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Tumor necrosis factor (TNF)-␣ has been reported to modulate brain injury, but remarkably, little is known about its effects on neurogenesis. We report that TNF-␣ strongly influences survival, proliferation, and neuronal differentiation in cultured subventricular zone (SVZ) neural stem/progenitor cells derived from the neonatal P1-3 C57BL/6 mice. By using single-cell calcium imaging, we

BackgroundHistamine is commonly acknowledged as an inflammatory mediator in peripheral tissues, leaving its role in brain immune responses scarcely studied. Therefore, our aim was to uncover the cellular and molecular mechanisms elicited by this molecule and its receptors in microglia-induced inflammation by evaluating cell migration and inflammatory mediator release.MethodsFirstly, we detected the expression of all known histamine receptor subtypes (H1R, H2R, H3R and H4R), using a murine microglial cell line and primary microglia cell cultures from rat cortex, by real-time PCR analysis, immunocytochemistry and Western blotting. Then, we evaluated the role of histamine in microglial cell motility by performing scratch wound assays. Results were further confirmed using murine cortex explants. Finally, interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) levels were evaluated by ELISA measurements to determine the role of histamine on the release of these inflammatory mediators.ResultsAfter 12 h of treatment, 100 μM histamine and 10 μg/ml histamine-loaded poly (lactic-co-glycolic acid) microparticles significantly stimulated microglia motility via H4R activation. In addition, migration involves α5β1 integrins, and p38 and Akt signaling pathways. Migration of microglial cells was also enhanced in the presence of lipopolysaccharide (LPS, 100 ng/ml), used as a positive control. Importantly, histamine inhibited LPS-stimulated migration via H4R activation. Histamine or H4R agonist also inhibited LPS-induced IL-1β release in both N9 microglia cell line and hippocampal organotypic slice cultures.ConclusionsTo our knowledge, we are the first to show a dual role of histamine in the modulation of microglial inflammatory responses. Altogether, our data suggest that histamine per se triggers microglia motility, whereas histamine impedes LPS-induced microglia migration and IL-1β release. This last datum assigns a new putative anti-inflammatory role for histamine, acting via H4R to restrain exacerbated microglial responses under inflammatory challenge, which could have strong repercussions in the treatment of CNS disorders accompanied by microglia-derived inflammation.

Brain inflammation is characterized primarily by microglia activation (1). Several stimuli, such as ATP (2), bloodderived factors, or microbial signals (e.g. lipopolysaccharide (LPS)), induce significant morphological changes in microglial cells (3). They become undistinguishable from active macrophages and are able to migrate and proliferate at sites of neuronal injury, where they release both neurotrophic and neurotoxic factors, and inflammatory mediators, such as adhesion molecules, cytokines, and complement molecules among others (4 -6). Consequently, microglia response remains controversial because it can either be beneficial or deleterious depending on the nature, concentration, and time of exposure to the activating stimulus, and the cellular interactions of the targeted tissue. Once the triggering stimulus wanes, microglia participate in the down-modulation of the immune response and in the regulation of their own apoptosis via secretion of antiinflammatory cytokines (3).One of the outcomes of microglia activation is the production of nitric oxide (NO) from the conversion of L-arginine to L-citrulline by Ca 2ϩ -independent inducible nitric oxide synthase (iNOS) 2 (7-9). NO is produced by numerous cells, and it is of particular importance for blood flow regulation, sleepwake cycle, food intake and thermal regulation, immune system function, and neuronal transmission (10). Particularly, in the central nervous system, NO regulation presents itself as an opportunity to intervene in human health. NO can grant neuroprotection through the following mechanisms: reduction of Ca 2ϩ influx, due to S-nitrosylation of caspase 3 and NR1 and NR2 subunits of the N-methyl-D-aspartate receptors, which leads to a decrease of cell death; activation of cyclic AMP-responsive element-binding protein and Akt via stimulation of the soluble guanylate cyclase-cyclic GMP-protein kinase G pathway; and generation of biliverdin, a precursor of bilirubin, which acts as an antioxidant and antinitrosive molecule, through the induction of the activity of heme oxygenase 1 (10).However, NO can act as a pathophysiological agent because it is associated with hypertension, diabetes, and heart failure among other pathologies (8). In the central nervous system, high amounts of NO inhibit mitochondrial cytochrome oxidase in neurons, causing them to depolarize and to release glutamate and ultimately to die by excitotoxicity via N-methyl-D-aspartate receptors (11,12). NO can also react with superoxide anions and form peroxynitrite, which detains strong oxidant properties and can damage cellular components when protein nitration takes place (10).

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