Sympathetic noradrenergic innervation of immune organs

Neuroscience in peripheral cancers: tumors hijacking nerves and neuroimmune crosstalk

Cancer neuroscience is an emerging field that investigates the intricate relationship between the nervous system and cancer, gaining increasing recognition for its importance. The central nervous system governs the development of the nervous system and directly affects brain tumors, and the peripheral nervous system (PNS) shapes the tumor microenvironment (TME) of peripheral tumors. Both systems are crucial in cancer initiation and progression, with recent studies revealing a more intricate role of the PNS within the TME. Tumors not only invade nerves but also persuade them through remodeling to further promote malignancy, creating a bidirectional interaction between nerves and cancers. Notably, immune cells also contribute to this communication, forming a triangular relationship that influences protumor inflammation and the effectiveness of immunotherapy. This review delves into the intricate mechanisms connecting the PNS and tumors, focusing on how various immune cell types influence nerve‒tumor interactions, emphasizing the clinical relevance of nerve‒tumor and nerve‒immune dynamics. By deepening our understanding of the interplay between nerves, cancer, and immune cells, this review has the potential to reshape tumor biology insights, inspire innovative therapies, and improve clinical outcomes for cancer patients.

The amphibian's spleen as a source of biomarkers for ecotoxicity assessment: Historical review and trends

Amphibians are very sensitive to many environmental changes, so these animals are considered good bioindicator models for ecotoxicology. Given the importance of the amphibian spleen for hematopoietic and immune responses, this can be a key organ for the evaluation of biomarkers to monitor the health of individuals in nature or in captivity. In this systematic review, we searched databases and summarized the main findings concerning the amphibian spleen as a source of possible biomarkers applied in different scientific fields. The searches resulted in 83 articles published from 1923 to 2022, which applied the use of splenic samples to evaluate the effects of distinct stressors on amphibians. Articles were distributed in more than twenty countries, with USA, Europe, and Brazil, standing out among them. Publications focused mainly on anatomical and histomorphological characterization of the spleen, its physiology, and development. Recently, the use of splenic biomarkers in pathology and ecotoxicology began to grow but many gaps still need to be addressed in herpetological research. About 85 % of the splenic biomarkers showed responses to various stressors, which indicates that the spleen can provide numerous biomarkers to be used in many study fields. The limited amount of information on morphological description and splenic anatomy in amphibians may be a contributing factor to the underestimated use of splenic biomarkers in herpetological research around the world. We hope that this unprecedented review can instigate researchers to refine herpetological experimentation, using the spleen as a versatile and alternative source for biomarkers in ecotoxicology.

Central regulation of stress-evoked peripheral immune responses

Stress-linked psychiatric disorders, including anxiety and major depressive disorder, are associated with systemic inflammation. Recent studies have reported stress-induced alterations in haematopoiesis that result in monocytosis, neutrophilia, lymphocytopenia and, consequently, in the upregulation of pro-inflammatory processes in immunologically relevant peripheral tissues. There is now evidence that this peripheral inflammation contributes to the development of psychiatric symptoms as well as to common co-morbidities of psychiatric disorders such as metabolic syndrome and immunosuppression. Here, we review the specific brain and spinal regions, and the neuronal populations within them, that respond to stress and transmit signals to peripheral tissues via the autonomic nervous system or neuroendocrine pathways to influence immunological function. We comprehensively summarize studies that have employed retrograde tracing to define neurocircuits linking the brain to the bone marrow, spleen, gut, adipose tissue and liver. Moreover, we highlight studies that have used chemogenetic or optogenetic manipulation or intracerebroventricular administration of peptide hormones to control somatic immune responses. Collectively, this growing body of literature illustrates potential mechanisms through which stress signals are conveyed from the CNS to immune cells to regulate stress-relevant behaviours and comorbid pathophysiology.

Psychoneuroimmunology in the time of COVID-19: Why neuro-immune interactions matter for mental and physical health

The brain and immune system are intricately connected, and perturbations in one system have direct effects on the other. This review focuses on these dynamic psychoneuroimmune interactions and their implications for mental and physical health in the context of the COVID-19 pandemic. In particular, we describe how psychological states influence antiviral immunity and the vaccine response, and how immune changes triggered by COVID (either via infection with SARS-CoV-2 or associated stressors) can influence the brain with effects on cognition, emotion, and behavior. We consider negative psychological states, which have been the primary focus of psychological research in the context of COVID-19 (and psychoneuroimmunology more generally). We also consider positive psychological states, including positive affect and eudaimonic well-being, given increasing evidence for their importance as modulators of immunity. We finish with a discussion of interventions that may be effective in improving immune function, the neuro-immune axis, and ultimately, mental and physical health.

Understanding the Role of Dopamine in Cancer: Past, Present, and Future

Dopamine (DA, 3-hydroxytyramine) is member of the catecholamine family and is classically characterized according to its role in the central nervous system as a neurotransmitter. In recent decades, many novel and intriguing discoveries have been made about the peripheral expression of DA receptors (DRs) and the role of DA signaling in both normal and pathological processes. Drawing from decades of evidence suggesting a link between DA and cancer, the DA pathway (DAP) has recently emerged as a potential target in antitumor therapies. Due to the onerous, expensive, and frequently unsuccessful nature of drug development, the repurposing of dopaminergic drugs for cancer therapy has the potential to greatly benefit patients and drug developers alike. However, the lack of clear mechanistic data supporting the direct involvement of DRs and their downstream signaling components in cancer represents an ongoing challenge that has limited the translation of these drugs to the clinic. Despite this, the breadth of evidence linking DA to cancer and non-tumor cells in the tumor microenvironment (TME) justifies further inquiry into the potential applications of this treatment modality in cancer. Herein, we review the literature characterizing the interplay between the DA signaling axis and cancer, highlighting key findings, and then propose rational lines of investigation to follow.

Contribution of adrenergic mechanisms for the stress-induced breast cancer carcinogenesis

Breast cancer is the most common and deadliest type of cancer in women. Stress exposure has been associated with carcinogenesis and the stress released neurotransmitters, noradrenaline and adrenaline, and their cognate receptors, can participate in the carcinogenesis process, either by regulating tumor microenvironment or by promoting systemic changes. This work intends to provide an overview of the research done in this area and try to unravel the role of adrenergic ligands in the context of breast carcinogenesis. In the initiation phase, adrenergic signaling may favor neoplastic transformation of breast epithelial cells whereas, during cancer progression, may favor the metastatic potential of breast cancer cells. Additionally, adrenergic signaling can alter the function and activity of other cells present in the tumor microenvironment towards a protumor phenotype, namely macrophages, fibroblasts, and by altering adipocyte's function. Adrenergic signaling also promotes angiogenesis and lymphangiogenesis and, systemically, may induce the formation of preneoplastic niches, cancer-associated cachexia and alterations in the immune system which contribute for the loss of quality of life of breast cancer patients and their capacity to fight cancer. Most studies points to a major contribution of β₂ -adrenoceptor activated pathways on these effects. The current knowledge of the mechanistic pathways activated by β₂ -adrenoceptors in physiology and pathophysiology, the availability of selective drugs approved for clinical use and a deeper knowledge of the basic cellular and molecular pathways by which adrenergic stimulation may influence cancer initiation and progression, opens the possibility to use new therapeutic alternatives to improve efficacy of breast cancer treatments.

Nerves in cancer

The contribution of nerves to the pathogenesis of malignancies has emerged as an important component of the tumour microenvironment. Recent studies have shown that peripheral nerves (sympathetic, parasympathetic and sensory) interact with tumour and stromal cells to promote the initiation and progression of a variety of solid and haematological malignancies. Furthermore, new evidence suggests that cancers may reactivate nerve-dependent developmental and regenerative processes to promote their growth and survival. Here we review emerging concepts and discuss the therapeutic implications of manipulating nerves and neural signalling for the prevention and treatment of cancer.

Effects of Brief Mood-Improving Interventions on Immunity: A Systematic Review and Meta-Analysis

OBJECTIVE

Positive mood has been associated with enhanced immune function. Interventions that improve mood could therefore provide a mechanism for optimizing immune-related health outcomes. Brief interventions that improve mood, also known as mood inductions, potentially offer a pragmatic approach to enhancing immune function for finite periods where this would be beneficial to health (e.g., in advance of vaccination or surgery). This review sought to systematically examine the evidence regarding the effects of brief, single-session positive mood interventions on immunity.

METHODS

Systematic searches of electronic databases were performed from earliest records to July 25, 2018. We identified 42 interventions suitable for inclusion, 6 of which were tested in multiple subpopulations. Random-effects meta-analyses were performed for pre-post experimental group immune outcomes measured in at least five intervention studies.

RESULTS

Although interventions were heterogeneous, 81% resulted in a statistically significant change in at least one immune parameter after the positive mood intervention for one or more of the subpopulations examined. However, studies were, in general, of low-to-moderate quality with small sample sizes (median n = 32) and did not examine the persistence or clinical relevance of the immune changes observed. Random-effects meta-analyses showed a significant medium-sized effect of interventions on increasing secretory IgA concentration (g = 0.65), a small but statistically significant effect for increased Interleukin-6 production (g = 0.12), and nonsignificant effects on natural killer cell activity (g = 0.15).

CONCLUSIONS

The current literature suggests that improvements in mood resulting from brief interventions can influence some immune parameters in ways indicative of enhanced immune function. However, there is a need for higher-quality research in this area that focuses on clinically relevant immune outcomes and mechanisms.

Interaction of neurotransmitters and neurochemicals with lymphocytes

Neurotransmitters and neurochemicals can act on lymphocytes by binding to receptors expressed by lymphocytes. This review describes lymphocyte expression of receptors for a selection of neurotransmitters and neurochemicals, the anatomical locations where lymphocytes can interact with neurotransmitters, and the effects of the neurotransmitters on lymphocyte function. Implications for health and disease are also discussed.

Neuroimmune Communication in Health and Disease

The immune and nervous systems are tightly integrated, with each system capable of influencing the other to respond to infectious or inflammatory perturbations of homeostasis. Recent studies demonstrating the ability of neural stimulation to significantly reduce the severity of immunopathology and consequently reduce mortality have led to a resurgence in the field of neuroimmunology. Highlighting the tight integration of the nervous and immune systems, afferent neurons can be activated by a diverse range of substances from bacterial-derived products to cytokines released by host cells. While activation of vagal afferents by these substances dominates the literature, additional sensory neurons are responsive as well. It is becoming increasingly clear that although the cholinergic anti-inflammatory pathway has become the predominant model, a multitude of functional circuits exist through which neuronal messengers can influence immunological outcomes. These include pathways whereby efferent signaling occurs independent of the vagus nerve through sympathetic neurons. To receive input from the nervous system, immune cells including B and T cells, macrophages, and professional antigen presenting cells express specific neurotransmitter receptors that affect immune cell function. Specialized immune cell populations not only express neurotransmitter receptors, but express the enzymatic machinery required to produce neurotransmitters, such as acetylcholine, allowing them to act as signaling intermediaries. Although elegant experiments have begun to decipher some of these interactions, integration of these molecules, cells, and anatomy into defined neuroimmune circuits in health and disease is in its infancy. This review describes these circuits and highlights continued challenges and opportunities for the field.

The cholinergic anti-inflammatory pathway revisited

Inflammatory bowel disease negatively affects the quality of life of millions of patients around the world. Although the precise etiology of the disease remains elusive, aberrant immune system activation is an underlying cause. As such, therapies that selectively inhibit immune cell activation without broad immunosuppression are desired. Inhibition of immune cell activation preventing pro-inflammatory cytokine production through neural stimulation has emerged as one such treatment. These therapeutics are based on the discovery of the cholinergic anti-inflammatory pathway, a reflex arc that induces efferent vagal nerve signaling to reduce immune cell activation and consequently mortality during septic shock. Despite the success of preclinical and clinical trials, the neural circuitry and mechanisms of action of these immune-regulatory circuits are controversial. At the heart of this controversy is the protective effect of vagal nerve stimulation despite an apparent lack of neuroanatomical connections between the vagus and target organs. Additional studies have further emphasized the importance of sympathetic innervation of these organs, and that alternative neural circuits could be involved in neural regulation of the immune system. Such controversies also extend to the regulation of intestinal inflammation, with the importance of efferent vagus nerve signals in question. Experiments that better characterize these pathways have now been performed by Willemze et al. in this issue of Neurogastroenterology & Motility. These continued efforts will be critical to the development of better neurostimulator based therapeutics for inflammatory bowel disease.

Chronic stress in mice remodels lymph vasculature to promote tumour cell dissemination

Chronic stress induces signalling from the sympathetic nervous system (SNS) and drives cancer progression, although the pathways of tumour cell dissemination are unclear. Here we show that chronic stress restructures lymphatic networks within and around tumours to provide pathways for tumour cell escape. We show that VEGFC derived from tumour cells is required for stress to induce lymphatic remodelling and that this depends on COX2 inflammatory signalling from macrophages. Pharmacological inhibition of SNS signalling blocks the effect of chronic stress on lymphatic remodelling in vivo and reduces lymphatic metastasis in preclinical cancer models and in patients with breast cancer. These findings reveal unanticipated communication between stress-induced neural signalling and inflammation, which regulates tumour lymphatic architecture and lymphogenous tumour cell dissemination. These findings suggest that limiting the effects of SNS signalling to prevent tumour cell dissemination through lymphatic routes may provide a strategy to improve cancer outcomes.

Adverse life events have been associated with reduced survival in cancer patients. Here, the authors explore the mechanism responsible and show that chronic stress in mice activates a signalling cascade in macrophages and tumour cells, which results in restructuring of the tumour lymphatic system, promoting metastasis.

The aetiopathogenesis of fatigue: unpredictable, complex and persistent

BACKGROUND

Chronic fatigue syndrome is a common condition characterized by severe fatigue with post-exertional malaise, impaired cognitive ability, poor sleep quality, muscle pain, multi-joint pain, tender lymph nodes, sore throat or headache. Its defining symptom, fatigue is common to several diseases.

AREAS OF AGREEMENT

Research has established a broad picture of impairment across autonomic, endocrine and inflammatory systems though progress seems to have reached an impasse.

AREAS OF CONTROVERSY

The absence of a clear consensus view of the pathophysiology of fatigue suggests the need to switch from a focus on abnormalities in one system to an experimental and clinical approach which integrates findings across multiple systems and their constituent parts and to consider multiple environmental factors.

GROWING POINTS

We discuss this with reference to three key factors, non-determinism, non-reductionism and self-organization and suggest that an approach based on these principles may afford a coherent explanatory framework for much of the observed phenomena in fatigue and offers promising avenues for future research.

AREAS TIMELY FOR DEVELOPING RESEARCH

By adopting this approach, the field can examine issues regarding aetiopathogenesis and treatment, with relevance for future research and clinical practice.

Sympathoadrenergic modulation of hematopoiesis: a review of available evidence and of therapeutic perspectives

Innervation of the bone marrow (BM) has been described more than one century ago, however the first in vivo evidence that sympathoadrenergic fibers have a role in hematopoiesis dates back to less than 25 years ago. Evidence has since increased showing that adrenergic nerves in the BM release noradrenaline and possibly also dopamine, which act on adrenoceptors and dopaminergic receptors (DR) expressed on hematopoietic cells and affect cell survival, proliferation, migration and engraftment ability. Remarkably, dysregulation of adrenergic fibers to the BM is associated with hematopoietic disturbances and myeloproliferative disease. Several adrenergic and dopaminergic agents are already in clinical use for non-hematological indications and with a usually favorable risk-benefit profile, and are therefore potential candidates for non-conventional modulation of hematopoiesis.

Shift Work in Rats Results in Increased Inflammatory Response after Lipopolysaccharide Administration: A Role for Food Consumption

The suprachiasmatic nucleus (SCN) drives circadian rhythms in behavioral and physiological variables, including the inflammatory response. Shift work is known to disturb circadian rhythms and is associated with increased susceptibility to develop disease. In rodents, circadian disruption due to shifted light schedules (jet lag) induced increased innate immune responses. To gain more insight into the influence of circadian disruption on the immune response, we characterized the inflammatory response in a model of rodent shift work and demonstrated that circadian disruption affected the inflammatory response to lipopolysaccharide (LPS) both in vivo and in vitro. Since food consumption is a main disturbing element in the shift work schedule, we also evaluated the inflammatory response to LPS in a group of rats that had no access to food during their working hours. Our results demonstrated that the shift work schedule decreased basal TNF-α levels in the liver but not in the circulation. Despite this, we observed that shift work induced increased cytokine response after LPS stimulation in comparison to control rats. Also, Kupffer cells (liver macrophages) isolated from shift work rats produced more TNF-α in response to in vitro LPS stimulation, suggesting important effects of circadian desynchronization on the functionality of this cell type. Importantly, the effects of shift work on the inflammatory response to LPS were prevented when food was not available during the working schedule. Together, these results show that dissociating behavior and food intake from the synchronizing drive of the SCN severely disturbs the immune response.

Autonomic nervous system and immune system interactions

The present review assesses the current state of literature defining integrative autonomic-immune physiological processing, focusing on studies that have employed electrophysiological, pharmacological, molecular biological, and central nervous system experimental approaches. Central autonomic neural networks are informed of peripheral immune status via numerous communicating pathways, including neural and non-neural. Cytokines and other immune factors affect the level of activity and responsivity of discharges in sympathetic and parasympathetic nerves innervating diverse targets. Multiple levels of the neuraxis contribute to cytokine-induced changes in efferent parasympathetic and sympathetic nerve outflows, leading to modulation of peripheral immune responses. The functionality of local sympathoimmune interactions depends on the microenvironment created by diverse signaling mechanisms involving integration between sympathetic nervous system neurotransmitters and neuromodulators; specific adrenergic receptors; and the presence or absence of immune cells, cytokines, and bacteria. Functional mechanisms contributing to the cholinergic anti-inflammatory pathway likely involve novel cholinergic-adrenergic interactions at peripheral sites, including autonomic ganglion and lymphoid targets. Immune cells express adrenergic and nicotinic receptors. Neurotransmitters released by sympathetic and parasympathetic nerve endings bind to their respective receptors located on the surface of immune cells and initiate immune-modulatory responses. Both sympathetic and parasympathetic arms of the autonomic nervous system are instrumental in orchestrating neuroimmune processes, although additional studies are required to understand dynamic and complex adrenergic-cholinergic interactions. Further understanding of regulatory mechanisms linking the sympathetic nervous, parasympathetic nervous, and immune systems is critical for understanding relationships between chronic disease development and immune-associated changes in autonomic nervous system function.

Mouse models of sepsis elicit spontaneous action potential discharge and enhance intracellular Ca2+ signaling in postganglionic sympathetic neurons

Sepsis is a severe systemic inflammatory disorder that rapidly activates the sympathetic nervous system to enhance catecholamine secretion from postganglionic sympathetic neurons and adrenal chromaffin cells. Although an increase in preganglionic drive to postganglionic sympathetic tissues has been known to contribute to this response for quite some time, only recently was it determined that sepsis also has direct effects on adrenal chromaffin cell Ca2+ signaling and epinephrine release. In the present study, we characterized the direct effects of sepsis on postganglionic sympathetic neuron function. Using the endotoxemia model of sepsis in mice, we found that almost a quarter of postganglionic neurons acquired the ability to fire spontaneous action potentials, which was absent in cells from control mice. Spontaneously firing neurons possessed significantly lower rheobases and fired a greater number of action potentials at twice the rheobase compared to neurons from control mice. Sepsis did not significantly affect voltage-gated Ca2+ currents. However, global Ca2+ signaling was enhanced in postganglionic neurons isolated from 1 to 24 h endotoxemic mice. A similar increase in the amplitude of high-K+-stimulated Ca2+ transients was observed during the cecal ligation and puncture model of sepsis. The enhanced excitability and Ca2+ signaling produced during sepsis likely amplify the effect of increased preganglionic drive on norepinephrine release from postganglionic neurons. This is important, as sympathetic neurons are integral to the anti-inflammatory autonomic reflex that is activated during sepsis.

Participation of interleukin 17A in neuroimmune interactions

Inflammation involving the helper T cell 17 (Th17) subset of lymphocytes has been implicated in a number of diseases that affect the nervous system. As the canonical cytokine of Th17 cells, interleukin 17A (IL-17A) is thought to contribute to these neuroimmune interactions. The main receptor for IL-17A is expressed in many neural tissues. IL-17A has direct effects on neurons but can also impact neural function via signaling to satellite cells and immune cells. In the central nervous system, IL-17A has been associated with neuropathology in multiple sclerosis, epilepsy syndromes and ischemic brain injury. Effects of IL-17A at the level of dorsal root ganglia and the spinal cord may contribute to enhanced nociception during neuropathic and inflammatory pain. Finally, IL-17A plays a role in sympathetic axon growth and regeneration of damaged axons that innervate the cornea. Given the widespread effects of IL-17A on neural tissues, it will be important to determine whether selectively mitigating the damaging effects of this cytokine while augmenting its beneficial effects is a possible strategy to treat inflammatory damage to the nervous system.

Neural regulation of gastrointestinal inflammation: role of the sympathetic nervous system

The sympathetic innervation of the gastrointestinal (GI) tract regulates motility, secretion and blood flow by inhibiting the activity of the enteric nervous system (ENS) and direct vasoconstrictor innervation of the gut microvasculature. In addition to these well-established roles, there is evidence that the sympathetic nervous system (SNS) can modulate GI inflammation. Postganglionic sympathetic neurons innervate lymphoid tissues and immune cells within the GI tract. Furthermore, innate and adaptive immune cells express receptors for sympathetic neurotransmitters. Activation of these receptors can affect a variety of important immune cell functions, including cytokine release and differentiation of helper T lymphocyte subsets. This review will consider the neuroanatomical evidence of GI immune cell innervation by sympathetic axons, the effects of blocking or enhancing SNS activity on GI inflammation, and the converse modulation of sympathetic neuroanatomy and function by GI inflammation.

Spread of classic BSE prions from the gut via the peripheral nervous system to the brain

An experimental oral bovine spongiform encephalopathy (BSE) challenge study was performed to elucidate the route of infectious prions from the gut to the central nervous system in preclinical and clinical infected animals. Tissue samples collected from the gut and the central and autonomic nervous system from animals sacrificed between 16 and 44 months post infection (mpi) were examined for the presence of the pathological prion protein (PrP(Sc)) by IHC. Moreover, parts of these samples were also bioassayed using bovine cellular prion protein (PrP(C)) overexpressing transgenic mice (Tgbov XV) that lack the species barrier for bovine prions. A distinct accumulation of PrP(Sc) was observed in the distal ileum, confined to follicles and/or the enteric nervous system, in almost all animals. BSE prions were found in the sympathetic nervous system starting at 16 mpi, and in the parasympathetic nervous system from 20 mpi. A clear dissociation between prion infectivity and detectable PrP(Sc) deposition became obvious. The earliest presence of infectivity in the brain stem was detected at 24 mpi, whereas PrP(Sc) accumulation was first detected after 28 mpi. In summary, our results decipher the centripetal spread of BSE prions along the autonomic nervous system to the central nervous system, starting already halfway in the incubation time.

Immune cells listen to what stress is saying: neuroendocrine receptors orchestrate immune function

Over the past three decades, the field of psychoneuroimmunology research has blossomed into a major field of study, gaining interests of researchers across all traditionally accepted disciplines of scientific research. This chapter provides an overview of our current understanding in defining neuroimmune interactions with a primary focus of discussing the neuroendocrine receptor activity by immune cells. This chapter highlights the necessity of neuroimmune responses as it relates to a better understanding of the pathophysiological mechanisms of health and disease.

Modeling the association between HR variability and illness in elite swimmers

PURPOSE

To determine whether HR variability (HRV), an indirect measure of autonomic control, is associated with upper respiratory tract and pulmonary infections, muscular affections, and all-type pathologies in elite swimmers.

METHODS

For this study, 7 elite international and 11 national swimmers were observed weekly for 2 yr. The indexes of cardiac autonomic regulation in supine and orthostatic position were assessed as explanatory variables by time domain (SD1, SD2) and spectral analyses (high frequency [HF] = 0.15-0.40 Hz, low frequency [LF] = 0.04-0.15 Hz, and HF/LF ratio) of HRV. Logistic mixed models described the relationship between the explanatory variables and the risk of upper respiratory tract and pulmonary infections, muscular affections, and all-type pathologies.

RESULTS

The risk of all-type pathologies was higher for national swimmers and in winter (P < 0.01). An increase in the parasympathetic indexes (HF, SD1) in the supine position assessed 1 wk earlier was linked to a higher risk of upper respiratory tract and pulmonary infections (P < 0.05) and to a higher risk of muscular affections (increase in HF, P < 0.05). Multivariate analyses showed (1) a higher all-type pathologies risk in winter and for an increase in the total power of HRV associated with a decline SD1 in supine position, (2) a higher all-type pathologies risk in winter associated with a decline in HF assessed 1 wk earlier in orthostatic position, and (3) a higher risk of muscular affections in winter associated with a decrease SD1 and an increase LF in orthostatic position.

CONCLUSIONS

Swimmers' health maintenance requires particular attention when autonomic balance shows a sudden increase in parasympathetic indices in the supine position assessed 1 wk earlier evolving toward sympathetic predominance in supine and orthostatic positions.

Cognitive awareness of carbohydrate intake does not alter exercise-induced lymphocyte apoptosis

OBJECTIVE

The purpose of this investigation was to determine whether cognitive awareness of carbohydrate beverage consumption affects exercise-induced lymphocyte apoptosis, independent of actual carbohydrate intake.

INTRODUCTION

Carbohydrate supplementation during aerobic exercise generally protects against the immunosuppressive effects of exercise. It is not currently known whether carbohydrate consumption or simply the knowledge of carbohydrate consumption also has that effect.

METHODS

Endurance trained male and female (N = 10) athletes were randomly assigned to one of two groups based on either a correct or incorrect cognitive awareness of carbohydrate intake. In the incorrect group, the subjects were informed that they were receiving the carbohydrate beverage but actually received the placebo beverage. Participants completed a 60-min ride on a cycle ergometer at 80% VO₂peak under carbohydrate and placebo supplemented conditions. Venous blood samples were collected at rest and immediately after exercise and were used to determine the plasma glucose concentration, lymphocyte count, and extent of lymphocyte apoptosis. Cognitive awareness, either correct or incorrect, did not have an effect on any of the measured variables.

RESULTS

Carbohydrate supplementation during exercise did not have an effect on lymphocyte count or apoptotic index. Independent of drink type, exercise resulted in significant lymphocytosis and lymphocyte apoptosis (apoptotic index at rest = 6.3 ± 3% and apoptotic index following exercise = 11.6 ± 3%, P < 0.01).

CONCLUSION

Neither carbohydrate nor placebo supplementation altered the typical lymphocyte apoptotic response following exercise. While carbohydrate supplementation generally has an immune-boosting effect during exercise, it appears that this influence does not extend to the mechanisms that govern exercise-induced lymphocyte cell death.

Neuroinvasion in prion diseases: the roles of ascending neural infection and blood dissemination

Prion disorders are infectious, neurodegenerative diseases that affect humans and animals. Susceptibility to some prion diseases such as kuru or the new variant of Creutzfeldt-Jakob disease in humans and scrapie in sheep and goats is influenced by polymorphisms of the coding region of the prion protein gene, while other prion disorders such as fatal familial insomnia, familial Creutzfeldt-Jakob disease, or Gerstmann-Straussler-Scheinker disease in humans have an underlying inherited genetic basis. Several prion strains have been demonstrated experimentally in rodents and sheep. The progression and pathogenesis of disease is influenced by both genetic differences in the prion protein and prion strain. Some prion diseases only affect the central nervous system whereas others involve the peripheral organs prior to neuroinvasion. Many experiments undertaken in different species and using different prion strains have postulated common pathways of neuroinvasion. It is suggested that prions access the autonomic nerves innervating peripheral organs and tissues to finally reach the central nervous system. We review here published data supporting this view and additional data suggesting that neuroinvasion may concurrently or independently involve the blood vascular system.

Changes in sympathetic activity in prion neuroinvasion

Prion diseases are neurodegenerative diseases affecting humans and animals in which the infectious agent or prion is PrP(res), a protease-resistant conformer of the cell protein PrP. The natural transmission route of prion diseases is peripheral infection, with the lymphoreticular system (LRS) and peripheral nerves being involved in animal models of scrapie neuroinvasion and human prion diseases. To study the effects of PrP neuroinvasion on sympathetic nerve function, we measured plasma catecholamine levels, blood pressure, heart rate, and PrP tissue levels in intraperitoneally or intracerebrally infected mice. The results indicate a specific alteration in sympathetic nerve function because the levels of noradrenaline (but not adrenaline) were increased in the animals infected peripherally (but not in those infected intracerebrally) and correlated with increased blood pressure. These findings confirm that prion neuroinvasion uses the sympathetic nervous system to spread from the periphery to the central nervous system after invading the LRS.

PrP expression, PrPSc accumulation and innervation of splenic compartments in sheep experimentally infected with scrapie

Background

In prion disease, the peripheral expression of PrP^C is necessary for the transfer of infectivity to the central nervous system. The spleen is involved in neuroinvasion and neural dissemination in prion diseases but the nature of this involvement is not known. The present study undertook the investigation of the spatial relationship between sites of PrP^Sc accumulation, localisation of nerve fibres and PrP^C expression in the tissue compartments of the spleen of scrapie-inoculated and control sheep.

Methodology/Principal Findings

Laser microdissection and quantitative PCR were used to determine PrP mRNA levels and results were compared with immunohistochemical protocols to distinguish PrP^C and PrP^Sc in tissue compartments of the spleen. In sheep experimentally infected with scrapie, the major sites of accumulation of PrP^Sc in the spleen, namely the lymphoid nodules and the marginal zone, expressed low levels of PrP mRNA. Double immunohistochemical labelling for PrP^Sc and the pan-nerve fibre marker, PGP, was used to evaluate the density of innervation of splenic tissue compartments and the intimacy of association between PrP^Sc and nerves. Some nerve fibres were observed to accompany blood vessels into the PrP^Sc-laden germinal centres. However, the close association between nerves and PrP^Sc was most apparent in the marginal zone. Other sites of close association were adjacent to the wall of the central artery of PALS and the outer rim of germinal centres.

Conclusions/Significance

The findings suggest that the degree of PrP^Sc accumulation does not depend on the expression level of PrP^C. Though several splenic compartments may contribute to neuroinvasion, the marginal zone may play a central role in being the compartment with most apparent association between nerves and PrP^Sc.

The spread of prions through the body in naturally acquired transmissible spongiform encephalopathies

Transmissible spongiform encephalopathies are fatal neurodegenerative diseases that are caused by unconventional pathogens and affect the central nervous system of animals and humans. Several different forms of these diseases result from natural infection (i.e. exposure to transmissible spongiform encephalopathy agents or prions, present in the natural environment of the respective host). This holds true also for scrapie in sheep, bovine spongiform encephalopathy in cattle, chronic wasting disease in elk and deer, or variant Creutzfeldt-Jakob disease in humans, all of which are assumed to originate predominantly from peroral prion infection. This article intends to provide an overview of the current state of knowledge on the spread of scrapie, chronic wasting disease, bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease agents through the body in naturally affected hosts, and in model animals experimentally challenged via the alimentary tract. Special attention is given to the tissue components and spreading pathways involved in the key stages of prion routing through the body, such as intestinal uptake, neuroinvasion of nerves and the central nervous system, and centrifugal spread from the brain and spinal cord to peripheral sites (e.g. sensory ganglia or muscles). The elucidation of the pathways and mechanisms by which prions invade a host and spread through the organism can contribute to efficient infection control strategies and the improvement of transmissible spongiform encephalopathy diagnostics. It may also help to identify prophylactic or therapeutic approaches that would impede naturally acquired transmissible spongiform encephalopathy infections.

Hematologic abnormalities within the first week after acute isolated traumatic cervical spinal cord injury: a case-control cohort study

STUDY DESIGN

Case-control cohort study.

OBJECTIVE

To evaluate 1) the hematologic abnormalities within the first week following isolated acute cervical spine trauma or spinal cord injury (SCI); and 2) the influence of age, sex, and severity of SCI on these hematologic abnormalities.

SUMMARY OF BACKGROUND DATA

Given that autonomic nervous system has a critical role in the regulation of the hematopoietic system, we sought to evaluate the potential association between hematologic abnormalities within the first week posttrauma and the severity of SCI.

METHODS

All consecutive individuals with isolated acute cervical spine trauma admitted to our institution from 1998 to 2000 were reviewed. Exclusion criteria included preexisting medical comorbidities and polytrauma. The study population was divided into a SCI group and a control group (individuals with spine trauma without neurologic impairment). The SCI group was subdivided into patients with motor complete SCI (American Spinal Injury Association [ASIA] Grades A/B) and individuals with motor incomplete SCI (ASIA Grades C/D).

RESULTS

There were 21 SCI individuals (15 male, 6 female; ages 17-83 years; mean, 57 years) and 11 controls (6 male, 5 female; ages 18-75 years; mean, 41 years). When controlled for age, SCI individuals showed a significantly higher frequency of reduced hemoglobin concentration (RHC), leukocytosis, lymphopenia, and thrombocytopenia than controls within the first week posttrauma. Blood hemoglobin concentration, lymphocyte, and platelet counts in the SCI group were significant lower than the controls. The SCI group showed a significant higher leukocyte count than the controls. The degree of RHC and lymphopenia was significantly correlated with the severity of SCI.

CONCLUSION

Our results indicate that patients with isolated cervical SCI have significantly greater frequency of RHC, leukocytosis, lymphopenia, and thrombocytopenia than controls during the first week posttrauma. The degree of RHC and lymphopenia was significantly associated with the severity of SCI. While the mechanisms underlying these clinically important hematologic consequences of SCI remain undetermined, evidence from the literature suggests that acute autonomic denervation of the hematopoietic system could play a key role.

Prion diseases of humans and farm animals: epidemiology, genetics, and pathogenesis

Neuronal vacuolation (spongiosis), neuronal death, and pronounced glial reactions are the hallmarks of transmissible spongiform encephalopathies (TSEs), or prion diseases. A wealth of physical, biochemical, and immunological evidence indicates that the TSE agent, termed prion, does not contain agent-specific nucleic acid encoding its own constituents, as is the case for all other infectious pathogens. Also, no adaptive immune responses are elicited upon infection. A defining feature of TSEs is the deposition, mainly in the brain and lymphoreticular tissues, of an aggregated and structurally abnormal protein, designated PrP(Sc) or PrP-res, which represents a conformational isomer of the ubiquitous surface protein PrP(C). Biochemical and genetic evidence link PrP and its gene to the disease. Although TSEs are by definition transmissible, a growing number of Prnp-associated non-infectious neurodegenerative proteinopathies are now being recognized.

Approaches to Therapy of Prion Diseases

Devising approaches to the therapy of transmissible spongiform encephalopathies, or prion diseases, is beset by many difficulties. For one, the nature of the infectious agent, the prion, is understood only in outline, and its composition, structure, and mode of replication are still shrouded in mystery. In addition, the mechanism of pathogenesis is not well understood. Because clinical disease affects mainly the brain parenchyme, therapeutic agents must be able to traverse the brain-blood barrier (BBB) or have to be introduced directly into the cerebrospinal fluid or brain tissue. And finally, because the disease is usually recognized only after onset of severe clinical symptoms, the question arises as to whether the neurodegenerative processes can be reversed to any extent after a successful eradication of the agent.

Increased splenocyte mitogenesis following sympathetic denervation in Xenopus laevis

Studies in mammals reveal that ablation of the sympathetic nervous system (SNS) can alter in vivo and in vitro parameters of immunity. To shed some light on the phylogenetic history of the interactions between the SNS and the immune system, we studied the effects of chemical sympathectomy on the proliferative response of frog splenocytes to mitogens. Adult Xenopus laevis were injected with 6-hydroxydopamine 3 days before removal of spleen cells for culture with mitogens. Splenocytes from sympathectomized frogs exhibited an increased proliferative response to the T cell mitogens PHA and ConA and the B cell mitogen, LPS. That sympathectomy appears to effect a release from tonic inhibition by the SNS in Xenopus is consistent with comparable experiments in mice. It also reveals a phylogenetically ancient origin for SNS-immune system communications.

Progress and problems in the biology, diagnostics, and therapeutics of prion diseases

The term "prion" was introduced by Stanley Prusiner in 1982 to describe the atypical infectious agent that causes transmissible spongiform encephalopathies, a group of infectious neurodegenerative diseases that include scrapie in sheep, Creutzfeldt-Jakob disease in humans, chronic wasting disease in cervids, and bovine spongiform encephalopathy in cattle. Over the past twenty years, the word "prion" has been taken to signify various subtly different concepts. In this article, we refer to the prion as the transmissible principle underlying prion diseases, without necessarily implying any specific biochemical or structural identity. When Prusiner started his seminal work, the study of transmissible spongiform encephalopathies was undertaken by only a handful of scientists. Since that time, the "mad cow" crisis has put prion diseases on the agenda of both politicians and the media. Significant progress has been made in prion disease research, and many aspects of prion pathogenesis are now understood. And yet the diagnostic procedures available for prion diseases are not nearly as sensitive as they ought to be, and no therapeutic intervention has been shown to reliably affect the course of the diseases. This article reviews recent progress in the areas of pathogenesis of, diagnostics of, and therapy for prion diseases and highlights some conspicuous problems that remain to be addressed in each of these fields.

Evolution of the thymus size in response to physiological and random events throughout life

During embryogenesis and in the early stages of life, the thymus is a crucial organ for the generation of the T cell repertoire. T cells are generated from hematopoietic stem cells already differentiated to precursor T cells in the bone marrow. These cells enter the thymus guided by chemotactic factors secreted by this organ. The complex maturation process takes place that ensures self-tolerance and homeostasis. Thymocytes that show autoreactivity do not leave the thymus, but rather die by apoptosis. The final percentage of mature T cells that survive to migrate from the thymus to the periphery is very low: at most 5%, under optimal conditions. The highest migration occurs in childhood and adulthood, at least in mice and humans; however, it declines throughout life and is minimal in the elderly. Under normal circumstances, the thymus commences involution soon after birth, and this involution correlates with the capacity to export mature T cells to the periphery. Hormones, cytokines, and neurotransmitters all play a role in this age-associated process, but the reasons for and mechanisms of this involution remain unknown. Apart from physiological conditions that change throughout life and govern age-related thymus evolution, random states and events provoked by intrinsic or extrinsic factors can induce either thymus involution, as in reversible transient thymic hypoplasias, or thymic hyperplasias. The age-associated involution, unlike transient involutions, follows a regular pattern for all individuals, though there are clear differences between the sexes. Nevertheless, even the age-associated involution seems to be reversible, raising the possibility of therapeutic strategies aimed at enhancing thymus function in the elderly.

Positioning of follicular dendritic cells within the spleen controls prion neuroinvasion

Peripheral infection is the natural route of transmission in most prion diseases. Peripheral prion infection is followed by rapid prion replication in lymphoid organs, neuroinvasion and progressive neurological disease. Both immune cells and nerves are involved in pathogenesis, but the mechanisms of prion transfer from the immune to the nervous system are unknown. Here we show that ablation of the chemokine receptor CXCR5 juxtaposes follicular dendritic cells (FDCs) to major splenic nerves, and accelerates the transfer of intraperitoneally administered prions into the spinal cord. Neuroinvasion velocity correlated exclusively with the relative locations of FDCs and nerves: transfer of CXCR5-/- bone marrow to wild-type mice induced perineural FDCs and enhanced neuroinvasion, whereas reciprocal transfer to CXCR5-/- mice abolished them and restored normal efficiency of neuroinvasion. Suppression of lymphotoxin signalling depleted FDCs, abolished splenic infectivity, and suppressed acceleration of pathogenesis in CXCR5-/- mice. This suggests that prion neuroimmune transition occurs between FDCs and sympathetic nerves, and relative positioning of FDCs and nerves controls the efficiency of peripheral prion infection.

The effect of emotional stress on the primary humoral immunity of rats

The effect of exposure to emotional stress on humoral immune function after injection with ovalbumin, a novel antigen, was studied in adult male Wistar rats. Emotional stress was induced by randomly giving empty water bottles to rats trained to drink water at set times. The results showed that emotional stress induced the decrease in spleen weight and specific immunoglobulin G antibody level to ovalbumin, and increased levels of epinephrine, norepinephrine and corticosterone. A decrease of antibody levels correlated negatively with an increase in plasma norepinephrine levels. These findings suggest that emotional stress can modulate immune function, and that sympathetic nervous system may be involved in this immunomodulation.

Disease-associated PrP in the enteric nervous system of scrapie-affected Suffolk sheep

Disease-associated prion protein (PrP(d)) in the enteric nervous system (ENS) of 20- to 24-month-old Suffolk sheep in the late subclinical and early clinical phase of scrapie was studied. Sites in the alimentary tract extending from the forestomachs and abomasum to the colon from scrapie-affected sheep (PrP(ARQ/ARQ)) and scrapie-resistant sheep (PrP(ARR/ARQ) and PrP(ARR/ARR)) were examined. PrP(d) was found only in scrapie-affected sheep and was most prominent in the ENS when abundant deposits of PrP(d) were also present in adjacent lymphoid nodules. Immunolabelling with the nerve fibre markers PgP 9.5 and neuron-specific enolase and the satellite cell marker glial fibrillary acidic protein revealed the extensive ganglionated networks of the myenteric and submucosal plexi. Fewer nerve fibres were present in the lamina propria, T-cell dominated interfollicular areas and dome regions of Peyer's patches. A substantial network of nerve fibres was detected in many lymphoid nodules of both the scrapie-affected and scrapie-resistant sheep. Nerve fibres were also detected within the capsule of lymphoid nodules. Electron microscopy revealed the presence of nerves in the lymphoid nodules, showing a close association with follicular dendritic cells, lymphocytes and tingible body macrophages. In demonstrating that lymphoid nodules in the Peyer's patches of scrapie-affected sheep possess a substantial network of nerve fibres, the present study shows that nodules provide close contact between nerve fibres and cell populations known to contain abundant PrP(d), including follicular dendritic cells and tingible body macrophages, and that gut-associated lymphoid nodules in sheep may represent an important site for neuroinvasion.

Prions and the immune system: a journey through gut, spleen, and nerves

For more than two decades it has been contended that prion infection does not elicit immune responses: transmissible spongiform encephalopathies do not go along with conspicuous inflammatory infiltrates, and antibodies to the prion protein are typically undetectable. Why is it, then, that prions accumulate in lymphoid organs, and that various states of immune deficiency prevent peripheral prion infection? This review revisits the current evidence of the involvement of the immune system in prion diseases, while attempting to trace the elaborate mechanisms by which peripherally administered prions invade the brain and ultimately cause damage. The investigation of these questions leads to unexpected detours, including the neurophysiology of lymphoid organs, and even the function of a prion protein homolog in male fertility.

Immune system and peripheral nerves in propagation of prions to CNS

Prions are not only unique in the way they replicate. Also the sequence of events triggered by peripheral prion infection, generically termed 'peripheral pathogenesis', sets prions aside from all other known pathogens. Whereas most bacteria, parasites, and viruses trigger innate and adaptive immune responses, the mammalian immune system appears to be remarkably oblivious to prions. Transmissible spongiform encephalopathies (TSEs) do not go along with inflammatory infiltrates, and antibodies to the prion protein are not typically raised during the course of the disease. On the other hand, there is conspicuous involvement of lymphoid organs, which accumulate sizeable concentrations of the infectious agent early during disease. Moreover, various states of immune deficiency can abolish peripheral pathogenesis and prevent 'take' of infection when prions are administered to peripheral sites. Here, we critically re-visit the current evidence for an involvement of the immune system in prion diseases, and will attempt to trace the elaborate mechanisms by which prions, upon entry into the body from peripheral sites, reach the brain.

Neuroendocrine regulation of immunity

A reciprocal regulation exists between the central nervous and immune systems through which the CNS signals the immune system via hormonal and neuronal pathways and the immune system signals the CNS through cytokines. The primary hormonal pathway by which the CNS regulates the immune system is the hypothalamic-pituitary-adrenal axis, through the hormones of the neuroendocrine stress response. The sympathetic nervous system regulates the function of the immune system primarily via adrenergic neurotransmitters released through neuronal routes. Neuroendocrine regulation of immune function is essential for survival during stress or infection and to modulate immune responses in inflammatory disease. Glucocorticoids are the main effector end point of this neuroendocrine system and, through the glucocorticoid receptor, have multiple effects on immune cells and molecules. This review focuses on the regulation of the immune response via the neuroendocrine system. Particular details are presented on the effects of interruptions of this regulatory loop at multiple levels in predisposition and expression of immune diseases and on mechanisms of glucocorticoid effects on immune cells and molecules.

Golli-myelin basic proteins delineate the nerve distribution of lymphoid organs

The golli-myelin basic proteins (MBPs) have been known to mark the nerve fiber extensions in both the peripheral nervous system (PNS) and the central nervous system. In this paper, we show that the nerve fibers revealed by neurofilament (NF) antibody staining in thymus and spleen, colocalized with golli in the capsular, trabecular (tr), and vasculature (v) systems. In the thymus, the density of these fibers was greater in the medulla than in the cortex. In the spleen, the golli immunoreactive fibers were seen within the capsule (ca), trabeculae, and along the artery tree, as well as the fine nerve fiber networks in the periarteriolar lymphoid sheath (PALS). Golli immunoreactivity appeared to colocalize with ER-TR7, a putative marker of connective tissue in lymphoid organs. However, further examination by Western blot analysis and immunohistochemistry performed on golli "knock out" mice showed that the antigens recognized by these two antibodies were different. The reason for the apparent colocalization of golli and ER-TR7 appears to be due to the close physical association of nerve fibers with connective tissue in these organs. These results suggest that golli immunoreactivity can visualize the distribution of nerve fibers in these lymphoid organs.

Sympathetic innervation of lymphoreticular organs is rate limiting for prion neuroinvasion

Transmissible spongiform encephalopathies are commonly propagated by extracerebral inoculation of the infectious agent. Indirect evidence suggests that entry into the central nervous system occurs via the peripheral nervous system. Here we have investigated the role of the sympathetic nervous system in prion neuroinvasion. Following intraperitoneal prion inoculation, chemical or immunological sympathectomy delayed or prevented scrapie. Prion titers in spinal cords were drastically reduced at early time points after inoculation. Instead, keratin 14-NGF transgenic mice, whose lymphoid organs are hyperinnervated by sympathetic nerves, showed reduction in scrapie incubation time and, unexpectedly, much higher titers of prion infectivity in spleens. We conclude that sympathetic innervation of lymphoid organs is rate limiting for prion neuroinvasion and that splenic sympathetic nerves may act as extracerebral prion reservoirs.

Mechanisms underlying chemical sympathectomy-induced suppression of herpes simplex virus-specific cytotoxic T lymphocyte activation and function

Lymphoid tissues are extensively innervated by noradrenergic fibers of the sympathetic nervous system. 6-hydroxydopamine (6-OHDA)-induced chemical sympathectomy is commonly used to assess the impact of this innervation on immune function. Using the glucocorticoid receptor antagonist RU486, the mineralocorticoid receptor antagonist spironolactone, and the beta-adrenergic receptor antagonist nadolol, the roles of corticosterone and norepinephrine in sympathectomy-mediated modulation of both the primary and memory cellular immune responses to herpes simplex virus type 1 (HSV-1) infection was investigated. We demonstrated that both of these immunomodulators play a role in mediating sympathectomy-induced suppression of the generation of HSV-specific primary cytotoxic T lymphocytes (CTL) and the activation of HSV-specific memory CTL (CTLm). Furthermore, we demonstrated a role for both Type I and Type II corticosteroid receptors in the regulation of HSV-specific immunity. Overall, these findings not only further support a role for neuroendocrine-mediated modulation of immune function, but also a need to exercise caution in attributing the effects of chemical sympathectomy to solely the absence of sympathetic innervation of lymphoid tissues.

The role of sympathetic innervation of the gut in regulating mucosal immune responses

The effects of chemical sympathectomy on the mucosal compartments of the immune system were examined in adult rats. Ablation of the sympathetic nervous system using 6-hydroxydopamine in recipient animals reduced the migration into Peyer's patches and mesenteric lymph nodes (MLN) of adoptively transferred cells from MLN of normal donors. The mucosal immune response to ovalbumin (OVA), assessed by enumeration of anti-OVA antibody containing cells (AOCC) in the lamina propria after intestinal immunisation, was reduced in animals sympathectomized prior to immunization. In order to identify whether this reduction in AOCC response in intestinally immunized sympathectomized animals was due to a defect in migration of AOCC precursors to the intestinal lamina propria, the effect of chemical sympathectomy on the appearance of AOCC in the gut of immunized animals after adoptive transfer of AOCC precursors was investigated. The IgA-specific AOCC response was significantly reduced in sympathectomized recipients compared to the control group. Taken together these results demonstrate that the peripheral sympathetic nervous system influences the migration and accumulation in vivo of both naive and memory/effector lymphocytes in mucosal lymphoid tissues.

Beta-blockade enhances adrenergic immunosuppression in rats via inhibition of melatonin release

We have recently shown in rats that an in vivo treatment with catecholamines via alpha 2-receptors leads to a pronounced suppression of T- and B-cell mitogen responses of peripheral blood lymphocytes (PBL), provided that a beta-blocker is administered concomitantly. Since melatonin (MEL) reportedly has stress-protective effects on several immune functions, and since the release of MEL from the pineal gland is inhibited by beta-blockade, we tested the effect of MEL substitution on T- and B-cell mitogen responses of PBL in rats treated with two s.c. implanted retard tablets containing noradrenaline (NA) and propranolol. It was found that an oral treatment with MEL (about 40 micrograms/animal) abolished the adrenergic immunosuppression. Furthermore, functional pinealectomy induced by constant light had a similar enhancing effect on the alpha 2-adrenergic immunosuppression as observed with beta-blockers, whereas PBL from animals kept at the regular light/dark interval were resistant to the treatment with the selective alpha 2-agonist clonidine. It is concluded that endogenous MEL effectively protects rat PBL from adrenergic immunosuppression, and that beta-blockers enhance the immunosuppressive property of alpha 2-adrenergic agents via blocking the night-time release of MEL.

Substance P and stress-induced changes in macrophages

The present paper further links nervous-endocrine-immune systems by describing influences of SP on the immune system, and more specifically, on macrophage function. We have discussed how macrophages are important to immune responses in that much of cellular and humoral responses depend on macrophage function. Macrophages are sensitive to stress in that cold-water stress causes increased cytokine production, either spontaneously (IL-1), or after induction with LPS (IL-6, TNF alpha). Increased cytokine levels (IL-1, IL-6) may induce acute phase reactants in the liver, which is presumably the mechanism operative in the studies indicating increases in acute phase reactants after certain stressors in animals. SP is a likely candidate to affect immune function. Previous data show that macrophages from various species have receptors for and respond to SP in vitro. SP stimulates phagocytic and chemotactic capacity, as well as increased cytokine, PGE2, and thromboxane B2 production. SP is also involved in neurogenic inflammation and is likely to be involved in the pathogenesis of several inflammatory diseases. Present data indicate SP's involvement in macrophage responses to stress. We have shown that stress induced differential SP receptor binding to peritoneal macrophages, although the precise nature of binding differences has not yet been clearly elucidated. Stress also induces more immunoreactive SP in the peritoneal fluid that bathes the peritoneal macrophages. We hypothesize that the two events, altered SP binding and concomitant increased ligand, are causally related. In addition to other correlational data showing concomitant increased SP binding plus ligand concentrations, there is more direct evidence that SP ligand may induce SP receptor expression since the SP antagonist, CP-96,345, prevents the induction of SP receptor mRNA in the staphylococcal toxin A-induced gastroenteritis (C. Pothoulakis and S. E. Leeman, personal communication). Further supporting our notion for a causal relationship we have found the elimination of SP in vivo (via capsaicin pretreatment) reduced SP binding, as has been previously reported. We have also examined the role of SP on stress-induced altered macrophage function in vitro. SP greatly enhanced the LPS-induced macrophage TNF alpha production from stressed animals; in contrast, it produced relatively little effect on macrophages from control animals. Capsaicin pretreatment diminished the enhanced cytokine production in response to stress, such that levels of TNF alpha and IL-6 approximated those of control mice. Taken together, past and present data suggest that (1) stress may initiate, or at least contribute to, an inflammatory response, and that (2) SP is involved in the macrophage stress response. SP has long been known to be involved in inflammatory processes; our data further suggest its role in mediating stress-induced cytokine alterations.