Corticotropin-releasing factor, vasopressin, and prostaglandins mediate, and nitric oxide restrains, the hypothalamic-pituitary-adrenal response to acute local inflammation in the rat

Changes in corticosterone concentrations and behavior during Mycoplasma gallisepticum infection in house finches (Haemorhous mexicanus)

Glucocorticoid stress hormones are important for energy mobilization as well as regulation of the immune system, and thus these hormones are particularly likely to both influence and respond to pathogen infection in vertebrates. In this study, we examined how the glucocorticoid stress response in house finches (Haemorhous mexicanus) interacts with experimental infection of the naturally-occurring bacterial pathogen, Mycoplasma gallisepticum (MG). We also investigated whether infection-induced concentrations of corticosterone (CORT), the primary glucocorticoid in birds, were associated with the expression of sickness behavior, the lethargy typically observed in vertebrates early in infection. We found that experimental infection with MG resulted in significantly higher CORT levels on day 5 post-infection, but this effect appeared to be limited to female house finches only. Regardless of sex, infected individuals with greater disease severity had the highest CORT concentrations on day 5 post-infection. House finches exposed to MG exhibited behavioral changes, with infected birds having significantly lower activity levels than sham-inoculated individuals. However, CORT concentrations and the extent of sickness behaviors exhibited among infected birds were not associated. Finally, pre-infection CORT concentrations were associated with reduced inflammation and pathogen load in inoculated males, but not females. Our results suggest that the house finch glucocorticoid stress response may both influence and respond to MG infection in sex-specific ways, but because we had a relatively low sample size of males, future work should confirm these patterns. Finally, manipulative experiments should be performed to test whether the glucocorticoid stress response acts as a brake on the inflammatory response associated with MG infection in house finches.

Enhanced functional connectivity involving the ventromedial hypothalamus following methamphetamine exposure

Methamphetamine (MA) consumption causes disruption of many biological rhythms including the sleep-wake cycle. This circadian effect is seen shortly following MA exposure and later in life following developmental MA exposure. MA phase shifts, entrains the circadian clock and can also alter the entraining effect of light by currently unknown mechanisms. We analyzed and compared immunoreactivity of the immediate early gene c-Fos, a marker of neuronal activity, to assess neuronal activation 2 h following MA exposure in the light and dark phases. We used network analyses of correlation patterns derived from global brain immunoreactivity patterns of c-Fos, to infer functional connectivity between brain regions. There were five distinct patterns of neuronal activation. In several brain areas, neuronal activation following exposure to MA was stronger in the light than the dark phase, highlighting the importance of considering circadian periods of increased effects of MA in defining experimental conditions and understanding the mechanisms underlying detrimental effects of MA exposure to brain function. Functional connectivity between the ventromedial hypothalamus (VMH) and other brain areas, including the paraventricular nucleus of the hypothalamus and basolateral and medial amygdala, was enhanced following MA exposure, suggesting a role for the VMH in the effects of MA on the brain.

Prostaglandins and n-3 polyunsaturated fatty acids in the regulation of the hypothalamic-pituitary axis

The hypothalamic-pituitary (H-P) axis integrates complex physiological and environmental signals and responds to these cues by modulating the synthesis and secretion of multiple pituitary hormones to regulate peripheral tissues. Prostaglandins are a component of this regulatory system, affecting multiple hormone synthesis and secretion pathways in the H-P axis. The implications of these actions are that physiological processes or disease states that alter prostaglandin levels in the hypothalamus or pituitary can impinge on H-P axis function. Considering the role of prostaglandins in mediating inflammation, the potential for neuroinflammation to affect H-P axis function in this manner may be significant. In addition, the mitigating effects of n-3 polyunsaturated fatty acids (n-3 PUFA) on the inflammation-associated synthesis of prostaglandins and their role as substrates for pro-resolving lipid mediators may also include effects in the H-P axis. One context in which neuroinflammation may play a role is in the etiology of diet-induced obesity, which also correlates with altered pituitary hormone levels. This review will survey evidence for the actions of prostaglandins and other lipid mediators in the H-P axis, and will address the potential for obesity-associated inflammation and n-3 PUFA to impinge on these mechanisms.

Role of hypothalamic corticotropin-releasing factor in mediating alcohol-induced activation of the rat hypothalamic-pituitary-adrenal axis

Alcohol stimulates the hypothalamic-pituitary-adrenal (HPA) axis through brain-based mechanisms in which endogenous corticotropin-releasing factor (CRF) plays a major role. This review first discusses the evidence for this role, as well as the possible importance of intermediates such as vasopressin, nitric oxide and catecholamines. We then illustrate the long-term influence exerted by alcohol on the HPA axis, such as the ability of a first exposure to this drug during adolescence, to permanently blunt neuroendocrine responses to subsequent exposure of the drug. In view of the role played by CRF in addiction, it is likely that a better understanding of the mechanisms through which this drug stimulates the HPA axis may lead to the development of new therapies used in the treatment of alcohol abuse, including clinically relevant CRF antagonists.

GIP-Dependent Expression of Hypothalamic Genes

GIP (glucose dependent insulinotrophic polypeptide), originally identified as an incretin peptide synthesized in the gut, has recently been identified, along with its receptors (GIPR), in the brain. Our objective was to investigate the role of GIP in hypothalamic gene expression of biomarkers linked to regulating energy balance and feeding behavior related neurocircuitry. Rats with lateral cerebroventricular cannulas were administered 10 μg GIP or 10 μl artificial cerebrospinal fluid (aCSF) daily for 4 days, after which whole hypothalami were collected. Real time Taqman™ RT-PCR was used to quantitatively compare the mRNA expression levels of a set of genes in the hypothalamus. Administration of GIP resulted in up-regulation of hypothalamic mRNA levels of AVP (46.9±4.5 %), CART (25.9±2.7 %), CREB1 (38.5±4.5 %), GABRD (67.1±11 %), JAK2 (22.1±3.6 %), MAPK1 (33.8±7.8 %), NPY (25.3±5.3 %), OXT (49.1±5.1 %), STAT3 (21.6±3.8 %), and TH (33.9±8.5 %). In a second experiment the same set of genes was evaluated in GIPR-/- and GIPR+/? mice to determine the effect of lack of GIP stimulation on gene expression. In GIPR-/- mice expressions of the following genes were down-regulated: AVP (27.1±7.5 %), CART (28.3±3.7 %), OXT (25.2±5.8 %), PTGES (23.9±4.5 %), and STAT3 (8.8±2.3 %). These results suggest that AVP, CART, OXT and STAT3 may be involved in energy balance-related hypothalamic circuits affected by GIP.

Seasonal changes in vertebrate immune activity: mediation by physiological trade-offs

Animals living in temporally dynamic environments experience variation in resource availability, climate and threat of infection over the course of the year. Thus, to survive and reproduce successfully, these organisms must allocate resources among competing physiological systems in such a way as to maximize fitness in changing environments. Here, we review evidence supporting the hypothesis that physiological trade-offs, particularly those between the reproductive and immune systems, mediate part of the seasonal changes detected in the immune defences of many vertebrates. Abundant recent work has detected significant energetic and nutritional costs of immune defence. Sometimes these physiological costs are sufficiently large to affect fitness (e.g. reproductive output, growth or survival), indicating that selection for appropriate allocation strategies probably occurred in the past. Because hormones often orchestrate allocations among physiological systems, the endocrine mediators of seasonal changes in immune activity are discussed. Many hormones, including melatonin, glucocorticoids and androgens have extensive and consistent effects on the immune system, and they change in systematic fashions over the year. Finally, a modified framework within which to conduct future studies in ecological immunology is proposed, viz. a heightened appreciation of the complex but intelligible nature of the vertebrate immune system. Although other factors besides trade-offs undoubtedly influence seasonal variation in immune defence in animals, a growing literature supports a role for physiological trade-offs and the fitness consequences they sometimes produce.

Twenty-four-hour variation of L-arginine/nitric oxide/cyclic guanosine monophosphate pathway demonstrated by the mouse visceral pain model

The L-arginine/nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) pathway is known to be involved in central and peripheral nociceptive processes. This study evaluated the rhythmic pattern of the L-arginine/NO/cGMP pathway using the mouse visceral pain model. Experiments were performed at six different times (1, 5, 9, 13, 17, and 21 h after light on) per day in male mice synchronized to a 12 h:12 h light-dark cycle. Animals were injected s.c. with saline, 2 mg/kg L-arginine (a NO precursor), 75 mg/kg L-N(G)-nitroarginine methyl ester (L-NAME, a NOS inhibitor), 40 mg/kg methylene blue (a soluble guanylyl cyclase and/or NOS inhibitor), or 0.1 mg/kg sodium nitroprusside (a nonenzymatic NO donor) 15 min before counting 2.5 mg/kg (i.p.) p-benzoquinone (PBQ)-induced abdominal constrictions for 15 min. Blood samples were collected after the test, and the nitrite concentration was determined in serum samples. L-arginine or L-NAME caused both antinociception and nociception, depending on the circadian time of their injection. The analgesic effect of methylene blue or sodium nitroprusside exhibited significant biological time-dependent differences in PBQ-induced abdominal constrictions. Serum nitrite levels also displayed a significant 24 h variation in mice injected with PBQ, L-NAME, methylene blue, or sodium nitroprusside, but not saline or L-arginine. These results suggest that components of L-arginine/NO/cGMP pathway exhibit biological time-dependent effects on visceral nociceptive process.

Cocaine- and amphetamine-regulated transcript activates the hypothalamic-pituitary-adrenal axis through a corticotropin-releasing factor receptor-dependent mechanism

Cocaine- and amphetamine-regulated transcript (CART) is a highly expressed hypothalamic transcript that is concentrated in areas associated with the stress response. There is evidence for a role of CART in the regulation of the hypothalamic-pituitary-adrenal (HPA) axis. However, it is not clear whether CART regulates activity of the HPA axis by directly stimulating ACTH release from pituitary corticotropes or through interaction with hypothalamic factors. To address this issue, the effects of central and peripheral administration of CART on the HPA axis were compared. Central administration of CART(55-102) (1 microg) significantly increased circulating levels of ACTH (481 +/- 122 vs. 93 +/- 14 pg/ml; CART vs. vehicle) and corticosterone (460 +/- 29 vs. 179 +/- 62 ng/ml; CART vs. vehicle). In contrast, iv injection of CART(55-102) (0.09-9.0 nmol/kg) did not significantly affect circulating levels of ACTH or corticosterone. The corticotropin-releasing factor (CRF) receptor antagonist Astressin B was used to determine whether CART(55-102) elicits ACTH secretion via a CRF receptor-dependent mechanism. Injection of Astressin B (50 microg/kg, iv) inhibited CART(55-102)-induced ACTH and corticosterone responses. The effects of CART(55-102) on CRF and arginine vasopressin (AVP) expression were also examined in static hypothalamic explants. RT-PCR analysis revealed a significant up-regulation of CRF and AVP mRNA levels after CART(55-102) (10 nm and 1 microm) treatment. Last, the effects of CART(55-102) on CRF- and AVP-mediated ACTH release was investigated in dispersed rat anterior pituitary cells. Incubation of CART(55-102) (10-100 nm) did not significantly affect ACTH release from anterior pituitary cells. Findings from the present study suggest that CART regulates activity of the HPA axis through a CRF-dependent central mechanism and not by means of direct interaction with pituitary corticotropes.

Upregulation of corticotropin-releasing hormone gene expression in the paraventricular nucleus of cyclophosphamide-induced cystitis in male rats

We examined the effects of cyclophosphamide (CP)-induced cystitis on the expression of corticotropin-releasing hormone (CRH) mRNA in the paraventricular nucleus (PVN) and the serum levels of adrenocorticotropic hormone (ACTH) using in situ hybridization histochemistry and radioimmunoassay. In addition, the expression of AVP heteronuclear (hn) RNA and neuronal nitric oxide synthase (nNOS) mRNA was also examined in the PVN of a CP-induced cystitis model. We found that the levels of CRH mRNA were significantly increased in the PVN at 2 h after intraperitoneal administration of CP compared to those in saline-treated rats. The CRH mRNA levels in the PVN peaked at 12 h after CP administration and the levels were still significantly higher than those in saline-treated group at 24 h after CP administration. The serum ACTH levels in CP-treated group were also significantly higher compared to those in saline-treated group at any of the time points examined. Unlike previous findings showing upregulation of nNOS mRNA and AVP hnRNA under somatic nociceptive states, the levels of nNOS mRNA and AVP hnRNA were unchanged in the PVN following CP-induced cystitis, visceral nociceptive stimulation. These results suggest that visceral nociceptive stimulation as well as somatic nociceptive stimulation may activate the hypothalamo-pituitary axis but the hypothalamic neuroendocrine responses produced by visceral nociceptive stimulation may be different from those produced by somatic nociceptive stimulation.

Genetic Models in Applied Physiology. Differential role of nitric oxide synthase isoforms in fever of different etiologies: studies using Nos gene-deficient mice

Male C57BL/6J mice deficient in nitric oxide synthase (NOS) genes (knockout) and control (wild-type) mice were implanted intra-abdominally with battery-operated miniature biotelemeters (model VMFH MiniMitter, Sunriver, OR) to monitor changes in body temperature. Intravenous injection of lipopolysaccharide (LPS; 50 microg/kg) was used to trigger fever in response to systemic inflammation in mice. To induce a febrile response to localized inflammation, the mice were injected subcutaneously with pure turpentine oil (30 microl/animal) into the left hindlimb. Oral administration (gavage) of N(G)-monomethyl-l-arginine (l-NMMA) for 3 days (80 mg. kg(-1). day(-1) in corn oil) before injection of pyrogens was used to inhibit all three NOSs (N(G)-monomethyl-d-arginine acetate salt and corn oil were used as control). In normal male C57BL/6J mice, l-NMMA inhibited the LPS-induced fever by approximately 60%, whereas it augmented fever by approximately 65% in mice injected with turpentine. Challenging the respective NOS knockout mice with LPS and with l-NMMA revealed that inducible NOS and neuronal NOS isoforms are responsible for the induction of fever to LPS, whereas endothelial NOS (eNOS) is not involved. In contrast, none of the NOS isoforms appeared to trigger fever to turpentine. Inhibition of eNOS, however, exacerbates fever in mice treated with l-NMMA and turpentine, indicating that eNOS participates in the antipyretic mechanism. These data support the hypothesis that nitric oxide is a regulator of fever. Its action differs, however, depending on the pyrogen used and the NOS isoform.

Effect of ketoprofen, lidocaine local anesthesia, and combined xylazine and lidocaine caudal epidural anesthesia during castration of beef cattle on stress responses, immunity, growth, and behavior

To determine the effects of burdizzo castration alone or in combination with ketoprofen (K), local anesthesia (LA), or caudal epidural anesthesia (EPI) on plasma cortisol, acute-phase proteins, interferon-gamma production, growth, and behavior of beef cattle, 50 Holstein x Friesian bulls (13 mo old, 307 +/- 5.3 kg) were assigned to (n = 10/treatment): 1) control (handled; C); 2) burdizzo castration (B); 3) B following K (3 mg/ kg of BW i.v.; BK); 4) B following LA (8 mL into each testis and 3 mL s.c. along the line where the jaws of the burdizzo were applied with 2% lidocaine HCl; BLA); and 5) B following EPI (0.05 mg/kg of BW of xylazine HCl and 0.4 mg/kg of BW of lidocaine HCl as caudal epidural; BEPI). The area under the cortisol curve against time was lower (P < 0.05) in BK than in B, BLA, or BEPI animals. On d 1 after treatment, plasma haptoglobin concentrations were higher (P < 0.05) in B, BLA, and BEPI than in BK animals. On d 3, haptoglobin and plasma fibrinogen concentrations were higher (P < 0.05) in all castration groups than in C. On d 7, haptoglobin and fibrinogen concentrations remained higher (P < 0.05) in BLA than in B and C animals. On d 1, concanavalin A-induced interferon-gamma production was lower (P < 0.05) in B, BLA, and BEPI than in C, but there was no difference between BK and C animals. From d -1 to 35, ADG was lower (P < 0.05) in B, BLA, and BEPI animals, but not in BK compared with C animals. Overall, there was a higher (P < 0.05) incidence of combined abnormal postures in B than in C, BK and BEPI animals. Although the use of K and EPI decreased (P < 0.05) these postures compared with B alone or B with LA, there was no difference between the K and EPI treatment. In conclusion, burdizzo castration increased plasma cortisol and acute-phase proteins, and suppressed immune function and growth rates. Local anesthesia prolonged the increase in acute-phase proteins. Ketoprofen was more effective than LA or EPI in decreasing cortisol and partially reversed the reduction in ADG following castration. The use of K or EPI was more effective than LA in decreasing pain-associated behavioral responses observed during the first 6 h after treatment. Systemic analgesia with ketoprofen, a non-steroidal antiinflammatory drug, was more effective in reducing inflammatory responses associated with castration than LA or EPI.

Role of nitric oxide in regulating the rat hypothalamic-pituitary-adrenal axis response to endotoxemia

This work examines the role of nitric oxide (NO) in the periphery (i.e., on the pituitary) and the brain (particularly on corticotropin-releasing factor [CRF] and vasopressin [VP] neurons in the paraventricular nucleus [PVN] of the hypothalamus) as a modulator of the ACTH response to lipopolysaccharide. We previously showed that NO restricted the pituitary response to VP while it facilitated the synthesis of PVN CRF and VP. In our experience, only relatively high doses of lipopolysaccharide (>50 microg/kg, injected intravenously [i.v.]) cause detectable increases in PVN neuronal activation. Our hypothesis, therefore, was that pituitary NO-VP interactions would predominate in rats injected with a low dose of lipopolysaccharide (0.5 microg/kg, i.v.) while the stimulatory influence of the gas on PVN neuronal activity would play an important role following i.v. injection of a large dose of lipopolysaccharide (50 microg/kg, i.v.). We observed that the ability of 0.5 microg/kg lipopolysaccharide to release ACTH was significantly enhanced by the subcutaneous (s.c.), but not the intracerebroventricular (i.c.v.) injection of L-NAME, an arginine derivative that blocks NO synthesis. The effect of s.c. L-NAME was reversed by immunoneutralization of endogenous VP, which indicated that in this model, the ability of lipopolysaccharide to release ACTH depended, at least in part, on the influence exerted by NO on the pituitary response to VP. In rats injected with the high lipopolysaccharide dose, the s.c. injection of L-NAME decreased plasma ACTH levels compared to those in rats pretreated with the vehicle. The effect of s.c. L-NAME was not significantly altered by VP antibodies. These results indicate that in this model, the primary influence of NO was exerted in the PVN and/or its afferents and that it did not depend on a peripheral, VP-mediated effect of the gas. On the one hand, these data are at odds with our finding that the i.c.v. injection of L-NAME only marginally altered the ACTH response to the large dose of lipopolysaccharide. As i.c.v. injected L-NAME should have primarily decreased hypothalamic, but not pituitary NOS, its only modest influence on ACTH release may have been due to a balance between stimulating and inhibiting effects of NO within the brain. As high doses of lipopolysaccharide increase brain levels of prostaglandin, monoamine, and proinflammatory cytokines, it will be important to investigate the influence exerted by NO on these secretagogues and on their interactions with PVN CRF and VP neurons, which may help us resolve the issues raised by our results. Collectively, these data support our hypothesis that the mechanisms mediating the ACTH response to a low lipopolysaccharide concentration involve the inhibitory VP-mediated influence of NO on pituitary activity. By contrast, the stimulatory effect of high doses of lipopolysaccharide on ACTH release depends, at least in part, on the ability of NO to upregulate PVN neuronal activity.

Interleukin-6 is an afferent signal to the hypothalamo-pituitary-adrenal axis during local inflammation in mice

The cytokines IL-1 and IL-6 are able to induce prostaglandin (PG)-dependent activation of the hypothalamo-pituitary-adrenal axis (HPAA) and are thought to play key roles in immune-neuroendocrine interactions during inflammation. The present study shows that inflammation induced by im injection of turpentine (TPS) in the hind limb of mice causes an increase in the plasma concentration of IL-6, but not that of IL-1 alpha or IL-1 beta, together with a prolonged (>18-h) activation of the HPAA. IL-6 plays a causal role in the TPS-induced elevation in HPAA activity, because the sustained (8-18 h) increases in 1) plasma corticosterone, 2) plasma ACTH, and 3) induction of c-Fos in the hypothalamic paraventricular nucleus are all markedly blunted in IL-6-deficient (IL-6(-/-)) mice. Peripheral administration of a neutralizing IL-6 antiserum inhibited the plasma corticosterone response of normal (C57BL/6) mice to hind limb inflammation to an extent similar to that seen in IL-6(-/-) mice, suggesting that the IL-6 responsible for the increased HPAA activity is produced, or acts, on the blood side of the blood-brain barrier. We also show that IL-6 in the circulation is induced almost exclusively at the local inflammatory site, where IL-1 beta is produced. Induction of IL-6 and activation of the HPAA are dependent upon prior activation of an IL-1 type I receptor, as both are inhibited in type I IL-1 receptor-deficient mice. Furthermore, hind limb inflammation induced cyclooxygenase-2 protein expression around the cerebrovasculature of normal (IL-6(+/+)), but not IL-6(-/-), mice. Based on these data, we propose that IL-6 is produced at the local inflammatory site under the control of IL-1 beta and is the circulating afferent signal that is in part responsible for elevated HPAA activity, possibly acting via eicosanoid production within the cerebrovasculature.

Effect of indomethacin on the c-fos expression in AVP and TH neurons in rat brain induced by lipopolysaccharide

The aim of the present study was to investigate the effect of indomethacin on the Fos expression in arginine vasopressin (AVP)-containing neurons in the hypothalamus and tyrosine hydroxylase (TH)-containing neurons in the locus coeruleus (LC) using dual-labeled immunohistochemistry. In the hypothalamus, intraperitoneal (i.p) injection of different doses [2.5 microg/100 g, 125 microg/100 g body weight (b.w.)] of lipopolysaccharide (LPS) induced a significant Fos expression in AVP neurons in the supraoptic nucleus (SON), the magnocellular division (mPVN) and the parvocellular division (pPVN) of the paraventricular nucleus (PVN). Pretreatment with the cyclooxygenase inhibitor indomethacin (0.8 mg/100 g b.w.) significantly blocked the Fos expression in these AVP neurons induced by a low dose of LPS (2.5 microg/100 g) but had no effect on the Fos expression induced by a high dose of LPS (125 microg/100 g). Similarly, in the brain stem, a large number of TH-positive neurons in the LC expressed Fos after administration of either dose of LPS. Indomethacin prevented the Fos expression induced only by a low dose of LPS, but not by a high dose of LPS. These results suggest that the activation of AVP neurons in PVN and SON and TH neurons in LC response to immune challenge might be mediated-at least partially-by prostaglandins.

Rat anterior pituitary folliculostellate cells are targets of interleukin-1beta and a major source of intrapituitary follistatin

Folliculostellate cells of the anterior pituitary are postulated to be an important source of factors, such as follistatin, that regulate pituitary function by intercellular communication. To gain further insight into the function of this cell type, folliculostellate cells were enriched from cultured rat anterior pituitary cells, and an immortalized cell line designated FS/D1h was established and characterized. These FS/D1h cells express S100 immunoreactivity and produce IL-6 but not pituitary hormones such as GH, ACTH, FSH, and LH. Importantly, FS/D1h cells express large amounts of follistatin mRNA and secrete the protein, as quantified indirectly by the amount of [(125)I]activin A immunoprecipitated with a follistatin antiserum. The FS/D1h cells also express alpha, betaA, and betaB inhibin/activin subunit mRNAs, but whether they produce the corresponding activins and inhibins has not been determined. The response of FS/D1h cells to agents thought to modulate folliculostellate cell function was evaluated. IL-1beta (0.005-5 nM) stimulated the secretion of follistatin and increased mRNA expression. In parallel, IL-6 secretion was stimulated. Dexamethasone, pituitary adenylate cyclase-activating polypeptide(1-27), and lipopolysaccharide but not testosterone, 12-O-tetradecanoylphorbol-13-acetate, or forskolin also increased follistatin secretion. Surprisingly, activin had no effect on follistatin mRNA levels, despite the fact that FS/D1h cells express ActRII, ActRIIB, and ALK-4 (ActRIB). Activin, on the other hand, induced Smad7 mRNA accumulation and exerted an antiproliferative effect on FS/D1h cells. Altogether, these observations support the possibility that follistatin originating from folliculostellate cells participates in mediating the effects of IL-1beta, glucocorticoids, and other agents on the response of pituitary cells to activins.

Comparison between the influence of the intravenous and intracerebroventricular injection of a nitric oxide donor on adrenocorticotropic hormone release and hypothalamic neuronal activity

We investigated the ability of the nitric oxide (NO) donor 3-morpholino-sydnonimine (SIN-1) to release adrenocorticotropic hormone (ACTH) and up-regulate hypothalamic neurones following its intravenous (i.v.) injection. i.v. SIN-1 (0.2-1.8 mg/kg) produced dose-related increases in plasma ACTH levels which were blocked by prior neutralization of endogenous corticotropin-releasing factor (CRF) but not by vasopressin antibodies. In contrast, the intracerebroventricular (i.c.v.) injection of 50-microg SIN-1 released significantly larger amounts of ACTH, a response blunted by either CRF or vasopressin antibodies. While i.c.v. SIN-1 markedly up-regulated transcripts of the immediate early gene NGFI-B in the paraventricular nucleus (PVN) of the hypothalamus, no such response was observed following the i.v. injection of up to 2.0 mg/kg SIN-1. Finally, we found no evidence that the influence of the peripheral administration of SIN-1 on ACTH secretion is mediated by altered pituitary responsiveness to CRF or vasopressin. The fact that NO has a profound hypotensive influence in the periphery suggests that it may have released ACTH through this mechanism, although the absence of PVN neuronal response in regions that are activated by decreased blood pressure casts some doubt on this hypothesis. As the systemic injection of arginine derivatives that block NOS activity potently augment the ACTH response to circulating pro-inflammatory cytokines or vasopressin, the present findings indicate that the mechanisms responsible for this phenomenon are distinct from those responsible for ACTH released by i.v. SIN-1.

Microinfusion of a nitric oxide donor in discrete brain regions activates the hypothalamic-pituitary-adrenal axis

We previously showed that the intracerebroventricular injection of the nitric oxide (NO) donor 3-morpholino-sydnonimine (SIN-1) released adrenocorticotropic hormone (ACTH) and upregulated transcripts for corticotropin-releasing factor (CRF) and vasopressin in the paraventricular nucleus (PVN) of the rat hypothalamus. In the present work, we microinfused SIN-1 into the PVN itself, the amygdala, the hippocampus or the frontal cortex to identify the brain regions that modulate the influence of NO on the hypothalamic-pituitary-adrenal (HPA) axis. Microinfusion into the PVN, which contains most of the CRF and vasopressin neurones that control HPA axis activity, significantly released ACTH. Microinfusion into the amygdala or the hippocampus, areas which also regulate HPA axis activity, similarly increased plasma ACTH levels. However, these responses were smaller and showed a delayed onset, compared to that observed following PVN treatment. In contrast, microinfusion of SIN-1 into the frontal cortex, which is not believed to exert a major direct influence on the HPA axis, was without effect. The observation that compared to microinfusion into the PVN, peak ACTH levels were both smaller and delayed when SIN-1 was microinfused into the amygdala or the hippocampus, and that SIN-1 only increased NO levels when injected into the PVN, suggests that the NO donor injected outside the PVN activates this nucleus by targeting pathways that connect it to these other regions rather than by leakage. Collectively, our results provide important clues regarding the putative role of these regions in modulating the influence of NO on the HPA axis.

Corticotropin-releasing hormone regulates IL-6 expression during inflammation

Stimulation of the hypothalamic-pituitary-adrenal (HPA) axis by proinflammatory cytokines results in increased release of glucocorticoid that restrains further development of the inflammatory process. IL-6 has been suggested to stimulate the HPA axis during immune activation independent of the input of hypothalamic corticotropin-releasing hormone (CRH). We used the corticotropin-releasing hormone-deficient (Crh(-/-)) mouse to elucidate the effect of CRH deficiency on IL-6 expression and IL-6-induced HPA axis activation during turpentine-induced inflammation. We demonstrate that during inflammation CRH is required for a normal adrenocorticotropin hormone (ACTH) increase but not for adrenal corticosterone rise. The paradoxical increase of plasma IL-6 associated with CRH deficiency suggests that IL-6 release during inflammation is CRH-dependent. We also demonstrate that adrenal IL-6 expression is CRH-dependent, as its basal and inflammation-induced expression is blocked by CRH deficiency. Our findings suggest that during inflammation, IL-6 most likely compensates for the effects of CRH deficiency on food intake. Finally, we confirm that the HPA axis response is defective in Crh(-/-)/IL-6(-/-) mice. These findings, along with the regulation of IL-6 by CRH, support the importance of the interaction between the immune system and the HPA axis in the pathophysiology of inflammatory diseases.

Nociceptive stimulation increases NO synthase mRNA and vasopressin heteronuclearRNA in the rat paraventricular nucleus

Nociceptive stimulation causes neuroendocrine responses such as arginine vasopressin (AVP) release and activation of the hypothalamo-pituitary-adrenal (HPA) axis. We examined the effects of nociceptive stimulation on the expression levels of neuronal nitric oxide synthase (nNOS) mRNA, heteronuclear (hn)RNA for AVP and AVP mRNA in the rat paraventricular nucleus (PVN) and supraoptic nucleus (SON), using in situ hybridization histochemistry. For nociceptive stimulation, formalin (5%) or saline was injected subcutaneously (s.c.) into the bilateral hind paws of rats. The expression of the nNOS gene in the PVN was significantly increased 2 and 6 h after s.c. injection of formalin in comparison with that in untreated and saline injected rats. The expression of the nNOS gene in the SON did not change in the untreated, saline- and formalin-injected rats. The AVP hnRNA in the PVN and SON was also significantly increased 15, 30 min and 2 h after s.c. injection of formalin, though AVP mRNA did not change at any time points that we studied. Plasma concentration of AVP was significantly increased 15 min after s.c. injection of formalin. These results suggest that NO in the PVN may be involved in nociceptive stimulation-induced neuroendocrine responses.

Relative importance of nitric oxide and carbon monoxide in regulating the ACTH response to immune and non-immune signals

The present work investigated the effect of nitric oxide (NO) or carbon monoxide (CO) in the ACTH response to an immune signal [the intravenous injection of interleukin-1 β (IL-1β)] or to a neurogenic stressor (mild intermittent inescapable foot shocks). The arginine derivative N(ω)-L-arginine methylester (L-NAME), which non-specifically inhibits NO formation induced by all constitutive forms of NO synthase (NOS), significantly augmented the effect of IL-1P,but blockade of CO formation with metalloporphyrins was without effect. On the other hand, L-NAME blunted the effect of shocks on the early phase of ACTH release, while we had reported earlier that metalloporphyrins exerted a similar effect. This effect was mimicked by blockade of neuronal (n) NOS by N(ω)-Propyl-L-arginine (PA), although the resulting decrease in hormone levels was less than that induced by L-NAME. These results indicate that endogenous NO, but not CO, interferes with ACTH released by a peripheral immune signal. In contrast, NO formed by nNOS enhances the ability of shocks to induce ACTH secretion.

The roles of carbon monoxide and nitric oxide in the control of the neuroendocrine stress response: complementary or redundant

There is widespread evidence in favour of nitric oxide (NO) acting as a gaseous neurotransmitter in the central nervous system, diffusing from its cells of origin and affecting surrounding neuronal tissue in evanescent three-dimensional waves. This is also true of the hypothalamus, where amongst other activities NO inhibits stimulation of corticotrophin-releasing hormone (CRH) and vasopressin release by inflammatory stressors, effects thought to be mediated by binding with soluble guanylate cyclase (sGC). Carbon monoxide is being increasingly recognised as another gaseous neuromodulator, but with principal effects on other hemoproteins such as cyclo-oxygenase, and a distinctly different profile of localisation.NO is predominantly a pro-inflammatory agent in the periphery while CO is often anti-inflammatory. In the hypothalamus, the actions of CO are also distinct from those of NO,with marked antagonistic effects on the inflammatory release of vasopressin, both in vitro and in vivo, but with little involvement in the regulation of CRH. Thus, it would appear that these apparently similar gases exert quite distinct and separate effects, although they cause broadly similar overall changes in the secretion of neuroendocrine stress hormones. We conclude that these two gases may play significant but different roles in the control of the neuroendocrine stress response, but one common feature may be attenuation of inflammation-induced release of stress hormones.

Does IL-6 release ACTH by exerting a direct effect in the rat anterior pituitary

Adult male rats were used to determine whether high circulating levels of the pro-inflammatory cytokine interleukin-6 (IL-6) were capable of releasing ACTH independently of endogenous corticotropin-releasing factor (CRF). On one hand, CRF antibodies or a potent CRF antagonist significantly decreased, but did not totally abolish the ACTH response to the intravenous(i.v.) injection of recombinant rat IL-6. These results suggest that this cytokine might act either directly on the pituitary, or can release ACTH through mechanisms that do not involve CRF. On the other hand, the CRF antagonist or antibodies significantly (but not totally) blocked ACTH secretion due to the i.v. injection of endotoxin (LPS) while enhancing the ability of this immune stimulus to increase serum IL-6 concentrations. These results indicate that during endotoxemia, even very elevated circulating IL-6 concentrations were notable to release large amounts of ACTH in the absence of CRF drive. These data also illustrate the ability of a CRF antagonist or CRF antibodies to significantly augment IL-6 secretion,which indicates an inhibitory influence of the endogenous peptide in the paradigm we used.As comparable findings were obtained in adrenal-intact and adrenalectomized rats, they suggest that endogenous CRF is involved in the IL-6 response to LPS independently of circulating corticosteroids or other adrenal factors.

Circulating interleukin-6 mediates the febrile response to localised inflammation in rats

Interleukin (IL)-6 is an important mediator of the host response to disease and has been proposed, largely based upon circumstantial evidence, as the principal endogenous circulating pyrogen responsible for activating CNS mechanisms in fever during infection and inflammation. In the present investigation, we studied the role of peripheral IL-6 in fever and its relationship with IL-1, itself an important endogenous pyrogen and a potent stimulus of IL-6 production. Injection of lipopolysaccharide (LPS) into a sterile, subcutaneous air pouch (i.po.) in rats evoked an increase in body temperature which peaked at 3 h, and which was abolished in animals pretreated (intraperitoneally) with IL-6 antiserum. The increase in body temperature was accompanied by a significant elevation in concentrations of (immunoreactive) IL-1 and IL-6 at the site of inflammation (pouch), but only IL-6 in the circulation and cerebrospinal fluids. We propose that much of the circulating IL-6 originates at the site of inflammation, since injection of human recombinant (hr)IL-6 (i.po.) was detected (10 min after the injection) in the plasma using an ELISA specific for human IL-6. However, despite the relatively high concentration of IL-6 injected (25 microg kg-1, i.po.), this cytokine had no effect on body temperature when injected alone, but did induce fever when co-injected with a non-pyrogenic dose (when given alone) of IL-1beta, and exacerbated the fever to a pyrogenic dose of IL-1beta. The results from the present study demonstrate that IL-6 is a circulating endogenous pyrogen during LPS-induced fever, which acts in concert with IL-1beta at the local site of inflammation, before entering the circulation. Circulating IL-6 can then activate CNS mechanisms resulting in the development of the febrile response during disease.

How do glucocorticoids influence stress responses? Integrating permissive, suppressive, stimulatory, and preparative actions

The secretion of glucocorticoids (GCs) is a classic endocrine response to stress. Despite that, it remains controversial as to what purpose GCs serve at such times. One view, stretching back to the time of Hans Selye, posits that GCs help mediate the ongoing or pending stress response, either via basal levels of GCs permitting other facets of the stress response to emerge efficaciously, and/or by stress levels of GCs actively stimulating the stress response. In contrast, a revisionist viewpoint posits that GCs suppress the stress response, preventing it from being pathologically overactivated. In this review, we consider recent findings regarding GC action and, based on them, generate criteria for determining whether a particular GC action permits, stimulates, or suppresses an ongoing stress-response or, as an additional category, is preparative for a subsequent stressor. We apply these GC actions to the realms of cardiovascular function, fluid volume and hemorrhage, immunity and inflammation, metabolism, neurobiology, and reproductive physiology. We find that GC actions fall into markedly different categories, depending on the physiological endpoint in question, with evidence for mediating effects in some cases, and suppressive or preparative in others. We then attempt to assimilate these heterogeneous GC actions into a physiological whole.

Nitric oxide stimulates ACTH secretion and the transcription of the genes encoding for NGFI-B, corticotropin-releasing factor, corticotropin-releasing factor receptor type 1, and vasopressin in the hypothalamus of the intact rat

We investigated the effect of the intracerebroventricular injection of the nitric oxide (NO) donor 3-morpholino-sydnonimine (SIN-1) on the release of adrenocorticotropin hormone (ACTH) and the neuronal response of hypothalamic neurons responsible for this release. Rats that were administered SIN-1 showed significant elevations in plasma ACTH levels, a response that was virtually abolished by antibodies against corticotropin-releasing factor (CRF) and significantly blunted by vasopressin (VP) antiserum. SIN-1 also upregulated heteronuclear (hn) transcripts for CRF and VP and messenger RNA (mRNA) levels for the immediate early gene NGFI-B and for CRF receptor type 1 (CRF-R(1)) in the parvocellular portion of the paraventricular nucleus (PVN) of the hypothalamus. Blockade of prostaglandin synthesis with ibuprofen did not alter the ACTH or the PVN response to SIN-1. The central nucleus of the amygdala and the supraoptic nucleus, regions that are involved in autonomic adjustments to altered cardiovascular activity, also responded to SIN-1 with elevated NGFI-B mRNA levels. However, the only change in mean arterial blood pressure caused by this NO donor was a transient and modest increase. To our knowledge, this is the first demonstration that in the intact rat NO stimulates the activity of PVN neurons that control the hypothalamic-pituitary-adrenal axis. It must be noted, however, that our results do not allow us to determine whether this effect was direct or mediated through PVN afferents. This study should help resolve the controversy generated by the use of isolated brain tissues to investigate the net effect of NO on hypothalamic peptide production.

Corticotropin-releasing hormone deficiency unmasks the proinflammatory effect of epinephrine

Traditionally, the adrenal gland has been considered an important endocrine component of the pathway to inhibit acute inflammation via hypothalamic corticotropin-releasing hormone (CRH)-mediated secretion of glucocorticoid. Immunoreactive CRH found in inflamed tissues is a potent proinflammatory factor. Using genetic and pharmacological models of CRH deficiency, we now show that CRH deficiency unmasks a major proinflammatory effect of epinephrine secreted from the adrenal medulla. Together, epinephrine and peripheral CRH stimulate inflammation, and glucocorticoid acts as a counterbalancing force in this regard. Our findings suggest that stimulation of the acute inflammatory response should be included with the other "fight-or-flight" actions of epinephrine.

Role of cytokines in testicular function

Inflammatory disease has been established to affect male reproductive function and fertility. Relevant inflammatory diseases include general and chronic infectious diseases as well as localized acute or chronic infections of the male genitourinary tract. Male accessory gland infections account for almost 15% of all cases of male infertility seen in infertility clinics while fertility usually is not a clinical objective among patients with acute systemic infections such as Gram-negative sepsis. Infections of the male accessory glands frequently are associated with increased counts of white blood cells in semen and elevated levels of proinflammatory cytokines in semen and the testis. There is a mounting body of evidence that demonstrates the importance of cytokines and chemokines in the regulation of testicular and glandular function during pathophysiological states as well as under normal physiological conditions when cytokines act as growth and differentiation factors. The purpose of this review is to examine the role of cytokines in the regulation of steroidogenesis and spermatogenesis in the testis under physiological and pathophysiological conditions and considers clinical investigations that help to improve the evaluation and treatment of male infertility.

Cytokines in the neuroendocrine system

Cytokines are important partners in the bidirectional network interrelating the immune and the neuroendocrine systems. These substances and their specific receptors, initially thought to be exclusively present in the immune system, have recently been shown to be also expressed in the neuroendocrine system. Cytokines can modulate the responses of all endocrine axes by acting at both the central and the peripheral levels. To explain how systemic cytokines may gain access to the brain, several mechanisms have been proposed, including an active transport through the blood-brain barrier, a passage at the circumventricular organ level, as well as a neuronal pathway through the vagal nerve. The immune-neuroendocrine interactions are involved in numerous physiological and pathophysiological conditions and seem to play an important role to maintain homeostasis.

Kalirin inhibition of inducible nitric-oxide synthase

Nitric oxide (NO) acts as a neurotransmitter. However, excess NO produced from neuronal NO synthase (nNOS) or inducible NOS (iNOS) during inflammation of the central nervous system can be neurotoxic, disrupting neurotransmitter and hormone production and killing neurons. A screen of a hippocampal cDNA library showed that a unique region of the iNOS protein interacts with Kalirin, previously identified as an interactor with a secretory granule peptide biosynthetic enzyme. Kalirin associates with iNOS in vitro and in vivo and inhibits iNOS activity by preventing the formation of iNOS homodimers. Expression of exogenous Kalirin in pituitary cells dramatically reduces iNOS inhibition of ACTH secretion. Thus Kalirin may play a neuroprotective role during inflammation of the central nervous system by inhibiting iNOS activity.

Urocortin is not a significant regulator of intermittent electrofootshock-induced adrenocorticotropin secretion in the intact male rat

Urocortin (Ucn) is a newly identified mammalian member of the CRF family of peptides. Ucn activates CRF receptors (both CRF-R1 and CRF-R2) with greater potency than CRF itself, suggesting that Ucn may play an endogenous role in eliciting (at least some) CRF receptor-mediated events. Because the most characterized physiological function of CRF receptors is the activation of pituitary ACTH secretion, we have compared the effects and potential endogenous roles of CRF and Ucn in regulating plasma ACTH concentrations in intact male rats. Synthetic rat Ucn injected i.v. (0.09-9.0 nmol/kg) elicited ACTH secretion in a dose-dependent manner, causing greater ACTH secretion than CRF at each dose tested. The increases in plasma ACTH concentrations produced by CRF or Ucn were virtually abolished by pretreatment with the CRF receptor antagonist, astressin (3 mg/kg), and were partially attenuated (by 27-37%) by an antiarginine vasopressin serum. These data indicate that both Ucn and CRF elicit ACTH secretion via CRF receptor-dependent mechanisms, and that the ACTH-releasing activities of both CRF and Ucn are potentiated by endogenous arginine vasopressin. Intravenous administration of rabbit anti-Ucn serum, which inhibited ACTH secretion produced by Ucn, but not CRF, had no statistically significant effect on either resting (midday) plasma ACTH concentrations or the rise in ACTH levels elicited by 30 min of intermittent electrofootshocks. By contrast, treatment with a rabbit anti-CRF serum that specifically inhibited the ACTH response to CRF lowered plasma concentrations in control unstressed rats and largely prevented the plasma ACTH response to electrofootshocks. These data indicate that although Ucn is a more potent ACTH secretagogue than CRF in the intact male rat, it is not a major endogenous regulator of pituitary ACTH secretion under basal (midday) conditions or during acute footshock stress.

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.

Inhibition of stress-induced plasma corticosterone levels by ginsenosides in mice: involvement of nitric oxide

Ginseng total saponins (GTS) injected intracerebroventricularly (i.c.v.) at doses of 0.1-1 microg inhibited the i.c.v. injection stress-induced plasma corticosterone levels in mice. The inhibitory action of GTS was blocked by co-administered N(G)-nitro-L-arginine methyl ester (L-NAME; 1.5 microg, i.c.v.), an inhibitor of nitric oxide synthase (NOS). Of the ginsenosides Rb1, Rb2, Rc, Rd, Re, Rf, Rg1, 20(S)-Rg3 and 20(R)-Rg3 injected i.c.v. at doses of 0.01-1 microg, 20(S)-Rg3 and Rc significantly inhibited the i.c.v. injection stress-induced plasma corticosterone levels. The inhibitory actions of 20(S)-Rg3 and Rc were blocked by co-administered L-NAME (1.5 microg, i.c.v.). These results suggest that GTS, 20(S)-Rg3 and Rc may inhibit the i.c.v. injection stress-induced hypothalamo-pituitary-adrenal response by inducing NO production in the brain.

Production of mice deficient in genes for interleukin (IL)-1alpha, IL-1beta, IL-1alpha/beta, and IL-1 receptor antagonist shows that IL-1beta is crucial in turpentine-induced fever development and glucocorticoid secretion

Interleukin (IL)-1 is a major mediator of inflammation and exerts pleiotropic effects on the neuro-immuno-endocrine system. To elucidate pathophysiological roles of IL-1, we have first produced IL-1alpha/beta doubly deficient (KO) mice together with mice deficient in either the IL-1alpha, IL-1beta, or IL-1 receptor antagonist (IL-1ra) genes. These mice were born healthy, and their growth was normal except for IL-1ra KO mice, which showed growth retardation after weaning. Fever development upon injection with turpentine was suppressed in IL-1beta as well as IL-1alpha/beta KO mice, but not in IL-1alpha KO mice, whereas IL-1ra KO mice showed an elevated response. At this time, expression of IL-1beta mRNA in the diencephalon decreased 1.5-fold in IL-1alpha KO mice, whereas expression of IL-1alpha mRNA decreased >30-fold in IL-1beta KO mice, suggesting mutual induction between IL-1alpha and IL-1beta. This mutual induction was also suggested in peritoneal macrophages stimulated with lipopolysaccharide in vitro. In IL-1beta KO mice treated with turpentine, the induction of cyclooxygenase-2 (EC 1.14.99.1) in the diencephalon was suppressed, whereas it was enhanced in IL-1ra KO mice. We also found that glucocorticoid induction 8 h after turpentine treatment was suppressed in IL-1beta but not IL-1alpha KO mice. These observations suggest that IL-1beta but not IL-1alpha is crucial in febrile and neuro-immuno-endocrine responses, and that this is because IL-1alpha expression in the brain is dependent on IL-1beta. The importance of IL-1ra both in normal physiology and under stress is also suggested.

Circadian-rhythm-dependent effects of L-NG-nitroarginine methyl ester (L-NAME) on morphine-induced analgesia

Circadian changes in the interactions between L-NG-nitroarginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, and morphine-induced antinociception were investigated by the mouse hot-plate test. Both the basal pain sensitivity and morphine-induced analgesia undergo significant 24 h variations. L-NAME (40 mg/kg, i.p.) alone did not show any antinociceptive activity, but potentiated morphine-induced analgesia when combined with morphine at all injection times. In terms of percentage absolute potentiation (%AP), L-NAME dramatically augmented the analgesic effect of morphine in the late dark period at 19 hours after lights on (HALO). It is concluded that nitric oxide (NO) is involved in the modulation of the analgesic effect of morphine; thus, the L-NAME and morphine combination might be beneficial in alleviating pain.

Reduced cartilage proteoglycan loss during zymosan-induced gonarthritis in NOS2-deficient mice and in anti-interleukin-1-treated wild-type mice with unabated joint inflammation

OBJECTIVE

To investigate the role of nitric oxide (NO) and interleukin-1 in (IL-1) joint inflammation and cartilage destruction during zymosan-induced gonarthritis (ZIA).

METHODS

Monarticular arthritis was elicited by intraarticular injection of zymosan. The effect of NO deficiency on arthritis was studied in mice with genetically disrupted NOS2. The role of IL-1 was examined by treating wild-type mice with neutralizing anti-murine IL-1(alpha+beta) antibodies. Joint swelling was measured externally by the increased uptake of circulating 99mtechnetium pertechnetate. Proteoglycan (PG) synthesis was assessed using 35S-sulfate incorporation into patellae ex vivo. Histology evaluated exudation and infiltration of leukocytes and the extent of cartilage destruction.

RESULTS

The proinflammatory mediators NO, IL-1, and IL-6 were released by the articular tissues during the first hours of inflammation. Interestingly, anti-IL-1 treatment moderately reduced, and NOS2 deficiency moderately enhanced, joint swelling. However, the influx of neutrophils into the joint occurred independently of IL-1 and NOS2 activities. In the first week of inflammation, chondrocyte PG synthesis was significantly suppressed and chondrocytes became unresponsive to their essential anabolic factor, insulin-like growth factor 1 (IGF-1). Anti-IL-1 treatment or NOS2 deficiency prevented the inhibition of PG synthesis, and the chondrocytes remained IGF-1 responsive. Intraarticular injections of IL-1alpha into NOS2-deficient mice did not affect PG synthesis, thus proving that NO mediated this IL-1 effect in vivo. Furthermore, histology showed that cartilage PG loss was markedly ameliorated in NOS2-deficient and anti-IL-1-treated mice. Intermediate cartilage pathology was found in mice that were heterozygous for disrupted NOS2.

CONCLUSION

IL-1 and NO play a minor role in edema and neutrophil influx, but a major role in cartilage destruction of ZIA. In this model of murine arthritis, cartilage destruction was, for the most part, caused by pronounced suppression of PG synthesis and IGF-1 unresponsiveness of the chondrocytes, which were induced by de novo-synthesized IL-1 and were mediated by NOS2 activation.

Cerebral interleukin-6 is neuroprotective during permanent focal cerebral ischemia in the rat

Interleukin-6 (IL-6) is a neurotrophic cytokine expressed in both neurons and glia. The present study shows that cerebral ischemia produced by permanent occlusion of the middle cerebral artery (MCAO) produces a dramatic increase in IL-6 bioactivity in the ischemic hemisphere within 2 hours of MCAO (167 +/- 55 IU versus sham: 50 +/- 35 IU), with further increases at 8 hours (3,456 +/- 1,162 IU) and 24 hours (6,088 +/- 1,772 IU). In a separate series of experiments, intracerebroventricular injection of recombinant IL-6 (3,100 or 31,000 IU) significantly reduced ischemic brain damage after MCAO (to 52% and 65% of controls, respectively). The large increase in endogenous IL-6 bioactivity in response to ischemia, together with the marked neuroprotection produced by exogenous IL-6 suggest that this cytokine is an important endogenous inhibitor of neuronal death during cerebral ischemia.

Corticotropin-releasing hormone induces skin mast cell degranulation and increased vascular permeability, a possible explanation for its proinflammatory effects

Mast cells are involved in atopic disorders, often exacerbated by stress, and are located perivascularly close to sympathetic and sensory nerve endings. Mast cells are activated by electrical nerve stimulation and millimolar concentrations of neuropeptides, such as substance P (SP). Moreover, acute psychological stress induces CRH-dependent mast cell degranulation. Intradermal administration of rat/human CRH (0.1-10 microM) in the rat induced mast cell degranulation and increased capillary permeability in a dose-dependent fashion. The effect of CRH on Evans blue extravasation was stronger than equimolar concentrations of the mast cell secretagogue compound 48/80 or SP. The free acid analog of CRH, which does not interact with its receptors (CRHR), had no biological activity. Moreover, systemic administration of antalarmin, a nonpeptide CRHR1 antagonist, prevented vascular permeability only by CRH and not by compound 48/80 or SP. CRHR1 was also identified in cultured leukemic human mast cells using RT-PCR. The stimulatory effect of CRH, like that of compound 48/80 on skin vasodilation, could not be elicited in the mast cell deficient W/Wv mice but was present in their +/+ controls, as well as in C57BL/6J mice; histamine could still induce vasodilation in the W/Wv mice. Treatment of rats neonatally with capsaicin had no effect on either Evans blue extravasation or mast cell degranulation, indicating that the effect of exogenous CRH in the skin was not secondary to or dependent on the release of neuropeptides from sensory nerve endings. The effect of CRH on Evans blue extravasation and mast cell degranulation was inhibited by the mast cell stabilizer disodium cromoglycate (cromolyn), but not by the antisecretory molecule somatostatin. To investigate which vasodilatory molecules might be involved in the increase in vascular permeability, the CRH injection site was pretreated with the H1-receptor antagonist diphenhydramine, which largely inhibited the CRH effect, suggesting that histamine was involved in the CRH-induced vasodilation. The possibility that nitric oxide might also be involved was tested using pretreatment with a nitric oxide synthase inhibitor that, however, increased the effect of CRH. These findings indicate that CRH activates skin mast cells at least via a CRHR1-dependent mechanism leading to vasodilation and increased vascular permeability. The present results have implications for the pathophysiology and possible therapy of skin disorders, such as atopic dermatitis, eczema, psoriasis, and urticaria, which are exacerbated or precipitated by stress.

Modulatory effect of L-NAME, a specific nitric oxide synthase (NOS) inhibitor, on stress-induced changes in plasma adrenocorticotropic hormone (ACTH) and corticosterone levels in rats: physiological significance of stress-induced NOS activation in hypothalamic-pituitary-adrenal axis

We investigated whether NG-nitro-L-arginine methyl ester (L-NAME), a specific inhibitor of nitric oxide synthase (NOS), can modify the stress-induced adrenocorticotropic hormone (ACTH) and corticosterone responses, because we found that immobilization-induced stress increases NOS mRNA and protein levels and enzyme activity in the adrenal cortex. The physiological significance of these phenomena, however, remains unknown. Plasma ACTH and corticosterone levels were determined by radioimmunoassay (RIA) of systemic blood samples and NOS enzyme activity was measured as the rate of [3H]arginine conversion to [3H]citrulline in the presence of tissue homogenate of adrenal cortex separated from the adrenal gland. The NOS enzyme activity in the adrenal cortex of rats pre-injected with saline at 2 h after the 2-h immobilization was significantly higher (P < 0.01) than that in the non-stressed controls. Pre-injection of L-NAME (100 mg/kg, s.c.) almost completely abolished the activity. This dose of L-NAME maintained a significantly elevated plasma corticosterone level (P < 0.05, compared with basal level) even 2 h after the 2-h stress, whereas the plasma corticosterone level in rats pre-injected with saline returned to the basal level at the same time point. Plasma ACTH level in L-NAME-pre-treated rats was higher than that in those pre-treated with saline 2 h after the stress, but the difference was not significant. This dose of L-NAME did not influence plasma ACTH or corticosterone levels under resting conditions without stress. These findings suggest that the stress-induced increase in NO synthesis in the adrenal cortex can modify the stress-induced corticosterone response to facilitate the recovery from the elevated corticosterone secretion by stress in the adrenal cortex to the resting basal level.

Role of nitric oxide in the physiopathology of pain

Many painful disorders, including joint dysfunctions such as rheumatoid arthritis (RA) or temporomandibular joint disorders (TMD), are associated with hyperthermia of the overlying skin. The same is true of certain intractable chronic pain conditions, such as chronic orofacial pain, which may be associated with TMD. We suggest that this skin hyperthermia, caused by regional vasodilation, is induced by extravascular nitric oxide (NO). Extravascular NO can be produced in the affected joint by osteoblasts, chondrocytes, and macrophages, by mechanical stimulation of endothelial cells, or by stimulated neurons. In view of a strong correlation between pain and skin hyperthermia in these disorders, and the evidence that NO enhances the sensitivity of peripheral nociceptors, we also suggest that at least this kind of pain is associated with excessive local level of NO. This hypothesis can be verified by dynamic area telethermometry, assessing the effect of NO on the sympathetic nervous function. This mechanism, which is in line with the general role of NO as a mediator between different organ systems, also may be relevant to any pain associated with enhanced immune response. Clinical implications of the proposed mechanism are discussed.

Inhibition of tumor necrosis factor-alpha action within the CNS markedly reduces the plasma adrenocorticotropin response to peripheral local inflammation in rats

The present study tested the hypothesis that the cytokine tumor necrosis factor-alpha (TNF-alpha) is an important CNS mediator of the hypothalamo-pituitary-adrenal (HPA) axis response to local inflammation in the rat. Recombinant murine TNF-alpha administered directly into the cerebroventricles of normal rats produced a dose-dependent increase in plasma adrenocorticotropin (ACTH) concentration. Local inflammation induced by the intramuscular injection of turpentine (50 microl/100 gm body weight) also produced an increase in plasma ACTH, peaking at 160-200 pg/ml at 7.5 hr after injection (compared with 10-30 pg/ml in controls). Intracerebroventricular pretreatment with either 5 microl of anti-TNF-alpha antiserum or 1-50 microg of soluble TNF receptor construct (rhTNFR:Fc) reduced the peak of the ACTH response to local inflammation by 62-72%. In contrast, intravenous treatment with the same doses of anti-TNF-alpha or rhTNFR:Fc had no significant effect on the ACTH response to local inflammation. Although these data indicated an action of TNF-alpha specifically within the brain, no increase in brain TNF-alpha protein (measured by bioassay) or mRNA (assessed using either in situ hybridization histochemical or semi-quantitative RT-PCR procedures) was demonstrable during the onset or peak of HPA activation produced by local inflammation. Furthermore, increased passage of TNF-alpha from blood to brain seems unlikely, because inflammation did not affect plasma TNF-alpha biological activity. Collectively these data demonstrate that TNF-alpha action within the brain is critical to the elaboration of the HPA axis response to local inflammation in the rat, but they indicate that increases in cerebral TNF-alpha synthesis are not a necessary accompaniment.

Effect of three different modes of alcohol administration on the activity of the rat hypothalamic-pituitary-adrenal axis

The present study compared the effect of different modes of alcohol administration on the activity of the hypothalamic-pituitary-adrenal (HPA) axis. In a first series of studies, we investigated the influence of the intraperitoneal (ip) and intragastric (ig) effect of acutely administered alcohol. Over a 3-hr period, alcohol induced dose-related increases in adrenocorticotropic hormone (ACTH) and alcohol levels in the circulation. There was a good correlation between blood ACTH and alcohol levels (ip treatment, R = 0.84; ig treatment, R = 0.79). Measurement of steady-state mRNA of the immediate early gene NGFI-B, taken as an index of neuronal activation in the paraventricular nucleus (PVN) of the hypothalamus of rats administered 3 g of alcohol/kg, indicated significant (p < 0.01) increases between 60 and 180 min after both ip and ig alcohol injection, with peak stimulation at 1 and 2 hr, respectively. Although NGFI-B mRNA levels had returned to control level in the parvicellular portion of the PVN of animals administered the drug ip 4 hr earlier, they were still significantly (p < 0.01) elevated 4 hr after ig treatment. A second series of studies used rats fed an alcohol diet containing 6.4% alcohol (w/v), or pair-fed. The rats were tested during the 4th or 6th night of treatment. Despite blood alcohol levels ranging between 0.060 and 0.140% w/v, there was no significant rise in plasma ACTH/corticosterone levels in animals fed the drug, and no detectable NGFI-B mRNA in their PVN. Collectively, these results indicate that both the ip and the ig acute injection of alcohol induced dose-related increases in plasma ACTH levels. PVN neuronal activation was also observed. In contrast, the alcohol diet had no effect on HPA hormone levels or PVN expression of NGFI-B.

Inhibition of gonadotropin-induced testosterone secretion by the intracerebroventricular injection of interleukin-1 beta in the male rat

The intracerebroventricular (icv) injection of the proinflammatory cytokine interleukin (IL)-1 beta is known to significantly decrease plasma LH levels in the male rat, thereby lowering testosterone (T) secretion. We show here that central administration of this cytokine (20-80 ng) also inhibits T secretion in response to human CG (hCG), an effect that is apparent already when IL-1 beta is injected 15 min before hCG. This phenomenon is independent of LH secretion because lowering LH levels with the potent GnRH antagonist Azaline B neither mimics nor affects the suppressive influence of icv IL-1 beta on the hCG-induced T secretory response. Elevations in plasma corticosterone levels do not seem to play a role either, because icv IL-1 beta is able to blunt hCG-induced T secretion in animals whose corticosterone has been removed by adrenalectomy or reduced by the administration of antibodies to CRF. Furthermore, the observation that icv IL-1 beta inhibits the T response to hCG before elevations in plasma IL-6 concentrations are detectable, and that central treatment with the cytokine is more effective than iv treatment, indicates that circulating levels of neither IL-1 beta nor IL-6 are important mediators of this effect. Collectively, these results lead us to propose that IL-1 beta of central origin influences neural pathways linking the brain and the testes, resulting in decreased testicular responses to hCG.

Selective inhibitors of nitric oxide synthase (NOS) implicate a constitutive isoform of NOS in the regulation of interleukin-1-induced ACTH secretion in rats

Nitric oxide synthase (NOS) exists in at least three distinct isoforms: an inducible NOS (NOS II), and two forms which are constitutively expressed-brain NOS (NOS I) and endothelial NOS (NOS III). We have previously shown that the NOS inhibitor, N(ω)-nitro-L-arginine methyl ester hydrochloride (L-NAME), markedly potentiates and prolongs the increase in plasma adrenocorticotropin (ACTH) concentrations produced by the intravenous injection of interleukin-1β (IL-1β) in the rat. However, the mechanism of action of L-NAME is unknown. The purpose of the present study was to determine the effects on IL-1β-induced ACTH secretion in the rat, of several NOS inhibitors, whose selectivity for the different NOS isoforms has been well characterized, and which lack the muscarinic receptor antagonist properties that have been reported for L-NAME. Subcutaneous (sc) pretreatment with L-NAME (50-300 μmol/kg) produced the expected pronounced exacerbation of the ACTH response to IL-1β. This effect was mimicked by N(G)-nitro-L-arginine, which preferentially inhibits constitutive forms of NOS. In contrast, aminoguanidine, a selective inducible NOS inhibitor at doses up to 3×1.8 mmol/kg, was without effect, suggesting that it is a constitutive form of NOS that regulates the ACTH response to IL-1β. Selective inhibition of brain NOS using either 7-nitro-indazole (administered intraperitoneally) or L-NAME (administered intracerebroventricularly) did not significantly alter ACTH concentrations after IL-1β. Collectively, these data indicate that NO restrains the ACTH response to IL-1β, and that the NO responsible for this effect is generated by a constitutive, most probably endothelial, isoform of NOS.