The role of macrophages in degeneration and immune-mediated demyelination of the peripheral nervous system

Higher pain perception and lack of recovery from neuropathic pain in females: a behavioural, immunohistochemical, and proteomic investigation on sex-related differences in mice

In experimental and clinical pain studies, the sex of subjects was rarely taken into account, even if nociceptive inputs appear to be processed and modulated by partially distinct neural mechanisms in each sex. In this study we analysed, in male and female mice, behavioural and neuronal responses in developing, maintaining, and recovering from neuropathic pain. Experiments were carried out in adult CD1 mice by using Chronic Constriction Injury (CCI) as neuropathic pain model. We investigated the temporal trend of mechanical nociceptive threshold together with functional recovery of the injured paw, and the immunofluorescence staining of proteins associated with nerve injury and repair and with spinal gliosis, 7 and 121days after CCI. A proteomic analysis on proteins extracted from sciatic nerves was also performed. Male mice showed a gradual decrease of CCI-induced allodynia, the complete recovery occurring 81days after the sciatic nerve ligation. On the contrary, in female mice, allodynia was still present 121days after CCI. Sex-dependent differences also resulted from immunofluorescence experiments: in sciatic nerve, the expression of P0 and Neu200 is greater in neuropathic males than in neuropathic females, suggesting faster nerve regeneration. Proteomic analysis confirmed sex-related differences of proteins associated with nerve regenerative processes. In addition, the reactive gliosis induced by CCI at day 7, as revealed by colocalization of glial fibrillary acidic protein (astrocytes) and CD11b (microglia) with phosphorylated p38, disappeared 121 days after CCI in male but not in female mice. These results may have important therapeutic implications for the treatment of neuropathic pain.

Chronic inflammatory demyelinative polyneuropathy

Chronic inflammatory demyelinative polyneuropathy (CIDP) is an acquired polyneuropathy presumably of immunological origin. It is characterized by a progressive or a relapsing course with predominant motor deficit. The diagnosis rests on the association of non-length-dependent predominantly motor deficit following a progressive or a relapsing course associated with increased CSF protein content. The demonstration of asymmetrical demyelinating features on nerve conduction studies is needed for diagnosis. The outcome depends on the amplitude of axon loss associated with demyelination. CIDP must be differentiated from acquired demyelinative neuropathies associated with monoclonal gammopathies. CIDP responds well to treatment with corticosteroids, intravenous immunoglobulins, and plasma exchanges, at least initially.

Neurophysiological approach to disorders of peripheral nerve

Disorders of the peripheral nerve system (PNS) are heterogeneous and may involve motor fibers, sensory fibers, small myelinated and unmyelinated fibers and autonomic nerve fibers, with variable anatomical distribution (single nerves, several different nerves, symmetrical affection of all nerves, plexus, or root lesions). Furthermore pathological processes may result in either demyelination, axonal degeneration or both. In order to reach an exact diagnosis of any neuropathy electrophysiological studies are crucial to obtain information about these variables. Conventional electrophysiological methods including nerve conduction studies and electromyography used in the study of patients suspected of having a neuropathy and the significance of the findings are discussed in detail and more novel and experimental methods are mentioned. Diagnostic considerations are based on a flow chart classifying neuropathies into eight categories based on mode of onset, distribution, and electrophysiological findings, and the electrophysiological characteristics in each type of neuropathy are discussed.

Modulation of the visceromotor reflex by a lumbosacral ventral root avulsion injury and repair in rats

Increased abdominal muscle wall activity may be part of a visceromotor reflex (VMR) response to noxious stimulation of the bladder. However, information is sparse regarding the effects of cauda equina injuries on the VMR in experimental models. We studied the effects of a unilateral L6-S1 ventral root avulsion (VRA) injury and acute ventral root reimplantation (VRI) into the spinal cord on micturition reflexes and electromyographic activity of the abdominal wall in rats. Cystometrogram (CMG) and electromyography (EMG) of the abdominal external oblique muscle (EOM) were performed. All rats demonstrated EMG activity of the EOM associated with reflex bladder contractions. At 1 wk after VRA and VRI, the duration of the EOM EMG activity associated with reflex voiding was significantly prolonged compared with age-matched sham rats. However, at 3 wk postoperatively, the duration of the EOM responses remained increased in the VRA series but had normalized in the VRI group. The EOM EMG duration was normalized for both VRA and VRI groups at 8-12 wk postoperatively. CMG recordings show increased contraction duration at 1 and 3 wk postoperatively for the VRA series, whereas the contraction duration was only increased at 1 wk postoperatively for the VRI series. Our studies suggest that a unilateral lumbosacral VRA injury results in a prolonged VMR to bladder filling using a physiological saline solution. An acute root replantation decreased the VMR induced by VRA injury and provides earlier sensory recovery.

Extrinsic cellular and molecular mediators of peripheral axonal regeneration

The ability of injured peripheral nerves to regenerate and reinnervate their original targets is a characteristic feature of the peripheral nervous system (PNS). On the other hand, neurons of the central nervous system (CNS), including retinal ganglion cell (RGC) axons, are incapable of spontaneous regeneration. In the adult PNS, axonal regeneration after injury depends on well-orchestrated cellular and molecular processes that comprise a highly reproducible series of degenerative reactions distal to the site of injury. During this fine-tuned process, named Wallerian degeneration, a remodeling of the distal nerve fragment prepares a permissive microenvironment that permits successful axonal regrowth originating from the proximal nerve fragment. Therefore, a multitude of adjusted intrinsic and extrinsic factors are important for surviving neurons, Schwann cells, macrophages and fibroblasts as well as endothelial cells in order to achieve successful regeneration. The aim of this review is to summarize relevant extrinsic cellular and molecular determinants of successful axonal regeneration in rodents that contribute to the regenerative microenvironment of the PNS.

Wallerian degeneration and peripheral nerve conditions for both axonal regeneration and neuropathic pain induction

Wallerian degeneration is a cascade of stereotypical events in reaction to injury of nerve fibres. These events consist of cellular and molecular alterations, including macrophage invasion, activation of Schwann cells, as well as neurotrophin and cytokine upregulation. This review focuses on cellular and molecular changes distal to various types of peripheral nerve injury which simultaneously contribute to axonal regeneration and neuropathic pain induction. In addition to the stereotypical events of Wallerian degeneration, various types of nerve damage provide different conditions for both axonal regeneration and neuropathic pain induction. Wallerian degeneration of injured peripheral nerve is associated with an inflammatory response including rapid upregulation of the immune signal molecules like cytokines, chemokines and transcription factors with both beneficial and detrimental effects on nerve regeneration or neuropathic pain induction. A better understanding of the molecular interactions between the immune system and peripheral nerve injury would open the possibility for targeting these inflammatory mediators in therapeutic interventions. Understanding the pleiotropic effects of cytokines/chemokines, however, requires investigating their highly specific pathways and precise points of action.

Local peripheral effects of mu-opioid receptor agonists in neuropathic pain in rats

Our study was designed to demonstrate peripheral antinociception of the mu-opioid receptor agonists: morphine (MF), [D-Ala(2), N-Me-Phe(4), Gly(5)-ol]enkephalin (DAMGO), endomorphin-1 (EM-1) and endomorphin-2 (EM-2) in Bennett's rat model of neuropathic pain. All the agonists were effective in antagonizing allodynia after their intraplantar (i.pl.) but not subcutaneous (s.c.) administration. Opioid peptides: DAMGO, EM-1 and EM-2 were more effective compared with corresponding doses of morphine (opioid alkaloid) in alleviating chronic pain. Peripheral mu-opioid receptors mediated the observed effects, as was evidenced by the i.pl. treatment with naloxone methiodide (active only at the site of injection) and by cyprodime, a selective mu-opioid receptor antagonist. These results have shown that opioid peptides are effective also after local treatment, and that their peripheral use may be of therapeutic interest in long-term management of chronic pain.

Nerve conduction studies in selected peripheral nerve disorders

PURPOSE OF REVIEW

The physiological properties of nerve and muscle are influenced by pathological changes and the aim of this review is to discuss recent contributions of electrophysiological studies to the understanding and diagnosis of selected peripheral nerve disorders. The relationships between pathology and physiology emphasize the close interdependence between electrophysiological studies, clinical deficits and other laboratory information. Attention should be paid to the strengths and limitations of electrophysiological methods, considering their impact on diagnosis and treatment of patients.

RECENT FINDINGS

Several studies have shown particular pathophysiological profiles associated with different antibody subtypes in autoimmune peripheral neuropathies and this association further supports the suggestion of pathological specificity in both acute and chronic neuropathy. The sensitivity and specificity of physiological profiles therefore become increasingly important since some of these neuropathies are accessible to treatment. On the other hand, the pathophysiological and clinical profiles may be heterogeneous in patients with some disorders. This could be related to a more indistinct division between different types of pathology with increased understanding of pathogenetic mechanisms. Moreover, new insights into disturbed axonal function have stimulated attempts to develop methods to explore normal and diseased human nerve function.

SUMMARY

The exploration of axonal membrane and ion-channel function has become accessible using studies of excitability and are of potential value where conventional studies only provide nonspecific evidence of the number of fibers and the integrity of myelin. These studies will presumably become increasingly important in the years ahead considering the lack of understanding of the functional disturbances in axonal neuropathies.

Interleukin-18 is induced in acute inflammatory demyelinating polyneuropathy

T lymphocytes of the Th1 subset producing the proinflammatory cytokine interferon-gamma (IFN-gamma) have been implicated in the pathogenesis of immune-mediated diseases of the peripheral nervous system (PNS) such as the acute Guillain-Barré syndrome (GBS) and its animal model experimental autoimmune neuritis (EAN). Interleukin-18 (IL-18) is a potent IFN-gamma-inducing cytokine that is synthesized as an inactive precursor molecule and cleaved by caspase-1 into its mature active form. In our present study we analyzed the expression of IL-18 and caspase-1 in the nerve roots of EAN rats using reverse transcriptase-polymerase chain reaction and immunocytochemistry. Using an enzyme-linked immunosorbent assay, we furthermore determined IL-18 protein levels in paired serum and cerebrospinal fluid (CSF) samples from patients with GBS as well as from noninflammatory neurologic disease (NIND) controls. In EAN, IL-18 and caspase-1 mRNA levels in the nerve roots increased during the stage of active disease progression. Immunocytochemically, both perivascular and parenchymal IL-18 protein expression was increased in the roots of EAN rats and mainly associated with ED1+ macrophages stained on serial sections. IL-18 serum levels were significantly higher in GBS patients than in NIND controls (238+/-71 vs. 42+/-7 pg/ml, P<0.001). Our data implicate the Th1-inducing cytokine IL-18 in the pathogenesis of acute immune-mediated PNS demyelination.

Matrix metalloproteinase expression and inhibition after sciatic nerve axotomy

Wallerian degeneration is characterized by breakdown of myelin and axons with subsequent macrophage infiltration and removal of the degenerating nerve components. Proteinases of the matrix metalloproteinase (MMP) family seem to play an important role in demyelinating processes, since some of their members have been shown to cleave myelin basic protein. In the present study we investigated the expression of MMP-2 and MMP-9 (gelatinases A and B) during myelin removal after peripheral nerve trauma. After transection of the sciatic nerve an upregulation of MMP-2 and MMP-9 with a first peak 12 h and a second peak 48 h after axotomy was observed by zymography. These peaks correlate with the breakdown of the blood-nerve barrier, the accumulation of granulocytes, and the invasion of macrophages into the damaged nerves, respectively. Furthermore, MMP-2 was found to be upregulated in the contralateral nontransected nerves. Immunocytochemistry for MMP-9 and in situ zymography identified MMP-reactive cells within the distal nerve stump. Chloracetate esterase staining was used to detect granulocytes, which accumulated at the transection site and were colocalized with the in situ zymography signal. Wallerian degeneration of the transected nerve could be delayed either by intraperitoneal injections of hydroxamate (Ro 31-9790), a nonspecific MMP inhibitor, or by local application of an MMP-9-specific antibody. Following these treatment strategies, a decreased number of invading macrophages was seen in the nerves associated with an increased amount of preserved myelin sheaths. These results suggest that the invasion of macrophages into a transected peripheral nerve is accompanied by an increased expression of MMPs, particularly MMP-9. Thus, MMPs may seem to play an important role in the breakdown of the blood-nerve barrier and subsequent cell recruitment from the systemic circulation into the damaged nerve.

The role of TNF-alpha during Wallerian degeneration

The role of TNF-alpha in the course of Wallerian degeneration of the sciatic nerve was studied in control and TNF-alpha deficient mice. In control animals, the characteristic phenomena of Wallerian degeneration such as axon and myelin degeneration as well as macrophage recruitment with subsequent myelin removal were observed. In TNF-alpha deficient mice, in contrast, macrophage recruitment into the degenerating nerves was impaired resulting in a delayed myelin removal. However, the myelin phagocytic capacity of macrophages was not affected as it could be demonstrated by a similar myelin load of control and TNF-alpha deficient macrophages. These data indicate that the main function of TNF-alpha during Wallerian degeneration is the induction of macrophage recruitment from the periphery without affecting myelin damage or phagocytosis.

Lack of cross-tolerance between the antinociceptive effects of systemic morphine and asimadoline, a peripherally-selective kappa-opioid agonist, in CCI-neuropathic rats

The development of tolerance following repeated doses of morphine hinders the treatment of clinical pain. We have previously shown that morphine tolerance develops in neuropathic rats without cross-tolerance to a systemic kappa-opioid agonist; in the current work, using paw-pressure vocalization thresholds, we studied the antinociceptive effect of the peripherally-selective kappa (kappa)-opioid agonist, asimadoline, in both morphine-tolerant and opioid-naïve rats 2 weeks after sciatic nerve injury. In naïve rats, intraplantar (i.pl.) injection of asimadoline into the nerve-injured paw, at doses of 10, 15 and 20 (but not 30) microg, dose-dependently relieved the mechanical allodynia-like behaviour. The kappa-opioid antagonist, norbinaltorphimine, (30 microg, i.pl.) reversed this action; injection of asimadoline (15 microg) into the contralateral paw (i.pl.) or i.v., however, had no effect. These results confirm that at low doses, asimadoline exerts its action only in the periphery. In morphine-tolerant rats (after 10 mg/kg s.c. , twice daily for 4 days) and naïve, saline-pretreated rats, asimadoline (15 microg, i.pl.) relieved the mechanical allodynia-like behaviour to the same extent, indicating no cross-tolerance between morphine and the peripherally-selective drug. Our findings show promise for the treatment of neuropathic pain with low doses of peripherally-selective kappa-opioids.

Major histocompatibility complex class II expression and macrophage responses in genetically proven Charcot-Marie-Tooth type 1 and hereditary neuropathy with liability to pressure palsies

This study examined major histocompatibility complex (MHC) class II expression and macrophage infiltration in sural nerve biopsies from patients with genetically proven Charcot-Marie-Tooth (CMT) 1A and 1B and hereditary neuropathy with liability to pressure palsies (HNPP) by immunocytochemistry. In both young and older patients with duplication of the PMP22 gene, MHC class II expression was consistently up-regulated and not closely related to the extent of macrophage infiltration. On the other hand, MHC class II expression was more variable in CMT1A and CMT1B caused by point mutations and in HNPP. The extent of nerve pathology as assessed by teased fiber preparations or electron microscopy was not predictive for the degree of MHC class II expression in CMT1/HNPP. We conclude that MHC class II up-regulation is a common feature in hereditary neuropathies. As shown for the animal model of globoid cell dystrophy, it is conceivable that increased expression of MHC class II molecules in CMT1 and HNPP accelerates nerve pathology.

Peripheral component in the enhanced antinociceptive effect of systemic U-69,593, a kappa-opioid receptor agonist in mononeuropathic rats

The contribution of a peripheral action of the kappa-opioid receptor agonist U-69,593 (trans-3,4-dichloro-N-methyl-N-[7-(1-pyrrolidinyl) cycloexil] benzene-acetamide methanesulfonate) in the augmented antinociceptive effect of this substance was investigated in a well-established rat model of peripheral unilateral neuropathy (chronic constriction of the common sciatic nerve). Relatively low dose of systemic U-69,593 (0.75 mg/kg intravenous (i.v.)) and intraplantar (i.pl.) low doses of specific antagonists of kappa-(nor-binaltorphimine) or mu-(D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2: CTOP) opioid receptors were used. Vocalization thresholds to paw pressure were used as a nociceptive test. The i.pl. injection of nor-binaltorphimine (10-15 microg injected into the nerve-injured hind paw) had no effect on the antinociceptive effect of U-69,593. Higher doses (20-30 microg i.pl. nor-binaltorphimine) significantly reduced the effect of U-69,593 on this paw but not on the contralateral paw, an effect which plateaued at 30 microg. By contrast, the i.pl. injection of CTOP (1 microg into the nerve-injured paw) had no effect on U-69,593 antinociception, whereas it reduced the effect of systemic morphine in these animals. The doses of nor-binaltorphimine used, injected into the contralateral paw or i.v., failed to modify the antinociceptive effects of U-69,593 on either paw. These results provide evidence for a peripheral component in the enhanced antinociceptive effect of systemic U-69,593 in this model of neuropathic pain.

Concentration-dependent effects of pentoxifylline on migration and myelin phagocytosis by macrophages

The effects of pentoxifylline (POX) on macrophage migration and myelin uptake were studied in an in vitro model of myelin phagocytosis. The POX is a phosphodiesterase inhibitor which inhibits TNF-alpha (tumor necrosis factor alpha) production and reduces ICAM-1 (intercellular adhesion molecule-1) expression by macrophages. Both of these molecules have earlier been shown to be involved in the process of myelin recognition and degradation. In the present series of experiments, cocultured peripheral nerves and macrophages were treated with different concentrations of POX. Untreated controls were massively invaded by macrophages which ingested the degenerating myelin sheaths. High concentrations of POX (100 microg ml(-1)) inhibited macrophage invasion of the nerves. Lower POX concentrations (50 microg ml(-1)), in contrast, lead to an increased myelin uptake by phagocytic cells without affecting macrophage migration. These data indicate that POX may regulate different effector functions of macrophages such as migration and myelin phagocytosis during Wallerian degeneration. This is important for inflammatory demyelinating conditions in the central or peripheral nervous system (PNS) in which macrophages are also important effector cells. Since POX is used as an immunomodulatory drug in demyelinating diseases, its effects on the described macrophage functions may be of high relevance. An increased myelin uptake during Wallerian degeneration may also support a more efficient axonal regeneration by removing axonal outgrowth inhibitors.

The role of the mouse macrophage scavenger receptor in myelin phagocytosis

Myelin phagocytosis during Wallerian degeneration and immune-mediated demyelination depends on the action of mononuclear cells of the monocyte/macrophage system. The present study investigated the role of the macrophage scavenger receptor, a trimeric membrane glycoprotein, in myelin uptake by macrophages. Two in vitro models of myelin phagocytosis were used: an organ culture model of mouse peripheral nerves exposed to cocultured macrophages and a quantitative flow cytometric assay. Different concentrations of the monoclonal rat anti-mouse scavenger receptor antibody (2F8) were applied to these systems to selectively block the macrophage scavenger receptor. Concentration-dependent effects on macrophage migration and myelin uptake were seen when the macrophage scavenger receptor was blocked by the antibody 2F8. Low concentrations reduced myelin phagocytosis by the invading macrophages; higher concentrations completely abolished macrophage invasion of the nerves. Using a quantitative flow cytometric assay it was also shown that the 2F8 antibody inhibits phagocytosis of myelin in a dose-dependent manner. These data indicate that the macrophage scavenger receptor is involved in myelin phagocytosis by macrophages.

The role of macrophages in Wallerian degeneration

The present review focuses on macrophage properties in Wallerian degeneration. The identification of hematogenous phagocytes, the involvement of cell surface receptors and soluble factors, the state of activation during myelin removal and the signals and factors leading to macrophage recruitment into degenerating peripheral nerves after nerve transection are reviewed. The main effector cells in Wallerian degeneration are hematogenous phagocytes. Resident macrophages and Schwann cells play a minor role in myelin removal. The macrophage complement receptor type 3 is the main surface receptor involved in myelin recognition and uptake. The signals leading to macrophage recruitment are heterogenous and not yet defined in detail. Degenerating myelin and axons are suggested to participate. The relevance of these findings for immune-mediated demyelination are discussed since the definition of the role of macrophages might lead to a better understanding of the pathogenesis of demyelination.

Role of macrophages in the stimulation and regeneration of sensory nerves by transposed granulation tissue and temporal aspects of the response

Application of granulation tissue, which is rich in macrophages, to a peripheral nerve induces a conditioning effect, in that it enhances the regeneration capability of peripheral nerves after a test crush lesion. The temporal aspects of this response and the role of macrophages and interleukin-1 beta (IL-1 beta) were studied in the sciatic nerves of 71 rats. Granulation tissue was implanted close to the sciatic nerve and test crush lesions were applied after various periods of time (0-21 days). Regeneration was evaluated after an additional two, three, four, or six days. Regeneration distances were longer in granulation-treated nerves than in nerves treated with subcutaneous tissue. Furthermore, in animals in which the test crush lesion was made at the same time as the granulation tissue was implanted (n = 6), regeneration distances were longer, 8.1 (0.8) mm compared with 7.2 (0.6), than those in which the crush was made after conditioning intervals of 3 (n = 6, 7.6 (0.4) compared with 6.9 (0.4), p = 0.03); 7 (n = 6, 7.4 (0.4) compared with 6.6 (0.1), p = 0.03); and 21 days [(n = 8, 7.2 (0.6) compared with 6.4 (0.5)]. Inactivation of the granulation tissue by freezing suppressed the conditioning effect. There were numerous ED1 and ED2 positive macrophages as well as positive staining for IL-1 beta in the granulation tissue on day 0. Positive staining for IL-1 beta was also seen in nerve fibres as well as in non-neuronal cells after a conditioning interval. The results suggest that regeneration is stimulated by factors released from the cells of the granulation tissue, and that the amount of factors released or the responsiveness of the regenerating nerve change during the conditioning interval.

Liposome-mediated monocyte depletion during wallerian degeneration defines the role of hematogenous phagocytes in myelin removal

Newly recruited hematogenous mononuclear cells of the monocyte/macrophage system are suggested to be important effector cells in myelin removal during Wallerian degeneration. Their role has extensively been studied in various in vitro and in vivo models. However, there has been much controversy concerning the role of hematogenous vs. resident cells of the peripheral nervous system in Wallerian degeneration. The present study used a recently established technique to deplete the hematogenous monocyte population by application of dichloromethylene diphosphonate-containing liposomes. Intravenously injected liposomes containing dichloromethylene diphosphonate (Cl2MDP) are ingested by macrophages and monocytes and cause temporary and selective depletion of these cells. The number of LFA-1- and Mac-1- positive macrophages within the nerves was significantly reduced when liposomes were injected shortly after nerve transsection. In these nerves, myelin degradation was significantly less, indicating an essential role of newly recruited phagocytes in this process. Macrophage invasion of degenerating nerves occurred within the first 2 days after transsection. Resident cells of the peripheral nerve participate in myelin removal since macrophage depletion did not completely abolish myelin degradation. These results confirm the important role of hematogenous phagocytes in myelin removal during Wallerian degeneration.

Further evidence for a peripheral component in the enhanced antinociceptive effect of systemic morphine in mononeuropathic rats: involvement of kappa-, but not delta-opioid receptors

The contribution of a peripheral action of morphine in the augmented antinociceptive effect of this substance was re-evaluated in a well established rat model of peripheral unilateral mononeuropathy (chronic constriction of the common sciatic nerve), using a relatively low dose of systemic morphine (1 mg/kg i.v.) and local low doses of specific antagonists of kappa- (nor-binaltorphimine) or delta-(naltrindole) opioid receptors. Vocalization thresholds to paw pressure were used as a nociceptive test. Escalating doses of nor-binaltorphimine (10-30 micrograms injected locally into the nerve injured paw) significantly and dose dependently reduced the effect of morphine on this paw but not on the contralateral paw, an effect which plateaued at 30 micrograms. By contrast, the local injection of naltrindole (30-40 micrograms into the nerve injured paw) had no effect on morphine analgesia. The doses of opioid receptor antagonists used, injected i.v., in the contralateral paw, or alone in the nerve injured paw had no significant effect. These results suggest that the peripheral effect of systemic morphine in this model of neuropathic pain could be mediated not only by mu- but also by kappa-opioid receptors.

Cytokines in inflammatory brain lesions: helpful and harmful

Multiple sclerosis (MS) is thought to be an autoimmune disease. In healthy individuals, the T cells of the immune system, when activated by an infectious agent, regularly traffic across an intact blood-brain barrier, survey the CNS and then leave. In MS, for reasons that are only gradually being understood, certain events in the peripheral immune response and in the brain cause some autoreactive T cells to stay in the CNS. Their presence initiates infiltration by other leukocytes and activation and recruitment of endogenous glia to the inflammatory process, ultimately leading to the destruction of myelin and the myelin-producing cell, the oligodendrocyte, and the dysfunction of axons. The key mediators in the subsequent cycles of histological damage and repair, and clinical relapse and remission are thought to be adhesion molecules, chemokines and cytokines.

The membrane attack complex of complement mediates peripheral nervous system demyelination in vitro

The present study used cocultures of rat dorsal root ganglia (DRG) and peritoneal macrophages to define the role of activated complement components during demyelination. The complement cascade was activated in vitro by treatment of the cultures with natural rat serum and lipopolysaccharides. Complement activation was examined by detection of the membrane attack complex of complement (MAC) with an antibody directed against rat C5-9. Detection of MAC in vitro by immunoelectron microscopy was associated with morphological changes of the myelin sheath. The sheath's regular structure was disrupted. Myelin lamellae were split and showed signs of decompaction. These changes were followed by a selective macrophage attack on myelin sheaths resulting in demyelination. Schwann cell viability was not affected by complement activation. Axons and sensory ganglion cells also survived this attack. The specificity of the complement effect was tested in experiments using treatment regimens with natural rat serum or lipopolysaccharides alone. In these experiments, no morphological changes of the myelin sheath were observed as well as no macrophage attack on myelin.

Visible light induced changes in the immune response through an eye-brain mechanism (photoneuroimmunology)

The immune system is susceptible to a variety of stresses. Recent work in neuroimmunology has begun to define how mood alteration, stress, the seasons, and daily rhythms can have a profound effect on immune response through hormonal modifications. Central to these factors may be light through an eye-brain hormonal modulation. In adult primates, only visible light (400-700 nm) is received by the retina. This photic energy is then transduced and delivered to the visual cortex and by an alternative pathway to the suprachiasmatic nucleus (SCN). The SCN is a part of the hypothalamic region in the brain believed to direct circadian rhythm. Visible light exposure also modulates the pituitary and pineal gland which leads to neuroendocrine changes. Melatonin, norepinephrine and acetylcholine decrease with light activation, while cortisol, serotonin, gaba and dopamine levels increase. The synthesis of vasoactive intestinal polypeptide (VIP), gastrin releasing peptide (GRP) and neuropeptide Y (NPY) in rat SCN has been shown to be modified by light. These induced neuroendocrine changes can lead to alterations in mood and circadian rhythm. All of these neuroendocrine changes can lead to immune modulation. An alternative pathway for immune modulation by light is through the skin. Visible light (400-700 nm) can penetrate epidermal and dermal layers of the skin and may directly interact with circulating lymphocytes to modulate immune function. However, even in the presence of phototoxic agents such as eosin and rose bengal, visible light did not produce suppression of contact hypersensitivity with suppresser cells. In contrast to visible light, in vivo exposure to UV-B (280-320 nm) and UV-A (320-400 nm) radiation can only alter normal human immune function by a skin mediated response. Each UV subgroup (B, A) induces an immunosuppressive response but by differing mechanisms involving the regulation of differing interleukins and growth factors. Some effects observed in humans are: inhibition of allergic contact dermatitis; inhibition of delayed hypersensitivity to an injected antigen; prolongation of skin-graft survival and induction of a tumor-susceptible state. The following article will review much of the progress in this field and explore possible areas of future research.

Mechanisms of macrophage recruitment in Wallerian degeneration

Monocytes/macrophages are important effector cells in myelin removal during Wallerian degeneration. Experiments with the mouse mutant C57BL/Ola revealed prolonged axonal survival and reduced phagocytic cell recruitment after nerve transsection. In the present study, we compared the course of Wallerian degeneration in peripheral nerves of C57BL and C57BL/Ola mice in vivo and in vitro. In vivo experiments confirmed earlier investigations describing a delayed degeneration in the C57BL/Ola mutant compared with C57BL mice which were used as control animals without abnormal degeneration. Quite different results were seen in experiments in vitro: degenerating nerve segments of C57BL/Ola mice revealed pronounced axonal breakdown even in the absence of non-resident phagocytic cells. There was no difference in vitro compared with degenerating nerves from C57BL mice. The differences observed between the in vivo and in vitro situations suggest that axonal breakdown plays an important role in the initiation of macrophage recruitment to degenerating peripheral nerves.

Immunopathogenesis and treatment of the Guillain-Barré syndrome--Part I

The etiology of the Guillain-Barré syndrome (GBS) still remains elusive. Recent years have witnessed important advances in the delineation of the mechanisms that may operate to produce nerve damage. Evidence gathered from cell biology, immunology, and immunopathology studies in patients with GBS and animals with experimental autoimmune neuritis (EAN) indicate that GBS results from aberrant immune responses against components of peripheral nerve. Autoreactive T lymphocytes specific for the myelin antigens P0 and P2 and circulating antibodies to these antigens and various glycoproteins and glycolipids have been identified but their pathogenic role remains unclear. The multiplicity of these factors and the involvement of several antigen nonspecific proinflammatory mechanisms suggest that a complex interaction of immune pathways results in nerve damage. Data on disturbed humoral immunity with particular emphasis on glycolipid antibodies and on activation of autoreactive T lymphocytes and macrophages will be reviewed. Possible mechanisms underlying initiation of peripheral nerve-directed immune responses will be discussed with particular emphasis on the recently highlighted association with Campylobacter jejuni infection.

Evidence for a peripheral component in the enhanced antinociceptive effect of a low dose of systemic morphine in rats with peripheral mononeuropathy

In a rat model of peripheral mononeuropathy produced by moderate constriction of the sciatic nerve, we have shown that various i.v. doses of morphine and selective opioid agonists produce potent and long-lasting antinociceptive effects on the vocalization threshold to paw pressure. For all the opioids, the antinociceptive effects were more marked for the paw on the nerve-injured side (nerve-injured paw) than for the sham-operated paw. One contributory mechanism could be a peripheral action of the opioid agonists in the nerve-injured paw. This hypothesis was tested in the present study, using systemic morphine and low doses of local naloxone or its quaternary salt naloxone methiodide, exhibiting peripherally acting antagonist properties. The effects of escalating doses of naloxone (0.5-2 microgram injected i.v. or intraplantar into the nerve-injured paw) or naloxone methiodide (5-30 micrograms into the nerve-injured paw) on the antinociceptive effect of morphine (1 mg/kg i.v.) were evaluated using the vocalization threshold to paw pressure in neuropathic rats at two weeks after placing ligatures, a time when the behavioural pain-related disorders have reached a maximum.(ABSTRACT TRUNCATED AT 250 WORDS)

Lymphocytic infiltration and expression of intercellular adhesion molecule-1 in photochemically induced ischemia of the rat cortex

The contribution of the immune system to the pathogenesis of ischemic lesions is still uncertain. We have analyzed leukocyte infiltration in photochemically induced focal ischemia of the rat parietal cortex by immunocytochemistry. Between 1 and 2 days after photothrombosis, CD5+ T cells adhered to subpial and cortical vessels and infiltrated the ischemic lesion prior to macrophages. By day 3 numerous T cells and some macrophages, whose number increased further between day 3 and day 7, had infiltrated the border zone around the lesion sparing the center. In addition, CD5-/CD8+ lymphocytes that probably represent natural killer cells were found. Intercellular adhesion molecule-1 (ICAM-1) was expressed on endothelial cells on days 1 and 2 and in the border zone on infiltrating leukocytes from day 3 to day 7. Starting on day 7, macrophages infiltrated the core of the lesion to remove debris. When the entire lesion was covered by macrophages at day 14, the number of T cells had decreased and ICAM-1 immunoreactivity was no longer found in or around the infarct. In conclusion, our study shows that ischemic lesions can lead to a local immune reaction in the CNS. Thus, blocking of lymphocyte-derived cytokines or cell adhesion molecules may provide a new approach to confining the sequelae of stroke.

Dorsal root ganglia cocultured with macrophages: an in vitro model to study experimental demyelination

The present investigation introduces an in vitro model to study macrophage properties during demyelination. Rat dorsal root ganglia (DRG) were cultured for obtaining myelinated peripheral nerve fibers. These cultures were exposed to non-resident macrophages. In untreated control cultures, there was no indication of myelin removal by the added macrophages. DRG were exposed to enzymatically generated oxygen radicals using the xanthin/xanthin oxidase or the glucose/glucose oxidase system. Assessment of Schwann cell viability and ultrastructural morphology revealed different patterns of cell cytotoxicity and morphological changes in different experiments. High concentrations caused complete tissue necrosis of the DRG, while low concentrations did not affect either cell viability or ultrastructural morphology. Under intermediate experimental conditions, oxygen radicals caused non-lethal Schwann cell damage leading to Schwann cell retraction and myelin sheath rejection. Myelin lamellae were disrupted and decompacted. These changes were followed by a selective macrophage attack on myelin sheaths, resulting in demyelination. Axons, Schwann cells and sensory ganglion cells survived this attack. The specificity of the oxygen radical effects was tested in experiments using the oxygen radical scavengers catalase and superoxide dismutase. Catalase prevented the described effects on cell morphology and subsequently blocked demyelination by non-resident macrophages.

Expression of NGF-receptors during immune-mediated and lysolecithin-induced demyelination of the peripheral nervous system

Nerve growth factor receptor, expressed in Schwann cells during early development of the PNS, is rarely found in the normal mature PNS. Following nerve transection nerve growth factor receptor is re-expressed at high levels in the Schwann cells of the denervated nerve fibres. In this study we asked if demyelination caused by an immune-mediated process or by physical destruction of myelin is associated with expression of nerve growth factor receptor, and if so, what cells are positive. We examined spinal roots and sciatic nerves from rats with experimental autoimmune neuritis and sciatic nerves from rats with focal demyelination produced by local application of lysolecithin. Both in 1 micron serial cryosections and in immunostained teased nerve fibres we found that the Schwann cells that were associated with demyelinated internodes expressed nerve growth factor receptor. Immunoreactivity for nerve growth factor receptor appeared first in a perinuclear ring, probably corresponding to the Golgi complex. In completely demyelinated internodes the postmitotic Schwann cells ensheathing the axons expressed nerve growth factor receptor on their plasmalemma. Neighbouring Schwann cells with intact myelin sheaths remained nerve growth factor receptor negative. In contrast, Schwann cells of neighbouring unmyelinated fibres expressed prominent nerve growth factor receptor immunoreactivity. These data further indicate that expression of nerve growth factor receptor by Schwann cells does not require axonal degeneration, but can be stimulated by some factor associated with acute demyelination.

Tumor necrosis factor-alpha in immune-mediated demyelination and Wallerian degeneration of the rat peripheral nervous system

This study reports on the immunocytochemical localization of tumor necrosis factor-alpha (TNF alpha) in immune-mediated demyelination and Wallerian degeneration of the rat peripheral nervous system (PNS) using teased nerve fiber preparations. In experimental autoimmune neuritis induced by active immunization (EAN) or by adoptive transfer of autoreactive T cells (AT-EAN), macrophages passing blood vessels as well as macrophages adherent to nerve fibers were TNF alpha-positive. Large post-phagocytic macrophages at later stages of demyelination were TNF alpha-negative. Intraperitoneal application of an anti-TNF alpha antibody to EAN rats significantly reduced the degree of inflammatory demyelination, suggesting a pathogenic role for TNF alpha. After nerve transection only macrophages located within degenerating nerve fibers were TNF alpha-positive, while those entering and leaving nerves were negative. TNF alpha produced by macrophages seems to be involved in immune-mediated demyelination and non-immune myelin degradation after axotomy. While interferon-gamma (IFN gamma) is present in EAN nerves and may act as a local stimulus for TNF expression, the nature of this signal in Wallerian degeneration in the absence of IFN gamma is unknown.