Possible role of the sympathetic nervous system in responses to interleukin-1

Inflammatory Signaling in Hypertension: Regulation of Adrenal Catecholamine Biosynthesis

The immune system is increasingly recognized for its role in the genesis and progression of hypertension. The adrenal gland is a major site that coordinates the stress response via the hypothalamic-pituitary-adrenal axis and the sympathetic-adrenal system. Catecholamines released from the adrenal medulla function in the neuro-hormonal regulation of blood pressure and have a well-established link to hypertension. The immune system has an active role in the progression of hypertension and cytokines are powerful modulators of adrenal cell function. Adrenal medullary cells integrate neural, hormonal, and immune signals. Changes in adrenal cytokines during the progression of hypertension may promote blood pressure elevation by influencing catecholamine biosynthesis. This review highlights the potential interactions of cytokine signaling networks with those of catecholamine biosynthesis within the adrenal, and discusses the role of cytokines in the coordination of blood pressure regulation and the stress response.

Landiolol, an ultra-short-acting β1-blocker, is useful for managing supraventricular tachyarrhythmias in sepsis

AIM: To investigate whether landiolol, an ultra-short-acting β1-antagonist, can safely and effectively control heart rate in septic patients with supraventricular tachyarrhythmias.

METHODS: We reviewed all patients with sepsis who admitted to our intensive care unit between January 2006 and December 2011. Sixty one septic patients suffered from supraventricular tachyarrhythmias (heart rate ≥ 120 bpm for > 1 h). Among 61 patients, 39 patients were treated with landiolol (landiolol group) and 22 patients were not treated with landiolol (control group). Arterial pressure, heart rate, cardiac rhythm, pulmonary arterial pressure and cardiac output (if a pulmonary arterial catheter was inserted) were compared between the 2 groups at 1, 8 and 24 h after the initiation of tachyarrhythmias.

RESULTS: Mean age and Acute Physiology and Chronic Health Evaluation II and Sequential Organ Failure Assessment scores were similar between the 2 groups. Paroxysmal atrial fibrillation/flutter (87%), paroxysmal atrial tachycardia (10%), and paroxysmal supraventricular tachycardia (3%) were observed. The initial landiolol dose administered was 6.3 ± 5.8 g/kg per minute. Rapid and substantial reduction of heart rate was observed in the landiolol group without any deterioration of hemodynamics. Landiolol significantly reduced heart rate (from 145 ± 14 bpm to 90 ± 20 bpm) compared to the control group (from 136 ± 21 bpm to 109 ± 18 bpm, P < 0.05). The conversion to sinus rhythm was observed more frequently in the landiolol group than in the control group at every point (P < 0.01 at 8 h; P < 0.05 at 1 and 24 h).

CONCLUSION: Landiolol safely reduced heart rate and, in part, converted to sinus rhythm in septic patients with supraventricular tachyarrhythmias.

Brown fat UCP1 is not involved in the febrile and thermogenic responses to IL-1beta in mice

The activity of brown adipose tissue (BAT), a site of nonshivering metabolic thermogenesis, has been reported to increase after interleukin (IL)-1beta/lipopolysaccharide injection. To clarify the possible contribution of BAT thermogenesis to whole body febrile response, we investigated febrile and thermogenic response to IL-1beta using mice deficient in uncoupling protein-1 (UCP1), a key molecule for BAT thermogenesis. In wild-type (WT) mice, IL-1beta injection (5 microg/kg ip) increased body temperature (+1.82 degrees C at 20 min), decreased physical activity (-37% at 1 h), and produced a slight and insignificant rise (+15% at 1 h) in oxygen consumption (Vo(2)). Vo(2) dependent on metabolic thermogenesis (DeltaVO2 thermogenesis) calculated by correcting the effect of physical activity was increased after IL-1beta injection (726 +/- 200 ml x h(-1) x kg(-1) at 1 h). Almost the same responses were observed in UCP1-deficient mice, showing 638 +/- 87 ml x h(-1) x kg(-1) of DeltaVO2 thermogenesis at 1 h. In contrast, CL316,243, a selective activator of BAT thermogenesis, increased body temperature, decreased physical activity, and produced a significant rise in Vo2 in WT mice, showing 1,229 +/- 35 ml x h(-1) x kg(-1) of DeltaVO2 thermogenesis at 1 h. These changes were not observed in UCP1-deficient mice. These results, conflicting with a previously proposed idea of a role of BAT in fever, suggest a minor contribution of BAT thermogenesis to IL-1beta-induced fever. In support of this, we found no effect of IL-1beta on triglyceride content and UCP1 mRNA level in BAT, in contrast with apparent effects of CL316,243.

Sympathetic activation and tachycardia in lipopolysaccharide treated rats are temporally correlated and unrelated to the baroreflex

The goal of this study was to investigate the sustained sympatho-excitation which occurs in sepsis and which accompanies the fall in blood pressure and to analyze its time-correlation with heart rate and the role of the baro-chemoreflexes. Rats anesthetized with pentobarbital were treated with lipolysaccharide (LPS) 20 mg/kg/20 min i.v. and mean blood pressure (MBP), heart rate (HR), rectal temperature and renal sympathetic nerve activity (RSNA) were recorded. LPS induced a fall in blood pressure, an increase in HR (+20%) and RSNA (+355%); the arterial PO2 and PCO2 remained stable and the injection was fatal within 4 h. Baroreceptor and chemoreceptor denervation accelerated the fall in MBP but did not change the survival time. Under those conditions; RSNA excitation was slightly more pronounced. During treatment with gallamine and under artificial respiration to avoid possible respiratory changes through the chemoreflex pathway, the effects of LPS remained, except for a decrease in arterial PO2. Electrolytic lesioning of the nucleus tractus solitarius or blocking the effects of baroreflex efferents by either an alpha1 or alpha2-adrenoceptor antagonists failed to alter the effects of LPS. After treatment with a beta-adrenoceptor antagonist, LPS increased RSNA but not HR and the survival time of the rats shortened. LPS administered i.c. (1 mg/kg) induced, with a short latency, effects comparable to those produced by i.v. injection. Surprisingly, the time correlation between RSNA and HR rhythms persisted when MBP dropped after LPS and moreover it reappeared in baroreceptor denervated rats after LPS. Thus under these conditions of altered baroreflex pathway and LPS induced sympathetic activation, the sympathetic output from the medulla appears to play a role in the correlation between heart rate and sympathetic nerve activity. These data indicate that the marked RSNA activation and the tachycardia are correlated and that the baroreflex and chemoreflex are not inhibited during sepsis but appear to be of minor importance in the sympathetic activation and in the blood pressure modifications.

Immunoactivation and Altered Intercellular Communication Mediate the Pathophysiology of Spinal Cord Injury

Evidence and inferences from clinical research, clinical observation, and literature review support an etiologic paradigm for the pathophysiology of spinal cord injury (SCI). According to this paradigm, changes in immunoregulation and in the activation of cytokines or intercellular adhesion molecules (ICAMs) contribute to many of the comorbidities, metabolic changes, and pathophysiologic sequelae observed after traumatic SCI. Cytokines and ICAMs are endogenously secreted molecules that serve as intercellular signals and immunoregulators. They modulate the activity of cells and influence the organization and function of tissues or organs. These intercellular signals are posited as molecular links between the damaged, decentralized nervous system of SCI and the acquired autonomic failure, neuroendocrine-immunoregulatory dysfunction, diminished central nervous system (CNS) regenerative capacity, and broad spectrum of pathology, organ failure, and generalized impairment of homeostasis caused by trauma to the spinal cord. These highly bioactive molecules may also mediate or facilitate the intralesional CNS axonal damage and peripheral neurologic deficits sustained at time of acute CNS injury. Ultimately, it should be possible to develop treatments that will block or modulate the local and systemic expression of cytokine or ICAM bioactivity. Such treatments might aid victims of SCI by diminishing overall morbidity or mortality, helping restore sensorimotor function and homeostasis, and enhancing longevity and quality of life.

Sympathetic nerve destruction in spleen in murine AIDS

In susceptible strains of mice, the LP-BM5 mixture of murine retroviruses induces the fatal immunodeficiency disease known as murine acquired immunodeficiency syndrome (murine AIDS or MAIDS). We have previously reported that murine AIDS produces a profound depletion of splenic norepinephrine (NE). Here, we demonstrate that NE depletion is limited to the spleen, a major site affected by LP-BM5 infection. NE depletion in the spleen is first observed at two weeks following LP-BM5 inoculation, concurrent with the onset of splenomegaly, and continues through 12 weeks post-infection. Neuroanatomical studies revealed that the reduction in NE is due to destruction of splenic sympathetic nerve fibers. Administration of the NE reuptake blocker desipramine did not prevent LP-BM5-induced NE depletion, suggesting that destruction is not caused by excess release and reuptake of NE. Elucidating the mechanism of MAIDS-induced sympathetic nerve destruction may provide insight into autonomic and peripheral neuropathies reported in people with AIDS.

Sympathetic neural response to immune signals involves nitric oxide: effects of exposure to alcohol in utero

In response to infection, inflammation, or injury, the neural-immune-endocrine networks are activated to restore or maintain stability in the internal environment. Disruption of any one of the functional components may impair the effectiveness of the immune response to challenges, and may consequently jeopardize the wellness of the host. Studies in the author's laboratory have shown that the normal activation of splenic sympathetic neurons in response to the endotoxin lipopolysaccharide, a tool frequently used to mimic infection or inflammation, does not occur in fetal alcohol-exposed (FAE) rats. The sympathetic innervation of lymphoid organs is considered an important immune modulator. Thus, the anomalous splenic sympathetic response may partly account for the impaired immunity associated with FAE. Although the underlying mechanism is far from clear, studies described in this report suggest that nitric oxide (NO), a gaseous free radical, is involved in the altered splenic sympathetic neural response to immune signals. The suggestion is supported by the following findings: (1) blockade of NO synthesis prevented the blunted sympathetic response to lipopolysaccharide or interleukin-1 in FAE rats, and (2) there was a further increase in NO formation in response to lipopolysaccharide in the FAE rats compared to their control cohorts. This was demonstrated by an augmented increase in the inducible NO synthase immunoreactivity in the spleen as well as in circulating levels of NO metabolites. It is suggested, therefore, that the altered splenic sympathetic response to immune signals involves excessive formation of NO that may account, at least in part, for the impaired immunity associated with FAE.

The sympathetic nervous system tonically inhibits peripheral interleukin-1beta and interleukin-6 induction by central lipopolysaccharide

To study the role of the sympathetic nervous system in the induction of inflammatory cytokines elicited by central lipopolysaccharide, sympathetic chemical denervation was performed by intraperitoneal injection of 6-hydroxydopamine. Rats received the neurotoxin according to the following schedule: 50 mg/kg on days 1 and 2, 100 mg/kg on days 3, 4 and 7. On day 8, lipopolysaccharide (2.5 microg/6 microl/rat) was injected intracerebroventricularly and rats were killed 2 h later. 6-Hydroxydopamine reduced noradrenaline and dopamine content in the spleen by 88.7% and 88.8% respectively, without affecting striatal contents indicating that the chemical sympathectomy had been effective and selective. In sympathectomized rats, lipopolysaccharide raised interleukin-1beta and interleukin-6 serum levels more than in control rats given the vehicle. Tumour necrosis factor-alpha serum levels in sympathectomized rats were no different from those in vehicle-treated rats. Interleukin-1beta and interleukin-6 messenger RNA expression, measured by northern blot analysis, was clearly detectable in adrenals and spleen of rats given lipopolysaccharide. Sympathectomy increased lipopolysaccharide-induced interleukin-1beta and interleukin-6 messenger RNA in adrenals and spleen. Corticosterone basal levels were raised by central lipopolysaccharide and not further changed by sympathectomy. The present study shows that sympathetic nervous system denervation enhances the synthesis and production of peripheral interleukin-1beta and interleukin-6 in rats given central lipopolysaccharide and suggests a tonic inhibitory control of the sympathetic nervous system on these inflammatory cytokines.

Infection-induced anorexia: active host defence strategy

In association with fever production, decreased food consumption is the most common sign of infection. This effect is often regarded as an undesirable manifestation of sickness. However, evidence suggests that just as many behaviours have now been shown to modify immunocompetence, infection-induced anorexia is a behaviour systematically organised for pathogen elimination. That is, anorexia is an active defence mechanism that is beneficial for host defence. This review details the mechanism of infection-induced anorexia, placing it within the framework of the intricately organised acute phase response--the host response to infection. Furthermore, the evolutionary, behavioural, metabolic and immunological consequences of infection-induced anorexia are outlined, each providing evidence for the beneficial nature of this response. The evidence suggests that food restriction is one of the important behavioural strategies that organisms have evolved for the fight against pathogenic invasion. Nevertheless, such benefits require fine homeostatic control, as chronic undernutrition has deleterious consequences for host defence.

Cracking the riddle of cancer anorexia

During tumor growth, anorexia and reduced food intake are among the major causes leading to malnutrition and eventually cachexia, which negatively affect patients' outcome. Consistent evidence from our laboratories in rats and humans indicates a key role for ventromedial hypothalamic (VMH) serotonergic system in the development of cancer anorexia. Thus, we postulated that during cancer, increased plasma tryptophan levels (the precursor of serotonin) lead to increased cerebrospinal fluid tryptophan concentrations and increased VMH serotonin synthesis, which then mediates the occurrence of anorexia. However, recent data strongly suggest that factors other than tryptophan supplied to the central nervous system might be involved in the pathogenesis of reduced food intake during tumor growth. Particularly, a significant role appears to be played by interleukin-1 (IL-1). We recently showed that IL-1 infusion in normal rats causes changes in food intake and its determinants, meal number and meal size, similar to those characterizing cancer anorexia, thus supporting the involvement of this cytokine in the development of anorexia. Interestingly, IL-1 and the VMH serotonergic system appear to be closely linked: peripherally infused IL-1 increases brain tryptophan and serotonin concentrations, while intracerebrally infused IL-1 increases neuronal firing rate and serotonin release. We therefore hypothesize that during tumor growth, increased production/secretion of IL-1 occurs, which facilitates the tryptophan supply to the brain. IL-1 can then also act on the VHM itself, where IL-1 receptors exist, to increase its neuronal activity and serotonin release. In other words, we believe that centrally acting IL-1 increases hypothalamic neuronal firing rate and serotonin release, while peripherally acting IL-1 is critical in supplying the hypothalamus with the precursor, tryptophan, in order to maintain the high rate of serotonin synthesis. Also, additional factors recently proposed as mediators of anorexia (including neuropeptide Y and nitric oxide) appear to be part of the hypothesized pathogenic mechanism.

Neuroendocrine-immune interactions in homeostasis and autoimmunity

Recent experimental evidence confirms the interrelationships between the central nervous, neuroendocrine and immune systems. Indeed, extensive duality exists in the use of neurotransmitters, hormones and receptors each system displays. In the present annotation, the effect of cytokines, soluble mediators of immune function, on the CNS and neuroendocrine systems is addressed and conversely, we discuss the modification of the immune compartment by the sympathetic nervous and neuroendocrine systems, with particular reference to the role of noradrenaline and corticosterone. Dysfunction between the systems is considered in the context of autoimmune conditions, with emphasis on experimental allergic encephalomyelitis and the contribution of corticosterone-driven T-cell apoptosis to recovery from the disease. Finally, we speculate on the relevance of neuroimmune interactions in the pathogenesis of multiple sclerosis.

Glucagon injected in the lateral hypothalamus stimulates sympathetic activity and suppresses monoamine metabolism

Glucagon injected in the lateral hypothalamus stimulates sympathetic activity and suppresses monamine metabolism. The central hypothesis underlying this study is that there is a reciprocal relationship between food intake and sympathetic activity to IBAT. This hypothesis was tested by using intrahypothalamic microinjections of glucagon, a peptide that has been reported to decrease food intake. Sympathetic nerve activity to interscapular brown adipose tissue (IBAT) was measured as electrophysiological discharges of sympathetic nerves to IBAT. The microinjection of glucagon into the lateral hypothalamus (LH) increased sympathetic nerve activity by +103.8 +/- 35.0% (mean +/- S.E.M.) from pre-injection basal level by 30 min after injection. There was a gradual return to baseline. Micro-injection of glucagon into the LH depressed food intake. Monoamine metabolism was measured by using a microdialysis probe attached to a guide cannula for microinjection of glucagon into the LH. After microinjection of glucagon, the dialysates were collected over 30 min intervals and assayed for norepinephrine (NE), serotonin (5-HT), dopamine (DA) and their metabolites (3-methoxy-4-hydroxyphenylglycol (MHPG); 5-hydroxyindole-3-acetic acid (5-HIAA); and 3,4-dihydroxyphenylacetic acid (DOPAC). Glucagon suppressed both NE and MHPG concentrations in the lateral hypothalamus (LH), and the concentration of DOPAC was also decreased. There was no change of 5-HT concentration but 5-HIAA levels were reduced by glucagon treatment. These data show that glucagon injected in the LH stimulates sympathetic activity and suggest that this may have occurred by suppression of norepinephrine, dopamine and serotonin turnover in the LH of freely moving rats. These data support the hypothesis of a reciprocal relationship between food intake and sympathetic activity.

Circulating levels of soluble interleukin 2 receptors are elevated in the sera of humans with spinal cord injury

A unique molecular regulatory mechanism or final common molecular pathway mediating the autonomic dysfunction and several pathobiologic sequelae of spinal cord injury (SCI) in humans has not been delineated. Although seemingly disparate in etiopathogenesis, much of the pathology caused by traumatic disruption of the spinal cord may be attributable to the pleiotropism demonstrated by a unique family of endogenous bioactive molecules, the interleukins. To begin testing this hypothesis, we examined the sera of patients with chronic SCI for elevations in interleukin 1 beta (IL-1 beta) and interleukin 2 receptor (IL-2R) and compared them to a control population of able-bodied subjects. In comparison to control subjects, a statistically significant increase in IL-2R was observed in patients with cervical spinal myelopathy. Elevated levels of IL-2R were not seen in paraplegic patients. Significant differences between the means and variances of serum IL-1 beta could not be detected among the study groups. We conclude that the sera of quadriplegic patients with chronic SCI contain elevated levels of IL-2R and suggest that the elevated levels of IL-2R may be of diagnostic, prognostic, and therapeutic importance.

Effects of cholecystokinin on sympathetic activity to interscapular brown adipose tissue

The effects of injecting cholecystokinin (CCK) into the third ventricle or into selected hypothalamic sites on electrical firing rate of sympathetic nerves to interscapular brown fat (IBAT) has been investigated in anesthetized rats. The hypothesis for these experiments was that there was a reciprocal relationship between sympathetic activity and food intake. Since CCK reduces food intake we predicted that CCK would stimulate sympathetic activity to IBAT. Following the injection of CCK into the third ventricle there was an increase in firing rate of sympathetic nerves to IBAT. When the peptide was injected into either the ventromedial hypothalamic nucleus (VMH) or lateral hypothalamic area (LHA), there was likewise an increase in sympathetic firing rate. The injection of CCK into the paraventricular nucleus produced a small decrease in sympathetic firing rate. In contrast, no effect was seen following injection of CCK into the preoptic area or dorsomedial hypothalamic nucleus. Thus, the VMH or LHA appear to be the principal hypothalamic areas mediating the stimulation of sympathetic activity to IBAT which is observed following the third ventricular injection of CCK. These studies support the hypothesis of a reciprocal relationship between the effects of CCK on the thermogenic component of the sympathetic nervous system and food intake and identify the VMH and LHA as the primary sites for this effect.