Sarah L. Kennedy

Catecholamines mediate stress-induced increases in peripheral and central inflammatory cytokines.

Proinflammatory cytokines act at receptors in the CNS to alter physiological and behavioral responses. Exposure to stressors increases both peripheral and central proinflammatory cytokines, yet the mechanism(s) of induction remain unknown. Experiments here examined the role of catecholamines in the in vivo induction of proinflammatory cytokines following tailshock stress. Rats were pretreated i.p. with 2.0 mg/kg prazosin (alpha1-adrenoceptor antagonist), 10.0 mg/kg propranolol (beta-adrenoceptor antagonist), or 5.0 mg/kg labetalol (alpha1- and beta-adrenoceptor antagonist) 30 min prior to tailshock exposure and plasma interleukin-1beta (IL-1beta) and IL-6, along with tissue interleukin-1beta from the hypothalamus, hippocampus, and pituitary were measured immediately following stressor termination. Prazosin attenuated stress-induced plasma IL-1beta and IL-6, but had no effect on tissue IL-1beta levels, while propranolol attenuated plasma IL-6 and blocked tissue IL-1beta elevation, and labetalol, which cannot cross the blood-brain barrier, attenuated plasma IL-1beta and IL-6, blocked pituitary IL-1beta, but had no effect on central tissue IL-1beta levels. Furthermore, administration of 50.0 mg/kg N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride, a neurotoxin that lesions neural projections from the locus coeruleus, prevented stress-induced elevation in hippocampal IL-1beta, a region highly innervated by the locus coeruleus, but had no effect on hypothalamic IL-1beta, a region that receives few locus coeruleus projections. Finally, i.p. injection of 5.0 mg/kg isoproterenol (beta-adrenoceptor agonist) was sufficient to induce circulating IL-1 and IL-6, and tissue IL-1beta. These data suggest catecholamines play an important role in the induction of stress-induced proinflammatory cytokines and that beta-adrenoceptors are critical for tissue IL-1beta induction, while both alpha- and beta-adrenoceptors contribute to the induction of plasma cytokines.

Voluntary freewheel running selectively modulates catecholamine content in peripheral tissue and c-fos expression in the central sympathetic circuit following exposure to uncontrollable stress in rats

Modulation of sympathetic drive to the spleen is one potential mechanism whereby physical activity prevents stress-induced splenic immune suppression in rats. The current study tested the hypothesis that voluntary freewheel running reduces peripheral sympathetic drive by modulating stress-induced activity of brain regions synaptically linked to sympathetically innervated peripheral organs, including the adrenals and spleen. To this end, adrenal and splenic catecholamine content and activity of the central sympathetic circuit indexed by c-Fos protein induction, elicited by acute exposure to inescapable tail shock, were measured. Stressor exposure depleted adrenal and splenic norepinephrine content and elicited a robust increase in c-Fos in the brains of sedentary rats. Physical activity status had no effect on adrenal norepinephrine content. Indicative of attenuated sympathetic drive to the spleen, however, 6 weeks of voluntary freewheel running diminished stress-induced splenic norepinephrine depletion, and significantly attenuated stress-induced c-Fos in specific brain regions responsible for sympathetic regulation, including tyrosine hydroxylase-immunoreactive neurons of the locus coeruleus, A5 cell group and rostral ventrolateral medulla. Results suggest that voluntary activity attenuates sympathetic drive to the spleen during stressor exposure by selectively modulating stress-induced activity of the central sympathetic circuit. The attenuation of sympathetic responses observed in this study may be one important mechanism for the protective effect of physical activity against stress-related illness and immunosuppression.

Role of central β-adrenergic receptors in regulating proinflammatory cytokine responses to a peripheral bacterial challenge

Elevation of proinflammatory cytokines in the brain have potent effects on altering physiological, behavioral, and cognitive processes. The mechanism(s) by which brain cytokines are induced during a peripheral immune challenge remains unclear since microorganisms/cytokines do not cross the blood-brain barrier (BBB). Recent studies indicate that central beta-adrenergic receptors (beta-ADRs) may mediate brain interleukin-1beta (IL-1) production. This has direct implications for the production of brain cytokines during a peripheral immune response since peripheral pathogens and cytokines rapidly stimulate brainstem catecholamine neurons via peripheral nerves and circumventricular pathways. Studies here examine the role of central beta-ADRs in regulating brain cytokine production following peripheral Escherichia coli (E. coli) challenge. Rats were centrally administered propranolol (beta-ADR antagonist) or vehicle followed by peripheral E. coli or saline and sacrificed 6h later for measurement of cytokines. Pre-treatment with propranolol completely blocked the induction of brain IL-1 following E. coli. Surprisingly, central propranolol also attenuated E. coli-induced peripheral cytokines. To examine whether the attenuated peripheral cytokine response following central propranolol administration was due leakage of propranolol into the general circulation and blockade of peripheral beta-blockade, nadolol (beta-ADR antagonist that does not cross the BBB) was administered peripherally prior to E. coli. Nadolol administration did not block central cytokine production following E. coli, but instead enhanced both peripheral and central proinflammatory cytokine production. Furthermore, central administration of isoproterenol (beta-ADR agonist) results in a time-dependent increase in brain IL-1 production. These data demonstrate central beta-ADRs may play a critical role to induce brain IL-1, while peripheral beta-ADRs inhibit cytokine response to bacterial challenge.

Splenic norepinephrine depletion following acute stress suppresses in vivo antibody response

Exposure to an intense acute stressor immediately following immunization leads to a reduction in anti-KLH IgM, IgG, and IgG2a, but not IgG1. Stress also depletes splenic norepinephrine (NE) content. Immunization during pharmacological (alpha-methyl-p-tyrosine) or stress-induced splenic NE depletion results in antibody suppression similar to that found in rats immunized prior to stressor exposure. Prevention of splenic NE depletion during stress by tyrosine, but not pharmacological elevation (mirtazapine) of NE, resulted in normal antibody responses. These data support the hypothesis that splenic NE depletion is necessary and sufficient for stress-induced suppression of antibody to a T-cell dependent antigen.

Non-coplanar polychlorinated biphenyl (PCB)-induced immunotoxicity is coincident with alterations in the serotonergic system

Attention to non-coplanar polychlorinated biphenyl (PCB) congeners in immunotoxicological research is increasing. However, the exact mechanism by which these congeners may induce immune dysfunction is still undefined. Because the serotonergic nervous system has been shown to be involved in the regulation of some immune responses, and also serves as a sensitive target for PCBs, the relationship (if any) between non-coplanar PCB exposure, immune responsiveness and the neurotransmitter serotonin (5-HT) was examined. Using bluegill sunfish (Lepomis macrochirus) as a model, changes in brain 5-HT levels, 5-HT synthesis and metabolism, and innate and cell-mediated immune parameters were evaluated following a single intraperitoneal injection of PCB 153 (5.0 or 50 μg/g body weight). Results revealed that 3 d following administration, PCB exposure decreased brain 5-HT levels (in the absence of effects on some enzymes involved in 5-HT synthesis and metabolism), increased oxyradical production by kidney phagocytes, and reduced splenic T- and B-lymphocyte proliferation. In vivo treatment of PCB-exposed fish with 5-hydroxy-L-tryptophan (the immediate precursor to 5-HT) ameliorated the observed PCB-induced immunotoxicity; in vitro treatment of immune cells from PCB-exposed fish with 5-HT failed to reverse the effects. Taken together, results from this study could suggest a link between PCB-induced alterations of brain 5-HT levels and subsequent immune dysfunction. These studies highlight the importance of indirect mechanisms of immunotoxicity, and, specifically, suggest a role for the neuroimmune axis in non-coplanar PCB-induced immune alterations.

Exercise and Stress Resistance: Neural-Immune Mechanisms

Stimulation of the sympathetic nervous system (SNS) and the release of norepinephrine (NE) is a powerful feature of the acute stress response that is adaptive when the response is acute and constrained. If SNS activation is frequent or excessive, however, it can contribute to negative health consequences including “metabolic syndrome” and immunosuppression. We recently reported that sedentary rats exposed to a well-characterized acute stressor (uncontrollable tailshock) excessively activate the SNS leading to depletion of NE below basal levels in some peripheral tissues. NE depletion specifically in the spleen suppresses the in vivo immunoglobulin response to an antigenic protein challenge (keyhole limpet hemocyanin, αKLH immunoglobulin (Ig)). Regular moderate physical activity (voluntary wheel running) buffers a wide array of negative consequences of acute stressor exposure including splenic NE depletion and αKLH Ig suppression. In the current chapter we will present the hypothesis that adaptations in the central sympathetic neurocircuit produced by physical activity constrain excessive stress-induced SNS responses, thereby preventing splenic NE depletion and αKLH Ig and anti-tetanus toxoid Ig suppression in physically active stressed rats.

Splenic norepinephrine depletion suppresses in vivo antibody response in physically active animals

dritic cell (DC). These studies aimed to understand how melatonin affects DCs’ differentiation and maturation using an in vitro bone marrow dendritic cells (BMDC) culture system. Since melatonin has also been shown to regulate the stress-induced hormone corticosterone (CORT), CORT was also included in the study. It was found that 24 h pretreatment with melatonin caused dose-responsive enhancement of LPS-induced DC maturation, while CORT, as expected, caused dose-responsive inhibition of DC maturation. Furthermore, DCs exposed to moderate amounts of melatonin greatly increased their IL-12 production. On the other hand, when BM cells were treated with hormones throughout the culture period without LPS stimulation, their development into DCs was not affected by melatonin, but was negatively affected by CORT. Surprisingly, when both hormones were applied, the effects of CORT were dominant in all cases. All together, melatonin positively regulates DCs during immune responses, but does not influence the CORT’s effects on DCs. Continuing studies will help the arising clinical use of DCs.

Regulation of brain IL-1 production following peripheral E. coli challenge: A role for the nucleus tractus solitarius and locus coeruleus

The relationship between stress and post-surgical WBC count among women undergoing total abdominal hysterectomy with bilateral salpingo oophorectomy (TAH-BSO) for suspected endometrial cancer Sally E. Jensen , Deidre B. Pereira , Stacy M. Dodd , Melissa Hosonitz , Daylene Ripley , Linda Morgan b a Department of Clinical and Health Psychology, University of Florida, USA b Department of Obstetrics and Gynecology, University of Florida, USA

Ovariectomy alters the induction of heat shock protein 72 in some stress-responsive tissues

In addition to its common use as a spice, the medical uses of garlic (Allium sativum) have been known for centuries. More recently, the anti-bacterial and anti-fungal activity of garlic has been verified and the anti-artherosclerosis, anti-carcinogenesis, and hypolipidemic activities for garlic and several of its constituents have been demonstrated. In addition, anti-oxidant, anti-inflammatory, anti-ageing, and anti-stress effects have been reported for a well-characterized aged garlic extract (AGE, Kyolic ). We have examined further the possible anti-stress effects of AGE. We first tested the effects of 15 min cold water immersion (15 C) on LPS (10 lg i.v.) induced plasma and splenic inflammatory cytokine production, as well as corticosterone and catecholamine levels. Blood and spleen were harvested 90 min following LPS injection. Relative to controls, cold water immersion produced a significant decrease in plasma levels of TNF-a and IL-6 and splenic levels of TNF-a, IL-1b, and IL-6. Also, cold water immersion produced a significant decrease in plasma corticosterone levels, but increased plasma norepinephrine and epinephrine levels. We next tested the effects of orally administering AGE (10 ml/ kg) daily via gavage for 5 days prior to 15 min cold water immersion challenge and i.v. LPS injection. Relative to rats pretreated with vehicle, the AGE treated animals showed an attenuation in the immunosuppressive effects of cold water immersion on plasma and spleen levels of IL-6, and splenic levels of IL-1b. The stress-induced suppression of TNF-a levels were not altered by AGE. However, AGE treatment blocked the stress-induced changes in plasma levels of corticosterone, norepinephrine and epinephrine. Thus, pretreatment with AGE was able to partially reverse the effects of cold water stress on LPS-induced cytokine production, and completely block the stress-LPS induced changes in plasma corticosterone and catecholamine levels. These results indicate that AGE can counteract some of the immunomodulatory effects of stress which may be mediated via AGE-induced changes in the neuroendocrine and autonomic nervous systems.

102 The female intracellular Hsp72 stress response

ther the immunoregulatory effects of counter-irritation, we have tested the effects of turpentine injections into themuscle (IM), skin (ID)or plantar foot (PF) of the hindlimbof rats on endotoxin (LPS) induced plasma and splenic cytokines and catecholamine levels and plasma corticosterone. One hour following saline or turpentine injections (50–100 ll), rats were injected IV with LPS (10 lg) and then sacrificed one hour later. Relative to saline injections, both IM and PF injections of turpentine produced a significant decrease in plasma and splenic levels of TNF protein whereas IL-1 and IL-6 levels were unaltered by pretreatment with turpentine. In addition, PF injections of turpentine produced a significant decrease of corticosterone levels. In contrast, the effects of ID injections of turpentine were limited to a significant increase in splenic TNF levels and a tendency to increase plasma TNF levels. To examine the role of the sympathetic nervous system, we pretreated rats IP with the peripheral beta-adrenergic blocking agent Nadolol (2 mg/kg) 30 min prior to an IM injection of saline or turpentine. LPS was injected 1 h post-turpentine/saline and the rats were sacrificed one hour later. Pretreatment with Nadolol blocked the suppression in splenic and plasma levels of TNF produced by IM turpentine, consistent with the sympathetic mediation of the immunoregulatory effects of counter-irritation. Our data indicate further that the immunomodulatory effects of ID turpentine may be quite distinct from that observed with IM and PF injections. Supported by the NIMH of the United States (MH 43778).