Cytokine-induced sickness behaviour: mechanisms and implications

Somatization: a psychoneuroimmune perspective

The concept of somatization has a long history in psychosomatic medicine. What is missing, however, is an understanding of the way patients are able to perceive and represent somatic symptoms. Recent advances in psychoneuroimmunology offer new perspectives in this area. Proinflammatory cytokines produced by cells of the innate immune system in response to pathogen-associated molecular patterns and to endogenous danger signals act on the central nervous system via afferent and humoral pathways to trigger a brain cytokine system that organizes the sickness response in its subjective, behavioral, and metabolic components. There is evidence that prolonged activation of this system can precipitate the development of depressive disorders in vulnerable patients. The mechanisms that are responsible for the transition from sickness to depression involve alterations in tryptophan metabolism. There is also some indication that the brain cytokine system can become sensitized in response to non-immune stressors or to immune stressors occurring early in life. All these new findings have the potential to contribute to a renewed biopsychological approach to somatization and somatoform disorders.

Inhibition of vagally mediated immune-to-brain signaling by vanadyl sulfate speeds recovery from sickness

To the ill patient with diabetes, the behavioral symptoms of sickness such as fatigue and apathy are debilitating and can prevent recuperation. Here we report that peripherally administered insulin-like growth factor 1 (IGF-1) attenuates LPS-dependent depression of social exploration (sickness) in nondiabetic (db/+) but not in diabetic (db/db) mice. We show that the insulin/IGF-1 mimetic vanadyl sulfate (VS) is effective at augmenting recovery from sickness in both db/+ and db/db mice. Specifically, peak illness was reached at 2 h for both VS and control animals injected with LPS, and VS mice recovered 50% faster than non-VS-treated animals. Examination of the mechanism of VS action in db/+ mice showed that VS paradoxically augmented peritoneal macrophage responsivity to LPS, increasing both peritoneal and ex vivo macrophage production of IL-1beta and IL-6 but not TNF-alpha. The effects of VS in promoting recovery from sickness were not restricted to LPS, because they were also observed after direct administration of IL-1beta. To explore the possibility that VS impairs immune-to-brain communication via vagal afferents, the vagally mediated satiety-inducing effects of cholecystokinin 8 were tested in db/+ mice. Cholecystokinin decreased food intake in saline-injected mice but not in VS-treated mice. VS also inhibited LPS-dependent up-regulation of IL-1beta and IL-6 mRNA in the brain, while increasing by 50% the cerebral expression of transcripts of the specific antagonist of IL-1 receptors IL-1RA and IL-1R2. Taken together, these data indicate that VS improves recovery from LPS-induced sickness by blocking vagally mediated immune-to-brain signaling and by up-regulating brain expression of IL-1beta antagonists.

IL-6 levels decrease with SSRI treatment in patients with major depression

OBJECTIVE

Some evidence indicates that an immune response with an increased production of proinflammatory cytokines often accompanies major depression. The objective of this study was to examine the serum levels of IL-6 in patients with major depression and the changes occurring in IL-6 levels during treatment with selective serotonin reuptake inhibitors (SSRI).

METHOD

Twenty-three patients with a DSM-IV diagnosis of major depressive disorder and 23 healthy matched controls were included in the study. The severity of depression was measured with the Hamilton rating scale for depression. Blood samples for IL-6 levels were obtained at baseline and at week 6 of treatment and IL-6 concentrations were evaluated using a solid phase sandwich enzyme immunoassay. All patients were treated with an SSRI.

RESULTS

The IL-6 levels showed no statistically significant difference between the patients and the controls at baseline. However, IL-6 levels after treatment with SSRIs were significantly lower compared with the baseline IL-6 levels of both the patients and the controls.

CONCLUSION

The results of this study suggest that proinflammatory cytokines show some changes during the course of treatment of major depression. These findings might also be considered as supporting the hypothesis of a modulatory role of antidepressants on the immune system.

Endotoxin- or pro-inflammatory cytokine-induced sickness behavior as an animal model of depression: focus on anhedonia

In humans, exposure to endotoxins or pro-inflammatory cytokines induces a number of neuropsychological symptoms collectively referred to as 'flu-like syndrome'. The degree of overlap between flu-like syndrome and major depressive disorder is considerable and a close linkage between these has been predicted to arise due to hypersecretion of endogenous pro-inflammatory cytokines and activation of the hypothalamic pituitary adrenal axis. In animals, exposure to pro-inflammatory cytokines or endotoxins induces a 'sickness behavior' syndrome that is analogous to flu-like symptoms observed in human patients. The goal of the current paper is to review evidence implicating endotoxin- or cytokine-induced sickness behavior as an animal model of depression, with an emphasis on reduced consumption of highly palatable substances as a defining feature.

Stress and depression in informal family caregivers of patients with Alzheimer’s disease

Family caregiving of older individuals with Alzheimer’s disease is becoming widespread in the USA and around the world because of the aging of the population. As a result, family members are increasingly being asked to perform complex tasks similar to those carried out by paid health or social service providers. Dementia caregiving presents unique and extreme challenges associated with caring for someone with cognitive and behavioral impairment. This article summarizes the extensive literature on dementia caregiving, identifies key issues and major findings regarding the definition and prevalence of caregiving, and reviews the epidemiological, cultural, individual and biological factors contributing to caregiver stress and depression. The author describes the psychiatric and physical health effects of caregiving and reviews various intervention approaches to improving caregiver burden, depression and quality of life. The author offers a perspective on future directions in dementia caregiver research and development of more effective interventions.

Effects of Interferon-β1a on the Hypothalamic-Pituitary-Adrenal Axis, Leukocyte Distribution and Mood States in Multiple Sclerosis Patients

Acute interferon-beta (IFN-beta) administration transiently activates the hypothalamic-pituitary-adrenal (HPA) axis, increases granulocytes, and reduces lymphocytes in peripheral blood. To test whether these effects are still present after long-term treatment, 13 patients with relapsing-remitting multiple sclerosis were analyzed at baseline, and 1, 2, 4, and 8 h after IFN-beta 1a injection at two occasions: at the initial administration and after 1 year of continuous treatment. Long-term treatment reduced the responsiveness of the HPA axis to the injection, and abolished the distributional changes in leukocyte numbers. One-year treatment with IFN-beta 1a did not induce mood alterations as assessed by the Profile of Mood States. These results suggest that long-term IFN-beta therapy has a profound impact on leukocyte distribution and the neuroendocrine response to the drug.

Depression and renal disease

Major depressive disorder (MDD) is a highly prevalent disease, frequently characterized by recurrent or chronic course, and by comorbidity with other medical illnesses. The lifetime prevalence of MDD ranges up to 17% in the general population, and it almost doubles in patients with diabetes (9-27%), stroke (22-50%), or cancer (18-39%). Moreover, MDD worsens the prognosis, quality of life, and treatment compliance of patients with comorbid medical illnesses. Similar to what is observed with other comorbid illnesses, MDD worsens the outcome of kidney disease patients by increasing both morbidity and mortality. Treatment of depressive symptoms in renal failure patients increases medication acceptability and therefore potentially improves the overall patient outcome. The issue of the safety of antidepressant treatment in subjects with renal failure is frequently counterbalanced by the risks associated with depression comorbidity, provided that antidepressants with a low volume of distribution and low protein binding are prescribed, and most important, at low initial doses. Screening for CYP isoenzyme interactions with current medications is also recommended before starting antidepressant treatment.

Impairment of blood-cerebrospinal fluid barrier properties by retrovirus-activated T lymphocytes: reduction in cerebrospinal fluid-to-blood efflux of prostaglandin E2

The choroid plexus epithelium forms the interface between the blood and the CSF. In conjunction with the tight junctions restricting the paracellular pathway, polarized specific transport systems in the choroidal epithelium allow a fine regulation of CSF-borne biologically active mediators. The highly vascularized stroma delimited by the choroidal epithelium can be a reservoir for retrovirus-infected or activated immune cells. In this work, new insight in the implication of the blood-CSF barrier in neuroinfectious and inflammatory diseases is provided by using a differentiated cellular model of the choroidal epithelium, exposed to infected T lymphocytes. We demonstrate that T cells activated by a retroviral infection, but not non-infected cells, reduce the transporter-mediated CSF-to-blood efflux of organic anions, in particular that of the potent pro-inflammatory prostaglandin PGE2, via the release of soluble factors. A moderate alteration of the paracellular permeability also occurs. We identified the viral protein Tax, oxygenated free radicals, matrix-metalloproteinases and pro-inflammatory cytokines as active molecules released during the exposure of the epithelium to infected T cells. Among them, tumour necrosis factor and interleukin 1 are directly involved in the mechanism underlying the decrease in some choroidal organic anion efflux. Given the strong involvement of CSF-borne PGE2 in sickness behaviour syndrome, these data suggest that the blood-CSF barrier plays an important role in the pathophysiology of neuroinflammation and neuroinfection, via changes in the transport processes controlling the CSF biodisposition of PGE2.

Clinical assessment of the entry into neurological state in rat experimental African trypanosomiasis

Human African trypanosomiasis, caused by Trypanosoma brucei (T.b.) gambiense or rhodesiense, evolves in two stages: haemolymphatic stage and meningo-encephalitic stages, the latter featuring numerous neurological disorders. In experimental models infected with diverse T.b. sub-species, body weight (BW) loss, drop in food intake (FI), and hypo-activity after an asymptomatic period suggest the occurrence of a similar two-stage organization. In addition to daily measurement of BW and FI, body core temperature (T(co)) and spontaneous activity (SA) were recorded by telemetry in T.b. brucei-infected rats. After a 10--12-day symptom-free period, a complex clinical syndrome occurred suddenly. If the animal survived the access, the syndrome re-occurred at approximately 5-day intervals until death. The syndrome was made of a drop in FI and BW, a sharp decrease in T(co) and a loss of SA, suggesting a brisk alteration of the central nervous system functioning. Such events confirm the existence of a two-stage disease development in experimental trypanosomiasis. The entry into the second stage is marked by the occurrence of the first access, BW follow-up being essential and often sufficient its determination.

Cytokine regulation of tryptophan metabolism in the hypothalamic-pituitary-adrenal (HPA) axis: implications for protective and toxic consequences in neuroendocrine regulation

AIM

Indoleamine 2,3-dioxygenase (IDO) catalyzation of tryptophan is the first rate-limiting step of the kynurenine pathway in the majority of tissues. The kynurenine pathway produces neurotoxic metabolites such as 3-hydroxykinurenine and quinolinic acid. IDO is inducible by the cytokine interferon-gamma (IFN-gamma) and has been proposed to mediate the sickness behavior of patients with infectious or other inflammatory diseases.To better understand the neuroendocrine component of cytokine induced sickness behavior we determined the effects of the pro-inflammatory cytokine IFN-gamma and the anti-inflammatory cytokine IL-10 on IDO expression in cells derived from the hypothalamic-pituitary-adrenal axis (HPA): GT1-7 hypothalamic, AtT-20 pituitary, and Y-1 adrenal cells.

METHODS

Reverse transcriptase polymerase chain reaction (RT-PCR) was performed to check the IDO expression from IFN-gamma and IL-10 treated cells such as GT1-7, AtT-20 and Y-1 cells.

RESULTS

We found that IFN-gamma induces IDO expression after 4 h treatment in GT1-7 and AtT-20 cells. IL-10 was also able to suppress IFN-gamma induced IDO expression in these cells. In Y-1 adrenal cells, IFN-gamma treatment had no effect on IDO expression.

CONCLUSIONS

Our results indicate that cytokines such as IFN-gamma and IL-10 are able to regulate IDO expression in cells of hypothalamic and pituitary origin. The ability of IL-10 to suppress IFN-gamma induced IDO expression implies that IL-10 has a putative neuroprotective role in the HPA axis. It can act at two levels, systemically by inhibiting sickness behavior-related Th1 cytokine synthesis and more centrally by inhibiting the kynurenine pathway.

Cytokines, stressors, and clinical depression: augmented adaptation responses underlie depression pathogenesis

By influencing the central nervous system, cytokines, which regulate immune function innately and adaptively, may play a key role in mediating depression-like neuro-behavioral changes. However, the similarity between cytokine and stressor-effects in animal models raises a question about the degree to which behavioral and neurochemical outcomes of cytokine challenge represent depressive disorder per se. The present review attempts to illustrate the degree of overlap between cytokines and stressors with respect to their effects on neurochemistry and behavior in animal models. The review also shows how short-term effects of cytokine exposure in typical animals may be discerned from characteristics that might otherwise be described as depression-like. By comparing outcomes of immune challenge in typical rodent strains (e.g., Sprague-Dawley [SD], Wistar) and an accepted animal model of depression (e.g., Fawn Hooded [FH] rodent strain), differences between short-term effects of cytokines and depression-like characteristics in rodents are demonstrated. Additionally, because it is known that preexisting vulnerability to depression may affect outcomes of immune challenge, we further compare immunological, biochemical and behavioral effects of cytokines between SD and FH rodent strains. Interestingly, the acute neurochemical and behavioral effects of the cytokine interleukin 1alpha (IL-1alpha) reveal stressor-like responses during behavioral habituation in both strains, though this appears to a stronger degree in FH animals. Further, the subacute response to IL-1alpha vastly differed between strains, indicating differences in adaptive mechanisms. Thus, stressor-like effects of immune challenge, particularly in FH animals, provide validation for recent "cross-sensitization" models of depression pathogenesis that incorporate immune factors.

Cytokine mRNA levels in brain and peripheral tissues of the rat: relationships with plus-maze behavior

There is evidence that interleukin (IL)-2 may be related to anxiety as measured in the elevated plus-maze. Recently, we showed that normal adult male Wistar rats can differ systematically in this test of avoidance behavior, that is, time spent on the open arms of the elevated plus-maze. Rats with low open arm time had higher striatal levels of IL-2 mRNA than those with high open arm time, but did not differ significantly in expression of other striatal cytokine mRNA. Here, we investigated whether these expression effects are anatomically specific to the striatum. Therefore, we asked in this double-blind study whether elevated plus-maze behavior may also be related to endogenous levels of cytokine mRNA in other brain regions, which play a role for anxiety, namely the amygdala, hippocampus, and the prefrontal cortex. Additionally, and as peripheral controls, immuno-neuro-endocrine relevant tissues (adrenal glands, spleen) were analyzed. Based on open arm time in the elevated plus-maze, male Wistar rats were divided into sub-groups with either low or high open arm time behavior. Then, IL-1beta, IL-2, IL-6, and tumor necrosis factor (TNF)-alpha cDNA levels were measured post-mortem using semi-quantitative, competitive, reverse transcription polymerase chain reaction. First, we found that cytokine expressions differed considerably between and within these central and peripheral tissues. Secondly, rats with high compared to low open arm time behavior showed higher IL-2 mRNA levels in the prefrontal cortex, which is an inverse pattern to what we recently found in the striatum. These results provide new evidence indicating that cytokine mRNA in the brain can be related to elevated plus-maze behavior and that this relationship is site (prefrontal cortex, striatum)- and cytokine mRNA-specific (IL-2).

Recombinant human interferon-alpha does not alter reward behavior, or neuroimmune and neuroendocrine activation in rats

Recombinant human interferon-alpha (IFN-alpha) induces depression, and neuroendocrine and neuroimmune activation, in a significant number of patients undergoing treatment for viral illnesses (e.g., hepatitis C), yet these effects have not been consistently reproduced in rodents. As such, we sought to determine the effects of acute or chronic IFN-alpha treatment on basic reward and immobility in the forced swim test (FST), neuroendocrine and neuroimmune activation, and monoamine turnover in brain. In the first experiment, male Wistar rats (N = 7/group) treated with human recombinant IFN-alpha (100,000 IU/kg, i.p.), as compared to saline, did not exhibit alterations to rate of sucrose pellet self-administration or total reinforcers obtained, corticosterone release, plasma IL-6 release, IL-1beta or IL-6 mRNA expression in hippocampus, or monoamine turnover in prefrontal cortex, striatum, nucleus accumbens, or amygdala. However, acute IFN-alpha decreased body weight and produced a trend toward reduced food consumption in the home cage 2 h after injection. In the second experiment, Wistar rats (N=4/group) were subjected to a chronic treatment regimen of saline or IFN-alpha (100,000 IU/kg, i.p.) once daily for 14 consecutive days. The data reveal that animals exposed to chronic IFN-alpha exhibited similar amounts of time immobile and similar latencies to primary immobility in the FST as compared to saline-treated controls. Chronic IFN-alpha did not induce corticosterone release, plasma TNF-alpha, or IL-6 release. Tissue monoamine analysis revealed that chronic IFN-alpha reduced DA levels in prefrontal cortex, and decreased 5-HT levels and increased 5-HT turnover in amygdala. In the third experiment, Wistar rats (N = 4/group) were exposed to either acute or chronic pegylated IFN-alpha (pegIFN-alpha: 3.25, 10 or 75 mg/kg, i.p.) at one of several time points from 1 h to 23 days. The data reveal that neither acute nor chronic pegIFN-alpha induced corticosterone release. Overall, the current report demonstrates that neither acute nor chronic IFN-alpha induced depressive-like behavior and neither IFN-alpha nor peg-IFN-alpha was capable of inducing neuroendocrine or neuroimmune activation. Despite the neurochemical alterations observed in the chronic treatment regimen, the data indicate that recombinant human IFN-alpha does not produce a robust model of depressive-like behavior in rodents.

Hépatite C, Interféron α et dépression : principales hypothèses physiopathologiques

Imputability of thymic disorders caused by IFNalpha during the chronic Hepatitis C treatment -- hepatitis C and depression -- the infection by the hepatitis C virus (HCV) is a major public health concern since it affects 1.2% in the French population. Eighty percent of those contaminated by HCV keep bearing the virus chronically although they remain asymptomatic during many years. HCV infection is associated with psychiatric symptoms like depression. Together with other factors (eg the severity of hepatic condition), depression may induce significant impairment in quality of life. Conversely, some psychiatric conditions may increase the risk of HCV infection. In drug-addicted subjects using intravenous route, HCV contamination rate ranges from 74 to 100%. Compared with general population, a higher HCV contamination rate has also been noticed in some other subgroups of subjects (patients with alcohol abuse or dependence, with alcohol-induced hepatic disease and psychiatric inpatients). However, no valid explanation to this phenomenon has been established. Interferon alpha and depression - Interferons are a variety of cytokines naturally produced by human tissues and have also been synthesized for therapeutic purposes (treatment of a variety of cancers and viral infections). Many psychobehavioural symptoms are observed under IFNalpha treatment. Among them, mood disorders are known to occur early after entry into treatment and to be within the reach of preventive measures. The reported frequency of depression during IFNalpha treatment ranges from 0 to 37%. This variation reflects either methodological biases (eg differences in psychiatric assessment) or the heterogeneity of the population of patients accepted in therapeutic protocols. Note that the adjunction of ribavirine to IFNalpha in therapeutic protocols has not brought any changes in the depression frequency. The causal relationship between IFNalpha administration and the occurrence of mood disorders has been tackled by various recent research works focusing on the importance of the immune system in the pathophysiology of depression. Miscellaneous pathophysiological hypotheses -- nature of the psychobehavioural symptomatology -- in addition to depressive symptoms, IFNalpha treatment also induces various cognitive impairments and disruptions in EEG patterns. These symptoms are consistent with a mild subcortical dementia. Data resulting from pharmacological trials in humans and in animals are controversial (eg IFNalpha-induced symptoms being alleviated by both immune and antidepressant therapies). However, the debate about the nature of the psychobehavioural disorders observed under IFNalpha treatment might be no longer relevant in the light of recent theories which regard depression as a maladaptive response to a particular form of stress, namely a deep and diffuse feeling of sickness ("malaise"). These theoretical views ascribe the production of depressive symptoms to a disruption in the immune function, mediated by the variety of cytokines. The therapeutic effects of anti-depressive drugs are thus attributed to their analgesic properties, reducing the "malaise" feeling underlying depressive symptoms. Necessity of a second messanger -- accordingly to current pathophysiological theories, depression results from disorders of various CNS functions, mainly limbic, monaminergic and neuroendocrinal systems. Though, exogenous IFNalpha does not cross the blood-brain barrier when unscathed and an intermediary mechanism is necessary. First to be addressed is the cytokines system itself since it is composed of numerous different molecules interacting in an infinite number of possible combinations. Some of these cytokines (eg some interleukins) both are activated by IFNalpha and can reach CNS; they are good candidates for the role of second messenger mediating the induction of psychobehavioural disorders. Second, keeping in mind that serotonin is a monoaminergic neurotransmitter classically involved in depression pathophysiology, other works have demonstrated that IFNalpha modulates the peripheral activity of indolamine-dioxygenase -- a regulating enzyme of serotonin metabolism -- possibly through lymphocyte T CD4 activation. Third, other authors have postulated an immune-induced vagal mechanism to explain depression caused by IFNalpha. Action of IFNalpha on the neuroendocrine and on neuromodulating functions: monoaminergic hypothesis -- cytokines could have an influence on the mood through their modulating role on the serotoninergic system. IFNalpha treatment is reported to produce: 1) a decrease in tryptophan availability for serotonin synthesis, 2) a decrease in the 5-HIAA level in the LCR, and 3) a modification of the central serotoninergic receptors. Moreover, selective inhibitors of serotonin transporters are effective to treat or prevent depression caused by IFNalpha. Many studies support the serotonin-transporter hypothesis: in vitro, both IFNalpha and interleukine 4 (IL-4) increases the expression of serotonin transporter gene, IFNalpha increases in the production of IL-4 by mononucleus cells (not found in vivo). Serotoninergic system can also be altered by a peripheral action of IFNalpha on trytophan catabolism by activating a concurrent pathway (known as "kynurenine pathway") to serotonin synthesis. Finally, serotonin-mediated vulnerability to the psychobehavioural effects of IFNalpha could be underlain by a polymorphism of serotonin transporter gene. Concerning the other monoaminergic systems, IFNalpha seems to have an amphetamine-like effect at its first administration, followed by a decrease in dopaminergic tone with chronic administration. Dopaminergic depletion, subsequent to psychostimulant abuse for instance, results in severe depressive syndromes. Interactions between IFNalpha and noradrenergic system have also been reported. Neuroendocrinian hypothesis -- when administered through central or peripheral way, IFNalpha simulates/inhibits the corticotrope axis and alters endorphin system as shown by the induction of analgesia, catatonia and behavioural slowdown that can be suppressed by opioid antagonists. IFNalpha neurotoxic effects are successfully treated by naltrexone. Lastly, IFNalpha is known to cause disorders in thyroid function that are likely to contribute to the production or aggravation of mood disorders.

CONCLUSION

A better understanding of pathophysiologic mechanisms underlying psychiatric side-effects of IFNalpha is essential to extend access to treatment to some categories of patients that remain excluded from the protocols. A better management of those psychiatric side effects should help the clinician not to draw aside patients at risk, ie patients with depression, drug and alcohol addiction. Treating them in a pragmatic and careful way is a major issue, since this population represents a high percentage of the potential candidates for interferon therapy.

In mice, production of plasma IL-1 and IL-6 in response to MPTP is related to behavioral lateralization

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces dopaminergic neuron death in substantia nigra and dopamine loss in striatum, similar to those observed in Parkinson disease. Given MPTP can also induce alterations in brain cytokines and in peripheral immune parameters, we hypothesize that MPTP can induce an elevation of plasma cytokines. We have previously shown that cytokine production depends on behavioral lateralization in certain conditions. Therefore, we further postulate that the MPTP-induced plasma cytokines are related to behavioral lateralization. To answer these questions, C57BL/6J male mice, selected for paw preference, were injected with 25 mg/kg MPTP ip for five consecutive days and were decapitated at day 1, day 3, or day 14 after the last injection. Striatal DA and DOPAC concentration were measured by HPLC and plasma levels of IL-1beta and IL-6 were quantified by ELISA. The results showed that after MPTP treatment, striatal DA content was dramatically decreased, IL-1beta levels increased on day 3, while IL-6 levels increased on day 14. Interestingly, behavioral lateralization influenced DA/DOPAC ratio as well as plasma IL-1beta and IL-6 levels. In left-pawed mice, MPTP induced a higher decrease of DA/DOPAC ratio than in right-pawed mice. The increase of IL-1beta was observed in left-pawed but not in right-pawed mice. The elevation of IL-6 was higher in right-pawed mice than in left-pawed mice. These results have clearly demonstrated our hypotheses, that MPTP can induce increase of plasma IL-1beta and IL-6 levels in mice, and this effect is shaped by behavioral lateralization.

Exaggerated neuroinflammation and sickness behavior in aged mice following activation of the peripheral innate immune system

Acute cognitive impairment (i.e., delirium) is common in elderly emergency department patients and frequently results from infections that are unrelated to the central nervous system. Since activation of the peripheral innate immune system induces brain microglia to produce inflammatory cytokines that are responsible for behavioral deficits, we investigated if aging exacerbated neuroinflammation and sickness behavior after peripheral injection of lipopolysaccharide (LPS). Microarray analysis revealed a transcriptional profile indicating the presence of primed or activated microglia and increased inflammation in the aged brain. Furthermore, aged mice had a unique gene expression profile in the brain after an intraperitoneal injection of LPS, and the LPS-induced elevation in the brain inflammatory cytokines and oxidative stress was both exaggerated and prolonged compared with adults. Aged mice were anorectic longer and lost more weight than adults after peripheral LPS administration. Moreover, reductions in both locomotor and social behavior remained 24 h later in aged mice, when adults had fully recovered, and the exaggerated neuroinflammatory response in aged mice was not reliably paralleled by increased circulating cytokines in the periphery. Taken together, these data establish that activation of the peripheral innate immune system leads to exacerbated neuroinflammation in the aged as compared with adult mice. This dysregulated link between the peripheral and central innate immune system is likely to be involved in the severe behavioral deficits that frequently occur in older adults with systemic infections.

Acute diclofenac treatment attenuates lipopolysaccharide-induced alterations to basic reward behavior and HPA axis activation in rats

RATIONALE

Non-steroidal anti-inflammatory drugs (NSAIDs) counteract stress hormone and pro-inflammatory cytokine activation, and are being considered as therapeutics for Alzheimer's and Parkinson's disease, and multiple sclerosis. Previous data from our laboratory revealed that repeated treatment with the NSAID diclofenac attenuated lipopolysaccharide (LPS)-induced alterations to reward behavior, implicating a role for NSAIDs in alleviating depressive-like behavior.

OBJECTIVES

To extend these findings, we sought to determine whether acute treatment with diclofenac would attenuate LPS-induced alterations to basic reward behavior, as well as neuroendocrine and neuroimmune function.

METHODS

Male, Wistar rats (n=8-9/grp) pressed a lever for sucrose pellet reward and after establishing a steady baseline were exposed to an injection of saline (1 ml/kg, SC) or diclofenac (2.5 mg/kg, SC) 30 min prior to a second injection of saline or LPS (20 microg/kg, IP).

RESULTS

In saline pre-treated rats, LPS significantly reduced rate of sucrose pellet self-administration and total reinforcers obtained, suggestive of an anhedonia response. In addition, LPS increased corticosterone release, increased plasma intereleukin (IL)-1beta release, increased IL-1beta and IL-6 mRNA in hippocampus, increased corticotropin releasing hormone (CRH) mRNA in pituitary, and decreased CRH-1 mRNA in pituitary. Importantly, the behavioral and neuroendocrine effects, but not neuroimmune effects, produced by LPS were significantly attenuated in rats pre-treated with diclofenac.

CONCLUSIONS

These new data provide a comprehensive assessment of the acute effects of diclofenac on LPS exposure in rats and confirm a role for NSAIDs in attenuating endotoxin-induced anhedonia. Of particular importance, the data reveal that the observed effects are mediated via the hypothalamic pituitary adrenal axis at the level of the pituitary or above.

Stress, depression, and anhedonia: caveats concerning animal models

Numerous animal models of depression have been advanced, each having multiple attributes and some limitations. This review provides caveats concerning etiologically valid animal models of depression, focusing on characteristics of the depressive subtype being examined (e.g. typical vs atypical major depression, dysthymia, melancholia), and factors that contribute to the interindividual behavioral variability frequently evident in stressor-related behavioral paradigms. These include the stressor type (processive vs systemic stressors), and characteristics of the stressor (controllability, predictability, ambiguity, chronicity, intermittence), as well as organismic variables (genetic, age, sex), experiential variables (stressor history, early life events) and psychosocial and personality factors that moderate stressor reactivity. Finally, a model of depression is reviewed that evaluates the effects of stressors on hedonic processes, reflected by responding for rewarding brain stimulation. Anhedonia is a fundamental feature of depression, and assessment of stressor-related reductions in the rewarding value of brain stimulation, especially when coupled with other potential symptoms of depression, provides considerable face, construct and predictive validity. Stressful events markedly impact rewarding brain stimulation, and this effect varies across strains of mice differentially reactive to stressors, is modifiable by antidepressant treatments, and allows for analyses of the contribution of different brain regions to anhedonic processes. The paradigm is sensitive to several factors known to acts as moderators of stress responses, but analyses remain to be conducted with regard to several such variables.

Cyclooxygenase inhibition attenuates endotoxin-induced spatial learning deficits, but not an endotoxin-induced blockade of long-term potentiation

Peripheral administration of lipopolysaccharide (LPS), a potent bacterial endotoxin, can cause a variety of central effects, including production of cytokines and cyclooxygenases in the brain, as well as peripheral increases in corticosterone. These, in turn, may contribute to neuroimmune-induced neurocognitive deficits. We show here LPS causes deficits in hippocampal-dependent spatial learning in the water maze but that treatment with ibuprofen, a broad-spectrum cyclooxygenase inhibitor, reverses the deficits induced in spatial learning by LPS. We also show that LPS causes an impairment in the induction of long-term potentiation in the dentate gyrus in vivo, a major contemporary model of learning and memory. No differences were found in corticosterone levels in trunk blood but we find a decrease in brain-derived neurotrophic factor (BDNF) expression in LPS group compared to saline controls. Paradoxically compared to the behavioral findings treatment with ibuprofen does not attenuate the LPS-induced impairment in LTP or BDNF concentration in tetanized tissue.

Central administration of transforming growth factor-alpha and neuregulin-1 suppress active behaviors and cause weight loss in hamsters

Transforming growth factor-alpha (TGF-alpha) is a candidate output signal of the hypothalamic circadian pacemaker. TGF-alpha is expressed in the suprachiasmatic nucleus (SCN) of rats, hamsters, and rhesus macaques [A. Kramer, F.C. Yang, P. Snodgrass, X. Li, T.E. Scammell, F.C. Davis and C.J. Weitz, Regulation of daily locomotor activity and sleep by hypothalamic EGF receptor signaling, Science, 294 (2001) 2511-5., X. Li, N. Sankrithi and F.C. Davis, Transforming growth factor-alpha is expressed in astrocytes of the suprachiasmatic nucleus in hamster: role of glial cells in circadian clocks, Neuroreport, 13 (2002) 2143-7., Y.J. Ma, M.E. Costa and S.R. Ojeda, Developmental expression of the genes encoding transforming growth factor alpha and its receptor in the hypothalamus of female rhesus macaques, Neuroendocrinology, 60 (1994) 346-59., Y.J. Ma, M.P. Junier, M.E. Costa and S.R. Ojeda, Transforming growth factor-alpha gene expression in the hypothalamus is developmentally regulated and linked to sexual maturation, Neuron, 9 (1992) 657-70.]. TGF-alpha reversibly inhibits wheel-running activity during long-term infusions into the third ventricle of hamsters (2 weeks, intracerebroventricular or ICV) [A. Kramer, F.C. Yang, P. Snodgrass, X. Li, T.E. Scammell, F.C. Davis and C.J. Weitz, Regulation of daily locomotor activity and sleep by hypothalamic EGF receptor signaling, Science, 294 (2001) 2511-5.], and this effect appears to be mediated by the epidermal growth factor receptor (EGFR or ErbB-1) [A. Kramer, F.C. Yang, P. Snodgrass, X. Li, T.E. Scammell, F.C. Davis and C.J. Weitz, Regulation of daily locomotor activity and sleep by hypothalamic EGF receptor signaling, Science, 294 (2001) 2511-5.]. Here, we demonstrate that this inhibitory effect is not restricted to wheel-running behavior or to mediation by the EGFR. Using direct observation, we found the effects of long-term TGF-alpha infusion (ICV, 12 microl/day, 3.3 microM) to be more general than previously reported. Other active behaviors such as grooming and feeding were reversibly inhibited and hamsters showed dramatic weight loss as a result of reduced feeding (34% of body weight over 19 days). TGF-alpha did not disrupt a non-behavioral rhythm, the rhythm in pineal melatonin. Wheel-running activity was also inhibited by another epidermal growth factor-like (EGF-like) peptide, neuregulin (NRG-1), that binds to different ErbB receptors. Like TGF-alpha, NRG-1 caused a significant weight loss. We also show that an acute injection of TGF-alpha inhibits activity (ICV, 5 microl, 3.3 microM over 2 min), with inhibition and recovery occurring over a few hours. Although the results are consistent with the proposed [A. Kramer, F.C. Yang, P. Snodgrass, X. Li, T.E. Scammell, F.C. Davis and C.J. Weitz, Regulation of daily locomotor activity and sleep by hypothalamic EGF receptor signaling, Science, 294 (2001) 2511-5.] role for EGF-like peptides in the daily regulation of activity, the actions of these peptides might also contribute to the behavioral etiology of diseases in which EGF-like peptides are expressed.

Long-term alterations in neuroimmune responses after neonatal exposure to lipopolysaccharide

Fever is an integral part of the host's defense to infection that is orchestrated by the brain. A reduced febrile response is associated with reduced survival. Consequently, we have asked if early life immune exposure will alter febrile and neurochemical responses to immune stress in adulthood. Fourteen-day-old neonatal male rats were given Escherichia coli lipopolysaccharide (LPS) that caused either fever or hypothermia depending on ambient temperature. Control rats were given pyrogen-free saline. Regardless of the presence of neonatal fever, adult animals that had been neonatally exposed to LPS displayed attenuated fevers in response to intraperitoneal LPS but unaltered responses to intraperitoneal interleukin 1beta or intracerebroventricular prostaglandin E(2). The characteristic reduction in activity that accompanies fever was unaltered, however, as a function of neonatal LPS exposure. Treatment of neonates with an antigenically dissimilar LPS (Salmonella enteritidis) was equally effective in reducing adult responses to E. coli LPS, indicating an alteration in the innate immune response. In adults treated as neonates with LPS, basal levels of hypothalamic cyclooxygenase 2 (COX-2), determined by semiquantitative Western blot analysis, were significantly elevated compared with controls. In addition, whereas adult controls responded to LPS with the expected induction of COX-2, adults pretreated neonatally with LPS responded to LPS with a reduction in COX-2. Thus, neonatal LPS can alter CNS-mediated inflammatory responses in adult rats.

Effects of intraperitoneal lipopolysaccharide on Morris maze performance in year-old and 2-month-old female C57BL/6J mice

Several studies have shown that systemic lipopolysaccharide (LPS) or interleukin-1beta (IL-1beta) may affect performance in various learning tasks, including the Morris water maze. In the current study, female C57BL/6J mice, either 2 months or 1 year of age, were given 5 days of testing followed by 3 days of rest, and then three additional days of testing. Mice either received a single LPS injection on day 1 and saline on days 2-5, LPS injections on days 1-5, or saline injections on days 1-5. Daily LPS administration significantly prolonged latency for the animals to find the platform, and decreased their swimming speed. Year-old mice treated with LPS each day also exhibited significantly higher levels of thigmotaxis in the maze. Despite effects on latency and swim speed, no effect of LPS treatment was observed for distance traveled to the platform or other measures that clearly indicate disruption of learning in the maze. On the other hand, age was a significant factor affecting both latency and distance, with older animals swimming greater distances to find the platform. Additionally, older animals were more adversely affected by daily LPS treatment. In this study, although LPS-induced performance impairments in the Morris water maze were noted, particularly in older animals, these effects were not clearly indicative of learning impairment per se.

Non-termination of sickness behavior as precipitating factor for mental disorders

Sickness behavior can be defined as a combination of coordinated behavioral and physiological changes that develop in response to any condition that elicits pro-inflammatory activity. It is an adaptational homeostasis initiated by the influence of pro-inflammatory cytokines on central nervous system neurohormonal functioning. This paper introduces the concept of non-termination of sickness behavior as a potential threat to mental health. In view of the similarities between the behavioral symptoms, the neuroendocrine and the cytokine profiles of sickness behavior and that of a number of mental disorders it is hypothesized that the inappropriate continuation of sickness behavior, (i.e., non-termination), after recovery from the initial disease, could form the basis for mental disturbances. This would be particularly relevant in individuals with alterations in stress vulnerability (altered activation threshold and impaired negative feedback), which may occur due to the combination of genetic disposition and priming by early life experiences.

Autonomic brainstem nuclei are linked to the hippocampus

Vagal nerve stimulation has been reported to enhance memory in both rats and humans, and to be an effective treatment for epilepsy in some patients, but the underlying neuroanatomical substrate(s) responsible for these effects remains unknown. Since there is no direct anatomical projection from the nucleus tractus solitarius, the main vagal relay site of the brain, to the hippocampus, we tested whether a multisynaptic pathway exists. Pseudorabies virus, a pig herpesvirus that can be used as a retrograde transneuronal tracer, was injected into the ventral CA1 hippocampus of rats, and after 4 days, pseudorabies virus infected neurons were identified in the general visceral portion of the nucleus tractus solitarius, with the majority being localized in the A2 noradrenergic cell group. Other autonomic brainstem nuclei, including the parabrachial nucleus, locus coeruleus, A1 and A5 noradrenergic cell groups, and C1 adrenergic cell group, were labeled. In order to identify some of the potential relay sites of the nucleus tractus solitarius-->hippocampal pathway, immunotoxin lesions of the ventral CA1 region were made that selectively destroyed either the noradrenergic or cholinergic fibers. After 2 weeks' recovery, pseudorabies virus was injected in this same CA1 area, and 4 days later, the transneuronal labeling in the nucleus tractus solitarius was reduced by approximately 65%. These findings suggest that the noradrenergic neurons of the locus coeruleus and cholinergic neurons of the medial septum/diagonal band are likely to be relay sites for this pathway. Other potential linkages are discussed. In summary, this is the first anatomical report to show that the general visceral region of nucleus tractus solitarius is linked via multisynaptic relays to the hippocampus.

Mutant mouse models of depression: Candidate genes and current mouse lines

Depression is a multifactorial and multigenetic disease. At present, three main theories try to conceptualize its molecular and biochemical mechanisms, namely the monoamine-, the hypothalamus-pituitary-adrenal- (HPA-) system- and the neurotrophin-hypotheses. One way to explore, validate or falsify these hypotheses is to alter the expression of genes that are involved in these systems and study their respective role in animal behavior and neuroendocrinological parameters. Following an introduction in which we briefly describe each hypothesis, we review here the different mouse lines generated to study the respective molecular pathways. Among the many mutant lines generated, only a few can be regarded as genetic depression models or as models of predisposition for a depressive syndrome after stress exposure. However, this is likely to reflect the human situation where depressive syndromes are complex, can vary to a great extent with respect to their symptomatology, and may be influenced by a variety of environmental factors. Mice with mutations of candidate genes showing depression-like features on behavioral or neurochemical levels may help to define a complex molecular framework underlying depressive syndromes. Because it is conceivable that manipulation of one single genetic function may be necessary but not sufficient to cause complex behavioral alterations, strategies for improving genetic modeling of depression-like syndromes in animals possibly require a simultaneous targeted dysregulation of several genes involved in the pathogenesis of depression. This approach would correspond to the new concept of 'endophenotypes' in human depression research trying to identify behavioral traits which are thought to be encoded by a limited set of genes.

The Darwinian concept of stress: benefits of allostasis and costs of allostatic load and the trade-offs in health and disease

Why do we get the stress-related diseases we do? Why do some people have flare ups of autoimmune disease, whereas others suffer from melancholic depression during a stressful period in their life? In the present review possible explanations will be given by using different levels of analysis. First, we explain in evolutionary terms why different organisms adopt different behavioral strategies to cope with stress. It has become clear that natural selection maintains a balance of different traits preserving genes for high aggression (Hawks) and low aggression (Doves) within a population. The existence of these personality types (Hawks-Doves) is widespread in the animal kingdom, not only between males and females but also within the same gender across species. Second, proximate (causal) explanations are given for the different stress responses and how they work. Hawks and Doves differ in underlying physiology and these differences are associated with their respective behavioral strategies; for example, bold Hawks preferentially adopt the fight-flight response when establishing a new territory or defending an existing territory, while cautious Doves show the freeze-hide response to adapt to threats in their environment. Thus, adaptive processes that actively maintain stability through change (allostasis) depend on the personality type and the associated stress responses. Third, we describe how the expression of the various stress responses can result in specific benefits to the organism. Fourth, we discuss how the benefits of allostasis and the costs of adaptation (allostatic load) lead to different trade-offs in health and disease, thereby reinforcing a Darwinian concept of stress. Collectively, this provides some explanation of why individuals may differ in their vulnerability to different stress-related diseases and how this relates to the range of personality types, especially aggressive Hawks and non-aggressive Doves in a population. A conceptual framework is presented showing that Hawks, due to inefficient management of mediators of allostasis, are more likely to be violent, to develop impulse control disorders, hypertension, cardiac arrhythmias, sudden death, atypical depression, chronic fatigue states and inflammation. In contrast, Doves, due to the greater release of mediators of allostasis (surplus), are more susceptible to anxiety disorders, metabolic syndromes, melancholic depression, psychotic states and infection.

Cardiac risk factors in patients with diabetes mellitus and major depression

OBJECTIVE

The prevalence of major depression is approximately 2-fold higher in patients with diabetes mellitus compared to medical controls. We explored the association of major depression with 8 cardiac risk factors in diabetic patients with and without evidence of cardiovascular disease (CVD).

DESIGN

A mail survey questionnaire was administered to a population-based sample of 4,225 patients with diabetes to obtain data on depression status, diabetes self-care (diet, exercise, and smoking), diabetes history, and demographics. On the basis of automated data we measured diabetes complications, glycosylated hemoglobin, medical comorbidity, low-density lipid levels, triglyceride levels, diagnosis of hypertension, and evidence of microalbuminuria. Separate analyses were conducted for subgroups according to the presence or absence of CVD.

SETTING

Nine primary care clinics of a nonprofit health maintenance organization.

MAIN RESULTS

Patients with major depression and diabetes were 1.5- to 2-fold more likely to have 3 or more cardiovascular risk factors as patients with diabetes without depression (62.5% vs 38.4% in those without CVD, and 61.3% vs 45% in those with CVD). Patients with diabetes without CVD who met criteria for major depression were significantly more likely to be smokers, to have a body mass index (BMI) > or = 30 kg/m2, to lead a more sedentary lifestyle, and to have HbA1c levels of >8.0% compared to nondepressed patients with diabetes without heart disease. Patients with major depression, diabetes, and evidence of heart disease were significantly more likely to have a BMI > or = 30 kg/m2, a more sedentary lifestyle, and triglyceride levels > 400 mg/dl than nondepressed diabetic patients with evidence of heart disease.

CONCLUSIONS

Patients with major depression and diabetes with or without evidence of heart disease have a higher number of CVD risk factors. Interventions aimed at decreasing these risk factors may need to address treatment for major depression in order to be effective.

Cytokines and psychopathology: lessons from interferon-alpha

Interferon-alpha is a potent inducer of the cytokine network and is notorious for causing behavioral alterations. Studies on interferon-alpha-treated patients reveal at least two distinct syndromes: 1) a mood/cognitive syndrome that appears late during interferon-alpha therapy is responsive to antidepressants and is associated with activation of neuroendocrine pathways and altered serotonin metabolism; and 2) a neurovegetative syndrome characterized by psychomotor slowing, and fatigue that appears early during interferon-alpha treatment is antidepressant nonresponsive and may be mediated by alterations in basal ganglia dopamine metabolism. Findings from interferon-alpha may provide important clues regarding the pathophysiology and treatment of cytokine-induced behavioral changes in medically ill patients, while also potentially modeling the development of neuropsychiatric symptoms in patients without medical disorders.

Behavioral and neurochemical responses in mice bearing tumors submitted to social stress

Through the proinflammatory cytokines secreted in response to inflammation or injury, the immune system produces physiological and behavioral alterations. This study analyzes the effects on behavior, mononuclear proliferative response and central monoamine activity in response to the inoculation of tumor cells in mice submitted to social stress. Two groups of male OF1 mice were used, one of which was inoculated with B16 melanoma cells. Both groups were subdivided into two new groups, with one being submitted to social stress through sensory contact model with a selected aggressive subject, and the other being handled without social interaction. Subjects were exposed to social stress for a 24-h period, with three 5 min intervals of direct physical interaction, where the behavior was recorded and assessed. One hour after the stress and/or handling, they were put down and samples taken for physiological assessment. Significant behavioral changes were found in subjects with implanted tumors, mainly characterized by an increase in avoidance behavior and a decrease in immobility, defense-submission and non-social exploration behavior, coupled with an increase in the spleen mononuclear cell proliferative response. Similarly, an increase was observed in the density of dopamine(2) (D(2))-receptors in the striatum (SRT) and an increase in dopaminergic (DOPAC/DA) and serotonergic (5HIAA/5HT) turnover in the hypothalamus. The increase in the density of D(2)-receptors in the SRT coincides with the decrease in some behaviors with a predominant motor component. The results indicate significant changes in the defensive strategy used to cope with situations of intense social stress in mice bearing tumors.

Fractalkine (CX3CL1) and fractalkine receptor (CX3CR1) distribution in spinal cord and dorsal root ganglia under basal and neuropathic pain conditions

Fractalkine is a unique chemokine reported to be constitutively expressed by neurons. Its only receptor, CX3CR1, is expressed by microglia. Little is known about the expression of fractalkine and CX3CR1 in spinal cord. Given that peripheral nerve inflammation and/or injury gives rise to neuropathic pain, and neuropathic pain may be partially mediated by spinal cord glial activation and consequent glial proinflammatory cytokine release, there must be a signal released by affected neurons that triggers the activation of glia. We sought to determine whether there is anatomical evidence implicating spinal fractalkine as such a neuron-to-glia signal. We mapped the regional and cellular localization of fractalkine and CX3CR1 in the rat spinal cord and dorsal root ganglion, under basal conditions and following induction of neuropathic pain, employing both an inflammatory (sciatic inflammatory neuropathy; SIN) as well as a traumatic (chronic constriction injury; CCI) model. Fractalkine immunoreactivity and mRNA were observed in neurons, but not glia, in the rat spinal cord and dorsal root ganglia, and levels did not change following either CCI or SIN. By contrast, CX3CR1 was expressed by microglia in the basal state, and the microglial cellular concentration was up-regulated in a regionally specific manner in response to neuropathy. CX3CR1-expressing cells were identified as microglia by their cellular morphology and positive OX-42 and CD4 immunostaining. The cellular distribution of fractalkine and CX3CR1 in the spinal circuit associated with nociceptive transmission supports a potential role in the mechanisms that contribute to the exaggerated pain state in these models of neuropathy.

Perinatal inflammatory cytokine challenge results in distinct neurobehavioral alterations in rats: implication in psychiatric disorders of developmental origin

Maternal stress, viral infection, and obstetric complications, which trigger cytokine signaling, are hypothesized to be involved in schizophrenia and its related disorders. The etiologic contribution of individual cytokines to such psychiatric disorders, however, remains to be evaluated. To estimate the impact of peripheral cytokine challenge on neurobehavioral development, we examined effects of four proinflammatory cytokines on rat neonates and their later behavioral performance. Sublethal doses of interleukin-1 alpha, interleukin-2, interleukin-6, or interferon-gamma were subcutaneously administered to rat pups for 9 days. These animals displayed alterations in physical development, including lower weight gain and/or accelerated eyelid opening. In addition, behavioral abnormalities related to fear/anxiety levels and sensorimotor gating emerged at different developmental stages, depending on the cytokine species administered. During juvenile stages, neonatal interleukin-2 treatment increased exploratory locomotor activity, whereas other cytokine treatments did not. At the post-puberty stage, however, the interleukin-2-induced abnormal motor activity became undetectable, whereas interleukin-1 alpha-treated rats developed abnormalities in startle response, prepulse inhibition (PPI), and social interaction. Subchronic treatment of an anti-psychotic drug, clozapine, ameliorated the impairment of prepulse inhibition without altering startle responses. These animal experiments illustrate that, during early postnatal development, inflammatory cytokine challenge in the periphery can induce future psycho-behavioral and/or cognitive impairments with various latencies, although the pathologic mechanisms underlying these abnormalities remain to be determined.

NF-kappaB p50-deficient mice show reduced anxiety-like behaviors in tests of exploratory drive and anxiety

The ubiquitous transcription factor nuclear factor (NF)-kappaB plays a prominent role in regulation of inflammatory immune responses and in cell survival. Recently, it has been found to be active in neurons, and mice lacking NF-kappaB subunits p50 or p65 show deficits in specific cognitive tasks. Here we demonstrate a strikingly low level of anxiety-like behavior in the p50(-/-) mouse. In an open field, the mutant mice showed significantly less defecation, more rearing, and more time spent in the center compartment relative to wild type control mice. The p50(-/-) mice also spent more time investigating a novel object placed in the open field. On the elevated plus maze, p50(-/-) mice spent more time on the open arms and had increased numbers of open arm entries relative to wild type. In group housing conditions, they did not establish dominant-subordinate hierarchies, whereas wild type control animals did so, in part, by whisker barbering and conspecific allogrooming. In tests of general health, sensorimotor function, and daily activity on a circadian rhythm, p50(-/-) mice were normal. Thus, absence of the p50 subunit of the NF-kappaB transcription factor, which results in altered NF-kappaB transcriptional activity in cells throughout the body and brain, alters neuronal circuitry underlying manifestation of emotional behavior. The p50 subunit appears to play a role in normal expression of certain forms of anxiety.

TNF-alpha accounts for short-term persistence of oxidative status in rat brain after two weeks of repeated stress

Inducible nitric oxide synthase (NOS-2) accounts for the accumulation of oxidative and nitrosative mediators in brain after stress. To determine whether and when repeated exposure to immobilization stress leads to persistent oxidative status in rat brain, male Wistar rats were immobilized for 6 h/day for 7 or 14 days (S7, S14). Cerebral cortices were obtained immediately after the last session of stress or 1 day later. Stress increased NOS-2 activity after S7 or S14. This enzymatic activity returned to basal values 1 day after S7, but not 1 day after S14. Stress increased malondialdehyde (MDA) accumulation in cortex after S7 and S14. MDA levels returned to basal values 1 day after S7 but not 1 day after S14. In order to elucidate the possible mechanisms involved in this short-term persistence of oxidative status, brain levels of the cytokine tumour necrosis factor alpha (TNF-alpha) were determined. TNF-alpha levels did not increase after S7 or 1 day after S7, but increased after S14 and 1 day after S14. This was paralleled by an increase in TNF-alpha converting enzyme (TACE) activity in brain. When the increase in TNF-alpha at S14 was blocked by BB1101, an inhibitor of TACE, or its effects were blocked with anti-TNF-alpha, the accumulation of MDA and NOS-2 activity 1 day after S14 did not take place. These findings indicate that TACE and TNF-alpha account for stress-induced short-term persistence of NOS-2 activity and MDA accumulation after 14 days of repeated exposure and support a possible neuroprotective role for specific blockers of TNF-alpha in this situation.

Bacterial endotoxin induces STAT3 activation in the mouse brain

In the present study, we investigated regulatory mechanisms of bacterial endotoxin-induced STAT3 activation in the brain. Intraperitoneal injection of lipopolysaccharide (LPS) dose-dependently (0.5-5000 microg/kg) induced STAT3 phosphorylation in the hypothalamus. LPS-induced STAT3 phosphorylation was peaked at 2-4 h and declined there after. Moreover, intracerebroventricular injection of LPS induced STAT3 phosphorylation in the cortex and the hippocampus, indicating that central as well as peripheral LPS can act in the brain to induce STAT3 activation. Glucocorticoids are known to play a physiological role in the feedback inhibition of immune/inflammatory responses in the endocrine system. Interestingly, we observed no effect of dexamethasone on LPS-induced STAT3 phosphorylation in the hypothalamus. These findings point to the important role of STAT3 in the neuroimmune interaction of inflammation in the brain.

Prolonged exposure to intermittent alcohol vapors decreases the ACTH as well as hypothalamic nitric oxide and cytokine responses to endotoxemia

BACKGROUND

Prolonged exposure to alcohol blunts the response of the hypothalamic-pituitary-adrenal (HPA) axis to various stressors, including the systemic injection of a lipopolysaccharide (LPS). We previously showed that decreased synthesis of the hypothalamic peptides corticotropin-releasing factor (CRF) and vasopressin (VP) played a central role in this phenomenon. However, the mechanisms that lead to decreased hypothalamic neuronal activity have not been identified. In the present work, we tested the hypothesis that alcohol decreased signals that are elicited by LPS and that stimulate hypothalamic CRF and VP synthesis, namely nitric oxide (NO) and the proinflammatory cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6).

METHODS

Adult male rats were exposed to intermittent (5 hr/day) alcohol vapors for 5 days. Control animals were kept in comparable chambers but not exposed to the vapors. On day 6, the animals received an injection of LPS through permanent indwelling intravenous cannulae. The dependent variables were plasma ACTH levels measured by IRMA (immunoradiometric assay); pituitary and hypothalamic TNF-alpha and IL-6 mRNA levels measured by RNase protection assay; basal activity of neuronal NO synthase measured by conversion of [14C]arginine to [14C]citrulline, the constitutive enzyme that synthesizes NO and modulates the influence of this gas on LPS-induced HPA axis activity; and basal and LPS-induced levels of citrulline (an index of NO formation) in the hypothalamus, measured by immunocytochemistry.

RESULTS

After injection with LPS, rats that were pretreated with alcohol exhibited a significantly (p < 0.01) decreased release of ACTH, compared with controls. There was no difference in basal NO synthase activity or hypothalamic citrulline levels. In contrast, LPS-induced hypothalamic citrulline levels were significantly (p < 0.01) lower in alcohol-exposed rats, as were pituitary TNF-alpha and IL-6 transcripts. In the hypothalamus, the TNF-alpha but not IL-6 response to LPS was also reduced.

CONCLUSIONS

These results indicate that prolonged exposure to alcohol decreases the ACTH, hypothalamic NO and TNF-alpha, and pituitary TNF-alpha and IL-6 responses to LPS. This suggests that altered NO and proinflammatory cytokine levels in the brain may modulate the inhibitory influence exerted by alcohol on the HPA axis response to endotoxemia.

Socioeconomic status and health: a neurobiological perspective

Socioeconomic status (SES) is one of the strongest predictors of health in industrial nations. This is especially true of societies with large disparities between rich and poor. Evidence suggests that the interactions between individuals of different SES play a crucial role in mediating the effects of SES on health. The question is why? Because humans are extremely social animals, their sense of well being is to a large extent determined by their social interactions. In hierarchical societies, individuals at every level of the hierarchy have to submit to those above and the recognition of this submissiveness generates emotions such as shame, anger and depression. These emotions lead to the activation of physiological alarm systems such as the hypothalamic pituitary adrenal axis and the sympathetic nervous system. The chronic activation of these systems alter their set points. This results in changes in the systems' different target organs responsible for diseases such as adult onset diabetes, hypertension, atherosclerosis, major depression and autoimmune diseases. Recent evidence from neurobiology show that one brain area, the amygdala, plays a pivotal role in processing social emotions. Anatomical and physiological studies of the amygdala in animals show how this area could play the central role in activating the alarm systems. This recent evidence brings a deeper level of plausibility to the postulated mechanisms of activation of the alarm systems by social emotions. Other experimental evidence also shed more light on the pathways responsible for translating psychosocial experiences into physiological perturbations.

Dehydroepiandrosterone-sulfate did not mitigate sickness behavior in mice

In response to lipopolysaccharide (LPS), macrophages secrete cytokines that transmit a message to the brain and induce sickness behavior. Because dehydroepiandrosterone (DHEA) and its sulfated ester (DHEA-S) reportedly improve mental health and modulate cytokine production, we hypothesized that DHEA-S administration would inhibit LPS-induced sickness behavior. Mice were provided drinking water with 0% or 0.01% DHEA-S for 2 weeks and then injected intraperitoneally with saline or LPS (1 microg). Sickness behavior was quantified using a social investigation paradigm, and DHEA-S in plasma and brain was determined at the study's end. DHEA-S did not affect water intake, food intake, or body weight during the 2-week period. As anticipated, LPS depressed social behavior. The maximum depression was observed 2 h postinjection, after which social investigation steadily increased until returning to baseline level at 8 h. DHEA-S did not mitigate the effects of LPS on social behavior even though DHEA-S in plasma and brain was increased 150- and 6-fold, respectively, in mice given DHEA-S. In a separate study, mice were given DHEA-S for 3 months and then challenged with LPS. Consistent with the first study, LPS reduced social behavior irrespective of DHEA-S treatment. However, 3 months administration of DHEA-S reduced the depression from baseline after injection of saline or LPS. DHEA-S in plasma and brain for mice given DHEA-S for 3 months was similar to that observed after 2 weeks. Collectively, these results suggest that DHEA-S has neuromodulatory effects but is ineffective at ameliorating LPS-induced sickness behavior.

The influence of systemic inflammation on inflammation in the brain: implications for chronic neurodegenerative disease

Systemic inflammation is associated with sickness behaviour and signals pass from the blood to the brain via macrophage populations associated with the brain, the perivascular macrophages and the microglia. The amplitude, or gain, of this transduction process is critically dependent on the state of activation of these macrophages. In chronic neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, or prion disease the pathology is associated with a highly atypical inflammatory response, characterised by the activation of the macrophage populations in the brain: the cells are primed. Recent evidence suggests that systemic inflammation may impact on local inflammation in the diseased brain leading to exaggerated synthesis of inflammatory cytokines and other mediators in the brain, which may in turn influence behaviour. These interactions suggest that systemic infections, or indeed any systemic challenge that promotes a systemic inflammatory response, may contribute to the outcome or progression of chronic neurodegenerative disease.

Dependence of Positive Effects of Granulocyte Colony-stimulating Factor on the Antibiotic Regimen: Evaluation in Rats with Polymicrobial Peritonitis

We tested the hypothesis that the ability of granulocyte colony-stimulating factor (G-CSF) to prevent death from fecal peritonitis is influenced by the composition of the antibiotic regimen with which it is administered. We used a rodent model of polymicrobial peritoneal contamination and infection and the concept of clinical modeling randomized trials (CMRTs), which includes the conditions of randomized, clinical trials and complex clinical interventions (e.g., anesthesia, volume substitution, antibiotics, surgery, postoperative analgesia). With the peritonitis model we obtained a mortality dose-response curve that was sensitive to antibiotic prophylaxis. G-CSF was most efficacious when it was administered both prophylactically and after the onset of peritonitis. Cefuroxime/metronidazole, ofloxacin/metronidazole, and amoxicillin/clavulanate improved survival in combination with G-CSF best, whereas cefotaxime or ceftriaxone with and without metronidazole did not. G-CSF administration was associated with improved polymorphonuclear neutrophil phagocytosis and enhanced bacterial clearance. Pro-inflammatory cytokine release (tumor necrosis factor-a, interleukin-6, macrophage inflammatory protein-2) was decreased in plasma and in the peritoneal fluid. Their expression was lowered in various organs on the protein and mRNA level. The results were used to design a clinical trial to test the ability of G-CSF to prevent serious infections in patients with colorectal cancer surgery. In this trial G-CSF application and antibiotic prophylaxis were performed with the most effective scheduling and combinations (cefuroxime/metronidazole and ofloxacin/metronidazole) as defined here.

Mild acute inflammatory stimulation induces transient negative mood

OBJECTIVE

This study aims to assess the mood changes induced by mild acute inflammatory stimulation (typhoid vaccination).

METHODS

Using a double blind study design, 26 healthy volunteers underwent baseline assessments of mood, financial strain and work stress and were randomised to injection of Salmonella typhi vaccine or placebo injection. Mood, symptoms and body temperature was assessed by a modified version of the Profile of Mood States at 1, 2, 3, 4, 6 and 8 h post injection.

RESULTS

Typhoid vaccination induces no increases in physical symptoms or temperature. Mood improved over the day in the placebo but not in the vaccine condition. Negative changes in mood following injection were correlated with chronic stress (financial strain) in the vaccination condition (r=-.65, P<.025).

CONCLUSION

A mild acute inflammatory stimulus induces transient negative mood, and responses were modulated by chronic stress. Implications for depressed mood in physical illness are discussed.

Influenza virus-induced sleep responses in mice with targeted disruptions in neuronal or inducible nitric oxide synthases

Influenza viral infection induces increases in non-rapid eye movement sleep and decreases in rapid eye movement sleep in normal mice. An array of cytokines is produced during the infection, and some of them, such as IL-1β and TNF-α, are well-defined somnogenic substances. It is suggested that nitric oxide (NO) may mediate the sleep-promoting effects of these cytokines. In this study, we use mice with targeted disruptions of either the neuronal NO synthase (nNOS) or the inducible NO synthase (iNOS) gene, commonly referred to as nNOS or iNOS knockouts (KOs), to investigate sleep changes after influenza viral challenge. We report that the magnitude of viral-induced non-rapid eye movement sleep responses in both nNOS KOs and iNOS KOs was less than that of their respective controls. In addition, the duration of rapid eye movement sleep in nNOS KO mice did not decrease compared with baseline values. All strains of mice had similar viral titers and cytokine gene expression profiles in the lungs. Virus was not isolated from the brains of any strain. However, gene expression in the brain stem differed between nNOS KOs and their controls: mRNA for the interferon-induced gene 2′,5′-oligoadenylate synthase 1a was elevated in nNOS KOs relative to their controls at 15 h, and IL-1β mRNA was elevated in nNOS KOs relative to their controls at 48 h. Our results suggest that NO synthesized by both nNOS and iNOS plays a role in virus-induced sleep changes and that nNOS may modulate cytokine expression in the brain.

Interleukin-1beta modulates state-dependent discharge activity of preoptic area and basal forebrain neurons: role in sleep regulation

Interleukin-1beta (IL-1) is a pro-inflammatory cytokine that has been implicated in the regulation of nonrapid eye movement (nonREM) sleep. IL-1, IL-1 receptors and the IL-1 receptor antagonist (ra) are present normally in discrete brain regions, including the preoptic area (POA) of the hypothalamus and the adjoining magnocellular basal forebrain (BF). The POA/BF have been implicated in the regulation of sleep-wakefulness. We hypothesized that IL-1 promotes nonREM sleep, in part by altering the state-dependent discharge activity of POA/BF neurons. We recorded the sleep-wake discharge profiles of 83 neurons in the lateral POA/BF and assessed the effects of IL-1, IL-1ra, and IL-ra + IL-1 delivered through a microdialysis probe on state-dependent neuronal discharge activity. IL-1 decreased the discharge rate of POA/BF neurons as a group (n = 55) but wake-related and sleep-related neurons responded differently. IL-1 significantly decreased the discharge rate of wake-related neurons. Of 24 wake-related neurons studied, 19 (79%) neurons exhibited a greater than 20% change in their discharge in the presence of IL-1 during waking. IL-1 suppressed the discharge activity of 18 of 19 responsive neurons. Of 13 sleep-related neurons studied, IL-1 increased the discharge activity of five and suppressed the discharge activity of four neurons. IL-1ra increased the discharge activity of four of nine neurons and significantly attenuated IL-1-induced effects on neuronal activity of POA/BF neurons (n = 19). These results suggest that the sleep-promoting effects of IL-1 may be mediated, in part, via the suppression of wake-related neurons and the activation of a subpopulation of sleep-related neurons in the POA/BF.

Rat brain vascular distribution of interleukin-1 type-1 receptor immunoreactivity: relationship to patterns of inducible cyclooxygenase expression by peripheral inflammatory stimuli

Interleukin-1 beta (IL-1 beta) is thought to act on the brain to induce fever, neuroendocrine activation, and behavioral changes during disease through induction of prostaglandins at the blood-brain barrier (BBB). However, despite the fact that IL-1 beta induces the prostaglandin-synthesizing enzyme cyclooxygenase-2 (COX-2) in brain vascular cells, no study has established the presence of IL-1 receptor type 1 (IL-1R1) protein in these cells. Furthermore, although COX inhibitors attenuate expression of the activation marker c-Fos in the preoptic and paraventricular hypothalamus after administration of IL-1 beta or bacterial lipopolysaccharide (LPS), they do not alter c-Fos induction in other structures known to express prostaglandin receptors. The present study thus sought to establish whether IL-1R1 protein is present and functional in the rat cerebral vasculature. In addition, the distribution of IL-1R1 protein was compared to IL-1 beta- and LPS-induced COX-2 expression. IL-1R1-immunoreactive perivascular cells were mostly found in choroid plexus and meninges. IL-1R1-immunoreactive vessels were seen throughout the brain, but concentrated in the preoptic area, subfornical organ, supraoptic hypothalamus, and to a lesser extent in the paraventricular hypothalamus, cortex, nucleus of the solitary tract, and ventrolateral medulla. Vascular IL-1R1-ir was associated with an endothelial cell marker, not found in arterioles, and corresponded to the induction patterns of phosphorylated c-Jun and inhibitory-factor kappa B mRNA upon IL-1 beta stimulation, and colocalized with peripheral IL-1 beta- or LPS-induced COX-2 expression. These observations indicate that functional IL-1R1s are expressed in endothelial cells of brain venules and suggest that vascular IL-1R1 distribution is an important factor determining BBB prostaglandin-dependent activation of brain structures during infection.

Intratracheal double-stranded RNA plus interferon-γ: A model for analysis of the acute phase response to respiratory viral infections

Double-stranded (ds)RNA is made as a by-product of viral replication. Synthetic dsRNA induces virtually all of the same systemic symptoms as acute viral infections, such as fever and malaise. In order to develop a model of respiratory viral infections (such as influenza) suitable for use in gene knockout mice (where the deleted gene may affect viral replication), we examined C57BL/6 mouse body temperature and locomotor activity responses to the synthetic dsRNA polyriboinosinic.polyribocytidylic acid (poly[rI.rC]) introduced via the intratracheal (IT) route. We compared the IT poly[rI.rC] responses to the well-characterized intraperitoneal (IP) poly[rI.rC] responses. IT poly[rI.rC] failed to induce an acute phase response (APR) in mice, in contrast to IP poly[rI.rC]. However, addition of interferon (IFN)gamma to the IT poly[rI.rC] inoculum induced sustained hypothermia and suppressed locomotor activity responses with similar kinetics to those responses seen in acute mouse influenza. We further examined cytokine, antiviral, muscarinic M2 receptor and inducible nitric oxide synthase gene expression at 5 hr in the lungs of IT challenged mice. These studies suggested that priming the lung with IFNgamma could enhance proinflammatory (IL1beta, IL6, TNFalpha) cytokine gene expression and suppress interferon gene expression compared to IT poly[rI.rC] alone. No differences were detected for the other genes examined. While further molecular characterization of the model is required, we demonstrate that IT challenge with combined poly[rI.rC] and IFNgamma closely simulates the APR to an acute respiratory virus, and may serve as a suitable model for analyzing the molecular basis of the viral APR in gene knockout mice.

Reduced immobility in the forced swim test in mice with a targeted deletion of the leukemia inhibitory factor (LIF) gene

Cytokines are a large and diverse group of polypeptides that are rapidly released in response to tissue injury, infection, and inflammation. Besides their effects in the periphery, cytokines also affect the central nervous system (CNS). There has been increasing interest in the potential role of cytokines in the behavioral features of depressive disorders. One cytokine that might be a candidate for a role in the etiology of depression is leukemia inhibitory factor (LIF). LIF mRNA has been detected in the hypothalamus, hippocampus, amygdala, cerebellum, cerebral cortex, and basal forebrain nuclei. The role of LIF in the CNS has not been fully elucidated. Based upon the hypothesis that cytokines might have a role in depression, the present study characterized the behavior of mice with a targeted disruption of the LIF gene (LIF knockouts) in the forced swim test, an animal model used to measure depressive-like behavior and the response to antidepressants. It was found that LIF knockout mice show reduced immobility in the forced swim test, suggesting that LIF might have a potential role in the etiology of some forms of depression.

Reversible inactivation of the dorsal vagal complex blocks lipopolysaccharide-induced social withdrawal and c-Fos expression in central autonomic nuclei

Peripheral administration of lipopolysaccharide (LPS), a potent activator of the immune system, induces symptoms of behavioral depression, such as social withdrawal, concommitant with increases in c-Fos expression in central autonomic network nuclei. Previous studies implicated vagal visceral sensory nerves in transduction of immune-related signals relevant to for the induction of social withdrawal, a symptom of behavioral depression. Vagal sensory nerves terminate in the dorsal vagal complex (DVC) of the brainstem, a region that functions to integrate visceral signals and may also play a role in modulating arousal and affect. The objective of the current study was to determine whether the DVC contributes to immunosensory pathways driving symptoms of social withdrawal associated with LPS-induced behavioral depression, using a reversible lesion technique to temporarily inactivate the DVC. To assess the effects of DVC inactivation on LPS-induced social withdrawal and the subsequent changes in brain activation, we used behavioral assessment of social withdrawal, and analyzed c-Fos expression, a marker of neuronal activation, in the central nucleus of the amygdala (CEA), bed nucleus of the stria terminalis (BST), hypothalamic paraventricular nucleus (PVN), and ventromendial preoptic area (VMPO). Two hours following intraperitoneal LPS injection, there was a significant increase in c-Fos immunoreactivity in forebrain regions in animals treated with LPS. DVC inactivation completely blocked LPS-induced social withdrawal and dramatically reduced LPS-induced Fos expression in all four forebrain regions assessed. Collectively, these findings support the idea that the DVC acts as an immune-behavior interface between the peripheral stimuli and brain areas involved in modulating social behavior.

Conditioned taste aversion with lipopolysaccharide and peptidoglycan does not activate cytokine gene expression in the spleen and hypothalamus of mice

Several reports show that behavioural and physiological components of the acute phase reaction can be conditioned. However, the mechanisms responsible for these effects remain obscure. The underlying assumption that the changes observed in conditioned animals are dependent on a conditioned production of cytokines has never been demonstrated. In the present study, the possibility of conditioning the production of cytokines or molecules implicated in their signalling pathways was tested by submitting mice to conditioned taste aversion with a new saccharin taste paired with intraperitoneal (i.p.) injections of lipopolysaccharide (LPS, 0.83 microg/g) or peptidoglycan (PGN, 20 microg/g). After two conditioning sessions, conditioned mice developed a clear aversion to saccharine that was not associated with activation of genes of the cytokine network either at the periphery, or in the hypothalamus, as demonstrated by a macroarray approach and confirmed by real time RT-PCR. In contrast, there was an activation of the genes coding for nuclear factor kappa B (NFkappaB) and mitogen activated protein kinase (MAPK) signalling pathways in the spleen and to a lesser extent in the hypothalamus. This modulation of the NFkappaB and MAPK signalling pathways is interpreted in terms of a possible conditioned sensitisation of the immune system.

From hormones to immunity: the physiology of immunology

Discoveries in the physiology of immunology have increased at an increasing rate during the past two decades. It is now recognized that the immune system is just another physiological system that regulates, and is regulated by, other physiological systems such as the brain. These advances make it clear that recent findings in genomic biology must be interpreted in the context of the environment in which animals and humans live. Lack of a strong genetic basis for significant human mental health disorders, such as major depression, points to the critical importance of interactions. Several examples of environmental x genetic x disease interactions are presented. Regulation of cells of the hematopoietic lineage by two genes that control over 80% of postnatal growth, growth hormone and IGF-I, are then highlighted. The reciprocal relationship of how proinflammatory cytokines from the immune system regulate the growth hormone/IGF-I axis is also summarized. Particular emphasis is placed upon TNFalpha-induced IGF-I resistance in neurons, muscle cells and epithelial cells. This cytokine regulation of hormone action may ultimately be more important for human and animal health than direct effects of growth hormone and IGF-I on hematopoietic cells. Wasting of AIDS patients is given as an important clinical example of how TNFalpha from an activated immune system reduces IGF-I sensitivity in multiple physiologic systems, including muscle, nervous and hematopoietic tissues.