| Subfornical organ (SFO) located at anterior roof of the third ventricle,hippocampal ventral commissure is on its dorsal, the interventricular foramen is on its ventral.On median sagittal section of rat brain, SFO is longer spindle in shape,its middle portion (body portion) is the widest in diameter, its anteroventral end (ventral stem) and postodorsal end (dorsal stem) are narrower. On coronal section of the rat brain the two stem portions are disk-like whereas the body portion is hemispherical in shape. Under light microscopic observation, its ependyma is composed of single cubic epithelium, in which the tanycytes with single cilium are in majority;its parenchymal portions are rich in microvasculature, among which there are a variety of cells densely, the majority of them appear to be the neuroendocrine-like cell and neuroglia and neurofibers are less in number.Under electron microscopic observation, capillaries of SFO are fenestrated ones, the endothelium of them are short of the tight junction,their basement membrane are not intact, the gaps between the endothelium and basement membrane are widened, to which the gaps within the endothelium are opened, the end feet of astrocytes surrond the capillaries not completely, and on the luminal surface of the endothelium some small vesicles are adhere to it, all of which suggesting SFO short of blood brain barrier (BBB). Therefore SFO belongs to a typical circumventricular organs (CVOs). SFO, Organum vasculum lamina terminalis (OVLT) and area postrema (AP) are also called the sensory CVOs (SCVOs) by Gross et al,which could sense changes of the blood-bearing molecular signals ,so called windows of the brain. It has been8confirmed that SFO may participate in many functions such as cardiovascular modulation, drinking behaviour, neuroendocrine regulation and so on,so that it play an important role in homeostasis. Though it has long been believed that CVOs might take part in immune reaction within the brain, but no detailed studies ever presented up to now.so this is a unsolved mystery indeed.The brain do have immune system itself, but it still belongs to an immune-privileged organ, that is another mystery. The present study is to investegate such significance of SFO standing for CVOs as sensing both blood-bearing immune signal molecules and chemical molecules in cerebrospinal fluid, and participating in modulation of brain's immune reaction with some morphological methods.According to its morphological characteristics, there are reasons to infer that SFO may take part in neuroimmunological modulation. It has been also proved that SCVO including SFO have distinct behavior in passing such blood-bearing cytokines as IL-1, TNF, and so on,so that we feel confident for feasibility of the present study.In the present study changes of NOS positive cells after injection of LPS and apoptotic ependymal cells, the relationship between expression of immediate early gene c-fos and astrocytes, and comparison of changes between SFO and rest regions of the brain in different time-points were investigated with NADPH-d histochemistry, apoptosis in SITU detection of TUNEL, TEM and SEM, fluorescein double labeling of immunohistochemistry, and laser scanning confocal microscope (CLSM).Endotoxin of colibacillus is a LPS produced by external coat of the G" bacteria.peripheral administration of LPS can induce several acute reaction such as high fever, lowering of pain threshold, speeding of metabolism, activating a series of neuroendocrine activities, and enhance of many hormone levels in plasma, suggesting immunological stress in the body.in such a condition what morphological changes could occur in the brain.NO has associated with inflammation and autoimmune reaction and influenced secretion of various interleukines, promoting production of IL-1a and IL- P , whereas inhibiting production of IL-6 derived from macrophages and hepatic macrophages, thus NO is recognized as a new immunomodulator. As a indicator of catalyzing production of NO, we observed the NOS-positive cell...
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