Effect of IL-1alpha on the release of norepinephrine in rat hypothalamus

Molecular mechanism of noradrenaline during the stress-induced major depressive disorder

Chronic stress-induced depression is a common hallmark of many psychiatric disorders with high morbidity rate. Stress-induced dysregulation of noradrenergic system has been implicated in the pathogenesis of depression. Lack of monoamine in the brain has been believed to be the main causative factor behind pathophysiology of major depressive disorder (MDD) and several antidepressants functions by increasing the monoamine level at the synapses in the brain. However, it is undetermined whether the noradrenergic receptor stimulation is critical for the therapeutic effect of antidepressant. Contrary to noradrenergic receptor stimulation, it has been suggested that the desensitization of β-adrenoceptor is involved in the therapeutic effect of antidepressant. In addition, enhanced noradrenaline (NA) release is central response to stress and thought to be a risk factor for the development of MDD. Moreover, fast acting antidepressant suppresses the hyperactivation of noradrenergic neurons in locus coeruleus (LC). However, it is unclear how they alter the firing activity of LC neurons. These inconsistent reports about antidepressant effect of NA-reuptake inhibitors (NRIs) and enhanced release of NA as a stress response complicate our understanding about the pathophysiology of MDD. In this review, we will discuss the role of NA in pathophysiology of stress and the mechanism of therapeutic effect of NA in MDD. We will also discuss the possible contributions of each subtype of noradrenergic receptors on LC neurons, hypothalamic-pituitary-adrenal axis (HPA-axis) and brain derived neurotrophic factor-induced hippocampal neurogenesis during stress and therapeutic effect of NRIs in MDD.

Relationships among the behavioral, noradrenergic, and pituitary-adrenal responses to interleukin-1 and the effects of indomethacin

Peripheral administration of interleukin-1 (IL-1) is known to activate the hypothalamo-pituitary-adrenal axis (HPA axis) and brain noradrenergic systems. We studied the relationship between these responses using in vivo microdialysis to assess the release of hypothalamic norepinephrine (NE), while simultaneously sampling blood for ACTH and corticosterone, and monitoring body temperature and behavior in freely moving rats. Rats were implanted with microdialysis probes in the medial hypothalamus, with intravenous catheters, and with telethermometers in the abdomen. Each rat was injected with saline and IL-1beta (1 microg ip) in random order, monitoring microdialysate NE, body temperature and plasma ACTH and corticosterone for 2-4 h after injection. Saline injections were followed by transient increases in microdialysate NE and in plasma ACTH and corticosterone. IL-1beta injections resulted in prolonged elevations of microdialysate NE, as well as plasma ACTH and corticosterone, and body temperature. IL-1beta also induced shivering and a prolonged depression of locomotor activity. Pretreatment with indomethacin (10 mg/kg sc) prevented the IL-1beta-induced increases in body temperature and the apparent increase in hypothalamic NE release, but only attenuated the IL-1beta-induced shivering and the increase in plasma ACTH. The results indicate a close temporal relationship between the release of NE and HPA axis activation. Such a relationship is also supported by the similar effects of indomethacin pretreatment on NE and ACTH. The shivering is likely involved in the increase in body temperature, but indomethacin only attenuated the shivering while it blocked the fever. However, the effects of indomethacin clearly indicate that neither the increase in body temperature nor the increase in hypothalamic NE release was essential for HPA axis activation. These results suggest that hypothalamic NE is involved in the IL-1-induced HPA axis activation, but that this is not the only mechanism by which the HPA axis is activated by intraperitoneally injected IL-1.

Effects of cytokines and infections on brain neurochemistry

Administration of cytokines to animals can elicit many effects on the brain, particularly neuroendocrine and behavioral effects. Cytokine administration also alters neurotransmission, which may underlie these effects. The most well studied effect is the activation of the hypothalamo-pituitary-adrenocortical (HPA) axis, especially that by interleukin-1 (IL-1). Peripheral and central administration of IL-1 also induces norepinephrine (NE) release in the brain, most markedly in the hypothalamus. Small changes in brain dopamine (DA) are occasionally observed, but these effects are not regionally selective. IL-1 also increases brain concentrations of tryptophan, and the metabolism of serotonin (5-HT) throughout the brain in a regionally nonselective manner. Increases of tryptophan and 5-HT, but not NE, are also elicited by IL-6, which also activates the HPA axis, although it is much less potent in these respects than IL-1. IL-2 has modest effects on DA, NE and 5-HT. Like IL-6, tumor necrosis factor-α (TNFα) activates the HPA axis, but affects NE and tryptophan only at high doses. The interferons (IFN's) induce fever and HPA axis activation in man, but such effects are weak or absent in rodents. The reported effects of IFN's on brain catecholamines and serotonin have been very varied. However, interferon-γ, and to a lesser extent, interferon-α, have profound effects on the catabolism of tryptophan, effectively reducing its concentration in plasma, and may thus limit brain 5-HT synthesis.Administration of endotoxin (LPS) elicits responses similar to those of IL-1. Bacterial and viral infections induce HPA activation, and also increase brain NE and 5-HT metabolism and brain tryptophan. Typically, there is also behavioral depression. These effects are strikingly similar to those of IL-1, suggesting that IL-1 secretion, which accompanies many infections, may mediate these responses. Studies with IL-1 antagonists, support this possibility, although in most cases the antagonism is incomplete, suggesting the existence of multiple mechanisms. Because LPS is known to stimulate the secretion of IL-1, IL-6 and TNFα, it seems likely that these cytokines mediate at least some of the responses, but studies with antagonists indicate that there are multiple mechanisms. The neurochemical responses to cytokines are likely to underlie the endocrine and behavioral responses. The NE response to IL-1 appears to be instrumental in the HPA activation, but other mechanisms exist. Neither the noradrenergic nor the serotonergic systems appear to be involved in the major behavioral responses. The significance of the serotonin response is unknown.

How ischaemic preconditioning protects small liver grafts

Interleukin-1 (IL-1) and transforming growth factor-beta (TGFbeta) are key inhibitors of hepatocyte proliferation after hepatectomy. IL-1 inhibition by heat shock proteins (HSPs) has been reported in inflammatory processes. A recent study indicated the benefits of ischaemic preconditioning in reduced-size orthotopic liver transplantation (ROLT). The present study examined: (a) the effect of ischaemic preconditioning on IL-1 and TGFbeta in ROLT; (b) whether preconditioning protects small liver grafts through HSP induction; and (c) whether the potential benefits of preconditioning on HSP is related to IL-1 inhibition. Our results, obtained with an IL-1 receptor antagonist, indicated the injurious effects of IL-1 in ischaemia-reperfusion (I/R) injury and established a relationship between IL-1 and growth factors. Thus, IL-1 reduced hepatocyte growth factor (HGF) and promoted TGFbeta release, thus contributing to the impaired liver regeneration associated with ROLT. Preconditioning inhibited IL-1 through nitric oxide (NO), thereby protecting against the injurious effects of IL-1. In addition, by another pathway independent of NO, preconditioning induced HSP70 and haem-oxygenase-1 (HO-1). HO-1 protected against I/R injury and liver regeneration, whereas the benefits resulting from HSP70 were mainly related to hepatocyte proliferation. These results suggest a mechanism that explains the effectiveness of preconditioning in ROLT. They suggest, too, that other strategies, in addition to preconditioning, that modulate IL-1 and/or HSPs could be considered in clinical situations requiring liver regeneration such as small liver grafts.

MAPK-dependent regulation of IL-1- and beta-adrenoreceptor-induced inflammatory cytokine production from mast cells: implications for the stress response

BACKGROUND

Catecholamines, such as epinephrine, are elaborated in stress responses, and mediate vasoconstriction to cause elevation in systemic vascular resistance and blood pressure. Our previous study has shown that IL-1 can induce mast cells to produce proinflammatory cytokines which are involved in atherogenesis. The aim of this study was to determine the effects of epinephrine on IL-1-induced proatherogenic cytokine production from mast cells.

RESULTS

Two ml of HMC-1 (0.75 x 106 cells/ml) were cultured with epinephrine (1 x 10-5 M) in the presence or absence of IL-1 beta (10 ng/ml) for 24 hrs. HMC-1 cultured alone produced none to trace amounts of IL-6, IL-8, and IL-13. IL-1 beta significantly induced production of these cytokines in HMC-1, while epinephrine alone did not. However, IL-6, IL-8, and IL-13 production induced by IL-1 beta were significantly enhanced by addition of epinephrine. The enhancing effect appears to involve NF-kappa B and p38 MAPK pathways. Flow cytometry showed the presence of beta1 and beta2 adrenoreceptors on resting mast cells. The enhancing effect of proatherogenic cytokine production by epinephrine was down regulated by the beta1 and beta2 adrenoceptor antagonist, propranolol, but not by the beta1 adrenoceptor antagonist, atenolol, suggesting the effect involved beta2 adrenoceptors. The enhancing effect of epinephrine on proatherogenic cytokine production was also down regulated by the immunosuppressive drug, dexamethasone.

CONCLUSIONS

These results not only confirm that an acute phase cytokine, IL-1 beta, regulates mast cell function, but also show that epinephrine up regulates the IL-1 beta induction of proatherogenic cytokines in mast cells. These data provide a novel role for epinephrine, a stress hormone, in inflammation and atherogenesis.

Acute effects of acephate and methamidophos and interleukin-1 on corticotropin-releasing factor (CRF) synthesis in and release from the hypothalamus in vitro

Acute effects of Ace, Meth and IL-1 on AChE activity, ACh and CRF mRNA levels in, and CRF-release from the hypothalamus were studied in vitro. The hypothalamus samples were dissected from the rat brain and were incubated in vitro with IL-1, Ace or Meth in the presence or absence of Dex, Atrop, PTL, PROP and GABA. Ace and Meth, but not IL-1, inhibited AChE activity, while all three compounds; (1) increased ACh and CRF mRNA levels in and CRF release from; (2) activated the CRE promoter region of CRF-gene in: and (3) increased cFos binding to the AP-1 region of the CRF-gene in the hypothalamus. Dex suppressed the effects of IL-1, possibly by inducing the nGRE regulatory sites of the CRF-gene. Dex, however, did not modulate the effects of Ace and Meth on the hypothalamus, which may be attributed to the failure of Dex to modulate the CRF-gene's nGRE regulatory sites. Atrop caused 80-90% inhibition of the effects of IL-1, but caused only 50-65% inhibition of the effects of Ace or Meth on CRF mRNA levels in and CRF release from the hypothalamus. PTL did not affect, while PROP slightly attenuated the effects of IL-1 and the insecticides on the hypothalamus. GABA attenuated the effects of the insecticides but not the effects of IL-1 on the hypothalamus. This suggests that the IL-1-induced augmentation of CRF synthesis in and release from the hypothalamus is mediated through a cholinergic pathway, while the insecticide-induced augmentation of CRF synthesis in and release from the hypothalamus is mediated through the cholinergic and GABAergic pathways. The insecticides, but not IL-1, disrupt feedback regulation of CRF synthesis in and release from the hypothalamus.

Regulation of the hypothalamo-pituitary-adrenal axis by cytokines

Many of the pro-inflammatory cytokines which are released in response to immune/inflammatory insults exert marked stimulatory influences on the hypothalamo-pituitary-adrenocortical (HPA) axis; they thus provoke the release of glucocorticoids which, in turn, temper the ensuing immune-inflammatory response and thereby complete a homeostatic neuroendocrine-immune regulatory loop. This article reviews the putative mechanisms by which cytokines, released acutely in response to such insults, activate the HPA axis, placing particular emphasis on the actions and interactions of tumour necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1) and interleukin-6 (IL-6) and on the counter-regulatory mechanisms that are in place.