Peripheral Administration Of Lipopolysaccharide Research Articles

Peripheral lipopolysaccharide administration transiently affects expression of brain-derived neurotrophic factor, corticotropin and proopiomelanocortin in mouse brain

Peripheral inflammation induced by intraperitoneal (i.p.) injection of Lipopolysaccharide (LPS) is known to cause functional impairments in the brain affecting memory and learning. One of mechanisms may be the interference with neurotrophin (NT) expression and function. In the current study we administered a single, high dose of LPS (3mg/kg, i.p.) into mice and investigated changes in brain-derived neurotrophic factor (BDNF) gene expression within 1-6 days after LPS injection. Crude synaptosomes were isolated from brain tissue and subjected to Western-blot analyses. We found transient reductions in synaptosomal proBDNF- and BDNF protein expression, with a maximal decrease at day 3 as compared to saline injected controls. The time course of reduction of BDNF mRNA in whole brain extracts parallels the decrease in protein levels in synaptosomes. LPS effects in the central nervous system (CNS) are known to crucially involve the activation of the hypothalamic-pituitary-adrenal (HPA) axis. We analysed the time course of corticotropin releasing hormone (CRH)- and proopiomelanocortin (POMC) mRNA expression. As observed for BDNF-, CRH- and POMC mRNA levels are also significantly reduced on day 3 indicating a comparable time course. These results suggest that peripheral inflammation causes a reduction of trophic supply in the brain, including BDNF at synaptic sites. The mechanisms involved could be a negative feedback of the activated HPA axis.

Effects of interleukin-1β and lipopolysaccharide on behavior of mice in the elevated plus-maze and open field tests

It has been postulated that infections, inflammatory processes and resulting cytokines may be causative factors in emotional disorders, including depression and anxiety. Support for this possibility has been sought in studies of animal behavior following administration of interleukin-1 (IL-1) and lipopolysaccharide (LPS). However, such treatments induce a variety of behavioral responses, collectively known as sickness behavior, some of which could affect the performance in tests used to assess anxiety and depression. Thus the effects of peripheral administration of IL-1β and LPS on the behavior of mice were studied in the elevated plus-maze (EPM) and the open field (OF). Mouse IL-1β (30, 100, 300, and 1000 ng) was injected intraperitoneally 30 or 60 min, and LPS (0.5, 1 and 5 μg) 120 min before the tests. IL-1β and LPS induced dose-dependent decreases in open arm entries and the time spent on the open arms in the EPM, effects considered to reflect anxiety-like behavior. However, entries to all arms were also reduced in a dose-dependent manner, indicating a decrease in general activity. In the OF, IL-1β and LPS decreased the number of line crossings in the center of the field, that can also be considered to reflect anxiety-like behavior. However, this effect was accompanied by a similar decrease in line crossings in the periphery, as well as in rears and climbs. Thus the doses of IL-1β and LPS necessary to induce these effects also decreased locomotor activity in the EPM and OF. Therefore, the behavioral responses induced by IL-1β and LPS in the EPM and the OF considered to reflect anxiety must be interpreted in the light of this reduction in overall activity. Thus the results do not provide unequivocal support for the suggestion that LPS or IL-1 mediate anxiety. Nevertheless, because infections, endotoxins, and the ensuing cytokines cause alterations in CNS norepinephrine and serotonin, they may contribute to emotionality, and perhaps to anxiety.

Pharmacological, but not genetic, disruptions in 5-HT 2C receptor function attenuate LPS anorexia in mice

Peripheral administration of bacterial lipopolysaccharide (LPS) elicits anorexia in several species, including rats and mice. There is strong evidence that antagonism of serotonergic activity at 2C receptors (5-HT 2CR) attenuates LPS anorexia in rats. Here we used pharmacological and genetic approaches to examine the role of the 5-HT 2CR in LPS anorexia in mice. In Experiment 1, SB 242084, a potent and selective 5-HT 2C antagonist (0.3 mg/kg) was injected intraperitoneally 15 min before intraperitoneal LPS (2 μg/kg) injections just prior to dark onset in c57BL/6 mice. Food intake was recorded 1, 2 and 4 h after LPS administration. In Experiment 2, we recorded 2, 4 and 24 h food intake following dark onset intraperitoneal LPS (0.125, 0.25, 0.5, 1 and 2 μg/kg) injections in mice with a genetic deletion of 5-HT 2CR and their WT controls. Our pharmacological results suggest that at least part of the anorexia following peripheral LPS administration is mediated by an increase in 5-HT-ergic activity at the 5-HT 2CR. Our genetic data, in contrast, suggest that 5-HT 2CR is not a necessary part of LPS anorexia.

Effect of peripherally administered lipopolysaccharide (LPS) on GTP cyclohydrolase I, tetrahydrobiopterin and norepinephrine in the locus coeruleus in mice

Lipopolysaccharide (LPS), an endotoxin released from the outer membranes of Gram-negative bacteria, triggers cells to synthesize and release inflammatory cytokines that may progress to septic shock in vivo. We found that LPS enhances tetrahydrobiopterin (BH4) biosynthesis by inducing the biosynthetic enzyme GTP cyclohydrolase I (GCH) in vitro in the mouse neuroblastoma cell line N1E-115. Furthermore, we observed that gene expression of GCH in the locus coeruleus (LC) in mice was enhanced by peripheral administration of LPS, resulting in increased concentrations of BH4, and norepinephrine, and its metabolite 4-hydroxy-3-methoxyphenylglycol (MHPG). These results suggest that tyrosine hydroxylase (TH) activity is increased by increased content of BH4 due to enhanced mRNA expression of GCH in the LC resulting in the increase in norepinephrine in the LC during endotoxemia. LPS in blood may act as a stressor to increase norepinephrine biosynthesis in the mouse LC.

Lipopolysaccharide impairs long-term potentiation and recognition memory and increases p75NTR expression in the rat dentate gyrus

The role of the neurotrophins, including nerve growth factor, in synaptic plasticity is well established. These proteins exert their effects via activation of Trk receptor tyrosine kinases and the p75 neurotrophin receptor (p75NTR). While Trk receptor activation is associated with functions such as cell survival, learning and enhancement of synaptic transmission, p75NTR can modulate long-term depression and has been reported to be a regulator of apoptosis. Peripheral administration of lipopolysaccharide (LPS) has been shown to exert a number of effects centrally, including inhibition of hippocampal synaptic plasticity. Here we report that LPS induces a blockade of long-term potentiation and recognition memory that is concomitant with increased expression of the p75NTR in dentate gyrus. In addition, LPS blocks plasticity-associated changes in nerve growth factor expression, TrkA activation and extracellular signal-regulated kinase activation. These data are consistent with the hypothesis that synaptic plasticity in the dentate gyrus is associated with changes in neurotrophin signaling and that the inhibition of these plastic changes by LPS may be due in part to its ability to impact on these signaling cascades.

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

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

Lipopolysaccharide has indomethacin-sensitive actions on Fos expression in topographically organized subpopulations of serotonergic neurons

Peripheral immune activation results in physiological and behavioral responses including changes in the level of behavioral arousal. One mechanism through which immune activation can influence these responses is via actions on brainstem neuromodulatory systems, including serotonergic systems. To investigate the effects of peripheral immune activation on serotonergic systems and behavior, and the potential role of prostanoids in mediating these effects, we compared the effects of intraperitoneal injections of lipopolysaccharide (LPS), in the presence or absence of the cyclooxygenase inhibitor indomethacin, on total plasma l-tryptophan concentrations, Fos expression in subdivisions of the brainstem raphe complex, and home cage behaviors. Peripheral LPS administration had no effect on total plasma l-tryptophan concentrations but increased Fos expression in serotonergic neurons selectively within the interfascicular (DRI) and ventrolateral (DRVL) subdivisions of the dorsal raphe nucleus 4 h following treatment; pretreatment with indomethacin blocked the LPS-induced increases in Fos expression within the DRI and DRVL. Peripheral LPS administration decreased measures of behavioral arousal including locomotion, rearing, climbing, and self-grooming; LPS administration had no effect on these behaviors in mice pretreated with indomethacin. The indomethacin-sensitive effects of LPS on Fos expression in the DRI may be due to selective activation of Type II serotonergic neurons which are largely restricted to the DRI region and have unique afferent regulatory mechanisms and behavioral correlates. Further studies of the effects of peripheral immune activation on DRI serotonergic systems may lead to a better understanding of the relationships among immune function, serotonergic systems, and behavior.

Regulation of expression of the novel IL‐1 receptor family members in the mouse brain

Members of the interleukin-1 (IL-1) family of cytokines are key mediators in the regulation of host defence responses and the development of inflammation in response to acute and chronic injury to the brain. Two major agonists, IL-1alpha and IL-1beta, bind to a membrane receptor complex composed of the type-1 IL-1 receptor (IL-1RI) and the accessory protein (IL-1RAcP). The discovery of new orphan members of the IL-1 receptor superfamily (including ST2/T1, IL-1Rrp2, TIGIRR1 and -2, SIGGIR, IL-18Ralpha and IL-18Rbeta) has increased speculation that alternative IL-1 ligands signalling pathways exist in the brain. We demonstrate here that all the IL-1R-like orphan receptors are expressed by many brain cell types including astrocytes, microglia, oligodendrocytic progenitor cells and neurons. IL-18Rbeta expression was significantly increased in response to treatment of mixed glia with bacterial lipopolysaccharide (LPS) in vitro, whereas expression of IL-1Rrp2 and TIGIRR1 was reduced. Furthermore, IL-18Rbeta, IL-1Rrp2, but not TIGIRR1 expression, was increased in the brain in vivo in response to peripheral administration of LPS or middle cerebral artery occlusion (MCA). These results suggest possible roles for newly identified members of the IL-1 receptor family in CNS diseases.

Systemic administration of lipopolysaccharide and interleukin-1β have different effects on memory consolidation

Sickness behaviour is an adaptive response to infection that includes lethargy, anorexia and of direct relevance to this work, learning and memory impairments. It has been suggested that proinflammatory cytokines may disrupt learning and memory by interfering with memory consolidation [C.R. Pugh, K. Kumagawa, M. Fleshner, L.R. Watkins, S.F. Maier, J.R. Rudy, Selective effects of peripheral lipopolysaccharide administration on contextual and auditory-cue fear conditioning, Brain Behav. Immun. 12 (1998) 212–229]. We tested whether systemic interleukin-1beta is sufficient to induce impairments in memory consolidation by comparing the effects of post-learning administration of interleukin-1beta with, the potent endotoxin, lipopolysaccharide; and saline, on retention of conditioned fear of a context. We administered an acute intraperitoneal injection of lipopolysaccharide, interleukin-1beta or saline immediately following a single conditioning episode in which rats received two tone-shock pairings. Two days following the learning episode, animals were tested for strength of conditioned responding to both the context and tone. Lipopolysaccharide-injected animals, but not interleukin-1beta-injected animals, exhibited less conditioned fear of context compared to saline-treated controls. All groups showed similar conditioned fear of tone. Our results suggest that systemic interleukin-1beta is not sufficient to disrupt memory consolidation, but rather, the synergistic actions of the proinflammatory cytokines released by lipopolysaccharide are required to disrupt memory consolidation.

#129 Learning impairments induced by peripheral lipopolysaccharide administration are dependent upon frequency, dose, and timing of administration

#129 Learning impairments induced by peripheral lipopolysaccharide administration are dependent upon frequency, dose, and timing of administration

Peripheral lipopolysaccharide administration impairs two-way active avoidance conditioning in C57BL/6J mice

Peripheral administration of lipopolysaccharide (LPS) or interleukin-1 (IL-1) may lead to alterations of CNS function and behavioral changes designated “sickness behavior.” Further, some experiments show evidence of LPS- and cytokine-mediated alterations in learning and memory. The current series of experiments examined the effects of a single or repeated intraperitoneal LPS injections, at a number of doses and time points before or after test sessions, on behavior in a two-way active avoidance conditioning paradigm. Subjects were able to avoid the mild shock stimulus, escape it, or fail to respond to it. Subjects treated with LPS at many, but not all, of the time points sampled showed impaired learning, by exhibiting significantly fewer avoidance responses than controls. Furthermore, an LPS-induced increase in non-cued inter-trial interval crossings was observed during the later days of testing, suggesting that a greater percentage of their avoidance responses was not conditioned and their behavior was less efficient. Taken together, the results suggest that LPS-treated animals showed a diminished association between conditioned stimulus (CS) and unconditioned stimulus (US). These results support the theory that peripheral immune stimuli may induce deleterious effects on learning, and extend the work to a negatively reinforced operant procedure.

Exaggerated neuroinflammation and sickness behavior in aged mice after activation of the peripheral innate immune system

Acute cognitive impairment (i.e., delirium) is common in elderly emergency department patients and frequently results from infections that are unrelated to the central nervous system. Since activation of the peripheral innate immune system induces brain microglia to produce inflammatory cytokines that are responsible for behavioral deficits, we investigated if aging exacerbated neuroinflammation and sickness behavior after peripheral injection of lipopolysaccharide (LPS). Microarray analysis revealed a transcriptional profile indicating the presence of primed or activated microglia and increased inflammation in the aged brain. Furthermore, aged mice had a unique gene expression profile in the brain after an intraperitoneal injection of LPS, and the LPS-induced elevation in the brain inflammatory cytokines and oxidative stress was both exaggerated and prolonged compared with adults. Aged mice were anorectic longer and lost more weight than adults after peripheral LPS administration. Moreover, reductions in both locomotor and social behavior remained 24 h later in aged mice, when adults had fully recovered, and the exaggerated neuroinflammatory response in aged mice was not reliably paralleled by increased circulating cytokines in the periphery. Taken together, these data establish that activation of the peripheral innate immune system leads to exacerbated neuroinflammation in the aged as compared with adult mice. This dysregulated link between the peripheral and central innate immune system is likely to be involved in the severe behavioral deficits that frequently occur in older adults with systemic infections.

Cyclooxygenase inhibition attenuates endotoxin-induced spatial learning deficits, but not an endotoxin-induced blockade of long-term potentiation

Peripheral administration of lipopolysaccharide (LPS), a potent bacterial endotoxin, can cause a variety of central effects, including production of cytokines and cyclooxygenases in the brain, as well as peripheral increases in corticosterone. These, in turn, may contribute to neuroimmune-induced neurocognitive deficits. We show here LPS causes deficits in hippocampal-dependent spatial learning in the water maze but that treatment with ibuprofen, a broad-spectrum cyclooxygenase inhibitor, reverses the deficits induced in spatial learning by LPS. We also show that LPS causes an impairment in the induction of long-term potentiation in the dentate gyrus in vivo, a major contemporary model of learning and memory. No differences were found in corticosterone levels in trunk blood but we find a decrease in brain-derived neurotrophic factor (BDNF) expression in LPS group compared to saline controls. Paradoxically compared to the behavioral findings treatment with ibuprofen does not attenuate the LPS-induced impairment in LTP or BDNF concentration in tetanized tissue.

Estradiol-mediated increases in the anorexia induced by intraperitoneal injection of bacterial lipopolysaccharide in female rats

Lipopolysaccharide (LPS) derived from the cell walls of gram-negative bacteria causes a robust acute phase response (APR) that includes fever, anorexia, and many other elements. Because immune system function, including some models of illness anorexia, is sexually differentiated, we investigated the sexual differentiation of the anorexia induced by intraperitoneal LPS injections in rats. Cycling female Long–Evans rats tested either during diestrus or estrus ate less following 6.25 μg/kg LPS than did intact males. Following 12.5 μg/kg LPS, females in estrus ate less than either females during diestrus or males. Similarly, a more pronounced anorexia occurred following 12.5, 25, and 50 μg/kg LPS in ovariectomized females that received cyclic estradiol treatment and were tested on the day modeling estrus than in untreated ovariectomized rats. LPS also increased the length of the rats' ovarian cycles, usually by a day, especially when injected during diestrus. As in male rats, when LPS injections were repeated in the same rats, both estradiol-treated and untreated rats failed to display any significant anorexia. The inhibitory effects of LPS on eating in intact and ovariectomized rats were expressed solely as decreases in spontaneous meal frequency, without significant alteration of spontaneous meal size. These data indicate that anorexia following peripheral LPS administration is sexually differentiated and that estradiol is sufficient to produce this response. The mechanism of the pathophysiological effect of estradiol on meal frequency appears to be different from the physiological effect of estradiol on food intake because the latter is expressed solely as a change in meal size.

Alpha-Melanocyte-Stimulating Hormone through Melanocortin-4 Receptor Inhibits Nitric Oxide Synthase and Cyclooxygenase Expression in the Hypothalamus of Male Rats

There is evidence that α-melanocyte-stimulating hormone (α-MSH) has immunomodulatory and anti-inflammatory actions within the brain. In this study, we tested whether these actions are due to inhibition of the synthesis of nitric oxide (NO) and prostaglandins induced by lipopolysaccharide (LPS). Since melanocortin subtype MC4 receptor has been detected in the hypothalamus, we investigated the effect of central administration of α-MSH and HS024 (a selective MC4 receptor antagonist) on the gene expression of inducible, neuronal and endothelial NO synthase (iNOS, nNOS and eNOS) and on cyclooxygenase (COX-1 and COX-2) expression in the mediobasal hypothalamus (MBH) of LPS-treated male Wistar rats. Peripheral administration of LPS (250 µg/rat, 3 h) induced iNOS and COX-2 gene expression in the MBH. This stimulatory effect was reduced by α-MSH (3 nmol/rat) injected 30 min before LPS. α-MSH and HS024 (1 nmol/rat) alone had no effect on iNOS and COX-2 expression. The action of α-MSH on LPS-induced iNOS and COX-2 mRNA levels was not observed in the presence of HS024, suggesting that MC4-R may be involved in the modulatory effect of α-MSH. None of these treatments produced any modifications in nNOS, eNOS and COX-1 expression in MBH. The increase in serum corticosterone levels induced by LPS was attenuated by α-MSH. Both LPS and α-MSH decreased serum LH and prolactin levels. HS024 failed to modify the inhibitory effects of LPS and α-MSH on prolactin release but reverted the effect of LPS on LH secretion, indicating that MC4-R activation may be involved in the effects of α-MSH on LH secretion in male rats. When we examined the in vitro effect of LPS (10 µg/ml) and LPS plus interferon-γ (IFN-γ, 100 ng/ml) on iNOS expression in MBH, an increase in iNOS mRNA levels was observed only in the presence of LPS + IFN-γ. This stimulatory effect was attenuated in the presence of α-MSH (5 µM), which by itself had no effect. No changes were found in nNOS, eNOS, COX-1 or COX-2 expression. These results indicate that α-MSH reduces the induction of iNOS and COX-2 gene expression at the hypothalamic level during endotoxemia and suggest that endogenous α-MSH may exert an inhibitory tone on iNOS and COX-2 transcription via MC4 receptors acting as a local anti-inflammatory agent within the hypothalamus.

Effects of lipopolysaccharide treatment on feeding of goldfish: role of appetite-regulating peptides

The gram-negative bacteria-derived endotoxin lipopolysaccharide (LPS) is known to play an important role in immune and neurological manifestations during bacterial infections. In mammals, peripheral or brain administration of LPS induces anorexia and is thought to exert its effects through activation of pro-inflammatory cytokines. In this study, we investigated the effects of peripheral (intraperitoneal, IP) and central (intracerebroventricular, ICV) injections of LPS on food intake of goldfish. Fish treated IP with 10, 25, 50, 100 or 250 ng/g LPS or ICV with 1, 10 and 100 ng/g LPS showed a significant dose-dependent decrease in food intake, compared to the saline-treated fish. We also examined the brain mRNA expression of several hypothalamic appetite-related neuropeptides in response to the administration of LPS. IP injections of LPS (100 ng/g) induced a decrease in NPY expression and an increase in CCK, CRF and CART expression. These results indicate that LPS is a potent anorexigenic factor in goldfish and that this endotoxin induces a reduction in appetite, at least in part, by influencing gene expression of appetite-related neuropeptides.

Reversible inactivation of the dorsal vagal complex blocks lipopolysaccharide-induced social withdrawal and c-Fos expression in central autonomic nuclei

Peripheral administration of lipopolysaccharide (LPS), a potent activator of the immune system, induces symptoms of behavioral depression, such as social withdrawal, concommitant with increases in c-Fos expression in central autonomic network nuclei. Previous studies implicated vagal visceral sensory nerves in transduction of immune-related signals relevant to for the induction of social withdrawal, a symptom of behavioral depression. Vagal sensory nerves terminate in the dorsal vagal complex (DVC) of the brainstem, a region that functions to integrate visceral signals and may also play a role in modulating arousal and affect. The objective of the current study was to determine whether the DVC contributes to immunosensory pathways driving symptoms of social withdrawal associated with LPS-induced behavioral depression, using a reversible lesion technique to temporarily inactivate the DVC. To assess the effects of DVC inactivation on LPS-induced social withdrawal and the subsequent changes in brain activation, we used behavioral assessment of social withdrawal, and analyzed c-Fos expression, a marker of neuronal activation, in the central nucleus of the amygdala (CEA), bed nucleus of the stria terminalis (BST), hypothalamic paraventricular nucleus (PVN), and ventromendial preoptic area (VMPO). Two hours following intraperitoneal LPS injection, there was a significant increase in c-Fos immunoreactivity in forebrain regions in animals treated with LPS. DVC inactivation completely blocked LPS-induced social withdrawal and dramatically reduced LPS-induced Fos expression in all four forebrain regions assessed. Collectively, these findings support the idea that the DVC acts as an immune-behavior interface between the peripheral stimuli and brain areas involved in modulating social behavior.

Brain-derived neurotrophic factor mRNA downregulation produced by social isolation is blocked by intrahippocampal interleukin-1 receptor antagonist

Manipulations that increase the expression of the pro-inflammatory cytokine interleukin-1β (IL-1β) in the hippocampus (e.g. peripheral administration of lipopolysaccharide, i.c.v. glycoprotein 120, social isolation) as well as the intrahippocampal injection of IL-1β following a learning experience, dramatically impair the memory of that experience if the formation of the memory requires the hippocampus. Here we employed social isolation to further study this phenomenon, as well as its relation to brain-derived neurotrophic factor (BDNF). BDNF was studied because of its well-documented role in the formation of hippocampally based memory. A 6 h period of social isolation immediately after contextual fear conditioning impaired memory for context fear measured 48 h later, and decreased BDNF mRNA in the dentate gyrus and the CA3 region of the hippocampus assessed immediately after the isolation. Moreover, an intrahippocampal injection of the IL-1 receptor antagonist prior to the isolation period prevented both the BDNF downregulation and the memory impairments produced by the isolation. These data suggest that hippocampal-dependent memory impairments induced by elevated levels of brain IL-1β may occur via an IL-1β-induced downregulation in hippocampal BDNF.

Differential induction of interleukin-I β mRNA in the brain parenchyma of Lewis and Fischer rats after peripheral injection of lipopolysaccharides

The expression of interleukin-1 beta (IL-1β) mRNA was compared in the brain of inflammatory susceptible LEW/N and resistant F344/N rats at 3, 6, and 12 h after peripheral administration of lipopolysaccharide (LPS) or saline. No differences between strains were observed in the circumventricular organs (CVOs) and choroid plexus. At 12 h after LPS administration, increased IL-1β mRNA expression was detected in the hypothalamus of LEW/N rats. In contrast, increased IL-1β mRNA expression was detected in the cerebral cortex of F344/N rats. These data show region-specific differences of IL-1β mRNA expression in the brain of these rat strains that differ in their susceptibility to inflammation.

Peripheral administration of lipopolysaccharide enhances the expression of guanosine triphosphate cyclohydrolase I mRNA in murine locus coeruleus

GTP cyclohydrolase I is the first and rate-limiting enzyme for the de novo biosynthesis of tetrahydrobiopterin, which is the cofactor for tyrosine hydroxylase. Lipopolysaccharide can modulate tetrahydrobiopterin production by upregulating GTP cyclohydrolase I protein expression in the locus coeruleus in the mouse brain. The increased supply of tetrahydrobiopterin in the locus coeruleus leads to increased tyrosine hydroxylase activity without affecting the level of tyrosine hydroxylase protein expression, resulting in an increase in norepinephrine turnover at the site. This study was performed to address whether the increase in GTP cyclohydrolase I protein is dependent on the de novo synthesis of GCH in the locus coeruleus. After i.p. administration of lipopolysaccharide, the mRNA expression of GTP cyclohydrolase I was examined. The expression level increased within 2 h, and reached to maximum level at 4 h after the lipopolysaccharide administration. However, the mRNA expression level of 6-pyruvoyl-tetrahydropterin synthase and sepiapterin reductase, both of which are involved successively after GTP cyclohydrolase I in tetrahydrobiopterin biosynthesis, were not affected by the lipopolysaccharide administration. These results suggest that GTP cyclohydrolase I upregulation alone is enough to modulate tetrahydrobiopterin production in the locus coeruleus. In addition, the mRNA level of tyrosine hydroxylase was also not affected by the lipopolysaccharide administration. Taken together, the data indicate that GTP cyclohydrolase I plays a crucial role in regulating norepinephrine biosynthesis by a pathway the activity of which is triggered by lipopolysaccharide i.p. administration.