Suzanne Y. Felten

Noradrenergic Sympathetic Neural Interactions with the Immune System: Structure and Function

Histochemical studies from our (Williams & Felten 1981, Williams et al. 1981, D. Felten et al. 1981, 1984, 1985, 1987a, 1987b, Livnat et al. 1985, Ackerman et al. 1986, S. Felten et al. 1987) and other laboratories (Giron et al. 1980, Bulloch & Pomeranz, 1984, Singh 1984, Walcott & MacLean 1985) have shown the presence of autonomic nerve fibers in specific compartments of both primary and secondary lymphoid organs. These nerve fibers are associated not only with blood vessels but also with lymphocytes and macrophages. We have demonstrated that the neurotransmitter norepinephrine (NE), present in the postganglionic sympathetic fibers that richly innervate lymphoid organs, acts in the spleen as both a paracrine secretion, available to receptors on cells in the white pulp, and a localized neurotransmitter in nerve terminals that directly contact T lymphocytes in the periarteriolar lymphatic sheath (PALS) (S. Felten et al. 1986, S. Felten & Olschowka 1987). We propose that NE in lymphoid organs fulfills the criteria for neurotransmission, estabUshed in more traditional efTector tissues such as the heart, and plays a role in the modulation of immune responses. This review summarizes evidence for neurotransmission, including presence and compartmentation of NE, transmitter release, post-synaptic receptors on cells of the immune system, and functional consequences of denervation and pharmacological manipulation of NE. We also review aspects of development, aging, and plasticity of noradrenergic (NA) fibers that enhance our understanding of their role in organs of the immune system.

Innervation of Lymphoid Tissue

Publisher Summary This chapter focuses on the location of nerves within organs of the immune system and the possible association of these nerves with specific compartments or cellular regions. It also focuses on neurotransmitters in these nerves, which act as signal molecules within the immune system. Lymphoid organs are composed of a reticular stroma that forms a meshwork that provides support for varying populations of cells of the immune system, many of which are mobile cells. Secondary lymphoid organs and accumulations have T-dependent areas and B-dependent areas. It is much more common to find innervation, whether noradrenergic or peptidergic, associated with the T-dependent areas. However, occasional fibers do seem to enter the follicles. There are also areas where T lymphocytes, B lymphocytes, macrophages, and other cells are mixed; these areas often are associated with large blood or lymph sinuses, where antigen presentation takes place, such as the marginal zone of the spleen and the medullary cords of the lymph nodes. These areas also are innervated largely by noradrenergic/NPY-containing fibers.

Transmural myocardial infarction in the dog produces sympathectomy in noninfarcted myocardium.

Because sympathetic fibers travel in the subepicardium and generally follow the coronary arteries in a basal to apical course, we tested the hypothesis that transmural myocardial infarction that involves this subepicardial region interrupts sympathetic axons traveling through the infarct and produces sympathetic denervation at noninfarcted sites apical to the infarction. A rapidly hardening vinyl latex solution injected into the first diagonal branch of the left anterior descending coronary artery produced the transmural myocardial infarction by embolizing the vasculature. Ten dogs were studied 90 minutes after coronary artery embolization (acute) and 12 dogs were studied 7–21 days after infarction (chronic). The integrity of the sympathetic innervation was tested in an open-chest preparation of the acutely and chronically infarcted dogs by measuring endocardial and epicardial effective refractory period changes during left and right stellate stimulation. Additionally, regional myocardial norepinephrine content and fluorescence were examined in the chronically infarcted dogs. Transmural infarction was verified using nitroblue tetrazolium staining. In the 10 acutely infarcted dogs, left and right stellate stimulation shortened the effective refractory period at all 56 sites examined before infarction and at 30 sites basal or lateral to the infarction after embolization. Twenty-six noninfarcted sites apical to, but not within, the zone of infarction did not respond to left or right stellate stimulation after infarction. In the 12 chronically infarcted dogs, left and right stellate stimulation shortened the effective refractory period at all 20 sites basal to infarction. In noninfarcted sites apical to the infarction, left stellate stimulation did not shorten the eifective refractory period at 23 of 41 sites, while right stellate stimulation was ineffective at 24 of 41 sites. Both left and right stellate stimulation were ineffective at 18 of 41 sites. Twelve of 41 sites apical to the infarct had normal effective refractory period shortening during left and right stellate stimulation. In both groups of dogs, norepinephrine infusion, 0.05, ug/kg/min, i.v., shortened the refractory period at all sites apical to the infarct that did not shorten refractory period in response to stellate stimulation. In chronically infarcted dogs, myocardial norepinephrine content was reduced at the denervated sites, and histologically reduced norepinephrine fluorescence in noninfarcted, denervated myocardium was found. We conclude that transmural myocardial infarction produces heterogeneous sympathetic denervation in noninfarcted sites apical to the area of necrosis. This denervation is probably the result of interrupting sympathetic nerves coursing from base to apex.

Long-term effect of MPTP in the mouse brain in relation to aging: neurochemical and immunocytochemical analysis

The long-term effect of the parkinsonism-inducing neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on central monoaminergic neurons in young (2-3 months) and aging (12 months) C57BL/6 mice has been studied using neurochemical and immunocytochemical techniques. MPTP treatment (4 x 20 mg/kg i.p. given 12 h apart) resulted in significant depletion of dopamine (DA) concentration in the striatum, substantia nigra, nucleus accumbens, and olfactory tubercle 1 week after treatment in both young and aging mice. Although a decreased DA concentration in the ventral tegmental area was not seen in young mice, aging mice did show a significant decrease. The extent of decrease of DA concentration was greater in aging mice than in young mice in all areas investigated except in dorsal striatum. The long-term effect of MPTP on DA neurons in young mice included considerable recovery of DA concentration in both nigrostriatal and mesolimbic DA systems following the initial profound depletion; such recovery was minimal in aging mice, even 3 months after MPTP treatment. In young mice treated with MPTP, no significant change of norepinephrine (NE) or serotonin (5-HT) concentration was observed in any area investigated while a significant decrease of NE and 5-HT concentration was seen in several brain areas investigated in aging mice. Immunocytochemical analysis revealed that the MPTP injection resulted in marked disappearance of tyrosine hydroxylase (TH)-immunoreactive (IR) fibers in striatum of both young and aging mice 1 week following treatment. Partial recovery of TH-IR fibers was seen 5 weeks or 3 months after MPTP treatment in young mice, while no such apparent recovery was seen in aging mice. Aging mice also showed significant decrease in the number of TH-positive cell bodies in the substantia nigra and ventral tegmental area through all periods investigated, while such a significant decrease was only seen in the substantia nigra of young mice 1 week after treatment. We conclude that aging mice are more sensitive to MPTP and show more widespread damage to the monoaminergic systems than young mice, suggesting that MPTP-treated aging mice provide a more useful model for studying anatomical and neurochemical characteristics of Parkinsons disease than young mice.

Sympathetic neural modulation of the immune system. I. Depression of T cell immunity in vivo and vitro following chemical sympathectomy

Chemical sympathectomy of adult mice with 6-hydroxydopamine (6-OHDA) either prior to or following epicutaneous sensitization with the trinitrophenyl (TNP) hapten decreased the delayed hypersensitivity (DH) response to ear challenge. To determine if uptake of 6-OHDA into sympathetic nerve terminals, and their subsequent destruction, was required for suppression of DH, the catecholamine uptake blocker, desipramine, was employed to block 6-OHDA-induced sympathetic denervation. Pretreatment with desipramine prevented the depression of DH. In vivo treatment with the beta blocker, propranolol, did not alter the 6-OHDA effect, eliminating the potential contribution of released catecholamines, acting on beta-adrenoceptors, to DH reduction. Sympathectomy before sensitization also diminished hapten-specific T cell reactivity of sensitized lymph node (LN) cells, as measured in vitro by IL-2 production and CTL generation. In vivo DNA synthesis in draining LN in response to immunization was modestly decreased following 6-OHDA. Thus, sympathetic denervation appears to impair T cell activity in vivo and in vitro. Overall, these results indicate the SNS plays a role in generation of cell-mediated immunity.

MPTP-treated young mice but not aging mice show partial recovery of the nigrostriatal dopaminergic system by stereotaxic injection of acidic fibroblast growth factor (aFGF)

Acidic fibroblast growth factor (aFGF) is a heparin-binding polypeptide that acts as a neurotrophic factor for certain central and peripheral neurons. Acidic FGF was injected stereotaxically into the striatum of young (2-month-old) and aging (12-month-old) C57BL/6 mice that were treated 1 week before with systemic injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP treatment (4 x 20 mg/kg, i.p. given 12 h apart) reduced tyrosine hydroxylase (TH)-immunoreactive (IR) fibers in the striatum and reduced dopamine (DA) concentration to 32% of the controls in young and 20% of the controls in aging mouse brain 5 weeks after administration. Although the DA concentration recovered to 43% of the controls in young mice following stereotaxic injection of aFGF 5 weeks after MPTP treatment, aging mice with such treatment did not show a significant recovery of DA concentration. Computerized image analysis of TH-IR fibers in the striatum also showed significant recovery in young mice treated with aFGF, while aging mice did not show a significant recovery. We conclude that treatment of MPTP-depleted young mice with aFGF results in partial recovery in the nigrostriatal DA system but such benefits decline with age.

Chronic dietary pergolide preserves nigrostriatal neuronal integrity in aged-Fischer-344 rats

Pergolide, a potent D2 presynaptic agonist with postsynaptic D2 agonist activity and some D1 agonist activity was administered in the diet (0.5 mg/kg/day) of male Fischer 344 rats from age 3 to age 26 months. We hypothesized that the potent D2 presynaptic activity would reduce the baseline release of dopamine (DA) and thereby slow the formation of toxic oxidative metabolites that lead to age-related deterioration of nigrostriatal DA neurons. Pair-fed rats served as controls. We observed age-related losses of fluorescent DA cell bodies in the substantia nigra pars compacta and of fluorescent DA terminals in the striatum; chronic pergolide administration prevented these losses. Pergolide administration also prevented the age-related diminution of DA fluorescence intensity in substantia nigra cell bodies. A large decline in 3H-DA uptake with age was partially prevented by pergolide administration. We found no age-related alteration in the concentration of DA in the striatum and pergolide did not alter this concentration. Pergolide treatment resulted in only minor alterations in striatal 3H-spiperone binding and no change in dendritic arborizations of either DA substantia nigra neurons or medium spiny striatal neurons. Pergolide administration also prevented an age-related decline in circulating FSH levels. The uptake data and quantitative morphological findings suggest that pergolide administration in the diet for 2 years exerts a protective effect on age-related deterioration of DA nigrostriatal neurons. This finding was consistent with clinical reports of a subset of patients with Parkinsons disease in whom long-term efficacy of pergolide therapy is observed.

Sympathetic innervation of lymph nodes in mice

Noradrenergic innervation of popliteal and mesenteric lymph nodes in mice was examined with fluorescence histochemistry. Dense varicose plexuses entered the nodes with the vasculature in the hilar region and continued with the vasculature into the medullary region. Fine, delicate varicosities and small vascular plexuses continued into the cortical and paracortical regions surrounding the germinal centers; some varicosities ended among lymphocytes. A subcapsular plexus contributed fibers into the cortical and paracortical regions. Chemical measurements revealed the presence of norepinephrine in lymph nodes that was depletable with 6-hydroxydopamine. Depletion of norepinephrine from lymph nodes with this agent resulted in a diminished primary immune response in draining lymph nodes following subcutaneous injection of an antigen in two mouse strains, but had no effect in two other strains. These findings suggest that noradrenergic fibers innervate both the vasculature and parenchymal regions of lymph nodes, and may participate in the modulation of immune responses in these organs.

Cardiac noradrenergic nerve terminal abnormalities in dogs with experimental congestive heart failure.

BACKGROUND We have shown previously that norepinephrine (NE) uptake activity is reduced in the failing right ventricle of animals with right heart failure (RHF) produced by tricuspid avulsion and progressive pulmonary constriction. However, it is unknown whether this defect in neuronal NE uptake is related to reduction of noradrenergic nerve terminals or whether these changes also occur in animals with left heart failure (LHF). It is also unknown whether increased NE release in heart failure contributes to the noradrenergic nerve abnormalities. METHODS AND RESULTS We measured myocardial NE content. NE uptake function, and noradrenergic nerve profiles in dogs with either RHF or LHF induced by rapid ventricular pacing. NE uptake activity was measured using [3H]NE, and noradrenergic nerve profiles were visualized by glyoxylic acid (SPG)-induced histofluorescence and tyrosine hydroxylase immunocytochemical staining. To study the effects of excess NE, we exposed normal dogs to 8 weeks of chronic NE infusion using subcutaneous osmotic minipumps. RHF and LHF animals exhibited reduced myocardial contractile function and congestive heart failure, as evidence by reduced cardiac output and elevated right atrial pressure. However, unlike that in LHF, left atrial pressure was not increased in RHF. The animals also showed an increase in plasma NE and a decrease in cardiac NE. In addition, SPG-induced histofluorescence correlated significantly with NE uptake activity (r = .712, P < .001) and tyrosine hydroxylase immunoreactive profiles (r = .569, P < .001) in the right ventricles of RHF dogs and in both ventricles of LHF dogs. The numbers of catecholaminergic profiles and tyrosine hydroxylase profiles significantly correlated with cardiac filling pressures. Chronic infusion of NE decreased heart rate in normal dogs but had no effect on either mean aortic pressure or left atrial pressure; like heart failure, it resulted in significant decreases in myocardial NE uptake activity and numbers of SPG-induced catecholaminergic histofluorescence and immunoreactive tyrosine hydroxylase profiles. CONCLUSIONS Myocardial NE uptake activity was reduced only in the failing ventricles with elevated filling pressure in RHF and LHF. These changes probably were caused by loss of noradrenergic nerve terminals in the failing ventricles, as evidenced by the reductions of catecholaminergic histofluorescence and tyrosine hydroxylase immunostained profiles. Furthermore, since similar reductions of myocardial NE uptake and noradrenergic nerve profiles could be produced by chronic NE infusion in normal dogs, elevated NE levels may play a role in the development of cardiac noradrenergic nerve abnormalities in congestive heart failure.

Sympathetic nervous system modulation of the immune system. III. Alterations in T and B cell proliferation and differentiation in vitro following chemical sympathectomy

Functional changes in lymph node (LN) and spleen lymphocytes were examined following sympathetic denervation of adult mice with 6-hydroxydopamine (6-OHDA). Sympathectomy reduced in vitro proliferation to concanavalin A (ConA) by LN cells and decreased LN Thy-1+ and CD4+ T cells. At the same time, ConA-induced interferon-gamma (IFN-gamma) production was increased, but interleukin-2 (IL-2) production was not altered. After sympathectomy, lipopolysaccharide (LPS)-stimulated proliferation of LN B cells was enhanced, in parallel with an increase in the proportion of sIgM+ cells. LPS-induced polyclonal IgM secretion was decreased, whereas polyclonal IgG secretion was dramatically enhanced. In the spleen, ConA and LPS responsiveness was reduced after sympathectomy, as was IL-2 and IFN-gamma production. The decreased proliferation was not associated with changes in splenic T and B cell populations. The uptake blocker desipramine prevented the 6-OHDA-induced changes in spleen and LN, indicating that these alterations were dependent upon neuronal destruction. These results provide evidence for heterogeneity of sympathetic nervous system regulation of T and B lymphocyte function and for organ-specific influences on immune function.