Parallel development of noradrenergic innervation and cellular compartmentation in the rat spleen

Infection in the Developing Brain: The Role of Unique Systemic Immune Vulnerabilities

Central nervous system (CNS) infections remain a major burden of pediatric disease associated with significant long-term morbidity due to injury to the developing brain. Children are susceptible to various etiologies of CNS infection partly because of vulnerabilities in their peripheral immune system. Young children are known to have reduced numbers and functionality of innate and adaptive immune cells, poorer production of immune mediators, impaired responses to inflammatory stimuli and depressed antibody activity in comparison to adults. This has implications not only for their response to pathogen invasion, but also for the development of appropriate vaccines and vaccination strategies. Further, pediatric immune characteristics evolve across the span of childhood into adolescence as their broader physiological and hormonal landscape develop. In addition to intrinsic vulnerabilities, children are subject to external factors that impact their susceptibility to infections, including maternal immunity and exposure, and nutrition. In this review we summarize the current evidence for immune characteristics across childhood that render children at risk for CNS infection and introduce the link with the CNS through the modulatory role that the brain has on the immune response. This manuscript lays the foundation from which we explore the specifics of infection and inflammation within the CNS and the consequences to the maturing brain in part two of this review series.

Prenatal alcohol-induced sex differences in immune, metabolic and neurobehavioral outcomes in adult rats

Prenatal alcohol exposure (PAE) can result in neurobehavioral anomalies, that may be exacerbated by co-occurring metabolic and immune system deficits. To test the hypothesis that the peripheral inflammation in adult PAE offspring is linked to poor glucose metabolism and neurocognitive deficits, pregnant Sprague-Dawley rats were exposed to ethanol vapor or ambient air during the latter half of gestation. We assessed, in adult offspring of both sexes, performance on a battery of neurocognitive behaviors, glucose tolerance, circulating and splenic immune cells by flow-cytometry, and circulating and tissue (liver, mesenteric adipose, and spleen) cytokines by multiplexed assays. PAE reduced both the ratio of spleen to body weight and splenic regulatory T-cell (Treg) numbers. PAE males, but not females exhibited an increase in circulating monocytes. Overall, PAE males exhibited a suppression of cytokine levels, while PAE females exhibited elevated cytokines in mesenteric adipose tissue (IL-6 and IL1α) and liver (IFN-γ, IL-1β, IL-13, IL-18, IL-12p70, and MCP-1), along with increased glucose intolerance. Behavioral analysis also showed sex-dependent PAE effects. PAE-males exhibited increased anxiety-like behavior while PAE-females showed decreased social interaction. PAE offspring of both sexes exhibited impaired recognition of novel objects. Multilinear regression modeling to predict the association between peripheral immune status, glucose intolerance and behavioral outcomes, showed that in PAE offspring, higher levels of adipose leptin and liver TNF- α predicted higher circulating glucose levels. Lower liver IL-1 α and higher plasma fractalkine predicted more time spent in the center of an open-field with sex being an additional predictor. Higher circulating and splenic Tregs predicted better social interaction in the PAE-offspring. Collectively, our data show that peripheral immune status is a persistent, sex-dependent predictor of glucose intolerance and neurobehavioral function in adult PAE offspring.

The spleen as a neuroimmune interface after spinal cord injury

Traumatic spinal cord injury (SCI) causes widespread damage to neurons, glia and endothelia located throughout the spinal parenchyma. In response to the injury, resident and blood-derived leukocytes orchestrate an intraspinal inflammatory response that propagates secondary neuropathology and also promotes tissue repair. SCI also negatively affects autonomic control over peripheral immune organs, notably the spleen. The spleen is the largest secondary lymphoid organ in mammals, with major roles in blood filtration and host defense. Splenic function is carefully regulated by neuroendocrine mechanisms that ensure that the immune responses to infection or injury are proportionate to the initiating stimulus, and can be terminated when the stimulus is cleared. After SCI, control over the viscera, including endocrine and lymphoid tissues is lost due to damage to spinal autonomic (sympathetic) circuitry. This review begins by examining the normal structure and function of the spleen including patterns of innervation and the role played by the nervous system in regulating spleen function. We then describe how after SCI, loss of proper neural control over splenic function leads to systems-wide neuropathology, immune suppression and autoimmunity. We conclude by discussing opportunities for targeting the spleen to restore immune homeostasis, reduce morbidity and mortality, and improve functional recovery after SCI.

Immune dysregulation may contribute to disease pathogenesis in spinal muscular atrophy mice

Spinal muscular atrophy (SMA) has long been solely considered a neurodegenerative disorder. However, recent work has highlighted defects in many other cell types that could contribute to disease aetiology. Interestingly, the immune system has never been extensively studied in SMA. Defects in lymphoid organs could exacerbate disease progression by neuroinflammation or immunodeficiency. Smn depletion led to severe alterations in the thymus and spleen of two different mouse models of SMA. The spleen from Smn depleted mice was dramatically smaller at a very young age and its histological architecture was marked by mislocalization of immune cells in the Smn^2B/- model mice. In comparison, the thymus was relatively spared in gross morphology but showed many histological alterations including cortex thinning in both mouse models at symptomatic ages. Thymocyte development was also impaired as evidenced by abnormal population frequencies in the Smn^2B/- thymus. Cytokine profiling revealed major changes in different tissues of both mouse models. Consistent with our observations, we found that survival motor neuron (Smn) protein levels were relatively high in lymphoid organs compared to skeletal muscle and spinal cord during postnatal development in wild type mice. Genetic introduction of one copy of the human SMN2 transgene was enough to rescue splenic and thymic defects in Smn^2B/- mice. Thus, Smn is required for the normal development of lymphoid organs, and altered immune function may contribute to SMA disease pathogenesis.

Influence of breast milk polyamines on suckling rat immune system maturation

The aim of this study was to ascertain whether the supplementation of polyamines present in breast milk, i.e. spermine (SPM) and spermidine (SPD), influenced the post-natal maturation of the systemic and intestinal immune system in rats. From birth, pups daily received SPM or SPD. At 5, 11 and 18 days old, small intestine intraepithelial lymphocytes (IEL), lamina propria lymphocytes (LPL) and splenocytes were phenotypically characterized. SPM and, less evidently, SPD accelerated the maturation of CD8+ IEL, and enhanced the presence of intraepithelial NK cells and IEL related with specific immune responses on the proximal and distal small intestine, respectively. Polyamines increased the percentage of more mature CD4+ LPL and enhanced the early presence of splenic B cells and, later, that of NK cells. However, no effect on Ig-secretory function was detected. These results suggest that breast milk polyamines improve the maturation of the rat intestinal and systemic immune system.

The influence of long term sound stress on histological structure of immune organs in broiler chickens

The aim of this paper was to examine the effect of different duration sound stress on immune organs of broiler chickens of different age. Nine groups, with 10 chickens in each group were included in experiment. The histological structure of bursa of Fabricius, thymus, and spleen were analyzed. The results indicated that the bursa of Fabricius, in relation to the other examined organs, was the most sensitive to this kind of stress. Histological changes of spleen and thymus were also observed, but less prominent except in chickens after more than 30 days of exposure to stress. According to our results, degree of histological changes of immune organs under the influence of sound stress depends on the length of exposure and age of chickens.

Neuritogenic effects of T cell-derived IL-3 on mouse splenic sympathetic neurons in vivo

To determine the role played by lymphocytes and cytokines in the growth of sympathetic neurons in vivo, the innervation and cytokine levels were examined in the spleens of SCID mice that lack T and B cells. Splenic noradrenaline, nerve growth factor (NGF), and IL-1beta levels were elevated in SCID mice. Immunohistochemical examination revealed that the density of tyrosine hydroxylase-positive (TH(+)) fibers of splenic central arteries in SCID mice was increased compared with wild-type C.B-17 mice, while SCID mice had significantly fewer TH(+) fibers in their periarteriolar lymphatic sheaths (PALS). Two weeks after SCID mice were injected with C.B-17 splenic T cells, their TH(+) fiber staining increased in the PALS. IL-3 levels increased significantly in SCID mice following T cell reconstitution, and the administration of anti-IL-3 Ab blocked the above T cell-induced increase in innervation in the PALS. Anti-IL-3 treatment also inhibited the regeneration of splenic sympathetic neurons in C.B-17 mice after they were chemically sympathetomized with 6-hydroxydopamine. Depletion of NK cells by anti-asialo GM1 promoted the splenic innervation in SCID mice, while there were no significant changes in the innervation between CD8(+) T cell-deficient beta(2)-microglobulin knockout mice and their wild type. Our results suggest that T cells (probably CD4(+) Th cells but not CD8(+) CTLs) play a role in regulating the sympathetic innervation of the spleen; this effect appeared to be mediated, at least in part, by IL-3. On the contrary, NK cells may exert an inhibitory effect on the sympathetic innervation.

Sympathetic modulation of immunity: relevance to disease

Optimal host defense against pathogens requires cross-talk between the nervous and immune systems. This paper reviews sympathetic-immune interaction, one major communication pathway, and its importance for health and disease. Sympathetic innervation of primary and secondary immune organs is described, as well as evidence for neurotransmission with cells of the immune system as targets. Most research thus far has focused on neural-immune modulation in secondary lymphoid organs, has revealed complex sympathetic modulation resulting in both potentiation and inhibition of immune functions. SNS-immune interaction may enhance immune readiness during disease- or injury-induced 'fight' responses. Research also indicate that dysregulation of the SNS can significantly affect the progression of immune-mediated diseases. However, a better understanding of neural-immune interactions is needed to develop strategies for treatment of immune-mediated diseases that are designed to return homeostasis and restore normal functioning neural-immune networks.

Enhancement of lysozyme stability and activity by polyamines

Spermine, a low molecular weight polyamine, administered orally to suckling rats induces the maturation of the small intestine. In this organ, lysozyme is an important component of the innate immunity. In this report, we analysed the binding of spermine to lysozyme and its effect on thermal inactivation of the protein by spectroscopy techniques. The activity of the enzyme was analysed in presence of spermine by lysoplate technique. We studied the effects of spermine ingestion by suckling rats on intestinal lysozyme activity and gene expression. We reported that spermine binds to lysozyme and increases in vitro the thermal stability and the activity of the protein. When administered orally to suckling rats, spermine increases the lysozyme activity in jejunum, but not in ileum. This increase is not due to a modification of the gene expression. The observed effects lead us to postulate that spermine could be used in some mammals as a promoter of the innate immunity.

Autonomic innervation of immune organs and neuroimmune modulation

1. Increasing evidence indicates the occurrence of functional interconnections between immune and nervous systems, although data available on the mechanisms of this bi-directional cross-talking are frequently incomplete and not always focussed on their relevance for neuroimmune modulation. 2. Primary (bone marrow and thymus) and secondary (spleen and lymph nodes) lymphoid organs are supplied with an autonomic (mainly sympathetic) efferent innervation and with an afferent sensory innervation. Anatomical studies have revealed origin, pattern of distribution and targets of nerve fibre populations supplying lymphoid organs. 3. Classic (catecholamines and acetylcholine) and peptide transmitters of neural and non-neural origin are released in the lymphoid microenvironment and contribute to neuroimmune modulation. Neuropeptide Y, substance P, calcitonin gene-related peptide, and vasoactive intestinal peptide represent the neuropeptides most involved in neuroimmune modulation. 4. Immune cells and immune organs express specific receptors for (neuro)transmitters. These receptors have been shown to respond in vivo and/or in vitro to the neural substances and their manipulation can alter immune responses. Changes in immune function can also influence the distribution of nerves and the expression of neural receptors in lymphoid organs. 5. Data on different populations of nerve fibres supplying immune organs and their role in providing a link between nervous and immune systems are reviewed. Anatomical connections between nervous and immune systems represent the structural support of the complex network of immune responses. A detailed knowledge of interactions between nervous and immune systems may represent an important basis for the development of strategies for treating pathologies in which altered neuroimmune cross-talking may be involved.

Splenic norepinephrine and serum corticosterone level fluctuations associated with bacteria-induced stress

Corticosterone (CORT) and norepinephrine (NE), two effector molecules of the hypothalamic-pituitary-adrenal (HPA) and the sympathetic-lymphoid (SL) axes, respectively, differentially influence murine host resistance to Listeria monocytogenes (LM). Serum CORT and splenic NE levels early (< or =24 h) after infection correlated positively with host resistance, as long as the LM burden did not exceed approximately 10(6) cfu LM per spleen. As previously reported, mice with right-circling preference (R-mice) have significantly greater host resistance to LM than those with left-circling preference (L-mice) and early after infection, R-mice had significantly higher serum CORT levels than L-mice. However, rapid pathogenesis with a high bacterial burden induced high activation of the HPA and SL axes, which prevented observable differences in the defense against LM, especially later in infection. With the high bacterial inoculum (10(5) LM), the splenic NE levels significantly increased, but no differences among R- and L-mice were discernible. We suggest that endogenous asymmetry of neuroimmune circuits contributes to differential host resistance, but the level of stress (bacterial inoculum) is critical. With regard to the neuroendocrine factors assessed, CORT, but not NE, levels significantly correlated with the enhanced defenses of R-mice in comparison to L-mice. The differential host resistance based on brain laterality seems to be more a function of the HPA axis and possibly other CNS effects on peripheral immunity than neurotransmitter release by the sympathetic innervation of the spleen.

Neural immune pathways and their connection to inflammatory diseases

Inflammation and inflammatory responses are modulated by a bidirectional communication between the neuroendocrine and immune system. Many lines of research have established the numerous routes by which the immune system and the central nervous system (CNS) communicate. The CNS signals the immune system through hormonal pathways, including the hypothalamic-pituitary-adrenal axis and the hormones of the neuroendocrine stress response, and through neuronal pathways, including the autonomic nervous system. The hypothalamic-pituitary-gonadal axis and sex hormones also have an important immunoregulatory role. The immune system signals the CNS through immune mediators and cytokines that can cross the blood-brain barrier, or signal indirectly through the vagus nerve or second messengers. Neuroendocrine regulation of immune function is essential for survival during stress or infection and to modulate immune responses in inflammatory disease. This review discusses neuroimmune interactions and evidence for the role of such neural immune regulation of inflammation, rather than a discussion of the individual inflammatory mediators, in rheumatoid arthritis.

p75NTR in the spleen: age-dependent changes, effect of NGF and 4-methylcatechol treatment, and structural changes in p75NTR-deficient mice

In addition to their well-known actions within the nervous system, neurotrophins and their receptors are involved in immune system functioning, as demonstrated by their wide distribution in lymphoid tissues and their in vitro actions on immunocompetent cells. Nevertheless, the in vivo roles of neurotrophin-receptor systems in lymphoid tissues, as well as the scope of their influence throughout development and adulthood, are yet to be clarified. In the present study, we used combined morphological and immunohistochemical techniques to investigate the presence and cellular localization of p75NTR, the pan-neurotrophin receptor protein, in rat spleen from newborns to aging individuals, and the structural and innervation changes in the spleens of p75NTR-deficient mice. In rats, p75NTR was expressed by splenic nerve fibers and dendritic cells in an age-regulated fashion, with maximal expression detected at 2 weeks. Consistently, the spleens of newborn mice lacking this receptor protein showed no signs of ingrowing sympathetic fibers, along with an absence of defined white pulp areas. The present findings suggest a prolonged role of p75NTR in the physiology of the spleen; at least during the embryonic development period, the receptor may be critical for correct innervation and compartmentalization processes to occur.

Neural-immune interactions in health and disease

Many lines of research have established the numerous routes by which the immune and central nervous systems (CNS) communicate. The CNS signals the immune system via hormonal and neuronal pathways and the immune system signals the CNS through similar routes via immune mediators and cytokines. The primary hormonal pathway by which the CNS regulates the immune system is the hypothalamic-pituitary-adrenal (HPA) axis, through the hormones of the neuroendocrine stress response. The sympathetic nervous system regulates immune system function 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 endpoint of the neuroendocrine response system.

Effects of interleukin-2 on the expression of corticotropin-releasing hormone in nerves and lymphoid cells in secondary lymphoid organs from the Fischer 344 rat

This study examined the influence of interleukin (IL)-2 on corticotropin releasing hormone (CRH) immunoreactivity in the Fischer 344 (F344) rat spleen. Rats were given either vehicle or 1, 10, 25, 50, 100, or 200 ng of human recombinant (hr)IL-2 by intraperitoneal (i.p.) injection, and were sacrificed 0.5, 1, 4, 12, or 24 h after treatment. Spleens and mesenteric lymph nodes were prepared for immunocytochemistry to localize CRH. In spleens from vehicle-treated animals, CRH immunoreactivity was present in several types of cells of the immune system, but CRH(+) nerves were not observed in either spleens or lymph nodes from vehicle-treated animals. Treatment with IL-2 induced CRH expression in nerves in the spleen in a dose- and time-dependent manner. CRH(+) nerves were not found in the mesenteric lymph nodes after IL-2 treatment, instead a dramatic time- and dose-dependent accumulation of CRH(+) cells (resembling small lymphocytes and large granular mononuclear cells) in the cortex and medulla. These findings indicate that IL-2 stimulates the synthesis of CRH in nerves that innervate the F344 rat spleen, and promote the appearance of CRH(+) immunocytes into draining mesenteric lymph nodes.

Effect of secretion of splenocytes after superior ovarian nerve section on the ovarian steroidogenesis

It is known that ovary and spleen are innervated extensively by afferent and efferent noradrenergic sympathetic nerve fibers from the celiac ganglion. Furthermore, immune cells located in the ovary influence the ovarian physiology. However, the peripheral interaction between the immune and neuroendocrine system is poorly understood. This work was undertaken to study the effect of superior ovarian nerve (SON) transection, in adult rats, on the number of splenocyte beta-adrenergic receptors and their possible relation to ovarian steroidogenesis, measuring the effect of secretions of those splenocytes on progesterone and estradiol release from the ovary. Seven days after SON transection, the splenocytes were isolated and then cultured for 48 h. Their number of beta-adrenergic receptors, measured using [125I]-cyanopindolol as ligand, increased, and their culture media, used to stimulate ovaries from 60-day-old intact (neither SON-transected nor sham-operated) rats in vitro on diestrous day 2 showed a decrease in progesterone release and an increase in estradiol release in relation to splenocyte culture media of control rats (sham-operated; p < 0.001, respectively). The effects of in vivo SON transection were simulated by an in vitro system modulating the splenocyte beta-adrenergic receptor number. The splenocytes from SON-transectioned rats were preincubated with and without norepinephrine (NE) 10(-6) M for 48 h, a low and high number of beta-adrenergic receptors respectively, and then were stimulated with NE 10(-6) M for 24 h. After that, the culture medium from splenocytes with a low number of beta-adrenergic receptors induced progesterone release from the ovaries of intact rats (p < 0. 001), but produced no change in estradiol release. The data suggest that splenocyte secretions, which participate in the ovarian steroidogenic response, particularly in progesterone release, might be controlled by adrenergic influences since the number of splenocyte beta-adrenergic receptors changes through SON-celiac ganglion-noradrenergic postganglionic innervation of the spleen. In estradiol release, probably other neurotransmitters than norepinephrine (NE) are involved when the SON is sectioned. In this paper we also show functional evidence for modulation of immune function by the sympathetic nervous system and its principal neurotransmitter, NE.

Involvement of NGF in the induction of increased noradrenergic innervation of the ureter in neonatally capsaicin-treated rats

Neonatal denervation of primary afferents with capsaicin leads to increased sympathetic innervation of the rat ureter. In the present study the development and the immunohistochemical characterization of this sympathetic hyperinnervation as well as the specific involvement of nerve growth factor (NGF) was investigated. Noradrenaline levels were found elevated in neonatally capsaicin-treated rats by 2 weeks of age and remained at that high level into adulthood. Injections of an anti-NGF antiserum during postnatal days (PN) PN 8-14, PN 13-19 or during PN 17-23 counteracted the capsaicin effect and reduced noradrenaline towards control levels. Immunohistochemical localization of tyrosine hydroxylase (TH), a marker for sympathetic nerve fibres, revealed that the capsaicin-induced hyperinnervation was mainly represented by fibres in deeper muscle layers and to a smaller extent by fibres in the submucosa. In control animals and in rats treated with capsaicin and anti-NGF antiserum fibres were mainly distributed in the adventitia and in the outer part of the smooth muscle layer. These results show that NGF is responsible for the development of an increased noradrenergic innervation in the rat ureter after neonatal capsaicin treatment.

Adrenergic regulation of macrophage-derived tumor necrosis factor-alpha generation during a chronic polyarthritis pain model

Increases in the levels of proinflammatory cytokines, such as TNF alpha, have been intricately linked with arthritis and the pathogenesis of several models of neuropathic pain. In addition, arthritis (as well as other types of persistent pain) is associated with increased sympathetic activity and alterations of other responses in autonomic nervous activity. Adrenergic regulation of LPS-stimulated TNF production by M phi isolated from rats with streptococcal-cell-wall (SCW)-induced arthritis has been examined. Serum TNF levels and the cellular composition of peritoneal exudates have also been assessed. M phi were obtained from: (1) normal control rats, (2) animals injected with complete Freund's adjuvant (CFA), 3 rats injected with SCW and arthritic, and (4) those injected with SCW, which failed to develop arthritis. Serum levels of TNF alpha in rats that develop arthritis are significantly greater (2.4 fold) than levels from the other groups. The proportion of OX19-positive T cell subpopulations are the same in peritoneal exudates from all groups. Immunocytochemical staining also reveals differences between M phi subgroups in the degree of activation. Peritoneal exudates from rats that develop arthritis contain a greater proportion of the high TNF producing subclass of M phi, as identified by positive ED3 staining (p < 0.001). In contrast, Ia antigen presenting M phi (OX6-positive) in the peritoneal exudate cells are only elevated in rats administered CFA. The selective blockade of adrenergic receptors by idazoxan or propranolol demonstrates that the constitutive involvement of either alpha 2 or beta-adrenergic regulation of M phi-derived TNF production is pronounced in rats with arthritis (p < 0.001). These investigations demonstrate a distinctive pattern of peripheral M phi populations in rats that develop chronic polyarthritic pain. We believe that identification of interactions between the adrenergic responses and proinflammatory cytokines will lead to the development of improved strategies to treat patients with chronic pain.

Plasticity of GAP-43 innervation of the spleen during immune response in the mouse. Evidence for axonal sprouting and redistribution of the nerve fibers

The amount and distribution of growth-associated protein (GAP-43)-like immunoreactive nerve fibers in the spleen of normal and immunized BALB/c mice were studied using immunohistochemical methods. A significant increase in the amount, as well as redistribution and morphological changes, of the GAP-43-like immunoreactive nerve fibers occurred in PPD (purified protein derivative from tuberculin) immunized animals. In the control animals, the GAP-43-like immunoreactive nerve fibers were found mainly distributed in association with vascular plexuses, with minor extension into the parenchyma of the inner zone of the periarterial lymph sheath. In the immunized animals, in addition to denser vascular plexuses, more fibers appeared in the outer zone of the periarterial lymph sheath, the marginal zone, and the red pulp, all known to be the sites where immune responding lymphocytes are located. Furthermore, the nerve fibers tended to have more branches and bear richer varicosities. The results suggest that active nerve remolding takes place in the spleen during immune response, which may serve as a mechanism through which the nervous system regulates immune responses.

Development of immune hyperinnervation in NGF-transgenic mice

Sympathetic innervation of lymphoid tissues is localized to specific tissue compartments, but little is known of the "factors" that are important in establishing this pattern during development. Numerous studies have shown interactions of nerve growth factor (NGF) with the immune system, which may include modulation of immune innervation. We previously have shown that NGF transgenic mice, which overexpress NGF in skin and not immune tissues, have a dramatic hyperinnervation of splenic marginal zone and peripheral lymph node medulla and capsule. The purpose of the current studies was to determine if the presence of elevated NGF would alter immune system development and the process of sympathetic ingrowth. The results show that the splenic innervation in NGF transgenics gradually diverged from controls during the first two postnatal weeks, with the greatest change occurring between postnatal days 13 and 16 when the splenic organization was reaching the adult pattern. In contrast, the peripheral lymph nodes were hyperinnervated at an earlier age. mesenteric lymph nodes never diverged from the normal pattern. NGF levels in transgenic spleen were much higher than controls at postnatal days 1 and 2, when little innervation was present, and declined as the tissue matured, possibly because of NGF uptake by the ingrowing sympathetic fibers. This suggests that immune tissues are capable of concentrating NGF, which in turn may modulate the level of innervation by the sympathetic nervous system.

Norepinephrine content in primary and secondary lymphoid organs is altered in rats with adjuvant-induced arthritis

Chemical sympathectomy of secondary lymphoid organs with sparing of the hind limbs exacerbates adjuvant-induced arthritis (AA) in Lewis rats supporting a role for noradrenergic (NA) innervation of the immune system in AA pathology. The present study examines sympathetic innervation of lymphoid organs from Lewis rats 32 days after treatment with complete Freund's adjuvant (CFA) or vehicle using fluorescence histochemistry for localization of catecholamines (CA) and high-performance liquid chromatography with electrochemical detection (LCEC) for measurement for norepinephrine. The thymus from AA rats was significantly reduced in size, while secondary lymphoid organs, i.e., spleen and draining lymph nodes (DLN), were significantly enlarged compared with that seen in vehicle-treated controls. Fluorescence histochemistry revealed no apparent differences in the density of NA innervation, or the intensity of staining in sympathetic nerves in any of the secondary lymphoid organs from AA rats compared with that observed in control animals. However, there was an apparent increase in the density of NA nerve fibers in the thymus of AA rats. Norepinephrine (NE) concentration (pmol NE per g or mg wet weight), in the thymus from AA rats was significantly increased. Conversely, a significant decrease in splenic and lymph node NE concentration was measured in adjuvant-treated animals compared with that seen in vehicle-treated rats. Total NE content (pmol NE per whole organ weight) in lymphoid organs was not altered, except in popliteal lymph nodes (PLN), where it was increased. Collectively, our findings suggest that changes in NA innervation of lymphoid organs from AA rats result largely from increases or decreases in organ mass. Since NE released from NA nerves acts in a paracrine fashion, changes in lymphoid tissue volume that result from enhanced proliferation, migration, or cell death can make a significant difference in the availability of NE for interaction with immune target cells in these organs, even in the absence of a change in NE metabolism. Decreased thymic weight and increased spleen and lymph node weight should increase and decrease NE availability for interaction with target cells, respectively. Additionally, in PLN (a site where the highest concentration of antigen is encountered) an increase in total NE content suggests compensatory changes in NE metabolism.

Effects of nerve growth factor on splenic norepinephrine and pineal N-acetyl-transferase in neonate rats exposed to alcohol in utero: neuroimmune correlates

Prenatal alcohol exposure (FAE) has been associated with multiple anomalies, including a selective developmental delay of sympathetic innervation in lymphoid organs. Sympathetic neurons require nerve growth factor (NGF) for their development and maintenance, and recent evidence has suggested that alcohol impairs the synthesis and/or biological activity of NGF in selected central and peripheral neurons. Thus, the present study examined the hypothesis that NGF administration to FAE rats during early postnatal development would reverse some of the peripheral sympathetic deficits. Neonate rats, FAE and the corresponding control cohorts, received daily treatments of NGF or cytochrome C (0.3 mg/kg; s.c.) for various time intervals, and were killed 24 hr or 10 days after the last treatment. The measured parameters included norepinephrine (NE) concentrations in the spleen and heart, which receive nor-adrenergic innervation from the coeliac ganglion and the superior cervical ganglion (SCG), respectively. In addition, we measured the activity of pineal N-acetyltransferase (NAT), the rate-limiting enzyme of melatonin biosynthesis, which depends on sympathetic innervation from the SCG. The data show that chronic, but not acute, NGF treatments reversed the FAE-related deficits in splenic NE concentrations as well as in pineal NAT activity in a time- and age-dependent manner. Sympathetic neurons play an important role in immune modulation. Thus, the altered splenic NE levels and pineal NAT activity may play a role in immune deficits associated with exposure to alcohol in utero.

Ultrastructure of sympathetic axons and their structural relationship with vascular smooth muscle

This review focuses on the more recent findings of the structure of sympathetic postganglionic axons and the association of their varicose terminals with vascular smooth muscle. These studies have investigated the innervation of a wide range of vessels from different regions of the vasculature in the rat, guinea pig and rabbit and have predominantly used serial sections and computerised three-dimensional reconstructions of entire varicosities. They have shown, contrary to previous studies conducted in the 1960s and 1970s, that sympathetic axon varicosities commonly form structurally specialised neuromuscular junctions with vascular smooth muscle cells of most resistance arteries and some small veins. In addition, they have shown that most axon varicosities innervating small arterioles and small mesenteric veins form neuromuscular junctions, indicating that neurotransmitter is primarily released at such neuromuscular junctions. This review discusses the structure of sympathetic neuromuscular junctions, their development, structural diversity and distribution on vessels from different regions of the vasculature. These more recent structural findings and their possible significance for our understanding of mechanisms involved in neural transmission in blood vessels is discussed.

Hierarchical cortical control of neuroimmunomodulatory pathways

The central nervous system and the immune system are both stimulus response systems with sophisticated memories mediating defence and adaptation to external and internal threats. There is mounting evidence that these two systems share their information in a bidirectional flow of cytokines, steroids, and neuropeptides. This review examines the influence of higher cognitive centres on immunity and highlights the central role played by the hypothalamus in enabling these two systems to function as an integrated unit to maintain homeostasis. The search for novel compounds that are capable of enhancing immunity by regulating these brain-immune feedback loops offers one of the most exciting areas for future neurobiological research.

Lymphoid tissues induce NGF-dependent and NGF-independent neurite outgrowth from rat superior cervical ganglia explants in culture

Induction of neurite outgrowth from superior cervical ganglia (SCG) by rat lymphoid tissues was studied using a tissue culture model. Neonatal rat SCG were cultured with 6-12-week-old rat thymus, spleen, or mesenteric lymph node (MLN) explants in a Matrigel layer, in defined culture medium without exogenous nerve growth factor (NGF). SCG were also co-cultured with neonatal rat heart (as positive control) or spinal cord (SC; as negative control). To determine whether inflammation affects the ability of lymphoid tissues to induce neurite outgrowth, we also examined MLN at various times after infecting rats with Nip-postrongylus brasiliensis (Nb-MLN). In one series of experiments, a single lymphoid tissue explant was surrounded by four SCG at a distance of 1 mm. The extent of neurite outgrowth was determined by counting the number of neurites 0.5 mm away from each ganglion at several time points. Adult thymus and, to a lesser extent, spleen had strong stimulatory effects on neurite outgrowth from SCG after 12 hr or more in culture. For thymus tissue, this was similar to the positive control heart explants. MLN from normal rats had minimal effect on neurite outgrowth; however, Nb-MLN showed a time-dependent enhancement of the neurite outgrowth, maximal at 3 weeks after infection. The relative efficacy of neurite outgrowth induction (heart > or = thymus > or = Nb-MLN > or spleen > or = MLN > or = SC) was confirmed in a second series of experiments where one SCG was surrounded by three different tissue explants. We then examined the role of 2.5S NGF, a well-known trophic factor for sympathetic nerves, in the lymphoid tissue-induced neurite outgrowth. Anti-NGF treatment of co-cultures of SCG and heart almost completely blocked the neurite outgrowth. Anti-NGF also significantly inhibited thymus- and spleen-induced neurite outgrowth, but not as effectively as heart-induced neuritogenesis (93, 80, and 77% inhibition at 24 hr; 86, 70, and 68% inhibition at 48 hr for heart, thymus, and spleen, respectively). On the other hand, anti-NGF inhibited only 8% of neurite outgrowth induced by 3-week post-infection Nb-MLN at 24 hr, and 41% at 48 hr. These data show that several adult rat lymphoid tissues exert neurotrophic/tropic effects. The predominant growth factor in thymus and spleen is NGF, while Nb-MLN produces factor(s) which is (are) immunologically distinguishable from NGF.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of alpha 2-adrenoceptors in rat lymph nodes and spleen: an autoradiographic study

The anatomical localization and pharmacological characteristics of alpha 2-adrenoceptors were studied in rat lymphoid tissues by quantitative autoradiography with [3H]bromoxidine as a ligand. In lymph nodes, a significant density of these receptors was found in the capsule, interfollicular cortex and medullary cords, while only very low densities were observed in the paracortex and germinal centres. In the spleen, these receptors appeared to be mainly distributed in the marginal zone of white pulp as well as in the red pulp. These results suggest a role for alpha 2-adrenoceptors in the interaction between nervous and immune systems.

Sympathetic nervous system modulation of the immune system. II. Induction of lymphocyte proliferation and migration in vivo by chemical sympathectomy

We have used chemical sympathectomy with 6-hydroxydopamine (6-OHDA) in adult mice to study the role of the sympathetic nervous system (SNS) in regulating cellular proliferation and migration in lymphoid organs. Following sympathectomy, an increase in inguinal and axillary lymph node (LN) weight and cellularity was observed. This increase paralleled increased cellular proliferation in vivo, as measured by uptake of [125I]deoxyuridine (125IUdR). Transient increases in cellular proliferation also were observed in spleen and bone marrow following sympathectomy. Administration of desipramine prior to 6-OHDA to prevent sympathectomy resulted in control levels of proliferation. beta-Adrenoceptor blockade just prior to or following 6-OHDA treatment did not alter the enhanced proliferation. Migration of normal 51Cr-labelled lymphocytes into inguinal and axillary LN was enhanced in sympathectomized recipients. Conversely, cells from sympathectomized animals showed diminished migration to these LN upon transfer into intact recipients. These results demonstrate that depletion of NA innervation alters cellular proliferation and lymphocyte migration in primary and secondary lymphoid organs.

Regional specificities in the distribution, chemical phenotypes, and coexistence patterns of neuropeptide containing nerve fibres in the human anal canal

Despite the pivotal clinical significance of the human anal canal, little is known about its total and specific innervation. This study assessed the comparative distribution and histotopology of nerve fibres immunoreactive for neural markers and a variety of regulatory active neuropeptides in the human anal canal by light microscopic immunohistochemistry. Depending on the epithelial zone and region of the anal canal, the neural elements were differentially immunoreactive for the pan-neural marker protein gene product 9.5, the catecholamine marker tyrosine hydroxylase, the neuroendocrine marker chromogranin A, and various neuropeptides. Protein gene product 9.5-immunoreactive nerve fibres were ubiquitously abundant in the anal canal. In the anal transitional zone, ectopic epithelial types were supplied by the same pattern of peptidergic nerves as the respective type of epithelium in normotopic location. In the dermis of the squamous zone and in the perianal epidermis, unusual distribution patterns of nerve fibres, referred to as areas of high nerve fibre density, were encountered. Double immunohistochemistry revealed region-specific coexistence patterns of neuropeptidergic nerve fibres, and novel peptide coexistence patterns were detected in anal nerve fibres. Subsets of nerve fibres formed close spatial relationships with chromogranin A-positive neuroendocrine cells, most frequently in the anal transitional zone. Chromogranin-A positive cells were shown to be present in the epithelium of perianal eccrine sweat glands. The differential distribution, peptide phenotypes and coexistence patterns of different nerve fibre populations in the human anal canal may reflect topospecific regulatory functions of neurally released neuropeptides in health and disease.

Immune system of the spontaneously hypertensive rat. I. Sympathetic innervation

Extensive bidirectional interactions are believed to exist between the sympathetic nervous system and the immune system. The spontaneously hypertensive rat (SHR) is known to possess both increased sympathetic nervous system activity with increased tissue catecholamine levels in several peripheral organs and a moderate T lymphocyte immune deficiency. We examined the development of innervation in both primary (thymus) and secondary (spleen) organs of the immune system of the SHR compared to immunocompetent Wistar-Kyoto (WKY), Fisher 344 (F-344), and Long Evan (LE) rats from birth through 24 weeks. Using glyoxylic acid-induced histofluorescence to visualize monoaminergic nerve fibers, coded specimens were examined and morphologically evaluated for the extent and distribution of innervation. The innervation of the SHR thymus was significantly increased at 2 and 12 weeks of age over the other strains. Unlike the control strains, splenic innervation in SHR was delayed until 2 weeks of age when it suddenly became exuberant. At 12 weeks, the innervation of the SHR spleen was increased over all control strains. By 24 weeks the innervation had regressed to a level comparable to the levels of the other rat strains in these tissues. During the suckling period, the size (weight) of the WKY spleen was larger and the level of innervation was decreased compared to the other strains. These strain-related differences in the development of sympathetic innervation of thymus and spleen likely reflect the complex, bidirectional interplay between the nervous and the immune systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Innervation of lymphoid organs and implications in development, aging, and autoimmunity

We now have substantial evidence demonstrating noradrenergic sympathetic and peptidergic innervation of both primary and secondary lymphoid organs. We have established criteria for norepinephrine, and some of the neuropeptides, as neurotransmitters, and have found changes in immune responsiveness following pharmacological manipulation of noradrenergic sympathetic or peptidergic nerves. Classic receptor binding studies have demonstrated a wide variety of target cells that possess beta-adrenoceptors and receptors for neuropeptides on cells of the immune system, including lymphocyte subsets, macrophages, accessory cells, or stromal elements. In this chapter we describe noradrenergic and peptidergic innervation of primary and secondary lymphoid organs in development, at maturation and during the normal aging process, and discuss possible functional implications of direct neural signals onto cells of the immune system at critical time points in the lifespan of an animal. Further, we examine for involvement of noradrenergic sympathetic and peptidergic innervation in the development and progression of several autoimmune disorders, including adjuvant-induced arthritis, New Zealand mice strains as a model for hemolytic anemia and lupus-like syndrome, and the experimental allergic encephalomyelitis model for multiple sclerosis.

Neonatal sympathetic denervation alters the development of in vitro spleen cell proliferation and differentiation

The ontogeny of spleen cell proliferation to T and B cell mitogens and immunoglobulin secretion, measured in vitro, was examined in neonatally sympathectomized Fischer 344 (F344) rats, administered the neurotoxic drug 6-hydroxydopamine (6-OHDA) from 1 to 3 days of age. Compared to cells from age-matched controls, spleen cells from neonatally sympathectomized animals, aged 7-14 days, exhibited a shift in the proliferative response to the T cell mitogen, concanavalin A (Con A), with reduced proliferation in the presence of low doses of Con A, but increased proliferation with higher doses. During the same period, from 7 to 14 days, the B cell mitogen STM/DxS inhibited proliferation by spleen cells from all rats, and no effect of sympathectomy was observed. As adult-like patterns of mitogen responsiveness emerged from 21 to 42 days of age, neonatally sympathectomized rats showed reduced proliferative responses of both T and B cells. This effect dissipated by 56 days of age. Polyclonal immunoglobulin (Ig) production by B cells was assessed in vitro in the presence or absence of STM/DxS. Neonatal sympathectomy resulted in reduced spontaneous IgM production throughout development. From 28 to 42 days of age, when mitogen-triggered IgM secretion first developed, neonatal sympathectomy decreased the magnitude of the response. By 56 days of age, mitogen-induced IgM secretion was no longer affected by sympathectomy, similar to the proliferative response. Gender influenced the time course of sympathectomy-induced changes in spleen cell proliferation and differentiation; however, the magnitude and direction of these changes were similar in both males and females. Desipramine, administered prior to 6-OHDA, prevented both sympathetic denervation and the 6-OHDA-induced changes in spleen cell responsiveness. This indicates that the alterations in immune function were dependent on NA nerve fiber destruction and were not simply the result of direct 6-OHDA action on other cells. The results of this study suggest that sympathetic innervation may play an important potentiating role in the development of the lymphoid system, through effects on lymphocyte proliferation and differentiation.

Peptidergic innervation of the Bursa Fabricii: interrelation with T-lymphocyte subsets

In birds, B-lymphocytes mature in a special immune organ, the Bursa Fabricii. This organ thus offers unique possibilities for the study of the microenvironment of B-lymphocyte differentiation. We previously reported tachykinin-, vasoactive intestinal peptide-, calcitonin gene-related peptide- and galanin-immunoreactive (ir) fibres in the chicken bursa. As judged from light microscopic studies, each of the peptides was found in fibres contacting B-lymphocytes. Vasoactive intestinal peptide-ir fibres contacted macrophages. Now, we demonstrate neuropeptide Y, indicating the sympathetic nervous system, in fibres associated with arteries, not entering the follicles. CD4- and CD8-positive T-lymphocytes were dispersed in bursal follicles and the connective tissue, most densely in subepithelial regions. We could not find close apposition of fibres with either T-cell subset. We conclude that the potential neuro-immune axis in the Bursa Fabricii may represent a neuro-B-cell-link with only indirect participation of T-lymphocytes. The sympathetic input may influence the bursal microenvironment primarily by regulating the blood supply.

Molecular anatomy of the neuro-immune connection

Light microscopic immunohistochemistry was employed to elucidate and compare the presence, distribution, and coexistence of various peptides, neuroendocrine markers and enzymes of the catecholamine pathway in nerves supplying lymphoid tissues in a variety of mammalian species. All lymphoid organs and tissues receive innervation by fibers containing dopamine-beta-hydroxylase and/or tyrosine hydroxylase, neural markers like protein gene product 9.5, synaptophysin and neurofilament and a varied spectrum of peptides. The prominent peptides were tachykinins (substance P, neurokinin A), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), and vasoactive intestinal polypeptide/peptide histidine isoleucine (VIP/PHI). Opioid innervation was variable. Double immunofluorescence revealed coexistence of tachykinins and CGRP and of tyrosine hydroxylase and NPY. A minor proportion of fibers showed coexistence of NPY and tachykinins and of VIP/PHI and tachykinins. The possible importance of the complex peptidergic innervation of lymphoid tissues in inflammation, allergy, inflammatory pain and psycho-neuro-immuno-endocrine network function is discussed. A special immunomodulatory role of the sensory neurons is suggested.

Neuropeptide-Y innervation of the rat spleen: another potential immunomodulatory neuropeptide

Neuropeptide-Y (NPY) is a 36 amino acid peptide that acts as a chemical messenger in the central and peripheral nervous systems. NPY often is found colocalized with the classical neurotransmitter norepinephrine (NE) and can potentiate the effects of this neurotransmitter postsynaptically in many systems. Using immunocytochemistry for NPY and specific lymphoid cell markers, we mapped the distribution of NPY-positive nerve fibers in the rat spleen. NPY-positive nerve fibers were present along the vasculature, trabeculae, and capsule, and also were found associated with specific lymphoid parenchymal compartments of the spleen, in close contact with lymphocytes and macrophages. These contacts were investigated further at the electron microscopic level. NPY-positive nerve terminals were found in close apposition with lymphocytes in the periarteriolar lymphatic sheath, and with lymphocytes and macrophages in the marginal zone. Previous studies have reported that postganglionic noradrenergic nerve fibers innervate specific lymphoid compartments of the rat spleen, with nerve terminals forming direct appositions with cells of the immune system. The possible colocalization of NPY and NE in these nerve fibers was investigated by chemical sympathectomy with 6-hydroxydopamine, followed by immunocytochemical labeling of NPY and tyrosine hydroxylase (TH), the rate-limiting enzyme in norepinephrine synthesis. Colocalization also was investigated by labeling for NPY with a fluorescent label, eluting the NPY, and staining for TH with diaminobenzidine as the label. These studies demonstrate that norepinephrine and NPY are colocalized in the postganglionic sympathetic nerve fibers of the rat spleen.(ABSTRACT TRUNCATED AT 250 WORDS)

Substance P innervation of spleen in rats: nerve fibers associate with lymphocytes and macrophages in specific compartments of the spleen

We investigated the distribution of SP+ nerve fibers in the spleen of adult male Fischer 344 rats. SP+ nerve fibers entered the spleen with the splenic artery in the hilar region, arborized along the venous sinuses, and extended from these larger plexuses into trabeculae and the surrounding red pulp. In the white pulp, SP+ nerve fibers were found in the marginal zone, and in the outer regions of the PALS among T lymphocytes. No SP+ nerve fibers were observed in association with the splenic capsule, the central arteries of the white pulp, or the follicles. SP levels in rat spleen were 5.7 +/- 0.4 ng/g wet wt. On the basis of the present findings of SP presence in nerve fibers in the spleen, and published evidence for SP receptors on lymphocytes and macrophages, we suggest that SP derived from nerve fibers in the spleen can act as a neurotransmitter with cells of the immune system as targets. These SP nerve fibers may be an important neural link between the nervous system and the immune system and may participate in modulation of immune reactivity and inflammatory responses.

Noradrenergic reinnervation of the rat spleen following chemical sympathectomy with 6-hydroxydopamine: pattern and time course of reinnervation

The time course and pattern of reinnervation of noradrenergic (NA) sympathetic nerve fibers into the spleen following acute chemical sympathectomy with the catecholamine neurotoxin 6-hydroxydopamine (6-OHDA) was examined in young adult male Fischer 344 rats using glyoxylic acid fluorescence histochemistry and neurochemical measurement of NE. Reinnervation proceeds initially along the splenic artery as it enters the hilus (1-5 days), extends into the hilar region (5-10 days), and later proceeds into the regions distal to the hilus (21-56 days), suggestive of orderly growth from the hilar region to distal regions. In all 6-OHDA-treated spleens, the compartmentation of NA innervation was similar to that observed in saline-injected controls, but the density of NA nerve fibers in these compartments differed according to the distance from the hilus. By 56 days postlesion, regions distal to the hilar blood vessels contained fewer NA profiles than their age-matched controls, suggesting that the anatomical process of reinnervation does not restore the density of fibers in a fashion identical to that of nondenervated controls. In contrast, splenic NE concentration at 56 days postdenervation did not differ from the concentration seen in nondenervated control spleens. We suggest that functional restoration of splenic innervation may involve metabolic and receptor compensation for the lack of complete fiber regrowth into regions of white pulp distal from the hilus.

Prenatal alcohol exposure alters the development of sympathetic synaptic components and of nerve growth factor receptor expression selectivity in lymphoid organs

Exposure to alcohol in utero has been associated with long-term immune deficits. In addition, adult mice exposed to alcohol prenatally display altered noradrenergic synaptic transmission selectively in lymphoid organs. This is consistent with the hypothesis that sympathetic neurons play an important role in immunomodulation. The development and maintenance of sympathetic neurons are critically dependent on nerve growth factor (NGF). Furthermore, NGF has been shown to modulate immune responses and NGF receptor expression has been localized to lymphoid organs. The present work examined the effects of prenatal alcohol exposure on the development and maturation of pre- and postsynaptic sympathetic components, including norepinephrine and beta-adrenoceptors, respectively, as well as the early expression of NGF receptors in lymphoid and other organs of the C57BL/6 mouse. Infant mice that were exposed to alcohol in utero displayed reduced levels of norepinephrine and beta-adrenoceptor density, as well as increased NGF receptor expression in the thymus and spleen, but not the heart. These selective changes may account, in part, for the persistent immune incompetence characteristic of fetal alcohol syndrome.

Lactational alcohol exposure elicits long-term immune deficits and increased noradrenergic synaptic transmission in lymphoid organs

Increasing evidence suggests that the sympathetic nervous system plays an important role in immunomodulation. While chronic alcohol consumption has been associated with immune deficits, the effects of exposure to alcohol during early postnatal life on subsequent immunocompetence and activity of sympathetic neurons in lymphoid organs are not known. This study examined the long-term effects of lactational alcohol consumption on cellular immune responses and noradrenergic synaptic transmission in lymphoid and other organs of the young adult C57BL/6 mouse. The data show that exposure to alcohol via the mother's milk was associated with long-term deficits in cellular immunity, including suppression of the local graft vs host and contact hypersensitivity responses. The animals also displayed enhanced noradrenergic synaptic transmission and decreased beta-adrenoceptor density selectively in lymphoid organs. These neuroimmune changes are particularly striking since body weight-gain of the suckling pups was normal and their blood alcohol concentration was considerably lower than that of the alcohol-consuming dam. This suggests an increased sensitivity of the nascent immune and nervous systems during the critical period of early postnatal development.

The effect of chemical sympathectomy on natural killer cells in mice

The nervous system affects immune regulation. We permanently ablated the sympathetic nervous system (SNS) of CBA mice with 6-OHDA at birth. Function of splenic natural killer (NK) cells in the sympathectomized mice was equivalent to controls at 2 weeks, but rose significantly above control levels at 4 weeks. NK cell function decreased below control values thereafter. NK cell numbers paralleled these changes in NK cell function. Our data suggest that the SNS may regulate the number and function of splenic NK cells during development.