| Objectives: The choroid plexuses (CPs), located within the brain ventricles, can be viewed as a tight epithelium enclosing a vascularized stroma, and as such form an interface between the blood and the cerebrospinal fluid (CSF). CSF secretion is obviously a key feature of the CPs. This secretion is the result of complex inorganic ion exchanges across the tight epithelium of the CP, mainly driven by the activities of the Na+- K+-ATPase located at the CSF-facing membrane of the epithelial cells, and of the carbonic anhydrase. By electron microscopic cytochemical techniques, we will focus on four enzymes in the choroid plexus epithelium of SD rats which are closely concerned with cell function (ATPase—providing energy, ACPase—the sign enzyme of lysosome),hoping to more realize the subcellular localization in choroid plexus epithelium.We will also discuss its significance in the secretion, absorbtion and circulation of CSF. It will offer morphological evidence for us to more realize the anatmization and physiology of the brain. At the same time, It will have wide application foreground in the pathogenesis of hydrocephalous, meningitis, neurodegeneration diseases and so on.Methods: 80 normal adult SD rats of both sexes are selected, weighted 200-350 gram, routine breeding, natruly illumination, randomely grouping into four groups for the four enzymes. After intraperitoneal hydrochloride aldehyde anesthesia,the choriod plexus of lateral, third, fourth ventricle are rapidly removed and immersed in the corresponding fixative for 1 hour for AKPase,5'-NTase and Mg2+-ATPase,and for 3 hour for ACPase cytochemistry. For AKPase, the lead citrate method is selected; For ACPase, the lead nitrate method is selected; For 5'-NTase,the Uusitalo-Karnovsky method is selected; For Mg2+-ATPase, the Wachstein-Meisel method is selected. Following fixation, the choriod plexus was washed 2 hour or overnight in a cold 0.1M cacodylate buffer pH 7.2 with 8% sucrose. The washed tissues were immensed in the incubation media at 37℃. The choriod plexus was rainsed again in the buffer solution, postfixed in 1% osmium tetroxide for 60min at 0-4℃,dehydrated in a graded series of acetone and then in propylene oxide and Epon mixture for endosmosis, and then embedded in Epon 812. After ultrathin sectioning with a LKB Ultrotome, the specimen were usually stained with uranyl acetate for 5 min, and observed at an JEM-1230 transmission electron microscope.Cytochemistry control experiment:(1)absence of the substrate in the incubation medium;(2)60℃for 30 min before incubation;(3)in the presence of specific inhibitor for incubation(levomisole for AKPase).Rsults: (1) Morphological Observation: There are three components in TEM: the capicillary core, the epithelium cells surrounding the connective tissue. The choroid plexus epithelium is cuboid monolayer, with its round or oval nucleus at the basal part. Lots of mitochondria, smooth endoplasmic reticulum, Golgi complex are at the top part of the epithelial cells. The free ribosomes and some lysosomes are diffusely through the cell cytoplasm. The apical surface is extended as numerous digiform microvilli, and on the basal surface of the cell, the plasmalemma tends to be extensively infolded. The lateral cell membranes of adjoining cells are tortuous, interdigitating, and possess an apical tight junction. The capillaries of the choroid plexus stroma are of the fenestrated type with very thin endothelial walls. The stromal connective tissue is composed of a loose network of collagen fibers, secreted by occasional elongated fibroblasts. Polymorphic epiplexus cells lie on the ventricular surface of the epithelial cells, in close association with the microvilli border. (2) The enzyme cytochemistry observation of Acid phosphatase on the Rat choroid plexus: In the transmission electron microscope, we observed that electron dense reaction products are only at the sites of lysosomes with prefixication in 2% paraformaldehyde and 2% glutaraldehyde ,we also qbserved positive reaction for this enzyme in the endocytoplasmic reticulum near the trans face of Golgi cisternae with prefixication in 2% paraformaldehyde and 0.5% glutaraldehyde. There are no reaction products in the control group and no difference between the three ventricles. (3) Ultrascytochemical observation of Alkaline phoshatase on the Rat choroid plexus epithelium: In the transmission electron microscope, we observed that electron dense reaction products are at the sites of the plasma membrane of mocrovilli and the basal infoldings, at the junctions between epithelial cells, in the firocytes of the stroma and the endothelial cells of the capillary wall. We also observed positive reaction for this enzyme in the cytoplasm, the plasma membrane of various cell organelles such as lysosome, Golgi omplexs, mitochondria etc. We see no difference between the three ventricles. (4) Ultracytochemical observation of Mg2+-ATPase on the Rat choroid plexus epithelium: In the transmission electron microscope, we observed that electron dense reaction products are at the sites of the plasma membrane of microvilli and the basal infoldings, at the junctions between epithelial cells. Mg2+-ATPase reaction products are also found at the stroma and the endothelium cells of the capillary vessels. There are no reaction products in the control group, and no differences are seen between the three ventricles. (5) Ultracytochemical observation of 5'-NTase on the Rat choroid plexus epithelium: In the transmission electron microscope, we observed that electron dense reaction products are at the junctions between epithelial cells. There are no reaction products neither at the sites of the plasma membrane of microvilli and the basal infoldings, nor at the stroma and the endothelium cells of the capillary vessels. There are no reaction products in the control group, and no differences are seen between the three ventricles.Conclusion: We discussed the subcellular localization of ACPase and speculated that the role of acid phosphatase in the choroid plexus is probably in the uptake of materials from the CSF or the storage of the waste products of cell metabolism. ACPase may play a great role in maintain internal environment homeostasis. We speculated that the role of Alkaline phosphatase in the choroid plexus is probably in preventing the entry of phosphate esters into brain tissue and/or participating in transphosphorylation process, and then participating in the active transport of some substances. It can also be considered as part of the enzyme barrier. The magnesium-activated ATPase at the borders of the choroid plexus epithelial cells might be interpreted in terms of its role in providing the energy needed for the passage of CSF formed in the cell cytoplasm to the ventricle of the brain. And the 5'-NTase between the epithelial cells may help to form the cell junction, be considered as part of the blood-cerebrospinal fluid barrier, and is likely to participate in signal transferation by producing adenosine. The 5'-NTase at the basal infoldings may be concerned with the metabolization of nucleic acid and matter transportation, and may play a great role in maintain nucleic acid homeostasis of the brain.
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