Mouse Choroid Plexus Research Articles

Mitochondrial content of choroid plexus epithelium.

The objective of the present study was to examine the apparent work capacity of one of the two separate membrane systems (the blood-cerebrospinal fluid barrier) that isolate the mammalian brain extracellular fluid (and cerebrospinal fluid, CSF) from plasma. Digitized analyses of electron-microscopic images provided estimates of mitochondrial volumes, which were expressed as a percentage of the cell cytoplasm. We recorded a high mitochondrial content of 12-15% in the cuboidal epithelium of primate choroid plexus, which was consistent in vervet, rhesus, and squirrel monkeys, as well as in baboons. Similarly high mitochondrial contents were observed in the rabbit, rat, and mouse choroid plexus. It has been postulated that the high mitochondrial content of brain endothelium is associated with maintaining the ionic gradients within the central nervous system. We observed that the mitochondrial content of the choroid plexus (where CSF is produced) was slightly higher than in (prior measurements of) the blood-brain barrier (BBB). In addition, surface areas at the apical borders of the choroid plexus epithelia (where the Na+K+ATPase activity has been localized) were increased 7- to 13-fold over the basal borders, in the primate species examined. The observation of high mitochondrial volumes in choroid plexus cells is consistent with the suggestion that increased mitochondrial densities seen in choroidal epithelia and BBB capillaries provide a metabolic work capability for both secretory activities and maintaining ionic gradients across blood-CSF barriers.

Whole cell Cl- conductances in mouse choroid plexus epithelial cells do not require CFTR expression.

Whole cell patch-clamp studies were performed with tissue isolated from the cystic fibrosis (CF) transgenic Cftrm1cam mouse, to determine whether anion currents in choroid plexus epithelial cells require the expression of cystic fibrosis transmembrane conductance regulator (CFTR). Inclusion of 0.25 mM adenosine 3',5'-cyclic monophosphate (cAMP) and 375 nM protein kinase A (PKA) in the pipette solution caused a significant activation of a Cl(-)-selective, inward-rectifying conductance in cells from wild-type and CF mice. The small, outward currents observed in wild-type and CF animals, however, were not activated by cAMP-PKA. There were no significant differences in the size of currents between wild-type, heterozygote, and CF cells in the presence or absence of cAMP-PKA. A second whole cell conductance was activated when cells from wild-type mice were swollen. These volume-activated currents were Cl- selective and exhibited outward rectification. They were Ca2+ independent and ATP dependent and blocked by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and 5-nitro-2-(3-phenylpropylamino)benzoic acid. The volume-activated channels were also activated in CF mutant cells, and there was no significant difference in the size of the volume-activated currents between wild-type, heterozygote, and CF cells. It is concluded that CFTR neither contributes to the whole cell conductance nor regulates the other anion conductances in choroid plexus epithelial cells.

The OB protein (leptin) pathway--a link between adipose tissue mass and central neural networks.

OB protein (also known as leptin), a previously unknown protein signal, is secreted from adipose tissue, circulates in the blood, probably bound to a family of binding proteins, and acts on central neural networks that regulate ingestive behavior and energy balance. OB protein provides a communication link from fat tissue and the brain. Rapidly accumulating evidence suggests that OB protein appears to play a major role in the control of body fat stores through coordinated regulation of feeding behavior, metabolism, autonomic nervous system and body energy balance in rodents, primates and humans. The field has rapidly moved from cloning of the ob gene to demonstration of complex regulation of ob gene expression in adipose tissue in rats and humans, and then the demonstration of potent biological activity of OB protein in ob/ob, diet-induced, and lean mice as well as obese and lean rats but not in db/db obese mice. A significant milestone was our demonstration that central administration of OB protein lead to reductions in food intake, body weight and alterations in metabolism consistent with activation of the autonomic nervous system. These findings were followed by the identification of a central binding site for labelled OB protein in the choroid plexus in ob/ob, db/db and lean mice as well as lean and obese Zucker rats. The expression cloning of a central receptor, OB-R, from the mouse choroid plexus soon followed. The OB-R receptor was found to be expressed in the choroid plexus, the hypothalamus as well as several peripheral tissues. OB-R exists in multiple forms; the two major forms are a short form (with a truncated intracellular domain) and long form (with the complete intracellular domain). The long form is thought to be the form that signals and mediates the biological effects of OB protein. Initial in situ hybridization studies have demonstrated the mRNA for the long form OB-R receptor to be localized to the hypothalamus as well as peripheral sites. Recently, it was demonstrated that the db gene encodes the OB-R receptor. Evidence has been provided for a specific transport system for OB protein to cross the blood-brain-barrier and enter the brain of mice, rats and humans. The rate of transport can be decreased by high plasma concentrations of OB protein. Thus, reduced entry of OB protein to the brain may be one of the mechanisms of reduced sensitivity of the OB protein pathway in obese individuals. OB protein appears to also play a role in the important neuroendocrine adaptive responses to fasting and in the control of reproduction. Therapeutic approaches to the treatment of obesity based on OB protein ranging from OB protein by injection to OB-R receptor agonists and to upregulation of OB signalling pathways are under intense investigation.

Coexpression of leptin receptor and preproneuropeptide Y mRNA in arcuate nucleus of mouse hypothalamus.

Leptin, the protein product of the adipose tissue-specific ob (obese) gene (1), reduces the body weight, adiposity and food intake of obese ob/ob mice on peripheral or central injection (2, 3, 4). [125I]leptin binding has been detected in mouse choroid plexus (5), from which a leptin receptor gene was expression cloned (5). The gene has at least 6 splice variants (6, 7). Leptin receptor mRNA was localized in the hypothalamus by in situ hybridization being particularly abundantly expressed in the arcuate nucleus (8). There is evidence linking the physiological effects of injected leptin with hypothalamic neuropeptide Y (9, 10) (NPY), which has potent central effects on food intake and energy balance (11), and is also expressed in the arcuate nucleus. Here we report dual in situ hybridization studies for leptin receptor and NPY gene expression in the mouse arcuate nucleus, where the majority of cells examined expressed both genes. This provides the first direct evidence that leptin acts on cells that express NPY mRNA.

OB protein binds specifically to the choroid plexus of mice and rats.

Binding studies were conducted to identify the anatomical location of brain target sites for OB protein, the ob gene product. 125I-labeled recombinant mouse OB protein or alkaline phosphatase-OB fusion proteins were used for in vitro and in vivo binding studies. Coronal brain sections or fresh tissue from lean, obese ob/ob, and obese db/db mice as well as lean and obese Zucker rats were probed to identify potential central OB protein-binding sites. We report here that recombinant OB protein binds specifically to the choroid plexus. The binding of OB protein (either radiolabeled or the alkaline phosphatase-OB fusion protein) and its displacement by unlabeled OB protein was similar in lean, obese ob/ob, and obese db/db mice as well as lean and obese Zucker rats. These findings suggest that OB protein binds with high affinity to a specific receptor in the choroid plexus. After binding to the choroid plexus receptor, OB protein may then be transported across the blood-brain barrier into the cerebrospinal fluid. Alternatively, binding of OB protein to a specific receptor in the choroid plexus may activate afferent neural inputs to the neural network that regulates feeding behavior and energy balance or may result in the clearance or degradation of OB protein. The identification of the choroid plexus as a brain binding site for OB protein will provide the basis for the construction of expression libraries and facilitate the rapid cloning of the choroid plexus OB receptor.

Identification and expression cloning of a leptin receptor, OB-R

The ob gene product, leptin, is an important circulating signal for the regulation of body weight. To identify high affinity leptin-binding sites, we generated a series of leptin-alkaline phosphatase (AP) fusion proteins as well as [125I]leptin. After a binding survey of cell lines and tissues, we identified leptin-binding sites in the mouse choroid plexus. A cDNA expression library was prepared from mouse choroid plexus and screened with a leptin-AP fusion protein to identify a leptin receptor (OB-R). OB-R is a single membrane-spanning receptor most related to the gp130 signal-transducing component of the IL-6 receptor, the G-CSF receptor, and the LIF receptor. OB-R mRNA is expressed not only in choroid plexus, but also in several other tissues, including hypothalamus. Genetic mapping of the gene encoding OB-R shows that it is within the 5.1 cM interval of mouse chromosome 4 that contains the db locus.

Metabolism-dependent binding of the heterocyclic amine Trp-P-1 in endothelial cells of choroid plexus and in large cerebral veins of cytochrome P450-induced mice

Trp-P-1 (3-amino-1,4-dimethyl-5H-pyrido(4,3-b)indole) is known to be metabolized by cytochrome P4501A (P4501A) to reactive intermediates which may bind irreversibly to tissue macromolecules. The irreversible binding of [3H]Trp-P-1 in the brain of NMRI-mice was studied by microautoradiography. There was a selective irreversible binding of radioactivity in endothelial cells following an i.v. or i.p. injection of [3H]Trp-P-1 (100 μg/kg or 1.5 mg/kg) in mice treated with the P4501A-inducing agent β-naphthoflavone (BNF). The binding of radioactivity was highest in capillary loops of the choroid plexus, less marked in large cerebral veins and in arachnoidal veins whereas no binding was observed in cerebral capillaries, arteries, neurons or in other brain cells. In endothelial cells of vehicle-treated control mice injected with [3H]Trp-P-1 no binding of radioactivity was observed. At incubation of brain slices with [3H]Trp-P-1, there was a marked irreversible binding of radioactivity in endothelial cells in the choroid plexus of BNF-treated mice but not in vehicle-treated control mice. The P4501A inhibitor ellipticine abolished the BNF-induced endothelial binding of [3H]Trp-P-1-derived radioactivity in vivo and in vitro. The marked binding of Trp-P-1-derived radioactivity in endothelial cells of the choroid plexus of BNF-treated mice demonstrate that a BNF-responsive enzyme activity, possibly P4501A, may be induced at this site and suggests that a P450-dependent enzyme activity be part of the blood-cerebrospinal fluid barrier regulating the transendothelial passage of compounds.

Regulation of mouse choroid plexus apical Cl − and K + channels by serotonin

Using patch-clamp techniques, we have characterized ion channels in the apical membrane of the mouse choroid plexus epithelium and have examined the effect of serotonin on these channels. When the pipette contained 140 mM KCl and the bath contained NaCl Ringer solution, cell-attached patches revealed both Cl − and K + channels. The Cl − channel was activated by hyperpolarizing membrane potentials, and 70% were also activated by large depolarizing potentials (pipette potential, V p , more than negative than −40 mV). The channel exhibited linear current-voltage (I–V) relations with a conductance of 4±1pS(n=30), and a reversal potential at V p =−14±1mV(n=30). The majority of the K + channels (84%) were activated by depolarizing membrane potentials. These exhibited linear I-V relations with a conductanc of18±1 pS(n=10) and a reversal potential at V p =−51±8mV(n=10). Serotonin (10 −6 M) increased the open probability ( P o ) of active Cl − channels (n=20) by an order of magnitude at the resting potential ( V p =0mV) as well as activating previously silent Cl − channels. In In contrast, complete inhibition of K + channel activity was observed in the majority of experiments. There was a 30 s delay after exposure of the tissue to serotonin, thereafter the K + channel was rapidly inhibited (within 1 min) prior to the stimulation of the Cl − channel. Stimulation of the Cl − channel by serotonin was abolished by mianserin (10 −3 M). We conclude that serotonin exerts its effect on apical Cl − channels via the 5-HT 1c receptor. The modulation of these channels by serotonin may be important to CSF secretion and its regulation.

Effects of the extracellular matrix on fetal choroid plexus epithelial cells: Changes in morphology and multicellular organization do not affect gene expression

We have developed a primary culture system for fetal mouse choroid plexus epithelial cells which maintains their differentiated phenotype. When grown on a reconstituted basement membrane substrate (Matrigel) epithelial cells formed aggregates which became embedded in the matrix and developed into characteristic and highly reproducible multicellular vesicular structures. These vesicles consisted of a squamous layer of epithelial cells with extensive attachment to the matrix substrate, surrounding a fluid-filled lumen. Electron microscopy showed that cells comprising these vesicles had a high degree of membrane specialization and polarized morphology which in many respects mimicked the in vivo morphology. Biochemical analyses demonstrated that under these culture conditions the tissue-specific pattern of gene expression of fetal choroid plexus epithelium was maintained. After 6 days in culture these cells contained approximately the same amount of transthyretin mRNA as the 12.5-day choroid plexus in vivo, and the level of total RNA per cell, which is proportional to the protein synthetic capability of the cells, was also maintained. The pattern of protein secretion was also very similar to that generated by fetal mouse choroid plexus cells in vivo. In contrast choroid plexus epithelial cells attached poorly to collagen I gels. Heterogeneous aggregates were formed in which cell-cell interactions were more extensive than cell-substrate interactions, and in no cases was a central lumen observed. Cells on the surface of large aggregates showed some evidence of membrane polarization, while the majority of cells in the cultures exibited little evidence of polarized morphology. Despite the striking difference in morphology and multicellular organization these cells still expressed high levels of transthyretin mRNA and maintained the same pattern of protein synthesis as cells cultured on Matrigel. These results indicate that the basement membrane is important for the organization of choroid plexus epithelial cells into a functional epithelium in vitro and thus presumably the maintenance of the integrity of the blood-brain barrier in vivo. In contrast to several other epithelial systems which have been studied, the type of extracellular matrix does not appear to directly influence tissue-specific gene expression by choroid plexus epithelial cells. Thus the level of gene expression is not dependent on the cytoarchitecture and multicellular organization of this cell type.

Stromal macrophages of the choroid plexus situated at an interface between the brain and peripheral immune system constitutively express major histocompatibility class II antigens

Using immunocytochemistry we have shown that there is a population of macrophages within the stroma of the choroid plexus of rats and mice which expresses high levels of major histocompatibility complex Class II antigens. In whole mount preparations of the choroid plexus, the morphology and regular distribution of these cells is similar to the Langerhans cells of the skin. These cells reside at an important interface between the central nervous system and the peripheral immune system and their possible role in immune-mediated diseases of the central nervous system is discussed.

Gap junctional intercellular communication between cultured ependymal cells, revealed by lucifer yellow CH transfer and freeze‐fracture

In order to analyze intercellular communication between ependymal cells in mammalian brain, we have studied gap junctional communication of ependymal and glial cells in long term primary cultures derived from fetal mouse or rat hypothalamus and choroid plexus obtained in serum supplemented media with two complementary methods: 1) dye transfer of Lucifer Yellow CH after intracellular microinjection of the different cellular types, and 2) freeze-fracture of the same cultured ependymal cells. In our culture conditions, we have shown that the GJIC capacity to transfer dye was very different according to cellular types microinjected with Lucifer Yellow CH in the following respects: 1) in ependymal cells, GJIC was always important: ciliated ependymal cells, which are numerous in hypothalamic ependymal cultures (10-120 coupled cells), choroidal ependymocytes in plexus cultures (15-250 coupled cells), and non-choroidal ependymocytes in diencephalic roof cultures (10-30 coupled cells), and 2) in astroglial cells found in these primary cultures, no GJIC was observed in spite of the presence of well-differentiated gap junctions revealed by freeze-fracture replicas. All these results show a strong GJIC in ependymal cells and indicate the very good functional state of these cells in vitro.

Substitution of murine transthyretin (prealbumin) regulatory sequences into the Moloney murine leukemia virus long terminal repeat yields infectious virus with altered biological properties

The effects of inserting cellular regulatory sequences from the murine transthyretin (TTR) gene into the Moloney murine leukemia virus (M-MuLV) long terminal repeat (LTR) were investigated. Transthyretin is expressed predominantly in the liver and choroid plexus in adult mice, and TTR upstream regulatory elements were previously shown to potentiate transcription in liver-derived cells. The effects of inserting the TTR distal enhancer and/or promoter-proximal sequences into an M-MuLV LTR lacking its enhancers were measured in three ways. (i) Chimeric LTRs were fused to the bacterial chloramphenicol acetyltransferase gene (cat) and tested for transient gene expression by transfection into liver-derived cells or NIH 3T3 fibroblasts. (ii) Infectious M-MuLV containing an altered LTR [delta Mo + TTR(PD) MuLV) was generated, and infectivity in culture on hepatocyte lines and NIH 3T3 cells was tested. (iii) Infection of delta Mo + TTR(PD) MuLV in vivo was tested by inoculating NFS/N mice and performing in situ hybridization of whole animal sections. Chimeric LTR-cat constructs showed higher levels of cat gene expression in liver-derived cell lines than in NIH 3T3 cells, indicating increased LTR activity in these cells. However, in vitro infection did not show significantly higher infectivity in hepatocytes for delta Mo + TTR(PD) M-MuLV than did wild-type M-MuLV. In vivo, delta Mo + TTR(PD) MuLV showed expression in the same tissues as with wild-type M-MuLV-inoculated mice, i.e., lymphoid organs and the intestines and, additionally, two novel sites not seen in wild-type M-MuLV-inoculated animals. Of 10 mice, 8 showed viral expression in the brain and 3 showed expression in the liver. Thus, insertion of TTR elements into the M-MuLV LTR altered LTR activity both in vitro and in vivo.

Choroidal ependymocytes in culture: Expression of markers of polarity and function

Long-term primary cultures derived from fetal mouse or rat choroid plexus were obtained in serum-supplemented media. Monoclonal and polyclonal antibodies to basolateral and apical membrane components were used to observe the expression of specific markers of polarity and function. Choroid plexus cultures and thin frozen sections of adult tissues were compared by immunocytochemistry. Two polyclonal antibodies directed against laminin and fibronectin were used on cultured choroid plexus and sectioned tissues, showing that fibronectin and laminin are located on the basolateral membrane domain in ependymocytes in vitro, as well as in vivo. Na+-K+ATPase was apically detected by light and electron microscopy with a monoclonal antibody (Mab H30) in both cultured cells and sectioned tissues. Double immunofluorescent staining with Mab H30 and affinity-purified polyclonal antibodies to the α subunit of G0 protein (G0α) demonstrated the relatively similar distribution of the two antigens on the apical face of the choroidal tissue, both in vivo and in vitro. The distribution of these markers shows a typical differentiation with maintenance of polarized features in choroidal ependymocytes in culture, testifying that this cell culture system constitutes an interesting model for studying the functional characteristics of ependymal cells of the choroid plexus.

Characterization of ependymal cells in hypothalamic and choroidal primary cultures

Long-term primary cultures derived from fetal mouse or rat hypothalamus and choroid plexus were obtained in serum-supplemented and chemically defined media. In order to identify and characterize cell types growing in our cultures, we used morphological features provided by phase-contrast, scanning and transmission electron microscopy. Immunological criteria were recognized, using antibodies against intermediate filament proteins (vimentin, gliofibrillar acid protein, cytokeratin, desmin, neurofilament proteins), actin, myosin, ciliary rootlets, laminin and fibronectin in single or double immunostaining, and monoclonal antibodies known to detect epitopes of ependymal or endothelial cells. Minor cell types such as astrocytes, fibroblasts and endothelial cells were distinguished. Ependymal cells, which exceeded 75% of the cultured cells, were identified by their cell shape and epithelial organization revealed by phase-contrast and transmission electron microscopy, by their apical differentiation evidenced by scanning and transmission electron microscopy, and by certain molecular markers ( e.g. gliofibrillar acid or ciliary rootlet proteins) detected by immunofluorescence. Four ependymal cell types were recognized: choroidal ependymocytes, ciliated and unciliated ependymal cells, and tanycytes. All these cultured ependymal cell types showed a remarkable resemblance to in vivo ependymocytes, in terms of marker expression and ultrastructural features.

CDNA cloning of a serotonin 5-HT1C receptor by electrophysiological assays of mRNA-injected Xenopus oocytes.

We describe a strategy for the cloning of neurotransmitter-receptor and ion-channel cDNAs that is based on electrophysiological assays of mRNA-injected Xenopus oocytes. This procedure circumvents the purification of these membrane proteins, which is hindered by their low abundance and their hydrophobic nature. It involves methods for RNA fractionation by high-resolution gel electrophoresis, directional cDNA cloning in a single-stranded vector, and screening of the cDNA library by voltage-clamp measurements of currents induced by serotonin in mRNA-injected oocytes. The applicability of our approach is demonstrated by the isolation of a serotonin receptor cDNA clone from a mouse choroid plexus papilloma. The clone was identified by hybrid-depletion and hybrid-selection procedures. The receptor expressed in oocytes injected with hybrid-selected RNA is fully functional, indicating that it is composed of a single subunit encoded by a 5-kilobase RNA. The pharmacology of the hybrid-selected receptor confirms that we have successfully cloned a serotonin 5-HT1C receptor cDNA.

Immunocytochemical localization of Na+,K+-ATPase catalytic polypeptide in mouse choroid plexus.

Na+,K+-ATPase plays a central role in the mechanism of cerebrospinal fluid secretion by the choroid plexus. We have used an antiserum to the 100 KD catalytic polypeptide of the enzyme purified from mouse brain (30) to localize the catalytic unit in mouse choroid plexus at the light and electron microscopic levels. Pre-embedding immunostaining with the peroxidase-conjugated second antibody technique showed that microvillar borders facing the ventricle were intensely reactive. In contrast, basal and lateral plasma membrane surfaces were devoid of activity. Identical localization was obtained with a post-embedding procedure in which protein A-gold was used to stain immunoreactive sites on thin sections of Lowicryl-embedded tissue. For comparison, immunogold staining was shown to be restricted to basolateral membranes of kidney medullary ascending thick limbs. The apical localization of Na+,K+-ATPase in choroid plexus is in striking contrast to the almost exclusive basolateral localization seen in other ion-transporting tissues. The immunocytochemical data are completely consistent with physiological data on choroidal epithelial transport and with light microscopic autoradiographic localization of [3H]-ouabain binding sites.

Interaction between Trypanosoma brucei and the ependymal cell of the choroid plexus

The fine structure of the normal choroid plexus of rats and mice and of those infected with Trypanosoma brucei was examined by transmission and scanning electron microscopy: extracellular trypomastigotes in the perivascular stroma predominate but the evidence presented suggests that they are derived both from stages in the blood and from others undergoing division within ependymal cells, a process which results in destruction of a large proportion of ependymal cells in the parts of choroid plexus affected. The choroid plexus maintains its integrity by regeneration of an outer layer of ependymal cells.

Transmission and scanning electron microscopic study of chlordecone (kepone) induced changes in the male mouse choroid plexus

To investigate the effects of the estrogenic insecticide chlordecone on the morphology of mouse choroid plexus, 4 different doses (100.0, 250.0, 500.0 and 1000.0 μg) of the chemical were administered intraperitoneally to groups of adult males. Concurrent with the chlordecone treatments, another group of males received 10.0 μg estradiol-17β; the control group was treated with sesame oil vehicle. After 15 days of daily chemical injections, the mice were terminated and the choroid plexus from fourth ventricle examined morphologically. Scanning (SEM) and transmission (TEM) electron microscopic examination of control choroid plexus showed the cuboidal epithelium profusely covered with microvilli. SEM examinations of choroid plexus epithelium after chlordecone treatments revealed dose-dependent, cell alterations that effected the microvilli and cell surfaces. After the highest chlordecone dose, microvilli were no longer visible, the choroidal cell membrane appeared either smooth or pitted and there was evidence of increased luminal debris. TEM observations of the same choroid plexus cells revealed vacuolated cytoplasm, dilated endoplasmic reticulum, vacuolated mitochondria with disrupted cristae and cellular degeneration. SEM and TEM examination of choroid plexus after estradiol treatments revealed similar cellular alterations to those recorded after chlordecone treatments. The possible significance of these data are discussed.

Aryl hydrocarbon hydroxylase in rat brain microsomes

Trp-P-1 (3-amino-1,4-dimethyl-5H-pyrido(4,3-b)indole) is known to be metabolized by cytochrome P4501A (P4501A) to reactive intermediates which may bind irreversibly to tissue macromolecules. The irreversible binding of [3H]Trp-P-1 in the brain of NMRI-mice was studied by microautoradiography. There was a selective irreversible binding of radioactivity in endothelial cells following an i.v. or i.p. injection of [3H]Trp-P-1 (100 μg/kg or 1.5 mg/kg) in mice treated with the P4501A-inducing agent β-naphthoflavone (BNF). The binding of radioactivity was highest in capillary loops of the choroid plexus, less marked in large cerebral veins and in arachnoidal veins whereas no binding was observed in cerebral capillaries, arteries, neurons or in other brain cells. In endothelial cells of vehicle-treated control mice injected with [3H]Trp-P-1 no binding of radioactivity was observed. At incubation of brain slices with [3H]Trp-P-1, there was a marked irreversible binding of radioactivity in endothelial cells in the choroid plexus of BNF-treated mice but not in vehicle-treated control mice. The P4501A inhibitor ellipticine abolished the BNF-induced endothelial binding of [3H]Trp-P-1-derived radioactivity in vivo and in vitro. The marked binding of Trp-P-1-derived radioactivity in endothelial cells of the choroid plexus of BNF-treated mice demonstrate that a BNF-responsive enzyme activity, possibly P4501A, may be induced at this site and suggests that a P450-dependent enzyme activity be part of the blood-cerebrospinal fluid barrier regulating the transendothelial passage of compounds.

Radioiodide uptake in brain, CSF, thyroid, and salivary glands of audiogenic seizure mice.

DBA/2J (DBA) mice are susceptible to audiogenic seizures (ASs) in an age-dependent manner. Anion transport as measured by radioiodide uptake was determined in thyroid gland, salivary gland, skeletal muscle, cerebral cortex, cerebellum, brainstem, and CSF from these mice at various ages. Anion transport was also determined in C57BL/6J(C57) mice, an AS-resistant strain. In thyroid, DBA mice had an enhanced ability to concentrate iodide at 21 days of age when they have maximal AS susceptibility, as compared with the same-aged C57 mice. This difference in thyroid function was less marked at 40 days of age, when DBA mice are less AS susceptible, and was absent at 110 days of age, when DBA mice are AS resistant. In brain, differences in iodide uptake were also noted between these two strains of mice at 21 days of age. DBA mice had an increased concentration of iodide in CSF, an indication that they have a defect in the transport of iodide out of the CSF across the choroid plexus. In addition, DBA mice had a lower ratio of cerebral cortex to CSF iodide, which suggests that DBA mice have a defect in the transport of this anion into cerebral cortical cells from brain interstitial fluid. These differences in iodide transport in brain decreased with age as the AS susceptibility of DBA mice decreased. These results suggest a relation between anion transport in thyroid gland, cerebral cortex, and choroid plexus and AS susceptibility in DBA mice at 21 days of age.