Blockade of angiotensin II AT1 receptors inhibits pressor action of centrally administered interleukin-1beta in Sprague Dawley rats

The aim of the present study was to evaluate the influence of intraventricular administration of recombinant rat interleukin-1beta (IL-1beta) on regulation of resting blood pressure and heart rate and to test the hypothesis that the brain angiotensinergic system is involved in regulation of hemodynamic parameters by centrally applied IL-1beta. The experiments were performed on Sprague Dawley rats, assigned to three series of experiments. In series 1 (control, n = 6), mean arterial pressure (MAP) and heart rate (HR) were recorded for 15 min under baseline conditions. This was followed by infusion of saline (0.9% sterile NaCl 5 microL/h) into the left cerebral ventricle (LCV). Measurements were continued during the next 60 min. In series 2 (n = 6) and 3 (n = 6) the experimental design was similar, except that in series 2 the animals were LCV infused with saline containing IL-1beta (100 ng/h) and in series 3 with saline containing IL-1beta (100 ng/h) and angiotensin type 1 (AT1) receptors antagonist (Losartan, 10 microg/h). LCV infusion of saline alone did not influence MAP and HR while administration of IL-1beta elicited significant increase in MAP, but not in HR. The pressor effect was absent during combined infusion of IL-1beta and Losartan. Results of the study provide evidence that centrally administered IL-1beta exerts pressor effect, and reveal that this effect is mediated by stimulation of the brain angiotensin system and requires activation of AT1 receptors.     

Interleukin-1β, but not IL-1α, mediates nerve growth factor secretion from rat astrocytes via type I IL-1 receptor

In astrocytes, nerve growth factor (NGF) synthesis and secretion is stimulated by the cytokine interleukin-1β (IL-1β). In the present study, the role of IL-1 receptor binding sites in the regulation of NGF release was evaluated by determining the pharmacological properties of astroglially localized IL-1 receptors, and, by comparing the effects of both the agonists (IL-1α and IL-1β) and the antagonist (IL-1ra)—members of the IL-1 family on NGF secretion from rat neonatal cortical astrocytes in primary culture. Using receptor-binding studies, binding of [¹²⁵I] IL-1β to cultured astrocytes was saturable and of high affinity. Mean values for the K_D and B_max were calculated to be 60.7±7.4 pM and 2.5±0.1 fmol mg^-1 protein, respectively. The binding was rapid and readily reversible. IL-1 receptor agonists IL-1α (K_i of 341.1 pM) and IL-1β (K_i 59.9 pM), as well as the antagonist IL-1ra (K_i 257.6 pM), displaced specific [¹²⁵I] IL-1β binding from cultured astrocytes in a monophasic manner. Anti-IL-1RI antibody completely blocked specific [¹²⁵I] IL-1β binding while anti-IL-1RII antibody had no inhibitory effect. Exposure of cultured astrocytes to IL-1α and IL-1β revealed the functional difference between the agonists in influencing NGF release. In contrast to IL-1β (10 U/ml), which caused a 3-fold increase in NGF secretion compared to control cells, IL-1α by itself had no stimulatory action on NGF release. The simultaneous application of IL-1α and IL-1β elicited no additive response. IL-1ra had no effect on basal NGF release but dose-dependently inhibited the stimulatory response induced by IL-1β. We concluded that IL-1β-induced NGF secretion from cultured rat cortical astrocytes is mediated by functional type I IL-1 receptors, whereas IL-1α and IL-1ra, in spite of their affinity for IL-1RI, have no effect on NGF secretion from these cells. Type II IL-1R is not present on rat neonatal cortical astrocytes.     

Behavioral effects of peripheral interleukin-1 administration in adult CD-1 mice: specific inhibition of the offensive components of intermale agonistic behavior

Peripheral administration of interleukin-1β (IL-1β) in rodents reduces exploratory behavior in a novel environment while decreasing social investigation of a juvenile conspecific. In this study we wanted to test the effects of peripherally administered IL-1β on another aspect of the mouse social repertoire, namely intraspecific fighting towards an adult male intruder. In the first experiment, sickness behavior induced by IL-1β (1 μg/mouse) in adult CD-1 mice was assessed by direct observation of behavioral changes following placement into a novel environment. Three hours after injection, subjects were individually introduced for 20 min in a cage with clean sawdust and a number of behavioral items recorded. Blood samples were collected at the end of the testing session. Body temperature was measured right before, 1 h and 3.5 h following injection. In IL-1β treated mice, exploration (assessed by measuring duration and frequency of Wall Rearing and Rearing behaviors) was nearly totally suppressed, while duration and frequency of behaviors such as Grooming, Bar Holding, and Digging were also markedly reduced. Administration of IL-1β significantly elevated CORT secretion above basal levels and, as previously reported for mice, induced hypothermia (about 2°C). In the second experiment, we assessed mice receiving IL-1β (0.25; 0.5 or 1 μg/mouse or saline solution) in a social context. Three hours after injection, subjects were placed into a neutral cage for 20 min with a non-injected adult male conspecific and aggressive behavior scored. Overall, IL-1β administration affected the social repertoire of treated mice in a dose-dependent fashion. Specifically, agonistic components of aggressive behavior were nearly totally suppressed, while the defensive elements, such as Upright Defensive posture, Upright Submissive posture, Crouching, or Flee were not affected by IL-1β. Overall these data support the notion that sickness behavior induced by IL-1β administration represents an organized behavioral strategy and is not an aspecific response to an illness-type of condition.     

Actinomycin D blocks interleukin-1α-induced pial arteriolar dilation and increased prostanoid production in newborn pigs

Effects of protein synthesis and cyclooxygenase inhibitors on interleukin-1α (IL-1α)- and histamine-induced pial arteriolar dilation and cerebrospinal fluid (CSF) prostanoid increases were examined in anesthetized piglets using closed cranial windows. Topical IL-la (10.8 μg) increased pial arteriolar diameter from 15 to 30 min after its infusion, and enhanced CSF prostanoids. Topical protein synthesis inhibitor, actinomycin D, at a concentration of 10⁻⁸ M attenuated and 10⁻⁸ M completely blocked both IL-1α-induced vasodilation and CSF prostanoid increase. Inhibition of prostaglandin H synthases with indomethacin blocked both vasodilation and CSF prostanoid increase by IL-1α. Topical histamine (10⁻⁶ M) also increased pial arteriolar diameter and CSF prostanoids but without the delay seen between IL-1α infusion and responses. These histamine effects were not modified by coinfusion of actinomycin D but blocked by indomethacin. These results suggest that, although IL-1α and histamine do share the same mechanism insofar as activation of prostaglandin synthesis is concerned, an additional step appears to be involved for IL-1α, likely involving de novo protein synthesis.     

Interleukin (IL)-6 and IL-1 beta act synergistically within the brain to induce sickness behavior and fever in rats

Pro-inflammatory cytokines interleukin (IL)-6 and IL-1β can act in the brain (centrally) to cause fever. Sickness behaviors which accompany fever also appear to involve the central action of IL-1β. We injected species-homologous rat IL-6 and IL-1β directly into the brains of conscious rats to examine the effect of these cytokines on fever, and two behaviors affected by sickness, voluntary wheel-running and food intake. Male Sprague–Dawley rats selected for their predisposition to spontaneously run on running wheels were used in the experiment. Each rat was anaesthetized and had a temperature-sensitive radiotransmitter implanted intra-abdominally, and a 23-gauge stainless steel guide cannula inserted stereotaxically over the lateral cerebral ventricle. Rats were randomly assigned to receive intracerebroventricular injections of three doses of either IL-1β or IL-6 (100 ng, 1 ng or 0.1 ng IL-1β and 200 ng, 20 ng or 2 ng IL-6), or one of three different combinations of IL-1β and IL-6. Rats receiving either IL-1β or IL-6 showed a dose-dependent increase in body temperature and decrease in wheel-running (ANOVA, p < 0.0001). Only rats receiving the highest dose of IL-1β significantly decreased food intake and body mass compared to rats receiving vehicle (ANOVA, p < 0.001). Doses of IL-1β and IL-6 which, when injected on their own were non-pyrogenic and did not affect food intake and body mass, induced fever and anorexia when they were co-injected centrally. These results show that species-homologous rat IL-6 and IL-1β can act directly within the brain to decrease voluntary activity and suggest they also can act synergistically to induce anorexia and fever.     

Sleep-wake behavior and responses to sleep deprivation of mice lacking both interleukin-1 beta receptor 1 and tumor necrosis factor-alpha receptor 1

Data indicate that interleukin (IL)-1β and tumor necrosis factor-α (TNFα) are involved in the regulation of non-rapid eye movement sleep (NREMS). Previous studies demonstrate that mice lacking the IL-1β type 1 receptor spend less time in NREMS during the light period, whereas mice lacking the p55 (type 1) receptor for TNFα spend less time in NREMS during the dark period. To further investigate roles for IL-1β and TNFα in sleep regulation we phenotyped sleep and responses to sleep deprivation of mice lacking both the IL-1β receptor 1 and TNFα receptor 1 (IL-1R1/TNFR1 KO). Male adult mice (IL-1R1/TNFR1 KO, n = 14; B6129SF2/J, n = 14) were surgically instrumented with EEG electrodes and with a thermistor to measure brain temperature. After recovery and adaptation to the recording apparatus, 48 h of undisturbed baseline recordings were obtained. Mice were then subjected to 6 h sleep deprivation at light onset by gentle handling. IL-1R1/TNFR1 KO mice spent less time in NREMS during the last 6 h of the dark period and less time in rapid eye movement sleep (REMS) during the light period. There were no differences between strains in the diurnal timing of delta power during NREMS. However, there were strain differences in the relative power spectra of the NREMS EEG during both the light period and the dark period. In addition, during the light period relative power in the theta frequency band of the REMS EEG differed between strains. After sleep deprivation, control mice exhibited prolonged increases in NREMS and REMS, whereas the duration of the NREMS increase was shorter and there was no increase in REMS of IL-1R1/TNFR1 KO mice. Delta power during NREMS increased in both strains after sleep deprivation, but the increase in delta power during NREMS of IL-1R1/TNFR1 KO mice was of greater magnitude and of longer duration than that observed in control mice. These results provide additional evidence that the IL-1β and TNFα cytokine systems play a role in sleep regulation and in the alterations in sleep that follow prolonged wakefulness.     

IL-1β increases intracellular calcium through an IL-1 type 1 receptor mediated mechanism in C6 astrocytic cells

Interleukin-1β (IL-1β) is a cytokine that regulates a variety of biological processes. In addition to its traditional role in the immune system, IL-1β plays an integral role in neural-immune and developmental processes in the nervous system. The pleiotropic ability of IL-1β may be due to the activation of different signal transduction mechanisms in specific cell types or under certain cellular conditions. We have previously demonstrated that IL-1β regulates healing and repair in the developing, mammalian nervous system. In the damaged perinatal mouse brain, IL-1β is expressed in astrocytes that change from a stellate to a spindle-shaped morphology. The spindle-shaped astrocytes enclose the wound, separating the healthy from damaged neural tissue. The shape change and subsequent repair processes are IL-1β activity-dependent, acting through the IL-1 type 1 receptor (IL-1R1), as co-application of the IL-1type 1 receptor antagonist protein (IL-1ra) blocks IL-1β induced effects. In the C6 astrocytic cell line, IL-1β induced similar shape changes and upregulated expression of the cytoskeletal protein, glial fibrillary acidic protein (GFAP). Since cytoskeletal changes, as well as specific signal transduction mechanisms, are associated with increases in intracellular calcium ([Ca²⁺]_i), studies were carried out to determine if increases in [Ca²⁺]_i induced by IL-1β occurred through activation of the IL-1R1 in C6 cells. Cells were treated with IL-1β and/or IL-1ra, followed by measurement of relative changes in [Ca²⁺]_i using fura-2 fluorescence imaging methods. IL-1β increased [Ca²⁺]_i levels in a dose and time dependent manner. Treatment with IL-1ra blocked IL-1β induced increases in [Ca²⁺]_i, indicating that IL-1β acts through the IL-1R1. Immunocytochemistry experiments showed that untreated C6 cells normally express IL-1β, IL-1ra, and IL-1R1. Thus, IL-1 system molecules may play a role in normal C6 astrocyte physiology.     

The antihyperalgesic activity of a selective P2X7 receptor antagonist, A-839977, is lost in IL-1αβ knockout mice

The pro-inflammatory cytokine interleukin-1β (IL-1β) has been implicated in both inflammatory processes and nociceptive neurotransmission. Activation of P2X7 receptors is the mechanism by which ATP stimulates the rapid maturation and release of IL-1β from macrophages and microglial cells. Recently, selective P2X7 receptor antagonists have been shown to reduce inflammatory and neuropathic pain in animal models. However, the mechanisms underlying these analgesic effects are unknown. The present studies characterize the pharmacology and antinociceptive effects of a structurally novel P2X7 antagonist. A-839977 potently (IC₅₀ = 20–150 nM) blocked BzATP-evoked calcium influx at recombinant human, rat and mouse P2X7 receptors. A-839977 also potently blocked agonist-evoked YO-PRO uptake and IL-1β release from differentiated human THP-1 cells. Systemic administration of A-839977 dose-dependently reduced thermal hyperalgesia produced by intraplantar administration of complete Freund's adjuvant (CFA) (ED₅₀ = 100 μmol/kg, i.p.) in rats. A-839977 also produced robust antihyperalgesia in the CFA model of inflammatory pain in wild-type mice (ED₅₀ = 40 μmol/kg, i.p.), but the antihyperalgesic effects of A-839977 were completely absent in IL-1αβ knockout mice. These data demonstrate that selective blockade of P2X7 receptors in vivo produces significant antinociception in animal models of inflammatory pain and suggest that the antihyperalgesic effects of P2X7 receptor blockade in an inflammatory pain model in mice are mediated by blocking the release of IL-1β.     

Cardiovascular effects of central administration of clonidine in conscious cats

The effects on arterial blood pressure and heart rate after an intracerebroventricular (i.c.v.) administration of clonidine were investigated using conscious normotensive cats. Injection of clonidine (5–10 μg; 5 μl; i.c.v.) elicited a decrease in mean arterial pressure (MAP) and heart rate (HR) in a dose-dependent manner. The highest dose of 10 μg of clonidine decreased MAP and HR by 39 ± 3 mmHg and 74 ± 5 b.p.m., respectively (n = 7). Pretreatment with yohimbine, the α₂-adrenoceptor antagonist (8 μg; 5 μl; i.c.v.) blocked the cardiovascular responses to a subsequent i.c.v. injection of 10 μg clonidine (n = 7). Furthermore, preadministration of cimetidine (100 μg; 5 μl; i.c.v.), the H₂ histamine receptor antagonist with imidazoline receptor activating properties, prevented the decreases in MAP and HR to a subsequent i.c.v. injection of 10 μg clonidine (n = 7). By contrast, pretreatment with the specific I₁ imidazoline receptor blocker, efaroxan (100–500 μg; 5 μl; i.c.v.), failed to inhibit the cardiovascular effects of an i.c.v. administration of 10 μg clonidine (n = 7). These results suggest that the effects of centrally administered clonidine on MAP and HR are probably not mediated through activation of the I₁ subtype of imidazoline receptors in conscious cats. However, the cardiovascular effects elicited by i.c.v. administration of clonidine appear to result from stimulation of central α₂-adrenergic or the H₂ histaminergic-like receptors.     

Etiology and site of temporal lobe epilepsy influence postictal cytokine release

Inflammatory mechanisms are involved in the pathogenesis of epilepsy. Vice versa, immune functions are regulated by the brain. We measured postictal changes in serum levels of the immuno-modulating cytokines IL-1β, IL-6 and TNFα in patients with well-defined temporal lobe epilepsy (TLE) and determined modifying factors. Serum levels of IL-1β, IL-6 and TNFα were quantified by ELISA at baseline as well as immediately, 1 h and 24 h after a complex partial (CPS) or secondary generalized tonic–clonic seizure (GTCS) during video-EEG monitoring in 25 patients suffering from temporal epilepsy. IL-6 increased by 51% immediately after the seizure (p < 0.01) and remained elevated for 24 h. This increase lacked in patients with hippocampal sclerosis (HS; n = 16, mean increase 28%, p > 0.5, vs. 112%, p < 0.01 in patients without HS). IL-6 levels were higher after right-sided seizures as compared to left-sided seizures 24 h after the seizure (8.7 pg/mL vs. 3.4 pg/mL, p < 0.05). In patients taking valproate (VPA, n = 9), the levels of IL-1β were higher as compared to patients not treated with VPA. The results suggest a relationship between the cytokine system and characteristics of TLE such as side and pathology.     

Losartan, nonpeptide angiotensin II-type 1 (AT1) receptor antagonist, attenuates pressor and sympathoexcitatory responses evoked by angiotensin II andL-glutamate in rostral ventrolateral medulla

We investigated the effect of losartan, a nonpeptide angiotensin II (Ang II)-type 1 (AT₁) receptor antagonist, on the responses evoked by Ang II andL-glutamate (L-Glu) in the rostral ventrolateral medulla (RVLM). Adult spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were anesthetized with halothane and artificially ventilated. Responses of mean arterial pressure (MAP), heart rate (HR) and splanchnic sympathetic nerve activity (SNA) to microinjection of Ang II (100 pmol) orL-Glu (2 nmol) into the RVLM were examined following microinjection of losartan (10 pmol–10 nmol). Ang II increased MAP (16 ± 1mmHg in SHR and16 ± 1mmHg in WKY) and SNA (9 ± 1%and10 ± 1%, respectively), which were significantly (P < 0.01) attenuated by pretreatment with losartan (100 pmol − 10 nmol) in both strains. In addition, the pressor and sympathoexcitatory responses evoked byL-Glu were attenuated by losartan in a dose-dependent manner. The increases of MAP evoked byL-Glu (53 ± 6mmHg in SHR and39 ± 3mmHg in WKY) were suppressed to 5 ± 3mmHg(P < 0.01) and 4 ± 2mmHg (P < 0.01), respectively, in the presence of 10 nmol of losartan. The increase of SNA was also markedly inhibited by higher doses of losartan. The cardiovascular responses evoked byL-Glu, however, were not attenuated by pretreatment with either 1 nmol of [Sar¹, Thr⁸]-Ang II or 10 nmol of potassium acetate, suggesting that the effect of losartan onL-Glu response may not be attributed to the blockade of Ang II receptor or to the high concentration of potassium. These results indicate that the AT₁ receptor is responsible, in part, for the vasomotor action of Ang II in the RVLM and losartan has an inhibitory effect on pressor and sympathoexcitatory responses evoked byL-Glu by mechanisms other than those mediated by Ang II receptors.     

Cerebral vessels express interleukin 1β after focal cerebral ischemia

Rapid and marked increased levels of expression of interleukin 1β (IL-1β) mRNA have been detected in animal models of cerebral ischemia. However, the protein production of IL-1β and the cellular sources of IL-1β are largely undefined after cerebral ischemia. In the present study, we have measured the cellular localization of IL-1β protein in brain tissue from non-ischemic and ischemic mice using immunohistochemistry. Male C57B/6J (n=45) mice were subjected to middle cerebral artery (MCA) occlusion by a clot or a suture. The mice were sacrificed at time points spanning the period from 15 min to 24 h after onset of the MCA occlusion. Non-operated and sham-operated mice were used as control groups. A monoclonal anti-IL-1β antibody was used to detect IL-1β. In the non-operated and sham-operated mice, a few IL-1β immunoreactive cells were detected scattered throughout both hemispheres. IL-1β immunoreactive cells increased in the ischemic lesion as early as 15 min and peaked at 1 h to 2 h after MCA occlusion. IL-1β immunoreactivity was detected in the cortex of the contralateral hemisphere 1 h after ischemia. By 24 h after onset of ischemia, IL-1β immunoreactivity was mainly present adjacent to the ischemic lesion and in the non-ischemic cortex. IL-1β immunoreactivity was found on endothelial cells and microglia. This study demonstrates an early bilateral expression of IL-1β on endothelium after MCA occlusion in mice.     

Brain-IL-1β induces local inflammation but systemic anti-inflammatory response through stimulation of both hypothalamic–pituitary–adrenal axis and sympathetic nervous system

It is well established that systemic inflammation induces a counter-regulatory anti-inflammatory response particularly resulting in deactivation of monocytes/macrophages. However, recently we demonstrated a systemic anti-inflammatory response without preceding signs of systemic inflammation in patients with brain injury/surgery and release of cytokines into the cerebrospinal fluid (CSF). In order to analyze the mechanisms and pathways of systemic immunodepression resulting from sterile cerebral inflammation we established an animal model using continuous intra-cerebroventricular (i.c.v.) or intra-hypothalamic (i.h.) infusion of rat recombinant (rr) tumor necrosis factor (TNF)-α and interleukin (IL)-1β for 48 h. Controls received intra-venous (i.v.) cytokine administration. Interestingly, i.c.v. and i.h. infusion of IL-1β but not TNF-α produced distinct signs of central nervous system (CNS) inflammation. Correspondingly, i.c.v. infusion of IL-1β particularly diminished the TNF-α but increased the IL-10 concentration in whole blood cultures after endotoxin stimulation. All parameters normalized within 48 h after termination of the infusion. Blocking the hypothalamic–pituitary–adrenal (HPA) axis by hypophysectomy (HPX) led to complete recovery of the diminished TNF-α concentration and temporarily inhibited the IL-10 increase. Blocking the sympathetic nervous system (SNS) transmission by application of the β₂-adrenoreceptor antagonist propranolol not only inhibited the increase but further downregulated the endotoxin induced IL-10 concentration in the media of whole blood cell cultures, whereas the TNF-α decrease was only partially prevented. Interestingly, HPX and propranolol also diminished the cell invasion into the CSF. In summary, activation of both the HPA axis and the SNS plays an important role in systemic anti-inflammatory response resulting from cytokines in brain and cerebral inflammation.     

Differential effects of central and peripheral injection of interleukin-1β on brain c-fos expression and neuroendocrine functions

Cytokines such as interleukin-1β (IL-1β) alter the activity of the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes in the rat. However, the brain sites at which IL-1β exerts these effects have not been well identified. The present study sought to identify some of these sites, using c-fos protein expression as an index of cellular activation. We also attempted to determine possible differences between the effects of peripheral and central injection of IL-1β on the activation of specific brain areas. Castrated male rats received intravenous (i.v.) or intracerebroventricular (i.c.v.) injections of IL-1β through a jugular catheter or a permanent cannula implanted in the right lateral ventricle, respectively. Blood samples were taken before, as well as 30 and 120 min after i.v. or i.c.v. IL-1β infusion in order to measure plasma ACTH and LH levels. Immediately thereafter, the rats were anesthetized with pentobarbital, then perfused. Their brains were removed and postfixed for one hour. Thirty-μm frozen sections were cut and approximately every fourth tissue section was processed for c-fos expression by an avidin-biotin-peroxidase method. Both i.v. (1 μg) and i.c.v. (100 ng) injection of IL-1β significantly increased plasma ACTH levels, but only i.c.v. treatment measurably inhibited LH secretion. I.c.v. infusion of the cytokine markedly augmented c-fos expression in the paraventricular nucleus (PVN) and the arcuate nucleus (ARC) of the hypothalamus. A large amount of CRF cells in the PVN contained labelled c-fos protein (as measured by a double labelling technique), which indicates that CRF perikarya in this hypothalamic region are activated by the central administration of IL-1β. In contrast, i.v. injection of IL-1β did not significantly alter c-fos expression in the PVN or the ARC of the hypothalamus. These results suggest that the increased HPA axis activity which follows the peripheral IL-1β administration, a phenomenon previously shown to depend on endogenous CRF, does not require immediate activation of hypothalamic CRF perikarya. Thus our results indicate that the stimulatory effect of blood-born cytokine may be exerted at the level of nerve terminals in the median eminence. In contrast, i.c.v.-injected IL-1β appears to activate the HPA axis through a stimulation of CRF neurons within the parvocellular part of PVN. Finally, we postulate that the increase in cellular activity observed in the ARC of the hypothalamus may be involved in the decrease in LH secretion observed after i.c.v. infusion of IL-1β.     

Intracerebral HIV glycoprotein (gp120) enhances tumor metastasis via centrally released interleukin-1

Infection with the human immunodeficiency virus (HIV) is associated with a high incidence of cancers. This relationship does not appear to be due to a direct effect of the virus, and may be mediated by neuroimmune interactions since the HIV glycoprotein, gp120, enters the brain soon after infection with HIV, and intracerebroventricular (i.c.v.) infusion of gp120 suppresses aspects of cellular and tumor immunity. It has been speculated that this suppression may be attributed to the release of interleukin-1 (IL-1) in the brain induced by gp120. Using an in vivo tumor model, we examined the effect of centrally administered gp120 on tumor metastasis and lung clearance of mammary adenocarcinoma (MADB106) tumor cells in rats, and the role played by brain IL-1 in mediating these effects. We demonstrate that central administration of gp120 (4 μg) significantly (p<0.05) increased the retention of tumor cells in the lungs and significantly (p<0.02) enhanced the development of tumor metastases. Central administration of IL-1β (10 ng) also significantly (p<0.05) increased retention of tumor cells in the lungs. The effect of gp120 on lung retention of tumor cells was blocked by co-administration of α-melanocyte stimulating hormone (α-MSH, 20 ng), a hormone that blocks many of the biological effects of IL-1, or the IL-1 receptor antagonist (50 μg). Given that systemic administration of gp120 or IL-1β had no effect on the retention of tumor cells in the lungs, these findings indicate that gp120-induced secretion of IL-1 within the brain most likely mediates the effects of gp120 on tumor metastasis. These findings suggest a possible neuroimmune mechanism to account for the increased incidence and aggressiveness of tumors in HIV-infected patients.     

Relative contributions of peripheral and central sources to levels of IL-1α in the cerebral cortex of mice: assessment with species-specific enzyme immunoassays

The peripheral administration or release of cytokines is associated with central nervous system (CNS) effects that are often due to the actions of cytokines behind the blood–brain barrier (BBB). It is not known whether the majority of cytokine behind the BBB is derived from blood or is released from the CNS in response to peripheral signals. We addressed this question for interleukin-1α (IL-1α) by infusing human IL-1α (humIL-1α) into mice and measuring humIL-1α and murine IL-1α (murIL-1α) in cerebral cortex and serum with specific, sensitive enzyme immunoassays. In adult mice receiving 50 μg/kg-24 h of humIL-1α subcutaneously for 48 h, brain and blood samples contained humIL-1α but no murIL-1α. This shows that in our study blood-borne IL-1α did not self-stimulate its release in blood or brain. The presence of humIL-1α in brain could only have originated from blood, where it was administered; the brain/blood ratio of 0.126 ml/g indicates that at steady state, brain levels reach about 12% of blood levels. In neonatal mice, both murIL-1α and humIL-1α were detected in brain and blood after the acute subcutaneous injection of humIL-1α. However, the vast majority of immunoactivity in blood and brain was humIL-1α. These results show that most of the IL-1α appearing in response to circulating IL-1α in areas of the CNS behind the BBB is due to passage across the BBB and not to release from stores endogenous to the CNS.     

Relationship of interleukin-1β and β2-microglobulin with neuropeptides in cerebrospinal fluid of patients with dementia of the Alzheimer type

We studied interleukin-1β (IL-1β), β₂-microglobulin (β₂-m, β-endorphin, substance P, neuropeptide Y and somatostatin concentrations in the cerebrospinal fluid of 13 patients with dementia of the Alzheimer type (DAT), 13 patients with multi-infarct dementia (MID) and 15 age-matched control subjects. Substance P was significantly lower in DAT than in controls (P < 0.05), as well as somatostatin in DAT as compared to both controls (P < 0.01) and MID (P < 0.05), whereas β₂-m was higher in DAT than in controls (P < 0.01). Neuropeptide Y, β-endorphin and IL-1β showed similar concentrations in the three groups studied. A significantly positive correlation was observed between IL-1β and substance P (r = 0.79, P < 0.01) and somtostatin (r = 0.75, P < 0.05) in DAT, which was not observed in MID. In addition, β₂-m showed a negative correlation with IL-1β (r = −0.73, P < 0.05) in DAT, and age correlated negatively with IL-1β in controls and MID, but positively in DAT. Therefore, these results support the idea that an altered relationship may exist in Alzheimer's disease between the nervous and immune system.     

Intercellular adhesion molecule-1 expression induced by interleukin (IL)-1β or an IL-1β fragment is blocked by an IL-1 receptor antagonist and a soluble IL-1 receptor

The effects of a recombinant human interleukin-1 (IL-1) receptor antagonist (IL-1ra) and a recombinant human soluble IL-1 receptor (sIL-1R) on cytokine-induced intercellular adhesion molecule-1 (ICAM-1) expression in a human glioblastoma cell line and a neuroblastoma cell line were determined. Cells were incubated with IL-1β, tumor necrosis factor (TNF)α and interferon (IFN)γ. Cells were also tested under identical conditions with an IL-1β synthetic peptide fragment (IL-1β_208–240) previously shown to possess biological activity. IL-1β, TNFα and IFNγ potentiated ICAM-1 expression in both cell lines in a dose-related manner. The IL-1β_208–240 fragments, corresponding to the rabbit, rat and human sequences, enhanced ICAM-1 expression in glioblastoma cells at high doses. ICAM-1 expression induced by IL-1β, rabbit IL-1β_208–240 and human IL-1β_208–240 was blocked by the IL-1ra, while TNFα- and IFNγ-induced ICAM-1 expression were not. ICAM-1 expression induced by IL-1β and human IL-1β_208–240 was also blocked by the sIL-1R. Our findings suggest that IL1β_208–240 acts as an IL-1β agonist in enhancing ICAM-1 expression in vitro and that this effect is receptor-mediated.     

Cardiovascular effects of intravenous administration of clonidine in conscious cats

We previously reported that cardiovascular effects elicited by intracerebroventricular (i.c.v.) administration of clonidine result from stimulation of central α₂-adrenergic and/or H₂-histaminergic receptors, but not via activation of I₁-imidazoline receptors in conscious cats. In this study, we investigated the effects on arterial blood pressure (MAP) and heart rate (HR) following an intravenous (i.v.) administration of clonidine using conscious cats. Injection of clonidine (2–10 μg/kg i.v.) elicited a decrease in mean arterial pressure (MAP) and heart rate (HR) dose-dependently. The dose of 10 μg/kg of clonidine decreased MAP and HR by 30±4 mmHg and 62±15 bpm, respectively. Intravenous or i.c.v. pretreatment with yohimbine, the α₂-adrenoceptor and 5-HT_1A receptor antagonist, blocked the cardiovascular responses to a subsequent i.v. injection of 10 μg/kg clonidine. However, i.v. or i.c.v. preadministration of cimetidine, the H₂-histamine receptor antagonist, failed to antagonize the decreases in MAP and HR to a subsequent i.v. injection of 10 μg/kg clonidine. In addition, i.c.v. or i.v. pretreatment with the I₁-imidazoline receptor blocker, efaroxan, failed to inhibit the cardiovascular effects of an i.v. administration of clonidine. These results demonstrate that i.v. clonidine evokes decreases in MAP and HR possibly via central α₂-adrenoceptor and/or 5-HT_1A receptors and not through H₂-histamine or I₁-imidazoline receptors.     

Cardiovascular effects elicited by central administration of physostigmine via M2 muscarinic receptors in conscious cats

The cardiovascular effects of an intracerebroventricular (i.c.v.) injection of physostigmine were studied using conscious cats. Physostigmine (5–25 μg: 5 μl) caused a dose-dependent increase in mean arterial pressure (MAP) and heart rate (HR). The highest dose (25 μg) increased MAP and HR by 32 ± 3 mmHg and 45 ± 5 beats/min, respectively (n = 5). Pre-administration of the muscarinic receptor antagonist, atropine (25 μg; i.c.v.) blocked the effects of physostigmine (25 μg; i.c.v.). Also, the pre-administration of the M₂ muscarinic antagonist, methoctramine (25 μg; i.c.v.), antagonized the cardiovascular effects of physostigmine without altering the baseline variables. However, the M₁ muscarinic antagonist, pirenzepine (100 μg; i.c.v.) did not alter baseline MAP or HR, and also failed to inhibit the cardiovascular responses to physostigmine. Similarly, the M₃ muscarinic blocker, 4-diphenyl-acetoxy-N-methylpiperidine methiodide (50 μg; i.c.v.), neither changed baseline cardiovascular variables nor blocked the effects of physostigmine. When the same cats were anesthetized with intravenous injection of sodium pentobarbital (25–30 mg/kg), physostigmine (25 μg; i.c.v.) evoked a decrease in MAP and HR of 13 ± 6 mmHg and 15 ± 6 bpm, respectively (n = 5). These results demonstrate that the increases in MAP and HR to the i.c.v. administration of physostigmine in conscious cats arepossibly mediated through stimulation of central M₂ muscarinic receptors. In addition, anesthesia reverses the effects elicited by the central administration of physostigmine to a decrease in MAP and HR.