Trauma-induced glial proliferation: possible involvement of the immune system

Ciclamilast ameliorates adjuvant-induced arthritis in a rat model

We assessed the effect of a novel and selective phosphodiesterase 4 (PDE4) inhibitor, ciclamilast, on chronic inflammation in adjuvant-induced arthritis (AIA), a rat model of rheumatoid arthritis (RA), and acute inflammation in the rat and mouse model of carrageenan-induced paw edema and peritonitis. Our results showed that daily oral administration of ciclamilast at 1, 3, and 10 mg/kg dose-dependently inhibited the increase in hind paw volume of rats with AIA. The inhibition of paw edema was associated with inhibition of both the production of cytokines such as TNF-α, IL-1β, and IL-6 and cell infiltration assessed in subcutaneous paw tissue. Moreover, there was significantly less tissue destruction in the ciclamilast-treated rats compared to the vehicle-treated rats, as assessed by radiographic analysis and histopathological evaluation. In the two acute inflammation models, ciclamilast inhibited carrageenan-induced paw edema in rats and inflammatory cell migration into the peritoneal cavity in mice in a dose-dependent manner. These results not only suggest that ciclamilast, as a disease-modifying antirheumatic drug (DMARD), can attenuate RA but also provide proof of principle that a PDE4 inhibitor may be useful for the treatment of arthritis.

Central administration of methotrexate reduces mechanical allodynia in an animal model of radiculopathy/sciatica

We have recently reported that injury to a lumbar root in a rat model of radiculopathy produces spinal glial activation associated with elevated proinflammatory cytokines. Based on our hypothesis that central neuroinflammatory processes may manifest clinically as radicular pain, we undertook pharmacological intervention using the immunosuppressive agent methotrexate (MTX). The L5 lumbar spinal root (central to the dorsal root ganglia) was exposed unilaterally and loosely constricted with chromic gut. In the prevention (phase I) study, MTX was administered intrathecally (1 mg/kg) and around the spinal root (1 mg/kg) at surgery and at days 2 and 4 postsurgery (group A). Saline injection was employed for the control group (group B). Sham operated animals were administered MTX to determine the potential for behavioral/neural side effects (group C). In the existing pain paradigm (phase II) study, the experiment was extended to day 14 with three additional groups. The same dose and method of delivery of MTX or saline was administered as in phase I in the first week on days 0, 2, and 4 and in the second week on days 7, 9, and 11 postsurgery. To measure the effects of MTX on existing behaviors saline was administered in the first week and MTX during the second (group D; Saline:MTX). The control group received saline during both weeks (group E; Saline:Saline). To examine the possible recurrence of radicular pain after MTX termination, MTX was given in the first week and saline in the second (group F; MTX:Saline). Gait disturbance and mechanical allodynia (using von Frey filaments) were assessed up to day 7 in the prevention study (Phase I) and day 14 in the existing pain paradigm (Phase II). The L5 spinal cord segments were harvested for assessment of immunohistochemical glial activation using the antibodies OX-42 (microglial marker) and glial fibrillary acidic protein (GFAP: astrocytic marker) and for the presence of Major Histocompatibility Complex (MHC) Class II expression. Group C (Sham+MTX) did not demonstrate any evidence of gait disturbance or mechanical allodynia after MTX administration. The rats in group B (Surgery+Saline) demonstrated mechanical allodynia from one day postsurgery to the time of euthanization. When allodynia was assessed using the 12 g von Frey filament, the MTX treated rats in group A showed significantly decreased mechanical allodynia as compared to the saline treated rats (group B) (repeated measured ANOVA, P<0.0001). In the phase II study, the rats in group D (Saline:MTX) and E (Saline:Saline) showed robust allodynia in the first week after the surgery. In the second week, mechanical allodynia significantly decreased in group D, while mechanical allodynia continued in the saline treated group (repeated measured ANOVA, P=0.0121). Allodynia was significantly attenuated in group F (MTX: Saline) as compared to the response in groups D and E at day 7 (one-way ANOVA, P<0.0001) and remained significantly lower as compared to group E up to day 11 postsurgery (one-way ANOVA, P9=0. 0013: P11=0.0048). OX-42 and GFAP expression were elevated in the gray matter of the L5 spinal section in all groups that underwent the root ligature with chromic gut (Groups A, B, D-F). There were no significant differences in glial activation between the groups. However, spinal expression of MHC II was markedly reduced in the MTX treated group as compared with the saline treated group. The exact mechanism of action of MTX in attenuating mechanical allodynia has not yet been elucidated. The present results indicate that MTX administration may offer a new treatment modality for radicular pain with or without disc herniation as well as directing new research into the development of novel immunomodulators for the treatment of chronic neuropathic and radicular pain.

Interleukin-2 as a neuroregulatory cytokine

Interleukin-2 (IL-2), the cytokine also known as T-cell growth factor, has multiple immunoregulatory functions and biological properties not only related to T-cells. In the past decade, substantial evidence accumulated to suggest that IL-2 is also a modulator of neural and neuroendocrine functions. First, extremely potent effects of IL-2 on neural cells were discovered, including activities related to cell growth and survival, transmitter and hormone release and the modulation of bioelectric activities. IL-2 may be involved in the regulation of sleep and arousal, memory function, locomotion and the modulation of the neuroendocrine axis. Second, the concept that IL-2 could act as a neuroregulatory cytokine has been supported by reports on the presence in rodent and human brain tissues of IL-2-like bioactivity, IL-2-like immunoreactivity, IL-2-like mRNA, IL-2 binding sites, IL-2 receptor (IL-2R alpha) and beta chain mRNA and IL-2R immunoreactivity. IL-2 and/or IL-2R molecules mainly localize to the frontal cortex, septum, striatum, hippocampal formation, hypothalamus, locus coeruleus, cerebellum, the pituitary and fiber tracts, such as the corpus callosum, where they are likely expressed by both neuronal and glial cells. Although the molecular biology of the brain IL-2/IL-2R system (including its relation to IL-15/IL-15R alpha) is not yet fully established by cloning and complete sequencing of all respective components, similarities (and to some extent differences) to peripheral counterparts are now apparent. The ability of IL-2 to readily penetrate the blood-brain barrier further suggests that this cytokine could regulate interactions between peripheral tissues and the central nervous system. Taken together, these data suggest that IL-2 of either immune and CNS origin can have access to functional IL-2R molecules on neurons and glia under normal conditions. Additionally, dysregulation of the IL-2/IL-2 receptor system could lead or contribute to functional and pathological alterations in the brain as in the immune system. Understanding the neurobiology of the IL-2/IL-2 receptor system should also help to explain neurologic, neuropsychiatric and neuroendocrine side effects occurring during IL-2 treatment of peripheral and brain tumors. Immunopharmacological manipulation either aiming at the activation or suppression of IL-2 signaling should consider functional interference with constitutive and inducible IL-2 receptors on brain cells in order to fulfil the high expectations associated with the use of this cytokine as a promising agent in immunotherapies, especially of brain tumors.

Macrophages and astroglial interactions in repair to brain injury

The response to brain injury appears to involve a well-coordinated interaction between microglia, extrinsic macrophages and glial cells. The proliferation of glial cells at the site of the injury appears necessary to reseal the brain. Most data support the view that glial cell (and fibroblast and endothelial cell) proliferation is driven by IL-1-like factors liberated by the invaded macrophages. Although less well established, most data, including our own suggest that glial cells contribute to the neutrotrophic response found after brain injury. In vitro evidence suggests that glial cell-mediated production of neurotrophic factors may also depend, like glial cell proliferation, on actions of interleukins (e.g., IL-1) at the site of the injury. Moreover, evidence of in vivo experiments, showing that immunosuppressants inhibit the glial response and that inhibition of glial proliferation suppresses the neurotrophic response are in line with this view. Restoration of the damaged brain site may also be compatible with the lack of T and B cell infiltration at the lesioned site. Factors such as prostaglandins and TGF-beta released from glial cells may be involved in controlling and counteracting a threatening immune attack. In conclusion, tissue repair in the brain appears to be centered around regulatory properties of glial cell proliferation, enhancement of neuronal growth and inhibition of a local immune response.

Epidermal growth factor treatment during early postnatal development: glutamine synthetase and glutamate decarboxylase activities in mouse brain

Results of experiments in cell cultures suggested that epidermal growth factor might influence an early stage of astroglial or neuronal cell differentiation. In order to evaluate this hypothesis the effects of subcutaneous and intracerebral treatment with epidermal growth factor on glutamine synthetase, an astroglial marker enzyme, and glutamate decarboxylase activity, a marker enzyme of GABAergic neurons, were investigated during postnatal development of mouse brain. Epidermal growth factor, at the dose used, induced the well-known effects of the in vivo treatment, such as a decrease in body weight and a precocious incisor eruption and eyelid opening. A decrease in forebrain and cerebellum wet weight was also observed. However, repeated epidermal growth factor treatment, during early postnatal life, failed to influence glutamine synthetase activity in forebrain or cerebellum, while a significant decrease was observed in the brain stem. No effect of epidermal growth factor on forebrain glutamate decarboxylase activity was observed. Although epidermal growth factor receptors have been detected in the newborn rodent brain, the role of this growth factor in brain development remains to be elucidated.

Effect of trophic factors, released after hippocampal injury, on astroglial cell proliferation

An increase in astrocyte mitogenic factors and in some specific astroglial enzymatic activities after neuronal injury has been observed. Our study is concerned with the effect of the intracerebral administration of ibotenic acid (IBO) into the rat hippocampus. IBO injection causes a selective degeneration of neurons while sparing afferent fibers. We observed a transient increase in glutamine synthetase activity, a well-known astroglial marker, reaching a peak at 9-15 days after injury in lesioned hippocampus. We investigated the presence of astrocyte mitogenic factors at various times after toxin injection. Crude extracts, prepared from lesioned hippocampi 4, 9, and 14 days after IBO injection, were tested for the ability to stimulate [methyl-3H]thymidine incorporation into rat astroglial cell cultures. Crude extracts prepared 9 and 14 days after IBO injection showed a higher mitogenic activity compared to extracts prepared 4 days after lesion. Mitogenic activity of injured brain extracts was suppressed by heat inactivation (100 degrees C for 10 min).

The astroglial response to autonomic tissue grafts

Autonomic (superior cervical) ganglia were grafted either into the IV ventricle where minimal trauma occurred or directly into the cerebral cortex which was necessarily traumatic. Previous studies have shown that host astroglia may migrate into autonomic tissue grafts. The purpose of the present study was to compare and contrast the astroglial response in allo- and autografts. By monitoring the host response in the two model sites using glial fibrillary acidic protein (GFAP) immunostaining in 1 micron plastic sections we sought to determine the role of injury stimulus in astroglial migration. In addition, these models could be used to investigate any potential differences in glial reactivity produced by allo- or autograft antigenic stimulation. In both ventricular and parenchymal locations, astroglia migrated progressively into allografts. Migration, which could have taken place along anastomotic vascular connections, began after one week and was continual, eventually replacing graft neural tissue. Astrocytic processes appeared enlarged and highly immunoreactive only as they entered the allografts or were in close association with the choroid plexus; adjacent host astrocytes were unaltered. Glial migration was greatly reduced in ventricular autografts but in the parenchymal site was nearly comparable to that of allografts. It was suggested that certain immunological factors may be involved in glial reactivity or migration considering the observed differences in the non-traumatic model whereas tissue damage stimulus played a major role in migration in both allo- and autografts. In no instances were typical astrocytic end-feet found on the autonomic graft vessels. The host astrocytic response to grafted autonomic tissue occurred significantly later (5-7 days) than the host endothelial response. This observation indicates that the graft vessels were original, intrinsic ones and the astrocytic invasion played no role in influencing endothelium with regards to brain-barrier properties.

Suloctidil increases the rat brain cortex microvascular regeneration after a lesion

A "cavity" lesion made by aspiration in the rat occipital cortex induces a parenchymal and a vascular reaction in its vicinity. The first was mainly characterized by cellular necrosis and gliosis, the second by an increase of the vascular network. In vehicle treated rats, a 50% significant increase of the vascular network was observed around the cavity 4 days after the lesion, in comparison to the uninjured contralateral cortex. The effects of a vasoactive substance, suloctidil, on the vascular reaction was studied in the brain cortex. A single oral dose of suloctidil (30 mg/kg; 2 hours before the sacrifice) gave the same effect as the vehicle group. After 8 days of suloctidil oral administration (30 mg/kg; twice daily: 4 days before lesion and 4 days after) a significant increase (123%) of the vascular network was observed around the cavity. The hypothetical ways by which a chronic treatment of suloctidil induces this increase of the neovascularization observed after cortical lesion are discussed.

Interleukin-2-like activity in injured rat brain

The lymphokine interleukin-2 (IL-2) promotes division and maturation of oligodendrocytes in culture. We now report that a IL-2-like activity was present in injured rat brain. The ion-exchange properties of this activity were similar to those of splenocyte IL-2 but its apparent molecular weight was higher. Brain IL-2-like activity was highest in the tissue immediately adjacent to the injury, reaching a maximal activity of about 8000 U/g tissue after 10 days postlesion. The mitogenic activity of injured-brain extracts on astrocytes and CTLL thymocytes was partially inhibited by monoclonal antibodies to murine IL-2 receptor. However, pure human IL-2 did not have mitogenic activity for cultured rat astrocytes. Purified astrocytes, alone or stimulated in a variety or ways, did not produce IL-2-like activity.

A new model for quantification of microvascular regeneration after a lesion of the rat cerebral cortex

The purpose of this study is to validate a method for the quantification of the neovascularization in the vicinity of a lesion made in the cerebral rat cortex. A cavity, made by aspiration in the occipital cortex of young rats, induces around the lesion a parenchymal and vascular reaction. The parenchymal reaction is characterized by cellular necrosis and gliosis. The vascularization is more dense around the cavity than in normal cortex. Morphometric analysis indicates, 8 days after the lesion, a 130% increase of the total length of the vessels in comparison to the contralateral normal cortex.

Hippocampal neurotrophic factor: characterization and response to denervation

The rat hippocampus contains an acidic macromolecular neurotrophic factor (NTF) which supports the survival of cultured chick ciliary ganglion cells. Hippocampal NTF increases approximately 2-fold from birth to adulthood with no further change with aging. Disruption of extrinsic inputs to the hippocampus from the entorhinal cortex, locus coeruleus or contralateral hippocampus, but not from the septum, results in an increase in the concentration of NTF in the hippocampus. Destruction of intrinsic hippocampal neurons by kainic acid treatment is accompanied by a large increase in hippocampal NTF, a result consistent with a glial origin for the factor. This conclusion is supported by the finding that a lesion-induced rise in NTF can be suppressed by administration of methotrexate, an inhibitor of gliosis.

The control of glial populations in brain: changes in astrocyte mitogenic and morphogenic factors in response to injury

Injury to rat brain induces a 3-10-fold increase in the activity of factors capable of stimulating astrocyte DNA synthesis and cell division in vitro. Maximum mitogenic activity was reached 10-15 days post-lesion in both the tissue surrounding the wound and in the gelfoam filling the wound cavity. Factors capable of transforming the astrocyte morphology from polygonal-flat to fibrous-like (morphogens) could also be observed in brain tissue and showed increased activity beginning at 10 days postlesion. On the other hand, morphogenic activity was very low or absent in gelfoam extracts until 15 days postlesion. Both mitogenic and morphogenic factors were nondiffusible and were partly temperature and trypsin sensitive, i.e. they had the properties of protein-like substances, but seemed different from both epidermal and fibroblast growth factors. As judged by their filtration behavior on Amicon membranes, the molecular weight of mitogens and morphogens ranged from lower than 30,000 to greater than 100,000. Inhibitors of both mitogenic and morphogenic activities with molecular weight lower than 30,000 seemed to be also present in the brain extracts. The factors described here can account for the processes of astrocytosis and astrogliosis observed in vivo in response to CNS injury.