Neutrophils contribute to sympathetic nerve terminal-dependent plasma extravasation in the knee joint of the rat

Acute inflammation in the joint: its control by the sympathetic nervous system and by neuroendocrine systems

Inflammation of tissues is under neural control involving neuroendocrine, sympathetic and central nervous systems. Here we used the acute experimental inflammatory model of bradykinin-induced plasma extravasation (BK-induced PE) of the rat knee joint to investigate the neural and neuroendocrine components controlling this inflammation. 1. BK-induced PE is largely dependent on the sympathetic innervation of the synovium, but not on activity in these neurons and not on release of norepinephrine. 2. BK-induced PE is under the control of the hypothalamo-pituitary-adrenal (HPA) system and the sympatho-adrenal (SA) system, activation of both leading to depression of BK-induced PE. The inhibitory effect of the HPA system is mediated by corticosterone and dependent on the sympathetic innervation of the synovium. The inhibitory effect of the SA system is mediated by epinephrine and β2-adrenoceptors. 3. BK-induced PE is inhibited during noxious stimulation of somatic or visceral tissues and is mediated by the neuroendocrine systems. The nociceptive-neuroendocrine reflex circuits are (for the SA system) spinal and spino-bulbo-spinal. 4. The nociceptive-neuroendocrine reflex circuits controlling BK-induced PE are under powerful inhibitory control of vagal afferent neurons innervating the defense line (connected to the gut-associated lymphoid tissue) of the gastrointestinal tract. This inhibitory link between the visceral defense line and the central mechanisms controlling inflammatory mechanisms in body tissues serves to co-ordinate protective defensive mechanisms of the body. 5. The circuits of the nociceptive-neuroendocrine reflexes are under control of the forebrain. In this way, the defensive mechanisms of inflammation in the body are co-ordinated, optimized, terminated as appropriate, and adapted to the behavior of the organism.

Function of the sympathetic supply in acute and chronic experimental joint inflammation

Joints are densely innervated by postganglionic sympathetic nerve fibers. These fibers control the blood flow in the joint and vascular permeability, either directly or indirectly, in cooperation with leukocytes. Chemical sympathectomy or suppression of adrenergic signaling significantly reduces inflammatory processes in the initial acute state of inflammation whereas the same procedures may increase inflammation at later stages. These findings indicate that the sympathetic nervous system supports the development of inflammation but may reduce inflammation at more chronic stages. During chronic inflammation the density of sympathetic nerve fibers in synovial tissue is reduced but other tyrosine hydroxylase-positive cells secreting noradrenaline appear in the inflamed joint. In addition to local vascular effects in the joint, the sympathetic nervous system influences numerous immune processes in the joint and in lymphoid organs. Hence the net effect of the sympathetic nervous system on inflamed tissue results from local sympathetic effects in the joint as well as from sympathetic influences on major systemic immune processes.

Localization of S100A8 and S100A9 expressing neutrophils to spinal cord during peripheral tissue inflammation

Investigation of hyperalgesia at the spinal transcriptome level indicated that carrageenan-induced inflammation of rat hind paws leads to a rapid but sustained increase in S100A8 and S100A9 expression, two genes implicated in the pathology of numerous inflammatory diseases including rheumatoid arthritis and gout. In situ hybridization revealed that the elevation occurred in neutrophils that migrate to the spinal cord vasculature during peripheral inflammation, not in spinal neurons or glial cells. Immunohistochemical analysis suggests, but does not prove, that these neutrophils abundantly release S100A8 and S100A9. Consistent with this, we detected an increase in ICAM and VCAM, both indicators of endothelial activation, a known trigger for secretion of S100A8 and S100A9. Migration of S100A8- and S100A9-expressing neutrophils to spinal cord is selective, since MCP-1- and CD68-expressing leukocytes do not increase in spinal cord vasculature during hind paw inflammation. Examination of many neutrophil granule mediators in spinal cord indicated that they are not regulated to the same degree as S100A8 and S100A9. Neutrophil migration also occurs in the vasculature of brain and pituitary gland during peripheral inflammation. Together, these findings suggest an interaction between a subpopulation of leukocytes and the CNS during peripheral tissue inflammation, as implied by an apparent release and possible diffusion of S100A8 and S100A9 through the endothelial blood-brain barrier. Although the present findings do not establish the neurophysiological or behavioral relevance of these observations to nociceptive processing, the data raise the possibility that selective populations of leukocytes may communicate the presence of disease or tissue damage from the periphery to cells in the central nervous system.

Arthritis and pain. Neurogenic origin of joint pain

Arthritis pain affects millions of people worldwide yet we still have only a limited understanding of what makes our joints ache. This review examines the sensory innervation of diarthroidal joints and discusses the neurophysiological processes that lead to the generation of painful sensation. During inflammation, joint nerves become sensitized to mechanical stimuli through the actions of neuropeptides, eicosanoids, proteinase-activated receptors and ion channel ligands. The contribution of immunocytes to arthritis pain is also reviewed. Finally, the existence of an endogenous analgesic system in joints is considered and the reasons for its inability to control pain are postulated.

Sexual dimorphism in the effect of nonhabituating stress on neurogenic plasma extravasation

The sympathoadrenal axis contributes to the sexual dimorphism of the inflammatory response. As stress both activates the sympathoadrenal axis and profoundly affects inflammation and inflammatory disease, we evaluated whether stress exerts a sexually dimorphic effect on a major component of the inflammatory response, plasma extravasation. We evaluated the effect of a nonhabituating stress, repeated intermittent sound (30 min/day for 4 days), on neurogenic synovial plasma extravasation, induced by bradykinin in the rat knee joint. Sound stress profoundly inhibited bradykinin-induced plasma extravasation in male rats, but profoundly enhanced it in female rats. These effects took 24 h to fully develop after the last exposure to stress. In gonadectomized males, bradykinin-induced plasma extravasation was lower than intact males, and sound stress now enhanced it, i.e. gonadectomized males were phenotypically like intact females. In gonadectomized females, bradykinin-induced plasma extravasation was greater than in intact adult females, and sound stress still enhanced it. Adrenal enucleation significantly attenuated the effect of sound stress on bradykinin-induced plasma extravasation in both male and female rats. We tested the hypothesis that these effects of sound stress were due to sustained enhanced plasma levels of stress hormones. Corticosterone and epinephrine, only when administered in combination, over five days, produced a qualitatively similar effect as sound stress, i.e. bradykinin-induced plasma extravasation was significantly decreased in males and increased in females. These findings suggest that a combined effect of the hypothalamic-pituitary adrenal and sympathoadrenal stress axes are responsible for the marked sexual dimorphism in the effect of stress on the inflammatory response.

Sympathetic modulation of acute cutaneous flare induced by intradermal injection of capsaicin in anesthetized rats

Much of the acute cutaneous neurogenic inflammation after intradermal injection of capsaicin (CAP) in rats is mediated by dorsal root reflexes (DRRs), which cause the release of inflammatory agents from primary afferent terminals. Sympathetic efferents modulate neurogenic inflammation by interaction with primary afferent terminals. In this study, we examined if DRR-mediated flare after CAP injection is subject to sympathetic modulation. Changes in cutaneous blood flow on the plantar surface of the foot were measured using a laser Doppler flow meter. After CAP injection, cutaneous flare spread more than 20 mm away from the site of CAP injection. However, this CAP-induced flare was significantly reduced after surgical sympathectomy. Decentralization of postganglionic neurons did not affect the flare induced by CAP injection. If the foot of sympathectomized rats was pretreated with an alpha(1)-adrenoceptor agonist (phenylephrine) by intra-arterial injection, the spread of flare induced by CAP injection could be restored. However, if the spinal cord was pretreated with a GABA(A) receptor antagonist, bicuculline, to prevent DRRs, phenylephrine no longer restored the CAP-evoked flare. An alpha(2)-adrenoceptor agonist (UK14,304) did not affect the CAP-evoked flare in sympathectomized rats. In sympathetically intact rats, blockade of peripheral alpha(1)-adrenoceptors with terazosin profoundly reduced the flare induced by CAP injection, whereas blockade of peripheral alpha(2)-adrenoceptors by yohimbine did not obviously affect the flare. Therefore the pathogenesis of acute neurogenic inflammation in the intradermal CAP injection model depends in part on intact sympathetic efferents and alpha(1)-adrenoceptors. Peripheral alpha(1)-adrenoceptors thus modulate the ability of capsaicin sensitive afferents to evoke the release of inflammatory agents from primary afferents by DRRs.

Annexin I is a local mediator in neural-endocrine feedback control of inflammation

Annexin I is a local mediator in neural-endocrine feedback control of inflammation. J. Neurophysiol. 80: 3120-3126, 1998. Activation of primary afferent nociceptors induces a neural endocrine-mediated inhibition of the inflammatory response via a circuit that includes ascending spinal pathways and activation of the hypothalamic-pituitary adrenal (HPA) axis. This circuit inhibits sympathetic neuron-dependent plasma extravasation (PE) in the rat knee joint produced by bradykinin (BK), but not sympathetic neuron-independent PE produced by platelet activating factor (PAF). Noxious (25 mA) but not non-noxious (2.5 mA) electrical stimulation significantly increased plasma corticosterone concentrations, and intravenous infusion of corticosterone (5 micrograms/min) mimicked inhibition of BK-induced PE produced by noxious stimulation. However, perfusion of corticosterone locally through the knee joint, at doses that do not have a systemic action (i.e., </=1 microM), did not inhibit BK-induced PE. Annexin I (lipocortin-1), a 37-kDa member of a family of phospholipid and calcium binding proteins, can mediate local anti-inflammatory effects of glucocorticoids via a mechanism that is partially dependent on inhibition of phospholipase A2 activity and adhesion and transmigration of polymorphonuclear leukocytes. Because BK-induced PE is dependent on both polymorphonuclear leukocytes and phospholipase A2 activity, we tested the hypothesis that the action of corticosterone to inhibit BK-induced PE is mediated by stimulating the production and release of annexin I. Perfusion of BK (150 nM) through the rat knee joint induces a rapid and sustained increase in PE. Co-perfusion of BK with annexin I (100 ng/ml) through the knee joint mimics the inhibition of BK-induced PE produced by noxious electrical stimulation or by intravenous corticosterone. Co-perfusion of BK with annexin I antibody (LCPS1, 1:60 dilution) prevented the inhibition of BK-induced PE produced by noxious electrical stimulation or intravenous corticosterone adminstration. PAF-induced PE, which is not dependent on polymorphonuclear leukocytes, was not inhibited by local perfusion of annexin I. These data suggest that the inhibitory effect of C-fiber activity on BK-induced PE, acting via an HPA circuit, is mediated by annexin I in the knee joint.

Endocrine and vagal controls of sympathetically dependent neurogenic inflammation

Recently the very significant role of the postganglionic sympathetic neuron (PGSN) terminal in the production of neurogenic inflammation has been appreciated. An important model of this sympathetically dependent inflammation is venular plasma extravasation (PE) and neutrophil attraction produced by local intra-articular injection of the potent inflammatory mediator bradykinin (BK). Sympathetic-dependent PE in the synovium has been proposed as a protective mechanism in arthritis. In a recent series of studies, a novel mechanism has been discovered by which activation of primary afferent nociceptors exerts a potent feedback inhibition of PGSN-dependent PE. Activation of nociceptive afferents was shown to be involved in this feedback system. Such a negative feedback control of the acute inflammatory response would have survival value; the inflammatory response, as initiated by a high degree of positive feedback, and the inflammatory process itself when persisting can result in significant tissue injury. If indeed HPA axis activity plays a significant physiological role in the modulation of neurogenic inflammation, then physiological processes that modulate the HPA axis would be expected to influence neurogenic inflammation. A dramatic effect of this kind has been demonstrated, in the rat, for vagal afferent activity. In the presence of subdiaphragmatic (or celiac branch) vagotomy, the potency of nociceptive afferent activity to inhibit sympathetically dependent, BK-induced PE was increased by four orders of magnitude compared to vagus-intact animal. Hypoactivity or hyperactivity of these vagally mediated mechanisms could contribute to diseases characterized by either an inadequate or an exaggerated inflammatory response.

Contribution of peripheral alpha 1A-adrenoceptors to pain induced by formalin or by alpha-methyl-5-hydroxytryptamine plus noradrenaline

We examined the peripheral adrenergic mechanisms involved in pain induced by alpha-methyl-5-hydroxytryptamine (alpha-methyl-5-HT) plus (+/-)-noradrenaline or prostaglandin E2 and by intraplantar formalin. Agents were injected s.c. into the plantar surface of rats' paws, and the paw lifting and licking response scored. Pain produced by alpha-methyl-5-HT (10 micrograms) plus noradrenaline (10 micrograms) was blocked by pretreatment with the alpha-adrenoceptor antagonists, phentolamine (10 micrograms) and prazocin HCl (alpha 1; 40 micrograms), but not by timolol (beta; 10 micrograms) or idazoxan (alpha 2; 40 micrograms). Phenylepherine, but not clonidine, substituted for noradrenaline to induce pain when combined with alpha-methyl-5-HT. The alpha 1A-adrenoceptor antagonist, WB-4101 (2-(2,6-dimethoxyphenoxyethyl) aminomethyl-1,4-benzodioxane HCl), but not the alpha 1B- adrenoceptor antagonist, chloroethylclonidine, also blocked the pain response produced by alpha-methyl-5-HT plus noradrenaline. Neither of these agents altered pain produced by alpha-methyl-5-HT plus prostaglandin E2 (0.1 microgram). Formalin-induced pain (1%, 50 microliters) was biphasic, and timolol increased the first phase response. The second phase was attenuated by 40% by phentolamine (10 micrograms) injected 10 min before formalin or at the beginning of the second phase; 30 micrograms did not produce a larger effect. Prazosin and WP-4101, but not idazoxan or chloroethylclonidine, also attenuated the second phase. Thus, activation of alpha 1A-adrenoceptors can contribute to pain, but pain induced by alpha-methyl-5-HT plus prostaglandin E2 is independent of adrenergic function, indicating that adrenergic function is not necessary for induction of pain by inflammatory mediators. alpha 1A-Adrenoceptor blockade attenuates pain when administered after development of pain, implying that peripheral adrenergic mechanisms contribute to ongoing maintenance of pain.

Mechanism of bradykinin-induced plasma extravasation in the rat knee joint

1. We have investigated the mechanism of bradykinin (BK)-induced plasma extravasation into the knee joint of the anaesthetized rat. Accumulation of [125I]-human serum albumin within the synovial cavity was used as a marker of increased vascular permeability. 2. Perfusion with BK (1 microM) produced significant plasma extravasation into the knee which was inhibited by co-perfusion of the selective bradykinin B2 receptor antagonist D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]-bradykinin (Hoe 140, 200 nM). 3. The bradykinin B1 receptor agonist, [des-Arg9]-BK (up to 100 mM), did not induce plasma extravasation into the knee joint, over this time period. 4. Chemical sympathectomy by chronically administered 6-hydroxydopamine (6-OHDA) did not inhibit bradykinin-induced plasma extravasation. Acute intra-articular perfusion with 6-OHDA (to stimulate transmitter release from sympathetic nerve terminals) at concentrations up to 50 mM did not induce significant plasma extravasation. Intra-articular perfusion of 100 mM 6-OHDA induced significant plasma extravasation but produced severe systemic toxicity. 5. The selective neurokinin1 (NK1) receptor antagonist, RP67580 (230 nmol kg-1), or receptor antagonists for the mast cell products histamine and 5-hydroxytryptamine did not significantly inhibit BK-induced plasma extravasation. 6. Co-perfusion of the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) (1 mM) did not significantly inhibit the response to BK. 133Xe clearance from L-NAME (1 mM)-injected joints was significantly (P < 0.05) reduced compared to D-NAME injected joints, suggesting a reduction in blood flow as a result of decreased basal NO production. Systemic administration of L-NAME at doses sufficient to produce significant and sustained elevation of blood pressure (5 or 30 mg kg-1, i.v. 15 min prior to BK perfusion) also failed to significantly inhibit the BK-induced response.7 We conclude that, in normal joints, BK induces plasma extravasation by acting on bradykinin B2 receptors and that this response is not dependent on secondary release of mediators from sympathetic nerve terminals, sensory nerves, mast cells or on generation of NO.

Neural regulation of neutrophil involvement in pulmonary inflammation

1. The high viscoelastic property of neutrophils is the major factor contributing to their extensive accumulation (more than 50% of circulating neutrophils) in the pulmonary microvasculature. 2. The cholinergic parasympathetic and adrenergic sympathetic nerves modulate the size of the pulmonary neutrophil pool by regulating arterial and venous pressures, increases in which promote or reduce neutrophil transit times, respectively. 3. Biochemical factors, such as the cytokines and complement, which act upon the neutrophils to increase their viscoelasticity and promote the interaction of neutrophil cell adhesion molecules with counter ligands on the endothelial cell, are the primary factors regulating the size of the pulmonary pool of vascular neutrophils. 4. The primary afferent nerves, through their release of substance P, are the most important neural elements regulating neutrophil accumulation and function. Substance P facilitates the actions of other inflammatory agents (e.g. LTB4, platelet activating factor) on neutrophil adhesion, migration and biochemical reactivity. 5. The sympathetic nervous system indirectly regulates neutrophil functions by regulating the release of an immunosuppressive factor from submandibular glands. 6. With continued, study of nervous system regulation of neutrophil function, the mechanisms by which psychological factors affect these cells will eventually be revealed.

Further substantiation of a significant role for the sympathetic nervous system in inflammation

This study provides significant new evidence substantiating a role of the postganglionic sympathetic neuron in plasma extravasation in the knee-joint of the rat. Increased plasma extravasation produced by the potent inflammatory mediator bradykinin was mimicked by 6-hydroxydopamine, a selective stimulator of sympathetic fibers. Various treatments (chemical sympathectomy, co-perfusion with the local anesthetic lidocaine, or co-perfusion with depolarizing concentrations of potassium) similarly modulated plasma extravasation induced by both bradykinin and 6-hydroxydopamine, but not that produced by platelet activating factor. We also showed that bradykinin is able to release norepinephrine in the knee-joint, indicating action on the sympathetic postganglionic neuron. In summary, these experiments provide substantial additional evidence supporting a significant contribution of the sympathetic post-ganglionic neuron terminal to inflammatory plasma extravasation.

Neurogenic and non-neurogenic mechanisms of plasma extravasation in the rat

We describe two distinct mechanisms for the enhancement of plasma extravasation in the knee joint of the rat. One is activated by bradykinin and is neurogenic; the other is activated by platelet-activating factor and is non-neurogenic. Bradykinin-induced synovial plasma extravasation is known to be dependent on the sympathetic postganglionic neuron terminal, and to involve prostaglandins, ATP, adenosine A2 receptor action, and the attraction and activation of neutrophils. In this study we found that bradykinin-induced plasma extravasation also involves endothelium-derived relaxing factor; specifically we found that bradykinin-induced plasma extravasation was antagonized stereospecifically by the inhibitor of endothelium-derived relaxing factor synthesis, NG-monomethyl-L-arginine. Perfused alone, platelet-activating factor produced an increase in synovial plasma extravasation which was markedly reduced by the platelet-activating factor receptor antagonists BN 52021 and WEB 2086 (these antagonists did not affect bradykinin-induced plasma extravasation). Platelet-activating factor-induced plasma extravasation was not affected by NG-monomethyl-L-arginine, indomethacin (a prostaglandin synthesis inhibitor), phenol 3-(5H-thiozolo[2,3b]quinazolin) (an A2 receptor adenosine antagonist), dextran sulfate (an inhibitor of leukocyte rolling), hydroxyurea (a depletor of leukocytes), chronic sympathectomy or the depletion of unmyelinated afferent fibers. Of note, the magnitude of platelet-activating factor-induced plasma extravasation was increased by co-perfusion with prostaglandin E2 and attenuated by co-perfusion with L-arginine; that is, two of the mediators involved in neurogenic bradykinin-induced plasma extravasation exerted an influence on non-neurogenic plasma extravasation. Separate mechanisms for bradykinin and platelet-activating factor plasma extravasation were further demonstrated in the streptozotocin-treated diabetic rat, in which there is a peripheral neuropathy.(ABSTRACT TRUNCATED AT 250 WORDS)

Potent antinociceptive effects of clonidine systemically administered in an experimental model of clinical pain, the arthritic rat

The effects of various doses of the alpha-2 adrenoceptor agonist clonidine administered systemically (30, 50 and 100 micrograms/kg i.v.), were investigated on the vocalization threshold to paw pressure in normal rats and in rats with Freund's adjuvant-induced arthritis. Previous results have suggested that there is an increase in the activity of the bulbospinal noradrenergic systems in these arthritic animals. In the present study, clonidine led to significant antinociceptive effects in both groups of rats. Clonidine was found to be highly effective in arthritic animals, even at the lower concentration: the elevation in threshold produced by 30 micrograms/kg i.v. was 160% in arthritic vs. 124% in normal rats. The effects of clonidine were prevented dose-dependently by pretreatment with yohimbine or idazoxan 250 to 1000 micrograms/kg i.v., in the two groups of rats, indicating clearly that the dose-dependent effects of i.v. clonidine are mediated by alpha-2 adrenoceptors.

Delta- and kappa-opioid agonists inhibit plasma extravasation induced by bradykinin in the knee joint of the rat

We used an experimental model of neurogenic inflammation, plasma extravasation induced by bradykinin or capsaicin, to study the effect of receptor-selective opioid agonists on plasma extravasation. Plasma extravasation was induced in the knee joint of the rat by continuous perfusion of either bradykinin (160 ng/ml), an inflammatory mediator produced at sites of tissue injury, that produces plasma extravasation significantly dependent on the sympathetic postganglionic neuron, or capsaicin (5 mg/ml), a C-fiber excitotoxin, that induces plasma extravasation that is dependent on both primary afferents and sympathetic post-ganglionic neurons. When selective delta-((d-Pen2,5)-enkephalin) or kappa-(trans-3,4-dichloro-N-methyl-N[2-(- pyrolidinyl)cyclohexyl]benzeneacetamide; U50,488H) opioid agonists were perfused with bradykinin, plasma extravasation was significantly attenuated. Co-perfusion of the non-selective opioid antagonist naloxone (1 microM), reversed this opioid-induced inhibition of bradykinin-induced plasma extravasation. In contrast, co-perfusion of a selective mu-opioid agonist (Tyr-d-Ala-Gly-NMe-Phe-Gly-ol) did not reduce bradykinin-induced plasma extravasation. Tyr-d-Ala-Gly-NMe-Phe-Gly-ol was, however, able to completely inhibit the plasma extravasation produced by capsaicin. These results suggest that delta- and kappa-, but not mu-selective opioids inhibit bradykinin-stimulated plasma extravasation, while a mu-selective opioid inhibits primary afferent-dependent plasma extravasation. Therefore, inhibition of neurogenic plasma extravasation by receptor-selective opioids may depend on the relative contribution to plasma extravasation of unmyelinated afferent and sympathetic postganglionic neuron terminals. Our findings can also explain, in part, the variation in anti-inflammatory effects of receptor-selective opioids reported in different inflammatory conditions.