Reduction in food and water intake induced by microinjection of interleukin-1 beta in the ventromedial hypothalamus of the rat

Cachexia: A systemic consequence of progressive, unresolved disease

Cachexia, a systemic wasting condition, is considered a late consequence of diseases, including cancer, organ failure, or infections, and contributes to significant morbidity and mortality. The induction process and mechanistic progression of cachexia are incompletely understood. Refocusing academic efforts away from advanced cachexia to the etiology of cachexia may enable discoveries of new therapeutic approaches. Here, we review drivers, mechanisms, organismal predispositions, evidence for multi-organ interaction, model systems, clinical research, trials, and care provision from early onset to late cachexia. Evidence is emerging that distinct inflammatory, metabolic, and neuro-modulatory drivers can initiate processes that ultimately converge on advanced cachexia.

Invited review: Mechanisms of hypophagia during disease

Suppression of appetite, or hypophagia, is among the most recognizable effects of disease in livestock, with the potential to impair growth, reproduction, and lactation. The continued evolution of the field of immunology has led to a greater understanding of the immune and endocrine signaling networks underlying this conserved response to disease. Inflammatory mediators, especially including the cytokines tumor necrosis factor-α and interleukin-1β, are likely pivotal to disease-induced hypophagia, based on findings in both rodents and cattle. However, the specific mechanisms linking a cytokine surge to decreased feeding behavior are more difficult to pin down and likely include direct effects on appetite centers in the brain, alteration of gastric motility, and modulation of other endocrine factors that influence appetite and satiety. These insights into the mechanisms for disease-induced hypophagia have great relevance for management of neonatal calves, mature cows transitioning to lactation, and cows experiencing mastitis; however, it is not necessarily the case that increasing feed intake by any means possible will improve health outcomes for diseased cattle. We explore conflicting effects of hypophagia on immune responses, which may be impaired by the lack of specific substrates, versus apparent benefits for controlling the growth of some pathogens. Anti-inflammatory strategies have shown promise for promoting recovery of feed intake following some conditions but not others. Finally, we explore the potential for early disease detection through automated monitoring of feeding behavior and consider which strategies may be implemented to respond to early hypophagia.

Inflammation and Skeletal Muscle Wasting During Cachexia

Cachexia is the involuntary loss of muscle and adipose tissue that strongly affects mortality and treatment efficacy in patients with cancer or chronic inflammatory disease. Currently, no specific treatments or interventions are available for patients developing this disorder. Given the well-documented involvement of pro-inflammatory cytokines in muscle and fat metabolism in physiological responses and in the pathophysiology of chronic inflammatory disease and cancer, considerable interest has revolved around their role in mediating cachexia. This has been supported by association studies that report increased levels of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) in some, but not all, cancers and in chronic inflammatory diseases such as chronic obstructive pulmonary disease (COPD) and rheumatoid arthritis (RA). In addition, preclinical studies including animal disease models have provided a substantial body of evidence implicating a causal contribution of systemic inflammation to cachexia. The presence of inflammatory cytokines can affect skeletal muscle through several direct mechanisms, relying on activation of the corresponding receptor expressed by muscle, and resulting in inhibition of muscle protein synthesis (MPS), elevation of catabolic activity through the ubiquitin-proteasomal system (UPS) and autophagy, and impairment of myogenesis. Additionally, systemic inflammatory mediators indirectly contribute to muscle wasting through dysregulation of tissue and organ systems, including GCs via the hypothalamus-pituitary-adrenal (HPA) axis, the digestive system leading to anorexia-cachexia, and alterations in liver and adipocyte behavior, which subsequently impact on muscle. Finally, myokines secreted by skeletal muscle itself in response to inflammation have been implicated as autocrine and endocrine mediators of cachexia, as well as potential modulators of this debilitating condition. While inflammation has been shown to play a pivotal role in cachexia development, further understanding how these cytokines contribute to disease progression is required to reveal biomarkers or diagnostic tools to help identify at risk patients, or enable the design of targeted therapies to prevent or delay the progression of cachexia.

Disturbance of taste reactivity and other behavioral alterations after bilateral interleukin-1β microinjection into the cingulate cortex of the rat

The anterior cingulate cortex (ACC), is known to be intimately involved in food-related motivational processes and their behavioral organization, primarily by evaluating hedonic properties of the relevant stimuli. In the present study, the involvement of cingulate cortical interleukin-1β (IL-1β) mediated mechanisms in a) gustation associated facial and somato-motor behavioral patterns of Wistar rats were examined in taste reactivity test (TR). In addition, b) conditioned taste aversion (CTA) paradigm was performed to investigate the role of these cytokine mechanisms in taste sensation associated learning processes, c) the general locomotor activity of the animals was observed in open field test (OPF), and d) the potentially negative reinforcing effect of IL-1β was examined in conditioned place preference test (CPP). During the TR test, species specific behavioral patterns in response to the five basic tastes were analyzed. Response rates of ingestive and aversive patterns of the cytokine treated and the control groups differed significantly in case of the weaker bitter (QHCl, 0.03 mM), and the stronger umami (MSG, 0.5 M) tastes. IL-1β itself did not elicit CTA, it did not interfere with the acquisition of LiCl induced CTA, and it also failed to cause place preference or aversion in the CPP test. In the OPF paradigm, however, significant differences were found between the cytokine treated and the control groups in the rearing and grooming, the number of crossings, and in the distance moved. Our results indicate the involvement of cingulate cortical IL-1β mechanisms in the control of taste perception and other relevant behavioral processes.

Assessment of social behavior directed toward sick partners and its relation to central cytokine expression in rats

Acute illness not only reduces the expression of social behavior by sick rodents, but can also lead to avoidance responses when detected by healthy, would-be social partners. When healthy animals interact with a sick partner, an intriguing question arises: does exposure to a sick conspecific elicit an anticipatory immune response that would facilitate defense against future infection? To address this question, healthy adult male Sprague-Dawley rats (N=64) were given a brief social interaction (30min) with a partner that was either sick (250μg/kg injection with lipopolysaccharide [LPS] 3h prior to test) or healthy (sterile saline injection). During this exposure, social behavior directed toward the healthy or sick conspecific was measured. Additionally, the impact of housing condition was assessed, with rats group- or isolate-housed. Immediately after social interaction, brains were harvested for cytokine assessments within socially-relevant brain structures (olfactory bulb, amygdala, hippocampus and PVN). As expected, behavioral results demonstrated that (i) there was a robust suppression of social interaction directed against sick conspecifics; and (ii) isolate-housing generally increased social behavior. Furthermore, examination of central cytokine expression in healthy experimental subjects revealed a modest increase in TNF-α in rats that interacted with a sick social partner, but only in the olfactory bulb. Among the LPS-injected partners, expected increases in IL-1β, IL-6, and TNF-α expression were observed across all brain sites. Moreover, IL-1β and IL-6 expression was exacerbated in LPS-injected partners that interacted with isolate-housed experimental subjects. Together, these data replicate and extend our prior work showing that healthy rats avoid sick conspecifics, and provide preliminary evidence for an anticipatory cytokine response when rats are exposed to a sick partner. These data also provide new evidence to suggest that recent housing history potently modulates cytokine responses evoked by LPS.

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.

Food and water intake, body temperature and metabolic consequences of interleukin-1β microinjection into the cingulate cortex of the rat

In order to elucidate whether cytokine mechanisms of the cingulate cortex (cctx) are important in the central regulation of homeostasis, in the present study, feeding-metabolic effects of direct bilateral microinjection of interleukin-1β (IL-1β) into the cctx of the rat have been investigated. Short- (2h), medium (12h) and long-term (24h) food and water intakes and body temperature were measured after the intracerebral administration of this primary cytokine or vehicle solution, with or without paracetamol pretreatment. The effect of IL-1β on the blood glucose level of animals was examined in glucose tolerance test (GTT), and concentrations of relevant plasma metabolites (total cholesterol, HDL, LDH, triglycerides, uric acid) were additionally also determined following the above microinjections. In contrast to causing no major alteration in the food and water intakes, the cytokine treatment evoked significant increase in the body temperature of the rats. Prostaglandin-mediated mechanisms were shown to have important role in the mode of this action of IL-1β, since paracetamol pretreatment partially prevented the development of the above mentioned hyperthermia. In the GTT, no considerable difference was observed between the blood glucose levels of the cytokine treated and control animals. Following IL-1β microinjection, however, significant decrease of HDL and total cholesterol was found. Our present findings indicate that elucidating the IL-1β mediated homeostatic control mechanisms in the cingulate cortex may lead to the better understanding not only the regulatory entities of the healthy organism but also those found in obesity, diabetes mellitus and other worldwide rapidly spreading feeding-metabolic disorders.

The mucosal immune system: master regulator of bidirectional gut-brain communications

Communication between the brain and gut is not one-way, but a bidirectional highway whereby reciprocal signals between the two organ systems are exchanged to coordinate function. The messengers of this complex dialogue include neural, metabolic, endocrine and immune mediators responsive to diverse environmental cues, including nutrients and components of the intestinal microbiota (microbiota-gut-brain axis). We are now starting to understand how perturbation of these systems affects transition between health and disease. The pathological repercussions of disordered gut-brain dialogue are probably especially pertinent in functional gastrointestinal diseases, including IBS and functional dyspepsia. New insights into these pathways might lead to novel treatment strategies in these common gastrointestinal diseases. In this Review, we consider the role of the immune system as the gatekeeper and master regulator of brain-gut and gut-brain communications. Although adaptive immunity (T cells in particular) participates in this process, there is an emerging role for cells of the innate immune compartment (including innate lymphoid cells and cells of the mononuclear phagocyte system). We will also consider how these key immune cells interact with the specific components of the enteric and central nervous systems, and rapidly respond to environmental variables, including the microbiota, to alter gut homeostasis.

Clenbuterol activates the central IL-1 system via the β2-adrenoceptor without provoking inflammatory response related behaviours in rats

The long-acting, highly lipophilic, β2-adrenoceptor agonist clenbuterol may represent a suitable therapeutic agent for the treatment of neuroinflammation as it drives an anti-inflammatory response within the CNS. However, clenbuterol is also known to increase the expression of IL-1β in the brain, a potent neuromodulator that plays a role in provoking sickness related symptoms including anxiety and depression-related behaviours. Here we demonstrate that, compared to the immunological stimulus lipopolysaccharide (LPS, 250μg/kg), clenbuterol (0.5mg/kg) selectively up-regulates expression of the central IL-1 system resulting in a mild stress-like response which is accompanied by a reduction in locomotor activity and food consumption in rats. We provide further evidence that clenbuterol-induced activation of the central IL-1 system occurs in a controlled and selective manner in tandem with its negative regulators IL-1ra and IL-1RII. Furthermore, we demonstrate that peripheral β2-adrenoceptors mediate the suppression of locomotor activity and food consumption induced by clenbuterol and that these effects are not linked to the central induction of IL-1β. Moreover, despite increasing central IL-1β expression, chronic administration of clenbuterol (0.03mg/kg; twice daily for 21days) fails to induce anxiety or depressive-like behaviour in rats in contrast to reports of the ability of exogenously administered IL-1 to induce these symptoms in rodents. Overall, our findings suggest that clenbuterol or other selective β2-adrenoceptor agonists could have the potential to combat neuroinflammatory or neurodegenerative disorders without inducing unwanted symptoms of depression and anxiety.

Lipopolysacharide Rapidly and Completely Suppresses AgRP Neuron-Mediated Food Intake in Male Mice

Although Agouti-related peptide (AgRP) neurons play a key role in the regulation of food intake, their contribution to the anorexia caused by proinflammatory insults has yet to be identified. Using a combination of neuroanatomical and pharmacogenetics experiments, this study sought to investigate the importance of AgRP neurons and downstream targets in the anorexia caused by the peripheral administration of a moderate dose of lipopolysaccharide (LPS) (100 μg/kg, ip). First, in the C57/Bl6 mouse, we demonstrated that LPS induced c-fos in select AgRP-innervated brain sites involved in feeding but not in any arcuate proopiomelanocortin neurons. Double immunohistochemistry further showed that LPS selectively induced c-Fos in a large subset of melanocortin 4 receptor-expressing neurons in the lateral parabrachial nucleus. Secondly, we used pharmacogenetics to stimulate the activity of AgRP neurons during the course of LPS-induced anorexia. In AgRP-Cre mice expressing the designer receptor hM3Dq-Gq only in AgRP neurons, the administration of the designer drug clozapine-N-oxide (CNO) induced robust food intake. Strikingly, CNO-mediated food intake was rapidly and completely blunted by the coadministration of LPS. Neuroanatomical experiments further indicated that LPS did not interfere with the ability of CNO to stimulate c-Fos in AgRP neurons. In summary, our findings combined together support the view that the stimulation of select AgRP-innervated brain sites and target neurons, rather than the inhibition of AgRP neurons themselves, is likely to contribute to the rapid suppression of food intake observed during acute bacterial endotoxemia.

Inflammatory Cytokines and Antipsychotic-Induced Weight Gain: Review and Clinical Implications

Antipsychotic medications (APs), particularly second-generation APs, are associated with significant weight gain in schizophrenia patients. Recent evidence suggests that the immune system may contribute to antipsychotic-induced weight gain (AIWG) via AP-mediated alterations of cytokine levels. Antipsychotics with a high propensity for weight gain, such as clozapine and olanzapine, influence the expression of immune genes, and induce changes in serum cytokine levels to ultimately down-regulate neuroinflammation. Since inflammatory cytokines are normally involved in anorexigenic responses, reduced inflammation has been independently shown to mediate changes in feeding behaviours and other metabolic parameters, resulting in obesity. Genetic variation in pro-inflammatory cytokines is also associated with both general obesity and weight change during AP treatment, and thus, may be implicated in the pharmacogenetics of AIWG. At this time, preliminary data support a cytokine-mediated model of AIWG which may have clinical utility in developing more effective metabolic monitoring guidelines and prevention measures. However, further research is still needed to clearly elucidate the validity of this immune model. This article reviews the evidence implicating inflammatory cytokines in AIWG and its potential clinical relevance.

For whom the endocannabinoid tolls: Modulation of innate immune function and implications for psychiatric disorders

Toll-like receptors (TLRs) mediate the innate immune response to pathogens and are critical in the host defence, homeostasis and response to injury. However, uncontrolled and aberrant TLR activation can elicit potent effects on neurotransmission and neurodegenerative cascades and has been proposed to trigger the onset of certain neurodegenerative disorders and elicit detrimental effects on the progression and outcome of established disease. Over the past decade, there has been increasing evidence demonstrating that the endocannabinoid system can elicit potent modulatory effects on inflammatory processes, with clinical and preclinical evidence demonstrating beneficial effects on disease severity and symptoms in several inflammatory conditions. This review examines the evidence supporting a modulatory effect of endocannabinoids on TLR-mediated immune responses both peripherally and centrally, and the implications for psychiatric disorders such as depression and schizophrenia.

The role of genetic variation across IL-1β, IL-2, IL-6, and BDNF in antipsychotic-induced weight gain

OBJECTIVES

Antipsychotics with high weight gain-inducing propensities influence the expression of immune and neurotrophin genes, which have been independently related to obesity indices. Thus, we investigated whether variants in the genes encoding interleukin (IL)-1β, IL-2, and IL-6 and brain-derived neurotrophic factor (BDNF) Val66Met are associated with antipsychotic-induced weight gain (AIWG).

METHODS

Nineteen polymorphisms were genotyped using Taqman(®) assays in 188 schizophrenia patients on antipsychotic treatment for up to 14 weeks. Mean weight change (%) from baseline was compared across genotypic groups using analysis of covariance (ANCOVA). Epistatic effects between cytokine polymorphisms and BDNF Val66Met were tested using Model-Based Multifactor Dimensionality Reduction.

RESULTS

In European patients, IL-1β rs16944*GA (P = 0.013, Pcorrected = 0.182), IL-1β rs1143634*G (P = 0.001, Pcorrected = 0.014), and BDNF Val66Met (Val/Val, P = 0.004, Pcorrected = 0.056) were associated with greater AIWG, as were IL-1β rs4849127*A (P = 0.049, Pcorrected = 0.784), and IL-1β rs16944*GA (P = 0.012, Pcorrected = 0.192) in African Americans. BDNF Val66Met interacted with both IL-1β rs13032029 (Val/Met+ TT, PPerm = 0.029), and IL-6 rs2069837 (Val/Val+ AA, PPerm = 0.021) in Europeans, in addition to IL-1β rs16944 (Val/Val+ GA, PPerm = 0.006) in African Americans.

CONCLUSIONS

SNPs across IL-1β and BDNF Val66Met may influence AIWG. Replication of these findings in larger, independent samples is warranted.

Patterns of FOS protein induction in singing female starlings

Females of many songbird species produce song, but information about the neural correlates of singing behavior is limited in this sex. Although well studied in males, activity in premotor song control regions and social behavior regions has not been examined in females during song production. Here, we examined the immediate early gene protein product FOS in both song control and social behavior brain regions after female starlings defending nest boxes responded to an unfamiliar female in a naturalistic setting. We found that females that sang in response to the intruder had much higher numbers of fos-immunoreactive neurons (fos-ir) in the vocal control regions HVC, the robust nucleus of the arcopallium (RA), and the dorsomedial part of the nucleus intercollicularis (DM of the ICo). In HVC, fos-ir correlated positively with song length. In RA, DM and Area X, fos-ir correlated positively with number of songs produced. In social behavior regions, singers showed higher fos-ir in the nucleus taeniae of the amygdala, the dorsal part of the bed nucleus of the stria terminalis, and the ventromedial hypothalamus than non-singers. Overall, patterns of fos-ir in song control regions in females were similar to those reported for males, but differences in fos-ir were identified in social behavior regions. These differences may reflect a distinct role for brain regions involved in social behavior in female song, or they may reflect differences in the social function of female and male song.

Behavioral, structural and molecular changes following long-term hippocampal IL-1β overexpression in transgenic mice

Chronic neuroinflammation is associated with many neurodegenerative and neurocognitive disorders, yet few animal models exist to study the behavioral effects of prolonged neuroinflammation. Therefore, we recently developed a transgenic mouse model harboring an interleukin-1β excisional activation transgene (IL-1β(XAT)). These mice display localized IL-1β overexpression and resultant neuroinflammation for up to 1 year following transgene induction. Initial behavioral studies demonstrated long-term memory deficits after 2 weeks of hippocampal IL-1β overexpression. In the present studies, we extend these behavioral studies both in scope and timing. We find long-term contextual but not auditory fear memory impairments following 3 months of IL-1β overexpression. On a battery of other behavioral tests, IL-1β overexpression in IL-1β(XAT) mice increased locomotor activity, especially in female mice, and had slight anxiolytic effects. No differences were found in operant conditioning or in basal or stress-induced CORT levels, despite profound hippocampal glial activation. Interestingly, the volume of discrete hippocampal cell layers was reduced after 6 but not 3 months of IL-1β overexpression. Therefore, this animal model provides a novel tool for examining the effects of chronic inflammation on discrete brain regions.

Alcoholism and inflammation: neuroimmunology of behavioral and mood disorders

Alcohol abuse changes behavior and can induce major mood disorders such as depression. Recent evidence in pre-clinical rodent models and humans now supports the conclusion that the innate immune system is an important physiological link between alcoholism and major depressive disorders. Deficiency of toll-like receptor 4 (TLR4), a protein that has been known to immunologists for 50 years, not only prevents lipopolysaccharide (LPS)-induced sickness behavior but recently has been demonstrated to induce resistance to chronic alcohol ingestion. Activation of the immune system by acute administration of LPS, a TLR4 agonist, as well as chronic infection with Bacille Calmette-Guérin (BCG), causes development of depressive-like behaviors in pre-clinical rodent models. Induction of an enzyme expressed primarily in macrophages and microglia, 2,3 indoleamine dioxygenase, shunts tryptophan catabolism to form kynurenine metabolites. This enzyme is both necessary and sufficient for expression of LPS and BCG-induced depressive-like behaviors in mice. New findings have extended these concepts to humans by showing that tryptophan catabolites of 2,3 indoleamine dioxygenase are elevated in the cerebrospinal fluid of hepatitis patients treated with the recombinant cytokine interferon-α. The remarkable conservation from mice to humans of the impact of inflammation on mood emphasizes the ever-expanding role for cross-talk among diverse physiological symptoms that are likely to be involved in the pathogenesis of alcohol abuse. These findings present new and challenging opportunities for scientists who are engaged in brain, behavior and immunity research.

Cancer induces inflammation and depressive-like behavior in the mouse: modulation by social housing

Considerable data demonstrate a high prevalence of depressive symptoms in cancer patients. This study introduces an experimental model to examine the effect of tumor on depressive-like behavior. Female C57BL/6 mice were injected i.p. with syngeneic ID8 ovarian carcinoma. Experiment 1 measured sucrose intake before and after tumor incubation to assess the effect of tumor on anhedonic depressive-like behavior. Experiment 2 examined effects of tumor and social housing on anhedonia and a second depressive-like behavior, tail suspension test (TST) immobility. Systemic proinflammatory and antiinflammatory cytokines were measured following each experiment. Additional behaviors assessed the specificity of tumor's effect on depressive-like behavior. Tumor caused a reduction in sucrose intake relative to baseline and control levels (P<.05). Moreover, individually-housed tumor-bearing mice exhibited a lower sucrose preference than group-housed tumor-bearing or control mice in either housing condition (P<.05). Although tumor-bearing mice exhibited less locomotion than controls (P<.001), there was no significant effect of tumor on TST immobility. Tumor caused higher levels of systemic proinflammatory and antiinflammatory cytokines and smaller body weight (P<.05), but appetite and motor capacity were not significantly affected. Statistical mediation analysis showed that circulating interleukin-6 partially mediated the effect between tumor and home cage locomotion (P<.01) but not between tumor and sucrose intake. It is concluded that tumor elicits anhedonic depressive-like behavior in a murine model of ovarian cancer. This may have important implications for etiology of depression in the clinical cancer setting.

A biological pathway linking inflammation and depression: activation of indoleamine 2,3-dioxygenase

This article highlights the evidence linking depression to increased inflammatory drive and explores putative mechanisms for the association by reviewing both preclinical and clinical literature. The enzyme indoleamine 2,3-dioxygenase is induced by proinflammatory cytokines and may form a link between immune functioning and altered neurotransmission, which results in depression. Increased indoleamine 2,3-dioxygenase activity may cause both tryptophan depletion and increased neurotoxic metabolites of the kynurenine pathway, two alterations which have been hypothesized to cause depression. The tryptophan-kynurenine pathway is comprehensively described with a focus on the evidence linking metabolite alterations to depression. The use of immune-activated groups at high risk of depression have been used to explore these hypotheses; we focus on the studies involving chronic hepatitis C patients receiving interferon-alpha, an immune activating cytokine. Findings from this work have led to novel strategies for the future development of antidepressants including inhibition of indoleamine 2,3-dioxygenase, moderating the cytokines which activate it, or addressing other targets in the kynurenine pathway.

Effect of feeding status on adjuvant arthritis severity, cachexia, and insulin sensitivity in male Lewis rats

We studied the effect of food restriction, overfeeding, and normofeeding on cachexia, inflammatory and metabolic parameters, and insulin sensitivity in chronic adjuvant arthritis (AA) in rats. Food restriction during AA increased circulating ghrelin, corticosterone, decreased leptin, and ameliorated arthrogram score and systemic inflammation compared to normofeeding. Overfeeding worsened arthrogram score and systemic inflammation, and led to lipid accumulation in the liver, but not to alterations of adipokine and ghrelin plasma levels relative to normofeeding. Independently of feeding status, AA induced cachexia, in which modulation of mRNA expressions for appetite-regulating neuropeptides (NPY, AgRP, POMC, CART) in the arcuate nucleus (ARC) does not play a primary role. The overexpression of IL-1β mRNA in the ARC suggests its role in the mechanisms of impaired energy balance during AA under all feeding conditions. Normal HOMA index in all arthritic groups does not indicate the development of insulin resistance by feeding interventions in these rats.

Sustained hippocampal IL-1beta overexpression impairs contextual and spatial memory in transgenic mice

Neuroinflammatory conditions such as traumatic brain injury, aging, Alzheimer's disease, and Down syndrome are often associated with cognitive dysfunction. Much research has targeted inflammation as a causative mediator of these deficits, although the diverse cellular and molecular changes that accompany these disorders obscure the link between inflammation and impaired memory. Therefore, we used a transgenic mouse model with a dormant human IL-1beta excisional activation transgene to direct overexpression of IL-1beta with temporal and regional control. Two weeks of hippocampal IL-1beta overexpression impaired long-term contextual and spatial memory in both male and female mice, while hippocampal-independent and short-term memory remained intact. Human IL-1beta overexpression activated glia, elevated murine IL-1beta protein and PGE(2) levels, and increased pro-inflammatory cytokine and chemokine mRNAs specifically within the hippocampus, while having no detectable effect on inflammatory mRNAs in the liver. Sustained neuroinflammation also reduced basal and conditioning-induced levels of the plasticity-related gene Arc.

Homeostatic alterations after IL-1beta microinjection into the nucleus accumbens of the rat

The present study investigates the effects of direct administration of interleukin-1beta (IL-1beta) into the nucleus accumbens (NAcc) on homeostatic regulation. Short- and long-term food intakes (FI), water intakes (WI) and body temperature (BT) were measured before and after bilateral microinjection of IL-1beta (with or without paracetamol pretreatment) into the NAcc of Wistar rats, and the effects were compared with those found in vehicle treated control animals. In addition, blood glucose levels, along with a glucose tolerance test (GTT), and plasma concentrations of metabolic parameters, such as total cholesterol, triglycerides, HDL, LDL and uric acid were determined in cytokine treated and control rats. Short-term FI and WI were suppressed after intraaccumbens application of IL-1beta. A significant increase of BT was also observed after the cytokine microinjection. Pretreatment with paracetamol failed to influence the anorexigenic, adipsogenic, and pyrogenic effects of IL-1beta. A definite glucose intolerance of the cytokine treated animals and their pathologically elevated blood glucose levels became obvious in the acute GTT. Following IL-1beta microinjection, plasma levels of triglycerides, total cholesterol and LDL were found increased. Our present findings show that the NAcc is an important site of action of IL-1beta mediated processes in central homeostatic regulation.

Central interleukin-10 attenuates lipopolysaccharide-induced changes in food intake, energy expenditure and hypothalamic Fos expression

Lipopolysaccharide (LPS) is often used to mimic acute infection and induces hypophagia, the selective partitioning of fat for energy, and fever. Interleukin-10 (IL-10) is an anti-inflammatory cytokine expressed in the brain which attenuates LPS-induced hypophagia; however the potential sites of interaction within the brain have not been investigated. Hypothalamic orexin (ORX) and melanin-concentrating hormone (MCH) regulate energy expenditure and food intake although the regulation of these neuropeptides through the interactions between central IL-10 and the inflammatory consequences of peripheral LPS have not been investigated. The present study in the rat investigated during the dark phase of the light-dark cycle the ability of central IL-10 (250 ng, i.c.v.) to attenuate the changes in food intake, energy substrate partitioning, and central Fos expression within the hypothalamus to peripheral LPS (100 microg/kg, i.p.); Fos expression changes specifically within ORX and MCH neurons were also investigated. Central IL-10 attenuated the peripheral LPS-induced hypophagia, reduction in motor activity, fever and reduction in respiratory exchange ratio. Central IL-10 also attenuated peripheral LPS-induced increases in Fos expression within ORX neurons and decreases in Fos expression within unidentified cells of the caudal arcuate nucleus. In contrast, both IL-10 and LPS injection independently decreased Fos expression within MCH neurons. The present study provides further insight into the interactions within the brain between the anti-inflammatory cytokine IL-10, the inflammatory consequences of LPS, and neuropeptides known to regulate energy expenditure and food intake.

MyD88 plays a key role in LPS-induced Stat3 activation in the hypothalamus

Infection causes the production of proinflammatory cytokines, which act on the central nervous system (CNS) and can result in fever, sleep disorders, depression-like behavior, and even anorexia, although precisely how cytokines regulate the functions of the CNS remain unclear. In the present study, we investigated the regulatory-molecular mechanisms by which cytokines affect hypothalamic function in a state of infection. The intraperitoneal administration of lipopolysaccharide (LPS), a ligand of Toll-like receptor 4 (TLR4), time-dependently (2-24 h) increased signal transducer and activator of transcription 3 (STAT3) phosphorylation in the hypothalamus and liver, which corresponded with anorexia observed within 24 h. Interestingly, the pattern of phosphorylation in response to LPS differed between the hypothalamus and liver. In the hypothalamus, LPS increased STAT3 phosphorylation from 2 h, with a peak at 4 h and a decline thereafter, whereas, in the liver, the peak activation of STAT3 persisted from 2 to 8 h. The time course of the LPS-induced expression of suppressor of cytokine signaling 3 (SOCS3), a STAT3-induced negative regulator of the Janus kinase-STAT pathway, was similar to that of STAT3 phosphorylation. Using mice deficient in myeloid differentiation primary-response protein 88 (MyD88), an adapter protein of TLR4, we found that LPS-induced STAT3 phosphorylation and SOCS3 expression in the hypothalamus and liver were predominantly mediated through MyD88. Moreover, we observed that MyD88-deficient mice were resistant to LPS-induced anorexia. Taken together, our findings reveal a novel mechanism, i.e., MyD88 plays a key role in mediating STAT3 phosphorylation and anorexia in the CNS in a state of infection and inflammation.

Animal models of anorexia and cachexia

BACKGROUND: Cachexia is a devastating syndrome of body wasting that worsens quality of life and survival for patients suffering from diseases such as cancer, chronic kidney disease and chronic heart failure. Successful treatments have been elusive in humans, leaving a clear need for the development of new treatment compounds. Animal models of cachexia are able to recapitulate the clinical findings from human disease and have provided a much-needed means of testing the efficacy of prospective therapies. OBJECTIVE: This review focuses on animal models of cachexia caused by cancer, chronic heart failure and chronic kidney disease, including the features of these models, their implementation, and commonly-followed outcome measures. CONCLUSION: Given a dire clinical need for effective treatments of cachexia, animal models will continue a vital role in assessing the efficacy and safety of potential treatments prior to testing in humans. Also important in the future will be the use of animal models to assess the durability of effect from anti-cachexia treatments and their effect on prognosis of the underlying disease states.

Time-Course Changes of Hormones and Cytokines by Lipopolysaccharide and Its Relation with Anorexia

We assessed the time course effects of lipopolysaccaride (LPS) on food intake, cytokines, and hormones in rats and evaluated the relation between LPS-induced anorexia and its possible causative factors. Food intake was reduced 2 h after LPS injection (500 microg/kg, intraperitoneally) and remained decreased for 24 h. Plasma TNF-alpha and IL-6 levels increased by LPS administration at 0.5 and 2 h, and at 2 and 4 h, respectively. Plasma leptin and glucose levels were elevated at 8 and 16 h, and insulin levels were elevated at 2, 4, 8, and 16 h in the LPS-injected group, as compared to the counterpart controls. IL-6 levels in the CSF were elevated at 2 and 4 h. Hypothalamic cytokines tended to increase as early as 0.5 h after LPS injection and remained increased until 16 h. LPS-induced anorexia was attenuated in insulin-deficient STZ rats and was abolished by insulin treatment. The hypothalamic expression of NPY, a target of insulin's anorexic effect, was decreased 2 h after LPS administration, and central NPY injection (3 nM) prevented LPS-induced anorexia. In conclusion, cytokines, insulin, and leptin levels evidence different time courses by LPS administration. In LPS-induced anorexia, insulin may constitute a newly found causative factor, whereas leptin appears to be uninvolved in an early period in rats.

Interleukin-6 and leptin mediate lipopolysaccharide-induced fever and sickness behavior

Pro-inflammatory cytokines, interleukin (IL)-1beta, IL-6 and tumor necrosis factor-alpha (TNF-alpha) synthesized by activated macrophages and monocytes in response to administration of lipopolysaccharide (LPS), are considered important mediators of fever and sickness behavior. We administered rat-specific antisera for TNF-alpha, IL-1beta, IL-6 and leptin, to determine the involvement of peripherally released cytokines in LPS-induced fever and sickness behavior, measured as suppression of voluntary wheel-running and food intake. Male Sprague-Dawley rats (approximately 200 g) selected for their predisposition to spontaneously run on running wheels were anaesthetized with a combination of ketamine hydrochloride (80 mg/kg i.m.) and xylazine (4 mg/kg i.m.) and implanted intra-abdominally with temperature-sensitive radiotelemeters. Rats were injected intraperitoneally with anti-rat sera to one of the following, TNF-alpha, IL-1beta, IL-6 or leptin or with pre-immune sheep serum, followed by a subcutaneous injection of either LPS (250 microg/kg) or sterile saline. Lipopolysaccharide administration induced a approximately 1.3 (0.2) degrees C fever lasting approximately 10 h and reduced voluntary running by 93 (8.6)% and food intake by 51 (21.3)% compared to the saline response (ANOVA, P<0.05). Injection of anti-IL-6 serum or anti-leptin serum abolished the LPS-induced fever, anti-TNF-alpha serum affected only the early phase of fever and anti-IL-1beta serum had no effect on fever (ANOVA, P<0.05). LPS-induced suppression of voluntary running and food intake were attenuated in rats receiving anti-IL-6 serum, while the decrease in food intake was totally abolished in rats receiving anti-leptin serum (ANOVA, P<0.05). Injection of anti-TNF-alpha or anti-IL-1beta serum had no effect on LPS-induced sickness behavior. Peripherally released IL-6 and leptin therefore appear to be important in regulating LPS-induced fever and sickness behavior.

Influence of feeding status on neuronal activity in the hypothalamus during lipopolysaccharide-induced anorexia in rats

Fasting attenuates disease-associated anorexia, but the mechanisms underlying this effect are not well understood. In the present study, we investigated the extent to which a 48 h fast alters hypothalamic neuronal activity in response to the anorectic effects of lipopolysaccharide in rats. Male rats were fed ad libitum or fasted, and were injected with i.p. saline or lipopolysaccharide (250 microg/kg). Immunohistochemistry for Fos protein was used to visualize neuronal activity in response to lipopolysaccharide within selected hypothalamic feeding regulatory nuclei. Additionally, food intake, body weight, plasma interleukin-1 and leptin levels, and the expression of mRNA for appetite-related neuropeptides (neuropeptide Y, proopiomelanocortin and cocaine-amphetamine-regulated transcript) were measured in a time-related manner. Our data show that the pattern of lipopolysaccharide-induced Fos expression was similar in most hypothalamic nuclei whatever the feeding status. However, we observed that fasting significantly reduced lipopolysaccharide-induced Fos expression in the paraventricular nucleus, in association with an attenuated lipopolysaccharide-induced anorexia and body weight loss. Moreover, lipopolysaccharide reduced fasting-induced Fos expression in the perifornical area of the lateral hypothalamus. Lipopolysaccharide-induced circulating levels of interleukin-1 were similar across feeding status. Finally, fasting, but not lipopolysaccharide, affected circulating level of leptin and appetite-related neuropeptides expression in the arcuate nucleus. Together, our data show that fasting modulates lipopolysaccharide-induced anorexia and body weight loss in association with neural changes in specific hypothalamic nuclei.

Homeostatic alterations induced by interleukin-1β microinjection into the orbitofrontal cortex in the rat

The present experiments were designed to elucidate the effect of direct orbitofrontal cortical administration of interleukin-1beta (IL-1beta) on the homeostatic regulation. Short- and long-term food intakes (FI), water intakes and body temperature (BT) were measured before and after a bilateral microinjection of IL-1beta (with or without paracetamol /P/ pretreatment) into the orbitofrontal cortex (OBF) of Wistar rats, and the effects were compared with those found in vehicle-treated and i.p. injected IL-1beta, IL-1beta+P or control animals. In addition, blood glucose levels (BGLs), along a glucose tolerance test, and plasma concentrations of insulin, leptin, cholesterol, triglycerides and urate were determined in cytokine treated and control rats. Short-term FI was suppressed after orbitofrontal cortical or peripheral application of IL-1beta. In the long-term FI, however, there was no significant difference among the groups. Cytokine microinjection into the OBF, similar to the i.p. administration, was also followed by a significant increase in BT. Pretreatment with P failed to influence the anorexigenic and hyperthermic effects of the centrally administered IL-1beta. The sugar load led to a diabetes-like prolonged elevation of BGL in the IL-1beta treated animals. Following cytokine administration, plasma levels of insulin and that of triglycerides were found decreased, whereas that of uric acid increased. The present findings confirm that the OBF is one of the neural routes through which IL-1beta exerts modulatory effect on the central homeostatic regulation.

Cytokines as mediators of depression: what can we learn from animal studies?

It has recently been postulated that cytokines may cause depressive illness in man. This hypothesis is based on the following observations: 1. Treatment of patients with cytokines can produce symptoms of depression; 2. Activation of the immune system is observed in many depressed patients; 3. Depression occurs more frequently in those with medical disorders associated with immune dysfunction; 4. Activation of the immune system, and administration of endotoxin (LPS) or interleukin-1 (IL-1) to animals induces sickness behavior, which resembles depression, and chronic treatment with antidepressants has been shown to inhibit sickness behavior induced by LPS; 5. Several cytokines can activate the hypothalamo-pituitary-adrenocortical axis (HPAA), which is commonly activated in depressed patients; 6. Some cytokines activates cerebral noradrenergic systems, also commonly observed in depressed patients; 7. Some cytokines activate brain serotonergic systems, which have been implicated in major depressive illness and its treatment. The evidence for each of these tenets is reviewed and evaluated along with the effects of cytokines in classical animal tests of depression. Although certain sickness behaviors resemble the symptoms of depression, they are not identical and each has distinct features. Thus the value of sickness behavior as an animal model of major depressive disorder is limited, so that care should be taken in extrapolating results from the model to the human disorder. Nevertheless, the model may provide insight into the etiology and the mechanisms underlying some symptoms of major depressive disorder. It is concluded that immune activation and cytokines may be involved in depressive symptoms in some patients. However, cytokines do not appear to be essential mediators of depressive illness.

Short- and long-term effects of interleukin-2 on weight, food intake, and hedonic mechanisms in the rat

In the present work, we investigated the short- and long-term effects of a single systemic injection of rat recombinant interleukin-2 on weight, food intake, and brain stimulation reward thresholds elicited from the ventral tegmental area. An inverted U-shaped dose-function was obtained with 0.5 microg producing the greatest increases in the threshold for rewarding brain stimulation which were sustained during the month long tests. No differences between groups in terms of maximum response rates, a measure of performance, were observed. Although all injected groups showed a minor decline in the rate of weight gain over time, percent efficiency of food utilization (percent weight gain/food intake) was the same across groups, suggesting that metabolic function was not affected by the cytokine. In animals with bilateral ventral tegmental area implants, there was no consistent correspondence between the threshold change obtained from ipsilateral stimulation and that associated with the contralateral site; side-to-side differences ranged from 0 to 100%, suggesting a specific interaction between cytokine activity and the locus of rewarding brain stimulation. These data suggest that peripheral IL-2 significantly modifies hedonic processes arising from medial forebrain bundle stimulation in a long-term manner. We further suggest that since this modulation appears to be notably site-specific, IL-2 receptors or its metabolites may not be evenly distributed within the medial forebrain bundle.

The hypothalamic-pituitary-adrenal axis and viral infection

The hypothalamic-pituitary-adrenal (HPA) axis plays an important immunomodulatory role during viral infection. Activation of the HPA axis ultimately leads to elevated plasma levels of glucocorticoid (GC) hormones with the ability to mediate adaptive behavioral, metabolic, cardiovascular and immune system effects. In this review, we focus on the modulation of anti-viral immunity and viral pathogenesis by the HPA axis.

Prior stressor exposure sensitizes LPS-induced cytokine production

Exposure to stressors often alters the subsequent responsiveness of many systems. The present study tested whether prior exposure to inescapable tailshock (IS) alters the interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, or IL-6 response to an injection of bacterial endotoxin (lipopolysaccharide; LPS). Rats were exposed to IS or remained as home cage controls (HCC); 24 h later animals were injected i.p. with either 10 microg/kg LPS or equilvolume sterile saline. IS significantly increased plasma TNF-alpha, IL-1beta, and pituitary, hypothalamus, hippocampus, cerebellum IL-1beta 1 h, but not 2 h, after LPS, compared to controls. Additional animals were injected with LPS or saline 4, 10, or 21 days after exposure to IS and tail vein blood was collected and assayed for IL-1beta. An enhanced plasma IL-1beta response occurred 4 days after IS, but was gone by 10 days. These results suggest that exposure to IS sensitizes the innate immune response to LPS by resulting in either a larger or a more rapid induction of proinflammatory cytokines.

Effects of interleukin-1beta on food-maintained behavior in the mouse

The present studies compared the effect of parenteral administration of the proinflammatory cytokine interleukin-1beta (IL-1beta) on food-seeking behavior under various conditions. IL-1beta (100 ng/mouse) decreased home cage consumption of sweetened milk to a greater extent in ad libitum fed mice than in mice that were food-restricted to maintain 85-90% of their free-feeding body weight. When operant responding for milk was maintained under a fixed-ratio 10 response (FR10) schedule of milk delivery, IL-1beta (30-300 ng/mouse) significantly decreased milk-maintained responding in mice fed ad libitum, but not in food-restricted mice. When food-restricted mice were trained under either an FR4 or FR32 response schedule of milk delivery, IL-1beta (100-300 ng/mouse) produced significant decreases in FR32, but not in FR4 responding. When responding was maintained under a progressive-ratio 10 response (PR10) schedule of milk delivery, IL-1beta (30-300 ng/mouse) dose-dependently decreased breaking points. These results indicate that the effects of IL-1beta on food-maintained behavior depend on both the level of motivation (as assessed by food restriction) and on the response cost for the milk (as assessed by ratio requirement). These findings suggest that motivational factors may be capable of attenuating some of the behavioral effects of these agents.

Site-specific actions of interleukin-1 on excitotoxic cell death in the rat striatum

The pro-inflammatory cytokine interleukin-1 (IL-1) contributes to and exacerbates many forms of neurodegeneration. When co-administered with the potent glutamatergic agonist S-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (S-AMPA) in the rat striatum, IL-1 induces marked and widespread cell death throughout the ipsilateral cortex. The mechanisms underlying this action of IL-1 are not known but may involve activation of polysynaptic neuronal pathways leading from the striatum to the cortex via other brain areas such as the hypothalamus. The aims of the present study were to identify specific sites of action of IL-1 in the rat striatum, in order to further understand these pathways. Ventral regions of the caudate-putamen and the lateral shell of the nucleus accumbens (NAcc) were particularly sensitive to the effects of IL-1 on excitotoxic damage. A high percentage of co-injections in these sites induced distant cortical damage, whereas injections in more dorsal areas of the caudate-putamen or core regions of the NAcc were less likely to result in cortical cell death. The 'positive' injection sites differ from the unresponsive areas in that they have extensive connections with the limbic system and it may be that IL-1 displays specific actions on limbic pathways that, in conjunction with AMPA/kainate receptor activation, contribute to the remote cell death in the cortex. These findings enhance our understanding of the actions of IL-1, and the mechanisms by which it participates in neurodegeneration through both local and long-range effects.

Is obesity an inflammatory condition?

Obesity may be a low-grade systemic inflammatory disease. Overweight and obese children and adults have elevated serum levels of C-reactive protein, interleukin-6, tumor necrosis factor-alpha, and leptin, which are known markers of inflammation and closely associated with cardiovascular risk factors and cardiovascular and non-cardiovascular causes of death. This may explain the increased risk of diabetes, heart disease, and many other chronic diseases in the obese. The complex interaction between several neurotransmitters such as dopamine, serotonin, neuropeptide Y, leptin, acetylcholine, melanin-concentrating hormone, ghrelin, nitric oxide, and cytokines and insulin and insulin receptors in the brain ultimately determines and regulates food intake. Breast-feeding of more than 12 mo is associated with decreased incidence of obesity. Breast milk is a rich source of long-chain polyunsaturated fatty acids (LCPUFAs) and brain is especially rich in these fatty acids. LCPUFAs inhibit the production of proinflammatory cytokines and enhance the number of insulin receptors in various tissues and the actions of insulin and several neurotransmitters. LCPUFAs may enhance the production of bone morphogenetic proteins, which participate in neurogenesis, so these fatty acids might play an important role in brain development and function. It is proposed that obesity is a result of inadequate breast feeding, which results in marginal deficiency of LCPUFAs during the critical stages of brain development. This results in an imbalance in the structure, function, and feedback loops among various neurotransmitters and their receptors, which ultimately leads to a decrease in the number of dopamine and insulin receptors in the brain. Hence, promoting prolonged breast feeding may decrease the prevalence of obesity. Exercise enhances parasympathetic tone, promotes antiinflammation, and augments brain acetylcholine and dopamine levels, events that suppress appetite. Acetylcholine and insulin inhibit the production of proinflammatory cytokines and provide a negative feedback loop for postprandial inhibition of food intake, in part, by regulating leptin action. Statins, peroxisome proliferator-activated receptor-gamma binding agents, non-steroidal antiinflammatory drugs, and infant formulas supplemented with LCPUFAs, and LCPUFAs themselves, which suppress inflammation, may be beneficial in obesity.

Reduced food intake in response to CGP 71683A may be due to mechanisms other than NPY Y5 receptor blockade

INTRODUCTION

The purpose of this study was to test the continuing validity of the hypothesis that neuropeptide Y (NPY) produced in the brain controls food intake through an interaction with the NPY Y(5) receptor subtype.

METHODS

The hypothesis was tested using CGP 71683A a potent and highly selective non-peptide antagonist of the NPY Y(5) receptor which was administered into the right lateral ventricle of obese Zucker fa/fa rats.

RESULTS

Intraventricular injection of 3.4 nmol/kg NPY increased food intake during a 2 h test period. Doses of CGP 71683A in excess of 15 nmol/kg (i.cv.) resulted in blockade of the increase in food intake produced by NPY. Repeated daily injection of CGP 71683A (30--300 nmol/kg, i.cv.) immediately before the dark phase produced a dose-dependent and slowly developing decrease in food intake. CGP 71683A has a low affinity for NPY Y(1), Y(2) and Y(4) receptors but a very high affinity for the NPY Y(5) receptor (Ki, 1.4 nM). Surprisingly, CGP 71683A had similarly high affinity for muscarinic receptors (Ki, 2.7 nM) and for the serotonin uptake recognition site (Ki, 6.2 nM) in rat brain. Anatomic analysis of the brain after treatment with CGP 71683A demonstrated an inflammatory response associated with the fall in food intake.

CONCLUSIONS

While the fall in food intake in response to CGP 71683A may have a Y(5) component, interactions with other receptors or inflammatory mediators may also play a role. It is concluded that CGP 71683A is an imprecise tool for investigating the role of the NPY Y(5) receptor in the control of physiological processes including food intake. International Journal of Obesity (2001) 25, 84-94

Central nervous system mechanisms contributing to the cachexia-anorexia syndrome

The cachexia-anorexia syndrome occurs in chronic pathophysiologic processes including cancer, infection with human immunodeficiency virus, bacterial and parasitic diseases, inflammatory bowel disease, liver disease, obstructive pulmonary disease, cardiovascular disease, and rheumatoid arthritis. Cachexia makes an organism susceptible to secondary pathologies and can result in death. Cachexia-anorexia may result from pain, depression or anxiety, hypogeusia and hyposmia, taste and food aversions, chronic nausea, vomiting, early satiety, malfunction of the gastrointestinal system (delayed digestion, malabsorption, gastric stasis and associated delayed emptying, and/or atrophic changes of the mucosa), metabolic shifts, cytokine action, production of substances by tumor cells, and/or iatrogenic causes such as chemotherapy and radiotherapy. The cachexia-anorexia syndrome also involves metabolic and immune changes (mediated by either the pathophysiologic process, i.e., tumor, or host-derived chemical factors, e.g., peptides, neurotransmitters, cytokines, and lipid-mobilizing factors) and is associated with hypertriacylglycerolemia, lipolysis, and acceleration of protein turnover. These changes result in the loss of fat mass and body protein. Increased resting energy expenditure in weight-losing cachectic patients can occur despite the reduced dietary intake, indicating a systemic dysregulation of host metabolism. During cachexia, the organism is maintained in a constant negative energy balance. This can rarely be explained by the actual energy and substrate demands by tumors in patients with cancer. Overall, the cachectic profile is significantly different than that observed during starvation. Cachexia may result not only from anorexia and a decreased caloric intake but also from malabsorption and losses from the body (ulcers, hemorrhage, effusions). In any case, the major deficit of a cachectic organism is a negative energy balance. Cytokines are proposed to participate in the development and/or progression of cachexia-anorexia; interleukin-1, interleukin-6 (and its subfamily members such as ciliary neurotrophic factor and leukemia inhibitory factor), interferon-gamma, tumor necrosis factor-alpha, and brain-derived neurotrophic factor have been associated with various cachectic conditions. Controversy has focused on the requirement of increased cytokine concentrations in the circulation or other body fluids (e.g., cerebrospinal fluid) to demonstrate cytokine involvement in cachexia-anorexia. Cytokines, however, also act in paracrine, autocrine, and intracrine manners, activities that cannot be detected in the circulation. In fact, paracrine interactions represent a predominant cytokine mode of action within organs, including the brain. Data show that cytokines may be involved in cachectic-anorectic processes by being produced and by acting locally in specific brain regions. Brain synthesis of cytokines has been shown in peripheral models of cancer, peripheral inflammation, and during peripheral cytokine administration; these data support a role for brain cytokines as mediators of neurologic and neuropsychiatric manifestations of disease and in the brain-to-peripheral communication (e.g., through the autonomic nervous system). Brain mechanisms that merit significant attention in the cachexia-anorexia syndrome are those that result from interactions among cytokines, peptides/neuropeptides, and neurotransmitters. These interactions could result in additive, synergistic, or antagonistic activities and can involve modifications of transducing molecules and intracellular mediators. Thus, the data show that the cachexia-anorexia syndrome is multifactorial, and understanding the interactions between peripheral and brain mechanisms is pivotal to characterizing the underlying integrative pathophysiology of this disorder.

Endogenous brain IL-1 mediates LPS-induced anorexia and hypothalamic cytokine expression

The present study was designed to determine the role of endogenous brain interleukin (IL)-1 in the anorexic response to lipopolysaccharide (LPS). Intraperitoneal administration of LPS (5-10 microgram/mouse) induced a dramatic, but transient, decrease in food intake, associated with an enhanced expression of proinflammatory cytokine mRNA (IL-1beta, IL-6, and tumor necrosis factor-alpha) in the hypothalamus. This dose of LPS also increased plasma levels of IL-1beta. Intracerebroventricular pretreatment with IL-1 receptor antagonist (4 microgram/mouse) attenuated LPS-induced depression of food intake and totally blocked the LPS-induced enhanced expression of proinflammatory cytokine mRNA measured in the hypothalamus 1 h after treatment. In contrast, LPS-induced increases in plasma levels of IL-1beta were not altered. These findings indicate that endogenous brain IL-1 plays a pivotal role in the development of the hypothalamic cytokine response to a systemic inflammatory stimulus.

Timecourse and corticosterone sensitivity of the brain, pituitary, and serum interleukin-1beta protein response to acute stress

Activation of peripheral immune cells leads to increases of interleukin-1beta (IL-1beta) mRNA, immunoreactivity, and protein levels in brain and pituitary. Furthermore, IL-1beta in brain plays a role in mediating many of the behavioral, physiological, and endocrine adjustments induced by immune activation. A similarity between the consequences of immune activation and exposure to stressors has often been noted, but the potential relationship between stress and brain IL-1beta has received very little attention. A prior report indicated that exposure to inescapable tailshocks (IS) raised levels of brain IL-1beta protein 2 h after IS, but only in adrenalectomized (and basal corticosterone replaced) subjects. The studies reported here explore this issue in more detail. A more careful examination revealed that IL-1beta protein levels in hypothalamus were elevated by IS in intact subjects, although adrenalectomy, ADX (with basal corticosterone replacement) exaggerated this effect. IL-1beta protein increases were already present immediately after the stress session, both in the hypothalamus and in other brain regions in adrenalectomized subjects, and no longer present 24 h later. Furthermore, IS elevated levels of IL-1beta protein in the pituitary, and did so in both intact and adrenalectomized subjects. IS also produced increased blood levels of IL-1beta, but only in adrenalectomized subjects. Finally, the administration of corticosterone in an amount that led to blood levels in adrenalectomized subjects that match those produced by IS, inhibited the IS-induced rise in IL-1beta in hypothalamus and pituitary, but not in other brain regions or blood.

Brain endothelial cell production of a neuroprotective cytokine, interleukin-6, in response to noxious stimuli

Brain endothelial cells (BECs), specialized cells of the blood-brain barrier (BBB), are ideally positioned to monitor and respond to events in the periphery. The present study examined their potential role in transducing immune signals to the brain and in responding to noxious stimuli. BECs were isolated from rhesus monkeys at 3 age points (fetal/neonatal, adult, and very old animals). Cells were then challenged in vitro with either an immune stimulus (interleukin-1 beta (IL-1 beta), or lipopolysaccharide (LPS)) or an oxidative challenge (hypoxia). BECs released interleukin-6 (IL-6), which is known to have neurotrophic and neuroprotective functions. Furthermore, higher amounts of IL-6 were released in both baseline and stimulated conditions by BECs derived from aged animals. This research indicates a pathway whereby immune signals may be communicated to the CNS and has revealed one way that the BBB may protect neuronal survival under challenge conditions.

Anhedonic and anxiogenic effects of cytokine exposure

Systemic interleukin IL-1 beta, TNF alpha, and IL-2 profoundly influenced central monoamine activity, as well as behavioral outputs. The effects of the various cytokines were clearly distinguishable from one another, although synergistic effects were detected between several of these cytokines and between the actions of cytokines and stressors. Acutely applied IL-2 appeared to affect reward processes, but did not affect anxiety. When chronically administered, this cytokine markedly influenced working memory in a spatial learning test. In contrast to IL-2, both IL-1 beta and TNF alpha appeared to provoke an anxiogenic action, and provoked clear signs of illness. While these cytokines induced anorexia, they did not appear to affect reward processes. IL-1 beta and TNF alpha were found to act synergistically, and the TNF alpha provoked a sensitization with respect to the action of subsequent TNF alpha treatment. The findings indicated that cytokine treatments profoundly influence extrahypothalamic neurochemical functioning and may thus impact on behavioral outputs. Analyses of the behavioral and neurochemical changes elicited by cytokines, and particularly TNF alpha, need to consider not only the immediate impact of such treatments, but also the proactive effects that may be engendered.

Brain IL-1beta increases neutrophil and decreases lymphocyte counts through stimulation of neuroimmune pathways

Leukocytosis after cerebral injury is well described and may participate in the generation of cerebral damage. However, the mechanisms of brain-induced leukocytosis are still speculative. Since it is known that proinflammatory cytokines are involved in neuroimmunomodulation and since others and we have demonstrated high cytokine levels in the cerebrospinal fluid following injury, we supposed that brain cytokines may also influence leukocyte counts. In order to evaluate this hypothesis, we established an animal model using continuous intracerebroventricular (i.c.v.), intrahypothalamic (i.h.), or intravenous infusion of the proinflammatory cytokines tumor necrosis factor (TNF)-alpha and IL-1beta. Controls received vehicle solution. With this experimental paradigm we could show that i.c.v. and i.h. infusion of IL-1beta but not TNF-alpha dramatically increased neutrophil counts, whereas lymphocytes dropped. Blocking the hypothalamic-pituitary-adrenal (HPA) axis by hypophysectomy abolished the neutrophilia, whereas the lymphopenia remained unchanged. Furthermore, application of the beta2-adrenoreceptor antagonist propranolol prevented the decrease of lymphocytes and diminished the neutrophilia. All parameters normalized within 48 h after termination of infusion. So, our results demonstrate that brain IL-1beta can modify blood leukocyte counts through stimulation of both the sympathetic nervous system (SNS) and the HPA axis.