Fine structure of ependymal cysts in and around the area postrema of the rat

Summary Peculiar cells forming cysts were observed in the area postrema and sometimes also in the choroid plexus and the tela chorioidea near the area postrema, and were studied in detail by electron microscopy. The cytological features of the cyst cell and its junctional relationship to neighboring cells imply that cyst cells are derived from ependymal and choroid epithelial cells. The cyst cells usually contact directly the perivascular spaces of postremal, choroidal or pial capillaries, where the cytoplasm is often considerably attenuated. The cystic lumen is commonly filled with a flocculent material. The limiting membrane of the cystic lumen, which frequently bears cilia and microvilli, has the same thickness as the surface cell membrane. In many cases, the cyst is surrounded by the cytoplasm of a single cell. In some cases, however, two cells participate in the formation of the cyst, although one is only a slender process and joined by a zonula occludens with the main cyst cell. Horseradish peroxidase (HRP) injected into the cerebrospinal fluid (CSF) space failed to enter the cystic lumen. A possible significance of the cyst in relation to the CSF and blood circulation was considered.     

Fine structure of synaptic contacts in the first order giant fibre system of the squid

Summary Scanning electron microscopy and the penetration of horseradish peroxidase, especially from the ventricular surface, has been utilized to determine the distinctive properties of the posterior portion of the area postrema. This part of the organ is characterized by a non-ciliated surface composed of flattened cells, which appear less permeable to cisternally injected peroxidase than the ciliated ependymal cells covering the anterior part of the area postrema. However, more diffuse and rapid penetration of peroxidase into the posterior region is achieved by way of the perivascular spaces which appear in direct communication with the CSF. No such filling is noted in the anterior area postrema. The posterior portion also contains cells which appear to be rapidly penetrated by horseradish peroxidase and which may be important as a sensing mechanism. The chief distinction of the anterior part of the area postrema appears to be the presence of vascular connections with the choroid plexus.This work has been supported in part by Grant NB08549-02 from the National Institute of Neurological Diseases and Stroke and Health Science Advancement Award F-304-FR06115.     

Intraventricular blood vessels associated with the deep pineal gland of the Mongolian gerbil,Meriones unguiculatus

Summary Intraventricular blood vessels and choroidal-like cells were studied using scanning electron microscopy and correlative light microscopy. The intraventricular blood vessels were covered on their ependymal surface with a layer of cells essentially identical to the ependyma of the choroid plexus in the gerbil. Similar choroidal-like cells were seen either singly or in clusters associated with the cerebrospinal fluid-contacting pinealocytes of the suprapineal recess. Processes of the cerebrospinal fluid-contacting pinealocytes were seen extending to and making contact with the choroidal-like cells. The intraventricular blood vessels appeared to be derived from the choroid plexus, and typically took one of three courses in and around the surface of the deep pineal: (1) the vessels or their equivalent were located in the suprapineal recess with no indication of penetration into the substance of the deep pineal; (2) the vessels coursed from the suprapineal recess around the anterior surface of the habenular commissure to enter the ventral surface of the deep pineal; or (3) the vessels entered the parenchyma of the deep pineal from its dorsal surface and could be seen coursing through the substance of the gland. The close association between the choroidal-like cells and the intraventricular blood vessels with the deep pineal gland add morphological support for the possibility of interaction between the cerebrospinal fluid, or perhaps the choroid plexus, and the deep pineal gland.     

Silver deposition in the central nervous system and the hematoencephalic barrier studied with the electron microscope

For the purpose of studying the hematoencephalic barrier as it is concerned with silver circulating in the blood stream, silver nitrate was vitally administered to rats in their drinking water over periods of 6 to 8 months. The cerebrum, cerebellum, medulla, area postrema, and choroid plexus were prepared for light and electron microscopy. Silver deposition was found in the perivascular spaces in the choroid plexus, area postrema, in the medulla surrounding the area postrema, and in minute quantities in the cerebrum, cerebellum, and most of the medulla. Two levels of the hematoencephalic barrier were apparently demonstrated in our investigations. The endothelial linings of the vessels in the cerebrum, cerebellum, and medulla constitute the first threshold of the hematoencephalic barrier (specifically here, blood-brain barrier). The cell membranes adjacent to the perivascular spaces form the second threshold, as follows:-the neuroglial cell membranes in the cerebrum, cerebellum, and medulla (blood-brain barrier); the membranes of the neuroglial cells in the area postrema (blood-brain barrier); and the membranes of the epithelial cells of the choroid plexus (blood-cerebrospinal fluid barrier). This study deals with silver deposition and does not infer that the penetration of ionic silver, if present in the blood stream, would necessarily be limited to the regions described. Bleb-like structures were observed to cover the epithelial cell surfaces in the choroid plexus. They may be cellular projections increasing the cell surface area or they may be secretory droplets.     

SILVER DEPOSITION IN THE CENTRAL NERVOUS SYSTEM AND THE HEMATOENCEPHALIC BARRIER STUDIED WITH THE ELECTRON MICROSCOPE

For the purpose of studying the hematoencephalic barrier as it is concerned with silver circulating in the blood stream, silver nitrate was vitally administered to rats in their drinking water over periods of 6 to 8 months. The cerebrum, cerebellum, medulla, area postrema, and choroid plexus were prepared for light and electron microscopy. Silver deposition was found in the perivascular spaces in the choroid plexus, area postrema, in the medulla surrounding the area postrema, and in minute quantities in the cerebrum, cerebellum, and most of the medulla. Two levels of the hematoencephalic barrier were apparently demonstrated in our investigations. The endothelial linings of the vessels in the cerebrum, cerebellum, and medulla constitute the first threshold of the hematoencephalic barrier (specifically here, blood-brain barrier). The cell membranes adjacent to the perivascular spaces form the second threshold, as follows:—the neuroglial cell membranes in the cerebrum, cerebellum, and medulla (blood-brain barrier); the membranes of the neuroglial cells in the area postrema (blood-brain barrier); and the membranes of the epithelial cells of the choroid plexus (blood-cerebrospinal fluid barrier). This study deals with silver deposition and does not infer that the penetration of ionic silver, if present in the blood stream, would necessarily be limited to the regions described. Bleb-like structures were observed to cover the epithelial cell surfaces in the choroid plexus. They may be cellular projections increasing the cell surface area or they may be secretory droplets.     

Expression of nerve growth factor receptor immunoreactivity in the rat choroid plexus.

The presence and localization of nerve growth factor receptors (NGFr) in the choroid plexus of the adult rat has been investigated immunohistochemically using an anti-rat NGFr monoclonal antibody (192-IgG). A moderate to strong immunoreaction was observed in the epithelial cells of the choroid plexus, whereas the choroidal blood vessels and connective tissue remained unlabelled. Moreover, no sex-differences were encountered in the NGFr immunoreaction intensity and Bouin fixative was more effective than 10% formaldehyde evidenciating the NGFr immunostain. Occasionally, ependymal cells displaying NGFr immunoreactivity were observed. Present data demonstrate that the choroid plexus of the rat contain NGFr, probably low-affinity NGFr, and suggest an involvement of NGF in the regulation of cerebrospinal fluid secretion, but the importance of these findings, if any, must be investigated in future studies.     

Ultrastructure of the Neurohypophysial Lobe of the Hagfish,Eptatretus stouti (Cyclostomata)

The neurohypophysial lobe is a thin-walled sac that, except for a few blood vessels, lacks any anatomical link with the adenohypophysis. Its wall consists of ependymal, fiber and palisade zones and is surrounded by blood vessels. The lobe is differentiated into distinct dorsal and ventral regions. The dorsal wall is doubly innervated by Gomori-positive axons arising in the anterior hypothalamus and by Gomori-negative fibers of unknown origin. Its surface is covered by an extensive vascular plexus. The ventral wall is innervated only by Gomori-negative fibers and is sparsely supplied with a few fine capillaries. All of the ependymal cells in both regions have the same ultrastructural appearance. The Gomori-positive or Type I axons are identified at the electron microscope level as fibers containing elementary granules with a diameter of 150–230 run. The Gomori-negative or Type II fibers contain dense-cored vesicles that vary from 80–125 nm in diameter. Both Type I and II fibers form synaptic-like complexes with the processes and end-feet of the ependymal cells. Type I axons also abut on the basal lamina bounding the perivascular spaces. It is suggested that the agranular reticulum of the ependymal cells may provide a transport pathway for neural products that are destined for release into the circulation. It is also possible that the ependyma itself is a target of neural activity.     

Differential Localization of Glutathione-S-Transferase Yp and Yb Subunits in Oligodendrocytes and Astrocytes of Rat Brain

Glutathione-S-transferase Yb subunits were recently identified in rat brain and localized to astrocytes, ependymal cells lining the ventricles, subventricular zone cells, and tanycytes. Another isoform, Yp (pi family), was detected in rat brain by immunoblotting, and its mRNA was detected by Northern hybridizations. Double immunofluorescence localized Yb and Yp in different glial cells. The strongly Yp-positive cells were identified as oligodendrocytes by virtue of their arrangement in rows in white-matter tracts, colocalization in strongly carbonic anhydrase-positive cells, and association with myelinated tracts in the corpus striatum. Ependymal cells in the choroid plexus and ventricular lining were also strongly Yp positive, whereas Yb was not detected in the choroid plexus. The occurrence of Yp at low levels in astrocytes was indicated after immunostaining by a sensitive peroxidase-antiperoxidase method, which revealed weak staining of those cells in the molecular layer of the cortex. The data suggest that Yb and Yp subunits are primarily localized to astrocytes and oligodendrocytes, respectively, and that both are absent from neurons. The glutathione-S-transferase in oligodendrocytes may participate in the removal of toxins from the vicinity of the myelin sheath. The finding of glutathione-S-transferases in ependymal cells and astrocytes in the brain also suggests that this enzyme could be a first line of defense against toxic substances.     

Sonic hedgehog is required for vascular outgrowth in the hindbrain choroid plexus

Critical to the exchange and metabolic functions served by tissues like brain choroid plexi and lung is the coherent development of an epithelial sheet of large surface area in tight apposition to an extensive vascular bed. Here, we present functional experiments in the mouse demonstrating that Sonic hedgehog (Shh) produced by hindbrain choroid plexus epithelium induces the extensive vascular outgrowths and vascular surface area fundamental to choroid plexus functions, but does not induce the more specialized endothelial cell features of fenestrations and bore size. Our findings indicate that these Shh-dependent vascular elaborations occur even in the presence of Vegf and other established angiogenic factors, suggesting either that the levels of these factors are inadequate in the absence of Shh or that a different set of factors may be more essential to choroid plexus outgrowth. Transducing the Shh signal is a perivascular cell—the pericyte—rather than the more integral vascular endothelial cell itself. Moreover, our findings suggest that hindbrain choroid plexus endothelial cells, as compared to other vascular endothelial cells, are more dependent upon pericytes for instruction. Thus, in addition to Shh acting on the progenitor pool for choroid plexus epithelial cells, as previously shown, it also acts on choroid plexus pericytes, and together serves the important role of coordinating the development of two disparate yet functionally dependent structures—the choroid plexus vasculature and its ensheathing epithelium.     

Enzymatic organization of the subcommissural organ.

In the subcommissural organ (SCO) of the guinea pig, rat, golden hamster, and mouse the activity and distribution of enzymes related to the energy-supplying metabolism and of some marker enzymes of different cell organelles have been investigated by means of mostly modified histochemical methods. The results were compared with findings in the ciliated ependyma of the ventricular wall and with those in the ependyma of the choroid plexus of the third ventricle. In the ependymal part of the SCO only a moderate activity of hexokinase is observed in its specialized columnar cells whereas a high activity is present both in the ciliated ependyma and the choroid plexus. - The staining pattern of glucose-6-phosphatase is similar to that of hexokinase but this enzyme is found is the SCO only. - Likewise hexokinase, glycogen granules and enzymes related to glycogen metabolism (phosphoglucomutase, uridine-diphosphoglucose pyrophosphorylase, glycogen synthetase and phosphorylase) are regularly found most numerous and active in the nuclear and supra-nuclear area of the ependymal part. These enzymes are less active in both the other ependymal regions. - Uridine-diphosphoglucose dehydrogenase could not be demonstrated in the SCO. The NADP-linked enzymes of the pentose phosphate shunt, glucose-6-phosphate and 6-phosphogluconate dehydrogenase, show a moderate activity which decreases also from the nuclear towards the apical area of the ependymal cells of the SCO. Enzymes of the glycolytic pathway, such as glucosephosphate isomerase, fructose-6-phosphate kinase, fructose-I,6-diphosphate aldolase, glyceraldehyde-3-phosphate and lactate dehydrogenase, are highly active in the SCO and are located mainly in the supranuclear area, too. Fructose-1,6-diphosphatase could not be demonstrated thus indicating that in the SCO the pathway is most probably only glycolytic but not gluconeogenetic. Compared to the ependyma of the ventricular wall and of the choroid plexus, in the SCO the M type subunits of lactate dehydrogenase predominate. Glycolytic enzymes are also very active in the choroid plexus but less in the ciliated ependyma. Compared to the ciliated ependyma and especially to the ependyma of the choroid plexus, the activities of enzymes which are only present in mitochondria (NAD-linked isocitrate dehydrogenase, succinate dehydrogenase, NAD-linked malate dehydrogenase after preextraction, cytochrome oxidase, 3-hydroxybutyrate and glycerolphosphate and glutamate dehydrogenase) are relatively low. Mitochondria are accumulated near the superior pole of the nuclei as well as in the most apical part of the ependymal cells. - The staining pattern of NADP-linked isocitrate and malate dehydrogenase as well as of NADH dehydrogenase suggests that these enzymes are localized both in and out of mitochondria. The extramitochondrial activity of the first two enzymes might be localized in the cytosol. The extramitochondrial activity of NADH dehydrogenase might be localized in the endoplasmic reticulum...     

Glymphatic distribution of CSF-derived apoE into brain is isoform specific and suppressed during sleep deprivation

Background

Apolipoprotein E (apoE) is a major carrier of cholesterol and essential for synaptic plasticity. In brain, it’s expressed by many cells but highly expressed by the choroid plexus and the predominant apolipoprotein in cerebrospinal fluid (CSF). The role of apoE in the CSF is unclear. Recently, the glymphatic system was described as a clearance system whereby CSF and ISF (interstitial fluid) is exchanged via the peri-arterial space and convective flow of ISF clearance is mediated by aquaporin 4 (AQP4), a water channel. We reasoned that this system also serves to distribute essential molecules in CSF into brain. The aim was to establish whether apoE in CSF, secreted by the choroid plexus, is distributed into brain, and whether this distribution pattern was altered by sleep deprivation.

Methods

We used fluorescently labeled lipidated apoE isoforms, lenti-apoE3 delivered to the choroid plexus, immunohistochemistry to map apoE brain distribution, immunolabeled cells and proteins in brain, Western blot analysis and ELISA to determine apoE levels and radiolabeled molecules to quantify CSF inflow into brain and brain clearance in mice. Data were statistically analyzed using ANOVA or Student’s t- test.

Results

We show that the glymphatic fluid transporting system contributes to the delivery of choroid plexus/CSF-derived human apoE to neurons. CSF-delivered human apoE entered brain via the perivascular space of penetrating arteries and flows radially around arteries, but not veins, in an isoform specific manner (apoE2?>?apoE3?>?apoE4). Flow of apoE around arteries was facilitated by AQP4, a characteristic feature of the glymphatic system. ApoE3, delivered by lentivirus to the choroid plexus and ependymal layer but not to the parenchymal cells, was present in the CSF, penetrating arteries and neurons. The inflow of CSF, which contains apoE, into brain and its clearance from the interstitium were severely suppressed by sleep deprivation compared to the sleep state.

Conclusions

Thus, choroid plexus/CSF provides an additional source of apoE and the glymphatic fluid transporting system delivers it to brain via the periarterial space. By implication, failure in this essential physiological role of the glymphatic fluid flow and ISF clearance may also contribute to apoE isoform-specific disorders in the long term.

     

THE SPECIFICITY AND SULFHYDRYL SENSITIVITY OF THE INOSITOL TRANSPORT SYSTEM OF THE CENTRAL NERVOUS SYSTEM

Abstract— The transport of two cyclohexitol stereoisomers, myo-inositol (inositol) and scyllo-inositol (scyllitol), from blood into the CNS in vivo and into the choroid plexus in vitro was studied. In vitro , the uptake of [³H]scyllitol or [³H]inositol by choroid plexuses, isolated from rabbits and incubated in artificial CSF, was measured. Both scyllitol and inositol inhibited [³H]scyllitol or [³H]inositol accumulation by the choroid plexus. Inositol competitively inhibited [³H]scyllitol accumulation and both isomers had a comparable affinity (K_t= 0.1 m m ) for the single cyclohexitol accumulation system. The other 6 stereoisomers tested had an order of magnitude less affinity for the cyclohexitol accumulation system of choroid plexus. Thiol reagents that penetrate cells inhibited inositol accumulation by choroid plexus more effectively than nonpenetrating thiol reagents. In vivo , in unanesthetized rabbits. the transport of unmetabolized [³H]inositol from blood into CSF, choroid plexus and brain was readily saturated by increasing the plasma levels of myo-inositol but not by the stereoisomer d -chiroinositol. Similarly, the transport of unmetabolized [³H]scyllitol into CSF, brain and choroid plexus was readily saturated by increasing the plasma levels of myo-inositol. Beside documenting the stereospecificity and thiol reagent sensitivity of the inositol transport mechanism of the choroid plexus, these results provide further evidence that the choroid plexus is a locus for cyclohexitol transport between blood and CSF. Moreover, they show that scyllitol, which, like inositol, is present at a higher concentration in brain than plasma, can be transported from blood into CSF and brain by the same system that transports inositol.     

Cystic Fibrosis Transmembrane Conductance Regulator Is Found Within Brain Ventricular Epithelium and Choroid Plexus

Abstract: The cystic fibrosis gene product, cystic fibrosis transmembrane conductance regulator (CFTR), functions as a CI⁻ channel that is regulated by cyclic AMP-dependent phosphorylation. We have investigated the expression of CFTR protein in the rodent brain by both western blotting of samples prepared by microdissection and immunohistochemistry. CFTR was found to be expressed in choroid plexus and ependyma. In tissue sections, CFTR-like immunoreactivity was concentrated in fine puncta localized about 1–2 µm from the CSF-contacting side of ependyma and choroid plexus. CFTR in choroid plexus may play a role in the regulation of the composition of CSF by cyclic AMP-elevating agents, but the role of this chloride transporter in ependymal function remains to be determined.     

Choroid plexus ependymal cells enhance neurite outgrowth from dorsal root ganglion neurons in vitro

The epithelial cells of the choroid plexus are a continuation of the ventricular ependymal cells and are regarded as modified ependymal cells. The present study was carried out to determine the influence of choroid plexus ependymal cells (CPECs) on axonal growth in vitro. Choroid plexuses were dissected from the fourth ventricle of postnatal day-1–10 mice, mechanically dissociated, and plated in fibronectin-coated culture dishes. CPECs had spread into monolayers with few endothelial cells in 3-week cultures. Some macrophages were scattered on the monolayer of CPECs. Dorsal root ganglia (DRG) were excised from mouse fetuses of 14-day gestation, dissociated with trypsin and cocultured on the CPEC monolayers. For comparison, dissociated DRG neurons were cocultured on astrocyte monolayers or cultured on laminin-coated plates. After 4.5 h culturing, the cultures were fixed and immunohistochemically double-stained for neurites and CPECs using antibodies against β-tubulin III and S-100 β, respectively. It was demonstrated that neurons extended many long neurites with elaborate branching on the surface of S-100-stained CPECs. In contrast, DRG neurons cultured on the astrocytes and on the laminin-coated plates had much shorter primary neurites with fewer branches than those cultured on the CPECs. The total length of neurites including primary neurites and their branches, of a single DRG neuron was 285 ± 14, 395 ± 15 and 565 ± 12 μm on the laminin-coated plates, on astrocytes and on CPECs, respectively. Scanning electron microscopy revealed extension of neurites with well-developed growth cones on the ependymal cells. These results suggest that CPECs have a great capacity to promote neurite outgrowth from DRG neurons in vitro.     

Relationship between orthogonal arrays of particles and tight junctions as demonstrated in cells of the ventricular wall of the rat brain

Summary Ependymal cells in the ventricular wall and in several circumventricular organs of the rat were compared by means of freeze-fracturing. In principle, tight junctions and orthogonal arrays of particles (OAP) do not coexist in the cells bordering the ventricular wall: (1) Ordinary ependymal cells of the rat possess OAP and are devoid of tight junctions. (2) Epithelial cells of the rat choroid plexus are connected by tight junctions; OAP are lacking here. In some cases, however, tight junctions and OAP coexist in the same cell. In the boundary zone between choroid plexus and ependyma of the rat, the density of OAP is very low, whereas the tight junctions are well developed. In the subfornical and the subcommissural organ (SCO) of the rat both structures are poorly developed; in the SCO they occur segregated in different membranous areas. An overview of the literature confirms that tight junctions and OAP mostly exclude each other. The possibility that in astrocytes and ependymal cells tight junctions may have been replaced by OAP during phylogeny is briefly discussed.Dedicated to Professor A. Bohle on the occasion of his 65th birthdayPresent address: Dept. of Biol., Univ. of Oregon, Eugene, Oregon, 97403, USA     

Localization of metallothionein in the brain of rat and mouse.

Metallothionein (MT) is a low molecular mass protein inducible by heavy metals such as cadmium (Cd), zinc, and copper, and having high affinity for these metals. In the present study, we investigated the immunohistological localization of MT in the brains of rats and mice. In adult rat brain, almost no MT immunostaining was observed, whereas in adult mouse brain strong MT immunostaining was found in the ependymal cells, some glial cells, arachnoid, and pia mater. No immunostaining was detected in neurons and endothelial cells. In younger rats (1-3 weeks old), strong MT immunostaining was observed in ependymal cells, choroid plexus epithelium, arachnoid, and pia mater. The overall MT concentration in adult mouse brain appeared higher than that of the brains of young and adult rats. When adult rats were administered Cd, MT was induced not only in some glial cells, ependymal cells, arachnoid, and pia mater but also in endothelial cells. Although Cd treatment resulted in an increase in the MT immunostaining in the specific cells described above, the MT induction was not great enough to significantly affect the overall MT level in the brain. The present result suggest a possible link of MT with cell growth of choroid plexus epithelium and ependymal cells, as well as a detoxifying role of MT in the blood-brain barrier and the cerebrospinal fluid-brain barrier.     

Immunohistochemical study of localization of gamma-glutamyl transpeptidase in the rat brain

Gamma-glutamyl transpeptidase (gamma-GTP) is a membrane-bound enzyme which is known to play a crucial role in active transport of amino acids across membrane barriers. We prepared a monoclonal antibody recognizing specifically rat gamma-GTP and investigated localization of the enzyme in the rat brain by immunohistochemistry with this antibody. The antigen was localized on the ependyma, epithelia of the choroid plexus and microvessels. More precise localization of gamma-GTP was examined with immuno-electron microscopy. The antigen was recognized on the microvilli and cilia of the ependymal cells, microvilli of the choroid epithelial cells and luminal membranes of the vascular endothelial cells.     

The choroid plexus removes beta-amyloid from brain cerebrospinal fluid

beta-Amyloid (Abeta) concentration in the cerebrospinal fluid (CSF) of the brain may be regulated by the choroid plexus, which forms a barrier between blood and brain CSF. Abeta uptake from CSF was determined as its volume of distribution (V(D)) into isolated rat choroid plexus tissue. The V(D) of [125I]Abeta1-40 was corrected by subtraction of the V(D) of [14C]sucrose, a marker for extracellular space and diffusion. Abeta uptake into choroid plexus was time and temperature dependent. Uptake of [125I]Abeta was saturable. Abeta uptake was not affected by addition of transthyretin or apolipoprotein E3. In studies with primary culture monolayers of choroidal epithelial cells in Transwells, Abeta permeability across cells, corrected by [(14)C]sucrose, was greater from the CSF-facing membrane than from the blood-facing membrane. Similarly, cellular accumulation of [125I]Abeta was concentrative from both directions and was greater from the CSF-facing membrane, suggesting a bias for efflux. Overall, these results suggest the choroid plexus selectively cleanses Abeta from the CSF by an undetermined mechanism(s), potentially reducing Abeta from normal brains and the brains of Alzheimer's disease patients.     

Adipose triglyceride lipase affects triacylglycerol metabolism at brain barriers

Currently, little is known about the role of intracellular triacylglycerol (TAG) lipases in the brain. Adipose triglyceride lipase (ATGL) is encoded by the PNPLA2 gene and catalyzes the rate-limiting step of lipolysis. In this study, we investigated the effects of ATGL deficiency on brain lipid metabolism in vivo using an established knock-out mouse model (ATGL-ko). A moderate decrease in TAG hydrolase activity detected in ATGL-ko versus wild-type brain tissue was accompanied by a 14-fold increase in TAG levels and an altered composition of TAG-associated fatty acids in ATGL-ko brains. Oil Red O staining revealed a severe accumulation of neutral lipids associated to cerebrovascular cells and in distinct brain regions namely the ependymal cell layer and the choroid plexus along the ventricular system. In situ hybridization histochemistry identified ATGL mRNA expression in ependymal cells, the choroid plexus, pyramidal cells of the hippocampus, and the dentate gyrus. Our findings imply that ATGL is involved in brain fatty acid metabolism, particularly in regions mediating transport and exchange processes: the brain-CSF interface, the blood-CSF barrier, and the blood-brain barrier.     

Histochemistry of proteases in ependyma, choroid plexus and leptomeninges

Aminopeptidase M (APM), aminopeptidase A (APA), dipeptidyl peptidase IV (DPP IV) and gamma-glutamyl transferase (GGT) were demonstrated histochemically in cryostat sections of the rat brain to show the reaction pattern of ependyma, choroid plexus and leptomeninges. GGT was only demonstrable in the cell membranes of ependymal cells and in the leptomeninges; however, APA, APM and DAP IV showed a variable degree of activity in the capillary endothelium of the choroid plexus as well as in the leptomeninges. On the basis of these results, it is postulated that peptides in the cerebrospinal fluid can be cleaved extraventricularly by the enzymes demonstrated in the leptomeninges.