Indomethacin prevents increased catecholamine turnover in rat brain following systemic endotoxin challenge

The effect of lipopolysaccharide (LPS) on inflammatory markers in blood and brain and on behavior in individually-housed pigs

Most of us have experienced deterioration of mood while ill. In humans, immune activation is associated with lethargy and social withdrawal, irritability and aggression; changes in social motivation could, in theory, lead to less functional interactions. This might also be the case for animals housed in close confinement. Tail biting in pigs is an example of damaging social behavior, and sickness is thought to be a risk factor for tail biting outbreaks. One possible mechanism whereby sickness may influence behavior is through cytokines. To identify possible mediators between immune activation and behavioral change, we injected 16 gilts with lipopolysaccharide (LPS; O111:B4; 1.5 μg kg^-1 IV through a permanent catheter). In LPS-treated pigs, a significant increase in cortisol, TNF-α, IL-1 receptor antagonist, IL-6, and IL-8 was observed alongside decreased activity within the first 6 h after the injection. CRP was elevated at 12 and 24 h after injection, and food intake was reduced for the first 24 h after injection. Three days post-injection, LPS pigs had lower levels of noradrenaline in their hypothalamus, hippocampus and frontal cortex compared to saline-injected pigs. Pigs injected with LPS also had higher levels of the pro-inflammatory cytokine IFN-γ in their frontal cortex compared to saline-injected pigs. Thus, a low dose of LPS can induce changes in brain cytokine levels and neurotransmitter levels that persist after inflammatory and stress markers in the periphery have returned to baseline levels.

Individual and interactive sex-specific effects of acute restraint and systemic IFN-γ treatment on neurochemistry

Compelling evidence supports the involvement of the pro-inflammatory cytokines, IL-6, IFN-α and TNF-α in depression and related stress-associated pathologies. A role has also been suggested for the Th1-type cytokine, IFN-γ, with most mechanistic accounts focusing on the cytokine's capacity to induce indoleamine 2,3-dioxygenase (IDO), leading to diminished tryptophan and the generation of kynurenine metabolites. Beyond these IDO-dependent routes, there is surprisingly little evidence directly linking IFN-γ to alterations of brain regional monoamine activity and HPA axis functioning. Our specific aims in the present study were twofold: 1) assess the behavioural, plasma corticosterone and brain regional monoamine effects of acute systemic IFN-γ, with or without short duration restraint stress (15 min), and 2) determine the sex-specific nature of these effects. As predicted, IFN-γ stimulated monoaminergic activity within a number of stressor-sensitive limbic brain regions, most notably the paraventricular nucleus of the hypothalamus, central amygdala and prefrontal cortex. While several of these effects were sex-specific, there was little in the way of synergism between the cytokine and stressor treatments. Nonetheless, IFN-γ did synergistically interact with acute restraint stress to increase plasma corticosterone concentrations, and this effect was most pronounced in the male mice. These data are among the first to show that systemically administered IFN-γ can alone or in conjunction with psychologically relevant stressor, modify brain regional monoamine activity and the plasma corticosterone response.

Prostaglandin F₂α modulates atrial chronotropic hyporesponsiveness to cholinergic stimulation in endotoxemic rats

Endotoxemia induces various physiological adaptive responses such as tachycardia. There is evidence to show that inflammatory tachycardia might be linked to a direct action of prostanoids on the cardiac pacemaker cells. Recent reports have indicated that systemic inflammation may uncouple of cardiac pacemaker from cholinergic neural control in experimental animals; however, the exact mechanism of this phenomenon is uncertain. This study was aimed to explore the hypothesis that prostanoids modulate atrial chronotropic hyporesponsiveness to cholinergic stimulation in endotoxemic rats. Male albino rats were given intraperitoneal injection of either saline or lipopolysaccharide (LPS, 1 mg/kg). 3 h after saline or LPS injection, the atria were isolated and chronotropic responsiveness to cholinergic stimulation was evaluated in an organ bath. The expression of atrial cyclooxygenases (COX)-1, COX-2 and COX-3 mRNA was assessed by quantitative real-time RT-PCR and cytosocalcium-dependent phospholipase A₂ (cPLA₂) activity was measured in the atria. The expression of atrial COX-2 mRNA and cPLA₂ activity increased significantly in endotoxemic atria (P<0.05). Incubation with prostaglandin F₂α (PGF₂α, 100 pM) could significantly decrease chronotropic response to cholinergic stimulation in vitro. Likewise, LPS injection could induce a significant hyporesponsiveness to cholinergic stimulation, and incubation of isolated atria with either indomethacin (5 µM) or AL-8810 (a PGF₂α antagonist, 10 µM) could reverse it (P<0.01, P<0.05, respectively), while SQ29548 (a thromboxane A₂ antagonist, 10 nM) was failed (P>0.05). Our data showed that PGF₂α may contribute to the atrial chronotropic hyporesponsiveness to cholinergic stimulation in endotoxemic rats.

Potential neuroprotective effect of ibuprofen, insights from the mice model of Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is one of the most common neurodegenerative diseases. An inflammatory reaction seems to be involved in the pathological process in PD. Prospective clinical studies with various nonsteroidal anti-inflammatory drugs (NSAIDs) have shown that ibuprofen decreases the risk of PD. In the present study we investigated the influence of ibuprofen on dopaminergic neuron injury in the mice model of PD.

METHODS

Twelve-month-old male C57Bl mice were injected with MPTP together with various doses of ibuprofen (10, 30 or 50 mg/kg), administered 1 h before MPTP injection for 7 consecutive days. Evaluation concerned dopamine content in the striatum, tyrosine hydroxylase (TH) protein and α-synuclein expression measured 7 and 21 days post MPTP administration (dpa).

RESULTS

MPTP caused injury to dopaminergic neuron endings in the striatum: dopamine content decreased by about 0% 7 dpa and by 85% 21 dpa; TH protein expression diminished by 21% 7 dpa; α-synuclein level decreased by 10 and 26% 7 and 21 dpa, respectively. Ibuprofen administration to mice treated with MPTP significantly increased the level of dopamine in the striatum 7 and 21 dpa. It also prevented TH protein decrease and increased α-synuclein level 21 dpa.

CONCLUSIONS

Ibuprofen was shown to protect neurons against MPTP-induced injury in the striatum. The possible mechanism of the neuroprotective effect of ibuprofen might be associated with decreased dopamine turnover and cyclooxygenases inhibition resulting in lower reactive oxygen species formation.

Thromboxane receptor activation enhances striatal dopamine release, leading to suppression of GABAergic transmission and enhanced sugar intake

The extracellular dopamine level is regulated not only by synaptic inputs to dopamine neurons but also by local mechanisms surrounding dopaminergic terminals. However, much remains to be investigated for the latter mechanism. Thromboxane A(2) is one of the cyclooxygenase products derived from arachidonic acid, and acts on its cognate G protein-coupled receptor [thromboxane receptor (TP)]. We show here that TP in the striatum locally facilitates dopamine overflow. Intrastriatal injection of a TP agonist increased extracellular dopamine levels in the striatum as measured by in vivo microdialysis. TP stimulation also augmented electrically evoked dopamine overflow from striatal slices. Conversely, TP deficiency reduced dopamine overflow evoked by N-methyl-d-aspartic acid (NMDA) and acetylcholine in striatal slices. TP immunostaining showed that TP is enriched in vascular endothelial cells. Pharmacological blockade of nitric oxide (NO) synthesis and genetic deletion of endothelial NO synthase (eNOS) suppressed NMDA/acetylcholine-induced dopamine overflow. This involvement of NO was abolished in TP-deficient slices, suggesting a role for eNOS-derived NO synthesis in TP-mediated dopamine overflow. As a functional consequence of TP-mediated dopamine increase, a TP agonist suppressed GABAergic inhibitory postsynaptic currents in medium spiny neurons through a D2-like receptor-dependent mechanism. Finally, TP is involved in sucrose intake, a dopamine-dependent motivational behavior. These data suggest that TP stimulation in the striatum locally facilitates dopamine overflow evoked by synaptic inputs via NO synthesis in endothelial cells.

Mollaret meningitis may be caused by reactivation of latent cerebral toxoplasmosis

Mollaret meningitis (MM) occurs mainly in females and is characterized by recurrent episodes of headache, transient neurological abnormalities, and the cerebrospinal fluid containing mononuclear cells. HSV-2 was usually identified as the causative agent. Recently, we found that recurrent headaches in non-HIV-infected subjects were due to acquired cerebral toxoplasmosis (CT). The aim of the study was therefore to focus on molecular pathomechanisms that may lead to reactivation of latent CT and manifest as MM. Literature data cited in this work were selected to illustrate that various factors may affect latent CNS Toxoplasma gondii infection/inflammation intensity and/or host defense mechanisms, i.e., the production of NO, cytokines, tryptophan degradation by indoleamine 2,3-dioxygenase, mechanisms mediated by an IFN-gamma responsive gene family, limiting the availability of intracellular iron to T. gondii, and production of reactive oxygen/nitrogen species, finally inducing choroid plexitis and/or vasculitis. Examples of triggers revealing MM and accompanying disturbances of IFN-gamma-mediated immune responses that control HSV-2 and T. gondii include: female predominance (female mice are more susceptible to T. gondii infection than males); HSV-2 infection (increased IFN-gamma, IL-12); metaraminol (increased plasma catecholamine levels, changes in cytokine expression favoring T(H)2 cells responses); probably cholesterol contained in debris from ruptured epidermoid cysts (decreased NO; increased TNF-alpha, IL-6, IL-8). These irregularities induced by the triggers may be responsible for reactivation of latent CT and development of MM. Thus, subjects with MM should have test(s) for T. gondii infection performed obligatorily.

Preoptic nitric oxide attenuates endotoxic fever in guinea pigs by inhibiting the POA release of norepinephrine

Lipopolysaccharide (LPS) administration induces hypothalamic nitric oxide (NO); NO is antipyretic in the preoptic area (POA), but its mechanism of action is uncertain. LPS also stimulates the release of preoptic norepinephrine (NE), which mediates fever onset. Because NE upregulates NO synthases and NO induces cyclooxygenase (COX)-2-dependent PGE2, we investigated whether NO mediates the production of this central fever mediator. Conscious guinea pigs with intra-POA microdialysis probes received LPS intravenously (2 μg/kg) and, thereafter, an NO donor (SIN-1) or scavenger (carboxy-PTIO) intra-POA (20 μg/μl each, 2 μl/min, 6 h). Core temperature (Tc) was monitored constantly; dialysate NE and PGE2 were analyzed in 30-min collections. To verify the reported involvement of α2-adrenoceptors (AR) in PGE2 production, clonidine (α2-AR agonist, 2 μg/μl) was microdialyzed with and without SIN-1 or carboxy-PTIO. To assess the possible involvement of oxidative NE and/or NO products in the demonstrated initially COX-2-independent POA PGE2 increase, (+)-catechin (an antioxidant, 3 μg/μl) was microdialyzed, and POA PGE2, and Tc were determined. SIN-1 and carboxy-PTIO reduced and enhanced, respectively, the rises in NE, PGE2, and Tc produced by intravenous LPS. Similarly, they prevented and increased, respectively, the delayed elevations of PGE2 and Tc induced by intra-POA clonidine. (+)-Catechin prevented the LPS-induced elevation of PGE2, but not of Tc. We conclude that the antipyretic activity of NO derives from its inhibitory modulation of the LPS-induced release of POA NE. These data also implicate free radicals in POA PGE2 production and raise questions about its role as a central LPS fever mediator.

Effects of cytokines and infections on brain neurochemistry

Administration of cytokines to animals can elicit many effects on the brain, particularly neuroendocrine and behavioral effects. Cytokine administration also alters neurotransmission, which may underlie these effects. The most well studied effect is the activation of the hypothalamo-pituitary-adrenocortical (HPA) axis, especially that by interleukin-1 (IL-1). Peripheral and central administration of IL-1 also induces norepinephrine (NE) release in the brain, most markedly in the hypothalamus. Small changes in brain dopamine (DA) are occasionally observed, but these effects are not regionally selective. IL-1 also increases brain concentrations of tryptophan, and the metabolism of serotonin (5-HT) throughout the brain in a regionally nonselective manner. Increases of tryptophan and 5-HT, but not NE, are also elicited by IL-6, which also activates the HPA axis, although it is much less potent in these respects than IL-1. IL-2 has modest effects on DA, NE and 5-HT. Like IL-6, tumor necrosis factor-α (TNFα) activates the HPA axis, but affects NE and tryptophan only at high doses. The interferons (IFN's) induce fever and HPA axis activation in man, but such effects are weak or absent in rodents. The reported effects of IFN's on brain catecholamines and serotonin have been very varied. However, interferon-γ, and to a lesser extent, interferon-α, have profound effects on the catabolism of tryptophan, effectively reducing its concentration in plasma, and may thus limit brain 5-HT synthesis.Administration of endotoxin (LPS) elicits responses similar to those of IL-1. Bacterial and viral infections induce HPA activation, and also increase brain NE and 5-HT metabolism and brain tryptophan. Typically, there is also behavioral depression. These effects are strikingly similar to those of IL-1, suggesting that IL-1 secretion, which accompanies many infections, may mediate these responses. Studies with IL-1 antagonists, support this possibility, although in most cases the antagonism is incomplete, suggesting the existence of multiple mechanisms. Because LPS is known to stimulate the secretion of IL-1, IL-6 and TNFα, it seems likely that these cytokines mediate at least some of the responses, but studies with antagonists indicate that there are multiple mechanisms. The neurochemical responses to cytokines are likely to underlie the endocrine and behavioral responses. The NE response to IL-1 appears to be instrumental in the HPA activation, but other mechanisms exist. Neither the noradrenergic nor the serotonergic systems appear to be involved in the major behavioral responses. The significance of the serotonin response is unknown.

Ascending brainstem pathways are not involved in lipopolysaccharide-induced suppression of thyrotropin-releasing hormone gene expression in the hypothalamic paraventricular nucleus

The nonthyroidal illness syndrome associated with fasting, infection, and chronic illness is characterized by low thyroid hormone levels and low or inappropriately normal TSH levels in circulating blood and reduced synthesis of TRH in hypophysiotropic neurons residing in the hypothalamic paraventricular nucleus (PVN). To test the hypothesis that ascending brainstem pathways are involved in mediation of bacterial lipopolysaccharide (LPS)-induced suppression of TRH mRNA in the PVN, we unilaterally transected brainstem pathways to the PVN and determined the effects of LPS on TRH gene expression and, as a control, on CRH gene expression in hypophysiotropic neurons using semiquantitative in situ hybridization histochemistry. The efficacy of the transection was determined by immunocytochemical detection of ascending adrenergic pathways in the PVN. In vehicle-treated animals, CRH mRNA in the PVN showed a significant reduction on the transected side compared with the intact side, whereas a significant increase in TRH mRNA was observed on the transected side compared with the intact side. After LPS administration (250 microg/100 g body weight), a dramatic increase in CRH mRNA was observed on the intact side, and a significantly lesser increase was found on the transected side. In contrast, LPS treatment resulted in reduction in TRH mRNA on the transected side compared with the intact side and a significant reduction in TRH mRNA on the transected side compared with vehicle-treated animals. These studies confirm an important role of ascending brainstem projections in LPS-induced activation of CRH gene expression, but indicate that they do not mediate the effect of LPS to inhibit hypophysiotropic TRH gene expression.

Dietary n-3 fatty acids selectively attenuate LPS-induced behavioral depression in mice

Systemic administration of bacterial lipopolysaccharide (LPS) induces a series of physiological and pathological alterations as well as behavioral depression in experimental animals. These alterations induced by LPS administration are known to be mediated by endogenous cytokines and arachidonate metabolites, which may be modulated by dietary n-3 fatty acids. Mice were fed a diet supplemented with n-3 or n-6 fatty acids for 4 weeks prior to LPS administration. Food-motivated behavior after intraperitoneal administration of LPS as compared with that before LPS administration was significantly depressed in the mice fed with the n-6 fatty-acid-rich diet (47% to 85% reduction; P<.05) but not significantly in the mice fed with the n-3 fatty-acid-rich diet. Depression of social exploration by intraperitoneal LPS administration in the n-3 fatty-acid-rich diet group (39% reduction vs. vehicle group) was significantly less in the n-6 fatty-acid-rich diet group (76% reduction vs. vehicle group; P<.05). The behavioral depressions induced by intracerebroventricular LPS injection were not significantly different between the two dietary groups (P=.60). The elevation of serum corticosterone and the hypoglycemic response following intraperitoneal LPS administration were not significantly different between the two dietary groups (P=.57 and P=.43, respectively). We demonstrate that dietary n-3 fatty acids attenuate behavioral depression in mice peripherally administered with LPS without affecting the increase in serum corticosterone and the decrease in serum glucose concentration.

Effects of endotoxin and tumor necrosis factor alpha on regional brain neurotransmitters in mice

Alterations in regional brain concentration of dopamine (DA), norepinephrine (NE), serotonin (5-HT) and their metabolites were investigated in male BALB/c mice injected intraperitoneally with bacterial lipopolysaccharide (LPS, 2 mg kg(-1)) or recombinant murine tumor necrosis factor alpha (TNFalpha, 0.1 mg kg(-1)) at 2, 6, 12 and 24 h after the injection. At 2 h post-injection the LPS administration resulted in hypothermia, which was not apparent at later time points. No consistent effects were observed by either LPS or TNFalpha on peripheral leukocyte counts or plasma transaminase levels. Both LPS and TNFalpha slightly elevated NE metabolism in the striatum at 2-12 h. Concentrations of DA and its metabolites were significantly elevated only in the hypothalamus following TNFalpha at 24 h. Tumor necrosis factor alpha exerted pronounced effects on 5-HT metabolism in most brain regions at 2 h. Results suggest that the effect of LPS is more complex compared with TNFalpha because of the endogenous production of other cytokines including the TNFalpha.

Estradiol-stimulated nitric oxide release in human granulocytes is dependent on intracellular calcium transients: evidence of a cell surface estrogen receptor

We tested the hypothesis that estrogen acutely stimulates constitutive nitric oxide synthase activity in human granulocytes by acting on a cell surface estrogen receptor (ER). The release of nitric oxide was measured in real time with an amperometric probe. Exposure of granulocytes to 17β-estradiol stimulated NO release within seconds in a concentration-dependent manner. The NO release was also stimulated by 17β-estradiol conjugated to bovine serum albumin (E2-BSA), which suggests mediation by a cell surface receptor. Tamoxifen, an ER inhibitor, antagonized the action of both 17β-estradiol and E2-BSA, whereas ICI 182,780, an inhibitor of the nuclear ER, had no effect. Using dual emission microfluorometry in a calcium-free medium, the 17β-estradiol–stimulated release of NO from granulocytes was shown to be dependent on intracellular calcium ([Ca2+]i) transients in a tamoxifen-sensitive process. Exposure to BAPTA-AM (1,2bis-(-aminophenoxy)ethans-N,N,N′,N′-tetraacetic acid tetra(acetoxyymethyl) ester), a [Ca2+]i chelator, reduced [Ca2+]i in response to E2-BSA, and depleting [Ca2+]i stores abolished the effect of 17β-estradiol on NO release. Confocal photomicrographs using E2-BSA–FITC (fluorescein isothiocyanate) revealed cell membrane reactivity. Estrogen-stimulated NO release had an immunosuppressive effect, and it initiated granulocyte rounding and loss of adherence in a tamoxifen-sensitive manner. Finally, using reverse transcriptase–polymerase chain reaction, human neutrophil granulocytes expressed ER but not ERβ, suggesting that ER may be the membrane receptor for 17β-estradiol. The study demonstrated that a physiological dose of estrogen down-regulates granulocyte activity by acutely stimulating NO release via the activation of a cell surface ER which is coupled to increases in [Ca2+]i.

Estradiol-stimulated nitric oxide release in human granulocytes is dependent on intracellular calcium transients: evidence of a cell surface estrogen receptor

We tested the hypothesis that estrogen acutely stimulates constitutive nitric oxide synthase activity in human granulocytes by acting on a cell surface estrogen receptor (ER). The release of nitric oxide was measured in real time with an amperometric probe. Exposure of granulocytes to 17β-estradiol stimulated NO release within seconds in a concentration-dependent manner. The NO release was also stimulated by 17β-estradiol conjugated to bovine serum albumin (E2-BSA), which suggests mediation by a cell surface receptor. Tamoxifen, an ER inhibitor, antagonized the action of both 17β-estradiol and E2-BSA, whereas ICI 182,780, an inhibitor of the nuclear ER, had no effect. Using dual emission microfluorometry in a calcium-free medium, the 17β-estradiol–stimulated release of NO from granulocytes was shown to be dependent on intracellular calcium ([Ca2+]i) transients in a tamoxifen-sensitive process. Exposure to BAPTA-AM (1,2bis-(-aminophenoxy)ethans-N,N,N′,N′-tetraacetic acid tetra(acetoxyymethyl) ester), a [Ca2+]i chelator, reduced [Ca2+]i in response to E2-BSA, and depleting [Ca2+]i stores abolished the effect of 17β-estradiol on NO release. Confocal photomicrographs using E2-BSA–FITC (fluorescein isothiocyanate) revealed cell membrane reactivity. Estrogen-stimulated NO release had an immunosuppressive effect, and it initiated granulocyte rounding and loss of adherence in a tamoxifen-sensitive manner. Finally, using reverse transcriptase–polymerase chain reaction, human neutrophil granulocytes expressed ER but not ERβ, suggesting that ER may be the membrane receptor for 17β-estradiol. The study demonstrated that a physiological dose of estrogen down-regulates granulocyte activity by acutely stimulating NO release via the activation of a cell surface ER which is coupled to increases in [Ca2+]i.

Basal nitric oxide limits immune, nervous and cardiovascular excitation: human endothelia express a mu opiate receptor

Nitric oxide (NO) is a major signaling molecule in the immune, cardiovascular and nervous systems. The synthesizing enzyme, nitric oxide synthase (NOS) occurs in three forms: endothelial (e), neuronal (n) and inducible (i) NOS. The first two are constitutively expressed. We surmise that in many tissues there is a basal level of NO and that the actions of several signaling molecules initiate increases in cNOS-derived NO to enhance momentary basal levels that exerts inhibitory cellular actions, via cellular conformational changes. It is our contention that much of the literature concerning the actions of NO really deal with i-NOS-derived NO. We make the case that cNOS is responsible for a basal or 'tonal' level of NO; that this NO keeps particular types of cells in a state of inhibition and that activation of these cells occurs through disinhibition. Furthermore, naturally occurring signaling molecules such as morphine, anandamide, interleukin-10 and 17-beta-estradiol appear to exert, in part, their beneficial physiological actions, i.e., immune and endothelial down regulation by the stimulation of cNOS. In regard to opiates, we demonstrate the presence of a human endothelial mu opiate receptor by RT-PCR and sequence determination, further substantiating the role of opiates in vascular coupling to NO release. Taken together, cNOS derived NO enhances basal NO actions, i.e., cellular activation state, and these actions are further enhanced by iNOS derived NO.

Lack of evidence for a role of serotonin in interleukin-1-induced hypophagia

Interleukin-1 (IL-1) administration depresses food intake in rodents. IL-1 is known to increase the metabolism of serotonin, which is known to affect feeding behavior. Thus, serotonin is an obvious candidate for a mediator of the hypophagic response to IL-1. Therefore, we tested the ability of serotonergic agonists and antagonists to alter the hypophagic responses to IL-1 and bacterial lipopolysaccharide (LPS). Hypophagia was assessed in ad lib-fed mice by recording the intake of sweetened milk in a 30-min period. Acute intraperitoneal administration of mouse IL-1beta reliably decreased milk intake. This hypophagic response was not affected by any of the serotonin antagonists tested, including 5-HT(1A) (WAY100135 and propranolol), 5-HT(1B) (GR127935), 5-HT(2) (ritanserin, ketanserin, SB206553, and RS102221), mixed 5-HT(1/2) (methysergide and metergoline), and 5-HT(3) (tropisetron) receptor antagonists. The 5-HT(1A) agonists (8-OH-DPAT and ipsapirone) and a 5-HT(1B) agonist (CGS12066B) known to decrease the activity of serotonergic neurons, also had no effect. Mice pretreated with 5,7-dihydroxytryptamine to deplete brain serotonin ate less, but, nevertheless, displayed similar hypophagic responses to mIL-1beta or LPS. The results suggest that serotonin is not involved in the decrease in short-term milk intake induced by mIL-1beta or LPS in mice that have been fed ad lib.

Molecular mechanisms of actions of interleukin-6 on the brain, with special reference to serotonin and the hypothalamo-pituitary-adrenocortical axis

Biological activities of the multifunctional cytokine, interleukin-6 (IL-6) include stimulation of B cell proliferation, immunoglobulin production, and initiation of the acute-phase response. IL-6 affects the CNS in that it activates the hypothalamo-pituitary-adrenocortical (HPA) axis and increases brain tryptophan and serotonin metabolism. IL-6 has been proposed as an important mediator of interaction between the neuroendocrine and immune systems. The peripheral and central effects of IL-6 are presumably mediated through its membrane receptor (IL-6R). IL-6, IL-6R and their respective mRNAs have been detected in several brain regions. Although the functions of cytokines overlap considerably, each displays its own characteristic properties. Expression of IL-6 in the brain has been observed in several CNS disorders, some of which have been associated with disorders of serotonin metabolism. It is proposed that interactions between IL-6 and brain serotonin is a complex process which involves corticotropin-releasing factor (CRF) and opioid peptides. It is likely that the molecular mechanisms underlying the actions of IL-6 on the HPA axis and its other brain functions involve the integrated effects of glutamate, Ca2+, 3',5'-cyclic AMP, protein kinase C, and other metabolic pathways.

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.

Variations of nucleus accumbens dopamine and serotonin following systemic interleukin-1, interleukin-2 or interleukin-6 treatment

The effects of systemically administered interleukin-1beta (1.0 microg), interleukin-6 (1.0 microg) and interleukin-2 (1.0 microg) on in vivo variations of monoamines were assessed in the nucleus accumbens. Administration of interleukin-1beta did not affect extracellular accumbal dopamine, provoked a modest rise of homovanillic acid, and prevented the decline of dihydroxyphenylacetic acid ordinarily seen in saline treated rats. Also, interleukin-1 provoked a modest increase of extracellular 5-hydroxyindoleacetic acid from the nucleus accumbens. Following exposure to the stress of a series of air-puffs, a still greater increase of accumbal 5-hydroxyindoleacetic acid was evident. In contrast to interleukin-1, systemic administration of interleukin-6 and interleukin-2 both induced marked reductions of interstitial dopamine levels. The air-puff exposure further enhanced these effects in rats that had received the cytokine treatment. As well, interleukin-6 and interleukin-2 were both found to reduce the homovanillic acid response associated with the stress, and interleukin-2 promoted a decline of homovanillic acid levels. Treatment with interleukin-6, like that of interleukin-1, prevented the decline of dihydroxyphenylacetic acid ordinarily observed over time, while interleukin-2 was without effect in this respect. Finally, interleukin-6 provoked a modest rise of 5-hydroxyindoleacetic acid, which was most apparent following air-puff exposure, while administration of interleukin-2 did not affect accumbal 5-hydroxyindoleacetic acid. It is suggested that the cytokines may influence the release of biogenic amines in the nucleus accumbens, but the profile of changes were cytokine-specific. As well, it appeared that the cytokines, particularly interleukin-1 and interleukin-6, may act synergistically with the stressor in promoting the amine variations. Systemic administration of cytokines clearly influenced monoamine activity at the nucleus accumbens, a region associated with both rewarding and aversive events. Thus, it may be expected that cytokine treatments may affect behavior. Moreover, it seems that the effects of interleukin-1 and interleukin-6 may be influenced by the presence of stressful stimuli. It ought to be underscored that although cytokines share features with the effects of stressors, most notably the variations of hypothalamic-pituitary-adrenal hormones, the pattern of central neurochemical changes elicited by the cytokines could be distinguished from the amine variations ordinarily associated with stressors.

Behavioral and neurochemical consequences of lipopolysaccharide in mice: anxiogenic-like effects

Systemic administration of lipopolysaccharide (LPS) induces sickness behaviors, as well as alterations of hypothalamic-pituitary-adrenal functioning commonly associated with stressors. In the present investigation, it was demonstrated that systemic LPS treatment induced a sickness-like behavioral profile (reduced active behaviors, soporific effects, piloerection, ptosis), which appeared to be dependent upon the novelty of the environmental context in which animals were tested. As well, LPS induced anxiogenic-like responses, including decreased time spent in the illuminated portion of a light-dark box, reduced open-arm entries in a plus-maze test, and decreased contact with a novel stimulus object in an open-field situation. The behavioral changes were accompanied by increased plasma ACTH and corticosterone levels. As well, LPS induced increased turnover of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) in the paraventricular nucleus (PVN), median eminence plus arcuate nucleus, hippocampus, as well as NE turnover within the locus coeruleus and DA turnover within the nucleus accumbens. Although these neurochemical variations were reminiscent of those elicited by stressors, LPS was not particularly effective in modifying DA activity within the prefrontal cortex or NE within the amygdala, variations readily induced by stressors. Whether the LPS-induced anxiogenic-like responses were secondary to the illness engendered by the endotoxin remains to be determined. Nevertheless, it ought to be considered that bacterial endotoxin challenge, and the ensuing cytokine changes, may contribute to emotionality and perhaps even anxiety-related behavioral disturbances.

Platelet and brain alpha 2-adrenoceptors and cardiovascular sensitivity to agonists in dogs suffering from endotoxic shock

We examined the changes in alpha 2-adrenoceptor binding on platelet and brain membranes of dogs treated with a non-lethal dose of endotoxin (0.1 mg/kg intravenously), and the alpha 2-adrenoceptor mediated cardiovascular effects during endotoxin shock. At 2 h, 24 h, and 7 days after endotoxin administration, the number of binding sites (Bmax) of [3H]yohimbine binding decreased and equilibrium dissociation constants (Kd) increased in platelets, whereas both Bmax and Kd decreased in either cerebral cortex or medulla oblongata. After 30 days of endotoxin administration, there were no significant differences in Bmax or Kd between the treated and untreated animals in both platelets and brain tissues. Significant positive correlations were observed for Bmax values between platelets and brain tissues, although negative correlations for Kd values between platelets and brain were not significant. Significant negative correlations were also observed between plasma catecholamine concentrations and platelet alpha 2-adrenoceptor number, and between plasma noradrenaline and medulla alpha 2-adrenoceptor number. Pretreatment with E coli endotoxin diminished cardiovascular effects such as bradycardia, hypotension, and increase in systemic vascular resistance induced by either i.v. clonidine or xylazine. This suggests that alpha 2-adrenoceptor activity is impaired in the central nervous system as well as in the peripheral vascular system during endotoxin shock. Therefore, platelets may in part represent a good model which reflects the alpha 2-adrenoceptor changes in the central nervous system and peripheral vascular system during and after endotoxin shock.

Depression, stress and immunological activation: the role of cytokines in depressive disorders

Traditionally, both stress and depression have been associated with impaired immune function and increased susceptibility to infectious and neoplastic disease. However over the last number of years a large body of evidence suggests that major depression is associated with signs of immunological activation. Moreover it has been suggested that cytokine hypersecretion may be involved in the aetiology of depressive disorders. The present article reviews the evidence from both clinical and experimental studies which implicates immunological activation and particularly hypersecretion of cytokines in the onset and maintenance of depressive illness. Both clinical and experimental studies indicate that stress and depression are associated with increased circulating concentrations of cytokines such as IL-1beta, IL-6 and gamma-IFN and positive acute phase proteins, and hyperactivity of the HPA-axis. In addition, it has been reported that immunological activation induces "stress-like" behavioural and neurochemical changes in laboratory animals. Although for many years it has been suggested that stress acts a predisposing factor to depressive illness, the precise mechanisms by which stress-induced depressive symptoms occur are not fully understood. Nevertheless, behavioural changes due to stress have often been explained in terms of changes in neurotransmitter function in the brain. In the present article increased cytokine secretion is implicated as a mechanism whereby stress can induce depression.

Differential effects of interleukin (IL)-1beta, IL-2 and IL-6 on responding for rewarding lateral hypothalamic stimulation

Bacterial endotoxin and interleukin-1 (IL-1) challenge induce a constellation of symptoms associated with illness. While such treatment may result in anhedonia, it is often difficult to dissociate this effect from the anorexia induced by these agents, particularly in paradigms that involve appetitive motivation. The present investigation assessed the effects of several systemically administered cytokines (IL-1beta, IL-2 and IL-6) on reward processes by evaluating responding for rewarding intracranial self-stimulation (ICSS) from the lateral hypothalamus. Systemic administration of interleukin-2 (IL-2) disrupted responding from the medial forebrain bundle, and this disturbance persisted as long as 1 week following initial cytokine treatment. In contrast to reinforced responding, following IL-2 treatment, non-reinforced behavior was unaffected, indicating that the cytokine did not provoke reward-unrelated performance deficits. It was suggested that the effects of IL-2 on ICSS likely do not involve motoric, soporific, attentional or cognitive changes, but instead involve specific actions on motivational arousal. Although IL-6 was previously found to produce mesolimbic dopamine (DA) changes as marked as those induced by IL-2, systemic IL-6 treatment did not influence responding for rewarding brain stimulation. Likewise, although IL-1 at the dosage used reliably induces sickness behavior, responding for rewarding brain stimulation was unaffected. Thus it seems that anhedonia is not necessarily a component of the sickness response associated with IL-1 treatment.

Effects of interleukin-1beta and mild stress on alterations of norepinephrine, dopamine and serotonin neurotransmission: a regional microdialysis study

The effects of systemically administered interleukin-1beta (1.0 microg) on in vivo variations of monoamines was assessed in several brain regions. Administration of the cytokine provoked a modest increase of extracellular 5-HIAA and HVA from the nucleus accumbens, and 5-HIAA from the hippocampus. Following mild neurogenic stressor (application of a series of air puffs), a still greater increase of accumbal 5-HIAA and HVA was evident, a transient increase of hippocampal 5-HT was noted and the 5-HIAA increases were augmented. Additionally, while the air puff stress was without effect on DOPAC and HVA in the prefrontal cortex of saline treated rats, a significant rise of these metabolites was apparent in rats treated with the cytokine. It appears that interleukin-1 administration may have effects on forebrain monoamines, and also results in greater neuronal reactivity to mild neurogenic stressors. This study reveals that although effects of neurogenic stressors (air puffs) and cytokine (somatic stressor) may share some similarities (e.g., HPA activation), the pattern of central neurochemical changes elicited by the cytokine could be distinguished from that induced by a more neurogenic stressor (air puffs), and that these effects showed selective synergism. These data also lend support to the contention that neurogenic stressors may have a much greater impact on central neurotransmission under conditions of immune activation.

Interleukin-2 decreases accumbal dopamine efflux and responding for rewarding lateral hypothalamic stimulation

Systemic administration of interleukin-2 (IL-2) provoked marked alterations of responding for rewarding brain stimulation from the medial forebrain bundle (MFB). In particular, when animals were tested for ICSS immediately following IL-2 treatment only a modest disturbance of responding was evident. However, if animals were subsequently exposed to repeated daily ICSS sessions (24-168 h) in the drug-free state, rightward shifts in the rate intensity functions and significant increases in reward thresholds were apparent. These results were dependent upon the presence of IL-2 during the initial ICSS session. If animals were tested for ICSS 24 h after IL-2 administration, without an intervening test, performance was unaffected. Evaluation of nonreinforced behavior after IL-2 treatment revealed that ICSS remained under stimulus control and the cytokine did not provoke reward-unrelated performance deficits. Dopamine (DA) activity in the nucleus accumbens has been implicated in goal-directed responding to positively reinforcing stimuli and in the present investigation, using in vivo microdialysis, it was observed that IL-2 markedly reduced DA release from this region. It was suggested that the protracted consequences of IL-2 on ICSS likely do not involve motoric, soporific, attentional or cognitive changes, but may be attributable to its specific actions on motivational arousal, possibly engendered by the cytokine-induced diminution of accumbal DA efflux.

Endotoxin produces a depressive-like episode in rats

Activation of the immune system produces psychological and physiological effects, which resemble the characteristics of depression. The present study was designed to investigate further, in rats, the similarity between the behavioral effects of immune activation and a model of depression in animals. Reduction in the preference for and consumption of saccharin solutions and suppression of sexual behavior were used as models of one essential feature of depression, the inability to experience pleasure (anhedonia). Other measures testing this model were the reduction in food consumption, body weight, locomotor activity, and social interaction. It was found that systemic injection of lipopolysaccharide (endotoxin), which is a potent activator of the immune system, significantly decreased saccharin preference in fluid-deprived rats. Lipopolysaccharide (LPS) also decreased free consumption of saccharin, but not water, in non-deprived rats. Several indices of male sexual behavior were significantly suppressed following LPS administration. Chronic, but not acute, treatment with the tricyclic antidepressant imipramine abolished the suppressive effect of LPS on saccharin preference. Moreover, chronic, but not acute, treatment with imipramine also reduced and facilitated the recovery from the suppressive effects of LPS on food consumption, body weight, social interaction and activity in the open-field test. The results suggest that activation of the immune system in rats produces anhedonia and other depressive-like symptoms, which can be attenuated or completely blocked by chronic treatment with an antidepressant drug.

Endotoxin administration stimulates cerebral catecholamine release in freely moving rats as assessed by microdialysis

In vivo microdialysis was used to measure changes in extracellular concentrations of catecholamines and indolamines in freely moving rats in response to administration of endotoxin (lipopolysaccharide, LPS). Dialysis probes were placed stereotaxically in either the medial hypothalamus or the medial prefrontal cortex. We used a repeated-measures design in which each rat received LPS or saline, and each subject was retested with the other treatment one week later. With the dialysis probes in the medial hypothalamus, intraperitoneal (ip) administration of LPS (5 micrograms) increased dialysate concentrations of norepinephrine (NE, 187%), dopamine (DA, 119%), and all their measured catabolites, except normetanephrine. Dialysate concentrations of NE and DA were elevated significantly in the fourth or fifth (20 min) collection period with a peak response at around 2 hr. They returned to baseline by about 4 hr. When the dialysis probes were placed in the medial prefrontal cortex, the same dose of LPS also elevated dialysate concentrations of NE and DA, but the increases were much smaller (ca. 20%). However, a dose of 100 micrograms LPS increased dialysate concentrations of NE and DA from the medial prefrontal cortex to an extent comparable to that of the 5 micrograms dose in the hypothalamus, and the response was more prolonged. Dialysate concentrations of serotonin could not be measured reliably, but those of its catabolite, 5-hydroxyindoleacetic acid (5-HIAA), were also elevated in both regions. The peak of 5-HIAA occurred at around 4 hr. Pretreatment of the rats with indomethacin (10 mg/kg ip) completely prevented the changes due to 100 micrograms LPS in the medial prefrontal cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of interleukin-1 in stress responses. A putative neurotransmitter

Recently, the central roles of interleukin-1 (IL-1) in physical stress responses have been attracting attention. Stress responses have been characterized as central neurohormonal changes, as well as behavioral and physiological changes. Administration of IL-1 has been shown to induce effects comparable to stress-induced changes. IL-1 acts on the brain, especially the hypothalamus, to enhance release of monoamines, such as norepinephrine, dopamine, and serotonin, as well as secretion of corticotropin-releasing hormone (CRH). IL-1-induced activation of the hypothalamo-pituitary-adrenal (HPA) axis in vivo depends on secretion of CRH, an intact pituitary, and the ventral noradrenergic bundle that innervates the CRH-containing neurons in the paraventricular nucleus of the hypothalamus. Recent studies have shown that IL-1 is present within neurons in the brain, suggesting that IL-1 functions in neuronal transmission. We showed that IL-1 in the brain is involved in the stress response, and that stress-induced activation of monoamine release and the HPA axis were inhibited by IL-1 receptor antagonist (IL-1Ra) administration directly into the rat hypothalamus. IL-1Ra has been known to exert a blocking effect on IL-1 by competitively inhibiting the binding of IL-1 to IL-1 receptors. In the latter part of this review, we will attempt to describe the relationship between central nervous system diseases, including psychological disorders, and the functions of IL-1 as a putative neurotransmitter.

Alterations in central catecholamines associated with immune responding in adult and aged mice

Central catecholamine alterations associated with immune activity are similar to those seen following stressor exposure. Inasmuch as aged animals exhibit more pronounced stressor-provoked alterations of central amines relative to younger animals, it was of interest to determine whether immune challenge would similarly induce more pronounced central amine variations in older animals. Fifteen-month old CD-1 mice challenged with 10(7) sheep red blood cells (SRBC) revealed an equivalent peak splenic plaque-forming cell response (4 days after antigen challenge) to that of 3-month-old mice challenged with 10(6) cells. Neither plasma adrenocorticotropic hormone (ACTH) nor corticosterone levels varied over days following immunization, although ACTH levels were generally higher in the older mice. In both age groups reductions of hypothalamic and locus coeruleus norepinephrine (NE) and increased accumulation of the metabolite MHPG coincided with (or preceded by 24 h) the peak immune response. However, increased accumulation of MHPG in the hypothalamus was greater and occurred earlier in the locus coeruleus of the aged mice. Likewise, at or about the time of peak immune responses nucleus accumbens dopamine (DA) levels were reduced and metabolites elevated in both age groups, while in the prefrontal cortex only DA metabolite levels were elevated. These data are commensurate with previous findings showing that SRBC inoculation may influence central neurotransmitters and that such effects correspond with the time of the peak immune responses. Moreover, in so far as hypothalamic NE utilization is concerned, it seems that the effects of SRBC inoculation are more pronounced in aged animals.

Time-dependent in vivo mesolimbic dopamine variations following antigenic challenge

Administration of sheep red blood cells (SRBC: 5 x 10(6)) to rats provoked an immune response which peaked 4 days following inoculation. Immune activation elicited an increase of in vivo extracellular dopamine (DA) in the nucleus accumbens, indicating increased release of DA from neurons. The DA alterations coincided with the time of the peak immune response, being significantly altered 4 days after inoculation, and declining to control levels thereafter. In contrast, the levels of serotonin metabolite, 5-hydroxyindoleacetic acid (5HIAA), were not affected by SRBC inoculation. These data are consistent with the supposition that antigenic challenge influences central neurotransmitters, and indicates that such effects are not restricted to the hypothalamus, but are apparent in mesolimbic regions. It is suggested that the antigenic challenge leads to effects comparable to those induced by stressors. As such, it might be expected that immune activation may come to produce behavioral alterations much like those engendered by stressors.

Eicosanoids and essential fatty acid modulation in chronic disease and the chronic fatigue syndrome

Abnormalities of Essential Fatty Acid (EFA) incorporation into phospholipid are found in chronic diseases. More recently changes in circulating EFA metabolites (EFAM) together with EFAM hypo-responsiveness of immune cells and EFAM production from cells have been found associated with disease. We hypothesize that changes in ratio of EFAMs are the normal physiological responses to stressors, but when stressors are excessive or prolonged, EFAM systems may become unpredictably hypo-responsive owing to factors such as receptor down regulation and substrate depletion. In time, many homeostatic system become deranged and held in that state by minor stressors. Literature review of chronic fatigue syndrome (CFS) shows hyper and hypo-responsiveness in immune function, several Hypothalamo-Pituitary (HP) axes and sympathetic nervous system, all relatable to dysfunctional changes in EFA metabolism. For the first time, we explain chronic immune system activation and hypo-responsive immune function in CFS; through EFAMs. Dietary EFA modulation (DEFA) can alter ratios of both membrane EFAs and produced EFAMs, and if maintained can restore hypo-responsive function. We discuss dietary strategies and relevance in CFS, and a case series of CFS patients applying DEFA with other titrated published managements which saw 90% gaining improvement within 3 months and more than 2/3 fit for full time duties. This hypothesis and DEFA may have relevance in other chronic conditions.

Neurochemical and neuroendocrine responses to Newcastle disease virus administration in mice

Mice injected intraperitoneally with Newcastle disease virus (NDV) responded with increased plasma concentrations of ACTH and corticosterone and increased hypothalamic concentrations of the tryptophan and of the norepinephrine catabolite, 3-methoxy,4-hydroxyphenylethyleneglycol (MHPG) and the serotonin catabolite, 5-hydroxyindoleacetic acid (5-HIAA). Two different strains of NDV, a lentogenic and a mesogenic one, elicited dose-dependent effects in these responses. Both strains elicited near maximal responses at doses around 1000 hemagglutination units. The maximal effects on ACTH, corticosterone and MHPG occurred around 2 h, but the effects on tryptophan and 5-HIAA were greatest at 8 h. Similar responses in plasma corticosterone, and cerebral tryptophan and 5-HIAA were observed following i.p. injection of polyinosinic-polycytidylic acid, but MHPG was not altered. The cyclo-oxygenase inhibitor, indomethacin, had little effect on the NDV-induced increases in plasma corticosterone and ACTH, and hypothalamic indolamines, but essentially ablated the MHPG response. The effect of NDV on plasma corticosterone, like that of endotoxin (LPS), was prevented by hypophysectomy, suggesting that the pituitary was required for these responses. These endocrine and neurochemical responses to NDV resemble those to interleukin-1 (IL-1) and LPS. Therefore we tested mice pretreated with the IL-1-receptor antagonist. This treatment prevented the neurochemical and plasma ACTH and corticosterone responses to IL-1, but did not alter those to LPS, and prevented the endocrine and neurochemical responses to NDV in approximately half of the animals. Thus IL-1 may be a mediator of the responses to NDV, but additional factors may also be involved.

Induction of aromatic L-amino acid decarboxylase mRNA by interleukin-1 beta and prostaglandin E2 in PC12 cells

Aromatic 1-amino acid decarboxylase (AADC) is involved in the synthesis of the putative neurotransmitters dopamine (DA), norepinephrine (NA) and 5-hydroxytryptamine (5-HT). We report here that the gene expression of AADC can be regulated by interleukin (IL) 1-beta and prostaglandin (PG) E2 in PC12 cells. The cells were treated with different doses of IL 1-beta and PGE2 for 3 days. Slot blot hybridization was performed to detect AADC mRNA and Western immunoblot to detect AADC protein. The cDNA probe for rat AADC was generated by the PCR method. IL 1-beta and PGE2 produced a dose- and time-dependent up-regulation in AADC mRNA levels (up to 200% of the control values) which was followed by a stable increase in AADC protein. The data further support the suggestion that AADC is a regulated enzyme and that the regulation occurs at the level of gene expression. Because IL-1 is synthesized, and acts locally, within the brain to influence neuronal and glial functions, it has been proposed to be a mediator with both beneficial and detrimental responses to inflammation and injury. The regulation of AADC by IL-1 may indicate a possible involvement for AADC in neuronal injury and recovery. Since IL-1 promotes PGE2 formation, its effects may be occurring by increasing level of PGE2.

Cytokine-specific central monoamine alterations induced by interleukin-1, -2 and -6

Cytokine-specific alterations of monoamine activity were evident in the hypothalamus, hippocampus and prefrontal cortex 2 h following peripheral administration of recombinant interleukin (IL)-1 beta, IL-2 and IL-6 (200 ng, i.p.) in male, BALB/c mice. IL-1 induced the broadest range of neurochemical changes, affecting central norepinephrine (NE), serotonin (5-HT) and dopamine (DA) activity. In particular, IL-1 enhanced NE turnover in the hypothalamus and hippocampus, 5-HT turnover in the hippocampus and prefrontal cortex (owing to increased utilization and reduced content of the transmitters in these brain regions), and enhanced DA utilization in the prefrontal cortex. IL-6 increased 5-HT and DA activity in the hippocampus and prefrontal cortex in a manner similar to IL-1, but failed to affect central NE activity. Moreover, IL-2 increased hypothalamic NE turnover (reflecting a profound increase in NE utilization) and enhanced DA turnover in the prefrontal cortex, but did not influence central 5-HT activity. Hence, these cytokines differentially altered neurochemical activity in brain regions that mediate neuroimmune interactions and that are influenced by physical and psychological stressors. In addition to the neurochemical changes, plasma corticosterone concentrations were profoundly enhanced in IL-1-treated animals, but not significantly altered by IL-2 or IL-6 treatment. The IL-1-induced corticosterone elevations did not significantly correlate with alterations of hypothalamic NE activity.

Neural and biochemical mediators of endotoxin and stress-induced c-fos expression in the rat brain

We and others have reported that c-fos protein is induced in the hypothalamus and brain stem of the rat following central and peripheral injections of endotoxin (lipopolysaccharide; LPS). We have now examined possible mechanisms through which LPS induces c-fos protein. The cyclooxygenase inhibitor indomethacin and the glutamate NMDA antagonist MK801 inhibited c-fos protein in the paraventricular nucleus (PVN), supraoptic nucleus (SON), and the A1/A2 regions of the brain stem induced by IP or IV injections of LPS (40 micrograms). The H1 histamine antagonist diphenhydramine, but not the H2 histamine antagonist cimetidine, reduced the amount of c-fos labeling. MK801 also attenuated the effects of stress (foot shock) on c-fos protein; however, indomethacin had no effect on c-fos protein induced by stress. We next examined the importance of visceral afferent innervation on the response to LPS or stress. Subdiaphragmatic vagotomy completely blocked the induction of c-fos protein following IP injections of LPS; however, vagotomy had a minimal effect on c-fos protein induced in the PVN and SON following IV injections of LPS, but potentiated c-fos induction following foot shock. Thus, prostaglandin synthesis, glutamate release, histamine receptors, and visceral afferents represent functional biochemical and neural pathways through which endotoxin activates c-fos protein in specific autonomic and neuroendocrine regulatory nuclei. Activation of NMDA glutamate receptors may represent a final common pathway for the induction of c-fos protein in the brain induced by both endotoxin and stress.

Cytokine-induced change in hypothalamic norepinephrine turnover: involvement of corticotropin-releasing hormone and prostaglandins

Changes in norepinephrine (NE) turnover in restricted brain regions were examined in rats after administration of the major mediators of the acute phase response, interleukin-1 beta (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF). An increase in NE turnover was observed after intraperitoneal injection of IL-1 (1 microgram/rat) in the whole hypothalamus and several specific hypothalamic nuclei, but not in the medulla oblongata and cerebral cortex. The stimulatory effect of IL-1 was mimicked by an intracerebroventricular injection of much lower doses of IL-1 (10-100 ng/rat). This IL-1-induced increase in hypothalamic NE turnover was blocked by the pretreatment with either indomethacin (cyclooxygenase inhibitor) or anti-corticotropin releasing hormone (CRH) antibody but not by naloxone. Intracerebroventricular injection of CRH increased NE turnover not only in the hypothalamus but also in the medulla oblongata and cerebral cortex. However, prostaglandin (PG) E2 and PGF2 alpha did not show such effect. It was therefore suggested that IL-1 activates noradrenergic neurons projecting to the hypothalamus by its direct action to the brain, and that CRH and eicosanoid-cyclooxygenase product(s) within the brain are involved in this process. In contrast, neither IL-6 nor TNF influenced brain NE turnover regardless of whether they were given intraperitoneally or intracerebroventricularly. Thus, although IL-6 and TNF, as well as IL-1, show common central effects such as fever and pituitary-adrenal activation, these effects may be independent of the activation of NE metabolism in the hypothalamus.

Differential induction of c-Fos immunoreactivity in hypothalamus and brain stem nuclei following central and peripheral administration of endotoxin

Lipopolysaccharide (LPS), an endotoxin associated with gram-negative bacteria, is a potent activator of the immune system. We have tested the effects of ICV infusions of LPS (10 ng) or Ringer's solution on the induction of the proto-oncogene protein c-Fos in the brain as well as plasma levels of corticosterone and splenic concentrations of norepinephrine (NE) and VIP. At 3 h post-ICV infusion of LPS, numerous labeled neurons were observed in the paraventricular nucleus (PVN) of the hypothalamus and the nucleus tractus solitarius (A2) region of the brain stem. Also, corticosterone and splenic NE and VIP levels were all elevated post-ICV LPS. Analysis of the time course for the induction of c-Fos protein in the brain following IP injections of LPS indicated that, relative to control injections, increased numbers of c-Fos-positive cells were detected in the PVN 0.5 h following IP injections (100 micrograms), peaked at 2-3 h postinjection, and then returned to control levels at later intervals. Additional dose-response data for IP LPS indicated a small increase in the number of labeled cells at a dose of 4.0 micrograms, and the number and staining intensity increased up to a dose of 100 micrograms. Corticosterone levels followed a similar pattern and were elevated at the 4.0 micrograms IP dose of LPS and increased to peak levels at 40 micrograms and higher. In contrast to ICV injections, splenic NE levels were unaltered by IP injections of LPS.(ABSTRACT TRUNCATED AT 250 WORDS)