What roles does the organum vasculosum laminae terminalis play in fever in rabbits?

Control of the Cutaneous Circulation by the Central Nervous System

The central nervous system (CNS), via its control of sympathetic outflow, regulates blood flow to the acral cutaneous beds (containing arteriovenous anastomoses) as part of the homeostatic thermoregulatory process, as part of the febrile response, and as part of cognitive-emotional processes associated with purposeful interactions with the external environment, including those initiated by salient or threatening events (we go pale with fright). Inputs to the CNS for the thermoregulatory process include cutaneous sensory neurons, and neurons in the preoptic area sensitive to the temperature of the blood in the internal carotid artery. Inputs for cognitive-emotional control from the exteroceptive sense organs (touch, vision, sound, smell, etc.) are integrated in forebrain centers including the amygdala. Psychoactive drugs have major effects on the acral cutaneous circulation. Interoceptors, chemoreceptors more than baroreceptors, also influence cutaneous sympathetic outflow. A major advance has been the discovery of a lower brainstem control center in the rostral medullary raphé, regulating outflow to both brown adipose tissue (BAT) and to the acral cutaneous beds. Neurons in the medullary raphé, via their descending axonal projections, increase the discharge of spinal sympathetic preganglionic neurons controlling the cutaneous vasculature, utilizing glutamate, and serotonin as neurotransmitters. Present evidence suggests that both thermoregulatory and cognitive-emotional control of the cutaneous beds from preoptic, hypothalamic, and forebrain centers is channeled via the medullary raphé. Future studies will no doubt further unravel the details of neurotransmitter pathways connecting these rostral control centers with the medullary raphé, and those operative within the raphé itself. © 2016 American Physiological Society. Compr Physiol 6:1161-1197, 2016.

Spatiotemporal nuclear factor interleukin-6 expression in the rat brain during lipopolysaccharide-induced fever is linked to sustained hypothalamic inflammatory target gene induction

Rats injected with lipopolysaccharide (LPS) show brain-controlled sickness symptoms, including fever. In these animals, early genomic activation of brain cells was previously monitored by immunohistochemical detection of transcription factors such as nuclear factor (NF)-κB or signal transducer and activator of transcription (STAT)3 and was linked to the initiation or maintenance of the febrile response. To investigate whether NF-IL6 might be another important transcription factor implicated in this kind of immune-to-brain signaling, rats were injected with LPS (100 μg/kg, intraperitoneally) or phosphate-buffered saline, and brains were analyzed by immunohistochemistry, real-time PCR, or Western blot 4, 6, 8, and 10 hours later. Moderate to strong LPS-induced nuclear NF-IL6 immunoreactivity (IR) occurred in a time-dependent manner within circumventricular organs, namely, the vascular organ of the lamina terminalis, the subfornical organ, the area postrema, and the median eminence, brain structures with a leaky blood-brain barrier. Furthermore, nuclear NF-IL6-IR was observed in the pituitary gland, the choroid plexus, and the meninges as well as blood vessels throughout the entire brain. Endothelial, microglial, and ependymal cells, astrocytes, perivascular macrophages, and neurons exhibited LPS-induced nuclear NF-IL6-IR; mRNA levels of NF-IL6, responsive inflammatory genes, and NF-IL6 protein levels were significantly elevated. As opposed to observations on STAT3 or NFκB, the percentage of NF-IL6-reactive cells increased in parallel to late phases of the febrile response. In conclusion, these results suggest a potential role for NF-IL6 in the maintenance or possibly the termination of LPS-induced fever. Moreover, we propose NF-IL6 to be a delayed brain cell activation marker.

Blood-brain barrier (BBB) disruption using a diagnostic ultrasound scanner and Definity in Mice

The objective of this work was to determine whether diagnostic ultrasound and contrast agent could be used to transcranially and nondestructively disrupt the blood-brain barrier (BBB) in mice under ultrasound image guidance and to quantify that disruption using magnetic resonance imaging (MRI) and magnetic resonance (MR) contrast agent. Each mouse was placed under isoflurane anesthesia and the hair on top of its skull was removed before treatment. A diagnostic ultrasound transducer was placed in a water bag coupled with gel on the mouse skull. Definity (ultrasound [US] contrast) and Magnevist (MR contrast) were injected concurrent with the start of a custom ultrasound transmission sequence. The transducer was translated along the rostral-caudal axis to insonify three spatial locations (2mm apart) along one half of the brain for each sequence. T1-weighted MR images were used to quantify the volume of tissue over which the BBB disruption allowed Magnevist to enter the brain, based upon increases in MR contrast-to-noise ratio (CNR) compared with the noninsonified portions of the brain. Ultrasonic frequency, pressure and pulse duration, as well as Definity dose and injection time were varied. Preliminary results suggest that a threshold exists for BBB opening dependent upon both pressure and pulse duration (consistent with reports in the literature performed at lower frequencies). A range of typical diagnostic frequencies (e.g., 5.0-8.0 MHz) generated BBB disruption. Comparable BBB opening was noted with varied delays between Definity injection and insonification (0-2 min) for a range of Definity concentrations (400-2400 microL/kg). The low-pressure, custom sequences (mechanical index [MI]< or =0.65) had minimal blood cell extravasation as determined by histologic evaluation. This study has shown the ability of a diagnostic ultrasound system, in conjunction with Definity, to open the BBB transcranially in a mouse model for molecules approximately 0.5 kDa in size. Opening was achieved at higher frequencies than previously reported and was localized under ultrasound image guidance. A typical, ultrasound imaging mode (pulsed wave [PW] Doppler) with specific settings (transmit frequency=5.7 MHz, gate size=15 mm, pulse repetition frequency=100 Hz, system power=15%) successfully opened the BBB, which facilitates implementation using the most of commercially available clinical diagnostic scanners. Localized opening of the BBB may have potential clinical utility for the delivery of diagnostic or therapeutic agents to the brain.

Prostaglandins and sickness behavior: old story, new insights

Previous evidence has shown that prostaglandins play a key role in the development of sickness behavior observed during inflammatory states. In particular, prostaglandin E2 (PGE2) is produced in the brain by a variety of inflammatory signals such as endotoxins or cytokines. Its injection has been also shown to induce symptoms of sickness behavior. The role of cyclooxygenase enzymes (COX), the rate-limiting enzymes converting arachidonic acid into prostaglandins, in sickness behavior has been extensively studied, and it has been demonstrated that strategies aiming at inhibiting these enzymes limit anorexia, body weight loss and fever in animals with inflammatory diseases. However, inhibiting COX activity may lead to negative gastric or cardiovascular effects, since COX enzymes play a role in the synthesis of others prostanoids with various and sometimes contrasting properties. Recently, prostaglandin E synthases (PGES), which specifically catalyze the final step of PGE2 biosynthesis, were characterized. Among these enzymes, the microsomal prostaglandin E synthase-1 (mPGES-1) was of a particular interest since it was shown to be up-regulated by inflammatory signals in a variety of cell types. Moreover, mPGES-1 was shown to be crucial for correct immune-to-brain communication and induction of fever and anorexia by pro-inflammatory agents. This review takes stock of previous knowledge and recent advances in understanding the role of prostaglandins and of their specific synthesizing enzymes in the molecular mechanisms underlying sickness behavior. The review concludes with a short summary of key questions that remain to be addressed and points out therapeutic developments in this research field.

Sensory circumventricular organs: central roles in integrated autonomic regulation

Circumventricular organs (CVO) play a critical role as transducers of information between the blood, neurons and the cerebral spinal fluid (CSF). They permit both the release and sensing of hormones without disrupting the blood-brain barrier (BBB) and as a consequence of such abilities the CVOs are now well established to have essential regulatory actions in diverse physiological functions. The sensory CVOs are essential signal transducers located at the blood-brain interface regulating autonomic function. They have a proven role in the control of cardiovascular function and body fluid regulation, and have significant involvement in central immune response, feeding behavior and reproduction, the extent of which is still to be determined. This review will attempt to summarize the research on these topics to date. The complexities associated with sensory CVO exploration are intense, but should continue to result in valuable contributions to our understanding of brain function.

Nuclear translocation of the transcription factor STAT3 in the guinea pig brain during systemic or localized inflammation

The purpose of the present study was to investigate a possible lipopolysaccharide (LPS)-induced activation of brain cells that is mediated by the pleiotropic cytokine interleukin-6 (IL-6) and its transcription factor STAT3 during systemic or localized inflammation. In guinea pigs, intra-arterial (i.a., 10 microg x kg(-1)) or intraperitoneal (i.p., 30 microg x kg(-1)) injections of bacterial LPS cause a systemic inflammatory response which is accompanied by a robust fever. A febrile response can also be induced by administration of LPS into artificial subcutaneously implanted Teflon chambers (s.c. 100 or 10 microg x kg(-1)), which reflects an experimental model that mimics local tissue inflammation. Baseline plasma levels of bioactive IL-6 determined 60 min prior to injections of LPS or vehicle amounted to 35-80 international units (i.u.) ml(-1). Within 90 min of LPS injection, plasma IL-6 rose about 1000-fold in the groups injected i.a. or i.p., about 50-fold in the group injected s.c. with 100 microg x kg(-1) LPS, and only 5-fold in guinea pigs injected with the lower dose of LPS (10 microg x kg(-1)). At this time point, a distinct nuclear translocation pattern of the transcription factor STAT3 became evident in several brain structures. Amongst those, the sensory circumventricular organs known to lack a tight blood-brain barrier such as the area postrema, the vascular organ of the lamina terminalis and the subfornical organ, as well as the hypothalamic supraoptic nucleus showed intense nuclear STAT3 signals in the i.a. or i.p. injected groups. In contrast a moderate (s.c. group, 100 microg x kg(-1)), or even no (s.c. group, 10 microg x kg(-1)), nuclear STAT3 translocation occurred in response to s.c. injections of LPS. These results suggest that STAT3-mediated genomic activation of target gene transcription in brain cells occurred only in those cases in which sufficiently high concentrations of circulating IL-6 were formed during systemic (i.a. and i.p. groups) or localized (s.c. group, 100 microg x kg(-1)) inflammation.

Antipyretic effect of acetaminophen by inhibition of glutamate release after staphylococcal enterotoxin A fever in rabbits

The present study was designed to determine whether the inhibition of glutamate release in organum vasculosum laminae terminalis (OVLT) of rabbit brain by acetaminophen might be protective in a whole-animal model of staphylococcal enterotoxin A (SEA) fever. Unanesthetized rabbits were administered intravenously with SEA, and both colonic temperature (Tco) and glutamate release in OVLT were measured simultaneously. The glutamate release in OVLT was measured with a microdialysis probe previously implanted. Both the Tco and glutamate release in OVLT were simultaneously increased following intravenous administration of SEA. The SEA-induced rise in both the Tco and the levels of glutamate release in OVLT were suppressed by pretreatment with intravenous injection of acetaminophen (1, 5 or 10 mg/kg). Furthermore, treatment of OVLT with acetaminophen (50-150 microg) attenuated the fever-like hyperthermia induced by intra-OVLT injection of glutamate. Our results show acetaminophen may reduce glutamate release in OVLT and result in antipyresis.

Cyclooxygenase Inhibitors Attenuate Augmented Glutamate Release in Organum Vasculosum Laminae Terminalis and Fever Induced by Staphylococcal Enterotoxin A

Both the hyperthermia and augmented glutamate release in the organum vasculosum laminae terminalis (OVLT) after an intravenous dose (30 ng/kg) of staphylococcal enterotoxin A (SEA) were significantly reduced by pretreatment with intravenous administration of cyclooxygenase inhibitors such as aspirin (1 - 10 mg/kg), sodium salicylate (1 - 10 mg/kg), or diclofenac (10 mg/kg). Intra-OVLT administration of 50 - 200 microg in 1.0 microl of either aspirin or sodium salicylate 60 min before or 120 min after an intra-OVLT dose (50 microg in 1.0 microl) of glutamate also significantly suppressed the glutamate-induced hyperthermia. These findings suggest that inhibition of cyclooxygenase receptor mechanisms suppresses SEA fever by inhibition of glutamate release in the OVLT of rabbit brain.

The organum vasculosum laminae terminalis in immune-to-brain febrigenic signaling: a reappraisal of lesion experiments

The organum vasculosum laminae terminalis (OVLT) has been proposed to serve as the interface for blood-to-brain febrigenic signaling, because ablation of this structure affects the febrile response. However, lesioning the OVLT causes many "side effects" not fully accounted for in the fever literature. By placing OVLT-lesioned rats on intensive rehydration therapy, we attempted to prevent these side effects and to evaluate the febrile response in their absence. After the OVLT of Sprague-Dawley rats was lesioned electrolytically, the rats were given access to 5% sucrose for 1 wk to stimulate drinking. Sucrose consumption and body mass were monitored. The animals were examined twice a day for signs of dehydration and treated with isotonic saline (50 ml/kg sc) when indicated. This protocol eliminated mortality but not several acute and chronic side effects stemming from the lesion. The acute effects included adipsia and gross (14% of body weight) emaciation; chronic effects included hypernatremia, hyperosmolality, a suppressed drinking response to hypertonic saline, and previously unrecognized marked (by approximately 2 degrees C) and long-lasting (>3 wk) hyperthermia. Because the hyperthermia was not accompanied by tail skin vasoconstriction, it likely reflected increased thermogenesis. After the rats recovered from the acute (but not chronic) side effects, their febrile response to IL-1beta (500 ng/kg iv) was tested. The sham-operated rats developed typical monophasic fevers ( approximately 0.5 degrees C), the lesioned rats did not. However, the absence of the febrile response in the OVLT-lesioned rats likely resulted from the untreatable side effects. For example, hyperthermia at the time of pyrogen injection was high enough (39-40 degrees C) to solely prevent fever from developing. Hence, the changed febrile responsiveness of OVLT-lesioned animals is given an alternative interpretation, unrelated to febrigenic signaling to the brain.

Selected contribution: role of IL-6 in LPS-induced nuclear STAT3 translocation in sensory circumventricular organs during fever in rats

Interleukin-6 (IL-6) is regarded as an endogenous mediator of lipopolysaccharide (LPS)-induced fever. IL-6 is thought to act on the brain at sites that lack a blood-brain barrier, the circumventricular organs (CVOs). Cells that are activated by IL-6 respond with nuclear translocation of the signal transducer and activator of transcription 3 molecule (STAT3) and can be detected by immunohistochemistry. We investigated whether the LPS-induced release of IL-6 into the systemic circulation was accompanied by a nuclear STAT3 translocation within the sensory CVOs. Treatment with LPS (100 microg/kg) led to a slight (1 h) and then a strong increase (2-8 h) in plasma IL-6 levels, which started to decline at the end of the febrile response. Administration of both pyrogens LPS and IL-6 (45 microg/kg) induced a febrile response with IL-6, causing a rather moderate fever compared with the LPS-induced fever. Nuclear STAT3 translocation in response to LPS was observed within the vascular organ of the lamina terminalis (OVLT) and the subfornical organ (SFO) 2 h after LPS treatment. To investigate whether this effect was mediated by IL-6, the cytokine itself was systemically applied and indeed an identical pattern of nuclear STAT3 translocation was observed. However, nuclear STAT3 translocation already occurred 1 h after IL-6 application and proved to be less effective compared with LPS treatment when analyzing OVLT and SFO cell numbers that showed nuclear STAT3 immunoreactivity after the respective pyrogen treatment. Our observations represent the first molecular evidence for an IL-6-induced STAT3-mediated genomic activation of OVLT and SFO cells and support the proposed role of these brain areas as sensory structures for humoral signals created by the activated immune system and resulting in the generation of fever.

Involvement of brain glutamate release in pyrogenic fever

Whether the glutamate release in the organum vasculosum laminae terminalis (OVLT) is attributable to genesis of a pyrogenic fever is unclear. The lack of information led us to evaluate the changes in glutamate concentrations of OVLT during the fever induced by staphylococcal enterotoxin A (SEA) in unanesthetized rabbits. Both the OVLT concentrations of glutamate and the colonic temperatures were simultaneously monitored during systemic injection of SEA, MK801 (an N-methyl-D-aspartate (NMDA) receptor channel blocker), ketamine (an NMDA receptor channel blocker), or normal saline. The extracellular dialysates in the brain were collected using a microdialysis probe previously placed in the OVLT region. The concentrations of glutamate in the microdialysates were measured by a high-pressure liquid chromatography in combination with a fluorescence detector. Systemic administration of SEA (30 ng x kg(-1) I.V.) increased both the concentrations of glutamate in the OVLT and the colonic temperatures. Glutamate appeared to rise slightly earlier than body temperature. Pretreatment or posttreatment with MK801 or ketamine significantly attenuated the SEA-induced augmenting glutamate release in the OVLT and fever in rabbits. The suppression of glutamate release appeared to start slightly earlier than temperature decline. In addition, the SEA-induced fever could be mimicked by direct injection of glutamate or SEA into the OVLT area. The fever induced by intra-OVLT injection of SEA or glutamate was significantly attenuated by pretreatment with an intra-OVLT dose of MK801 (5 microg) or ketamine (10 microg). The results suggest that glutamatergic pathways in the OVLT region are in pyrogenic fever genesis.

Involvement of tyrosine kinase in the pyrogenic fever exerted by NOS pathways in organum vasculosum laminae terminalis

Nitric oxide synthase (NOS) is an enzyme which has a distinct cytokine-inducible isoform (iNOS). Many cytokine receptors have an intracellular tyrosine kinase domain. Here we have used two tyrosine kinase inhibitors (genistein and lavendustin A) to investigate the potential role of tyrosine kinase activation in the induction on both iNOS and fever caused by lipopolysaccharide (LPS) in rabbits. Direct administration of LPS into the organum vasculosum laminae terminalis (OVLT) increased iNOS expression. These increases paralleled the increase in deep body temperature in unanesthetized rabbits. Pretreatment with genistein or lavendustin A not only reduced the fever but also attenuated the iNOS expression in the OVLT following an intra-OVLT dose of LPS. These results suggest that tyrosine phosphorylation is part of the signal transduction mechanism that mediates the induction of both iNOS and fever elicited by LPS in the OVLT of rabbit brain.

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

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

Prostaglandin E2 in the pathogenesis of fever. An update

Prostaglandin E2 (PGE2) is recognized as a key intermediate in the sequence of events leading to fever. Normally undetectable or barely detectable in brain, it rises selectively on exposure to an infectious noxa and the attendant generation of pyrogenic cytokines outside and, in the case of interleukin (IL)-6, inside the brain. The mechanism by which pyrogens in the circulation promote the appearance of PGE2 within the confines of brain is not clear, and it is not known how PGE2 activation is selective with IL-6 being induced in brain. We have found that the cerebral microvasculature is not suitable as a source of PGE2 in response to blood-borne pyrogens. In addition, we show that IL-6 differs from other pyrogens in being able to stimulate specifically PGE2 synthesis. Nevertheless, brain-derived IL-6 does not appear to be necessary for PGE2 activation and the attendant fever. We conclude that signal-transducing mechanisms operating across the blood-brain barrier are most critical for the development of the febrile response to a systemic noxa.

Mechanisms and sites of pyrogenic action exerted by staphylococcal enterotoxin A in rabbits

The febrile responses induced by i.v. administrations of staphylococcal enterotoxin A (SEA) was mimicked by direct injection of SEA into the organum vasculosum laminae terminalis (OVLT) in unanesthetized rabbits. Compared with the febrile responses induced by i.v. injection of SEA, the OVLT route of injection required a much lower dose of SEA to produce a similar fever. Furthermore, the fever induced by intra-OVLT or i.v. injection of SEA was significantly attenuated by pretreatment with intra-OVLT injection of anisomycin (a protein synthesis inhibitor), indomethacin or diclofenac (inhibitors of cyclo-oxygenase (COX)), and aminoguanidine or dexamethasone (inhibitors of inducible nitric oxide synthase (iNOS)). These results suggest that COX or iNOS pathway in the OVLT mediate the SEA-induced fever in rabbits.

Dexamethasone administered into organum vasculosum laminae terminalis of rabbits induced antipyresis via inhibiting nitric oxide pathway in situ

Direct administration of lipopolysaccharide (LPS) into the organum vasculosum laminae terminalis (OVLT) increased the amount of nitric oxide (NO) release and inducible NO synthase expression. These increases paralleled the increase in deep body temperature in unanesthetized rabbits. Pretreatment with dexamethasone, a synthetic glucocorticoid, not only reduced the fever but also attenuated the NO release and the inducible NO synthase expression in the OVLT following an intra-OVLT dose of LPS. The data suggest that steroids such as dexamethasone exert their antipyresis by inhibiting the NO pathway in the OVLT of rabbit brain.

Anteroventral third ventricle lesion suppresses fever, but not stress-induced hyperthermia in rats

Body core temperature (Tco) of unrestrained rats was monitored to compare the effects of electrolytic lesion of the anteroventral third ventricle (AV3V) region on stress-induced hyperthermia or lipopolysaccharide (LPS)-induced fever. We found that stress-induced hyperthermia was not significantly reduced by AV3V lesion, whereas pyrogen-induced fever was significantly lower in rats in which the lesion completely ablated the organum vasculosum laminae terminalis (OVLT), located in the AV3V region. The results indicate that although the central neural elements producing both stress- and pyrogen-induced elevations in Tco may be prostaglandin related, stress hyperthermia is not activated by mechanisms in the OVLT region, as is fever induced by LPS.

Differential responsiveness of obese (fa/fa) and lean (Fa/Fa) Zucker rats to cytokine-induced anorexia

Pathophysiological and pharmacological concentrations of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) in the cerebrospinal fluid (CSF) induce anorexia in normal rats. Obesity in humans and rodents is associated with increased TNF-alpha messenger RNA and protein levels in various cell types. This suggests that obese individuals may have differential regulation of cytokine production and dissimilar responsiveness to cytokines. In the present study, we investigated the effects of the intracerebroventricular (ICV) microinfusion of TNF-alpha (50, 100, and 500 ng/rat), IL-1 beta (1.0, 4.0, and 8.0 ng), and TNF-alpha (100 ng) plus IL-1 beta (1.0 ng) on obese (fa/fa) and lean (Fa/Fa) Zucker rats. The results show that: TNF-alpha and IL-1 beta, and the concomitant administration of TNF-alpha and IL-1 beta decreased the short-term (4 hours), nighttime (12 hours), and total daily food intakes in obese and lean rats; IL-1 beta was more potent relative to TNF-alpha; obese rats showed greater responsiveness to IL-1 beta: 8.0 ng IL-1 beta, for example, decreased the 12-hour food intake by 52% in obese and 22% in lean rats. On the other hand, obese and lean rats did not exhibit a significantly different responsiveness to the anorexia induced by 50, 100, or 500 ng TNF-alpha at the 4-hour period; and the concomitant ICV administration of TNF-alpha and IL-1 beta induced anorexia with additive (4-hour period) or synergistic (12-hour and 24-hour periods) effects in obese rats. The effect of TNF-alpha plus IL-1 beta in lean rats was greater than additive for the 12-hour and 24-hour periods. The difference in suppression of total daily food intake by TNF-alpha plus IL-1 beta in obese (-43%) versus lean (-23%) rats was significantly different (p < 0.01). The results show that obese (fa/fa) and lean (Fa/Fa) Zucker rats have differential responsiveness to the ICV microinfusion of two different classes of cytokines.

Endothelial cells of the rat brain vasculature express cyclooxygenase-2 mRNA in response to systemic interleukin-1 beta: a possible site of prostaglandin synthesis responsible for fever

We previously showed that intraperitoneal injection of lipopolysaccharide induced cyclooxygenase-2 (COX-2) mRNA in as yet unidentified cells of blood vessels and leptomeninges in the rat brain and proposed a possible role of these cells as the source of prostaglandin E2 in the genesis of fever (Cao et al., Brain Res., 697 (1995) 187-196). In the present study, to proceed further with this line of research, we addressed the following two questions: first, does a pyrogenic dose of interleukin-1 beta (IL-1 beta), an endogenous pyrogen, induce COX-2 mRNA in the brain blood vessels and leptomeninges? Secondly, if it does, what type of cells are positive for COX-2 mRNA? Intraperitoneal injection of recombinant human IL-1 beta (30 micrograms/kg) induced fever in rats and an in situ hybridization study revealed that faint but significant COX-2 mRNA signals appeared in the blood vessels and leptomeninges at 1.5 h after the injection (the early rising phase of fever). The mRNA signals increased in number and intensity at 4 h (early plateau phase), decreased at 6.5 h (early recovery phase), and completely disappeared by 10 h after the injection (late recovery phase). The COX-2 mRNA positive cells in the blood vessels were likely to be the endothelial cells since the corresponding cells in the adjacent mirror-imaged section also expressed mRNAs for intracellular adhesion molecule-1 and the type-I interleukin-1 receptor, although those in the leptomeninges still remained unidentified. These results imply that circulating IL-1 beta acts on its receptor on the endothelial cells of the brain vasculature to induce COX-2 mRNA, which is possibly responsible for the elevated level of PGE2 seen during fever.

Nitric oxide synthase-cyclo-oxygenase pathways in organum vasculosum laminae terminalis: possible role in pyrogenic fever in rabbits

1. Fever was induced in rabbits by administration of Escherichia coli endotoxin (lipopolysaccharide; LPS; 0.001-10 micrograms) into the organum vasculosum laminae terminalis (OVLT). Deep body temperature was evaluated over a period of 7 h. 2. The LPS-induced febrile response was mimicked by intra-OVLT injection of the nitric oxide (NO) donors, S-nitroso-acetylpenicillamine (SNAP, 1-10 micrograms), sodium nitroprusside (SNP, 50 micrograms), or hydroxylamine (10 micrograms), the cyclic GMP analogue 8-bromo-cyclic GMP (8-Br-cyclic GMP, 10-100 micrograms), or prostaglandin E2 (PGE2, 0.2 micrograms). 3. Dexamethasone (Dex, a potent inhibitor of the transcription of inducible NO synthase, iNOS, 10 micrograms), anisomycin (a protein synthesis inhibitor, 100 micrograms), L-N5-(1-iminoethyl)ornithine (L-NIO; an irreversible NOS inhibitor, 10-200 micrograms), aminoguanidine (a specific iNOS inhibitor, 1000 micrograms), or NG-methyl-L-arginine acetate (L-NMMA, a NOS inhibitor, 100 micrograms) inhibited fever induced by LPS when injected into the OVLT 1 h before LPS injection. An intra-OVLT dose of 1000 micrograms of NG-nitro-L-arginine methyl ester (L-NAME, a potent inhibitor of constitutive NOS) did not exhibit antipyretic effects. 4. Methylene blue (an inhibitor of NOS and soluble guanylate cyclase, 1-10 micrograms), 6-(phenylamino)-5,8-quinolinedione (LY-83583; an inhibitor of soluble guanylate cyclase and NO release, 20 micrograms), or indomethacin (an inhibitor of cyclo-oxygenase, COX, 400 micrograms) inhibited fever induced by LPS when injected into the OVLT 1 h before LPS injection. Pretreatment with methylene blue or haemoglobin (a NO scavenger, 100 micrograms) attenuated the fever induced by intra-OVLT injection of SNAP. 5. The PGE2-induced fever was potentiated, rather then attenuated, by pretreatment with an intra-OVLT dose of animoguanidine (1000 micrograms), L-NMMA (100 micrograms) or L-NIO (200 micrograms). 6. These results suggest that iNOS-COX pathways in the OVLT represent an important mechanism for modulation of pyrogenic fever in rabbits.

Inhibition of nitric oxide synthase or cyclo-oxygenase pathways in organum vasculosum laminae terminalis attenuates interleukin-1 beta fever in rabbits

Fever was induced in rabbits by i.v. administration of lipopolysaccharide (LPS) or administration of interleukin-1 beta (IL-1 beta) into the organum vasculosum laminae terminalis (OVLT). Intra-OVLT injection of IL-1 receptor antagonist (IL-lra), 1 h before LPS or IL-1 beta injection, inhibited the LPS- or IL-1 beta-induced fever. Dexamethasone (a potent inhibitor of the transcription of inducible nitric oxide synthase, iNOS), L-N5-(1-iminoethyl)ornithine (an irreversible NOS inhibitor), aminoguanidine (a specific iNOS inhibitor), or indomethacin (an inhibitor of cyclo-oxygenase, COX) also inhibited IL-1 beta-induced fever when injected into the OVLT 1 h before IL-1 beta injection. These results suggest that iNOS or COX pathways in the OVLT mediate the IL-1 beta-induced fever in rabbits.

Molecular characterization of the mouse prostanoid EP1 receptor gene

A partial cDNA, corresponding to the mouse prostaglandin E2 receptor subtype EP1, was isolated from mouse brain cDNA using a degenerate primer PCR strategy. Using the cDNA fragment as a probe, the EP1 receptor gene was isolated and characterized. The gene consists of three exons, of which the first is non-coding, and is contained within a 3.5-kb region. The coding nucleotide sequence determined is identical to that of the published mouse EP1 cDNA. The positions of the introns correspond to those of the thromboxane A2 and prostaglandin D receptor genes. No alternative splicing of the EP1 receptor gene could be detected. PCR and specific primers designed from the genomic sequence were used to amplify the coding part of the isolated gene from kidney cDNA. The cDNA obtained was cloned into a eukaryotic expression vector, and stably transfected Chinese hamster ovary cell lines were established. The cells respond to prostaglandin E2 with intracellular Ca2+ mobilization, as expected for this prostanoid receptor subtype. In situ hybridization was used to localize the EP1 receptor transcript in different mouse tissues. Significant hybridization was detected only in the collecting ducts of the kidney, and in the paraventricular and supraoptic nuclei of the hypothalamus. The expression of the EP1 receptor in the hypothalamus suggests that this prostanoid receptor is involved in mediating the fever response evoked by prostaglandin E2.