Activation of the hypothalamus-pituitary-adrenal axis by bacterial endotoxins: routes and intermediate signals

Response to LPS in female offspring from sows treated with cortisol during pregnancy

Prenatal stress has been shown to program responsiveness of the hypothalamus-pituitary-adrenal axis (HPA-axis) and behavior in offspring. In pig husbandry, sows are exposed to stressful conditions during gestation. Previously, cortisol treatment of pregnant sows has been shown to alter stress responsiveness and immunological parameters in their piglets. In the present study, we explored whether cortisol treatment of pregnant sows affects the offspring's response to an inflammatory stimulus. Sows were treated orally with cortisol either during the first, second, or third period of gestation, or received a placebo during this period. At 8 weeks of age, female offspring were injected intravenously with lipopolysaccharide (LPS). Offspring of sows that received cortisol during the first and third period of gestation showed a higher fever response to LPS. Cortisol treatment of sows during gestation did not affect offspring's response to LPS with regard to their cortisol response. LPS-induced sickness behavior, which was measured as the latency time in a human approach test, appeared to recover more quickly in offspring from sows that received cortisol during the second period of gestation. These results suggest that prenatal cortisol exposure programs responsiveness to inflammatory stimuli in female piglets.

Specificity and generality of the involvement of catecholaminergic afferents in hypothalamic responses to immune insults

Catecholamine-containing projections from the medulla have been implicated in the mediation of activational responses of the paraventricular nucleus of the hypothalamus (PVH) provoked by moderate doses of interleukin-1 (IL-1). To test the generality of this mechanism, rats bearing unilateral transections of aminergic projections were challenged with intravenous IL-1 (2 microg/kg), bacterial lipopolysaccharide (LPS; 0.1, 2.0, or 100 microg/kg), or saline and perfused 3 hours later; their brains were then prepared for quantitative analysis of Fos induction and relative levels of corticotropin-releasing factor (CRF) mRNA. LPS provoked a robust and dose-related increase in Fos expression within the PVH on the intact side of the brain at all doses tested; the response to IL-1 approximated that to the lowest LPS dose. On the lesioned side, Fos induction was significantly reduced at all dosage levels but was eliminated only at the lowest dosage. The percentage reduction was greatest (75%) in IL-1-challenged rats and was progressively less in animals treated with increasing LPS doses (67, 59, and 46%, respectively). Specificity of aminergic involvement was tested by using intra-PVH administration of the axonally transported catecholamine immunotoxin, antiDBH-saporin. This treatment abolished IL-1-induced elevations of Fos-ir and CRF mRNA in the PVH but left intact comparable responses to restraint stress. These data support a specific involvement of ascending catecholaminergic projections in mediating PVH responses to IL-1 and LPS. Residual Fos induction seen in lesioned animals in response to higher doses of LPS provides a basis for probing additional circuits that may be recruited in a hierarchical manner in response to more strenuous or complex immune insults.

Early social isolation alters behavioral and physiological responses to an endotoxin challenge in piglets

Psychosocial stress in the form of maternal deprivation and social isolation during early postnatal life induces persistent alterations in behavioral and physiological mechanisms of adaptation. One consequence may be an increased susceptibility to diseases in later life. Therefore, the aim of the present study was to investigate in domestic piglets the effects of a repeated social isolation (2 h daily from day 3 to day 11 of age) on behavioral, endocrine and immune responses to an endotoxin challenge with lipopolysaccharide (LPS) 1 day or 45 days after the isolation period. Peripheral LPS administration caused serious sickness behavior (somnolence, shivering, vomiting) and provoked profound increases in circulating tumor necrosis factor-alpha (TNF-alpha), ACTH and cortisol concentrations. The prior social isolation treatment enhanced signs of sickness and impaired suckling behavior. Early isolated piglets responded to LPS by an increase of shivering on day 12 and by increased vomiting on day 56 compared to controls. Further, there were considerable delays and reductions of time isolated piglets spent suckling on day 12. The repeated isolation stressor diminished TNF-alpha increases after LPS, whereas stress hormone levels were not significantly affected by isolation treatment. Finally, stronger relationships between signs of sickness and physiological measures were revealed in early isolated piglets. The duration of somnolence in isolated piglets was related to changes of cortisol and TNF-alpha concentrations, and the highest impact on duration of shivering was found for changes in cortisol and corticosteroid binding globulin levels. The present results suggest a sustained adaptive sensitization of coping with infection by social stress experience during early development in piglets.

Effect of 3-Phenyl-2-Propene-1-ol on PGE2 release from rat cerebral microvascular endothelial cells stimulated by IL-1beta

Fever, an elevation in body temperature, is thought to be terminally mediated by prostaglandin E(2) (PGE(2)). Both Guizhi Tang (GZT) and its active fraction A (Fr.A) showed an antipyretic effect in rats. 3-Phenyl-2-propene-1-ol was one of the active compounds isolated from Fr.A. In the present study, we examined the influence of interleukin-1beta (IL-1beta) on prostaglandin E(2) (PGE(2)) release, and the effect of 3-phenyl-2-propene-1-ol on IL-1beta-induced PGE(2) release from rat cerebral endothelial cells (rCMEC). Cultured rCMEC were used in the study. In vitro, cells express typical phenotypic markers of brain endothelium. Using a monoclonal antibody against von Willebrand factor, immunocytochemical analysis revealed positive immunoreactivity in the cytoplasm of cultured cells. rCMEC were incubated in M199 medium containing IL-1beta in the presence or absence of 3-phenyl-2-propene-1-ol. After incubation, the conditioned media were collected and the amount of PGE(2) was measured by enzyme-linked immunosorbent assay (ELISA). IL-1beta increased the production of PGE(2) in a dose- and time-dependent manner. 3-Phenyl-2-propene-1-ol significantly decreased IL-1beta-induced PGE(2) release in a dose-dependent manner. Our results indicate that 3-phenyl-2-propene-1-ol inhibits the PGE(2) release from rCMEC stimulated by IL-1beta, and may have an antipyretic effect.

Successful antidepressant therapy restores the disturbed interplay between TNF-alpha system and HPA axis

BACKGROUND

In depressed patients, alterations in the hypothalamo-pituitary-adrenocortical (HPA) system are the most consistent neurobiological finding. HPA axis activity and cytokines are intrinsically intertwined: inflammatory cytokines stimulate adrenocorticotropic hormone (ACTH) and cortisol secretion, while, in turn, glucocorticoids suppress the synthesis of proinflammatory cytokines.

METHODS

We examined alterations in plasma levels of tumor necrosis factor-alpha (TNF-alpha), levels of its soluble receptors p55 (sTNF-R p55) and p75 (sTNF-R p75) as well as changes in the HPA system function using the combined dexamethasone/corticotropin-releasing hormone (dex/CRH) test on admission and at discharge in 70 depressed inpatients without inflammation.

RESULTS

On admission, TNF-alpha levels were inversely associated with the ACTH response to the combined dex/CRH test. Changes in TNF-alpha, sTNF-R p55, and sTNF-R p75 plasma levels from admission to discharge were positively correlated with the dex/CRH test outcome at discharge. Subgroup analysis revealed that this association was restricted to those patients achieving remission. In this subgroup, TNF-alpha levels at discharge were also positively correlated with dex/CRH test response at discharge.

CONCLUSIONS

Our results suggest that elevated HPA axis activity in acute depression suppresses TNF-alpha system activity, while after remission, when HPA axis activity has normalized, the TNF-alpha system seems to gain influence on the HPA system.

New role of the trigeminal nerve as a neuronal pathway signaling brain in acute periodontitis: participation of local prostaglandins

The systemic induction of cytokines and prostaglandins plays a key role in the development of fever. However, whether fever is triggered by local injection of lipopolysaccharide (LPS) and the involvement of locally produced prostaglandins in periodontal tissue has never been assessed. Thus, we tested the hypothesis that the trigeminal nerve is a neuronal pathway that signals the brain during acute periodontitis, and this response involves prostaglandin induction. Rats were given a gingival intra-pouch injection of sterile saline or Escherichia coli lipopolysaccharide, at doses of 10 and 100 microg/kg. Some animals were pre-treated with the local anesthetic mepivacaine or had the peripheral branches of the trigeminal nerves transected. Another group of animals were pre-treated (locally or systemically) with the nonselective inhibitor of cyclooxygenases diclofenac. Body core temperature (T (b)) was measured by means of biotelemetry before and after injections. LPS elicited a dose-dependent increase in T (b), which was abolished by mepivacaine, bilateral transection of the peripheral branches of the trigeminal nerve, or local treatment with diclofenac. The results indicate that there is an activation of periodontal nerves to induce fever by LPS. It also shows that local formation of prostaglandins plays a role in fever development. Moreover, immunohistochemistry detected c-fos expression in the subnucleus caudalis of spinal trigeminal nucleus and in the preoptic area of the hypothalamus 2 and 3 h after LPS injection, further confirming the role of trigeminal nerve signaling brain in acute periodontitis.

Influence of the estrous cycle on tolerance development to LPS-induced sickness behaviors in rats

The relations between the estrous cycle, inflammatory responses and the development of tolerance to endotoxin were examined. Female Long-Evans rats were injected intraperitoneally with lipopolysaccharide (LPS; 200 microg/kg) or saline vehicle at 08:00h on either diestrus (D) or proestrus (P). Ninety-five minutes after injection locomotor activity was assessed in an automated non-novel open-field for 20 min. To assess tolerance development to LPS, rats were re-injected at the next identical stage (i.e. 4 days later; groups: DD, PP) or at the alternate stage (i.e. 6 days later; groups: DP, PD) of the estrous cycle and locomotor activity was again assessed. On Test Day 1 all groups injected with LPS exhibited similar significant activity decrements, regardless of the stage of the estrous cycle. However, on Test Day 2 rats which received both injections of LPS during proestrus (PP) showed no signs of tolerance development, whereas rats in all other groups were tolerant to LPS. In a follow up study, the time between injections was extended to 8 days. Still the animals injected both times at proestrus showed no signs of tolerance to LPS after the second injection. Thus, the stages of the estrous cycle both at the time of initial exposure and of re-exposure appear critical in the formation of behavioral tolerance to LPS in rats.

Cinnamaldehyde reduces IL-1beta-induced cyclooxygenase-2 activity in rat cerebral microvascular endothelial cells

Cinnamaldehyde is a principle compound isolated from Guizhi-Tang, which is a famous traditional Chinese medical formula used to treat influenza, common cold and other pyretic conditions. The aim of the present study was to investigate the effects of cinnamaldehyde on expression and activity of cyclooxygenase (COX) and prostaglandin E(2) (PGE(2)) in rat cerebral microvascular endothelial cells (RCMEC). RCMEC were cultured, and identified by immunohistochemistry for von Willebrand factor in cytoplasm of the cells. Then cells were incubated in M199 medium containing interleukin (IL)-1beta in the presence or absence of cinnamaldehyde. After incubation, the medium was collected and the amount of PGE(2) was measured by enzyme-linked immunosorbent assay (ELISA). The cells were harvested, mRNA expression and activity of COX were analyzed by real-time reverse transcription-polymerase chain reaction (RT-PCR) with SYBR Green dye and ELISA respectively. Positive immunostaining for von Willebrand factor was present diffusely in the cytoplasm of >95% RCMEC. IL-1beta increased the mRNA expression and activity of COX-2, and production of PGE(2) in a dose- and time-dependent manner in RCMEC, while mRNA and activity of COX-1 were not significantly altered. Cinnamaldehyde significantly decreased IL-1beta-induced COX-2 activity and PGE(2) production in a dose-dependent manner, while it showed no inhibitory effect on IL-1beta-induced COX-2 mRNA expression in cultured RCMEC. In conclusion, cinnamaldehyde reduces IL-1beta-induced COX-2 activity, but not IL-1beta-induced COX-2 mRNA expression, and consequently inhibits production of PGE(2) in cultured RCMEC.

Social interactions alter proinflammatory cytokine gene expression and behavior following endotoxin administration

Sick animals display a constellation of behaviors, including anhedonia, anorexia, and reduced social interactions. Acute infection eliminates female mating behavior, but fails to attenuate mating behavior in male rats. These results have been attributed to the different reproductive strategies and parental investment of the two sexes. Males putatively suppress the symptoms of infection in order to "deceive" females into mating. We sought to investigate the mechanisms responsible for this suppression. Adult male CD-1 mice were treated with lipopolysaccharide (LPS; a component of bacterial cell walls; 400 microg/kg), then paired 2 h later with a receptive female or juvenile male or remained isolated. Blood samples and brains of the males were collected 3 h post-LPS; hypothalamic interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNFalpha) gene expression was measured using RT-PCR. Contrary to our prediction, exposure to a female increased hypothalamic IL-1 and TNFalpha gene expression. LPS treatment significantly decreased testosterone and increased corticosterone secretions. Social interactions altered absolute corticosterone concentrations in saline-injected animals only. In order to determine whether increased production of hypothalamic cytokines reflected increased severity of sickness responses, body temperature was monitored in a second group of mice implanted with telemetric transmitters. Body mass, food intake, and consumption of sweetened condensed milk (a highly favored food) were also monitored in these mice for 72 h post-injection. LPS injections reduced milk intake, an effect that was modulated by social interactions; however, fever was unaltered relative to isolated animals. These results suggest that social interactions can adjust behavioral responses to infection although the ultimate cause of this adjustment remains unspecified.

Glucocorticoids down-regulate lipopolysaccharide-induced de novo production of neurotensin mRNA in the rat hypothalamic, paraventricular, corticotrophin-releasing hormone neurons

OBJECTIVE

Intraperitoneal injection of the endotoxin lipopolysaccharide (LPS) produces inflammation accompanied by activation of the immune system and the secretion of cytokines. Cytokines stimulate the hypothalamo-pituitary-adrenal (HPA) axis to release the anti-inflammatory corticosterone which controls its own production by acting on the HPA axis. Upstream in the HPA axis are neuroendocrine corticotrophin-releasing hormone (CRH) neurons located in the paraventricular nucleus (PVN), whose multipeptidergic phenotype changes during inflammation: while CRH mRNA is up-regulated in these conditions, neurotensin (NT) mRNA expression is induced de novo. The negative feedback control of glucocorticoids on CRH production is well documented; however, their action on NT production in the PVN of the hypothalamus is poorly documented. The aim of this study was to determine if glucocorticoids modulate the de novo production of NT during inflammation.

METHODS

Using quantitative in situ hybridization histochemistry, we examined whether the absence (adrenalectomy) or excess (corticosterone implants) of glucocorticoids modulate de novo production of NT mRNA in the PVN during inflammation induced by LPS treatment.

RESULTS

A relatively low dose of LPS (50 microg/kg) that is not efficient to induce NT mRNA production in the PVN becomes efficient after adrenalectomy. Moreover, corticosterone excess reduces LPS-induced production of NT mRNA in the PVN.

CONCLUSION

Glucocorticoids exert a negative control on NT mRNA production in the PVN of the hypothalamus, and this effect requires that NT mRNA production be triggered, such as during inflammation.

2-Methoxycinnamaldehyde Reduces IL-1.BETA.-Induced Prostaglandin Production in Rat Cerebral Endothelial Cells

Prostaglandin E2 (PGE2) works as a common final mediator of the febrile. Guizhi-Tang, one of the most famous traditional Chinese medical formula used to treat influenza, common cold and other pyretic conditions, was previously reported to reduce the production of PGE 2 in rats. 2-Methoxycinnamaldehyde is a principle compound isolated from Guizhi-Tang. The aim of the present study was to investigate the effects of 2-methoxycinnamaldehyde on PGE2 production of rat cerebral endothelial cells (CECs). 2-Methoxycinnamaldehyde dose-dependently inhibited interleukin (IL)-1beta-induced PGE2 production in CECs with IC50 values of 174 microM. IL-1beta stimulation increased the protein, activity and mRNA expression of cyclooxygenase (COX)-2 but not COX-1. 2-Methoxycinnamaldehyde reduced IL-1beta-induced protein and activity of COX-2, but did not influence the COX-2 mRNA expression. Our results show that prostaglandin production in CECs during stimulated conditions is sensitive to inhibition by 2-methoxycinnamaldehyde and suggest that 2-methoxycinnamaldehyde may reduce COX-2 protein level and activity but not COX-2 mRNA.

Protection from neuronal damage evoked by a motivational excitation is a driving force of intentional actions

Motivation may be understood as an organism's subjective attitude to its current physiological state, which somehow modulates generation of actions until the organism attains an optimal state. How does this subjective attitude arise and how does it modulate generation of actions? Diverse lines of evidence suggest that elemental motivational states (hunger, thirst, fear, drug-dependence, etc.) arise as the result of metabolic disturbances and are related to transient injury, while rewards (food, water, avoidance, drugs, etc.) are associated with the recovery of specific neurons. Just as motivation and the very life of an organism depend on homeostasis, i.e., maintenance of optimum performance, so a neuron's behavior depends on neuronal (i.e., ion) homeostasis. During motivational excitation, the conventional properties of a neuron, such as maintenance of membrane potential and spike generation, are disturbed. Instrumental actions may originate as a consequence of the compensational recovery of neuronal excitability after the excitotoxic damage induced by a motivation. When the extent of neuronal actions is proportional to a metabolic disturbance, the neuron theoretically may choose a beneficial behavior even, if at each instant, it acts by chance. Homeostasis supposedly may be directed to anticipating compensation of the factors that lead to a disturbance of the homeostasis and, as a result, participates in the plasticity of motivational behavior. Following this line of thought, I suggest that voluntary actions arise from the interaction between endogenous compensational mechanisms and excitotoxic damage of specific neurons, and thus anticipate the exogenous compensation evoked by a reward.

Catecholamines mediate stress-induced increases in peripheral and central inflammatory cytokines

Proinflammatory cytokines act at receptors in the CNS to alter physiological and behavioral responses. Exposure to stressors increases both peripheral and central proinflammatory cytokines, yet the mechanism(s) of induction remain unknown. Experiments here examined the role of catecholamines in the in vivo induction of proinflammatory cytokines following tailshock stress. Rats were pretreated i.p. with 2.0 mg/kg prazosin (alpha1-adrenoceptor antagonist), 10.0 mg/kg propranolol (beta-adrenoceptor antagonist), or 5.0 mg/kg labetalol (alpha1- and beta-adrenoceptor antagonist) 30 min prior to tailshock exposure and plasma interleukin-1beta (IL-1beta) and IL-6, along with tissue interleukin-1beta from the hypothalamus, hippocampus, and pituitary were measured immediately following stressor termination. Prazosin attenuated stress-induced plasma IL-1beta and IL-6, but had no effect on tissue IL-1beta levels, while propranolol attenuated plasma IL-6 and blocked tissue IL-1beta elevation, and labetalol, which cannot cross the blood-brain barrier, attenuated plasma IL-1beta and IL-6, blocked pituitary IL-1beta, but had no effect on central tissue IL-1beta levels. Furthermore, administration of 50.0 mg/kg N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride, a neurotoxin that lesions neural projections from the locus coeruleus, prevented stress-induced elevation in hippocampal IL-1beta, a region highly innervated by the locus coeruleus, but had no effect on hypothalamic IL-1beta, a region that receives few locus coeruleus projections. Finally, i.p. injection of 5.0 mg/kg isoproterenol (beta-adrenoceptor agonist) was sufficient to induce circulating IL-1 and IL-6, and tissue IL-1beta. These data suggest catecholamines play an important role in the induction of stress-induced proinflammatory cytokines and that beta-adrenoceptors are critical for tissue IL-1beta induction, while both alpha- and beta-adrenoceptors contribute to the induction of plasma cytokines.

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.

Asymmetrical distribution of brain interleukin-6 depends on lateralization in mice

The central nervous system can regulate the peripheral immune system. Moreover, differences between left and right hemispheres (neurochemical brain asymmetries) and behavioral lateralization (functional brain asymmetries) affect immune responses. The molecular basis of brain-immune interactions remains insufficiently understood. Cytokines regulate immune responses, possibly through activation of the hypothalamic-pituitary-adrenal (HPA) axis. HPA axis activities are related to behavioral lateralization and brain asymmetry. Given IL-6 plays a role in asymmetrical brain immunomodulation, one might expect the IL-6 distribution in brain to be asymmetrical and to depend on behavioral lateralization. In order to start to test this hypothesis, male C57BL/6J mice were selected for paw preference and assessed for IL-6 levels in right and left cortex and hippocampus by enzyme linked immunosorbent assay. The results showed asymmetrical distribution of brain IL-6 in left-pawed animals and ambidextrous animals, but not in right-pawed animals, both in cortex and hippocampus. Furthermore, we found a correlation between IL-6 hemispheric distribution and the degree of behavioral lateralization both in cortex and hippocampus. Altogether, these results suggest that brain IL-6 could be a mediator of asymmetrical immunomodulation by the central nervous system.

Paraventricular nucleus neurons producing neurotensin after lipopolysaccharide treatment project to the median eminence

Inflammation consists in secretion of cytokines that stimulate the hypothalamo-pituitary-adrenal (HPA) axis to release the anti-inflammatory corticosterone. Upstream in this axis are corticotropin-releasing hormone (CRH) neurons in the paraventricular nucleus (PVN) whose multipeptidergic phenotype changes: both corticotropin-releasing hormone mRNAs and neurotensin mRNAs are up-regulated. Combining in situ hybridization with a retrograde neuronal marker, we demonstrated that neurotensin-containing neurons in the paraventricular nucleus project to the median eminence.

[Pathophysiological role of endotoxins, a common denominator to various diseases]

A growing number of investigations point to endotoxin or lipopolysaccharide as a central player in many pathophysiological states and diseases. Endotoxins are one of the most toxic biological contaminants continuously shed by both dead and live Gram negative bacteria. Endotoxins induce the primitive form of defense called innate immunity. Endotoxins have been related to inflammatory reactions observed in patients suffering from respiratory distress syndrome, multiorgan failure and septic shock, hepatic diseases, or in subjects affected by graft versus host disease after allogeneic transplantation. As our understanding of the molecular mechanisms underlying pathologies progresses, more diseases involving endotoxins emerge. Although these illnesses are multifactorial, the objective of this article is to review some of the common and distinct processes involving endotoxins in various disease states.

Role for CD14, TLR2, and TLR4 in bacterial product-induced anorexia

The cell surface component CD14 and the toll-like receptors 2 and 4 (TLR2 and TLR4) are important in mediating the immune responses to bacterial products in mammals. Using mice genetically deficient in CD14, TLR2, or TLR4, we studied the role of these molecules in the anorectic effects of LPS and muramyl dipeptide (MDP). CD14 or TLR2 knockout (KO) and TLR4-deficient (TLR4-DEF) mice as well as corresponding wild-type (WT) colittermates were injected intraperitoneally at dark onset with LPS (2 microg/mouse), MDP (10 mg/kg), interleukin-1 beta (IL-1 beta, 150 ng/mouse), or vehicle, and food intake was recorded. LPS and MDP reduced food intake in WT mice of all genotypes tested. The anorectic effect of LPS was attenuated (P < 0.04) in CD14-KO and TLR4-DEF mice but not in TLR2-KO (P > 0.05). The anorectic effect of MDP was blunted in CD14-KO and TLR2-KO (P < 0.02) mice but not in TLR4-DEF mice. IL-1 beta reduced food intake similarly in all genotypes tested. These results indicate that CD14 is involved in mediating the anorectic effects of both LPS and MDP. Furthermore, TLR4 and TLR2 are specifically involved in mediating the anorectic effects of LPS and MDP, respectively. The results are consistent with the hypothesis that TLR4 functions as the true LPS receptor and that TLR2 is involved in recognition of gram-positive bacterial products.

Induction of immune activation by a novel immunomodulatory oligonucleotide without thymocyte apoptosis

Bacterial DNA and synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs (CpG DNA) can potently stimulate innate immunity. While the actions of CpG DNA resemble those of LPS, these molecules stimulate distinct Toll-like receptors as well as cell types. In a previous study, we showed that a CpG ODN could induce cytokine production but, unlike LPS, did not induce thymocyte apoptosis. In this study, we have further investigated these differences using as a model a second-generation immunostimulatory oligonucleotide called HYB2048. Following administration to normal BALB/c mice, HYB2048-induced IL-12 but not IL-6 production. Under conditions in which LPS induced thymocyte apoptosis, HYB2048 did not cause significant cell death and, furthermore, did not block apoptosis induced by LPS. The levels of corticosterone induced by HYB2048 were also significantly lower than those induced by LPS. This pattern of activation could distinguish CpG DNA from LPS in its effects on the immune system.

Thermoeffector neuronal pathways in fever: a study in rats showing a new role of the locus coeruleus

It is known that brain noradrenaline (norepinephrine) mediates fever, but the neuronal group involved is unknown. We studied the role of the major noradrenergic nucleus, the locus coeruleus (LC), in lipopolysaccharide (LPS)-induced fever. Male Wistar rats had their LC completely ablated electrolytically or their catecholaminergic LC neurones selectively lesioned by microinjection of 6-hydroxydopamine; the controls were sham-operated. Both lesions resulted in a marked attenuation of LPS (1 or 10 microg kg(-1), i.v.) fever at a subneutral (23 degrees C) ambient temperature (Ta). Because electrolytic and chemical lesions produced similar effects, the role of the LC in fever was further investigated using electrolytic lesions only. The levels of prostaglandin (PG) E2, the terminal mediator of fever, were equally raised in the anteroventral third ventricular region of LC-lesioned and sham-operated rats during the course of LPS fever, indicating that LC neurones are not involved in febrigenic signalling to the brain. To investigate the potential involvement of the LC in an efferent thermoregulatory neuronal pathway, the thermoregulatory response to PGE(2) (25 ng, i.c.v.) was studied at a subneutral (23 degrees C, when fever is brought about by thermogenesis) or neutral (28 degrees C, when fever is brought about by tail skin vasoconstriction) Ta. The PGE2-induced increases in metabolic rate (an index of thermogenesis) and fever were attenuated in LC-lesioned rats at 23 degrees C, whereas PGE2-induced skin vasoconstriction and fever normally developed in LC-lesioned rats at 28 degrees C. The LC-lesioned rats had attenuated PGE2 thermogenesis despite the fact that they were fully capable of activating thermogenesis in response to noradrenaline and cold exposure. It is concluded that LC neurones are part of a neuronal network that is specifically activated by PGE2 to increase thermogenesis and produce fever.

Burn injury enhances brain prostaglandin E2 production through induction of cyclooxygenase-2 and microsomal prostaglandin E synthase in cerebral vascular endothelial cells in rats

OBJECTIVES

To examine whether peripheral burn injury in rats elevates prostaglandin E2 in the central nervous system and to determine where in the central nervous system enzymes responsible for prostaglandin E2 synthesis are expressed.

DESIGN

Prospective controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Sprague-Dawley rats.

INTERVENTIONS

Rats received either approximately 25% full-thickness burn injury or sham treatment. At 36 hrs after the injury, the cerebrospinal fluid was sampled to measure prostaglandin E2, and the brain and the spinal cord were sampled for immunohistochemical detection of cyclooxygenase-2 and microsomal-type prostaglandin E2 synthase, enzymes that are responsible for prostaglandin E2 production.

MEASUREMENTS AND MAIN RESULTS

The prostaglandin E2 concentration in the cerebrospinal fluid was significantly elevated in the injured rats, and this elevation was suppressed by a cyclooxygenase-2-specific inhibitor, NS398. Only in the injured rats, cyclooxygenase-2 and microsomal-type prostaglandin E synthase proteins were detected in vascular endothelial cells throughout the central nervous system with no regional difference. A double-immunofluorescence study revealed that cyclooxygenase-2 and microsomal-type prostaglandin E synthase were coexpressed in the perinuclear region of the endothelial cells.

CONCLUSIONS

These results indicate that peripheral burn injury induces cyclooxygenase-2 and microsomal-type prostaglandin E synthase in endothelial cells of the central nervous system. These enzymes likely elevate the cerebrospinal fluid concentration of prostaglandin E2, a prostanoid that, in turn, activates prostaglandin E2 receptors on the central nervous system neurons involved in the general symptoms following burn injury.

Endotoxin inhibits the surge secretion of gonadotropin-releasing hormone via a prostaglandin-independent pathway

Immune/inflammatory challenges, such as bacterial endotoxin, disrupt gonadotropin secretion and ovarian cyclicity. We previously determined that endotoxin can block the estradiol-induced LH surge in the ewe. Here, we investigated mechanisms underlying this suppression. First, we tested the hypothesis that endotoxin blocks the estradiol-induced LH surge centrally, by preventing the GnRH surge. Artificial follicular phases were created in ovariectomized ewes, and either endotoxin or vehicle was administered together with a surge-inducing estradiol stimulus. In each ewe in which endotoxin blocked the LH surge, the GnRH surge was also blocked. Given this evidence that endotoxin blocks the estradiol-induced LH surge at the hypothalamic level, we began to assess underlying central mechanisms. Specifically, in view of the prior demonstration that prostaglandins mediate endotoxin-induced suppression of pulsatile GnRH secretion in ewes, we tested the hypothesis that prostaglandins also mediate endotoxin-induced blockade of the surge. The prostaglandin synthesis inhibitor flurbiprofen was delivered together with endotoxin and the estradiol stimulus. Although flurbiprofen abolished endotoxin-induced fever, which is a centrally generated, prostaglandin-mediated response, it failed to reverse blockade of the LH surge. Collectively, these results indicate endotoxin blocks the LH surge centrally, suppressing GnRH secretion via a mechanism not requiring prostaglandins. This contrasts with the suppressive effect of endotoxin on GnRH pulses, which requires prostaglandins as intermediates.

Prostaglandins mediate lipopolysaccharide effects upon cholecystokinin and neurotensin phenotypes in neuroendocrine corticotropin-releasing hormone neurons: in situ hybridization evidence in the rat

Intraperitoneal injection of the endotoxin lipopolysaccharide produces an inflammation accompanied by immune system activation and secretion of cytokines that stimulate the hypothalamo-pituitary-adrenal (HPA) axis to release the anti-inflammatory corticosterone. Upstream in HPA axis are neuroendocrine corticotropin-releasing hormone neurons in the paraventricular nucleus whose multipeptidergic phenotype changes during inflammation: coexisting corticotropin-releasing hormone and cholecystokinin mRNAs are up-regulated whereas neurotensin mRNA expression is induced de novo. These changes may be mediated by prostaglandins released from perivascular and microglial cells in response to circulating cytokines. We examined by quantitative in situ hybridization histochemistry whether blockade of prostaglandin synthesis by indomethacin alters phenotypic expression in paraventricular nucleus neurons after lipopolysaccharide. Because indomethacin also elevated circulating corticosterone, animals were adrenalectomized and corticosterone replaced. Results showed that i.p. indomethacin administration suppressed lipopolysaccharide effects in a phenotype non-specific manner: one injection was sufficient to prevent both the increase in corticotropin-releasing hormone and cholecystokinin mRNAs expression and the induction of neurotensin mRNA expression. Therefore, neuroendocrine corticotropin-releasing hormone neurons with different peptidergic phenotypes appear to respond as a whole in the acute phase response to systemic infection.

Hypothalamo-pituitary-adrenal function in patients with depressive disorders is correlated with baseline cytokine levels, but not with cytokine responses to hydrocortisone

Dysfunction of the hyopthalamo-pituitary adrenal (HPA) system is frequently found in major depression. In addition, signs of non-specific inflammatory system activation have been reported. However, very little is known about interactions between the HPA and immune systems in depressive patients. To assess HPA system function, we performed a combined dexamethasone suppression and corticotropin-releasing hormone stimulation (DEX/CRH) test in 14 depressive patients. Moreover, baseline nocturnal plasma levels of the inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor (TNF)-alpha were measured. In addition, the system was challenged with an intraveneous pulsatile injection of hydrocortisone (1 mg/kg body weight in total) and again cytokine levels were measured across one night. Baseline TNF-alpha levels were negatively correlated with the amount of ACTH released upon CRH stimulation during the DEX/CRH test. Acute hydrocortisone administration suppressed TNF-alpha and IL-6 levels independently of baseline HPA system activity. We conclude that chronic HPA system overactivity in depressed patients might compromise the production of inflammatory cytokines under baseline conditions. However, the responsivity of the cytokine production to acutely administered glucocorticoids does not seem to correlate with the state of the HPA system.

Virus and host factors that mediate the clinical and behavioral signs of experimental herpetic encephalitis. A short auto-review

Experimental models that mimic the clinical syndrome of human viral encephalitis and represent HSV-1 neurotropism were utilized to investigate neuro-pharmacologic changes mediating clinical and behavioral manifestations of encephalitic infection of the central nervous system with HSV-1-induced rapid activation of the hypothalamic--pituitary--adrenocortical (HPA) axis and production of brain derived interleukin-1 (IL-1) and prostaglandin E2 (PG-E2), independently of viral replication. HSV-1 infection induced clinical signs of fever, motor hyperactivity and aggressive behavior. These manifestations were dependent on a permissive action of circulating glucocorticoids and not related to the degree of viral replication in the brain. Hyperthermia and HPA axis activation were also specifically dependent on HSV-1-induced brain IL-1 and PG-E2. The chronic neurological sequel or fatal outcome of HSV-1 encephalitis may be due to viral replication and brain tissue destruction, which are dependent on virus encoded virulence genes. In contrast, the clinical and behavioral signs in the acute phase are a result of activation of neurochemical systems, including cytokines, prostaglandinds and catecholamines. Circulating glucocorticoids play an essential role in mediating the physiologic actions of HSV-1-induced brain products and the clinical syndrome of encephalitis.

Histamine and prostaglandin interaction in regulation of oxytocin and vasopressin secretion

Prostaglandins and histamine in the hypothalamus are involved in the regulation of oxytocin and vasopressin secretion, and appear to be involved in the mediation of pituitary hormone responses to immunochallenges. Therefore, we investigated in conscious male rats: (i) whether blockade of H1 or H2 receptors affected the oxytocin and vasopressin responses to prostaglandins and (ii) whether blockade of prostaglandin synthesis affected the oxytocin and vasopressin responses to histamine or to Escherichia coli lipopolysaccharide (LPS), in order to determine any interaction between prostaglandins and histamine in the hypothalamus. Oxytocin secretion was dose-dependently stimulated by intracerebroventricular infusion of 1 or 5 microg of PGE1, PGE2 or PGF2alpha, with PGE2 being the most potent of the compounds used. Prior central infusion of the H1 receptor antagonist mepyramine or the H2 receptor antagonist cimetidine significantly inhibited the oxytocin response to all three prostaglandins by approximately 50%. Vasopressin secretion was increased by PGE1 but not by PGE2 or PGF2alpha. The stimulatory effect of PGE1 was almost annihilated by prior administration of mepyramine or cimetidine. Central infusion of histamine or immunochallenge with LPS administered intraperitoneally increased oxytocin and vasopressin secretion four- and two-fold, respectively. Pretreatment with systemic injection of the prostaglandin synthesis inhibitor indomethacin dose-dependently reduced the oxytocin response and prevented the vasopressin response to histamine or LPS. We conclude that histamine and PGE1, PGE2 or PGF2alpha interact in the regulation of oxytocin secretion, whereas histamine and only PGE1 interact in the regulation of vasopressin secretion. Furthermore, histamine as well as LPS may affect oxytocin and vasopressin neurones via activation of prostaglandins, probably in the hypothalamic supraoptic nucleus.

Neural immune pathways and their connection to inflammatory diseases

Inflammation and inflammatory responses are modulated by a bidirectional communication between the neuroendocrine and immune system. Many lines of research have established the numerous routes by which the immune system and the central nervous system (CNS) communicate. The CNS signals the immune system through hormonal pathways, including the hypothalamic-pituitary-adrenal axis and the hormones of the neuroendocrine stress response, and through neuronal pathways, including the autonomic nervous system. The hypothalamic-pituitary-gonadal axis and sex hormones also have an important immunoregulatory role. The immune system signals the CNS through immune mediators and cytokines that can cross the blood-brain barrier, or signal indirectly through the vagus nerve or second messengers. Neuroendocrine regulation of immune function is essential for survival during stress or infection and to modulate immune responses in inflammatory disease. This review discusses neuroimmune interactions and evidence for the role of such neural immune regulation of inflammation, rather than a discussion of the individual inflammatory mediators, in rheumatoid arthritis.

The role of interleukin-6 in stress-induced hyperthermia and emotional behaviour in mice

Psychological stress influences behaviour as well as autonomic functions such as body temperature. The mechanism that induces hyperthermia during stress is unknown. A recent hypothesis suggests that interleukin-6 (IL-6), an endogenous pyrogen, elevates body temperature during stress. To investigate the role of IL-6 during stress, we measured mRNA levels of IL-6 by quantitative PCR in various tissues 60 min after exposure of mice to open field stress. IL-6 mRNA was elevated in the hypothalamus three-fold and in the pituitary two-fold. However, there was no difference between the increase in body temperature after exposure to 60 min open field stress in wild-type controls (35.2+/-0.6-37.3+/-0.5 degrees C) and IL-6-deficient animals (34.8+/-0.4-37.0+/-0.3 degrees C). In contrast to body temperature, emotional behaviour differed between wild-type controls and IL-6-deficient mice. IL-6-deficient animals showed higher locomotor activity in an open field and lower levels of exploration of the open arms of the elevated plus maze than control animals. These data suggest that IL-6 plays an important role in the control of emotionality, but not in the regulation of body temperature after psychological stress.

Interleukin 1beta modulates rat subfornical organ neurons as a result of activation of a non-selective cationic conductance

The circumventricular organs (CVOs) are ideal locations at which circulating pyrogens may act to communicate with the CNS during an immune challenge. Their dense vasculature and fenestrated capillaries allow direct access of these pyrogens to CNS tissue without impediment of the blood-brain barrier (BBB). One such CVO, the subfornical organ (SFO), has been implicated as a site at which the circulating endogenous pyrogen interleukin 1beta (IL-1beta) acts to initiate the febrile response. This study was designed to determine the response of rat SFO neurons to IL-1beta (1 nM to 100 fM) using whole-cell current-clamp and voltage-damp techniques. We found that physiological(subseptic) concentrations of IL-1beta (1 pM, 500 fM, 100 fm) induced a transient depolarization in SFO neurons accompanied by a significant increase in spike frequency. In contrast,pharmacological (septic) concentrations of IL-1beta (1 nM) evoked a sustained hyperpolarization. While depolarizations in response to IL-1beta were abolished by treatment of cells with the IL-1 receptor antagonist (IL-1ra), hyperpolarizations were still observed. Voltage-clamp analysis revealed that the majority (85 %) of SFO neurons responding to IL-1beta with depolarization (29 of 34 cells) exhibited an electrophysiological profile characterized by a dominant delayed rectifier potassium current (DIK), a conductance that we also found to be reduced to 84.4 +/- 3.3 % of control by bath application of IL-1beta. In addition, using slow voltage ramps we demonstrated that IL-1beta activates a non-selective cationic current (INSC) with a reversal potential of -38.8 +/- 1.8 mV. These studies identify the cellular mechanisms through which IL-1beta can influence the excitability of SFO neurons and, as a consequence of such actions, initiate the febrile response to exogenous pyrogens.

Acute and conditioned sickness reduces morphine analgesia

Animals made ill by intraperitoneal injection with toxins, such as lithium chloride (LiCl) or lipopolysaccharides (LPS), or presented with cues associated with LiCl become hyperalgesic [Pain 56 (1994) 227]. The descending pronociceptive neurocircuitry and spinal pharmacology that underlie these effects bear the same features as those that mediate analgesic tolerance to morphine [Neurosci. Biobehav. Rev. 23 (1999) 1059]. Thus, we examined whether LiCl, LPS or cues paired with LiCl could reduce morphine analgesia. Morphine analgesia in the tail flick test was reduced 24 h but not 7 days following injection with LiCl, and 24 h following injection with LPS. In addition, morphine analgesia was reduced in the hot plate test 40 min and 24 h following LiCl. Furthermore, these effects occurred in the absence of detectable hyperalgesia indicating that illness-induced tolerance was not the result of an increase in pain sensitivity offsetting analgesia. Finally, rats tested in a context associated with LiCl demonstrated less morphine analgesia than rats tested in a context not associated with LiCl or rats naive to LiCl suggesting that illness activates descending mechanisms that antagonize analgesia rather than simply desensitizing opioid receptors. Thus, in addition to provoking hyperalgesia, illness-inducing agents also activate endogenous antianalgesic mechanisms.

Evidence for a role of the 5-HT2C receptor in central lipopolysaccharide-, interleukin-1 beta-, and leptin-induced anorexia

We examined the role of serotonin (5-HT) and the 5-HT(1A) and 5-HT(2C) receptors in the anorectic effects of centrally administered lipopolysaccharide (LPS), interleukin-1 beta (IL-1 beta), and leptin. Food intake was measured in rats after intracerebroventricular (ICV) injections of LPS (20 ng), IL-1 beta (10 ng), or leptin (1 microg) at lights out, followed by intraperitoneal (IP) injections of either the 5-HT(1A) autoreceptor agonist 8-hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT) (125 microg/kg) or the 5-HT(2C) receptor antagonist SB 242084 (0.3 mg/kg) at the onset of anorexia. SB 242084 significantly attenuated the food intake reduction caused by all compounds (all P<.01). IP 8-OH-DPAT attenuated ICV IL-1 beta-induced anorexia (P<.01). We also tested the involvement of the median raphe 5-HT(1A) receptors in peripheral LPS- and IL-1 beta-induced anorexia. Rats were injected intraperitoneally with either LPS (100 microg/kg) or IL-1 beta (2 microg/kg) at lights out, and 8-OH-DPAT (4 nmol) was administered directly into the median raphe nucleus at the onset of anorexia. Median raphe injections of 8-OH-DPAT significantly attenuated both IL-1 beta- and LPS-induced anorexia (both P<.01). These results implicate the 5-HT(2C) receptors in the mediation of central LPS-, IL-1 beta-, and leptin-induced anorexia. Our results also suggest that the midbrain raphe nuclei play a role in mediating the anorectic response to peripheral LPS and IL-1 beta.

Destructive arthritis in vaccinated interferon gamma-deficient mice challenged with Borrelia burgdorferi: modulation by tumor necrosis factor alpha

We found that Borrelia burgdorferi-vaccinated gamma interferon-deficient (IFN-gamma(0)) mice challenged with B. burgdorferi developed prominent chronic destructive osteoarthropathy. When these mice were treated with anti-tumor necrosis factor alpha (TNF-alpha) antibody, the severity of the destructive osteoarthritis was enhanced and affected the mobility of the animals. In addition, extensive swelling of the hind paws occurred. In contrast, treatment of B. burgdorferi-vaccinated, challenged IFN-gamma(0) mice with recombinant TNF-alpha (rTNF-alpha) inhibited the development of arthritis, including swelling of the hind paws. Moreover, treatment of vaccinated, challenged IFN-gamma(0) mice with anti-TNF-alpha inhibited fourfold the production of an antibody that kills B. burgdorferi, while treatment of vaccinated, challenged IFN-gamma(0) mice with rTNF-alpha slightly elevated the level of the borreliacidal antibody. These results suggest that the level of TNF-alpha directly or indirectly regulates the production of borreliacidal antibody and the development of vaccine-induced destructive Lyme osteoarthritis. Studies are in progress to determine the mechanism by which TNF-alpha-dependent cytokines generate the destructive arthritis.

Maternal behavior changes after immune challenge of neonates with developmental effects on adult social behavior

To examine whether maternal responsiveness during interactions with endotoxin-treated pups contributes to long-term effects on social development, neonatal mice were fostered on postnatal day 1 to dams from three selectively bred lines that differ in social behaviors. On day 5, neonates were administered saline or 0.5 mg/kg endotoxin (lipopolysaccharide, i.p.). Observations of undisturbed dams and litters on days 2, 4, 6, and 8 showed modest line differences in maternal behaviors. At the peak intensity of the transient illness induced by endotoxin (3 hr postinjection on day 5), dams increased licking and decreased time off-nest for endotoxin, but not saline-treated pups. As adults, fostered-reared males were observed in brief social interactions. Males exposed to endotoxin early in life showed changes in adult social behaviors that depended on foster dam line as well as individual differences in maternal responsiveness. Maternal responsiveness to stressed neonates can ameliorate the social-developmental effects of early illness.

Evidence that the anorexia induced by lipopolysaccharide is mediated by the 5-HT2C receptor

Rats consistently reduce their food intake following injections of bacterial lipopolysaccharides (LPS). Because inhibition of serotonergic (5-HT) activity by 8-OH-DPAT (5-HT(1A) activation) attenuates LPS-induced anorexia, we conducted a series of studies to examine whether other 5-HT-receptors are involved in the mediation of peripheral LPS-induced anorexia. In all experiments, rats were injected with LPS (100 microg/kg body weight [BW] ip) at lights out (hour 0). Antagonists were administered peripherally at hour 4, shortly after the onset of anorexia, which presumably follows the enhanced cytokine production after LPS. Food intake was then recorded during the subsequent 2 h or longer. 5-HT receptor antagonists cyanopindolol and SB 224289 (5-HT(1B)), ketanserin (5-HT(2A)), RS-102221 (5-HT(2C)), and metoclopramide (5-HT(3)) failed to attenuate LPS-induced anorexia. In contrast, both ritanserin (5-HT(2A/C)-receptor antagonist) (0.5 mg/kg BW) and SB 242084 (5-HT(2C)) (0.3 mg/kg BW) attenuated LPS-induced anorexia at doses that did not alter food intake in non-LPS-treated rats (all P<.01). Our results suggest that at least part of the anorexia following peripheral LPS administration is mediated through an enhanced 5-HT-ergic activity and the 5-HT(2C) receptor.

Hypothalamic pituitary adrenal axis and immune responses to endotoxin in rats with chronic adjuvant-induced arthritis

We investigated the effect of immune challenge with LPS in both control rats and rats with adjuvant-induced arthritis (AA). Fourteen day-AA rats showed the expected activation of the hypothalamic-pituitary adrenal axis associated with increases in vasopressin mRNA and paradoxical decreases in corticotropin-releasing hormone (CRH) mRNA in parvocellular neurons of the hypothalamic paraventricular nucleus (PVN). However, following LPS there was an increase in both CRH and vasopressin mRNA in the PVN. Neither control rats nor rats with AA had measurable plasma levels of IL-6, but plasma levels of IL-1beta were 2.7-fold higher in AA animals. Following LPS injection both IL-1beta and IL-6 increased more markedly in AA than in control rats. Neither controls nor AA rats expressed IL-1beta or IL-6 mRNA in the brain. However, following LPS these were induced in the subfornical organ, choroid plexus, and median eminence of both groups of animals. The areas expressing IL-1b mRNA were larger in the AA animals and exhibited a punctate pattern throughout the brain parenchyma and PVN. These data reveal an increased peripheral and central immunological response to LPS during the chronic inflammatory process of AA, providing a mechanism through which inflammatory disease can influence the response to a novel immunological challenge.

Multifocal necrotizing leukoencephalopathy in septic shock

OBJECTIVE

Multifocal necrotizing leukoencephalopathy, characterized by multiple microscopic foci of necrosis involving the white matter of the pons, has been described mainly after chemotherapy or radiotherapy for brain cancer and in HIV infection. The role of circulating cytokines has been suggested but remains to be assessed.

DESIGN

Prospective case series.

SETTING

A 26-bed general medical intensive care unit at a university hospital.

PATIENTS

Septic shock patients. MEASUREMENTS AND PATIENTS: In three patients who died from septic shock, careful postmortem examination of the brain was performed, including studies of neuronal apoptosis and cytokine expression.

MAIN RESULTS

In one patient, typical lesions of multifocal necrotizing leukoencephalopathy were seen. As compared with control 1 and control 2 who did not have multifocal necrotizing leukoencephalopathy, marked lesions of the pons, including vacuolization, apoptosis, microglial activation, and expression of tumor necrosis factor-alpha and interleukin-1beta, were observed in the case. Simultaneously, case 1 had markedly increased circulating levels for tumor necrosis factor-alpha, interleukin-1beta, interleukin-6, interleukin-8, interleukin-10, soluble tumor necrosis factor receptor II, and for interleukin-1 receptor antagonist.

CONCLUSION

Septic shock is a newly described cause of multifocal necrotizing leukoencephalopathy, probably mediated by an excessive systemic inflammatory response.

Does cortisol mediate endotoxin-induced inhibition of pulsatile luteinizing hormone and gonadotropin-releasing hormone secretion?

Bacterial endotoxin (lipopolysaccharide), a commonly used model of immune/inflammatory stress, inhibits reproductive neuroendocrine activity and concurrently induces a profound stimulation of the hypothalamo-pituitary-adrenal axis. We employed two approaches to test the hypothesis that enhanced secretion of cortisol mediates endotoxin-induced suppression of pulsatile GnRH and LH secretion in the ovariectomized ewe. First, we mimicked the endotoxin-induced increase in circulating cortisol by delivering the glucocorticoid in the absence of the endotoxin challenge. Within 1-2 h, experimentally produced increments in circulating cortisol suppressed pulsatile LH secretion in a dose-dependent fashion. Second, we blocked the endotoxin-induced stimulation of cortisol secretion using the drug metyrapone, which inhibits the 11-beta hydroxylase enzyme necessary for cortisol biosynthesis. In the absence of a marked stimulation of cortisol secretion, endotoxin still profoundly inhibited pulsatile GnRH and LH secretion. We conclude that, although enhanced cortisol secretion may contribute to endotoxin-induced suppression of reproductive neuroendocrine activity, the marked stimulation of the glucocorticoid is not necessary for this response. Our findings are consistent with the hypothesis that immune/inflammatory stress inhibits reproductive neuroendocrine activity via more than one inhibitory pathway, one involving enhanced secretion of cortisol and the other(s) being independent of this glucocorticoid.

The effect of endotoxin administration on the secretory dynamics of oxytocin in follicular phase mares: relationship to stress axis hormones

The primary aim of this study was to define the secretory dynamics of oxytocin and vasopressin in pituitary venous effluent from ambulatory horses during acute endotoxaemia, a stimulus that may release both hormones. Our secondary aim was to investigate the role of oxytocin in regulating adrenocorticotropic hormone (ACTH) secretion by comparing oxytocin, vasopressin, corticotropin-releasing hormone (CRH) and ACTH secretory profiles during endotoxaemia and by monitoring the ACTH response to oxytocin administration. Pituitary venous blood was collected nonsurgically continuously and divided into 1-min segments from eight follicular phase mares. Four mares were sampled for 30 min before and 3.5 h after receiving an i.v. infusion of bacterial endotoxin (TOX). Four control mares were sampled for 2.5 h without infusion of TOX. Another three follicular phase mares were given 5 U of oxytocin to replicate the peak response to TOX and pituitary blood collected every 1 min for 10 min before and 15 min after injection. Endotoxin raised the secretion rates of all hormones measured. All hormones were released episodically throughout the experiment, with TOX increasing the amplitude of peaks in each hormone. Peaks in oxytocin and vasopressin were coincident in each treated mare. Similarly, ACTH peaks were coincident with peaks of oxytocin and vasopressin in each treated mare, and with peaks of CRH in three mares. However, oxytocin administration did not affect ACTH secretion. We conclude that during endotoxaemia in horses: (i) oxytocin and vasopressin are secreted synchronously; (ii) oxytocin is unlikely to be acting as an ACTH secretagogue since inducing peak oxytocin concentrations observed during TOX does not raise ACTH; and therefore (iii) the close relationship between oxytocin and ACTH secretion is circumstantial and due to the fact that oxytocin secretion is concurrent with that of vasopressin, a proven ACTH secretagogue in horses.

Site-specific modulation of LPS-induced fever and interleukin-1 beta expression in rats by interleukin-10

Bacterial lipopolysaccharide (LPS) induces fever that is mediated by pyrogenic cytokines such as interleukin (IL)-1 beta. We hypothesized that the anti-inflammatory cytokine IL-10 modulates the febrile response to LPS by suppressing the production of pyrogenic cytokines. In rats, intravenous but not intracerebroventricular infusion of IL-10 was found to attenuate fever induced by peripheral administration of LPS (10 microg/kg iv). IL-10 also suppressed LPS-induced IL-1 beta production in peripheral tissues and in the brain stem. In contrast, central administration of IL-10 attenuated the febrile response to central LPS (60 ng/rat icv) and decreased IL-1 beta production in the hypothalamus and brain stem but not in peripheral tissues and plasma. Furthermore, intravenous LPS upregulated expression of IL-10 receptor (IL-10R1) mRNA in the liver, whereas intracerebroventricular LPS enhanced IL-10R1 mRNA in the hypothalamus. We conclude that IL-10 modulates the febrile response by acting in the periphery or in the brain dependent on the primary site of inflammation and that its mechanism of action most likely involves inhibition of local IL-1 beta production.

Bacterial lipopolysaccharide-induced coordinate downregulation of arginine vasopressin receptor V3 and corticotropin-releasing factor receptor 1 messenger ribonucleic acids in the anterior pituitary of endotoxemic steers

AVP and CRF are potent stimulators of pituitary ACTH secretion in cattle. Actions of AVP and CRF at the anterior pituitary are mediated by AVP receptor V3 (V3) and CRF receptor 1 (CRFR1). The primary objective of these studies was to determine the effect of systemic inflammatory stress on V3 and CRFR1 mRNAs in the bovine anterior pituitary. Holstein steers (n = 20) were injected with 200 ng/kg bacterial lipopolysaccharide (LPS) and tissues collected 0, 2, 4, 12, and 24 h later. All animals responded to LPS administration with an increase in body temperature, plasma ACTH, and cortisol (p < 0.05). Abundance of anterior pituitary V3 mRNA was decreased at 2, 4, and 12 h following LPS administration (p < 0.05) and returned to basal by 24 h. A similar temporal regulation of pituitary CRFR1 mRNA (p < 0.05), but not pituitary pro-opiomelanocortin (POMC) mRNA, was observed following LPS administration. Similar downregulation of CRFR1 mRNA was not observed in other brain regions following LPS administration (cerebellum, hypothalamus). Our results indicate that V3 and CRFR1 mRNAs are coordinately downregulated in the anterior pituitary during systemic inflammatory stress. Decreased AVP and CRF receptor expression may help regulate the pituitary-adrenal response to stress.

Long-term consequences of social stress on corticosterone and IL-1beta levels in endotoxin-challenged rats

Social stress has strong and long-lasting effects on autonomic nervous, neuroendocrine and behavioural functioning. The functionality of the immune system is profoundly influenced by autonomic nervous and neuroendocrine activities. Changes in sympathetic-adrenal and hypothalamic-pituitary-adrenocortical (HPA) axis activities as observed during and after social defeat, therefore, probably represent an important factor in the modulation of the immune response. In the present study, the impact of social defeat stress on the responsiveness of the immune system was studied by the presentation of a systemic inflammatory challenge through the injection of the bacterial endotoxin lipopolysaccharide (LPS). Male Wistar rats were subjected twice to social defeat 7 days apart. One week after the second defeat, they were injected with LPS in a low (150 microg/kg; D<LPS) or a high dose (375 microg/kg; D>LPS). Another group of defeated rats was injected with saline. Control, nondefeated rats also received the immune challenges. Previously defeated rats responded to the high dose of LPS with a deficient corticosterone (CORT) response resulting in an aggravated interleukin-1beta (IL-1beta) response 4 h after LPS injection. Furthermore, the experiments indicated that mortality rates after LPS administration were high in previously defeated rats, whereas mortality was absent in nondefeated rats. The results indicate that social stress has long-lasting effects on the functioning of the immune system and that it can seriously compromise the effectiveness of the adrenocortical response in containing some immunological defense mechanisms.

The relationship of some negative events and psychological factors to periodontal disease in an adult Swedish population 50 to 80 years of age

BACKGROUND

Clinical observations and epidemiological studies suggest that experiences of negative life events, especially those manifested as depression, may contribute to an increased susceptibility to periodontal disease.

OBJECTIVE

In the present study, the prevalence of some negative life events and psychological factors and their relation to periodontal disease were investigated. The sample consisted of individuals 50-80 years of age from an extensive cross-sectional epidemiological study performed in 1993 in the city of Jönköping, Sweden.

METHOD

298 dentate individuals from the Jönköping study were randomly selected. Clinical and radiographic examinations included registration of the number of existing teeth, plaque index, gingival index, pocket depth, and alveolar bone loss. In addition, a questionnaire about socioeconomic status, life events, and psychological and stress-related factors was used.

RESULTS

The results revealed that, in addition to the well-documented periodontal disease risk factors such as increased age, oral hygiene status, and smoking, the loss of a spouse (being a widow or widower) and the personality trait of exercising extreme external control were also associated with severe periodontal disease.

CONCLUSION

The findings support recent studies suggesting that traumatic life events such as the loss of a spouse may increase the risk for periodontal disease. Above all, the present results indicate that an individual's ability to cope with stressful stimuli (coping behavior), as measured by the beliefs of locus of control of reinforcements may play a role in the progression of periodontal disease.

Physical and inflammatory stressors elevate circadian clock gene mPer1 mRNA levels in the paraventricular nucleus of the mouse

Stress induces secretion of corticosterone through activation of the hypothalamic-pituitary-adrenal axis. This corticosterone secretion is thought to be controlled by a circadian clock in the suprachiasmatic nucleus (SCN). The hypothalamic paraventricular nucleus (PVN) receives convergent information from both stress and the circadian clock. Recent reports demonstrate that mammalian orthologs (Per1, Per2, and Per3) of the Drosophila clock gene Period are expressed in the SCN, PVN, and peripheral tissues. In this experiment, we examined the effect of physical and inflammatory stressors on mPer gene expression in the SCN, PVN, and liver. Forced swimming, immobilization, and lipopolysaccharide injection elevated mPer1 gene expression in the PVN but not in the SCN or liver. A stress-induced increase in mPer1 expression was observed in the corticotropin-releasing factor-positive cells of the PVN; however, the stressors used in this study did not affect mPer2 expression in the PVN, SCN, or liver. The present study suggests that a stress-induced disturbance of circadian corticosterone secretion may be associated with the stress-induced expression of mPer1 mRNA in the PVN.

Reduced adrenal response to bacterial lipopolysaccharide in interleukin-6-deficient mice

Administration of bacterial lipopolysaccharide (LPS) in rodents induces the release of pro-inflammatory cytokines [tumor necrosis factor (TNF), interleukin (IL)-1, IL-6] and of ACTH and corticosterone. IL-6 is probably an important cytokine in the interaction between the immune system and the hypothalamus-pituitary-adrenal (HPA) axis, but so far the role of IL-6 in lipopolysaccharide (LPS)-induced HPA activation has not been established unequivocally. We examined the effects of intraperitoneal administration of LPS (range 0.25-2000 pg/mouse) on plasma corticosterone, TNFalpha and IL-1alpha levels in IL-6-deficient (IL-6 -/-) and wildtype control (IL-6 +/+) mice. Plasma corticosterone levels increased within one hour in both mouse strains. The corticosterone response was significantly reduced in IL-6 -/- mice, but no differences in TNFalpha or in IL-1alpha plasma levels were found between the two strains. Next, we studied the involvement of IL-1alpha or TNFalpha in the responses to LPS in IL-6 -/- and IL-6 +/+ mice by infusion of recombinant human IL-1 receptor antagonist (IL-1ra), or by injection of anti-TNFalpha antibodies. Pretreatment with IL-1ra or with anti-TNFalpha did not affect the corticosterone response to LPS, neither in IL-6 -/-, nor in IL-6 +/+ mice. Our data suggest that in the stimulation of the HPA axis by LPS in mice blockade of either IL-1alpha or TNFalpha may be compensated for by other mediators. The reduced adrenal response after LPS administration found in IL-6 -/- mice indicates a distinct role for IL-6 in the activation of the HPA axis by LPS.

Acute effects of purified and UV-inactivated Herpes simplex virus type 1 on the hypothalamo-pituitary-adrenocortical axis

Herpes simplex virus type 1 (HSV-1) is a common cause of viral encephalitis, manifested by neuroendocrine and behavioral changes. We have previously demonstrated that HSV-1 induces marked hypothalamo-pituitary-adrenocortical (HPA) axis activation. In this study we characterized the acute effects of HSV-1 on the HPA axis occurring before viral replication and appearance of clinical signs of encephalitis. Since in previous studies we used crude virus preparations which may contain immune factors produced by the infected cells, we tested here the effects of purified HSV-1 virions. HSV-1 was propagated on Vero cells and virions were purified by centrifugation in sucrose gradients. Inactivation of viral infectivity was achieved by UV-irradiation, which caused a million-fold decrease in virus titer, as determined by plaque assay. Intracerebroventricular (ICV) inoculation of crude or purified virions induced a dose dependent increase in serum corticosterone and corticotropin (ACTH). This effect was maximal within 3.5 h postinfection and lasted for 72 h. ICV inoculation of UV-inactivated purified virions caused a marked increase in serum corticosterone and ACTH at 3.5 h, but in contrast to the effect of the active virus, the hormone levels gradually decreased at 24 h, and returned to basal levels at 72 h postinfection. HSV-1-induced HPA axis activation at 3.5 h was completely abolished by pretreatment with interleukin-1 receptor antagonist, injected ICV. Adrenalectomized rats failed to respond to ICV inoculation of purified HSV-1 by increase in ACTH. In contrast, these rats responded to ICV injection of LPS.

IN CONCLUSION

(1) HSV-1 can acutely activate the HPA axis before and independently of any viral replication; (2) HSV-1-induced HPA axis activation depends on a permissive action of circulating glucocorticoids and on host derived brain interleukin-1.

Effect of repeated lipopolysaccharide administration on tissue cytokine expression and hypothalamic-pituitary-adrenal axis activity in rats

The effects of chronic immune challenge on cytokine expression and hypothalamic-pituitary-adrenal axis (HPA) axis responses to stress were studied in Wistar rats after administration of increasing doses of lipopolysaccharide (LPS). Repeated LPS (R-LPS) decreased body weight and increased adrenal weight and pituitary pro-opiomelanocortin mRNA levels. LPS injection increased plasma adrenocorticotropic hormone (ACTH) and corticosterone but the effect was attenuated in R-LPS. Plasma corticosterone but not ACTH responses to restraint were also reduced in R-LPS. Basal and restraint-stimulated corticotropin releasing hormone (CRH) mRNA levels were lower in R-LPS, but responses to a new LPS injection were similar to controls. In contrast, type 1 CRH receptor (CRH-R1) mRNA responses to both LPS and restraint were blunted in R-LPS. Vasopressin mRNA levels in parvocellular neurones were higher in R-LPS, and increased further after restraint but not after a new LPS injection. Glucocorticoid receptor (GR) levels in the paraventricular nucleus (PVN) increased after a single LPS or R-LPS (24 h after the last injection) but declined after a new injection in R-LPS. Interleukin (IL)-1beta and IL-6 mRNAs increased in the pituitary, spleen and circumventricular organs after single or R-LPS, suggesting that cytokines may contribute to the activation of the HPA axis though pathways from the circumventricular organs as well as paracrine effects in the pituitary. The data show that (i) adaptation of the HPA axis during repeated LPS injection involves increases in vasopressin : CRH expression ratios in parvocellular neurones; (ii) that hypothalamic CRH and vasopressin responses to acute stimulation are independent of CRH-R1 expression in the PVN; and (iii) there is a dissociation between pituitary and adrenal responses to acute stress suggesting a decrease of adrenal sensitivity to ACTH.

Impaired activation of AP-1 and altered expression of constituent proteins in rat adrenal during ageing

Oxidative stress appears to be one of the primary factors contributing to an age related decline in steroidogenic response in rat adrenocortical and testicular Leydig cells. In this report we concentrate on age-related changes in the DNA binding activity of the transcription factor AP-1 which is particularly responsive to changes in cellular oxidative conditions: adrenal nuclear extracts from young mature (5 months) and old (24 months) rats treated with, and without, lipopolysaccharide (LPS) were studied. AP-1 binding activity, as measured by electrophoretic mobility shift assays (EMSA), was diminished approximately 70% with age in unstimulated adrenals. Following LPS treatment, AP-1 binding activity increased significantly in the adrenals of both young and old animals; however, the level of AP-1 binding achieved in LPS-stimulated old rats was less than that observed for LPS-stimulated young rats. There was no corresponding change in the binding activity of housekeeping transcription factors SP-1 and OCT-1. To further understand these observations, compositional changes in the members of the AP-1 DNA-binding complex were examined by a super-shift assay and Western blot analysis. In adrenals from old rats, a significant decrease in the amount of Fra2 was noted under basal conditions, whereas, substantial decreases in c-Fos, Jun D and c-Jun were observed in response to LPS treatment. In contrast, basal levels of JunB, an inhibitor of the trans-activating function of c-Jun and repressor of AP-1-dependent transcription, were significantly elevated in adrenals from old rats compared to young rats. Together, these findings suggest that ageing-induced oxidative stress may contribute to impaired functional expression of AP-1 by differentially regulating the steady state levels of AP-1 components. The observed decrease in AP-1 binding activity in ageing adrenals is most likely due to decreased expression of the AP-1 activating components (c-Fos, c-Jun, JunD, etc.) and increased expression of JunB, resulting in a switch from transcriptionally active AP-1 complexes observed in young rats to less efficient JunB containing complexes in old rats.