model using repeated central lipopolysaccharide (LPS) infusion. The levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 mRNA were examined in the brain regions of the prefrontal cortex, amygdala, and hippocampus using real-time polymerase chain reaction (RT-PCR). It was found that both chronic swim stress and repeated central LPS infusion induced depressive-like behaviors, including decreased body weight, reduced saccharin preference, and increased immobility time or shortened latency of immobility in the tail suspension test. Central TNF-α mRNA expression was elevated in both models and central IL-6 mRNA expression was unchanged in both models. Central IL-1β mRNA expression was increased only in the chronic immune activation model. The findings from this study suggest that TNF-α may be a common risk factor for inflammation in depressive disorders.

A potential role for the acid-sensing T cell death associated gene-8 (TDAG8) receptor in depression-like behavior

Inflammation has been suggested to contribute to the pathophysiology of depression. The T cell death associated gene-8 (TDAG8) receptor is a proton-sensing G-protein-coupled receptor (GPCR) expressed on immune cells in both the CNS and periphery. Previous work has shown modulation of inflammation by the TDAG8 receptor, with pro-inflammatory responses reported in the central nervous system (CNS). Given the link between depression and inflammation, the aim of the present study was to investigate the role of TDAG8 in depression relevant behaviors. Mice deficient in TDAG8 (TDAG8(-/-)) were tested in the forced swim test (FST) and sucrose preference paradigm. TDAG8 deficiency resulted in significant attenuation of immobility in the FST as compared to wild type TDAG8 (TDAG8(+/+)) mice. These differences were not due to alterations in motor activity evoked by TDAG8 deficiency as TDAG8(+/+) and TDAG8(-/-) mice displayed similar activity in the home cage or in a novel context. TDAG8(-/-) mice showed significantly higher consumption of sucrose compared to wild type mice although sucrose preference was not significantly different between genotypes. Collectively, our results support the involvement of the TDAG8 receptor in behavioral response relevant to depression. Further investigation is required to validate TDAG8 as a novel target linking inflammation and depression.

Neuroimmune mechanisms of stress: sex differences, developmental plasticity, and implications for pharmacotherapy of stress-related disease

The last decade has witnessed profound growth in studies examining the role of fundamental neuroimmune processes as key mechanisms that might form a natural bridge between normal physiology and pathological outcomes. Rooted in core concepts from psychoneuroimmunology, this review utilizes a succinct, exemplar-driven approach of several model systems that contribute significantly to our knowledge of the mechanisms by which neuroimmune processes interact with stress physiology. Specifically, we review recent evidence showing that (i) stress challenges produce time-dependent and stressor-specific patterns of cytokine/chemokine expression in the CNS; (ii) inflammation-related genes exhibit unique expression profiles in males and females depending upon individual, cooperative or antagonistic interactions between steroid hormone receptors (estrogen and glucocorticoid receptors); (iii) adverse social experiences incurred through repeated social defeat engage a dynamic process of immune cell migration from the bone marrow to brain and prime neuroimmune function and (iv) early developmental exposure to an inflammatory stimulus (carageenin injection into the hindpaw) has a lasting influence on stress reactivity across the lifespan. As such, the present review provides a theoretical framework for understanding the role that neuroimmune mechanisms might play in stress plasticity and pathological outcomes, while at the same time pointing toward features of the individual (sex, developmental experience, stress history) that might ultimately be used for the development of personalized strategies for therapeutic intervention in stress-related pathologies.

On the time course, generality, and regulation of plasma progesterone release in male rats by stress exposure

Although progesterone is most commonly regarded in terms of its role in the female estrous cycle, reproductive behavior, and pregnancy, progesterone is also a precursor to corticosterone (CORT) and is released from the adrenal glands of both sexes in response to stress. However, the relationship between plasma CORT and progesterone during times of stress has not been well established. To better characterize dynamic changes in progesterone release as a result of stressor exposure, plasma progesterone levels were measured using enzyme immunoassay under multiple conditions, including after stress exposure (footshock, restraint, and forced swim), manipulations of the hypothalamic-pituitary-adrenal axis (injection of metyrapone or dexamethasone, or adrenalectomy), and in response to CRH and ACTH injections. When plasma levels of ACTH, CORT, and progesterone were analyzed across studies, CORT and progesterone were found to be highly correlated and rarely dissociated. Additionally, it appears that in male rats, the adrenal glands are the principle source of circulating progesterone in response to stress. Interestingly, a detailed time course indicated lack of a circadian rhythm of progesterone secretion, despite a robust rhythm of circulating CORT. The current studies provide critical new information on the coincident release of progesterone and CORT in response to stress and their somewhat paradoxical dissociation across the circadian rhythm. These findings provide an important foundation for future studies that will examine the role of stress-induced progesterone in behavioral, neuroimmune, and neuroendocrine responses to stress.

Interleukin-1β-immunoreactive neurons in the hippocampus and paraventricular nucleus of the hypothalamus after stress stimulation in aged versus adult rats

It is believed that the impact of stress on interleukin-1β (IL-1β) depends on the ontogenetic age. This study examines the influence of acute or chronic exposure to forced-swim (FS) stress or high-light open-field (HL-OF) stimulation on the expression of IL-1β. Double immunofluorescence staining was used to reveal the density of IL-1β/NeuN (NeuN is a neuronal nuclear marker)-immunoreactive (-ir) cells in the hippocampal subfields CA1 and CA3, dentate gyrus (DG), and paraventricular nucleus (PVN) of the hypothalamus. Adult postnatal day 90 (P90) and aged (P720) rats were used in this experiment. The data showed a significant increase in the density of IL-1β/NeuN-ir cells in the CA1, CA3, DG, and PVN in P720 nonstressed rats in relation to P90 control animals. Neither FS nor HL-OF acute stimulation caused alteration in the density of IL-1β-ir neurons in any of the investigated structures in P90 and P720 rats in comparison with control groups. However, chronic FS caused a significant increase in CA3 and DG of P720 rats, and chronic HL-OF led to a significant increase in the density of IL-1β-ir neurons in the PVN of P90 rats and in all hippocampal subfields of P720 animals. These results indicate that chronic HL-OF stimulation is a factor that induces changes in the number of IL-1β-ir neurons in the PVN of adult rats, whereas both chronic FS and HL-OF are aggravating factors for the hippocampus of aged (P720) animals.

Glial activation and post-synaptic neurotoxicity: the key events in Streptozotocin (ICV) induced memory impairment in rats

In the present study the role of glial activation and post synaptic toxicity in ICV Streptozotocin (STZ) induced memory impaired rats was explored. In experiment set up 1: Memory deficit was found in Morris water maze test on 14-16 days after STZ (ICV; 3mg/Kg) administration. STZ causes increased expression of GFAP, CD11b and TNF-α indicating glial activation and neuroinflammation. STZ also significantly increased the level of ROS, nitrite, Ca(2+) and reduced the mitochondrial activity in synaptosomal preparation illustrating free radical generation and excitotoxicity. Increased expression and activity of Caspase-3 was also observed in STZ treated rat which specify apoptotic cell death in hippocampus and cortex. STZ treatment showed decrease expression of post synaptic markers CaMKIIα and PSD-95, while, expression of pre synaptic markers (synaptophysin and SNAP-25) remains unaltered indicating selective post synaptic neurotoxicity. Oral treatment with Memantine (10mg/kg) and Ibuprofen (50 mg/kg) daily for 13 days attenuated STZ induced glial activation, apoptotic cell death and post synaptic neurotoxicity in rat brain. Further, in experiment set up 2: where memory function was not affected i.e. 7-9 days after STZ treatment. The level of GFAP, CD11b, TNF-α, ROS and nitrite levels were increased. On the other hand, apoptotic marker, synaptic markers, mitochondrial activity and Ca(2+) levels remained unaffected. Collective data indicates that neuroinflammatory process and oxidative stress occurs earlier to apoptosis and does not affect memory function. Present study clearly suggests that glial activation and post synaptic neurotoxicity are the key factors in STZ induced memory impairment and neuronal cell death.

The inflamed axis: the interaction between stress, hormones, and the expression of inflammatory-related genes within key structures comprising the hypothalamic-pituitary-adrenal axis

Acute stress increases the expression of cytokines and other inflammatory-related factors in the CNS, plasma, and endocrine glands, and activation of inflammatory signaling pathways within the hypothalamic-pituitary-adrenal (HPA) axis may play a key role in later stress sensitization. In addition to providing a summary of stress effects on neuroimmune changes within the CNS, we present a series of experiments that characterize stress effects on members of the interleukin-1β (IL-1) super-family and other inflammatory-related genes in key structures comprising the HPA axis (PVN, pituitary and adrenal glands), followed by a series of experiments examining the impact of exogenous hormone administration (CRH and ACTH) and dexamethasone on the expression of inflammatory-related genes in adult male Sprague-Dawley rats. The results demonstrated robust, time-dependent, and asynchronous expression patterns for IL-1 and IL-1R2 in the PVN, with substantial increases in IL-6 and COX-2 in the adrenal glands emerging as key findings. The effects of exogenous CRH and ACTH were predominantly isolated within the adrenals. Finally, pretreatment with dexamethasone severely blunted neuroimmune changes in the adrenal glands, but not in the PVN. These findings provide novel insight into the relationship between stress, the expression of inflammatory signaling factors within key structures comprising the HPA axis, and their interaction with HPA hormones, and provide a foundation for better understanding the role of cytokines as modulators of hypothalamic, pituitary and adrenal sensitivity.

Standardized Extract of Bacopa monniera Attenuates Okadaic Acid Induced Memory Dysfunction in Rats: Effect on Nrf2 Pathway

The aim of the present study is to investigate the effect of standardized extract of Bacopa monnieri (memory enhancer) and Melatonin (an antioxidant) on nuclear factor erythroid 2 related factor 2 (Nrf2) pathway in Okadaic acid induced memory impaired rats. OKA (200 ng) was administered intracerebroventricularly (ICV) to induce memory impairment in rats. Bacopa monnieri (BM-40 and 80 mg/kg) and Melatonin (20 mg/kg) were administered 1 hr before OKA injection and continued daily up to day 13. Memory functions were assessed by Morris water maze test on days 13–15. Rats were sacrificed for biochemical estimations of oxidative stress, neuroinflammation, apoptosis, and molecular studies of Nrf2, HO1, and GCLC expressions in cerebral cortex and hippocampus brain regions. OKA caused a significant memory deficit with oxidative stress, neuroinflammation, and neuronal loss which was concomitant with attenuated expression of Nrf2, HO1, and GCLC. Treatment with BM and Melatonin significantly improved memory dysfunction in OKA rats as shown by decreased latency time and path length. The treatments also restored Nrf2, HO1, and GCLC expressions and decreased oxidative stress, neuroinflammation, and neuronal loss. Thus strengthening the endogenous defense through Nrf2 modulation plays a key role in the protective effect of BM and Melatonin in OKA induced memory impairment in rats.

The impact of ventral noradrenergic bundle lesions on increased IL-1 in the PVN and hormonal responses to stress in male sprague dawley rats

The impact of acute stress on inflammatory signaling within the central nervous system is of interest because these factors influence neuroendocrine function both directly and indirectly. Exposure to certain stressors increases expression of the proinflammatory cytokine, Il-1β in the hypothalamus. Increased IL-1 is reciprocally regulated by norepinephrine (stimulatory) and corticosterone (inhibitory), yet neural pathways underlying increased IL-1 have not been clarified. These experiments explored the impact of bilateral lesions of the ventral noradrenergic bundle (VNAB) on IL-1 expression in the paraventricular nucleus of the hypothalamus (PVN) after foot shock. Adult male Sprague Dawley rats received bilateral 6-hydroxydopamine lesions of the VNAB (VNABx) and were exposed to intermittent foot shock. VNABx depleted approximately 64% of norepinephrine in the PVN and attenuated the IL-1 response produced by foot shock. However, characterization of the hypothalamic-pituitary-adrenal response, a crucial prerequisite for interpreting the effect of VNABx on IL-1 expression, revealed a profound dissociation between ACTH and corticosterone. Specifically, VNABx blocked the intronic CRH response in the PVN and the increase in plasma ACTH, whereas corticosterone was unaffected at all time points examined. Additionally, foot shock led to a rapid and profound increase in cyclooxygenase-2 and IL-1 expression within the adrenal glands, whereas more subtle effects were observed in the pituitary gland. Together the findings were the 1) demonstration that exposure to acute stress increased expression of inflammatory factors more broadly throughout the hypothalamic-pituitary-adrenal axis; 2) implication of a modest role for norepinephrine-containing fibers of the VNAB as an upstream regulator of PVN IL-1; and 3) suggestion of an ACTH-independent mechanism controlling the release of corticosterone in VNABx rats.

The effects of central pro-and anti-inflammatory immune challenges on depressive-like behavior induced by chronic forced swim stress in rats

Although increasing evidence demonstrates that both chronic stressors and inflammatory immune activation contribute to pathophysiology and behavioral alterations associated with major depression, little is known about the interaction effect of central inflammatory immune activation and stress on depressive-like behavior. Our previous work has shown that 14-day chronic forced swim stress induces significant depressive-like behavior. The present investigation assessed whether pro-inflammatory cytokine and anti-inflammatory cytokine challenges have differential interaction effect on depressive-like behavior induced by chronic forced swim stress in rats. The pro-inflammatory and anti-inflammatory immune challenges were achieved respectively by central administration of lipopolysaccharide (LPS), a pro-inflammatory cytokine inducer, and interleukin-10 (IL-10), an anti-inflammatory cytokine. It was found that either central LPS treatment alone or chronic forced swim stress alone significantly induced depressive-like behavior, including reduced body weight gain, reduced saccharin preference and reduced locomotor activity. However, there was no significant synergistic or additive effect of central LPS treatment and stress on depressive-like behavior. LPS treatment did not exacerbate the depressive-like behavior induced by forced swim stress. Nevertheless, IL-10 reversed depressive-like behavior induced by forced swim stress, a finding indicating that IL-10 has antidepressant effect on behavioral depression induced by stress. The present findings provide new insight into the complexity of the immunity-inflammation hypothesis of depression.

Not all stress is equal: CREB is not necessary for restraint stress reinstatement of cocaine-conditioned reward

Stress elicits relapse to cocaine seeking in humans and in animal models. Cyclic AMP response element binding protein (CREB) is required for swim stress-induced reinstatement of cocaine conditioned place preference. However, the role of CREB in other stress-induced reinstatement models has not been examined. To determine whether CREB is required across different stressors we examined the ability of restraint to elicit reinstatement of cocaine-conditioned place preference in wild-type and CREBαΔ mutant mice. In contrast to previously published differences in swim stress-induced reinstatement, both wild-type and CREBαΔ mutant mice demonstrated restraint stress elicited reinstatement of cocaine-conditioned reward. While CREB is necessary for swim stress-elicited zif268 expression within the nucleus accubmens (NAc) shell and prelimbic cortex (PrL), restraint-stress-elicited comparable increases in zif268 expression within these regions in both wild-type and CREBαΔ mutant mice. Our findings suggest that not all stressors engage the same circuits or molecular mechanisms to elicit reinstatement behavior.

Corticosteroids limit microglial activation occurring during acute stress

Our previous studies demonstrated that exposure of animals to acute stress immediately induced morphological microglial activation in the brain. Here we investigated the effects of adrenal corticoids on microglial activation following acute stress. We compared microglial activation in vivo in adrenalectomized (ADX), Sham-operated (SHM), and adrenalectomy plus corticosterone (CORT) administered rats exposed to a 2-h period of acute water restraint stress. We found that: (1) acute stress induced microglial activation in SHM rats; (2) acute stress robustly enhanced microglial activation in ADX rats; (3) CORT treatment significantly reduced the effects of adrenalectomy. Thus, while acute stress has the ability to activate microglia, the magnitude of activation is negatively regulated by CORT. Glucocorticoids may serve as an important endogenous suppressive signal limiting neuroinflammation that might otherwise occur during stress.

Attractiveness of illness-associated odorant cues in female rats is modulated by ovarian hormones, but not associated with pro-inflammatory cytokine levels

Odorant cues released by rodents play a key role in mate preference/selection. The goal of the following series of studies was to determine the impact of acute illness, and the potential role of the inflammatory response, on the release of illness-associated odor cues from female rats. Adult female Sprague-Dawley rats were injected with lipopolysaccharide (LPS, 100 μg/kg) and their soiled bedding was used as a stimulus to naïve male odor recipients. While odored bedding from sick males elicited a robust avoidance response evidenced by decreased sniffing, avoidance and burying behavior, odored bedding from sick females elicited only a reduction in sniffing, indicating a reduction in odor attractiveness. Odor cues from ovariectomized, but not sham-operated females decreased sniffing behavior and increased avoidance in male odor recipients. Acute estradiol benzoate (EB, 20 μg/kg) replacement into ovariectomized females restored the investigatory response of male recipients toward odor cues, while LPS administration into ovariectomized oil or EB treated females had little impact on odor attractiveness. Measurement of cytokines in both brain (the paraventricular nucleus of the hypothalamus) and blood from female odor donors indicated increased expression of TNF-α, IL-1β, and IL-6 following LPS, which was not affected by EB treatment. These findings illustrate a critical sexual dimorphism by demonstrating that acute illness reduces the attractiveness of female odor, whereas odor cues from sick males are highly aversive. Moreover, the attractiveness of female odor appears to be associated with circulating ovarian hormone levels, but not central or peripheral inflammatory cytokines.

Enhancement of the hypothalamic-pituitary-adrenal axis but not cytokine responses to stress challenges imposed during withdrawal from acute alcohol exposure in Sprague-Dawley rats

RATIONALE

Alcohol withdrawal is associated with reduced activity, increased anxiety, and other signs of distress.

OBJECTIVE

The goal of the current studies was to determine whether acute ethanol exposure would alter hypothalamic-pituitary-adrenal (HPA) axis reactivity and cytokine responses to stress challenges imposed during the withdrawal period.

METHODS

Male Sprague-Dawley rats were intubated with 4 g/kg of ethanol to simulate acute binge-like ethanol intake. After characterizing the blood ethanol concentrations (BECs; Experiment 1), exploratory activity in a novel environment was explored at 10, 14 and 18 h after ethanol (Experiment 2) to characterize altered activity patterns indicative of withdrawal. In Experiment 3, rats were exposed to footshock during withdrawal to examine whether prior ethanol exposure would alter cytokine and HPA axis responses to stress. Experiments 4 and 5 investigated HPA axis sensitivity and gene expression changes during restraint imposed during withdrawal.

RESULTS

Prior ethanol exposure produced a period of stress hyper-reactivity evidenced by an enhanced HPA axis response (increased corticosterone and adrenocorticotropic hormone) observed during withdrawal. While this hyper-reactivity in response to two different stress challenges (novel environment and restraint) was accompanied by profound behavioral changes indicative of withdrawal, no alterations in cytokine changes evoked by stress were observed.

CONCLUSIONS

Taken together, these findings provide support for the hypothesis that alcohol withdrawal enhances HPA axis reactivity to stress challenges, though not likely as the result of heightened inflammatory signaling, and may have implications for understanding the mechanisms by which stress impacts relapse drinking in humans.

Chronic intermittent cold stress sensitizes neuro-immune reactivity in the rat brain

Chronic stress contributes to many neuropsychiatric disorders in which the HPA axis, cognition and neuro-immune activity are dysregulated. Patients with major depression, or healthy individuals subjected to acute stress, present elevated levels of circulating pro-inflammatory markers. Acute stress also activates pro-inflammatory signals in the periphery and in the brain of rodents. However, despite the clear relevance of chronic stress to human psychopathology, the effects of prolonged stress exposure on central immune activity and reactivity have not been well characterized. Our laboratory has previously shown that, in rats, chronic intermittent cold stress (CIC stress, 4°C, 6h/day, 14 days) sensitizes the HPA response to a subsequent novel stressor, and produces deficits in a test of cognitive flexibility that is dependent upon prefrontal cortical function. We have hypothesized that CIC stress could potentially exert some of these effects by altering the neuro-immune status of the brain, leading to neuronal dysfunction. In this study, we have begun to address this question by determining whether previous exposure to CIC stress could alter the subsequent neuro-immune response to an acute immunological challenge (lipopolysaccharide, LPS) or an acute heterologous stressor (footshock). We examined the response of the pro-inflammatory cytokines, IL1β and IL6, the enzyme cyclooxygenase 2, and the chemokines, CXCL1 and MCP-1 in plasma, hypothalamus and prefrontal cortex. There was no effect of CIC stress on basal expression of these markers 24h after the termination of stress. However, CIC stress enhanced the acute induction of the pro-inflammatory cytokines, IL1β and particularly IL6, and the chemokines, CXCL1 and MCP-1, in plasma, hypothalamus and prefrontal cortex in response to LPS, and also sensitized the hypothalamic IL1β response to acute footshock. Thus, sensitization of acute pro-inflammatory responses in the brain could potentially mediate some of the CIC-dependent changes in HPA and cognitive function.

Corticotropin releasing factor-1 receptor antagonism alters the biochemical, but not behavioral effects of repeated interleukin-1β administration

Activation of the immune system via administration of cytokines is used for the treatment of chronic viral infections such as hepatitis C and for cancers resistant to radiotherapy. Cytokine-based treatments induce a range of "sickness" behaviors (e.g. depression, anxiety, pain, anorexia, and fatigue). Activation of the hypothalamic pituitary-adrenal axis via the induction of corticotropin releasing factor (CRF) may underlie these unwanted side effects. This study used repeated systemic injections of the pro-inflammatory cytokine interleukin-1β (IL-1β) to model the sickness behaviors and biochemical effects of immune system activation. We assessed the ability of CRF type I receptor (CRF(1)) antagonism to reduce biochemical and behavioral signs of sickness induced by IL-1β treatment. Forty Wistar rats were assigned to one of four groups: 1) saline+vehicle; 2) saline+DMP904 (CRF(1) antagonist); 3) IL-1β+vehicle; 4) IL-1β+DMP904. Rats received intraperitoneal injections of either DMP904 or vehicle and of IL-1β or saline for six days. Sickness behavior was evaluated using body weight assessments and forced swim testing (FST). Blood and brain samples were collected to measure cytokine, p38 mitogen-activated protein kinase (MAPK), and phospho-p38 MAPK levels using multiplex techniques. There were significant reductions in body weights and FST immobility times associated with IL-1β administration. Rats administered IL-1β had significantly higher serum levels of IL-10, but not interferon-γ. Within the hippocampus, IL-1β reduced levels of p38 MAPK, but had no impact on levels of phospho-p38 MAPK except in the presence of DMP904. When administered alone, DMP904 had no significant effect on p38 MAPK or phospho-p38 MAPK in the hippocampus, but when given with IL-1β led to increased phosphorylation of p38 MAPK. IL-1β and DMP904 reduced levels of p38 MAPK within the hypothalamus, while co-administration of IL-1β and DMP904 abolished the effects of either drug alone. IL-1β decreased immobility time in the FST, and led to reductions in body weight, changes in serum cytokine levels and p38 MAPK regulation within the hippocampus and hypothalamus. DMP904 blocked some of the neurochemical effects of IL-1β, but did not impact the behavioral measures, or serum cytokines. Thus, additional studies will be needed to determine whether CRF(1) antagonism is an effective treatment for cytokine-induced sickness. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Rat strain differences in restraint stress-induced brain cytokines

Induction of brain cytokines during times of stress has potent effects on altering behavior, mood, and cognitive functioning. Currently, it is unknown why exposure to some stressors such as tailshock and footshock elevate brain cytokines, while exposure to swim, predator odor, and restraint stress do not. Recent data indicate that brain noradrenergic signaling mediates brain cytokine production suggests magnitude of norepinephrine release during stress may be critical in initiating brain cytokine production. The aim of the current study was to investigate stress-induced brain cytokines between rat strains that differ in their magnitude of stress responsiveness as measured by brain norepinephrine and HPA responses. Sprague-Dawley and Fischer rats were placed in a restraint bag for 1 h or 2 h and sacrificed immediately following stressor termination. Exposure to restraint significantly elevated hypothalamic interleukin (IL)-1β and IL-1 receptor type (R) 2 mRNA after 1 h and IL-1β protein after 2 h in the high stress responsive Fischer rats, but not in Sprague-Dawley rats. IL-6, IL-1R1, Il-1 receptor antagonist (RA), and cyclooxygenase (Cox)-2 mRNA were not altered and neither there was expression of any cytokines in the hippocampus or circulating cytokines in either strain. Administration of desipramine (a norepinephrine reuptake inhibitor) to Sprague-Dawley rats was sufficient either alone or in combination with stress to increase IL-1β mRNA in the hypothalamus and desipramine combined with stress was sufficient to increase IL-1R2 mRNA in the hypothalamus. These data support our hypothesis that there is a critical threshold of brain norepinephrine necessary to stimulate brain cytokines, which may help to explain why severe stressors are more commonly reported to induce brain cytokines. These data also suggest an organisms' susceptibility to stress-induced brain cytokine production, depends on responsiveness and regulation of noradrenergic neurons.

The role of neuroinflammation in the release of aversive odor cues from footshock-stressed rats: Implications for the neural mechanism of alarm pheromone

Stressed animals have been known to release aversive chemosignals toward which conspecifics show avoidance-like responses. The present studies assessed whether inflammatory cytokine responses provoked by footshock stress modulate odor signals released from male rats. Male rats were exposed to 30min of intermittent footshock (60 shocks, 1.0mA, 100ms each, variable ITI of 30s) or remained in their home cages as non-stressed controls. Real time RT-PCR analysis of brain tissues indicated that footshock increased the pro-inflammatory cytokine, IL-1β and hnCRH as well as c-fos mRNA expressions in the paraventricular nucleus, and the bed nucleus of the stria terminalis, and increased plasma corticosterone levels. Soiled bedding collected from rats exposed to 30-min, but not 5-min, of footshock elicited a differential response, as expressed by decreased sniffing and increased avoidance in male test subjects. Soiled bedding from rats given corticosterone injection (s.c. 1.25 or 3.75mg/ml) 3h before bedding collection evoked no avoidance response in odor-recipients. Furthermore, ICV infusion of the anti-inflammatory cytokine IL-10 (20 or 200ng) into the stimulus animals 30-min before a 30-min footshock session, had no effect on plasma corticosterone levels in the stimulus animals, but attenuated the release of aversive odor as indicated by dose-dependently diminished avoidance in odor-recipient rats. These results demonstrated that stressed rats release odorant cues that cause other rats to move away from the source of the signal. Such stress-induced chemosignals may be mediated by inflammatory cytokine responses in the brain.

In animal models, psychosocial stress-induced (neuro)inflammation, apoptosis and reduced neurogenesis are associated to the onset of depression

Recently, the inflammatory and neurodegenerative (I&ND) hypothesis of depression was formulated (Maes et al., 2009), i.e. the neurodegeneration and reduced neurogenesis that characterize depression are caused by inflammation, cell-mediated immune activation and their long-term sequels. The aim of this paper is to review the body of evidence that external stressors may induce (neuro)inflammation, neurodegeneration and reduced neurogenesis; and that antidepressive treatments may impact on these pathways. The chronic mild stress (CMS) and learned helplessness (LH) models show that depression-like behaviors are accompanied by peripheral and central inflammation, neuronal cell damage, decreased neurogenesis and apoptosis in the hippocampus. External stress-induced depression-like behaviors are associated with a) increased interleukin-(IL)1β, tumor necrosis factor-α, IL-6, nuclear factor κB, cyclooxygenase-2, expression of Toll-like receptors and lipid peroxidation; b) antineurogenic effects and reduced brain-derived neurotrophic factor (BDNF) levels; and c) apoptosis with reduced levels of Bcl-2 and BAG1 (Bcl-2 associated athanogene 1), and increased levels of caspase-3. Stress-induced inflammation, e.g. increased IL-1β, but not reduced neurogenesis, is sufficient to cause depression. Antidepressants a) reduce peripheral and central inflammatory pathways by decreasing IL-1β, TNFα and IL-6 levels; b) stimulate neuronal differentiation, synaptic plasticity, axonal growth and regeneration through stimulatory effects on the expression of different neurotrophic factors, e.g. trkB, the receptor for brain-derived neurotrophic factor; and c) attenuate apoptotic pathways by activating Bcl-2 and Bcl-xl proteins, and suppressing caspase-3. It is concluded that external stressors may provoke depression-like behaviors through activation of inflammatory, oxidative, apoptotic and antineurogenic mechanisms. The clinical efficacity of antidepressants may be ascribed to their ability to reverse these different pathways.

Cytokines mediated inflammation and decreased neurogenesis in animal models of depression

In patients with major depression or in animal models of depression, significantly increases in the concentrations of pro-inflammatory cytokines have been consistently reported. Proinflammatory cytokines can stimulate the hypothalamic-pituitary-adrenal (HPA) axis to release stress hormone, glucocorticoids. As a consequence of excessive inflammatory response triggered by pro-inflammatory cytokines in the periphery, free radicals, oxidants and glucocorticoids are over-produced, which can affect glial cell functions and damage neurons in the brain. Indeed, decreased neurogenesis and the dysfunction of neurotrophic system (up- or down-regulations of neurotrophins and their receptors) have been recently found. Effective treatments for depressive symptoms, such as antidepressants and omega-3 fatty acids can increase or modulate neurotrophic system and enhance neurogenesis. However, the relationship between glial cells; microglia (mostly involved in neuroinflammation) and astrocytes (producing neurotrophins), and the contribution of inflammation to decreased neurogenesis and dysfunction of neurotrophic system are almost unknown. This review first introduces changes in behavior, neurotransmitter, cytokine and neurogenesis aspects in depressed patients and several animal models of depression, secondly explores the possible relationship between pro- and anti-inflammatory cytokines and neurogenesis in these models, then discusses the effects of current treatments on inflammation, neurotrophic system and neurogenesis, and finally pointes out the limitations and future research directions.

Stress-dependent changes in neuroinflammatory markers observed after common laboratory stressors are not seen following acute social defeat of the Sprague Dawley rat

Exposure to acute stress has been shown to increase the expression of pro-inflammatory cytokines in brain, blood and peripheral organs. However, the nature of the inflammatory response evoked by acute stress varies depending on the stressor used and species examined. The goal of the following series of studies was to characterize the consequences of social defeat in the Sprague Dawley (SD) rat using three different social defeat paradigms. In Experiments 1 and 2, adult male SD rats were exposed to a typical acute resident-intruder paradigm of social defeat (60 min) by placement into the home cage of a larger, aggressive Long Evans rat and brain tissue was collected at multiple time points for analysis of IL-1β protein and gene expression changes in the PVN, BNST and adrenal glands. In subsequent experiments, rats were exposed to once daily social defeat for 7 or 21 days (Experiment 3) or housed continuously with an aggressive partner (separated by a partition) for 7 days (Experiment 4) to assess the impact of chronic social stress on inflammatory measures. Despite the fact that social defeat produced a comparable corticosterone response as other stressors (restraint, forced swim and footshock; Experiment 5), acute social defeat did not affect inflammatory measures. A small but reliable increase in IL-1 gene expression was observed immediately after the 7th exposure to social defeat, while other inflammatory measures were unaffected. In contrast, restraint, forced swim and footshock all significantly increased IL-1 gene expression in the PVN; other inflammatory factors (IL-6, cox-2) were unaffected in this structure. These findings provide a comprehensive evaluation of stress-dependent inflammatory changes in the SD rat, raising intriguing questions regarding the features of the stress challenge that may be predictive of stress-dependent neuroinflammation.

Dysregulated neuronal-microglial cross-talk during aging, stress and inflammation

Communication between neurons and microglia is essential for maintaining homeostasis in the central nervous system (CNS) during both physiological and inflammatory conditions. While microglial activation is necessary and beneficial in response to injury or disease, excessive or prolonged activation can have deleterious effects on brain function and behavior. To prevent inflammation-associated damage, microglia reactivity is actively modulated by neurons in the healthy brain. Age or stress-induced disruption of normal neuronal-microglial communication could lead to an aberrant central immune response when additional stressors are applied. Recent work suggests that both aging and stress shift the CNS microenvironment to a pro-inflammatory state characterized by increased microglial reactivity and a reduction in anti-inflammatory and immunoregulatory factors. This review will discuss how heightened neuroinflammation associated with aging and stress may be compounded by the concomitant loss of neuronally derived factors that control microglial activation, leaving the brain vulnerable to excessive inflammation and neurobehavioral complications upon subsequent immune challenge.