| Although the blood brain barrier (BBB) restricts free entrance of blood immune cells and large molecules into central nervous system, some infection-associated molecules like lipopolysaccharide can cross BBB whose permeability is increased during pathological condition and across the fenestrated capillaries of the circumventricular organs into the brain parenchyma to activate glia cells through its receptors on glia to evoke inflammatory reaction in brain and activate the hypothalamic-pituitary-adrenal axis. SEB (staphylococcal enterotoxin B ) is a kind of superantigen of which the influence on brain cells has not been systematically studied. Toll-like receptor 4 (TLR4) is the possible receptor of SEB, and major histocompability complex (MHC) class II molucules can bind to SEB too. Since glia cell express TLR4 and MHC classII molucules, we postulate that SEB may evoke immune reaction in brain and activate the hypothalamic-pituitary-adrenal axis. To confirm this hypothesis, we designed the following experiments.In order to get convincing results in our experiments, we modified the way to implant the cannula system for introcerebroventricular injection in Experiment One. We found succedaneums for some imported devices and devised instruments for fixing the cannula on thestereotaxic device made in China as well as on other stereotaxic device. And the using of cannula protector let the cannula system be fixed on the skull more soundly, and made it possible for the cannula system to be reused.In Experiment Two, we intracerebroventricularly injected SEB into rats brain to investigate whether glia cells and the paraventricular nucleus of hypothalamus(PVN) canreact to SEB by observing ERK1/2 phosphoration, IL-1β expression in the brain. And we intracerebroventricularly injected LPS as positive controls.The rats were domesticated for more than a week after the cannula implantation surgery. Then SEB/LPS/NS were injected intracerebroventricularly. We observed that:(1)Under basal condition,astrocytes on the meninges and ependyma cells express IL-1β, ependyma cells express small quantity of IL-1β, but there is few cells express IL-1β in brain parenchyma.(2) 3h and 6h after SEB i.c.v. injection, the expression of IL-1β of parenchymal microglia and astrocytes was induced,.Astrocytes in the glia scar express IL-1β when there is no immune stimulation, and their IL-lp expressions were upregulated 3h and 6h after SEB i.c.v. injection. And these phenomenon disappeared 12h after the injection.(3) 3h and 6h after SEB i.c.v. injection, SEB led to the phosphoration of ERK1/2 in microglia.(4)Only a small portion of pERK1/2 positive cells express IL-1β.(5) ERK1/2 in neurons of medial parvocellular and anterior parvicellular portions of PVN were phosphorated 3h and 6h after SEB i.c.v. injection. I.c.v. injection of LPS led to similar reaction on glia and PVN neurons.In Experiment Three, we observed the expression of APC surface moleculars (OX-6, B7-1, B7-2) and dendritic cell marker--OX-62 in the brain after SEB i.c.v. injection. We observed that: (1)The injury made by cannula implantaion led to the appearance of positive cells with the microglial morphology (OX-6+ B7-1+ B7-2+ OX-62+) around the cannula, and the cell number increased 12h after SEB injection. (2) There are few OX-6+ or B7-1+ or B7-2+ or OX-62+ cells in NS i.c.v.injected brains or surgical control brains except the parenchyma around the cannula. But 12h after SEB i.c.v.injection, positive cells with the microglial morphology (OX-6+ B7-1+ B7-2+ OX-62+) appeared in several brain regions including olfactory peduncle , septal area ,caudate-putmen, periamygdaloid cortex,dentate gyrus, medial habenular nucleus, dorsal thalamic nucleus, parenchymal around the third ventricle, arcuate nucleus,area postrema. And we postulate that these cells had the identity of both dendritic cells and microglia.Conclusion: the above results indicate that, (1) The innate immune function of glia was transient activated shortly after SEB i.c.v. injection. (2) When phenomenon in (1) weakened 12h after injecyion, large number of dendritic cells appeared in brain , thus...
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