Co-localization of interleukin-1 receptor type I and interleukin-1 receptor antagonist with vasopressin in magnocellular neurons of the paraventricular and supraoptic nuclei of the rat hypothalamus

Microglial Activation Modulates Neuroendocrine Secretion During Experimental Sepsis

Sepsis promotes an inflammatory state in the central nervous system (CNS) that may cause autonomic, cognitive, and endocrine changes. Microglia, a resident immune cell of the CNS, is activated in several brain regions during sepsis, suggesting its participation in the central alterations observed in this disease. In this study, we aimed to investigate the role of microglial activation in the neuroendocrine system functions during systemic inflammation. Wistar rats received an intracerebroventricular injection of the microglial activation inhibitor minocycline (100 μg/animal), shortly before sepsis induction by cecal ligation and puncture. At 6 and 24 h after surgery, hormonal parameters, central and peripheral inflammation, and markers of apoptosis and synaptic function in the hypothalamus were analyzed. The administration of minocycline decreased the production of inflammatory mediators and the expression of cell death markers, especially in the late phase of sepsis (24 h). With respect to the endocrine parameters, microglial inhibition caused a decrease in oxytocin and an increase in corticosterone and vasopressin plasma levels in the early phase of sepsis (6 h), while in the late phase, we observed decreased oxytocin and increased ACTH and corticosterone levels compared to septic animals that did not receive minocycline. Prolactin levels were not affected by minocycline administration. The results indicate that microglial activation differentially modulates the secretion of several hormones and that this process is associated with inflammatory mediators produced both centrally and peripherally.

Interleukin-1 receptor type 1 is overexpressed in neurons but not in glial cells within the rat superficial spinal dorsal horn in complete Freund adjuvant-induced inflammatory pain

Background

All known biological functions of the pro-inflammatory cytokine interleukin-1β (IL-1β) are mediated by type 1 interleukin receptor (IL-1R1). IL-1β–IL-1R1 signaling modulates various neuronal functions including spinal pain processing. Although the role of IL-1β in pain processing is generally accepted, there is a discussion in the literature whether IL-1β exerts its effect on spinal pain processing by activating neuronal or glial IL-1R1. To contribute to this debate, here we investigated the expression and cellular distribution of IL-1R1 in the superficial spinal dorsal horn in control animals and also in inflammatory pain.

Methods

Experiments were performed on rats and wild type as well as IL-1R1-deficient mice. Inflammatory pain was evoked by unilateral intraplantar injection of complete Freund adjuvant (CFA). The nociceptive responsiveness of control and CFA-treated animals were tested daily for withdrawal responses to mechanical and thermal stimuli before and after CFA injection. Changes in the expression of 48 selected genes/mRNAs and in the quantity of IL-1R1 protein during the first 3 days after CFA injection were measured with the TaqMan low-density array method and Western blot analysis, respectively. The cellular localization of IL-1R1 protein was investigated with single and double staining immunocytochemical methods.

Results

We found a six times and two times increase in IL-1R1 mRNA and protein levels, respectively, in the dorsal horn of CFA-injected animals 3 days after CFA injection, at the time of the summit of mechanical and thermal allodynia. Studying the cellular distribution of IL-1R1, we found an abundant expression of IL-1R1 on the somatodendritic compartment of neurons and an enrichment of the receptor in the postsynaptic membranes of some excitatory synapses. In contrast to the robust neuronal localization, we observed only a moderate expression of IL-1R1 on astrocytes and a negligible one on microglial cells. CFA injection into the hind paw caused a remarkable increase in the expression of IL-1R1 in neurons, but did not alter the glial expression of the receptor.

Conclusion

The results suggest that IL-1β exerts its effect on spinal pain processing primarily through neuronal IL-1R1, but it can also interact in some extent with IL-1R1 expressed by astrocytes.

Modulating Effect of Cytokines on Mechanisms of Synaptic Plasticity in the Brain

After accumulation of data showing that resident brain cells (neurons, astrocytes, and microglia) produce mediators of the immune system, such as cytokines and their receptors under normal physiological conditions, a critical need emerged for investigating the role of these mediators in cognitive processes. The major problem for understanding the functional role of cytokines in the mechanisms of synaptic plasticity, de novo neurogenesis, and learning and memory is the small number of investigated cytokines. Existing concepts are based on data from just three proinflammatory cytokines: interleukin-1 beta, interleukin-6, and tumor necrosis factor-alpha. The amount of information in the literature on the functional role of antiinflammatory cytokines in the mechanisms of synaptic plasticity and cognitive functions of mature mammalian brain is dismally low. However, they are of principle importance for understanding the mechanisms of local information processing in the brain, since they modulate the activity of individual cells and local neural networks, being able to reconstruct the processes of synaptic plasticity and intercellular communication, in general, depending on the local ratio of the levels of different cytokines in certain areas of the brain. Understanding the functional role of cytokines in cellular mechanisms of information processing and storage in the brain would allow developing preventive and therapeutic means for the treatment of neuropathologies related to impairment of these mechanisms.

Direct pro-inflammatory effects of prorenin on microglia

Neuroinflammation has been implicated in hypertension, and microglia have been proposed to play an important role in the progression of this disease. Here, we have studied whether microglia are activated within cardiovascular regulatory area(s) of the brain during hypertension, especially in high blood pressure that is associated with chronic activation of the renin-angiotensin-system. In addition, we determined whether prorenin, an essential component of the renin-angiotensin-system, exerts direct pro-inflammatory effects on these microglia. Our data indicate that two rodent models which display neurogenic hypertension and over activation of the renin-angiotensin-system in the brain (sRA mice and spontaneously hypertensive rats) exhibit microglial activation, and increased levels of pro-inflammatory cytokines, in the paraventricular nucleus of the hypothalamus, an area crucial for regulation of sympathetic outflow. Further, the renin-angiotensin-system component prorenin elicits direct activation of hypothalamic microglia in culture and induction of pro-inflammatory mechanisms in these cells, effects that involve prorenin receptor-induced NFκB activation. In addition, the prorenin-elicited increases in cytokine expression were fully abolished by microglial inhibitor minocycline, and were potentiated by pre-treatment of cells with angiotensin II. Taken together with our previous data which indicate that pro-inflammatory processes in the paraventricular nucleus are involved in the hypertensive action of renin-angiotensin-system, the novel discovery that prorenin exerts direct stimulatory effects on microglial activation and pro-inflammatory cytokine production provides support for the idea that renin-angiotensin-system -induced neurogenic hypertension is not restricted to actions of angiotensin II alone.

Subfornical organ mediates sympathetic and hemodynamic responses to blood-borne proinflammatory cytokines

Proinflammatory cytokines play an important role in regulating autonomic and cardiovascular function in hypertension and heart failure. Peripherally administered proinflammatory cytokines, such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), act on the brain to increase blood pressure, heart rate, and sympathetic nerve activity. These molecules are too large to penetrate the blood-brain barrier, and so the mechanisms by which they elicit these responses remain unknown. We tested the hypothesis that the subfornical organ (SFO), a forebrain circumventricular organ that lacks a blood-brain barrier, plays a major role in mediating the sympathetic and hemodynamic responses to circulating proinflammatory cytokines. Intracarotid artery injection of TNF-α (200 ng) or IL-1β (200 ng) dramatically increased mean blood pressure, heart rate, and renal sympathetic nerve activity in rats with sham lesions of the SFO (SFO-s). These excitatory responses to intracarotid artery TNF-α and IL-1β were significantly attenuated in SFO-lesioned (SFO-x) rats. Similarly, the increases in mean blood pressure, heart rate, and renal sympathetic nerve activity in response to intravenous injections of TNF-α (500 ng) or IL-1β (500 ng) in SFO-s rats were significantly reduced in the SFO-x rats. Immunofluorescent staining revealed a dense distribution of the p55 TNF-α receptor and the IL-1 receptor accessory protein, a subunit of the IL-1 receptor, in the SFO. These data suggest that SFO is a predominant site in the brain at which circulating proinflammatory cytokines act to elicit cardiovascular and sympathetic responses.

Peripheral osmotic stimulation inhibits the brain's innate immune response to microdialysis of acidic perfusion fluid adjacent to supraoptic nucleus

During the brain's innate immune response microglia, astroglia and ependymal cells resolve/repair damaged tissue and control infection. Released interleukin-1beta (IL-1beta) reaching cerebroventricles stimulates circumventricular organs (CVOs; subfornical organ, SFO; organum vasculosum lamina terminalis, OVLT), the median preoptic nucleus (MePO), and magnocellular and parvocellular neurons in the supraoptic (SON) and paraventricular (PVN) nuclei. Hypertonic saline (HS) also activates these osmosensory CVOs and neuroendocrine systems, but, in contrast to IL-1beta, inhibits the peripheral immune response. To examine whether the brain's innate immune response is attenuated by osmotic stimulation, sterile acidic perfusion fluid was microdialyzed (2 microl/min) in the SON area of conscious rats for 6 h with sterile HS (1.5 M NaCl) injected subcutaneously (15 ml/kg) at 5 h. Immunohistochemistry identified cytokine sources (IL-1beta(+); OX-42(+) microglia) and targets (IL-1R(+); inducible cyclooxygenase, COX-2(+); c-Fos(+)) near the probe, in CVOs, MePO, ependymal cells, periventricular hypothalamus, SON, and PVN. Inserting the probe stimulated magnocellular neurons (c-Fos(+); SON; PVN) via the MePO (c-Fos(+)), a response enhanced by HS. Microdialysis activated microglia (OX-42(+); amoeboid/hypertrophied; IL-1beta(+)) in the adjacent SON and bilaterally in perivascular areas of the PVN, periventricular hypothalamus and ependyma, coincident with c-Fos expression in ependymal cells and COX-2 in the vasculature. These microglial responses were attenuated by HS, coincident with activating parvocellular and magnocellular neuroendocrine systems and elevating circulating IL-1beta, oxytocin, and vasopressin. Acidosis-induced cellular injury from microdialysis activated the brain's innate immune response by a mechanism inhibited by peripheral osmotic stimulation.

Neurosteroid biosynthesis: enzymatic pathways and neuroendocrine regulation by neurotransmitters and neuropeptides

Neuroactive steroids synthesized in neuronal tissue, referred to as neurosteroids, are implicated in proliferation, differentiation, activity and survival of nerve cells. Neurosteroids are also involved in the control of a number of behavioral, neuroendocrine and metabolic processes such as regulation of food intake, locomotor activity, sexual activity, aggressiveness, anxiety, depression, body temperature and blood pressure. In this article, we summarize the current knowledge regarding the existence, neuroanatomical distribution and biological activity of the enzymes responsible for the biosynthesis of neurosteroids in the brain of vertebrates, and we review the neuronal mechanisms that control the activity of these enzymes. The observation that the activity of key steroidogenic enzymes is finely tuned by various neurotransmitters and neuropeptides strongly suggests that some of the central effects of these neuromodulators may be mediated via the regulation of neurosteroid production.

Interleukin-6 activates arginine vasopressin neurons in the supraoptic nucleus during immune challenge in rats

The increase of plasma arginin-vasopressin (AVP) release, which translates hypothalamic AVP neuron activation in response to immune challenge, appears to occur independently of plasma osmolality or blood pressure changes. Many studies have shown that major inflammatory mediators produced in response to peripheral inflammation, such as prostaglandin (PG)-E(2) and interleukin (IL)-1beta, excite AVP neurons. However, in vivo electrical activation of AVP neurons was still not assessed in relation to plasma AVP release, osmolality, or blood pressure or to the expression and role of inflammatory molecules like PG-E(2), IL-1beta, IL-6, and tumor necrosis factor-alpha (TNFalpha). This study aims at elucidating those factors that underlie the activation of AVP neurons in response to immune stimulation mimicked by an intraperitoneal injection of lipopolysaccharide (LPS) in male Wistar rats. LPS treatment concomittanlty decreased diuresis and increased plasma AVP as well as AVP neuron activity in vivo, and these effects occurred as early as 30 min. Activation was sustained for more than 6 h. Plasma osmolality did not change, whereas blood pressure only transiently increased during the first hour post-LPS. PG-E(2), IL-1beta, and TNFalpha mRNA expression were raised 3 h after LPS, whereas IL-6 mRNA level increased 30 min post-LPS. In vivo electrophysiological recordings showed that brain IL-6 injection increased AVP neuron activity similarly to peripheral LPS treatment. In contrast, brain injection of anti-IL-6 antibodies prevented the LPS induced-activation of AVP neurons. Taken together, these results suggest that the early activation of AVP neurons in response to LPS injection is induced by brain IL-6.

Interleukin-1beta release in the supraoptic nucleus area during osmotic stimulation requires neural function

Interleukin (IL)-1beta is present throughout the magnocellular neuroendocrine system and co-depletes with oxytocin and vasopressin from the neural lobe during salt-loading. To examine whether IL-1beta is released from the dendrites/soma of magnocellular neurones during osmotic stimulation, microdialysis adjacent to the supraoptic nucleus (SON) in conscious rats was combined with immunocapillary electrophoresis and laser-induced fluorescence detection to quantify cytokine in 5-min dialysates collected before (0-180 min; basal), and after (180-240 min), hypertonic saline injected s.c. (1.5 m NaCl). Osmotic release of IL-1beta was compared after inhibiting local voltage-gated channels for Na+ (tetrodotoxin) and Ca2+ (cadmium and nickel) or by reducing intracellular Ca2+ stores (thapsigargin). Immunohistochemistry combined with microdialysis was used to localise cytokine sources (IL-1beta+) and microglia (OX-42+). Under conditions of microdialysis, the basal release of IL-1beta+ in the SON area was measurable and stable (pg/ml; mean +/- SEM) from 0-60 min (2.2 +/- 0.06), 60-120 min (2.32 +/- 0.05) and 120-180 min (2.33 +/- 0.06), likely originating locally from activated microglia (OX42+; IL-1beta+; ameboid, hypertrophied) and magnocellular neurones expressing IL-1beta. In response to osmotic stimulation, IL-1beta increased progressively in dialysates of the SON area by a mechanism dependent on intracellular Ca2+ stores sensitive to thapsigargin and, similar to dendritic secretion of oxytocin and vasopressin, required local voltage-gated Na+ and Ca2+ channels for activation by osmoregulatory pathways from the forebrain. During osmotic stimulation, neurally dependent release of IL-1beta in the SON area likely upregulates osmosensitive cation currents on magnocellular neurones (observed in vitro by others), to facilitate dendritic release of neurohypophysial hormones.

Interleukin-1 receptor antagonist reduces the magnitude of the pressor response to acute stress

The purpose of the present study was to establish the effect of chronic central interleukin-1 receptors blockade and central chronic infusion of interleukin-1 beta (IL-1beta) on cardiovascular response to an acute stressor. The experiments were performed on 12-14-week-old, male WKY rats, divided into three experimental groups. Each group was subjected to chronic intracerebroventricular (ICV) infusion of one of the following compounds: saline (control, group C), recombinant rat IL-1 receptor antagonist (IL-ANT group) or interleukin-1 beta (IL-1B group). After 5 days of the ICV infusions mean arterial blood pressure (MABP) and heart rate (HR) were recorded continuously under baseline conditions and after the application of an air jet stressor. The stressor was applied three times with 10-min intervals. There were no significant differences in MABP and HR between groups under baseline conditions and immediately before the application of the three consecutive air jets. After the first stressor the IL-ANT group responded with a significantly lower increase in blood pressure than the control and IL-1B group. After the application of the two following air jets only the trend for an intergroup difference was present. The results of the present study provide further evidence that cytokines play an important role in the regulation of the circulatory system. The most important new finding is that the magnitude of the pressor response to the alarming stress is strongly influenced by IL-1 receptors in the brain.

Interleukin-1beta: a bridge between inflammation and excitotoxicity?

Interleukin-1 (IL-1) is a proinflammatory cytokine released by many cell types that acts in both an autocrine and/or paracrine fashion. While IL-1 is best described as an important mediator of the peripheral immune response during infection and inflammation, increasing evidence implicates IL-1 signaling in the pathogenesis of several neurological disorders. The biochemical pathway(s) by which this cytokine contributes to brain injury remain(s) largely unidentified. Herein, we review the evidence that demonstrates the contribution of IL-1beta to the pathogenesis of both acute and chronic neurological disorders. Further, we highlight data that leads us to propose IL-1beta as the missing mechanistic link between a potential beneficial inflammatory response and detrimental glutamate excitotoxicity.

Inflammation in the nervous system--physiological and pathophysiological aspects

There is ample evidence for the occurrence of inflammatory processes in most major neurodegenerative disorders, both in acute conditions such as traumatic brain injury and stroke, and in chronic disorders such as Alzheimer's disease, epilepsy, amyotrophic lateral sclerosis and Parkinson's disease. Studies on inflammatory factors such as pro- and antiinflammatory cytokines in experimental models of neurodegenerative disorders suggest that they are not merely bystanders, but may be involved in the neurodegenerative process. In addition, there are findings indicating that inflammatory factors may have beneficial effects on the nervous system, particularly during development of the nervous system. The challenge is to understand when, where and during which circumstances inflammation and inflammatory factors are positive or negative for neuronal survival and functioning. Some of our studies on cytokines, particularly the interleukin-1 system, are summarised and discussed in relation to neurodegeneration, cognition, and temperature changes.

Response of interleukin-1beta in the magnocellular system to salt-loading

Drinking 2% NaCl decreases interleukin (IL)-1beta in the neural lobe and enhances IL-1 Type 1 receptor expression in magnocellular neurones and pituicytes. To quantify cytokine depletion from the neural lobe during progressive salt loading and determine whether the changes are reversible and correspond with stores of vasopressin (VP) or oxytocin (OT), rats were given water on day 0 and then 2% NaCl to drink for 2, 5, 8 or 5 days followed by 5 days of water (rehydration). Control rats drinking only water were pair-fed amounts eaten by 5-day salt-loaded animals. Animals were decapitated on day 8, the neural lobe frozen and plasma hormones analysed by radioimmunoassay (OT, VP) or enzyme-linked immunosorbent assay (IL-1beta). IL-1beta, VP and OT in homogenates of the neural lobe were quantified by immunocapillary electrophoresis with laser-induced fluorescence detection. Differences were determined by ANOVA, Tukey's t-test, Dunnett's procedure, Fisher's least significant difference and linear regression analysis. In response to salt-loading, rats lost body weight similar to pair-fed controls, drank progressively more 2% NaCl and excreted greater urine volumes. Plasma VP increased at days 2 and 8 of salt-loading, whereas osmolality, OT and cytokine were enhanced after 8 days with IL-1beta remaining elevated after rehydration. In the neural lobe, all three peptides decreased progressively with increasing duration of salt-loading (IL-1beta, r2 = 0.98; OT, r2 = 0.94; VP, r2 = 0.93), beginning on day 2 (IL-1beta; VP) or 5 (OT), with only VP replenished by rehydration. IL-1beta declined more closely (P < 0.0001; ANOVA interaction analysis) with OT (r2 = 0.96) than VP (r2 = 0.86), indicative of corelease from the neural lobe during chronic dehydration. Local effects of IL-1beta on magnocellular terminals, pituicytes and microglia in the neural lobe with activation of forebrain osmoregulatory structures by circulating cytokine may sustain neurosecretion of OT and VP during prolonged salt-loading.

Centrally administered interleukin-1 beta sensitizes to the central pressor action of angiotensin II

The objective of the present study was to find out whether brain vasopressin (AVP) and angiotensin II (Ang II) are involved in pressor response to intracerebroventricular (ICV) infusion of interleukin-1 beta (IL-1beta). The experiments were performed on conscious, 12- to 14-week-old Sprague-Dawley rats. Mean arterial blood pressure (MAP) and heart rate (HR) were recorded continuously under baseline conditions and during ICV infusion periods. In the first part of the study, the rats were ICV-infused with one of the following: 0.9% NaCl saline (5 microl/h-control), IL-1beta (100 ng/h), angiotensin AT1 receptor antagonist (losartan 10 microg/h), IL-1beta together with losartan, V1 receptors antagonist (V1ANT), d(CH2)5[Tyr(Me)2,Ala-NH2(9)]AVP, 400 ng/h) or IL-1beta together with V1ANT. Saline infusion did not influence MAP, while administration of IL-1beta elicited a significant but transient increase in MAP. The pressor response to IL-1beta was abolished by losartan but not by V1ANT. On the other hand, combined administration of IL-1beta and V1ANT resulted in increase in HR, which was absent during infusion of IL-1beta alone. In the second part of the study after ICV pretreatment with IL-1beta or 0.9% NaCl (control), the rats received ICV infusion of one of the following: 0.9% NaCl saline, subpressor dose of Ang II (5 ng/15 s) or subpressor dose of AVP (5 ng/15 s). Subpressor doses of Ang II and AVP did not influence MAP and HR in saline-pretreated rats. The same dose of Ang II but not AVP applied in IL-1beta-pretreated rats resulted in a significant increase in MAP. The study provides evidence that IL-1beta through its action in the brain increases sensitivity to central pressor action of Ang II. Additionally, we found that AVP and in particular V1 receptors do not play important role in the central pressor action of IL-1beta, however, they may influence its effect on HR regulation.

Neural-immune interface in the rat area postrema

The area postrema functions as one interface between the immune system and the brain. Immune cells within the area postrema express immunoreactivity for the pro-inflammatory cytokine, interleukin-1beta following challenge with immune stimulants, including lipopolysaccharide (from bacterial cell walls). As a circumventricular organ, the area postrema accesses circulating immune-derived mediators, but also receives direct primary viscerosensory signals via the vagus nerve. Neurons in the area postrema contribute to central autonomic network neurocircuitry implicated in brain-mediated host defense responses. These experiments were directed toward clarifying relationships between immune cells and neurons in the area postrema, with a view toward potential mechanisms by which they may communicate. We used antisera directed toward markers indicating microglia (CR3/CD11b; OX-42), resident macrophages (CD163; ED-2), or dendritic cell-like phenotypes (major histocompability complex class II; OX-6), in area postrema sections from lipopolysaccharide-treated rats processed for light, laser scanning confocal, and electron microscopy. Lipopolysaccharide treatment induced interleukin-1beta-like immunoreactivity in immune cells that either associated with the vasculature (perivascular cells, a subtype of macrophage) or associated with neuronal elements (dendritic-like, and unknown phenotype). Electron microscopic analysis revealed that some immune cells, including interleukin-1beta-positive cells, evinced membrane apposition with neuronal elements, including dendrites and terminals, that could derive from inputs to the area postrema such as vagal sensory fibers, or intrinsic area postrema neurons. This arrangement provides an anatomical substrate by which immune cells could directly and specifically influence individual neurons in the area postrema, that may support the induction and/or maintenance of brain responses to inflammation.

IL-1β directly excites isolated rat supraoptic neurons via upregulation of the osmosensory cation current

Previous studies have shown that IL-1β can excite the magnocellular neurosecretory cells (MNCs) of the hypothalamus. However, it is not known whether IL-1β can have direct IL-1 receptor type 1 (IL-1R1)-mediated effects on MNCs, and little is known about the cellular mechanisms by which IL-1β influences electrical activity in these cells. Here, we used patch-clamp recordings to examine the effects of IL-1β on acutely isolated rat MNCs. We found that IL-1β directly excites MNCs in a dose-dependent manner and that this response can be blocked by an inhibitor of the IL-1R1. Voltage-clamp analysis of the current evoked by IL-1β revealed a linear current-voltage relationship between −90 and −20 mV, and a reversal potential near −35 mV. This value was not affected by reducing the concentration of chloride ions in the external solution, indicating the involvement of a nonselective cation conductance. The effects of IL-1β were inhibited by Na-salicylate, an inhibitor of cyclooxygenase. Moreover. the effects of IL-1β were mimicked and occluded by PGE2, and were inhibited by AH-23848, an antagonist of the PGE2 type 4 (i.e., EP4) receptor. The current evoked by IL-1β was also abolished by 100 μM gadolinium (Gd3+), but was significantly larger when examined in cells preshrunk by negative pressure applied via the recording pipette. IL-1β alone did not cause changes in cell volume nor in the mechanosensitivity of MNCs. We conclude that IL-1β directly excites MNCs via an IL-1R1-mediated induction of PGE2 synthesis and EP4 receptor-dependent autocrine upregulation of the nonselective cation conductance that underlies osmoreception.

Interleukin-1beta depolarizes magnocellular neurons in the paraventricular nucleus of the hypothalamus through prostaglandin-mediated activation of a non selective cationic conductance

Interleukin-1beta (IL-1beta) is involved in hypothalamic regulation of the neuroimmune response by influencing the synthesis and secretion of corticotropin releasing hormone (CRH), vasopressin (VP) and other stress-related mediators. VP secretion from magnocellular (MNC) neurons of the paraventricular nucleus (PVN) of the hypothalamus at the posterior pituitary and/or median eminence contributes to increasing adrenocorticotropin hormone (ACTH) output and ultimately glucocorticoid release, which then contributes to the stress response. In this study, using whole-cell patch clamp recordings from neurons in a slice preparation of the rat PVN, we show that MNC neurons are also influenced by IL-1beta. In response to 1 nM IL-1beta, 62% of MNC neurons tested depolarized (mean depolarization=10.9+/-1.4 mV); effects which were maintained in the presence of a sodium channel blocker, tetrodotoxin (TTX). The effects of IL-1beta on MNC neurons were blocked in the presence of a specific cyclooxygenase (COX)-2 inhibitor, NS-398, indicating a dependence on prostaglandins (PG) in mediating these effects. In response to direct application of 1 muM PGE2, 57% of MNC neurons depolarized, exhibiting a membrane potential change similar to that induced by IL-1beta (mean depolarization=7.8+/-1.1 mV). Voltage clamp experiments examining the effects of PGE2 on the currents evoked by slow voltage ramps revealed activation of a conductance characteristic of a non-selective cationic conductance (NSCC) (voltage-independent, with a reversal potential of -41.8+/-7.6 mV), suggesting that this prostanoid directly modifies cationic currents in MNC neurons. These data provide evidence that IL-1beta depolarizes MNC neurons in the PVN as a result of prostaglandin-mediated activation of a NSCC.

Prostaglandin E2 mediates cellular effects of interleukin-1beta on parvocellular neurones in the paraventricular nucleus of the hypothalamus

Abstract Interleukin-1beta (IL-1beta) is involved in hypothalamic regulation of corticotrophin-releasing hormone secretion, autonomic activation and consequent downstream modulation of the neuroimmune response. Previously, we have shown that IL-1beta depolarises parvocellular neurones in the paraventricular nucleus (PVN) of the hypothalamus, and these effects are dependent on attenuation of gamma-amino butyric acid (GABA)-ergic input. In the present study, using whole-cell patch clamp recordings of rat neurones in a slice preparation of the PVN, we show that the effects of IL-1beta are abolished in the presence of a cyclooxygenase (COX)-2 inhibitor, NS-398, indicating a dependence on prostaglandin (PG) synthesis and activation. In response to 1 microM PGE2, 64% of parvocellular neurones tested exhibited a clear depolarisation, which was abolished in the presence of tetrodotoxin (TTX). Furthermore, neurones responsive to both IL-1beta and PGE2 exhibited a decrease in the frequency of inhibitory post-synaptic potentials, suggesting that effects of these modulators are mediated via a decrease in GABA-ergic input to these neurones. A proportion (44% and 40%, respectively) of putative GABA-ergic neurones in the halo region surrounding the PVN demonstrated hyperpolarising responses to 1 nM IL-1beta and 1 microM PGE2, and these effects were maintained in TTX. Furthermore, direct hyperpolarising effects of IL-1beta were blocked in the presence of NS-398. Together, these data suggest that PGE2, synthesised in response to IL-1beta-activation of COX-2 expressing cells, directly hyperpolarises putative GABA-ergic neurones in the halo zone surrounding and projecting to the PVN, resulting in a decrease in GABA-ergic input to parvocellular neurones and consequent depolarisation. These data further elucidate the cellular mechanisms by which IL-1beta exerts its neuroimmune-related actions in the PVN.

Rat brain vascular distribution of interleukin-1 type-1 receptor immunoreactivity: relationship to patterns of inducible cyclooxygenase expression by peripheral inflammatory stimuli

Interleukin-1 beta (IL-1 beta) is thought to act on the brain to induce fever, neuroendocrine activation, and behavioral changes during disease through induction of prostaglandins at the blood-brain barrier (BBB). However, despite the fact that IL-1 beta induces the prostaglandin-synthesizing enzyme cyclooxygenase-2 (COX-2) in brain vascular cells, no study has established the presence of IL-1 receptor type 1 (IL-1R1) protein in these cells. Furthermore, although COX inhibitors attenuate expression of the activation marker c-Fos in the preoptic and paraventricular hypothalamus after administration of IL-1 beta or bacterial lipopolysaccharide (LPS), they do not alter c-Fos induction in other structures known to express prostaglandin receptors. The present study thus sought to establish whether IL-1R1 protein is present and functional in the rat cerebral vasculature. In addition, the distribution of IL-1R1 protein was compared to IL-1 beta- and LPS-induced COX-2 expression. IL-1R1-immunoreactive perivascular cells were mostly found in choroid plexus and meninges. IL-1R1-immunoreactive vessels were seen throughout the brain, but concentrated in the preoptic area, subfornical organ, supraoptic hypothalamus, and to a lesser extent in the paraventricular hypothalamus, cortex, nucleus of the solitary tract, and ventrolateral medulla. Vascular IL-1R1-ir was associated with an endothelial cell marker, not found in arterioles, and corresponded to the induction patterns of phosphorylated c-Jun and inhibitory-factor kappa B mRNA upon IL-1 beta stimulation, and colocalized with peripheral IL-1 beta- or LPS-induced COX-2 expression. These observations indicate that functional IL-1R1s are expressed in endothelial cells of brain venules and suggest that vascular IL-1R1 distribution is an important factor determining BBB prostaglandin-dependent activation of brain structures during infection.

3,4‐Methylenedioxymethamphetamine increases interleukin‐1β levels and activates microglia in rat brain: studies on the relationship with acute hyperthermia and 5‐HT depletion

3,4-Methylenedioxymethamphetamine (MDMA) administration to rats produces acute hyperthermia and 5-HT release. Interleukin-1beta (IL-1beta) is a pro-inflammatory pyrogen produced by activated microglia in the brain. We examined the effect of a neurotoxic dose of MDMA on IL-1beta concentration and glial activation and their relationship with acute hyperthermia and 5-HT depletion. MDMA, given to rats housed at 22 degrees C, increased IL-1beta levels in hypothalamus and cortex from 1 to 6 h and [(3)H]-(1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)3-isoquinolinecarboxamide) binding between 3 and 48 h. Increased immunoreactivity to OX-42 was also detected. Rats became hyperthermic immediately after MDMA and up to at least 12 h later. The IL-1 receptor antagonist did not modify MDMA-induced hyperthermia indicating that IL-1beta release is a consequence, not the cause, of the rise in body temperature. When MDMA was given to rats housed at 4 degrees C, hyperthermia was abolished and the IL-1beta increase significantly reduced. The MDMA-induced acute 5-HT depletion was prevented by fluoxetine coadministration but the IL-1beta increase and hyperthermia were unaffected. Therefore, the rise in IL-1beta is not related to the acute 5-HT release but is linked to the hyperthermia. Contrary to IL-1beta levels, microglial activation is not significantly modified when hyperthermia is prevented, suggesting that it might be a process not dependent on the hyperthermic response induced by MDMA.

Interleukin-1 beta depolarizes paraventricular nucleus parvocellular neurones

Interleukin-1 beta (IL-1 beta) is involved in hypothalamic regulation of corticotropin releasing hormone (CRH) secretion and consequent downstream modulation of the neuroimmune response. In this study, whole-cell patch clamp recordings of rat parvocellular neurones in a slice preparation of the paraventricular nucleus (PVN) of the hypothalamus were performed to examine the cellular effects of IL-1 beta. In response to 1 nm IL-1 beta, 65% of parvocellular neurones tested exhibited a clear depolarization, which was abolished in the presence of tetrodotoxin (TTX). This depolarization was partially dependent on nitric oxide formation, as demonstrated by attenuation of the response in the presence of N-omega-nitro-L-arginine methylester, a nitric oxide synthase inhibitor. The effects of IL-1 beta on responsive parvocellular neurones were associated with a decrease in the frequency of inhibitory post synaptic potentials (IPSPs). Bicuculline administration blocked the effects of IL-1 beta, suggesting that this cytokine modulates GABA-ergic output, resulting in a decrease in inhibitory input (IPSPs) and consequent depolarization. These data support the conclusion that IL-1 beta influences the excitability of parvocellular neurones in the PVN, as a secondary consequence of nitric oxide generation and modulation of GABAergic inhibitory input to these cells. They elucidate cellular correlates underlying the well-established neuroimmune roles of IL-1 beta in the paraventricular nucleus of the hypothalamus.

Increased sensitivity to N-methyl-D-aspartate receptor-induced excitotoxicity in cerebellar granule cells from interleukin-1 receptor type I-deficient mice

The effects of chronic exposure to excitatory amino acids (EAAs) were examined in cultured cerebellar granule cells (CGCs) from wild type (WT) and interleukin-1 receptor type I (IL-1RI)-deficient mice. After 8 days in culture, the cells were exposed to 100 microM glutamate or 300 microM N-methyl-D-aspartate (NMDA) for 24 h. Analysis of cell viability, as assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay and phase-contrast microscopy revealed that CGCs from IL-1RI-deficient mice were more vulnerable to EAAs as compared to the WT controls. The results indicate that IL-1RI signalling is important for neuronal survival. The effect of glutamate on the CGCs from IL-1RI-deficient mice was decreased by the non-competitive NMDA-receptor antagonist MK-801, supporting the involvement of NMDA receptors in the glutamate-induced excitotoxicity.

Interleukin-1 receptor immunoreactivity in sympathetic vascular and non-vascular neurons in guinea-pig coeliac ganglion

Immunoreactivity (IR) for the interleukin-1 receptor type I (IL1RI) was examined in sympathetic neurons in guinea-pig coeliac ganglion using multiple-labelling immunofluorescence. IL1RI-IR was present in 8% of sympathetic neurons in untreated preparations. The proportion of neurons with IL1RI-IR increased significantly after incubation in interleukin-6 (200 ng/ml) for 2-4 h (16-26% neurons), or after incubation for 4 h without cytokine (16%), with interleukin-1beta (IL1beta, 200 ng/ml; 18%) or tumour necrosis factor-alpha (200 ng/ml; 16%). This increase occurred predominantly in neuropeptide Y-IR, vasoconstrictor neurons. IL1RI-IR also was present in varicose axons, some of which projected from the gut, and in vascular smooth muscle cells and endothelium. These potential binding sites for the proinflammatory cytokine, IL1beta, on vasoconstrictor neurons and blood vessels may modulate sympathetic regulation of intestinal blood flow in inflammatory conditions.

Hypothalamic pituitary adrenal axis and hypothalamic-neurohypophyseal responsiveness in water-deprived rats

The differential effects of osmotic stimulation on magnocellular and parvocellular hypothalamic neurons were studied by analysis of corticotropin-releasing hormone (CRH) and vasopressin (VP) expression in controls and 48-h water-deprived rats subjected to either restraint for 1 h or a single lipopolysaccharide injection (250 microg/100 g). Water deprivation reduced basal CRH mRNA levels but the increments following 4 h of restraint or 6 h lipopolysaccharide (LPS) injection were similar to those in controls. In contrast, water deprivation had no effect on basal VP heteronuclear RNA (hnRNA) and mRNA levels in parvocellular neurons, but responses to restraint or LPS injection were reduced. VP expression in magnocellular paraventricular and supraoptic nuclei, and plasma sodium and vasopressin were higher in water-deprived rats, changes which were unaffected by restraint. LPS injection reduced VP mRNA but not hnRNA levels in magnocellular neurons and increased plasma vasopressin levels only in water-deprived rats independently of changes in plasma sodium. This was accompanied by an increase in vasopressin mRNA content in the posterior pituitary. The data show that the blunted ACTH responses to acute stress during chronic osmotic stimulation are correlated with the inability of parvocellular neurons to increase VP rather than CRH expression. In addition, LPS-induced endotoxemia causes disturbances of the magnocellular vasopressinergic system with an unexpected potentiation of osmotic simulated VP secretion. The lack of increase in VP transcription after LPS and changes in VP mRNA distribution suggest that endotoxemia affect the secretory process at the levels of the neurohypophyseal axon terminal.

Gene regulation in the magnocellular hypothalamo-neurohypophysial system

The hypothalamo-neurohypophysial system (HNS) is the major peptidergic neurosecretory system through which the brain controls peripheral physiology. The hormones vasopressin and oxytocin released from the HNS at the neurohypophysis serve homeostatic functions of water balance and reproduction. From a physiological viewpoint, the core question on the HNS has always been, "How is the rate of hormone production controlled?" Despite a clear description of the physiology, anatomy, cell biology, and biochemistry of the HNS gained over the last 100 years, this question has remained largely unanswered. However, recently, significant progress has been made through studies of gene identity and gene expression in the magnocellular neurons (MCNs) that constitute the HNS. These are keys to mechanisms and events that exist in the HNS. This review is an inventory of what we know about genes expressed in the HNS, about the regulation of their expression in response to physiological stimuli, and about their function. Genes relevant to the central question include receptors and signal transduction components that receive and process the message that the organism is in demand of a neurohypophysial hormone. The key players in gene regulatory events, the transcription factors, deserve special attention. They do not only control rates of hormone production at the level of the gene, but also determine the molecular make-up of the cell essential for appropriate development and physiological functioning. Finally, the HNS neurons are equipped with a machinery to produce and secrete hormones in a regulated manner. With the availability of several gene transfer approaches applicable to the HNS, it is anticipated that new insights will be obtained on how the HNS is able to respond to the physiological demands for its hormones.

Diffusion and action of intracerebroventricularly injected interleukin-1 in the CNS

Interleukin-1beta acts on the CNS to induce fever, neuroendocrine activation and behavioural depression. We have previously demonstrated that interleukin-1beta is synthesized in glial cells and macrophages of circumventricular organs and choroid plexus after intraperitoneal administration of bacterial lipopolysaccharide. Whether, and how, interleukin-1beta produced in glial cells affects neuronal functioning is unknown. Diffusion throughout the extracellular space is an important pathway by which factors produced by glial cells act on distant cells, a phenomenon coined "volume transmission". The present study assessed diffusion of recombinant rat interleukin-1beta, recombinant human interleukin-1 receptor antagonist and 10mol. wt dexran in the rat CNS after intracerebroventricular administration to model interleukin-1beta release from choroid plexus. Immunocytochemistry with specific antibodies directed against interleukin-1beta and interleukin-1 receptor antagonist revealed that these molecules rapidly penetrated into periventricular tissue and spread along white matter fibre bundles and blood vessels in the caudoputamen, hypothalamus and amygdala. The transcription factor nuclear factor kappa B and the immediate-early gene product Fos were detected immunocytochemically to reveal interleukin-1beta action. Intracerebroventricular infusion of interleukin-1beta induced nuclear factor kappa B translocation in choroid plexus, ependymal cells, basolateral amygdala, cerebral vasculature and meninges. Fos immunoreactivity was found in the supraoptic and paraventricular hypothalamus and central amygdala. We propose that intracerebroventricular injected interleukin-1beta can enter the brain parenchyma and act as a "volume transmission" signal in, for example, the basolateral amygdala where it might activate a neuronal projection to the central amygdala.

Cytokines regulate expression of the type 1 interleukin-1 receptor in rat hippocampal neurons and glia

Interleukin-1 beta is a key mediator of inflammation and stress in the central nervous system (CNS). This cytokine induces CNS glial cells to produce numerous additional cytokines and growth factors under inflammatory conditions. We have investigated regulation of the signal transducing type 1 interleukin-1 receptor (IL-1R1) in the CNS. In vivo, IL-1R1 was not detected in glial cells under basal conditions but was strongly induced after a stab lesion. Cultured astrocytes were used to identify specific signals that regulate expression of the receptor. IL-1R1 mRNA and protein were induced by inflammatory stimuli including tumor necrosis factor (TNF alpha) and IL-1 beta itself. Although expression of the receptor was not detected in glia under basal conditions in vivo, pyramidal neurons in the hippocampus expressed the IL-1 receptor in the normal, unlesioned brain. Cultured embryonic hippocampal neurons were used to investigate specific stimuli that regulate IL-1R1 in neurons. As in astrocytes, IL-1 and TNF alpha induced expression of IL-1R1. The expression of IL-1R1 in hippocampal neurons suggests a possible role for IL-1 in regulating neuronal function, and indicates that these neurons may be directly influenced by cytokines.

Effects of vagotomy on lipopolysaccharide-induced brain interleukin-1beta protein in rats

The production of interleukin-1beta (IL-1beta) in brain is thought to be a critical step in the induction of central manifestations of the acute phase response, and the vagus nerve has been implicated in immune-to-brain communication. Thus, this study examined the effects of intraperitoneal (i.p.) injections of lipopolysaccharide (LPS) on brain IL-1beta protein levels in control and subdiaphragmatically vagotomized rats. In the first experiment, vagotomized and sham-operated male Sprague-Dawley rats were injected i.p. with one of three doses (10, 50, 100 microg/kg) of LPS or vehicle (sterile, pyrogen-free saline) and sacrificed 2 h after the injection. In the second experiment, vagotomized and sham-operated rats were injected i.p. with 100 microg/kg LPS or vehicle and sacrificed 1 h after the injection. The i.p. injection of LPS dose-dependently increased IL-1beta protein levels in the hypothalamus, hippocampus, dorsal vagal complex, cerebellum, posterior cortex, and pituitary 2 h after the injection. Brain and pituitary IL-1beta levels were also significantly increased 1 h after the injection of 100 microg/kg LPS. There were no significant differences in brain IL-1beta levels between sham-operated and vagotomized rats at either the 2 h or 1 h time points. The current data are consistent with previous studies showing increases in brain IL-1beta after peripheral injections of LPS, and support the notion that brain IL-1beta is a mediator in the illness-induction pathway. Furthermore, these data indicate that, at the doses and times tested, subdiaphragmatic vagal afferents are not crucial for LPS-induced brain IL-1beta protein.

Interleukin-1 is a key regulator of matrix metalloproteinase-9 expression in human neurons in culture and following mouse brain trauma in vivo

An acute trauma to the CNS rapidly results in the upregulation of inflammatory cytokines that include interleukin-1 (IL-1). We report here that the levels of several matrix metalloproteinases (MMPs) are also elevated following a corticectomy trauma injury to the mouse CNS. The delayed upregulation of MMPs compared to that for IL-1 suggests the possibility that inflammatory cytokines regulate MMP production in CNS trauma. To resolve this, we developed a method to isolate and maintain highly enriched human fetal neurons or astrocytes in culture and examined the regulation by cytokines of the activity of a subgroup of MMPs, the gelatinases (MMP-2 and -9). While both neuronal and astrocytic cultures displayed comparable MMP-2 activity, as evidenced by gelatin zymography, levels of MMP-9 were proportionately higher in neurons compared to astrocytes. Of a variety of cytokines and growth factors tested in vitro, only IL-1beta was effective in increasing the neuronal expression of MMP-9. Finally, an IL-1 receptor antagonist attenuated the increase of neuronal MMP-9 in culture and abolished the injury-induced increase of MMP-9 in the mouse brain. These results implicate IL-1beta as a key regulator of neuronal MMP-9 in culture and of the elevation of MMP-9 that occurs following mouse CNS trauma.

Expression of interleukin 1 alpha and beta, and interleukin 1 receptor antagonist mRNA in the rat central nervous system after peripheral administration of lipopolysaccharides

Interleukin 1alpha (IL-1alpha) and IL-1beta, and the endogenous IL-1 receptor antagonist (IL-1ra) are known members of the IL-1 family. Using in situ hybridization histochemistry we demonstrated that following endotoxin injection (lipopolysaccharides, LPS, 2.0 mg/kg, i.p.) a time dependent expression and partly different expression patterns of the cytokines occurred within the rat brain and pituitary gland. All cytokines were observed in the choroid plexus. In addition, IL-1ra mRNA expressing cells were observed scattered in the brain parenchyma, whereas scattered IL-1beta mRNA expressing cells were restricted to central thalamic nuclei, the dorsal hypothalamus, and cortical regions, such as the parietal and frontal cortex. A strong IL-1beta mRNA expression was found in the circumventricular organs. In the pituitary gland, a low IL-1alpha and a high IL-1beta mRNA expression was observed, with the highest density of cytokine-expressing cells seen in the posterior pituitary. The cell types expressing the mRNA's of IL-1alpha, IL-1beta and IL-1ra were identified as monocytes in the circumventricular organs and the pituitary gland, and as microglia in the brain parenchyma. In conclusion, the present findings revealed that cytokine production in response to a peripheral endotoxin challenge mainly occurs in peripherally derived monocytes in the circumventricular organs and the pituitary gland. IL-1beta is the predominant form expressed, whereas the expression of IL-1alpha mRNA and IL-1ra mRNA is lower. Our observations support the view that peripherally derived IL-1 may play a role in the induction of centrally mediated illness symptoms.

"Inflammatory" cytokines: neuromodulators in normal brain?

If cytokines are constitutively expressed by and act on neurons in normal adult brain, then we may have to modify our current view that they are predominantly inflammatory mediators. We critically reviewed the literature to determine whether we could find experimental basis for such a modification. We focused on two "proinflammatory" cytokines, interleukin (IL)-1 and tumor necrosis factor-alpha (TNFalpha) because they have been most thoroughly investigated in shaping our current thinking. Evidence, although equivocal, indicates that the genes coding for these cytokines and their accessory proteins are expressed by neurons, in addition to glial cells, in normal brain. Their expression is region- and cell type-specific. Furthermore, bioactive cytokines have been extracted from various regions of normal brain. The cytokines' receptors selectively are present on all neural cell types, rendering them responsive to cytokine signaling. Blocking their action modifies multiple neural "housekeeping" functions. For example, blocking IL-1 or TNFalpha by several independent means alters regulation of sleep. This indicates that these cytokines likely modulate in the brain behavior of a normal organism. In addition, these cytokines are likely involved in synaptic plasticity, neural transmission, and Ca2+ signaling. Thus, the evidence strongly suggests that these cytokines perform neural functions in normal brain. We therefore propose that they should be thought of as neuromodulators in addition to inflammatory mediators.

Animal models of neuroimmune interactions in inflammatory diseases

Animal models have been used successfully to study various aspects of neural-immune interactions. Although different approaches carry certain advantages and disadvantages, current high sensitivity screening and manipulation methods coupled with molecular and genetic approaches can be successfully used to tease out the neural pathways that regulate inflammatory disease and the effects of immune molecules, such as interleukins, on neuronal function and pathology. Newer methodologies that measure gene expression of thousands of genes will in the future add to the ability to evaluate complex systems interactions in whole animal models. This review addresses the advantages and disadvantages of some of these approaches in the context of application to neural-immune interactions.