Activated macrophages and microglia induce dopaminergic sprouting in the injured striatum and express brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor. (1/3431)

Nigrostriatal dopaminergic neurons undergo sprouting around the margins of a striatal wound. The mechanism of this periwound sprouting has been unclear. In this study, we have examined the role played by the macrophage and microglial response that follows striatal injury. Macrophages and activated microglia quickly accumulate after injury and reach their greatest numbers in the first week. Subsequently, the number of both cell types declines rapidly in the first month and thereafter more slowly. Macrophage numbers eventually cease to decline, and a sizable group of these cells remains at the wound site and forms a long-term, highly activated resident population. This population of macrophages expresses increasing amounts of glial cell line-derived neurotrophic factor mRNA with time. Brain-derived neurotrophic factor mRNA is also expressed in and around the wound site. Production of this factor is by both activated microglia and, to a lesser extent, macrophages. The production of these potent dopaminergic neurotrophic factors occurs in a similar spatial distribution to sprouting dopaminergic fibers. Moreover, dopamine transporter-positive dopaminergic neurites can be seen growing toward and embracing hemosiderin-filled wound macrophages. The dopaminergic sprouting that accompanies striatal injury thus appears to result from neurotrophic factor secretion by activated macrophages and microglia at the wound site.  (+info)

The central cannabinoid receptor (CB1) mediates inhibition of nitric oxide production by rat microglial cells. (2/3431)

Upon activation, brain microglial cells release proinflammatory mediators, such as nitric oxide (NO), which may play an important role in the central nervous system antibacterial, antiviral, and antitumor activities. However, excessive release of NO has been postulated to elicit immune-mediated neurodegenerative inflammatory processes and to cause brain injury. In the present study, the effect of cannabinoids on the release of NO from endotoxin/cytokine-activated rat cortical microglial cells was evaluated. A drug dose-dependent (0.1 microM-8 microM) inhibition of NO release from rat microglial cells was exerted by the cannabinoid receptor high-affinity binding enantiomer (-)-CP55940. In contrast, a minimal inhibitory effect was exerted by the lower affinity binding paired enantiomer (+)-CP56667. Pretreatment of microglial cells with the Galphai/Galphao protein inactivator pertussis toxin, cyclic AMP reconstitution with the cell-permeable analog dibutyryl-cAMP, or treatment of cells with the Galphas activator cholera toxin, resulted in reversal of the (-)-CP55940-mediated inhibition of NO release. A similar reversal in (-)-CP55940-mediated inhibition of NO release was effected when microglial cells were pretreated with the central cannabinoid receptor (CB1) selective antagonist SR141716A. Mutagenic reverse transcription-polymerase chain reaction, Western immunoblot assay using a CB1 receptor amine terminal domain-specific antibody, and cellular colocalization of CB1 and the microglial marker Griffonia simplicifolia isolectin B4 confirmed the expression of the CB1 receptor in rat microglial cells. Collectively, these results indicate a functional linkage between the CB1 receptor and cannabinoid-mediated inhibition of NO production by rat microglial cells.  (+info)

CNS wound healing is severely depressed in metallothionein I- and II-deficient mice. (3/3431)

To characterize the physiological role of metallothioneins I and II (MT-I+II) in the brain, we have examined the chronological effects of a freeze injury to the cortex in normal and MT-I+II null mice. In normal mice, microglia/macrophage activation and astrocytosis were observed in the areas surrounding the lesion site, peaking at approximately 1 and 3 d postlesion (dpl), respectively. At 20 dpl, the parenchyma had regenerated. Both brain macrophages and astrocytes surrounding the lesion increased the MT-I+II immunoreactivity, peaking at approximately 3 dpl, and at 20 dpl it was similar to that of unlesioned mice. In situ hybridization analysis indicates that MT-I+II immunoreactivity reflects changes in the messenger levels. In MT-I+II null mice, microglia/macrophages infiltrated the lesion heavily, and at 20 dpl they were still present. Reactive astrocytosis was delayed and persisted at 20 dpl. In contrast to normal mice, at 20 dpl no wound healing had occurred. The rate of apoptosis, as determined by using terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling, was drastically increased in neurons of ipsilateral cortex of the MT-I+II null mice. Our results demonstrate that MT-I+II are essential for a normal wound repair in the CNS, and that their deficiency impairs neuronal survival.  (+info)

Thromboembolic events predispose the brain to widespread cerebral infarction after delayed transient global ischemia in rats. (4/3431)

BACKGROUND AND PURPOSE: Transient distal platelet accumulation after common carotid artery thrombosis (CCAT) leads to hemodynamic, metabolic, and molecular events that may influence the response of the postthrombotic brain to secondary insults. We investigated how a thromboembolic insult would affect histopathological outcome when combined with an ischemic insult induced 24 hours later. METHODS: Three groups of rats underwent either (1) CCAT+10 minutes of normothermic 2-vessel occlusion (n=6), (2) CCAT+sham ischemia procedures (n=6), or (3) sham CCAT procedures+10 minutes of 2-vessel occlusion (n=6). At 7 days, rats were perfused for quantitative histopathological and immunocytochemical analysis. RESULTS: Rats undergoing combined insults (group 1) had significantly larger areas of ischemic injury (P<0.05) within the cerebral cortex, striatum, and thalamus compared with the other, single-injury groups. Increased ischemic damage included selective neuronal necrosis, infarction, and focal hemorrhage. By means of glial fibrillary acidic protein immunocytochemistry and lectin histochemistry, reactive astrocytes and microglia were found to be associated with widespread tissue necrosis. In contrast, infrequent infarction or CA1 hippocampal neuronal necrosis was observed in groups 2 and 3, respectively. CONCLUSIONS: A prior thromboembolic event is a risk factor for widespread cerebral infarction and hemorrhage when combined with a delayed ischemic insult. The understanding of what factors enhance the susceptibility of the postthrombotic brain to secondary insults may aid in the development of neuroprotective strategies to be applied after transient ischemic attacks to prevent the initiation of stroke.  (+info)

Cyclopentenone prostaglandins suppress activation of microglia: down-regulation of inducible nitric-oxide synthase by 15-deoxy-Delta12,14-prostaglandin J2. (5/3431)

Mechanisms leading to down-regulation of activated microglia and astrocytes are poorly understood, in spite of the potentially detrimental role of activated glia in neurodegeneration. Prostaglandins, produced both by neurons and glia, may serve as mediators of glial and neuronal functions. We examined the influence of cyclopentenone prostaglandins and their precursors on activated glia. As models of glial activation, production of inducible nitric-oxide synthase (iNOS) was studied in lipopolysaccharide-stimulated rat microglia, a murine microglial cell line BV-2, and IL-1beta-stimulated rat astrocytes. Cyclopentenone prostaglandins were potent inhibitors of iNOS induction and were more effective than their precursors, prostaglandins E2 and D2. 15-Deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) was the most potent prostaglandin among those tested. In activated microglia, 15d-PGJ2 suppressed iNOS promoter activity, iNOS mRNA, and protein levels. The action of 15d-PGJ2 does not appear to involve its nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) because troglitazone, a specific ligand of PPARgamma, was unable to inhibit iNOS induction, and neither troglitazone nor 15d-PGJ2 could stimulate the activity of a PPAR-dependent promoter in the absence of cotransfected PPARgamma. 15d-PGJ2 did not block nuclear translocation or DNA-binding activity of the transcription factor NFkappaB, but it did inhibit the activity of an NFkappaB reporter construct, suggesting that the mechanism of suppression of microglial iNOS by 15d-PGJ2 may involve interference with NFkappaB transcriptional activity in the nucleus. Thus, our data suggest the existence of a novel pathway mediated by cyclopentenone prostaglandins, which may represent part of a feedback mechanism leading to the cessation of inflammatory glial responses in the brain.  (+info)

T cell immunity induced by allogeneic microglia in relation to neuronal retina transplantation. (6/3431)

Microglia share a lineage relationship with bone marrow-derived monocytes/macrophages and dendritic cells, and their inclusion in retinal and brain transplants may function as "passenger leukocytes. " In other solid allografts, passenger leukocytes are the primary sources of immunogenicity, triggering alloimmune rejection. We have conducted a series of in vitro and in vivo studies examining the capacity of microglia cultured from forebrain to activate alloreactive T cells and to induce and elicit alloimmunity. Cultured microglia expressed class II MHC molecules and costimulatory molecules (B7-1, B7-2, and CD40), and they secreted IL-12. Cultured microglia injected s.c. into naive recipients induced allospecific delayed hypersensitivity and elicited delayed hypersensitivity directed at alloantigens. Cultured microglia differed from conventional APCs by secreting significant amounts of mature TGF-beta2, but smaller amounts of IL-12. Moreover, while both cultured microglia and conventional APC stimulated T cell proliferation in vitro, microglia directed the responding T cells toward the Th2 pathway in which IL-4, but not IL-2 and IFN-gamma, was secreted. The abilities of microglia to secrete TGF-beta2, to stimulate alloreactive Th2 cells, and to induce anterior chamber associated immune deviation when injected into the eye of naive allogeneic mice suggest that they are not typical passenger leukocytes. The unique functional properties of cultured microglia may account for the capacity of neonatal retinal tissue transplanted into the eye to alter the systemic alloimmune response in a manner that delays, but does not prevent, graft rejection.  (+info)

The origin and function of soluble CD14 in experimental bacterial meningitis. (7/3431)

Murine experimental meningitis models induced by either Escherichia coli LPS, live Streptococcus pneumoniae, or Listeria monocytogenes were used to study the origin and potential function of soluble CD14 (sCD14) in the brain during bacterial meningitis. Whereas intracerebral infection caused only a minor and/or transient increase of sCD14 levels in the serum, dramatically elevated concentrations of sCD14 were detected in the cerebrospinal fluid. Reverse-transcriptase PCR and FACS analysis of the leukocytes invading the subarachnoid compartment revealed an active amplification of CD14 transcription and concomitant surface expression. These findings were confirmed by in situ hybridization and immunohistochemical analysis. In contrast, parenchymal astrocytes and microglial cells were shown not to significantly contribute to the elevated levels of sCD14. Simultaneous intracerebral inoculation of rsCD14 and S. pneumoniae resulted in a markedly increased local cytokine response. Taken together, these data provide the first evidence that sCD14 can act as an inflammatory co-ligand in vivo. Thus, during bacterial meningitis, sCD14 is massively released by intrathecal leukocytes, and the sCD14 found in the cerebrospinal fluid can play an important role in the pathogenesis of this disease.  (+info)

Down-regulation of microglial cyclo-oxygenase-2 and inducible nitric oxide synthase expression by lipocortin 1. (8/3431)

1. Activated microglial cells are believed to play an active role in most brain pathologies, during which they can contribute to host defence and repair but also to the establishment of tissue damage. These actions are largely mediated by microglial secretory products, among which are prostaglandins (PGs) and nitric oxide (NO). 2. The anti-inflammatory protein, lipocortin 1 (LC1) was reported to have neuroprotective action and to be induced by glucocorticoids in several brain structures, with a preferential expression in microglia. In this paper we tested whether the neuroprotective effect of LC1 could be explained by an inhibitory effect on microglial activation. 3. We have previously shown that bacterial endotoxin (LPS) strongly stimulates PGE2 and NO production in rat primary microglial cultures, by inducing the expression of the key enzymes cyclo-oxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), respectively. 4. Dexamethasone (DEX, 1-100 nM) and LC1-derived N-terminus peptide (peptide Ac2-26, 1-100 microg ml(-1)) dose-dependently inhibited the production of both PGE2 and NO from LPS-stimulated microglia. The inhibitory effects of DEX on NO and of the peptide on NO and PGE2 synthesis were partially abrogated by a specific antiserum, raised against the N-terminus of human LC1. The peptide Ac2-26 did not affect arachidonic acid release from control and LPS-stimulated microglial cultures. 5. Western blot experiments showed that the LPS-induced expression of COX-2 and iNOS was effectively down-regulated by DEX (100 nM) and peptide Ac2-26 (100 microg ml(-1)). 6. In conclusion, our findings support the hypothesis that LC1 may foster neuroprotection by limiting microglial activation, through autocrine and paracrine mechanisms.  (+info)