Induction by lipopolysaccharide of cyclooxygenase-2 mRNA in rat brain; its possible role in the febrile response

Prostanoid receptor subtypes

Prostanoids are a group of lipid mediators that include the prostaglandins (PG) and thromboxanes (TX). Upon cell stimulation, prostanoids are synthesized from arachidonic acid via the cyclooxygenase (COX) pathway and released outside the cells to exert various physiological and pathological actions in a variety of tissues and cells. The activities of prostanoids are mediated by specific G protein-coupled receptors, which have been classified on the basis of pharmacological experiments into eight types and subtypes according to their responsiveness to selective agonists and antagonists. These prostanoid receptors have been cloned from various species including human, and their distinct binding properties and signal transduction pathways have been characterized by analyses of cells expressing each receptor. Furthermore, the distribution patterns of prostanoid receptor mRNAs have been determined in tissues and cells for various species. This information is useful for understanding the molecular basis of the pathophysiological actions of prostanoids.

Carbon monoxide as a novel central pyrogenic mediator

Carbon monoxide (CO) are produced by heme oxygenase (HO), and HO was detected in hypothalamus. However, the roles of CO produced in hypothalamus was not fully elucidated. So, we tested the effects of CO on body temperature because preoptic-anterior hypothalamus was known as the presumptive primary fever-producing site. CO-saturated aCSF (4 microl, i.c.v.) and hemin (10 microg, i.c.v.) elicited marked febrile response. Pretreatment with indomethacin completely inhibited CO- and hemin-induced fever. Zinc protoporphyrin-IX (10 microg, i.c.v.) or ODQ (50 microg, i.c.v.) partially reduced hemin-induced febrile response. Dibutyryl-cGMP (100 microg, i.c.v.) produced profound febrile response and this febrile response was attenuated by indomethacin. These results indicate that endogenous CO may have a role as a pyrogenic mediator in CNS and CO-mediated pyresis is dependent on prostaglandin production and partially on activation of soluble guanylate cyclase.

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.

Role of cyclooxygenase-2 in neuronal cell cycle activity and glutamate-mediated excitotoxicity

In previous studies we found that neuronal overexpression of human cyclooxygenase (COX)-2 in transgenic mice potentiated excitotoxicity in vivo and in vitro. To clarify the molecular mechanisms involved in COX-2-mediated potentiation of excitotoxicity, we used cDNA microarray to identify candidate genes the expression of which is altered in the cerebral cortex of homozygous human hCOX-2 transgenic mice. We found that the mRNA expression of the cell cycle kinase (CDK) inhibitor-inhibitor kinase (INK) p18(INK4), a specific inhibitor of CDK 4,6, which controls the activation of the retinoblastoma (Rb) tumor suppressor protein phosphorylation, was decreased in the brain of adult hCOX-2 homozygous transgenics. Conversely, chronic treatment of the hCOX-2 transgenics with the preferential COX-2 inhibitor nimesulide reversed the hCOX-2-mediated decrease of cortical p18(INK4) mRNA expression in the brain. Further in vitro studies revealed that in primary cortico-hippocampal neurons derived from homozygous hCOX-2 transgenic mice, COX-2 overexpression accelerates glutamate-mediated apoptotic damage that is prevented by the CDK inhibitor flavoperidol. Moreover, treatment of wild-type primary cortico-hippocampal neuron cultures with the COX-2 preferential inhibitor nimesulide significantly attenuated glutamate-mediated apoptotic damage, which coincided with inhibition of glutamate-mediated pRb phosphorylation. These data indicate that hCOX-2 overexpression causes neuronal cell cycle deregulation in the brain and provides further rationale for targeting neuronal COX-2 in neuroprotective therapeutic research.

Involvement of postsynaptic EP4 and presynaptic EP3 receptors in actions of prostaglandin E2 in rat supraoptic neurones

We have reported that supraoptic nucleus (SON) neurones are excited by prostaglandin E2 (PGE2) presumably via dual postsynaptic PG receptors, FP receptors and unidentified EP receptors, and that presynaptic EP receptors may also be involved in the excitation. In the present study, to clarify the receptor mechanism of the PGE2-mediated actions on SON neurones, we studied the pre- and postsynaptic effects of four newly developed EP agonists that are selective for each of the four EP receptors, EP1-4, on rat SON neurones using extracellular recording and whole-cell patch-clamp techniques. The EP4 agonist ONO-AE1-329 mimicked the excitatory effects of PGE2, whereas the EP1 agonist ONO-DI-004, the EP2 agonist ONO-AE1-257 and the EP3 agonist ONO-AE-248 had little or no effect. The effects of ONO-AE1-329 were unaffected by the EP1/FP/TP antagonist, ONO-NT-012, which potently suppressed the excitation caused by the FP agonist fluprostenol and PGE2. ONO-AE1-329 caused marked excitation when responses to fluprostenol were desensitized by repeated applications of fluprostenol. Patch-clamp analysis in SON neurones showed that ONO-AE1-329 induced inward currents at a holding potential of -70 mV and the reversal potential of the currents was -35.1 +/- 2.3 mV. On the other hand, the frequency of spontaneous inhibitory postsynaptic currents recorded from SON slice preparations was suppressed by ONO-AE-248, but unaffected by the other three EP agonists. These results suggest that SON neurones possess postsynaptic EP4 receptors and that gamma-aminobutyric acid neurones innervating SON neurones possess presynaptic EP3 receptors in their terminals. Activation of the two EP receptors may be involved in the excitatory regulation of SON neurones by PGE2.

Pyrogenic cytokines injected into the rat cerebral ventricle induce cyclooxygenase-2 in brain endothelial cells and also upregulate their receptors

Peripheral immunological insults induce interleukin (IL)-1 beta and IL-6 in the brain. To elucidate the mechanism(s) of fever evoked by these brain-derived cytokines, and possible interactions between them, we examined in rats: (i) whether cyclooxygenase-2 is responsible for fever evoked by central injection of these cytokines; (ii) if so, where in the brain cyclooxygenase-2 is induced; (iii) where the receptors for these cytokines are located; and (iv) how the expression of these receptors is influenced by the cytokines. Intracerebroventricular injection of these cytokines evoked fever that was suppressed by a cyclooxygenase-2 inhibitor. Brain endothelium was the site of cyclooxygenase-2 induction by these cytokines. IL-1 receptor (IL-1R) was constitutively expressed in brain endothelium, and its mRNA was further upregulated by either cytokine. IL-6R mRNA was constitutively expressed in the cerebral cortex, and was newly induced in as yet unidentified cells in brain blood vessels by either cytokine. Messenger RNAs for cyclooxygenase-2, IL-1R, and IL-6R were often observed in the same blood vessels. These results suggest that COX-2 induced in brain endothelium is, at least in part, involved in the fever evoked by these cytokines, and that one possible interaction between these two cytokines is mutual upregulation of their receptors in the endothelium or perivascular cells, resulting in augmentation of their actions.

Effects of heme oxygenase system on the cyclooxygenase in the primary cultured hypothalamic cells

Endogenous carbon monoxide (CO) shares with nitric oxide (NO) a role as a putative neural messenger in the brain. Both gases are believed to modulate CNS function via an increase in cytoplasmic cGMP concentrations secondary to the activation of soluble guanylate cyclase (sGC). Recently CO and NO were proposed as a possible mediator of febrile response in hypothalamus. NO has been reported to activate both the constitutive and inducible isoform of the cyclooxygenase (COX). Thus, we investigated whether CO arising from heme catabolism by heme oxygenase (HO) is involved in the febrile response via the activation of COX in the hypothalamus. PGE2 which is a final mediator of febrile response released from primary cultured hypothalamic cells was taken as a marker of COX activity. PGE2 concentration was measured with EIA kits. Exogenous CO (CO-saturated medium) and hemin (a substrate and potent inducer of HO) evoked an increase in PGE2 release from hypothalamic cells, and these effects were blocked by methylene blue (an inhibitor of sGC). And membrane permeable cGMP analogue, dibutyryl-cGMP elicited significant increases in PGE2 release. These results suggest that there may be a functional link between HO and COX enzymatic activities. The gaseous product of hemin through the HO pathway, CO, might play a role through the modulation of the COX activity in the hypothalamus.

Activation of prostanoid EP(3) and EP(4) receptor mRNA-expressing neurons in the rat parabrachial nucleus by intravenous injection of bacterial wall lipopolysaccharide

Systemic inflammation activates central autonomic circuits, such as neurons in the pontine parabrachial nucleus. This activation may be the result of afferent signaling through the vagus nerve, but it may also depend on central prostaglandin-mediated mechanisms. Recently, we have shown that neurons in the parts of the parabrachial nucleus that are activated by immune challenge express prostaglandin receptors of the EP(3) and EP(4) subtypes, but it remains to be determined if the prostaglandin receptor-expressing neurons are identical to those that respond to immune stimuli. In the present study, bacterial wall lipopolysaccharide was injected intravenously in adult male rats and the expression of c-fos mRNA and of EP(3) and EP(4) receptor mRNA was examined with complementary RNA probes labeled with digoxigenin and radioisotopes, respectively. Large numbers of neurons in the external lateral parabrachial subnucleus, a major target of vagal-solitary tract efferents, expressed c-fos mRNA. Quantitative analysis showed that about 60% (range 40%-79%) of these neurons also expressed EP(3) receptor mRNA. Conversely, slightly more than 50% (range 48%-63%) of the EP(3) receptor-expressing neurons in the same subnucleus coexpressed c-fos mRNA. In contrast, few EP(4) receptor-expressing neurons were c-fos positive, with the exception of a small population located in the superior lateral and dorsal lateral subnuclei. These findings show that immune challenge activates central autonomic neurons that could be the target of centrally produced prostaglandin E(2), suggesting that synaptic signaling and paracrine mechanisms may interact on these neurons.

Expression of cyclooxygenase enzymes in rat hypothalamo-pituitary-adrenal axis: effects of endotoxin and glucocorticoids

Prostaglandins play a key role in mediating the hypothalamo-pituitary-adrenocortical (HPA) responses to immune insults. This study aimed to provide some insight into the relative contributions of the constitutive and inducible forms of cyclooxygenase (COX-1 and COX-2) to the generation of these prostanoids by examining the effects of (1) endotoxin treatment on the expression of COX-1 and COX-2 mRNAs in the various components of the HPA axis in control and glucocorticoid pretreated rats, and (2) selective inhibition of COX-2 on the production of corticosterone by adrenal tissue in vitro. Endotoxin caused a marked rise in COX-2 mRNA in the adrenal gland that was evident 3 and 6 h after the injection and was prevented by pretreatment with dexamethasone. It also induced a modest increase in COX-2 mRNA in the hypothalamus but not in the hippocampus or anterior pituitary gland. By contrast, COX-1 mRNA was largely unaffected by the drug treatments in all tissues studied. In vitro the selective COX-2 inhibitor SC-236 caused a marked reduction in adrenocorticotropic hormone-driven corticosterone release, as did the nonselective COX inhibitor, indomethacin. These results support a role of COX-2 in the manifestation of the HPA responses to endotoxin, particularly within the adrenal gland.

How circulating cytokines trigger the neural circuits that control the hypothalamic-pituitary-adrenal axis

It is now no secret that the brain plays a crucial role in organizing, adapting and restraining the systemic inflammatory response via a complex cascade of mechanisms involving proteins of the innate immune system, molecules of the proinflammatory signal transduction pathways, prostaglandins (PGs) and specific populations of neurons. These neuronal circuits, in particular those controlling autonomic functions, are all together involved in engaging the physiological responses that may help eliminating the foreign material and adjust the inflammatory events to prevent detrimental consequences. For instance, elevation in plasma glucocorticoid levels is one of the most powerful endogenous and well-controlled feedback on the pro-inflammatory signal transduction machinery taking place across the organisms. The main Center that controls this neuroendocrine system is the paraventricular nucleus of the hypothalamus (PVN) that receives neuronal projections from numerous hypothalamic and extra-hypothalamic nuclei and areas. There is now compelling evidence that molecules produced by cells of the blood-brain barrier (BBB) may bind to their cognate receptors expressed at the surface of neurons that are responsible to trigger the hypothalamic-pituitary adrenal (HPA) axis. This review presents the new molecular insights regarding the pro-inflammatory signal transduction pathways that occur in these cells and how they are related to the neuroendocrine circuits mediating the increase in plasma glucocorticoid levels during systemic and localized immunogenic insults.

Cyclooxygenase and Alzheimer's disease: implications for preventive initiatives to slow the progression of clinical dementia

Industry and academia are devoting a tremendous amount of resources to the testing of anti-inflammatory drugs for the treatment of Alzheimer's disease (AD). This trend is the result of the growing consensus supporting the inflammatory hypothesis of AD. If anti-inflammatory strategies succeed in slowing the rate of disease progression, the impact on patients and families could be enormous. However, given the large number of candidates in the pool of anti-inflammatory drugs and given their widely divergent activities, it is essential to use methods which optimizes drug selection and study design. Pilot studies of anti-inflammatory regimens are useful in determining tolerability. However, these studies have limited value in estimating effective size since disease-modification, rather than symptomatic improvement, is the ultimate goal. Better understanding of the influence of inflammatory activity and the specific mechanisms which play an early role in the progression of the disease, will improve the likelihood of successfully identifying an effective anti-inflammatory treatment strategy. This review outlines directions in research that address possible contributions of cyclooxygenase (COX)-2, COX-1 and other inflammatory mediators to AD neurodegeneration. Finally, this article addresses potential interventions designed to control segments of classical inflammatory cascades in the brain in which cyclooxygenase is highly implicated. These considerations are critical to understand the role of cyclooxygenase in the clinical progression of AD.

Cyclooxygenase 1 is not essential for hypophagic responses to interleukin-1 and endotoxin in mice

Numerous studies have shown that the effects of interleukin-1 (IL-1) and endotoxin (LPS) on behavior are sensitive to cyclooxygenase (COX) inhibitors. However, neither the location of the COX involved nor the specific isoform, COX1 or COX2, is known. A previous study using selective COX1 and COX2 inhibitors did not provide an unequivocal answer. Therefore, we tested the response of sweetened milk ingestion to IL-1 and LPS in mice in which the COX1 or the COX2 gene was deleted (COX1ko and COX2ko). When IL-1beta was administered 90 min before the milk, COX1ko mice showed responses similar to those of normal mice. In contrast, COX2ko mice exhibited responses considerably less than normal, with some mice showing no response. Indomethacin pretreatment almost prevented the feeding responses to IL-1 in normal and COX1ko mice. The milk intake response to LPS in COX1ko mice was like that of normal mice. The results from COX1ko mice suggest that COX1 is not necessary for the decreased milk intake following IL-1 and LPS. The results from COX2ko mice are consistent with the involvement of COX2 in the IL-1-induced depression of milk intake, but other mechanisms may effect decreases in sweetened milk intake.

Coexpression of microsomal-type prostaglandin E synthase with cyclooxygenase-2 in brain endothelial cells of rats during endotoxin-induced fever

Fever is triggered by an elevation of prostaglandin E(2) (PGE(2)) in the brain. However, the mechanism of its elevation remains unanswered. We herein cloned the rat glutathione-dependent microsomal prostaglandin E synthase (mPGES), the terminal enzyme for PGE(2) biosynthesis, and examined its induction in the rat brain after intraperitoneal injection of pyrogen lipopolysaccharide (LPS). In Northern blot analysis, mPGES mRNA was weakly expressed in the brain under the normal conditions but was markedly induced between 2 and 4 hr after the LPS injection. In situ hybridization study revealed that LPS-induced mPGES mRNA signals were mainly associated with brain blood vessels, especially vein or venular-type ones, in the whole brain area. Immunohistochemical study demonstrated that mPGES-like immunoreactivity was expressed in the perinuclear region of brain endothelial cells, which were identified as von Willebrand factor-positive cells. Furthermore, in the perinuclear region of the endothelial cells, mPGES was colocalized with cyclooxygenase-2 (COX-2), which is the enzyme essential for the production of the mPGES substrate PGH(2). Inhibition of cyclooxygenase-2 activity resulted in suppression of both PGE(2) level in the CSF and fever (Cao et al., 1997), suggesting that the two enzymes were functionally linked and that this link is essential for fever. These results demonstrate that brain endothelial cells play an essential role in the PGE(2) production during fever by expressing COX-2 and mPGES.

Changes in the immune system in depression and dementia: causal or co-incidental effects?

It is now widely accepted that psychological stress and psychiatric illness can compromise immune function. Furthermore the mechanisms whereby such changes occur are probably associated with the activities of the cytokines and other inflammatory mediators of the immune system which are known to initiate changes in behaviour. This review aims to summarise the experimental and clinical evidence that implicates the pro-inflammatory cytokines in the pathological changes seen in major depression and in Alzheimer's disease (AD). In major depression, evidence is provided to show that both activation (e.g., macrophage activity, acute phase proteins) and inhibition (e.g., natural killer cell activity) of the immune system occur. Many of the behavioural changes seen in depression are simulated by three pro-inflammatory cytokines (IL-1, IL-6 and TNF-alpha), which may produce their impact on the brain by activating cyclooxygenase, nitric acid synthase and corticotrophin releasing factor. Effective antidepressant treatments largely attenuate the immune changes thereby raising the possibility that the normalisation of central biogenic amine function that are conventionally implicated in the cause of depression may be secondary to those of the pro-inflammatory cytokines. With respect to AD, while the cause(s) are unknown, there is both experimental and clinical evidence to suggest that inflammatory processes in the brain caused in particular by TNF-alpha together with the subsequent rise in free radicals, are instrumental in causing the pathological changes which underlie the disease. Evidence in favour of the inflammatory hypothesis is supported by the finding that nonsteroidal anti-inflammatory drugs slow down the progression of the disease.Although, more research is needed into the inter-relationships between the various pro-inflammatory cytokines and the behavioural changes invoked in major depression and AD, the immunological hypothesis has been important in stimulating new concepts regarding the causes of the pathological changes in these diseases and how effective drug treatments may attenuate them.

The Cycloxygenase-2 inhibitor SC58236 is neuroprotective in an in vivo model of focal ischemia in the rat

Focal ischemia was induced in the fronto-parietal region of rat brain, by injection of Rose Bengal, followed by light activation. Focal ischemia was accompanied by formation of PGD(2) peaking 60-90 min post irradiation and declining thereafter. Increased Cycloxygenase-2 (COX-2) expression was also observed. Control ischemic rats showed distinct morphological alterations with necrosis of neurons, glial cells and blood vessels, surrounded by a halo with pyknotic cells with cytoplasm swelling and vacuolization. Compound SC58236, a selective COX-2 inhibitor, dose-dependently prevented, ischemia-induced eicosanoid formation (area under the curve (AUC) of controls: 3.11 +/- 0.87; AUC of 20 mg/kg SC58236: 0.39 +/- 0.24), and caused significant reduction of damaged area (30.7 and 18.9% at SC58236 20 and 6.6 mg/kg), suggesting that selective inhibitors of COX-2 are neuroprotective.

Fever induction pathways: evidence from responses to systemic or local cytokine formation

The immune and central nervous systems are functionally connected and interacting. The concept that the immune signaling to the brain which induces fever during infection and inflammation is mediated by circulating cytokines has been traditionally accepted. Administration of bacterial lipopolysaccharide (LPS) induces the appearance of a so-termed "cytokine cascade" in the circulation more or less concomitantly to the developing febrile response. Also, LPS-like fever can be induced by systemic administration of key cytokines (IL-1 beta, TNF-alpha, and others). However, anti-cytokine strategies against IL-1 beta or TNF-alpha along with systemic injections of LPS frequently lead to attenuation of the later stages of the febrile response but not of the initial phase of fever, indicating that cytokines are rather involved in the maintenance than in the early induction of fever. Within the last years experimental evidence has accumulated indicating the existence of neural transport pathways of immune signals to the brain. Because subdiaphragmatic vagotomy prevents or attenuates fever in response to intraperitoneal or intravenous injections of LPS, a role for vagal afferent nerve fibers in fever induction has been proposed. Also other sensory nerves may participate in the manifestation of febrile responses under certain experimental conditions. Thus, injection of a small dose of LPS into an artificial subcutaneous chamber results in fever and formation of cytokines within the inflamed tissue around the site of injection. This febrile response can be blocked in part by injection of a local anesthetic into the subcutaneous chamber, indicating a participation of cutaneous afferent nerve signals in the manifestation of fever in this model. In conclusion, humoral signals and an inflammatory stimulation of afferent sensory nerves can participate in the generation and maintenance of a febrile response.

Effect of acute lipopolysaccharide administration on (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2 aminopropane-induced wet dog shake behavior in rats: comparison with body weight change and locomotor activity

1. Several reports have shown that serotonin (5-HT)2A receptor density and its function are altered after physiological or pharmacological stress. To examine whether an acute administration of lipopolysaccharide (LPS), a bacterial endotoxin, affected 5-HT2A receptor function, wet dog shakes of male Wistar rats were observed after a subcutaneous injection of DOI, a 5-HT2A receptor agonist following LPS treatment. Body weight change and locomotor activity were also observed. 2. DOI (1 mg/kg)-induced WDS significantly decreased after 400 or 1000 microg/kg LPS treatment compared with that of control rats 1 and 3 hr after injection, and WDS completely recovered 8 hr after LPS treatment. Treatment with 10 mg/kg indomethacin (IND) or 1 mg/kg naltrexone (NLTX) canceled the effect of 400 microg/kg LPS on DOI-induced WDS. 3. Body weight decrease was significantly greater in LPS-treated rats compared with control rats 3, 5 and 8 hr after treatment. Treatment with IND (10 mg/kg) significantly recovered the reduction in body weight induced by 400 microg/kg LPS. Treatment with NLTX (1 mg/kg) also prevented the LPS effect on body weight decrease. 4. Eight hr after treatment with LPS (400 microg/kg), the rats showed significant attenuation of locomotor activity. IND (10 mg/kg) treatment abolished the inhibitory effect of LPS on locomotor activity, and NLTX (1 mg/kg) also improved the decrease in locomotion 8 hr after LPS treatment. 5. Plasma tumor necrosis factor (TNF)-alpha concentration dramatically increased 1 hr after the injection of 400 microg/kg LPS, and returned almost to the basal level 3 hr later. Next, rats were injected with 50 microg/kg TNF-alpha intraperitoneally, and body weight change and DOI-induced WDS was determined 3 hr after TNF-alpha injection. Body weight loss was significantly greater in rats treated with TNF-alpha. On the other hand, DOI-induced WDS was not altered when rats were treated with TNF-alpha. 6. These results suggest that acute treatment with LPS inhibited 5-HT2A receptor-mediated behavior via cyclooxygenase and opioid receptor activation, but that the inhibition of the WDS by LPS appears to be independent of TNF-alpha production.

Relationship of EP(1-4) prostaglandin receptors with rat hypothalamic cell groups involved in lipopolysaccharide fever responses

The action of prostaglandin E(2) (PGE(2)) in the preoptic area is thought to play an important role in producing fever. Pharmacologic evidence suggests that, among the four subtypes of E-series prostaglandin (EP) receptors, i.e., EP(1), EP(2), EP(3), and EP(4), the EP(1) receptor mediates fever responses. In contrast, evidence from mice with EP receptor gene deletions indicates that the EP(3) receptor is required for the initial (<1 hour) fever after intravenous (i.v.) lipopolysaccharide (LPS). To investigate which subtypes of EP receptors mediate systemic infection-induced fever, we assessed the coexpression of Fos-like immunoreactivity (Fos-IR) and EP(1-4) receptor mRNA in nuclei in the rat hypothalamus that have been shown to be involved in fever responses. Two hours after the administration of i.v. LPS (5 microg/kg), Fos-IR was observed in the ventromedial preoptic nucleus, the median preoptic nucleus, and the paraventricular hypothalamic nucleus. In these nuclei, EP(4) receptor mRNA was strongly expressed and the Fos-IR intensely colocalized with EP(4) receptor mRNA. Strong EP(3) receptor mRNA expression was only seen within the median preoptic nucleus but Fos-IR showed little coexpression with EP(3) receptor mRNA. EP(2) receptor mRNA was not seen in the PGE(2) sensitive parts of the preoptic area. Although approximately half of the Fos-immunoreactive neurons also expressed EP(1) receptor mRNA, EP(1) mRNA expression was weak and its distribution was so diffuse in the preoptic area that it did not represent a specific relationship. In the paraventricular nucleus, EP(4) mRNA was found in most Fos-immunoreactive neurons and levels of EP(4) receptor expression increased after i.v. LPS. Our findings indicate that neurons expressing EP(4) receptor are activated during LPS-induced fever and suggest the involvement of EP(4) receptors in the production of fever.

Cyclooxygenase (COX)-1 expressing macrophages/microglial cells and COX-2 expressing astrocytes accumulate during oligodendroglioma progression

Cyclooxygenases (COX, prostaglandin endoperoxide synthases, PGG/H synthases) are potent mediators of edema, impeding blood flow and immunomodulation in the pathologically altered brain. Two COX iso-enzymes have been associated with brain disease, the constitutively expressed COX-1 and the cytokine-inducible COX-2. We have used single and double labeling immunohistochemistry to analyse COX-1 and COX-2 expression in twenty-six primary WHO grade II oligodendrogliomas, sixteen primary WHO grade III anaplastic oligodendrogliomas, twenty-seven matched recurrences and ten neuropathologically unaltered brains. COX-1 immunoreactivity was predominantly observed in macrophages/microglial cells. The number of COX-1 expressing macrophages/microglial cells was significantly lower in primary oligodendrogliomas than in primary anaplastic oligodendrogliomas (P<0.0001) and in anaplastic oligodendroglioma relapses (P=0.011). Patients with low COX-1 labeling scores in the primary tumors had significantly longer time to progression and overall survival (P=0.0285) than those with high COX-1 labeling scores. COX-2 immunoreactivity was predominantly observed in disseminated neurons and astrocytes. In glioblastoma multiforme relapses, accumulation of COX-2 expressing astrocytes was observed surrounding areas of focal necrosis. The number of COX-2 expressing astrocytes was significantly (P=0.0471) lower in primary oligodendrogliomas than in high grade oligodendroglioma relapses. These data provide convincing evidence for the differential accumulation of cyclooxygenase isoforms during oligodendroglioma progression in vivo.

Cytokine signals propagate through the brain

Interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFalpha) are proinflammatory cytokines that are constitutively expressed in healthy, adult brain where they mediate normal neural functions such as sleep. They are neuromodulators expressed by and acting on neurons and glia. IL-1 and TNFalpha expression is upregulated in several important diseases/disorders. Upregulation of IL-1 and/or TNFalpha expression, elicited centrally or systemically, propagates through brain parenchyma following specific spatio-temporal patterns. We propose that cytokine signals propagate along neuronal projections and extracellular diffusion pathways by molecular cascades that need to be further elucidated. This elucidation is a prerequisite for better understanding of reciprocal interactions between nervous, endocrine and immune systems.

Heme oxygenase-1 in lesions of rat experimental autoimmune encephalomyelitis and neuritis

The enzyme heme oxygenase-1 (HO-1) is reducing heme to the gaseous mediator carbon monoxide, to iron and the antioxidant biliverdin. The inducible expression of HO-1 is considered a protective cellular mechanism against reactive oxygen intermediates. Further, carbon monoxide (CO) is a regulator of cGMP synthesis, of NO-synthetases and cyclooxygenases, thereby indirectly modulating reactive processes. Here we report expression of HO-1 in rat experimental autoimmune encephalomyelitis (EAE) and neuritis (EAN). With both models, similar results were obtained: HO-1 was localized predominantly to infiltrating, monocytic, but only rarely to ramified microglial cells or astrocytes surrounding the inflammatory lesions. Prominent expression by monocytic cells was seen from day 11 after immunization correlating with the development of neurologic disease. Further, local expression is persistent for long after cessation of neurologic signs. Thus, HO-1 could be considered a factor in the formation and resolution of inflammatory autoimmune lesions of the nervous system.

Nonsteroidal anti-inflammatory drugs, acetaminophen, cyclooxygenase 2, and fever

Nonsteroidal anti-inflammatory drugs (NSAIDs) are frequently used antipyretic agents that most probably exert their antifever effect by inhibiting cyclooxygenase (COX)-2. Thus, COX-2-selective drugs or null mutation of the COX-2 gene reduce or prevent fever. Acetaminophen is antipyretic and analgesic, as are NSAIDs, but it lacks the anti-inflammatory and anticoagulatory properties of these drugs. This has led to the speculation that a COX variant exists that is inhibitable by acetaminophen. An acetaminophen-inhibitable enzyme is inducible in the mouse J774.2 monocyte cell line. Induction of acetaminophen-inhibitable prostaglandin E(2) synthesis parallels induction of COX-2. Thus, inhibition of pharmacologically distinct COX-2 enzyme activity by acetaminophen may be the mechanism of action of this important antipyretic drug.

Anorexia of infection: current prospects

The anorexia of infection is part of the host's acute phase response (APR). Despite being beneficial in the beginning, long lasting anorexia delays recovery and is ultimately deleterious. Microbial products such as bacterial cell wall compounds (e.g., lipopolysaccharides and peptidoglycans), microbial nucleic acids (e. g., bacterial DNA and viral double-stranded RNA), and viral glycoproteins trigger the APR and presumably also the anorexia during infections. Microbial products stimulate the production of proinflammatory cytokines (e.g., interleukins [ILs], tumor necrosis factor-alpha, interferons), which serve as endogenous mediators. Several microbial products and cytokines reduce food intake after parenteral administration, suggesting a role of these substances in the anorexia during infection. Microbial products are mainly released and cytokines are produced in the periphery during most infections; they might inhibit feeding through neural and humoral pathways activated by their peripheral actions. Activation of peripheral afferents by locally produced cytokines is involved in several cytokine effects, but is not crucial for the anorectic effect of microbial products and IL-1beta. Cytokines increase leptin expression in the adipose tissue, and leptin may contribute to, but is also not essential for, the anorectic effects of microbial products and cytokines. In addition, a direct action of cytokines and microbial products on the central nervous system (CNS) is presumably involved in the anorexia during infection. Cytokines can reach CNS receptors through circumventricular organs and through active or passive transport mechanisms or they can act through receptors on endothelial cells of the brain vasculature and stimulate the release of subsequent mediators such as eicosanoids. De novo CNS cytokine synthesis occurs in response to peripheral infections, but its role in the accompanying anorexia is still open to discussion. Central mediators of the anorexia during infection appear to be neurochemicals involved in the normal control of feeding, such as serotonin, dopamine, histamine, corticotropin releasing factor, neuropeptide Y, and alpha-melanocyte-stimulating hormone. Reciprocal, synergistic, and antagonistic interactions between various pleiotropic cytokines, and between cytokines and neurochemicals, form a complex network that mediates the anorexia during infection. Current knowledge on the mechanisms involved suggests some therapeutic options for treatment. Substances that block common key steps in cytokine synthesis or cytokine action, or inhibitors of eicosanoid synthesis, may hold more promise than attempts to antagonize specific cytokines. To target the neurochemical mediation of the anorexia during infection may be even more efficient. Future research should address these neurochemical mechanisms and the cytokine actions at the blood-brain barrier. Further unanswered questions concern the modulation of the anorexia during infection by gender and nutritional state.

Prolonged cyclooxygenase-2 induction in neurons and glia following traumatic brain injury in the rat

Cyclooxygenase-2 (COX2) is a primary inflammatory mediator that converts arachidonic acid into precursors of vasoactive prostaglandins, producing reactive oxygen species in the process. Under normal conditions COX2 is not detectable, except at low abundance in the brain. This study demonstrates a distinctive pattern of COX2 increases in the brain over time following traumatic brain injury (TBI). Quantitative lysate ribonuclease protection assays indicate acute and sustained increases in COX2 mRNA in two rat models of TBI. In the lateral fluid percussion model, COX2 mRNA is significantly elevated (>twofold, p < 0.05, Dunnett) at 1 day postinjury in the injured cortex and bilaterally in the hippocampus, compared to sham-injured controls. In the lateral cortical impact model (LCI), COX2 mRNA peaks around 6 h postinjury in the ipsilateral cerebral cortex (fivefold induction, p < 0.05, Dunnett) and in the ipsilateral and contralateral hippocampus (two- and six-fold induction, respectively, p < 0.05, Dunnett). Increases are sustained out to 3 days postinjury in the injured cortex in both models. Further analyses use the LCI model to evaluate COX2 induction. Immunoblot analyses confirm increased levels of COX2 protein in the cortex and hippocampus. Profound increases in COX2 protein are observed in the cortex at 1-3 days, that return to sham levels by 7 days postinjury (p < 0.05, Dunnett). The cellular pattern of COX2 induction following TBI has been characterized using immunohistochemistry. COX2-immunoreactivity (-ir) rises acutely (cell numbers and intensity) and remains elevated for several days following TBI. Increases in COX2-ir colocalize with neurons (MAP2-ir) and glia (GFAP-ir). Increases in COX2-ir are observed in cerebral cortex and hippocampus, ipsilateral and contralateral to injury as early as 2 h postinjury. Neurons in the ipsilateral parietal, perirhinal and piriform cortex become intensely COX2-ir from 2 h to at least 3 days postinjury. In agreement with the mRNA and immunoblot results, COX2-ir appears greatest in the contralateral hippocampus. Hippocampal COX2-ir progresses from the pyramidal cell layer of the CA1 and CA2 region at 2 h, to the CA3 pyramidal cells and dentate polymorphic and granule cell layers by 24 h postinjury. These increases are distinct from those observed following inflammatory challenge, and correspond to brain areas previously identified with the neurological and cognitive deficits associated with TBI. While COX2 induction following TBI may result in selective beneficial responses, chronic COX2 production may contribute to free radical mediated cellular damage, vascular dysfunction, and alterations in cellular metabolism. These may cause secondary injuries to the brain that promote neuropathology and worsen behavioral outcome.

Focal accumulation of cyclooxygenase-1 (COX-1) and COX-2 expressing cells in cerebral malaria

Intravascular sequestration and altered cytokine expression patterns are key determinators of CNS lesion formation in patients with cerebral malaria (CM). Among others, altered prostaglandin concentrations were revealed by clinical trials in peripheral blood of CM patients. Prostaglandin synthesis is controlled by cyclooxygenases (COX, prostaglandin endoperoxide synthase, PGG/H synthase) and COX expression has been attributed a key role in immunomodulation, hemostasis and inflammation in a wide variety of pathologically altered brain tissues. We have now analyzed expression of COX-1 and COX-2 in brains of patients with CM by immunohistochemistry. Double labeling experiments were used to verify the cellular identity of COX-1 and COX-2 expressing cells. Compared to healthy controls, significant (P=0.0006) accumulation of COX-1 expressing macrophages/microglial cells was detected in Dürck's granulomas. Accumulations of COX-2 expressing endothelial cells (P=0.0006) and COX-2 expressing astrocytes (P=0.0012) were detected in CM brain parenchyma. The restricted expression and accumulation of COX-1 and COX-2 in CM brains adds convincing evidence for the participation of cyclooxygenases in the formation of fever, inflammation and granuloma in these patients.

Distribution and function of prostanoid receptors: studies from knockout mice

Recent developments in the molecular biology of the prostanoid receptors has allowed the investigation of the physiological roles of each individual receptor type and subtype. The following article reports the prostanoid receptor distributions deduced from Northern blot and in situ hybridization analyses, summarizes the phenotypes of each receptor knockout mice, and discusses recent studies investigating the effects of each receptor deficiency on the inflammatory response and female reproductive processes. The combination of expression pattern and knockout analyses enabled us to determine which receptor expressed in a particular cell is important for the maintenance of normal and/or pathological physiology. The results from these analyses may be useful in the development of novel therapeutics that can selectively manipulate prostanoid-mediated actions.

Effects of vagotomy and bacterial lipopolysaccharide on food intake and expression of cyclooxygenase-2 mRNA in rat brain vessels

Effects of bilateral subdiaphragmatic vagotomy on food intake and expression of cyclooxygenase-2 mRNA in cerebral vessels in rats intraperitoneally injected with bacterial lipopolysaccharide were studied using in situ hybridization technique. Low doses of lipopolysaccharide decreased food intake in sham-operated animals, but did not affect this parameter in vagotomized rats. Comparison of hybridization signals in brain slices showed that low doses of endotoxin did not affect expression of cyclooxygenase-2 mRNA in vessels of control and experimental animals. High doses of lipopolysaccharide reduced food intake in vagotomized and sham-operated rats and elevated cyclooxygenase-2 mRNA expression in vascular endothelial cells of the brain parenchyma and meninges. The data suggest that the vagus nerve activates central structures responsible for manifestation of anorexia after intraperitoneal injection of low doses of lipopolysaccharide. High doses of endotoxin activate the vagus-independent mechanism of cyclooxygenase-2 synthesis in the endothelium of cerebral vessels. It is assumed that prostaglandins synthesized by cyclooxygenase-2 diffuse into the brain parenchyma and cause anorexia by activating target nerve structures.

Oroxylin A inhibition of lipopolysaccharide-induced iNOS and COX-2 gene expression via suppression of nuclear factor-kappaB activation

Polyphenols are major components of many traditional herbal remedies, which exhibit several beneficial effects including anti-inflammation. The exact mechanism of the anti-inflammatory action of polyphenols, however, has not been determined. In the present study, we examined the effects of eight different polyphenols isolated from Chinese herbs, including two flavonoids (myricitrin and oroxylin A), four ellagitannins (penta-O-galloyl-beta-glucopyranose, woodfordin C, oenothein B, and cuphiin D1), and two anthraquinones (emodin and physcion), on lipopolysaccharide (LPS)-induced nitric oxide (NO) production, and inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) gene expression in RAW264.7 macrophages. The results indicated that only oroxylin A and emodin concentration-dependently inhibited LPS-induced NO production. The remaining compounds slightly inhibited LPS-induced NO production only at the highest concentration examined. Furthermore, oroxylin A inhibited the expression of LPS-induced iNOS and COX-2 proteins and mRNAs without an appreciable cytotoxic effect on RAW264.7 cells. Emodin also inhibited LPS-induced iNOS protein as potently as oroxylin A, but it inhibited LPS-induced iNOS mRNA expression only slightly and did not affect COX-2 mRNA and proteins. This was consistent with the findings that oroxylin A but not emodin or physcion inhibited prostaglandin E(2) synthesis induced by LPS. The inhibitory effects of oroxylin A on LPS-induced iNOS and COX-2 gene expression were also demonstrated in Bcl-2-overexpressing RAW264.7 macrophages, suggesting that oroxylin A inhibition of iNOS and COX-2 expression was not due to its antioxidant effect. Furthermore, oroxylin A but not emodin blocked nuclear factor-kappaB (NF-kappaB) binding and transcriptional activation associated with decreased p65 proteins in the nucleus induced by LPS. These results indicated that oroxylin A, an active component in Huang Qin, inhibited LPS-induced iNOS and COX-2 gene expression by blocking NF-kappaB activation, whereas emodin inhibition of LPS-induced iNOS expression may be mediated by a different transcription factor.

Basic biology and clinical application of specific cyclooxygenase-2 inhibitors

In summary, COX-2 is a highly regulated gene product that catalyzes the local production of PGs in pathologic and physiologic situations (Figure 1). It is clear that COX-2 is the isoform responsible for production of the PGs that mediate inflammation, pain, and fever. However, the role for COX-2 in normal physiology is still being defined. Specific COX-2 inhibitors represent a significant conceptual advance in therapy for patients with arthritis. Although there is no expectation of superior efficacy, clinical trials suggest that efficacy will be comparable with that of nonselective NSAIDs. Clinical trials demonstrate the potential for clinically meaningful reductions in the incidence of the most serious GI complications found with nonselective NSAIDs, i.e., ulcer, perforation, and GI bleeding. Over the next several years, treatment of large numbers of patients with specific COX-2 inhibitors will help to define the biology of COX-2. The magnitude of this advance in the therapy of rheumatic diseases is yet to be accurately determined, but the development of specific COX-2 inhibitors may afford significant new treatment options for many patients.

Chronic overexpression of proinflammatory cytokines and histopathology in the brains of rats infected with Trypanosoma brucei

Overproduction of proinflammatory cytokines in the brains of transgenic animals causes brain pathology. To investigate the relationship between brain cytokines and pathology in the brains of animals with adult-onset, pathophysiologically induced brain cytokine expression, we studied rats infected with the parasite Trypanosoma brucei. Several weeks after infection, in situ hybridization histochemistry showed a pattern of chronic overexpression of the mRNAs for proinflammatory cytokines interleukin-1beta and tumor necrosis factor-alpha in the brains of the animals. Similar spatiotemporal inductions of mRNAs for inhibitory factor kappaBalpha and interleukin-1beta converting enzyme were found and quantified. The mRNAs for inducible nitric oxide synthase and interleukin-1 receptor antagonist were highly localized to the choroid plexus, which showed evidence of structural abnormalities associated with the parasites' presence there. The mRNAs for interleukin-6, interferon-gamma, and inducible cyclooxygenase showed restricted induction patterns. Another set of animals was processed for degeneration-induced silver staining, TdT-mediated dUTP-digoxigenin nick end-labeling (TUNEL) staining, glial fibrillary acidic protein (GFAP) immunohistochemistry, and several other histological markers. Apoptosis of scattered small cells and degeneration of certain nerve fibers was found in patterns spatially related to the cytokine mRNA patterns and to cerebrospinal fluid diffusion pathways. Furthermore, striking cytoarchitectonically defined clusters of degenerating non-neuronal cells, probably astrocytes, were found. The results reveal chronic overexpression of potentially cytotoxic cytokines in the brain and selective histopathology patterns in this natural disease model. J. Comp. Neurol. 414:114-130, 1999. Published 1999 Wiley-Liss, Inc.

Prostanoid receptors: structures, properties, and functions

Prostanoids are the cyclooxygenase metabolites of arachidonic acid and include prostaglandin (PG) D(2), PGE(2), PGF(2alpha), PGI(2), and thromboxne A(2). They are synthesized and released upon cell stimulation and act on cells in the vicinity of their synthesis to exert their actions. Receptors mediating the actions of prostanoids were recently identified and cloned. They are G protein-coupled receptors with seven transmembrane domains. There are eight types and subtypes of prostanoid receptors that are encoded by different genes but as a whole constitute a subfamily in the superfamily of the rhodopsin-type receptors. Each of the receptors was expressed in cultured cells, and its ligand-binding properties and signal transduction pathways were characterized. Moreover, domains and amino acid residues conferring the specificities of ligand binding and signal transduction are being clarified. Information also is accumulating as to the distribution of these receptors in the body. It is also becoming clear for some types of receptors how expression of their genes is regulated. Furthermore, the gene for each of the eight types of prostanoid receptor has been disrupted, and mice deficient in each type of receptor are being examined to identify and assess the roles played by each receptor under various physiological and pathophysiological conditions. In this article, we summarize these findings and attempt to give an overview of the current status of research on the prostanoid receptors.

COX-2 and Alzheimer's disease: potential roles in inflammation and neurodegeneration

Epidemiological and clinical data suggest that nonsteroidal anti-inflammatory drugs (NSAIDs) are beneficial in the treatment and prevention of Alzheimer's disease (AD). NSAIDs act by inhibiting cyclooxygenase, an enzyme that occurs in constitutive and inducible isoforms, known respectively as COX-1 and COX-2. Recognition that COX-2 plays a key role in inflammation led to the hypothesis that COX-2 might represent the primary target for NSAIDs in AD, consistent with inflammatory processes occurring in AD brain. This review highlights recently gathered evidence leading to a more complex view of the role of COX-2 in AD, including evidence that COX-2 directly contributes to neuronal vulnerability. Consideration of these roles is critical for the rational implementation of NSAID therapy in AD.

Interleukins and tumor necrosis factor as inhibitors of food intake

Cytokines, such as interleukins and tumor necrosis factor-alpha (TNFalpha), are produced in response to immune stimulation and have systemic effects, mediated by the central nervous system (CNS). Interleukins, in particular interleukin [IL]-1beta, and TNFalpha reduce food intake after peripheral and central administration, suggesting that they contribute to the anorexia during various infectious, neoplastic and autoimmune diseases. Because cytokines are mainly produced in the periphery during most of these diseases, IL-1beta and TNFalpha may inhibit feeding indirectly through neural and humoral pathways activated by their peripheral actions. Activation of afferent nerve fibers by locally produced cytokines in the periphery is involved in several cytokine effects, but is not crucial for the anorectic effect of systemic immune stimulation. Cytokines increase OB protein (leptin) expression in the adipose tissue, and leptin may contribute to, but is also not essential for, the anorectic effects of cytokines. Finally, circulating IL-1beta and TNFalpha may act directly on the brain or cytokine synthesis in the brain may contribute to the anorectic effect of systemic immune stimulation. Central mediators of the anorectic effects of cytokines appear to be neurochemicals involved in the normal control of feeding, such as serotonin, corticotropin releasing factor, histamine, alpha-melanocyte stimulating hormone, and neuropeptide Y. The well-documented cytokine production in the gut in relation to feeding and the expression of TNFalpha by adipocytes suggest that IL-1beta and TNFalpha may also play a role in the control of normal feeding and energy balance. All in all, reciprocal, synergistic and antagonistic interactions between various pleiotropic cytokines and between cytokines and neurochemicals form a complex network that mediates the effects of cytokines on feeding and energy balance.

Potentiation of excitotoxicity in transgenic mice overexpressing neuronal cyclooxygenase-2

In this study we describe the generation of a transgenic mouse model with neuronal overexpression of the human cyclooxygenase-2, h(COX)-2, to explore its role in excitotoxicity. We report that overexpression of neuronal hCOX-2 potentiates the intensity and lethality of kainic acid excitotoxicity in coincidence with potentiation of expression of the immediate early genes c-fos and zif-268. In vitro studies extended the in vivo findings and revealed that glutamate excitotoxicity is potentiated in primary cortico-hippocampal neurons derived from hCOX-2 transgenic mice, possibly through potentiation of mitochondrial impairment. This study is the first to demonstrate a cause-effect relationship between neuronal COX-2 expression and excitotoxicity. This model system will allow the systematic examination of the role of COX-2 in mechanisms of neurodegeneration that involve excitatory amino acid pathways.

Distribution, regulation and colocalization of the genes encoding the EP2- and EP4-PGE2 receptors in the rat brain and neuronal responses to systemic inflammation

It is currently believed that prostaglandin (PG) of E2 type plays a crucial role in transferring the information received from circulating immune factors to brain parenchymal cells. Although PGE2 is synthesized quite essentially by cells of the blood-brain barrier, the organization and regulation of its receptor subtypes within neuronal elements remain unknown. In this study, intravenous (i.v.) injection of the endotoxin lipopolysaccharide (LPS) or recombinant rat interleukin-1beta (IL-1beta), and intramuscular (i.m.) injection of turpentine were used as different models of systemic immune stimuli. Rats were perfused at various times after the insults (30 min to 24 h), their brains cut and hybridized with full-length rat cRNA probes. Double-labelling procedures were accomplished to determine the cellular phenotype and activity. A very distinct distribution of both EP2 and EP4 receptors was found across the brain under basal conditions; the hybridization signal for the type 2 was detected in the bed nucleus of the stria terminalis (BNST), lateral septum, subfornical organ (SFO), ventromedial hypothalamic nucleus (VMH), central nucleus of the amygdala (CeA), locus coeruleus (LC) and the area postrema (AP), whereas the ventral septal/anterior preoptic area, the magnocellular paraventricular nucleus (PVN), supraoptic nucleus, parabrachial nucleus, LC, the nucleus of the solitary tract (NTS) and the ventrolateral medulla (VLM) exhibited moderate to strong levels for the EP4 mRNA under basal conditions. Upregulation of the genes encoding EP2 and EP4 receptors was detected in selective regions and neuronal populations during systemic inflammatory challenges. The most dramatic one being the robust transcriptional activation of the EP4 subtype within corticotropin-releasing factor (CRF) neurons of the parvocellular PVN following i.v. LPS and IL-1beta injection, and the localized i.m. aggression. These neurons of the endocrine hypothalamus as well as those of numerous autonomic-related nuclei were activated by the proinflammatory cytokine, as they were immunoreactive (ir) to Fos nuclear protein. The EP4 transcript was also present in activated catecholaminergic neurons of the LC, NTS and VLM, although only the A1 cell group exhibited an increase in EP4 transcription in response to circulating IL-1beta. Moreover, the systemic immunogenic insults caused a significant increase in the EP2 mRNA levels in the CeA, SFO, AP and the leptomeninges. These data provide a distinct pattern of EP2 and EP4 expression throughout the rat brain under both basal and immune-challenged conditions, and underlie the possible role of the EP4 subtype in mediating the effects of PGE2 on different autonomic and neuroendocrine functions. The presence of Fos-ir nuclei in various populations of EP4 neurons of IL-1beta-treated animals clearly supports this concept and suggests that the selectivity of the neuronal response during systemic inflammation may depend on the expression of specific PGE2 receptors in key structures of the brain.

Localization of cytosolic phospholipase A2 messenger RNA mainly in neurons in the rat brain

Ca2(+)-sensitive 85,000 mol. wt cytosolic phospholipase A2 plays an essential role in the selective and stimulus-dependent release of arachidonic acid from membrane phospholipids. Cytosolic phospholipase A2-catalysed lipid mediators including arachidonic acid and its metabolites have been suggested to be involved in a variety of neuronal functions in the CNS. Since the cellular localization of cytosolic phospholipase A2 is still controversial and obscure, we tried an improved method of rapid processing of each specimens and succeeded in obtaining intense signals of cytosolic phospholipase A2 messenger RNA in the normal rat brain by northern blot analysis and in situ hybridization. Northern blot analysis showed the abundant distribution of cytosolic phospholipase A2 messenger RNA in most regions of the brain, with intense signals observed in the pineal gland and pons. Macroautoradiographs prepared after in situ hybridization with three different antisense riboprobes gave essentially similar patterns of localization; significant signals were widely detected in the gray matter of various regions, i.e. the olfactory bulb, cerebral cortex, hippocampus, amygdala, several thalamic and hypothalamic nuclei and cerebellum. Microautoradiographs showed that most of the intense signals were predominant in neurons, and that faint signals were from glial cells and other non-neuronal cells in the choroid plexus, inner surface cells of veins and the leptomeninges. In addition, the cycloheximide treatment increased the cytosolic phospholipase A2 messenger RNA level in the same cell populations originally possessing messenger RNA signals. Predominant expression of cytosolic phospholipase A2 messenger RNA in neurons may provide the basis for the contribution of cytosolic phospholipase A2-catalysed lipid mediators to a variety of neurotransmission and synaptic functions in the CNS.

Distribution of cyclooxygenase-1 and cyclooxygenase-2 mRNAs and proteins in human brain and peripheral organs

We used the techniques of reverse transcriptase-polymerase chain reaction, Western blotting and immunohistochemistry to evaluate the expression of cyclooxygenase (COX)-1 and -2 in brain and peripheral organs of Alzheimer disease (AD) and control cases. We found both COX-1 and COX-2 to be constitutively expressed in all organs tested, i.e., brain, heart, liver, kidney, spleen and intestine. COX-2 was substantially upregulated in affected areas of AD brain and in infarcted areas of human heart. COX-1 was only mildly upregulated in AD brain. Immunohistochemically, COX-2 was strongly expressed in the perinuclear, dendritic and axonal areas of pyramidal neurons, with enhanced staining in AD. These data suggest a special role for COX-2 in neuronal function.

The effect of indomethacin on the cytokine cascade and body temperature following burn injury in rats

This study investigates the hypothesis that indomethacin's ability to prevent "fever" following burn injury in rats is mediated via decreased plasma concentrations of IL-6, the putative mediator of increased body temperature. Sprague-Dawley rats had radio transmitters and osmotic pumps containing indomethacin placed in the peritoneal cavity. Seven days later full thickness scald burns to 50% of the body surface area were produced. Following burn injuries, daily blood samples were obtained from a carotid catheter for assay of lipopolysaccharide (LPS), interleukin-1alpha (IL-1alpha), IL-1beta, tumor necrosis factor-alpha (TNF-alpha) and IL-6. In addition, body temperature (T(B)) and activity index were obtained every five minutes by telemetry. There were four experimental groups: burn + indomethacin (B-In); burn + polyethylene glycol (Peg) (B-Peg); control + indomethacin (C-In); and control + Peg (C-Peg). Burned animals demonstrated a significant two-fold increase in plasma IL-1alpha levels (p=0.004) and a seven-fold increment in IL-6 (p=0.0001) through the 7th PBD, and indomethacin administration had no significant effect upon the cytokine plasma levels. There were no significant increases in IL-1beta, TNF-alpha or LPS in any group. Indomethacin eliminated the chronic increase in T(B) following burn injury, and this effect was not produced by changes in plasma levels of the endogenous pyrogens IL-1alpha and IL-6.

Prostaglandin-endoperoxide H synthase-2 expression in human thyroid epithelium. Evidence for constitutive expression in vivo and in cultured KAT-50 cells

Prostaglandin-endoperoxide H synthase (PGHS) (EC 1.14.99.1) expression was examined in human thyroid tissue and in KAT-50, a well differentiated human thyroid epithelial cell line. PGHS-1 is found constitutively expressed in most healthy tissues, whereas PGHS-2 is highly inducible and currently thought to be expressed, with few exceptions, only in diseased tissues. Surprisingly, PGHS-2 mRNA and protein were easily detected in normal thyroid tissue. KAT-50 cells express high levels of constitutive PGHS-2 mRNA and protein under basal culture conditions. Compounds usually associated with PGHS-2 induction, including interleukin-1beta (IL-1beta), phorbol 12-myristate 13-acetate, and serum transiently down-regulated PGHS-2 expression. Human PGHS-2 promoter constructs (-1840/+123 and -831/+123) fused to a luciferase reporter and transfected into untreated KAT-50 cells exhibited substantial activity. NS-398, a highly selective inhibitor of PGHS-2 could inhibit substantial basal prostaglandin E2 production. Exogenous IL-1 receptor antagonist or IL-1alpha neutralizing antibodies could attenuate constitutive PGHS-2 expression in KAT-50 cells, suggesting that endogenous IL-1alpha synthesis was driving PGHS-2 expression. Our findings suggest that normal thyroid epithelium expresses high constitutive levels of PGHS-2 in situ and in vitro and this enzyme is active in the generation of prostaglandin E2. Thus, unprovoked PGHS-2 expression might be considerably more widespread in healthy tissues than is currently believed.

Neuronal death and survival in two models of hypoxic-ischemic brain damage

Two unilateral hypoxic-ischemia (HI) models (moderate and severe) in immature rat brain have been used to investigate the role of various transcription factors and related proteins in delayed neuronal death and survival. The moderate HI model results in an apoptotic-like neuronal death in selectively vulnerable regions of the brain while the more severe HI injury consistently produces widespread necrosis resulting in infarction, with some necrosis resistant cell populations showing evidence of an apoptotic type death. In susceptible regions undergoing an apoptotic-like death there was not only a prolonged induction of the immediate early genes, c-jun, c-fos and nur77, but also of possible target genes amyloid precursor protein (APP751) and CPP32. In contrast, increased levels of BDNF, phosphorylated CREB and PGHS-2 were found in cells resistant to the moderate HI insult suggesting that these proteins either alone or in combination may be of importance in the process of neuroprotection. An additional feature of both the moderate and severe brain insults was the rapid activation and/or proliferation of glial cells (microglia and astrocytes) in and around the site of damage. The glial response following HI was associated with an upregulation of both the CCAAT-enhancer binding protein alpha (microglia only) and NFkappaB transcription factors.

Cyclooxygenases-1 and -2 are differentially localized to microglia and endothelium in rat EAE and glioma

Cyclooxygenases (COX) mediate a wide variety of derangements observed during diseases of the brain. Their overexpression is involved in the mediation of inflammation, immunomodulation, blood flow, apoptosis and fever. Here, we have analyzed the localization of COX-1 and COX-2 in rat experimental autoimmune encephalomyelitis (EAE), C6 glioblastoma and 9L gliosarcoma by immunohistochemistry. In healthy brain, COX-1 was expressed in single macrophages/microglial cells. Neurons and few endothelial cells expressed COX-2. In EAE, we observed an increase in COX-1+ macrophages/microglial cells and COX-2+ endothelial cells that was closely linked to disease progression. Both COX-1+ macrophages/microglial cells and COX-2+ endothelial cells were abundant in areas of cellular infiltration. In C6 and 9L tumors, high numbers of COX-1+ macrophages/microglial cells and COX-2+ endothelial cells were found both in the tumor parenchyma and in areas of infiltrative tumor growth. Double labeling experiments confirmed expression of COX-2 in vWF+ (endothelial) cells and COX-1 in ED1+ (macophages), OX6+ (MHC class II) and in W3/13+ (lymphoblasts) cells. These data provide further evidence that expression of COX-1 in macrophages/microglial cells and COX-2 in endothelial cells might represent important regulatory mechanisms in inflammatory processes associated with autoimmunity and neoplasia of the rat brain.

Lipopolysaccharide injected into the cerebral ventricle evokes fever through induction of cyclooxygenase-2 in brain endothelial cells

Activation of the arachidonic acid cascade is an essential step for the development of fever during brain inflammation. We investigated the brain sites where this activation takes place by use of a rat model of brain inflammation. Intracerebroventricular administration of lipopolysaccharide but not of its vehicle evoked fever. The fever was markedly suppressed when the rats had been pretreated with a cyclooxygenase-2-specific inhibitor. In situ hybridization and immunohistochemical studies revealed that cyclooxygenase-2 mRNA and its protein were induced by lipopolysaccharide in blood vessels near the cerebral ventricles and in those in the subarachnoidal space. Double immunohistochemical staining revealed that these cyclooxygenase-2-positive cells were mostly endothelial cells. The time course of fever and that of cyclooxygenase-2 induction in the endothelial cells were in parallel. Cyclooxygenase-2 mRNA in a certain type of telencephalic neurons was also upregulated by the intracerebroventricular administration, but this neuronal response occurred both in vehicle-injected rats and in lipopolysaccharide-injected ones to the same extent. Therefore, the neuronal response was not essential to the development of fever. These results suggest that brain endothelial cells play a crucial role in the development of fever during brain inflammation by activating their arachidonic acid cascade.

Upregulation of COX-2 and CGRP expression in resident cells of the Borna disease virus-infected brain is dependent upon inflammation

Infection of immunocompetent adult rats with Borna disease virus (BDV) causes severe encephalitis and neural dysfunction. The expression of COX-2 and CGRP, genes previously shown to be implicated in CNS disease and peripheral inflammation, was dramatically upregulated in the cortical neurons of acutely BDV-infected rats. Neuronal COX-2 and CGRP upregulation was predominantly seen in brain areas where ED1-positive macrophages/microglia accumulated. In addition, COX-2 expression was strongly induced in brain endothelial cells and the number of COX-2 immunoreactive microglial cells was increased. In contrast, despite increased expression of viral antigens, neither COX-2 nor CGRP expression was altered in the CNS of BDV-infected rats treated with dexamethasone, or tolerant to BDV. Thus, increased CGRP and COX-2 expression in the BDV-infected brain is the result of the inflammatory response and likely to be involved in the pathogenesis of virus-induced encephalitis.

Regulation of the hypothalamic-pituitary-adrenal axis by cytokines: actions and mechanisms of action

Glucocorticoids are hormone products of the adrenal gland, which have long been recognized to have a profound impact on immunologic processes. The communication between immune and neuroendocrine systems is, however, bidirectional. The endocrine and immune systems share a common "chemical language," with both systems possessing ligands and receptors of "classical" hormones and immunoregulatory mediators. Studies in the early to mid 1980s demonstrated that monocyte-derived or recombinant interleukin-1 (IL-1) causes secretion of hormones of the hypothalamic-pituitary-adrenal (HPA) axis, establishing that immunoregulators, known as cytokines, play a pivotal role in this bidirectional communication between the immune and neuroendocrine systems. The subsequent 10-15 years have witnessed demonstrations that numerous members of several cytokine families increase the secretory activity of the HPA axis. Because this neuroendocrine action of cytokines is mediated primarily at the level of the central nervous system, studies investigating the mechanisms of HPA activation produced by cytokines take on a more broad significance, with findings relevant to the more fundamental question of how cytokines signal the brain. This article reviews published findings that have documented which cytokines have been shown to influence hormone secretion from the HPA axis, determined under what physiological/pathophysiological circumstances endogenous cytokines regulate HPA axis activity, established the possible sites of cytokine action on HPA axis hormone secretion, and identified the potential neuroanatomic and pharmacological mechanisms by which cytokines signal the neuroendocrine hypothalamus.