Nitric oxide mediates central activation of sympathetic outflow induced by interleukin-1 beta in rats

Cyclooxygenase and nitric oxide synthase pathways mediate the respiratory effects of TNF-α in rats

TNF-α is the key inflammatory cytokine. TNF-α receptors are expressed in brain stem regions involved in respiratory control and also in the carotid bodies, which are the sensory organs monitoring arterial blood O₂. We hypothesised that the circulating tumour necrosis factor (TNF)-α may affect the lung ventilation and modulate the hypoxic ventilatory response via activation of cyclooxygenase (COX) and nitric oxide synthase (NOS) pathways. The aim of the current study was to compare the respiratory effects of TNF-α before and after pretreatment with diclofenac or L-NG-nitro arginine methyl ester (L-NAME) nonspecific inhibitors of COX and NOS, respectively. The hypoxic ventilatory response was measured in anaesthetised rats using rebreathing techniques. We found that TNF-α increased the lung ventilation in normoxia but decreased the ventilatory response to hypoxia. Pretreatment with each of these inhibitors reduced respiratory effects of TNF-α. We believe that activation of COX and NOS-related pathways and also "cross-talk" between them mediates the TNF-α respiratory effects and underlies the impact of inflammation on the respiratory function.

Innervation and serotoninergic receptors of the testis interact with local action of interleukin-1beta on steroidogenesis

Testosterone secretion by Leydig cells is affected by interleukin-1beta (IL-1beta). The aim of the present study was to investigate whether partial denervation of the testis or local administration of a serotonin (5-HT) receptor antagonist could alter the changes in testicular steoidogenesis induced by IL-1beta. Intratesticular administration of IL-1beta was combined with vasectomy or local injection of ketanserin (5-HT type 2 receptor antagonist) in immature hemicastrated rats and the effect of the interventions on testicular steroidogenesis was studied. One day after treatment with local injection of IL-1beta induced a significant rise in testosterone secretion that could be prevented by vasectomy (that also means transection of the inferior spermatic nerve). In a model in which neither IL-1beta nor ketanserin interfered with steroidogenesis, administration of the receptor antagonist just prior to IL-1beta treatment significantly reduced testosterone secretion. Data indicate interaction between testicular nerves and IL-1beta action and interaction between testicular 5-HT2 receptors and local effect of IL-1beta on testosterone secretion.

Effect of subdiaphragmatic vagotomy on bacterial DNA-induced IL-1β expression in the mouse hypothalamus

We investigated whether bacterial DNA (CpG-DNA)-induced IL-1beta expression in the mouse hypothalamus is mediated via afferent vagus nerve. Subdiaphragmatic vagotomy did not modify the CpG-DNA (i.p.)-induced IL-1beta expression in the hypothalamus, indicating that CpG-DNA-induced IL-1beta expression is independent of the afferent vagus nerve originating from the subdiaphragmatic organs. On the other hand, we observed the Toll-like receptor 9 mRNA expression in the hypothalamus, suggesting that circulating CpG-DNA acts directly in the brain.

Inducible nitric oxide synthase is involved in corticotropin-releasing hormone-mediated central sympatho-adrenal outflow in rats

Brain nitric oxide (NO), recognized as a neurotransmitter or a neuromodulator, is mainly generated either by neuronal NO synthase (NOS) or by inducible NOS. NO has been shown to activate cyclooxygenase (a prostaglandin-forming enzyme) in addition to guanylate cyclase. Recently, we reported that the intracerebroventricularly (i.c.v.) administered corticotropin-releasing hormone (CRH) increases plasma catecholamines through brain cyclooxygenase-dependent mechanisms in rats. In the present experiments, therefore, we examined whether NO is involved in the CRH-induced increase of plasma catecholamines using urethane-anesthetized rats. I.c.v. administered CRH increased plasma noradrenaline and adrenaline in a dose-dependent manner (0.5, 1.5, and 3.0 nmol/animal). The CRH (1.5 nmol/animal, i.c.v.)-induced increase of plasma catecholamines was reduced by N(omega)-nitro-L-arginine methyl ester (a non-selective inhibitor of NOS) [111 nmol (30 microg)/animal, i.c.v.], but not by the same dose of N(omega)-nitro-D-arginine methyl ester (an inactive isomer of N(omega)-nitro-L-arginine methyl ester). The CRH-induced increase of plasma catecholamines was also reduced either by cycloheximide (an inhibitor of protein synthesis) [107 nmol (30 microg)/animal, i.c.v.] or by S-methylisothiourea (an inhibitor of inducible NOS) [71 nmol (20 microg) and 711 nmol (200 microg)/animal, i.c.v.]. These results suggest the involvement of brain inducible NOS in the CRH-induced activation of the central sympatho-adrenomedullary outflow in rats.

Cholecystokinin inhibits food intake independent of interleukin-1 beta expression in the brain

Increasing evidence has suggested that cholecystokinin (CCK) is involved in immune-to-brain communication. The afferent vagus nerve is an important component for transmitting peripheral immune signals to the brain, such as those determining interleukin (IL)-1beta expression in the brain and anorexia. In the present study, we investigated whether the anorexic effect of CCK, which also activates the afferent vagus nerve, is mediated via IL-1beta expression in the brain. CCK-8 dose-dependently (8-320 microg/kg, i.p.) inhibited food intake in mice. However, IL-1beta transcripts in the hypothalamus, the hippocampus and the brainstem were not significantly increased after the administration of CCK-8, even at the larger dose of 320 microg/kg. These findings suggest that the CCK-induced inhibition of food intake may be independent of IL-1beta production in the brain, and indicate the diverse role of CCK in the regulation of the neuro-immune interaction.

Central interleukin-1beta antibody increases renal and splenic sympathetic nerve discharge

We tested the hypothesis that intracerebroventricular (lateral ventricle) administration of interleukin-1beta (IL-1beta) antibody increases the level of sympathetic nerve discharge (SND) in alpha-chloralose-anesthetized rats. Mean arterial pressure (MAP), heart rate (HR), and SND (splenic and renal) were recorded before (Preinfusion), during (25 min), and for 45 min after infusion of IL-1beta antibody (15 microg, 50 microl icv) in baroreceptor-intact (intact) and sinoaortic-denervated (SAD) rats. The following observations were made. First, intracerebroventricular infusion of IL-1beta antibody (but not saline and IgG) significantly increased MAP and the pressor response was higher in SAD compared with intact rats. Second, renal and splenic SND were significantly increased during and after intracerebroventricular IL-1beta antibody infusion and sympathoexcitatory responses were higher in SAD compared with intact rats. Third, intracerebroventricular administration of a single dose of IL-1beta antibody (15 microg, 5 microl for 2 min) significantly increased splenic and renal SND in intact rats. These results suggest that under the conditions of the present experiments central neural IL-1beta plays a role in the tonic regulation of SND and arterial blood pressure.

Role of brain thromboxane A2 in the release of noradrenaline and adrenaline from adrenal medulla in rats

Plasma noradrenaline reflects the release from adrenal medulla and sympathetic nerves; however, the exact mechanisms of adrenal noradrenaline release remain to be elucidated. The present study was designed to characterize the source of plasma noradrenaline induced by centrally administered vasopressin and corticotropin-releasing hormone (CRH) in urethane-anesthetized rats. Intracerebroventricularly administered vasopressin (0.2 nmol/animal) and CRH (1.5 nmol/animal) elevated plasma levels of noradrenaline and adrenaline. Intracerebroventricularly administered indomethacin [1.2 micromol (500 microg)/animal] (an inhibitor of cyclooxygenase) abolished the elevations of both noradrenaline and adrenaline induced by vasopressin and CRH. Intracerebroventricularly administered furegrelate [1.8 micromol (500 microg)/animal] (an inhibitor of thromboxane A(2) synthase) abolished the elevations of both noradrenaline and adrenaline induced by vasopressin, while the reagent only attenuated the elevation of plasma adrenaline evoked by CRH. Acute bilateral adrenalectomy abolished the elevation of both noradrenaline and adrenaline induced by vasopressin, while the procedure reduced only the elevation of adrenaline induced by CRH. These results suggest that the release of noradrenaline from adrenal medulla and sympathetic nerves is mediated by different central mechanisms. The vasopressin-induced noradrenaline release from adrenal medulla is mediated by brain thromboxane A(2)-mediated mechanisms, while the CRH-induced noradrenaline release from sympathetic nerves is mediated by brain prostanoid (other than thromboxane A(2))-mediated mechanisms. The vasopressin- and CRH-induced adrenaline release from adrenal medulla is also mediated by brain thromboxane A(2)-mediated mechanisms in rats.

Inhibition of leptin-induced IL-1beta expression by glucocorticoids in the brain

Leptin is an important circulating signal for the regulation of food intake and body weight. Glucocorticoids were suggested to play a physiological role in the feedback inhibition of immune/inflammatory responses. In the present study, we examined whether these neuroendocrine effects of glucocorticoids are linked to changes in the leptin-induced expression of IL-1beta and STAT3 activation in the brain. Intravenous injection of leptin induced IL-1beta expression in the hypothalamus. Pretreatment with dexamethasone dose dependently inhibited leptin-induced IL-1beta expression in the hypothalamus. Moreover, dexamethasone inhibited leptin-induced IL-1beta expression in the primary cultured glial cells. In contrast, pretreatment with dexamethasone did not inhibit leptin-induced STAT3 phosphorylation in the hypothalamus. These effects of dexamethasone may not be due to the change in the expression level of the leptin receptor Ob-Ra and Ob-Rb isoforms. Therefore, it is suggested that glucocorticoid negatively regulates leptin-induced IL-1beta expression in the brain.

Vasopressin V(1) receptor-mediated activation of central sympatho-adrenomedullary outflow in rats

The present study was designed to characterize the vasopressin receptor subtype involved in the vasopressin-induced activation of the central sympatho-adrenomedullary outflow using urethane-anesthetized rats. Intracerebroventricularly (i.c.v.) administered vasopressin (0.1, 0.2 and 0.5 nmol/animal) dose-dependently elevated plasma levels of adrenaline and noradrenaline (adrenaline>noradrenaline). The vasopressin (0.2 nmol/animal)-induced elevation of both catecholamines was significantly attenuated by [d(CH(2))(5)(1),Tyr(Me)(2),Arg(8)]-vasopressin, a selective vasopressin V(1) receptor antagonist, in a dose-dependent manner (0.1 and 0.2 nmol/animal, i.c.v.). The same doses (0.1 and 0.2 nmol/animal, i.c.v.) of [1-adamantaneacetyl(1),D-Tyr(Et)(2),Val(4),Abu(6), Arg(8,9)]-vasopressin, a potent vasopressin V(2) receptor antagonist, had no effect; however, a large dose of this antagonist (1.6 nmol/animal, i.c.v.) effectively reduced the vasopressin-induced elevation of catecholamines. On the other hand, [5-dimethylamino-1-[4-(2-methylbenzoylamino)benzoyl]-2,3,4,5-tetrahydro-1H-benzazepine], a selective vasopressin V(2) receptor antagonist (5 and 10 nmol/animal, i.c.v.), had no effect on the vasopressin-induced elevation of catecholamines. The vasopressin-induced elevation of catecholamines was abolished by indomethacin, an inhibitor of cyclooxygenase (1.2 micromol/animal, i.c.v.). These results suggest that the vasopressin activates the central sympatho-adrenomedullary outflow by brain vasopressin V(1) receptor- and cyclooxygenase-dependent mechanisms in rats.

Brain inducible nitric oxide synthase is involved in interleukin-1beta-induced activation of the central sympathetic outflow in rats

Nitric oxide (NO) has been recognized as a neurotransmitter or a neuromodulator in the central nervous system. Brain NO is mainly generated either by neuronal NO synthase (NOS) or by inducible NOS. Previously we reported that central NO is involved in the elevation of plasma noradrenaline levels induced by intracerebroventricularly (i.c.v.) administered interleukin-1beta in rats [Eur. J. Phamacol. 317 (1996) 61]. In the present study, therefore, we tried to characterize which type of NOS isoforms is involved in the cytokine-induced responses using selective inhibitors of each NOS isoform in urethane-anesthetized rats. I.c.v. administered interleukin-1beta (100 ng/animal) elevated plasma levels of noradrenaline but not adrenaline. The cytokine-induced elevation of plasma noradrenaline levels was attenuated by cycloheximide, an inhibitor of protein synthesis, in a dose-dependent manner (10 and 20 microg/animal, i.c.v.). S-ethylisothiourea (0.1 and 0.5 microg/animal, i.c.v.), an inhibitor of inducible NOS, dose-dependently reduced the cytokine-induced elevation of plasma noradrenaline levels, while 7-nitroindazole (5 and 10 microg/animal, i.c.v.), an inhibitor of neuronal NOS, had no effect. These results suggest the involvement of brain inducible NOS in the interleukin-1beta-induced activation of the central sympathetic outflow in rats.

Roles of brain prostaglandin E2 and thromboxane A2 in the activation of the central sympatho-adrenomedullary outflow in rats

We examined the effects of centrally administered active metabolites of the arachidonic acid cascade on activation of the central sympatho-adrenomedullary outflow using urethane-anaesthetized rats. Intracerebroventricularly (i.c.v.) administered prostaglandin E(2) (0.3 nmol/animal) significantly elevated plasma levels of noradrenaline while levels of adrenaline were not affected. Prostaglandin D(2), prostaglandin F(2 alpha) and prostaglandin I(2) at the same dose (0.3 nmol/animal, i.c.v.) had no effect on plasma levels of either catecholamine. Thromboxane A(2) mimetic, 7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo [2.2.1]hept-2-yl], [1S-[1 alpha,2 alpha(Z),3beta(1E,3S),4 alpha]]-5-heptenoic acid (I-BOP) (5 and 10 pmol/animal) microinjected into the paraventricular nucleus of the hypothalamus significantly elevated plasma levels of adrenaline, but had little effect on plasma levels of noradrenaline. The I-BOP-induced (10 pmol/animal) elevation of plasma adrenaline levels was abolished by (+)-(1R,2R,3S,4S)-(5Z)-7-(3-[4-3H]-phenylsulphonyl-aminobicyclo[2.2.1]hept-2-yl)hept-5-enoic acid sodium salt [(+)-S-145] (a blocker of thromboxane A(2) receptors) [625 nmol (250 micro g)/animal, i.c.v.]. These results suggest that brain prostaglandin E(2) and thromboxane A(2) are respectively involved in the activation of the central sympathetic and adrenomedullary outflow in rats.

Leptin regulates interleukin-1beta expression in the brain via the STAT3-independent mechanisms

Leptin is known to be an important circulating signal for regulation of food intake and body weight. These effects were suggested to be mediated through the hypothalamic center via the Ob-Rb receptor (long isoform of leptin receptor). Although short isoforms of leptin receptor exist in many regions of the brain, there has been little in vivo functional study of these areas such as for leptin's target site. We report here that peripherally applied leptin increased interleukin (IL)-1beta transcripts in many regions of the brain such as the hypothalamus, the hippocampus, the cortex, the cerebellum and the brainstem. Although leptin did not induce STAT3 activation or suppressor of cytokine signaling3 (SOCS3) expression in the hypothalamus of the db/db mice, which lack a functional Ob-Rb receptor, leptin increased the IL-1beta levels to similar extents as normal mice. Therefore, a novel function of leptin is suggested as the induction of IL-1beta expression in many regions of the brain via STAT3-independent mechanisms.

Renal injury caused by intrarenal injection of phenol increases afferent and efferent renal sympathetic nerve activity

Intrarenal injection of phenol in rats causes a persistent elevation in blood pressure (BP) and in norepinephrine (NE) secretion from the posterior hypothalamus (PH), and downregulation of neuronal nitric oxide synthase (nNOS) and interleukin-1beta (IL-1beta) in the PH. These studies suggest that afferent impulses from the kidney to the brain may be responsible for hypertension associated with renal injury. Downregulation of nNOS and IL-1beta, two modulators of sympathetic nervous system (SNS) activity may mediate this activation. In this study we measured the effects of intrarenal phenol injection on peripheral SNS activity by direct renal nerve recording, plasma NE, nNOS, and IL-1beta abundance in the brain. We also determined whether renal denervation or administration of clonidine prevented these effects of phenol. Acutely, the phenol injection increased both afferent and efferent renal sympathetic nerve activity, decreased urinary sodium excretion, and increased plasma NE. Three weeks after the phenol injection, BP and plasma NE remained elevated. Renal denervation and pretreatment with clonidine prevented the increase in BP and plasma NE caused by phenol. Chronic renal injury caused by phenol was associated with decreased abundance of IL-1beta and nNOS in the PH. These studies have shown that a renal injury caused by phenol injection increases BP and central as well as peripheral SNS activity, which persist long after the injury. Renal denervation and antiadrenergic drugs abolish the effects of phenol on BP and plasma NE. Because NO and IL-1beta modulate SNS activity, the stimulatory action of phenol on the SNS could be mediated by downregulation of nNOS and IL-1beta in the brain.

Losartan reduces central and peripheral sympathetic nerve activity in a rat model of neurogenic hypertension

We have developed a new model of neurogenic hypertension in the rat, in which hypertension is caused by injecting 50 microL of 10% phenol in the lower pole of one kidney. Administration of phenol in the kidney causes an immediate and persistent rise in blood pressure (BP), norepinephrine (NE) secretion from the posterior hypothalamic nuclei (PH), and renal sympathetic nerve activity (RSNA). Because angiotensin II (Ang II) is known to stimulate central and peripheral sympathetic nervous system (SNS) activity, we have tested the hypothesis that losartan, a specific Ang II AT1 receptor antagonist, may lower BP, at least in part, by SNS inhibition. To this end, we studied the effects of losartan on BP and SNS activity following intrarenal phenol injection. Central SNS activity was measured by NE secretion from the PH using a microdialysis technique, and peripheral SNS activity was measured by direct recording of renal nerve activity. At the end of the experiments, brains were isolated and interleukin (IL)-1beta and nitric oxide synthase (NOS) mRNA gene expression was measured by RT-PCR in the PH, paraventricular nuclei (PVN), and locus ceruleus (LC). The intrarenal injection of phenol raised BP, as well as central and renal SNS activity, but reduced the abundance of IL-1beta and neuronal NOS (nNOS) mRNA in the PH, PVN, and LC. Whether injected intravenously or in the lateral ventricle, losartan caused a significant (P<0.01) and dose-dependent inhibition of the effects of phenol on BP, NE secretion from the PH, and RSNA. Losartan also caused a significant (P<0.01) and dose-dependent rise in IL-1beta and nNOS-mRNA gene expression in the PH, PVN, and LC of phenol-injected rats. In conclusion, these studies have shown that the intrarenal injection of phenol causes a rise in central and renal SNS activity and a decrease in IL-1beta and nNOS-mRNA in the PH, PVN, and LC. Losartan prevented the rise in BP and SNS activity, as well as the decrease in IL-1beta and nNOS mRNA abundance caused by phenol. These studies have demonstrated that the antihypertensive action of losartan in the phenol renal injury model is largely mediated by inhibition of central and peripheral SNS activity and suggest that activation of IL-1beta and nNOS, 2 important modulators of central SNS activity, mediates the inhibitory action of losartan on SNS activity.

Downregulation of neuronal nitric oxide synthase and interleukin-1beta mediates angiotensin II-dependent stimulation of sympathetic nerve activity

There is substantial evidence that angiotensin II (Ang II) enhances sympathetic nervous system (SNS) activity. We recently observed that nitric oxide and interleukin-1beta (IL-1beta) exert a tonic inhibitory action on central SNS activity. Moreover, in 2 rat models of neurogenic hypertension, one caused by intrarenal injection of phenol and the other by 5/6 nephrectomy, we observed that losartan, an Ang II type 1 receptor blocker, inhibits SNS activity and increases the abundance of IL-1beta and the neuronal isoform of nitric oxide synthase (nNOS) in the posterior hypothalamic nuclei (PH), paraventricular nuclei (PVN), and locus ceruleus (LC). This raises the possibility that the stimulatory effects of Ang II on central SNS activity may be mediated by inhibition of nNOS and IL-1beta. To test this hypothesis, we studied the effect of an intracerebroventricular (ICV) infusion of Ang II on blood pressure (BP), norepinephrine (NE) secretion from the PH, renal SNS activity (RSNA), and abundance of IL-1beta and nNOS mRNA in the PH, PVN, and LC of normal Sprague-Dawley rats. Finally, we measured the concentration of nitrite/nitrate in the dialysate collected from the PH after Ang II or vehicle. ICV infusion of Ang II (100 ng/kg body wt dissolved in 10 microL of artificial cerebrospinal fluid) raised BP, RSNA, and NE secretion from the PH compared with control rats. Ang II reduced the abundance of IL-1beta and nNOS mRNA in the PH, PVN, and LC. Pretreatment with losartan (10 microg/kg body wt dissolved in 10 microL of aCSF) given ICV 20 minutes before Ang II abolished the effects of Ang II on BP, RSNA, and NE secretion from the PH and IL-1beta and nNOS mRNA. Ang II also decreased the secretion of NO from the PH. In conclusion, these studies suggest that Ang II inhibits the expression of IL-1beta and nNOS in the brain. Because locally produced NO exerts a tonic inhibitory action on SNS activity, the decrease in NO expression caused by Ang II results in greater SNS activity.

Subdiaphragmatic vagotomy fails to inhibit intravenous leptin-induced IL-1beta expression in the hypothalamus

Leptin is known to be an important circulating signal for regulation of food intake and body weight. Recent evidence has suggested that leptin is involved in infection and inflammation. The afferent vagus nerve is known to be an important component for transmitting peripheral immune signals to the brain, such as interleukin (IL)-1beta expression in the brain, anorexia, and fever responses. In the present study, we investigated whether intravenous leptin-induced IL-1beta expression in the hypothalamus is mediated via afferent vagus nerve. IL-1beta transcripts in the hypothalamus were significantly increased on RT-PCR assessment 1 h after the administration of leptin (1 mg/kg iv) to mice. Subdiaphragmatic vagotomy did not significantly modify intravenous leptin-induced IL-1beta expression in the hypothalamus compared with that in sham-treated mice. These data suggest that circulating leptin directly acts in the brain independently of afferent vagus nerve input originating from the subdiaphragmatic organs.

Role of brain arachidonic acid cascade on central CRF1 receptor-mediated activation of sympatho-adrenomedullary outflow in rats

The present experiments were designed to characterize the mechanisms involved in the corticotropin releasing factor (CRF)-induced activation of central sympatho-adrenomedullary outflow in rats. Intracerebroventricularly (i.c.v.) administered CRF and urocortin (0.5, 1.5 and 3.0 nmol/animal) effectively and dose-dependently elevated plasma levels of adrenaline and noradrenaline, and the effect of urocortin was almost the same as that of CRF. The elevation of catecholamines induced by CRF and urocortin (1.5 nmol/animal) was reduced by CP-154,526(butyl-ethyl-(2,5-dimethyl-7-(2,4,6trimethylphenyl)-7H-pyrrolo [2,3-d] pyrimidin-4-yl]amine), a selective CRF1 receptor antagonist, in a dose dependent manner (1.2 and/or 2.4 micromol/animal, i.c.v.), and abolished by indomethacin (1.2 micromol/animal, i.c.v.), an inhibitor of cyclooxygenase. Furegrelate (1.8 micromol/animal, i.c.v.), an inhibitor of thromboxane A2 synthase, abolished the CRF-induced elevation of adrenaline, but had no effect on the evoked release of noradrenaline. These results suggest that activation of brain CRF1 receptor facilitates the central sympathetic and adrenomedullary outflow in distinct central pathways in rats; brain thromboxane A2 is involved in the central adrenomedullary outflow; an active metabolite of arachidonic acid other than thromboxane A2 (probably prostaglandin E2) may be involved in the central sympathetic outflow.

Interleukin-1beta and neurogenic control of blood pressure in normal rats and rats with chronic renal failure

Increased sympathetic nervous system (SNS) activity plays a role in the genesis of hypertension in rats with chronic renal failure (CRF). The rise in central SNS activity is mitigated by increased local expression of neuronal nitric oxide synthase (NOS) mRNA and NO(2)/NO(3) production. Because interleukin (IL)-1beta may activate nitric oxide in the brain, we have tested the hypothesis that IL-1beta may modulate the activity of the SNS via regulation of the local expression of neuronal NOS (nNOS) in the brain of CRF and control rats. To this end, we first found that administration of IL-1beta in the lateral ventricle of control and CRF rats decreased blood pressure and norepinephrine (NE) secretion from the posterior hypothalamus (PH) and increased NOS mRNA expression. Second, we observed that an acute or chronic injection of an IL-1beta-specific antibody in the lateral ventricle raised blood pressure and NE secretion from the PH and decreased NOS mRNA abundance in the PH of control and CRF rats. Finally, we measured the IL-1beta mRNA abundance in the PH, locus coeruleus, and paraventricular nuclei of CRF and control rats by RT-PCR and found it to be greater in CRF rats than in control rats. In conclusion, these studies have shown that IL-1beta modulates the activity of the SNS in the central nervous system and that this modulation is mediated by increased local expression of nNOS mRNA.

Nitric oxide regulates body temperature, neuronal activation and interleukin-1 beta gene expression in the hypothalamic paraventricular nucleus in response to immune stress

An immune challenge initiates a complex cascade of events in the body including important responses from the central nervous system. As nitric oxide (NO) has been implicated in the central regulation of neuroendocrine and autonomic responses, this study was performed to determine if NO regulates physiological responses, neuronal activation, and/or interleukin-1 beta (IL-1 beta) gene expression in the paraventricular nucleus of the rat hypothalamus (PVN) in response to intravenous endotoxin, lipopolysaccharide (LPS, 100 microg/kg). Intracerebroventricular injections of NO synthase (NOS) inhibitors (7-nitroindazole sodium salt for neuronal NOS, N(G)-nitro-L-arginine for neuronal NOS and endothelial NOS, and aminoguanidine for inducible NOS) in LPS-treated rats showed that inhibition of NOS eliminated the drop in body temperature and led to increased neuronal activation in the PVN as assessed by immunohistochemistry for Fos-like immunoreactivity. Activation of NO-producing PVN neurons was also increased in these rats suggesting that NO influences neuronal NOS activity in PVN neurons. Finally, increased IL-1 beta gene expression in the PVN of LPS-treated rats receiving N(G)-nitro-L-arginine showed that NO regulates brain IL-1 beta gene expression. The results obtained with the NOS inhibitors support the hypothesis that NO produced from eNOS in the brain participates in temperature regulation, and inhibits PVN neuronal activity and IL-1 beta gene expression during immune stress.

Electrical stimulation of afferent vagus nerve induces IL-1beta expression in the brain and activates HPA axis

Possible roles of the afferent vagus nerve in regulation of interleukin (IL)-1beta expression in the brain and hypothalamic-pituitary-adrenal (HPA) axis were examined in anesthetized rats. Levels of IL-1beta mRNA and protein in the brain were measured by comparative RT-PCR and ELISA. Direct electrical stimulation of the central end of the vagus nerve was performed continuously for 2 h. The afferent stimulation of the vagus nerve induced increases in the expression of mRNA and protein levels of IL-1beta in the hypothalamus and the hippocampus. Furthermore, expression of corticotropin-releasing factor mRNA was increased in the hypothalamus 2 h after vagal stimulation. Plasma levels of ACTH and corticosterone were also increased by this stimulation. The present results indicate that activation of the afferent vagus nerves itself can induce production of IL-1beta in the brain and activate the HPA axis. Therefore, the afferent vagus nerve may play an important role in transmitting peripheral signals to the brain in the infection and inflammation.

Brain phospholipase A(2)-arachidonic acid cascade is involved in the activation of central sympatho-adrenomedullary outflow in rats

The present experiments were designed to explore the role of the brain phospholipase A(2)-arachidonic acid cascade in the activation of central sympatho-adrenomedullary outflow in rats, using melittin (an activator of phospholipase A(2)) and arachidonic acid. Intracerebro-ventricularly administered melittin (2.5, 10, and 25 microg/animal) or arachidonic acid (75, 150, 300 microg/animal) effectively and dose dependently elevated plasma levels of adrenaline and noradrenaline. The elevation of both catecholamines induced by melittin (10 microg/animal) was abolished by centrally administered mepacrine (an inhibitor of phospholipase A(2)), but not by neomycin (an inhibitor of phospholipase C). However, mepacrine had no effect on the increase induced by arachidonic acid (150 microg/animal). Indomethacin (an inhibitor of cyclooxygenase) abolished all responses induced by melittin and arachidonic acid. Furegrelate (an inhibitor of thromboxane A(2) synthase) abolished the elevation of adrenaline induced by melittin and arachidonic acid, but had no effect on the elevation of noradrenaline induced by these compounds. These results suggest that activation of the brain phospholipase A(2)-arachidonic acid cascade facilitates the central sympatho-adrenomedullary outflow in rats. Brain thromboxane A(2) is involved in the activation of central adrenomedullary outflow and an active metabolite of arachidonic acid other than thromboxane A(2) may be involved in activation of the central sympathetic outflow.

Losartan reduces sympathetic nerve outflow from the brain of rats with chronic renal failure

Sympathetic nervous system (SNS) activity, measured by norepinephrine (NE) turnover rate, was greater in the posterior hypothalamic (PH) nuclei, the paraventricular nuclei (PVN), and the locus coeruleus (LC) of 5/6 nephrectomised (CRF) rats than of control rats. NE secretion from the PH was also greater in CRF than in control rats. These findings demonstrate that SNS activity plays an important role in the genesis of hypertension associated with CRF. The increase in central SNS activity was mitigated by increased local expression of nitric oxide synthase (NOS)-mRNA and nitric oxide (NOx) production. Because angiotensin II may stimulate the central SNS, we tested the hypothesis that losartan, a specific angiotensin II AT(1)-receptor antagonist, may lower blood pressure (BP), at least in part, by central noradrenergic inhibition. To this end, we studied two groups of CRF rats. One group received losartan (10 mg/kg body weight) in drinking water between the 3rd and 4th week after nephrectomy, the second group received drinking water without losartan. SNS activity was measured by NE secretion from the PH using the microdialysis technique. NOS-mRNA gene expression was also measured by RT-PCR in the PH, PVN, and LC of CRF and control rats. Losartan reduced systolic BP from 184+/-3.7 to 152+/-3.1 mmHg and NE secretion from the PH from 340+/-9.7 to 247+/-4.8 pg/ml. CRF rats treated with losartan manifested a significant (p<0.01) increase in the expression of nNOS-mRNA in the PH (from 84+/-1.2 to 99+/-2.6), the PVN (from 44+/-1.5 to 63+/-2.1), and the LC (from 59+/-6.7 to 76+/-2.1). CRF rats also manifested a significant increase (p<0.01) in the expression of IL-1beta the PH (from 41.6+/-2.8 to 54.3+/-1.4), PVN (from 44+/-1.9 to 54+/-1.5), and LC (from 35.5+/-1.6 to 53.5+/-1.9). In conclusion, these studies suggest that the antihypertensive action of losartan in CRF rats may be mediated, at least in part, by inhibition of central SNS outflow. The studies also suggest that the inhibitory action of losartan on the SNS may be mediated by activation of IL-1beta, which, in turn, stimulates nNOS, an important modulator of central SNS activity.

In vivo evidence that activation of tyrosine kinase is a trigger for lipopolysaccharide-induced fever in rats

We measured the rectal temperature of free-moving, conscious rats after intracerebroventricular (i.c.v.) injections of lipopolysaccharide (LPS) and interleukin-1beta (IL-1beta) with or without various antagonists to investigate the mechanisms involved in LPS-induced fever. LPS (3 microg) elicited significant increases in rectal temperature, which lasted from 0.5 h to more than 8 h after administration. This febrile response was inhibited by pretreatment with L-nitro-arginine (LNA), indomethacin (IND), genistein (GEN), tyrphostin 46 and anti-rat IL-1beta antibody (anti-IL-1beta Ab), but was not inhibited by pretreatment with daidzein or chelerythrine (CHE) into the ventricle. LPS (0.3 microg) following orthovanadate (i.c.v.) produced fever, although the small amount of LPS (0.3 microg) or orthovanadate alone showed no effect on rectal temperature. I.c.v. injections of IL-1beta also induced fever of approximately 4-h duration. This effect was inhibited by pretreatment with IND and anti-IL-1beta Ab, but was not inhibited by pretreatment with LNA, GEN or CHE into the ventricle. These findings demonstrate that in the central nervous system, LPS increases IL-1beta production after activation of tyrosine kinase and NO synthase, and IL-1beta promotes prostaglandin production resulting in increased rectal temperature. Activation of tyrosine kinase in the central nervous system is probably a trigger for the febrile response induced by LPS.

Central actions of nitric oxide in regulation of autonomic functions

The identification of nitric oxide (NO) as a gaseous, nonconventional neurotransmitter in the central nervous system has led to an explosion of studies aimed at learning about the roles of NO, not only at a cellular level, but also in regulating the activity of specific physiological systems that are coordinated by the brain. In the 1980s, publications began to appear which pointed to a role for NO in regulating peripheral autonomic function. In the 1990s, it became apparent that NO also acts centrally to affect autonomic responses. In this review, I will discuss the state of the current knowledge about the central role of NO in physiological functions which are related specifically to the control of sympathetic output. Studies which do not differentiate a central from a peripheral role for NO in these functions have not been included. After a brief discussion about the cellular events in which NO is involved, the distribution of NO-producing neurons in central autonomic areas of the brain will be presented. The more general actions of central NO in regulating sympathetic activity, as assessed with i.c.v. injections of pharmacological agents, will be followed by more specific sites of action achieved with microinjections into discrete brain areas. The review will be concluded with discussions about central NO in two physiological states of sympathetic imbalance, hypertension and stress.

Cardiorespiratory responses to interleukin-1beta in adult rats: role of nitric oxide, eicosanoids and glucocorticoids

Interleukin-1beta (IL-1beta) receptors are abundantly expressed in brain stem regions involved in respiratory control. We hypothesized that systemic administration of IL-1beta would increase ventilation (V(E )), and that nitric oxide, eicosanoids, and glucocorticoid receptors would modulate IL-1beta-induced cardioventilatory responses. Intravenous injections of three doses (37.5 ng kg(-1), 75 ng kg(-1 ) and 150 ng kg(-1)) of IL-1b induced monophasic increases in (V(E)), heart rate (HR), and blood pressure (BP) which had a distinctly different onset and duration of action compared to IL-1beta-induced body temperature elevations. Pre-treatment with the nitric oxide inhibitor L-NAME was associated with decreased peak V(E) responses, without affecting the latency and duration of IL-1beta. L-NAME also enhanced HR responses while pressor responses were attenuated. Eicosanoid inhibition with indomethacin resulted in markedly attenuated V responses. However, cardiovascular responses to IL-1beta were not modified by indomethacin. In contrast, pre-treatment with dexamethasone, was not associated with any changes in the IL-1beta-induced V(E), HR, or BP responses. We conclude that IL-1beta increases of V(E) are dose-dependent and are not time-locked with the pyrexic response suggesting the possibility that distinct neural pathways may underlie these responses. In addition, nitric oxide and eicosanoid-dependent mechanisms modulate IL-1beta ventilatory effects.

Thromboxane A2 is involved in the nitric oxide-induced central activation of adrenomedullary outflow in rats

The central effect of 3-morpholinosydnonimine, a nitric oxide donor, on the sympatho-adrenomedullary system was investigated in urethane-anesthetized rats. Intracerebroventricular administration of 3-morpholinosydnonimine (100, 250 and 500 microg/animal) induced a marked elevation of adrenaline levels and a slight elevation of noradrenaline levels in the plasma. These 3-morpholinosydnonimine (250 microg/animal)-induced elevations of catecholamines were abolished by intracerebroventricular treatments with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-l-oxyl 3-oxide (750 microg/animal), a nitric oxide scavenger, and indomethacin (500 microg/animal), a cyclo-oxygenase inhibitor, but not with superoxide dismutase (250 units/animal), a superoxide anion scavenger. Furthermore, the 3-morpholinosydnonimine (250 microg/animal)-induced elevation of plasma adrenaline levels was abolished by intracerebroventricular treatments with thromboxane A2 synthase inhibitors [furegrelate (100, 250 and 1000 microg/animal) and carboxyheptyl imidazole (500 microg/animal)], and also with thromboxane A2 receptor blockers [(+)-S-145 (100, 250 and 1000microg/animal) and SQ29548 (8microg/animal)]. The elevation of noradrenaline levels was, however, not attenuated by these thromboxane A2-related test agents. The present results indicate that nitric oxide but not peroxynitrite markedly activates central adrenomedullary outflow. Thromboxane A2 in the brain is probably involved in this central activation of adrenomedullary outflow.