Production and Secretion of Adrenomedullin by Cultured Choroid Plexus Carcinoma Cells

Abstract: Adrenomedullin is a potent vasodilator peptide that was originally isolated from pheochromocytoma. The production and secretion of adrenomedullin by cultured choroid plexus carcinoma cells were studied by radioimmunoassay and northern blot hybridization. Choroid plexus carcinoma is a rare malignant tumor derived from the epithelium of the choroid plexus. Immunoreactive adrenomedullin was detected in the conditioned medium of choroid plexus carcinoma cells (40.8 ± 7.5 fmol/10⁵ cells/24 h; mean ± SEM, n = 5). Reverse-phase HPLC of the conditioned medium showed one major peak of the immunoreactive peptide eluting in the position of synthetic human adrenomedullin and two smaller peaks eluting earlier. Addition of interleukin-1β (10 ng/ml) alone or in combination with three cytokines, interferon-γ (100 U/ml), tumor necrosis factor-α (20 ng/ml), and interleukin-1β (10 ng/ml), caused significant increases in the immunoreactive adrenomedullin concentrations in the medium (∼175 and 293% of the control level, respectively). Northern blot analysis showed the expression of 1.6-kb adrenomedullin mRNA in the total RNA sample prepared from cultured choroid plexus carcinoma cells. Treatment with either interleukin-1β or the combination of three cytokines caused significant increases in levels of adrenomedullin mRNA in parallel with those in immunoreactive adrenomedullin concentrations in the conditioned medium. These findings raise a possibility that adrenomedullin is secreted from the choroid plexus and has physiological roles in the CNS via the CSF. In addition, adrenomedullin secreted from choroid plexus carcinoma may be related to the pathophysiology of the tumor.     

Three-dimensional observation of the fibroblast-like cells associated with the rat myenteric plexus,with special reference to the interstitial cells of Cajal

Summary An extensive cellular network becomes visible over the myenteric plexus of the rat after removal of the overlying tissues under the scanning electron microscope. The cells are mainly stellate and have many slender processes via which they interconnect. They form a three-dimensional network and are closely associated with the ganglia and nerve bundles, and also extend over the smooth muscle cells. They are considered to correspond to the interstitial cells of Cajal because of their peculiar arrangement and their topography. Transmission electron-microscopic evidence demonstrates that the majority of those cells have features of fibroblasts. Gap junctions and intermediate junctions are observed between these fibroblast-like cells, and also between them and smooth muscle cells. Examination of serial thin sections reveals that single fibroblast-like interstitial cells connect to both circular and longitudinal muscle cells via gap junctions. It is suggested that the network of interstitial cells conducts electrical signals.     

Failure to demonstrate serotonergic neurons in the myenteric plexus of the rat

Summary Several recent studies suggested that serotonergic neuron-like elements are present in the guinea pig ileum. The present paper reports an extensive study of the digestive tract of the rat with the use of a histofluorescence technique. Administration of the serotonin precursor, tryptophan, associated with a monoamine oxidase inhibitor, did not allow histochemical demonstration of rapidly fading, yellow fluorescent, 6-hydroxydopamine-resistant neurons; conversely such neurons were readily detected in the brain. It is concluded that serotonergic neuron-like elements cannot be detected histochemically in the rat myenteric plexus area after chemical sympathectomy.     

Lipidkugeln im Plexusepithel von Rana temporaria L.

Zusammenfassung Das Plexusepithel von Rana temporaria L. enthält zwei verschiedene Typen von Lipidkugeln, die einen Durchmesser bis zu 8 erreichen können. Diese Einschlüsse haben keine Zytomembran. Die Struktur der Einschlußkörper wird mit Hinweisen auf die Fixierung und den Stoffwechsel diskutiert.

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Lipid droplets in the epithelium of the choroid plexus of Rana temporaria L.

Summary The epithelium of the choroid plexus of Rana temporaria L. contains two different types of spherical lipid inclusions up to 8 in diameter. The droplets do not have a limiting membrane. The preservation and metabolism of the lipid bodies are discussed.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Sub cellular Fractionation of the Longitudinal Smooth Muscle/Myenteric Plexus of Dog Ileum: Dissociation of the Distribution of Two Plasma Membrane Marker Enzymes

The distribution of plasma membrane markers, the sodium pump [evaluated as ouabain-sensitive, potassium-stimulated p-nitrophenyl phosphatase (K+-pNPPase)], [3H]saxitoxin binding, and 5'-AMPase, was studied in the subcellular fractions prepared from the homogenates of the longitudinal smooth muscle/myenteric plexus of dog ileum. The K+-pNPPase activity and [3H]-saxitoxin binding were found to be predominantly associated with the synaptosomal fraction as indicated by the high level of these activities in the crude synaptosomal fraction and by the copurification of K+-pNPPase and [3H]saxitoxin binding, but not 5'-AMPase, with several synaptosomal markers during the fractionation of the crude synaptosomal fraction on density gradients. In contrast to the K+-pNPPase activity and [3H]saxitoxin binding, the 5'-AMPase activity was found to be concentrated in the microsomal pellet. Further fractionation of microsomes on density gradient resulted in copurification of 5'-AMPase but not K+-pNPPase or [3H]saxitoxin binding, with other smooth muscle plasma membrane-bound enzymes, such as high-affinity Ca2+-ATPase, Mg2+-ATPase, and Ca2+-ATPase. It was concluded that in the longitudinal smooth muscle/myenteric plexus, the sodium pump activity is present in higher density in the neuronal plasma membranes whereas 5'-AMPase activity is concentrated in the smooth muscle plasma membranes.     

Transport of Prostaglandins and Other Eicosanoids by the Choroid Plexus: Its Characterization and Physiological Significance

Choroid plexi from the lateral ventricles of rabbits, cats, and dogfish (Mustelus canis) were used to characterize the prostaglandin (PG) uptake process and to establish its kinetic parameters and substrate specificity. The apparent Kt for PGF2 alpha transport by the rabbit choroid plexus was 20 microM; the Jmax was 27 nmol g-1 min-1. The Ki of inhibition of PGF2 alpha transport by PGE2 was 20 microM; the Jmax of PGF2 alpha transport was unaltered by PGE2. A concentration of p-aminohippuric acid of up to 1 mM did not appreciably affect the Kt or the Jmax of PGF2 alpha transport. The rate of PGF2 alpha accumulation by rabbit choroid plexus was reduced by incubation at 4 degrees C, under anaerobic conditions, in the absence of sodium or in the presence of ouabain, probenecid, or bromcresol green. The choroid plexi of all three species also accumulated thromboxane B2, PGI2, and 6-keto-PGF1 alpha, suggesting that most, if not all, eicosanoids are substrates for this transport system. It is concluded that the choroid plexus transport system satisfies all the criteria of an active, energy-dependent transport system and that this system functions effectively at concentrations of eicosanoids present in the ventricular system under normal or pathological conditions. Hence, this transport system must make an important contribution to the pharmacokinetics of eicosanoids within the brain.     

H2 Histamine Receptors on the Epithelial Cells of Choroid Plexus

A major site of cerebrospinal fluid production in vertebrates is the choroid plexus. The epithelial cells of the choroid plexus accumulate intracellular cyclic AMP in response to several effectors, including histamine. Since histamine is known to regulate fluid secretion in the stomach via H2 histamine receptors, we asked whether H2 receptors might also be present on epithelial cells of bovine choroid plexus. Using agonists and antagonists of histamine, we show that an agonist and antagonist pair specific for the H2 subtype were clearly more effective than an H1 agonist and antagonist pair in mimicking or inhibiting histamine stimulation of cellular cyclic AMP. Analysis by Schild plot allowed assignment of an apparent dissociation constant to the H2 antagonist metiamide which was 34-fold lower than that of its H1 counterpart, diphenhydramine. These results indicate that epithelial cells of the choroid plexus possess H2 histamine receptors.     

GABA, Glutamic Acid Decarboxylase, and GABA Transaminase Levels in the Myenteric Plexus in the Intestine of Humans and Other Mammals

Abstract: Regional distribution of endogenous γ- aminobutyric acid (GABA), its synthesizing enzyme, glutamic acid decarboxylase (GAD), and metabolic enzyme, GABA transaminase (GABA-T), were determined in the intestinal tract of guinea pigs and cats and the findings compared with the number of ganglion cells in Auerbach's plexus. There were positive correlations among the GABA contents and the numbers of neural cells of the plexus. The precise localization of GABA and GAD in individual layers (mucosa, circular and longitudinal muscles, and Auerbach's plexus) in the human and cat colon was also determined. The endogenous GABA contents and GAD activity were the highest in Auerbach's plexus in tissues of both species. These results indicate that GABA is synthesized and localized in Auerbach's plexus and probably plays a significant role in the enteric nervous system.     

Riboflavin Homeostasis in the Central Nervous System

Abstract: The mechanisms by which riboflavin, which is not synthesized in mammals, enters and leaves brain, CSF, and choroid plexus were investigated by injecting [¹⁴C]riboflavin intravenously or intraventricularly. Tracer amounts of [¹⁴C]riboflavin with or without FMN were infused intravenously at a constant rate into normal, starved, or probenecid-pretreated rabbits. At 3 h, [¹⁴C]riboflavin readily entered choroid plexus and brain, and, to a much lesser extent, CSF. Over 85% of the [¹⁴C]riboflavin in brain and choroid plexus was present as [¹⁴C]FMN and [¹⁴C]FAD. The addition of 0.2 mmol/kg FMN to the infusate markedly depressed the relative entry of [¹⁴C]riboflavin into brain, choroid plexus, and, less so, CSF, whereas starvation increased the relative entry of [¹⁴C]riboflavin into brain and choroid plexus. After intraventricular injection (2 h), most of the [¹⁴C]riboflavin was extremely rapidly cleared from CSF into blood. Some of the [¹⁴C]riboflavin entered brain, where over 85% of the ¹⁴C was present as [¹⁴C]FMN plus [¹⁴C]FAD. The addition of 1.2³μmol FAD (which was rapidly hydrolyzed to riboflavin) to the injectate decreased the clearance of [¹⁴C]riboflavin from CSF and the phosphorylation of [¹⁴C]riboflavin in brain. Probenecid in the injectate also decreased the clearance of [¹⁴C]riboflavin from CSF. These results show that the control of entry and exit of riboflavin is the mechanism, at least in part, by which total riboflavin levels in brain cells and CSF are regulated. Penetration of riboflavin through the blood-brain barrier, saturable efflux of riboflavin from CSF, and saturable entry of riboflavin into brain cells are three distinct parts of the homeostatic system for total riboflavin in the central nervous system.