Expression of chemokine receptors in the rat brain

RANTES: a new prostaglandin dependent endogenous pyrogen in the rat

Fever, a hallmark of disease, is a highly complex process initiated by the action of a number of endogenous pyrogens on the thermosensitive cells of the brain. We describe the activity of RANTES, a chemotactic cytokine, as intrinsically pyrogenic in the rat, when it is delivered directly to the thermosensitive region of the rat's anterior hypothalamic, pre-optic area (AH/POA). RANTES, microinjected into the AH/POA in a dose of 1, 5, 10, 15, 25 or 50 pg, produces an immediate and intense dose-related fever following injection. Increasing the dose to 100 pg did not result in a further increase in the febrile response. No significant change in body temperature was produced by heat-inactivated RANTES. The intrahypothalamic injection of antibodies against RANTES (2.0 microg, 15 min prior to RANTES) significantly blocked the fever induced by this chemokine. Pretreatment with ibuprofen blocked the fever induced by RANTES. In order of potency, the magnitude of the febrile response induced by RANTES was greater than that produced with equipotent doses of either macrophage inflammatory protein-1beta or interleukin-6. The results thus demonstrate that RANTES is the most potent endopyrogen discovered thus far and exerts its action directly on pyrogen-sensitive cells of the AH/POA through a prostaglandin-dependent pathway.

Proinflammatory cytokine, chemokine, and cellular adhesion molecule expression during the acute phase of experimental brain abscess development

Brain abscess represents the infectious disease sequelae associated with the influx of inflammatory cells and activation of resident parenchymal cells in the central nervous system. However, the immune response leading to the establishment of a brain abscess remains poorly defined. In this study, we have characterized cytokine and chemokine expression in an experimental brain abscess model in the rat during the acute stage of abscess development. RNase protection assay revealed the induction of the proinflammatory cytokines interleukin (IL)-1alpha, IL-1beta, IL-6, and tumor necrosis factor-alpha as early as 1 to 6 hours after Staphylococcus aureus exposure. Evaluation of chemokine expression by reverse transcription-polymerase chain reaction demonstrated enhanced levels of the CXC chemokine KC 24 hours after bacterial exposure, which correlated with the appearance of neutrophils in the abscess. In addition, two CC chemokines, monocyte chemoattractant protein-1 and macrophage inflammatory protein-1alpha were induced within 24 hours after S. aureus exposure and preceded the influx of macrophages and lymphocytes into the brain. Analysis of abscess lesions by in situ hybridization identified CD11b+ cells as the source of IL-1beta in response to S. aureus. Both intercellular adhesion molecule-1 and platelet endothelial cell adhesion molecule expression were enhanced on microvessels in S. aureus but not sterile bead-implanted tissues at 24 and 48 hours after treatment. These results characterize proinflammatory cytokine and chemokine expression during the early response to S. aureus in the brain and provide the foundation to assess the functional significance of these mediators in brain abscess pathogenesis.

Thermal hyperalgesia and mechanical allodynia produced by intrathecal administration of the human immunodeficiency virus-1 (HIV-1) envelope glycoprotein, gp120

Astrocytes and microglia in the spinal cord have recently been reported to contribute to the development of peripheral inflammation-induced exaggerated pain states. Both lowering of thermal pain threshold (thermal hyperalgesia) and lowering of response threshold to light tactile stimuli (mechanical allodynia) have been reported. The notion that spinal cord glia are potential mediators of such effects is based on the disruption of these exaggerated pain states by drugs thought to preferentially affect glial function. Activation of astrocytes and microglia can release many of the same substances that are known to mediate thermal hyperalgesia and mechanical allodynia. The aim of the present series of studies was to determine whether exaggerated pain states could also be created in rats by direct, intraspinal immune activation of astrocytes and microglia. The immune stimulus used was peri-spinal (intrathecal, i.t.) application of the Human Immunodeficiency Virus type 1 (HIV-1) envelope glycoprotein, gp120. This portion of HIV-1 is known to bind to and activate microglia and astrocytes. Robust thermal hyperalgesia (tail-flick, TF, and Hargreaves tests) and mechanical allodynia (von Frey and touch-evoked agitation tests) were observed in response to i.t. gp120. Heat denaturing of the complex protein structure of gp120 blocked gp120-induced thermal hyperalgesia. Lastly, both thermal hyperalgesia and mechanical allodynia to i.t. gp120 were blocked by spinal pretreatment with drugs (fluorocitrate and CNI-1493) thought to preferentially disrupt glial function.

Glial and neuronal cells express functional chemokine receptor CXCR4 and its natural ligand stromal cell-derived factor 1

Chemokines are a family of proteins that chemoattract and activate cells by interacting with specific receptors on the surface of their targets. The chemokine stromal cell-derived factor 1, (SDF1), binds to the seven-transmembrane G protein-coupled CXCR4 receptor and acts to modulate cell migration, differentiation, and proliferation. CXCR4 and SDF1 are reported to be expressed in various tissues including brain. Here we show that SDF1 and CXCR4 are expressed in cultured cortical type I rat astrocytes, cortical neurons, and cerebellar granule cells. In cortical astrocytes, prolonged treatment with lipopolysaccharide induced an increase of SDF1 expression and a down-regulation of CXCR4, whereas treatment with phorbol esters did not affect SDF1 expression and down-modulated CXCR4 receptor expression. We also demonstrated the ability of human SDF1alpha (hSDF1alpha) to increase the intracellular calcium level in cultured astrocytes and cortical neurons, whereas in the same conditions, cerebellar granule cells did not modify their intracellular calcium concentration. Furthermore, in cortical astrocytes, the simultaneous treatment of hSDF1alpha with the HIV-1 capside glycoprotein gp120 inhibits the cyclic AMP formation induced by forskolin treatment.