Neuroendocrine regulatory mechanisms in the choroid plexus-cerebrospinal fluid system

Vasopressin gene expression in rat choroid plexus

Vasopressin (VP) levels in cerebrospinal fluid (CSF) change in response to physiological stimuli and under various pathological conditions. The sources of CSF VP have yet to be clarified, however. In the present study, we provide evidence indicating that VP is synthesized in the choroid plexus, the primary site of CSF formation. All experiments were performed on adult male Sprague-Dawley rats. The presence of VP mRNA in choroid plexus epithelium was demonstrated by in situ hybridization histochemistry using the 35S-labeled riboprobe that was complementary to cDNA fragment of rat VP encoding the C-terminus part of proVP. In situ hybridization findings were confirmed by reverse transcriptase-polymerase chain reaction analysis. Immunohistochemistry for VP-associated neurophysin (VP-NP), a polypeptide component of proVP, revealed subapical accumulation of VP-NP-immunopositive product in choroidal epithelial cells. Immunoprecipitation and immunoblotting of choroidal protein extracts with anti-VP-NP antibody demonstrated the presence of a approximately 10-kD polypeptide that was also detected in hypothalamus. We hypothesize that the choroid plexus-derived VP exerts autocrine and/or paracrine effects on tissues near the CSF system.

Inhibition by lead of production and secretion of transthyretin in the choroid plexus: its relation to thyroxine transport at blood-CSF barrier

Long-term, low-dose Pb exposure in rats is associated with a significant decrease in transthyretin (TTR) concentrations in the CSF. Since CSF TTR, a primary carrier of thyroxine in brain, is produced and secreted by the choroid plexus, in vitro studies were conducted to test whether Pb exposure interferes with TTR production and/or secretion by the choroid plexus, leading to an impaired thyroxine transport at the blood-CSF barrier. Newly synthesized TTR molecules in the cultured choroidal epithelial cells were pulse-labeled with [35S]methionine. [35S]TTR in the cell lysates and culture media was immunoprecipitated and separated by SDS-PAGE, and quantitated by autoradiography and liquid scintillation counting. Pb treatment did not significantly alter the protein concentrations in the culture, but inhibited the synthesis of total [35S]TTR (cells + media), particularly during the later chase phase. Two-way ANOVA of the chase phase revealed that Pb exposure (30 microM) significantly suppressed the rate of secretion of [35S]TTR compared to the controls (p < 0.05). Accordingly, Pb treatment caused a retention of [35S]TTR by the cells. In a two-chamber transport system with a monolayer of epithelial barrier, Pb exposure (30 microM) reduced the initial release rate constant (kr) of [125I]T4 from the cell monolayer to the culture media and impeded the transepithelial transport of [125I]T4 from the basal to apical side of epithelial cells by 27%. Taken together, these in vitro data suggest that sequestration of Pb in the choroid plexus hinders the production and secretion of TTR by this tissue. Consequently, this may alter the transport of thyroxine across this blood-CSF barrier.

AVP V1 receptor-mediated decrease in Cl- efflux and increase in dark cell number in choroid plexus epithelium

The cerebrospinal fluid (CSF)-generating choroid plexus (CP) has many V1 binding sites for arginine vasopressin (AVP). AVP decreases CSF formation rate and choroidal blood flow, but little is known about how AVP alters ion transport across the blood-CSF barrier. Adult rat lateral ventricle CP was loaded with 36Cl-, exposed to AVP for 20 min, and then placed in isotope-free artificial CSF to measure release of 36Cl-. Effect of AVP at 10(-12) to 10(-7) M on the Cl- efflux rate coefficient (in s-1) was quantified. Maximal inhibition (by 20%) of Cl- extrusion at 10(-9) M AVP was prevented by the V1 receptor antagonist [beta-mercapto-beta, beta-cyclopentamethyleneproprionyl1,O-Me-Tyr2,Arg8]vasopressin. AVP also increased by more than twofold the number of dark and possibly dehydrated but otherwise morphologically normal choroid epithelial cells in adult CP. The V1 receptor antagonist prevented this AVP-induced increment in dark cell frequency. In infant rats (1 wk) with incomplete CSF secretory ability, 10(-9) M AVP altered neither Cl- efflux nor dark cell frequency. The ability of AVP to elicit functional and structural changes in adult, but not infant, CP epithelium is discussed in regard to ion transport, CSF secretion, intracranial pressure, and hydrocephalus.

Distinct sites of insulin-like growth factor (IGF)-II expression and localization in lesioned rat brain: possible roles of IGF binding proteins (IGFBPs) in the mediation of IGF-II activity

Although expression of the IGF-II has been demonstrated within the central nervous system (CNS), past studies have failed to reveal its precise roles or responses subsequent to a traumatic injury. To demonstrate that IGF-II, IGFBP, and IGF receptor (-R) expression alters in response to a penetrating CNS injury, we used the techniques of ribonuclease protection assay, in situ hybridization, immunohistochemistry, Western blotting, and RIA. Under normal physiology, IGF-II expression is restricted to the mesenchymal support structures of the brain, including the choroid plexus, where its expression is coincident with that of IGFBP-2. Between 1-7 days post lesion (dpl), in the acute phase following a penetrant wound to the CNS, IGF-II and IGF-IIR protein, but not messenger RNA, were colocalized, with IGF-I, IGF-IR, and IGFBP-1, -2, -3, and -6, to neurons, macrophages, astrocytes, and microglia within the damaged tissue. Within the cerebrospinal fluid (CSF), levels of IGF-II peptide increased to peak at 7 dpl. IGFBP-2, -3, and -6 were also observed within the CSF, with IGFBP-2 predominating and exhibiting an increase in binding efficiency from 7-10 dpl. In the chronic phase of injury (7-14 dpl), an increase in both IGF-II, IGF-IIR and IGFBP-5 messenger RNA and protein was observed specifically and focally in the marginal astrocytes forming the limiting glial membrane of the wound. Thus, our evidence suggests that there are two mechanisms of action for IGF-II within the injured rat brain. During the acute phase, the secretion of IGF-II from the choroid plexus into the CSF is up-regulated, resulting in increased transport of the peptide to the wound. In the CSF, transported IGF-II is complexed to IGFBP-2 and essentially demonstrates an endocrine mode of action with a balance of locally produced IGFBPs modulating its bioactivity in the wound. Later in the wounding response, levels of IGF-II decline in the CSF and the wound neuropil, possibly with the aid of increased IGFBP-5 levels that may help to locally sequester and down-regulate IGF-II activity. Hence, in the chronic phase of the injury response, IGF-II reasserts itself to a predominantly autocrine/paracrine role restricted to the mesenchymal support structures, including the glia limitans, which may help reestablish and maintain tissue homeostasis.

The epithelial inward rectifier channel Kir7.1 displays unusual K+ permeation properties

Rat and human cDNAs were isolated that both encoded a 360 amino acid polypeptide with a tertiary structure typical of inwardly rectifying K+ channel (Kir) subunits. The new proteins, termed Kir7.1, were <37% identical to other Kir subunits and showed various unique residues at conserved sites, particularly near the pore region. High levels of Kir7.1 transcripts were detected in rat brain, lung, kidney, and testis. In situ hybridization of rat brain sections demonstrated that Kir7.1 mRNA was absent from neurons and glia but strongly expressed in the secretory epithelial cells of the choroid plexus (as confirmed by in situ patch-clamp measurements). In cRNA-injected Xenopus oocytes Kir7.1 generated macroscopic Kir currents that showed a very shallow dependence on external K+ ([K+]e), which is in marked contrast to all other Kir channels. At a holding potential of -100 mV, the inward current through Kir7.1 averaged -3.8 +/- 1.04 microA with 2 mM [K+]e and -4.82 +/- 1.87 microA with 96 mM [K+]e. Kir7.1 has a methionine at position 125 in the pore region where other Kir channels have an arginine. When this residue was replaced by the conserved arginine in mutant Kir7.1 channels, the pronounced dependence of K+ permeability on [K+]e, characteristic for other Kir channels, was restored and the Ba2+ sensitivity was increased by a factor of approximately 25 (Ki = 27 microM). These findings support the important role of this site in the regulation of K+ permeability in Kir channels by extracellular cations.

Alternative pathways of neural control of the immune process

Less well established alternative neuromodulatory pathways are neuropeptide-mediated axon reflexes of sensory neurons, gut immunotrafficing, gut transmucosal transport of endogenous bacterial toxin, and the direct secretion of immunoregulatory cytokines by the brain. TNF-alpha and IL-1ra enter peripheral blood after their intracerebroventricular (i.c.v.) injection. Closed head injury or stroke increases blood IL-6 and the acute phase response; neuroblastomas immunosuppress by secreting TGF-beta. The IL-6 that appears in the blood after i.c.v. IL-1 in the rat is partly derived by secretion from the brain into the superior sagital sinus (Romero et al.; 1996. Am. J. Physiol. 270: R518) and is not dependent on peripheral sympathetic activation. Central endothelium and choroid plexus are potential sources of sagital sinus IL-6. TNF-alpha, which appears in blood after i.c.v. LPS, but not IL-1 beta, is due largely to toxin leaving the brain compartment and activating peripheral immunoreactive tissues. Antigens and cytokine immunoregulators drain into cervical lymph. Changes in glial milieu induced by intrinsic neuronal activity could by secretion from brain to blood modulate peripheral immunoreactivity.

Ependymal and choroidal cells in culture: characterization and functional differentiation

During the past 10 years, our teams developed long-term primary cultures of ependymal cells derived from ventricular walls of telencephalon and hypothalamus or choroidal cells (modified ependymal cells) derived from plexuses dissected out of fetal or newborn mouse or rat brains. Cultures were established in serum-supplemented or chemically defined media after seeding on serum-, fibronectin-, or collagen-laminin-coated plastic dishes or semipermeable inserts. To identify and characterize cell types growing in our cultures, we used morphological features provided by phase contrast, scanning, and transmission electron microscopy. We used antibodies against intermediate filament proteins (vimentin, glial fibrillary acidic protein, cytokeratin, desmin, neurofilament proteins), actin, myosin, ciliary rootlets, laminin, and fibronectin in single or double immunostaining, and monoclonal antibodies against epitopes of ependymal or endothelial cells, to recognize ventricular wall cell types with immunological criteria. Ciliated or nonciliated ependymal cells in telencephalic cultures, tanycytes and ciliated and nonciliated ependymal cells in hypothalamic cultures always exceeded 75% of the cultured cells under the conditions used. These cells were characterized by their cell shape and epithelial organization, by their apical differentiations observed by scanning and transmission electron microscopy, and by specific markers (e.g., glial fibrillary acidic protein, ciliary rootlet proteins, DARPP 32) detected by immunofluorescence. All these cultured ependymal cell types remarkably resembled in vivo ependymocytes in terms of molecular markers and ultrastructural features. Choroidal cells were also maintained for several weeks in culture, and abundantly expressed markers were detected in both choroidal tissue and culture (Na+-K+-dependent ATPase, DARPP 32, G proteins, ANP receptors). In this review, the culture models we developed (defined in terms of biological material, media, substrates, duration, and subculturing) are also compared with those developed by other investigators during the last 10 years. Focusing on morphological and functional approaches, we have shown that these culture models were suitable to investigate and provide new insights on (1) the gap junctional communication of ependymal, choroidal, and astroglial cells in long-term primary cultures by freeze-fracture or dye transfer of Lucifer Yellow CH after intracellular microinjection; (2) some ionic channels; (3) the hormone receptors to tri-iodothyronine or atrial natriuretic peptides; (4) the regulatory effect of tri-iodothyronine on glutamine synthetase expression; (5) the endocytosis and transcytosis of proteins; and (6) the morphogenetic effects of galactosyl-ceramide. We also discuss new insights provided by recent results reported on in vitro ependymal and choroidal expressions of neuropeptide-processing enzymes and neurosecretory proteins or choroidal expression of transferrin regulated through serotoninergic activation.

Decreased expression of natriuretic peptide A receptors and decreased cGMP production in the choroid plexus of spontaneously hypertensive rats

Atrial natriuretic peptide receptor (ANP) subtypes and their signal transduction response were characterized in choroid plexus of spontaneously hypertensive (SHR) and normotensive (WKY) rats. We found two ANP receptor subtypes, guanylate cyclase coupled and uncoupled, in both rat strains. Binding of ANP was lower in SHR choroid plexus when compared to WKY. The lower ANP binding in SHR was the result of a decrease of binding to the guanylate cyclase-coupled receptor subtype A, a decrease that correlated well with the decreased ANP-induced cGMP formation in SHR. Forskolin stimulated cGMP production to the same extent in both strains. In WKY rats, ANP increased basal and forskolin-stimulated cAMP production; conversely, in SHR, ANP did not affect the basal level of cAMP and inhibited the forskolin-stimulated cAMP production. These results demonstrate differences in ANP receptor subtype expression, and ANP signal transduction in choroid plexus of hypertensive and normotensive rats, which is of possible significance to the central mechanisms of blood pressure control.

Primary culture of choroidal epithelial cells: characterization of an in vitro model of blood-CSF barrier

A primary rat choroidal epithelial cell culture system was developed to investigate mechanisms of heavy metal toxicity on the blood-cerebrospinal fluid (CSF) barrier. Epithelial cells were dissociated from choroidal tissue by pronase digestion and cultured in standard DMEM culture media supplemented with 10% fetal bovine serum and 10 ng epithelial growth factor per ml. The procedure yielded 2-5 x 10(4) cells from pooled plexuses of three to four rats, and a viability of 77-85%. The cultures displayed a dominant polygonal type of epithelial cells, with a population doubling time of 2-3 d. The cultures were of distinct choroidal epithelial origins. For example, immunocytochemical studies using monospecific rabbit anti-rat TTR polyclonal antibody revealed a strong positive stain of transthyretin (TTR), a thyroxine transport protein exclusively produced by the choroidal epithelia. Also, reverse-transcriptase polymerase chain reaction (PCR) confirmed the presence of specific TTR mRNA in the cultures. The cultures were further adapted to grow on a freely permeable membrane sandwiched between two culture chambers. The formation of an impermeable confluent monolayer occurred within 5 d after seeding and was verified by the presence of a steady electrical resistance across the membrane (80 +/- 10 ohm per cm2). The epithelial barriers appeared to actively transport [125I]-thyroxine from the basal to apical chamber. These results suggest that this primary cell culture system possesses typical choroidal epithelial characteristics and appears to be a suitable model for in vitro mechanistic investigations of blood-CSF barrier.

Choroidal readaptation to gravity in rats after spaceflight and head-down tilt

To determine when choroidal structures were restored after readaptation to Earth gravity or orthostatic position, fine structure and protein distribution were studied in rat choroid plexus dissected either 6 h [Space Life Sciences-2 (SLS-2) experiments] or 2 days [National Institutes of Health-Rodent 1 (NIH-R1) experiments] after a spaceflight, or 6 h after head-down tilt (HDT) experiments. Apical alterations were noted in choroidal cells from SLS-2 and HDT animals, confirming that weightlessness impaired choroidal structures and functions. However, the presence of small apical microvilli and kinocilia and the absence of vesicle accumulations showed that the apical organization began to be restored rapidly after landing. Very enlarged apical microvilli appeared after 2 days on Earth, suggesting increased choroidal activity. However, as distributions of ezrin and carbonic anhydrase II remained altered in both flight and suspended animals after readaptation to Earth gravity, it was concluded that choroidal structures and functions were not completely restored, even after 2 days in Earth's gravity.

Interactions of beta-amyloids with the blood-brain barrier

Blood-borne beta-amyloids (A beta s) could affect brain function by (1) crossing the BBB to directly interact with brain tissues or (2) altering BBB function by interacting with the brain capillaries that make up the BBB. Several radioactively labeled A beta s have been examined for such interactions. Blood-borne A beta 1-28 is hindered from accumulating in brain by a slow rate of passage across the BBB and by robust enzymatic degradation. A beta 1-40, but not A beta 40-1 or A beta 1-42, is sequestered by brain capillaries, raising the possibility that it could affect BBB function. Small amounts of circulating A beta 1-40 are recovered intact from CSF and brain. A beta 1-40 is degraded by aluminum-sensitive, calcium-dependent intracellular enzymes. Apo-J, which can bind A beta, has been shown with an in situ method to be transported by a saturable system across the BBB. However, our recent work has shown that this system is not operable in vivo, probably because the transporter is saturated at physiological blood levels. In conclusion, A beta s have been shown to interact with and to cross the BBB.

The presence of arginine vasopressin and its mRNA in rat choroid plexus epithelium

Arginine vasopressin (AVP) plays an important role in the regulation of secretory function and hemodynamics of choroid plexus, the primary site of cerebrospinal fluid (CSF) production. In the present study, localization of AVP and its transcripts in choroid plexus of adult male Sprague-Dawley rats was studied by immunohistochemistry and in situ hybridization histochemistry, respectively. For immunohistochemical analysis, AVP-specific polyclonal rabbit antibody was employed. Plasmid, pGrVP, containing a 232-bp fragment of rat AVP cDNA encoding the C-terminus of proAVP, was used as a probe to detect AVP mRNA. AVP-immunoreactive product was predominantly localized close to the apical (CSF-facing) membrane of choroidal epithelium while AVP transcripts were distributed throughout the cytoplasm of the cells. Our findings indicate that AVP is synthesized in choroid plexus epithelium, which suggests autocrine and/or paracrine actions of this peptide in choroidal tissue.

Expression of serotonin transporter mRNA in rat brain: presence in neuronal and non-neuronal cells and effect of paroxetine

The expression of serotonin transporter mRNA in rat brain was-examined by in situ hybridisation. Hybridisation was observed in cells of the known serotonergic nuclei and no other neuronal populations. It was also associated with ependymal cells of the aqueduct which may indicate a specialisation of this part of the ventricular system in anatomical and neurophysiological terms. The effect of the selective serotonin reuptake inhibitor paroxetine on neuronal expression of the serotonin transporter mRNA was examined. Quantitation at the cellular level in the dorsal and median raphe nuclei was carried out by analysis of the mean number of silver grains per cell in autoradiographed sections. No significant change (P > 0.1) in serotonin transporter mRNA expression was observed following 21 day administration of paroxetine (5 mg/kg per day).

Beta-trace gene expression is regulated by a core promoter and a distal thyroid hormone response element

We isolated and characterized the human beta-Trace protein (betaTP) gene promoter. betaTP, also known as prostaglandin D2 synthase, is a lipocalin secreted from the choroid plexus and meninges into cerebrospinal fluid. Basal transcription of the betaTP gene is directed from a core promoter found within the first 325 bases of the 5'-flanking sequence. The betaTP gene promoter is responsive to thyroid hormone (3,3',5-triiodothyronine, T3) and efficiently repressed by unliganded human thyroid hormone receptor beta (TRbeta). Functional analysis of the betaTP promoter in TE671 cells revealed that responsiveness to T3 occurs in sequences 2.5 kilobase pairs 5' of the start site. Within the hormone-responsive region we identified a thyroid hormone response element (TRE) located from -2576 to -2562 base pairs relative to the transcription start site. The betaTP TRE is composed of two directly repeated consensus half-sites separated by a 3-base pair space (DR3). The betaTP TRE forms specific complexes with TRbeta. We have shown that a gene active in the choroid plexus and meninges is responsive to T3. T3 may play a role in the regulated transport of substances into the cerebrospinal fluid and ultimately the brain.

Effects of an 11-day spaceflight on the choroid plexus of developing rats

Cellular distributions of ezrin, a cytoskeletal protein involved in apical cell differentiation in choroid plexus, and carbonic anhydrase II, which is partly involved in the cerebrospinal fluid production, were studied by immunocytochemistry, at the level of choroidal epithelial cells from the lateral, third and fourth ventricles in normal or experimental fetuses, in parallel with the ultrastructure of apical microvilli, observed by transmission electron microscopy. We compared choroid plexuses from developing normal rats (gestational day 15 to birth) with choroid plexuses from 20-day-old rat fetuses, developed for 11 days in space, aboard a space shuttle (NASA STS-66 mission, NIH-R1 experiments), from gestational day 9 to day 20. The main changes observed in fetuses developed in space were demonstrated by immunocytochemistry and concerned the distribution of ezrin and carbonic anhydrase II. Thus, in fetuses developing in space, ezrin was strongly detected in the choroidal cytoplasm and weakly associated to the membrane in the apical domain of the choroid plexus from the fourth ventricle. Such alterations suggested that choroid plexus from rat fetal brain displays a delayed maturation under a micro-gravitational environment. In contrast, intense immunoreactions to anti-carbonic anhydrase II antibodies showed that this enzyme is very abundant in rats developed in space, compared to ground control fetuses.

Autoregulation of blood flow to choroid plexus of rabbits

Blood flow to the choroid plexus (CP) of rabbits was measured before and during an increase in arterial pressure (AP). Blood flow returned to control levels in the CP of the lateral and fourth ventricles of the brain when AP was increased 63% by i.v. infusion of norepinephrine. However, when AP was increased 68% by occlusion of the descending thoracic aorta, blood flow to the CP of the fourth ventricle remained elevated, while blood flow to the CP of the lateral ventricles returned to the control level. Our findings suggest that blood flow to the CP of the lateral ventricles autoregulates during nonpharmacological or pharmacological increases in AP, while blood flow to CP of the fourth ventricle does not autoregulate during nonpharmacological increases in AP.

Plasticity of astrocytes of the ventral glial limitans subjacent to the supraoptic nucleus

We present evidence of gross morphological changes in astrocytes of the ventral glial limitans (VGL) associated with a well-known model of central nervous system (CNS) plasticity: the hypothalamic supraoptic nucleus (SON). Activity of SON magnocellular neuroendocrine cells (MNCs) was stimulated in experimental rats by substitution of 2% saline for drinking water for 2 or 9 days. Light microscopic measures revealed that a significant decrease in VGL thickness, by 34%, occurred with 9 days of stimulation. Astrocyte nuclei of 9-day dehydrated animals were also found to be 39% closer to the pial surface when compared with controls. Electron microscopy revealed a reorientation of individual astrocytes from a direction perpendicular (vertical) to the pial surface, to one parallel (horizontal) to this region. Vertically oriented astrocytes were found to be greater in the control group, by 49%, when compared with the 9-day dehydrated group, where cells were predominantly horizontal in orientation. Vertically oriented cells were further analyzed as to the direction of their vertical projections. Control, 2-day dehydrated and 9-day rehydrated animals, had more vertical cells which were oriented toward the pial surface when compared with 9-day dehydrated animals, where the relatively few vertically oriented astrocytes were significantly more likely to project toward the dendritic zone. In animals allowed to rehydrate for 9 days following a period of dehydration, these changes returned toward control levels. We conclude that astrocytes in vivo are capable of reversible gross morphological changes over a relatively short time.

Establishment and characterization of choroid plexus carcinoma cell lines: connection between choroid plexus and immune systems

Murine choroid plexus cell lines were produced from choroid plexus carcinoma generated in transgenic mice harboring the viral oncogene simian virus 40 large tumor antigen under transcriptional control of an intronic enhancer region from the human immunoglobulin heavy chain (IgH) gene. Two morphologically distinct cell lines have been cloned. These established cell lines retained the characteristics of choroid plexus cells in that they expressed such choroid plexus cell marker or related proteins as transthyretin and alpha2-macroglobulin. They were tumorigenic in nude mice. In the cell lines, the muA and muB (HE2) motifs within the IgH intronic enhancer were active and we also demonstrated the existence of the proteins binding to these motifs, suggesting a potential link between the choroid plexus and immune systems. It is considered that these binding proteins act as trans-activators for the enhancer and may belong to the class of ETS-related proteins. These cell lines and xenografts should be useful materials for analyses of choroid plexus functions.

Chronic lead exposure alters transthyretin concentration in rat cerebrospinal fluid: the role of the choroid plexus

The choroid plexus, which is responsible for the maintenance of the biochemical milieu of the cerebrospinal fluid (CSF), avidly sequesters Pb. In order to test the hypothesis that chronic Pb exposure may impair choroid plexus function, male weanling Sprague-Dawley rats were exposed to Pb in drinking water at doses of 0, 50, or 250 micrograms Pb/ml (as Pb acetate) for 30, 60, or 90 days. The function of the choroid plexus was assessed as reflected by CSF concentrations of transthyretin (TTR, a major CSF protein manufactured by brain choroid plexus) and CSF essential metal ions (Ca2+, Mg2+, K+, and Na+). TTR concentrations were determined by radioimmunoassay using a monospecific rabbit anti-rat TTR polyclonal antibody, and CSF metal ions analyzed by flame atomic absorption spectrophotometry. Two-way ANOVA of CSF TTR concentrations revealed highly significant dose (p < 0.0001), time (p < 0.0223), and dose-by-time effects (p < 0.0379). Moreover, the percentage of reduction of CSF TTR was directly correlated with Pb concentrations in the choroid plexus (r = 0.703, p < 0.05). Pb exposure significantly increased CSF concentrations of Mg2+, but did not markedly altered CSF concentrations of Ca2+, K+, and Na+. Histopathologic examination under the light microscope did not show distinct alterations of plexus structure in Pb-treated rats. Since TTR is responsible for transport of thyroid hormones to the developing brain, we postulate that the depression of choroid plexus TTR production (and/or secretion) by Pb may impair brain development in young animals by depriving the CNS of thyroid hormones.

Characterization and localization of bradykinin B2 receptors in the guinea-pig using a radioiodinated HOE140 analogue

The potent bradykinin B2 receptor antagonist analogue, [125I]HPP-HOE140, ([125I]-3-4-hydroxyphenyl-propionyl-D-Arg0-[Hyp3, Thi5,D-Tic7, Oic8]bradykinin), was used to localize and characterize guinea-pig tissue bradykinin B2 receptors. Analysis of competition for the radioligand binding, using membrane preparations of lung, ileum and uterus, revealed the presence of a high- and low-affinity binding site: at the high-affinity site, the apparent Ki for the various bradykinin B2 receptor ligands ranged from 0.26 to 2.13 nM for HPP-HOE140, from 0.25 to 1.45 nM for HOE140, from 129 to 625 nM for D-Arg0[pHyp3,Phe7]bradykinin and from 0.05 to 1.11 nM for bradykinin. At the low-affinity site, the apparent Ki values ranged from 4.90 to 10.5 nM, from 1.23 to 1.90 nM, 4760 nM and from 2.01 to 62.1 nM, respectively. By contrast, the bradykinin Bi receptor antagonist, des-Arg9[Leu8]bradykinin did not compete for [125I]HPP-HOE140 binding from membrane preparations at concentrations up to 1 microM. Using in vitro autoradiography on tissue sections, intense binding was observed in the lamina propria of the villi of ileum and the arteriolar smooth muscle cells in lung. In the uterus, dense binding was found in the inner third of the myometrium and over epithelial cells of the glandular endometrium, while diffuse binding was observed throughout the endometrial stroma. In the brain, intense binding was observed in the nucleus of the solitary tract, spinal trigeminal tract and area postrema of the hindbrain, the middle cerebral arteries, and the choroid plexus of the third and lateral ventricles. Moderate binding was observed in the CA3 region of the hippocampus and posterior and ventroposterior thalamic nuclei. In the spinal cord, high-density binding occurred in the laminae I and II of the dorsal horn. Unlike previous autoradiographic localization studies of the bradykinin B2 receptor using radiolabeled bradykinin, the radiolabeled antagonist HPP-HOE140 did not bind to bradykinin-degrading peptidases, such as angiotensin-converting enzyme, and displayed subtype specificity. Therefore, binding studies with [125I]HPP-HOE140 offers high sensitivity and specificity for characterization, quantitation and localization of subtypes of bradykinin B2 receptors in tissues, and offers new information on uterine and brain bradykinin B2 receptors.

Differential distribution of nicotinamide adenine dinucleotide phosphate-diaphorase and neural nitric oxide synthase in the rat choroid plexus. A histochemical and immunocytochemical study

This study used NADPH diaphorase (NADPHd) histochemistry and neuronal nitric oxide synthase immunocytochemistry to examine the localization of nitric oxide synthase in the choroid plexus of the lateral ventricles and the fourth ventricle of rat brain. That the NADPHd reaction product in choroid plexus was specific to nitric oxide synthase was evaluated: (i) by comparison to immunocytochemical labelling for nitric oxide synthase; and (ii) by comparing NADPHd histochemical staining in choroid plexus and brain (rich in nitric oxide synthase-positive and NADPHd-positive neurons) in the presence or absence of iodonium diphenyl or dichlorophenolindophenol, two potent albeit non-selective inhibitors of nitric oxide synthase activity. In brain, NADPHd histochemistry homogeneously stained neuronal cell bodies, axons and dendrites, while it produced particulate cytoplasmic staining of all epithelial cells in the choroid plexuses of the lateral and fourth ventricles. Within the choroid plexus of the lateral ventricles, NADPHd-positive nerve fibres were also observed around blood vessels and coursing among the epithelial cells. The distribution of immunoreactivity for nitric oxide synthase in brain and in nerve fibres in the choroid plexuses of the lateral ventricles resembled the distribution of histochemical labelling for NADPHd. Choroid plexus epithelial cells were, however, devoid of nitric oxide synthase immunoreactivity. Consistent with this, iodonium diphenyl and dichlorophenolindophenol (0.1 mM) inhibited NADPHd histochemical staining in brain neurons and in choroid plexus nerve fibres, but not in choroid plexus epithelial cells. These results demonstrate that the choroid plexus of the lateral ventricles in rat brain is innervated by nitric oxide synthase-positive nerve fibres. These nitric oxide synthase-positive nerve fibres may have an important role in the regulation of cerebrospinal fluid balance. Although choroid plexus epithelial cells contain an enzyme with NADPHd activity, this enzyme is not nitric oxide synthase.

NADPH-diaphorase histochemistry of rat choroid plexus blood vessels and epithelium

Choroid plexus is the major source of cerebrospinal fluid. The hemodynamics and secretory function of this tissue are controlled by multiple endocrine and neural mechanisms. Nitric oxide (NO) has been demonstrated to play an important role in regulating choroidal blood flow. In the present study, performed on adult male Sprague-Dawley rats, we employed a NADPH-diaphorase (NADPH-d) histochemical method to localize nitrergic innervation of choroidal blood vessels. This approach was based on previous observations that NADPH-d colocalizes with NO synthase, a synthetic enzyme for NO, in the central and peripheral nervous systems. NADPH-d-positive nerve fibers were found to accompany both large arteries and veins and blood microvessels (possibly arterioles) located in choroidal stroma. NADPH-d reaction product was also localized to the vascular endothelial lining and choroidal epithelial cells. All the above sources of NO may play important roles in the regulation of secretory and hemodynamic functions of the choroid plexus.

Vasopressin in the cerebrospinal fluid of febrile children with or without seizures

Immaturity in water and electrolyte balance in the brain has been considered to increase the susceptibility of young animals and children to febrile convulsions (FCs). Arginine-vasopressin (AVP) is involved in the regulation of several centrally mediated events such as modulation of fever and the ease with which water permeates into and out of the brain. To evaluate the possible role of AVP in the control of water balance and susceptibility to convulsions during fever we measured the AVP concentration in the cerebrospinal fluid (CSF) and plasma of febrile children with or without convulsions. The febrile population consisted of 47 children, of whom 29 experienced seizures during fever. Seven children with epileptic symptoms and 18 children without seizures were included as nonfebrile controls. The CSF AVP concentration in febrile children without seizures and in nonfebrile convulsive children was significantly lower (0.60 +/- 0.07 pmol/l, mean +/- SEM, P < 0.01 and 0.65 +/- 0.19 pmol/l, P < 0.05, respectively) than in nonfebrile children without convulsions (0.83 +/- 0.06 pmol/l). However, the levels of CSF AVP were not significantly different in children with FCs (0.71 +/- 0.06 pmol/l) compared with other groups. CSF AVP correlated with the CSF osmolality (r = 0.33, P = 0.02). No statistical differences in plasma AVP levels between the groups could be found. The present data provide support for the hypothesis of synchronous regulation of osmolality and AVP concentration in CSF. During fever the concentration of CSF AVP was lower in nonconvulsive children compared with nonfebrile nonconvulsive children. CSF AVP levels were not affected in febrile children by convulsions.

Osmolality and electrolytes in cerebrospinal fluid and serum of febrile children with and without seizures

During acute febrile diseases mild disturbances of water and electrolyte balance occur frequently. It has been suggested that changes in electrolyte balance, in particular hyponatraemia, might predispose a child to convulsions during febrile illness; however, the changes of electrolytes in the CSF are not known. We have studied the effects of fever and convulsions on water and electrolyte balance in CSF and serum by measuring osmolality and electrolyte concentrations in children. The febrile population consisted of 60 children, 36 of whom had seizures during fever. Twenty-one children without convulsions and nine children with epileptic symptoms were nonfebrile controls. We noticed that CSF is subject to changes in osmolality and electrolyte concentration during fever, while convulsions do not exhibit such changes. CSF osmolality and sodium concentrations were lower in febrile children than in nonfebrile controls. The osmolality in febrile children with convulsions was 3.8% (P < 0.01) and without seizures 3.5% (P < 0.01) lower than in nonfebrile nonconvulsive children. The changes in CSF sodium concentration, and to a lesser extent potassium and chloride concentrations, paralleled those of CSF osmolality. A positive correlation was observed between the CSF and serum osmolatities (r = 0.73, P < 0.0001), and sodium concentrations (r = 0.63, P < 0.0001). A negative correlation between the body temperature and both CSF osmolality (r = -0.66, P < 0.0001) and sodium concentration (r = -0.59, P < 0.0001) exhibits also the important regulative role of increased body temperature.

CONCLUSION

Fever is an important factor for disturbances in fluid and electrolyte balance. The alterations in CSF osmolality and sodium concentration do not, however, give an unambiguous explanation for the susceptibility to simple febrile seizures.

Increase in vasopressin binding sites in the human choroid plexus in Alzheimer's disease

Vasopressin binding sites were determined in the choroid plexus of five Alzheimer's disease patients and five non-demented controls using the 125I-labelled linear V1a-antagonist. The Alzheimer's disease patients showed a twofold increase in the density of vasopressin binding sites, whereas the increase in the affinity constant Kd did not reach significance.

A systematic histochemical investigation in mammals of the dense glycocalyx glycosylations common to all cells bordering the interstitial fluid compartment of the brain

Microanatomical evidence is presented that the intercellular fluid (ICF) compartment of the central nervous tissue is lined entirely and exclusively by heavily glycosylated cells, with glycoconjugates exposed primarily at the apical cell surface, fronting the CSF or blood. On both common ependymal cells and on those specialised to form the choroid plexus epithelium, oligosaccharides coat the cilia and microvilli at the apical surface, and also the smoother lateral and basal cell surfaces. In the ependyma, folded and wrinkled structures seem especially associated with freely exposed carbohydrates. On cerebral endothelial cells, oligosaccharides coat the luminal surface densely and the basal surface lightly. The patterns of carbohydrate distribution thus vary from one cell type to another, but the different cell types all bear essentially the same set of oligosaccharides, variations being due largely to degree of terminal sialylation. Furthermore, the same set of oligosaccharides borders the brain in a broad spectrum of mammals, including pouched and placental mammals. In both epithelia and endothelia, the lectin binding sites visualised in fixed and embedded preparations were shown to be exposed likewise at the cell surfaces in unfixed tissues and so able to bind molecules present in the fluid (CSF or blood) bathing the cells in vivo. This phylogenetically ancient enclosure of the ICF compartment in a "ring of sugars" is suggested to relate to regulation of the central neuronal microenvironment.

Choroidal responses in microgravity. (SLS-1, SLS-2 and hindlimb-suspension experiments)

Fluid and electrolyte shifts occurring during human spaceflight have been reported and investigated at the level of blood, cardiovascular and renal responses. Very few data were available concerning the cerebral fluid and electrolyte adaptation to microgravity, even in animal models. It is the reason why we developed several studies focused on the effects of spaceflight (SLS-1 and SLS-2 programs, carried on NASA STS 40 and 56 missions, which were 9- and 14-day flights, respectively), on structural and functional features of choroid plexuses, organs which secrete 70-90% of cerebrospinal fluid (CSF) and which are involved in brain homeostasis. Rats flown aboard space shuttles were sacrificed either in space (SLS-2 experiment, on flight day 13) or 4-8 hours after landing (SLS-1 and SLS-2 experiments). Quantitative autoradiography performed by microdensitometry and image analysis, showed that lateral and third ventricle choroid plexuses from rats flown for SLS-1 experiment demonstrated an increased number (about x 2) of binding sites to natriuretic peptides (which are known to be involved in mechanisms regulating CSF production). Using electron microscopy and immunocytochemistry, we studied the cellular response of choroid plexuses, which produce cerebrospinal fluid (CSF) in brain lateral, third and fourth ventricles. We demonstrated that spaceflight (SLS-2 experiment, inflight samples) induces changes in the choroidal cell structure (apical microvilli, kinocilia organization, vesicle accumulation) and protein distribution or expression (carbonic anhydrase II, water channels,...). These observations suggested a loss of choroidal cell polarity and a decrease in CSF secretion. Hindlimb-suspended rats displayed similar choroidal changes. All together, these results support the hypothesis of a modified CSF production in rats during long-term (9, 13 or 14 days) adaptations to microgravity.

Overlapping and differential expression of BIG-2, BIG-1, TAG-1, and F3: four members of an axon-associated cell adhesion molecule subgroup of the immunoglobulin superfamily

Axon-associated cell adhesion molecules (AxCAMs) play crucial roles in the formation, maintenance, and plasticity of functional neuronal networks. We report here a molecular cloning of a novel AxCAM, BIG-2. BIG-2 is a member of TAG-1/F3 subgroup of the immunoglobulin (Ig) superfamily, with six Ig-like domains, four fibronectin type III-like repeats, and a glycosyl phosphatidylinositol-anchoring domain. Recombinant BIG-2 protein had a neurite outgrowth-promoting activity when used as a substrate for neurons in vitro. To survey the spatial expression pattern of BIG-2 in comparison with other TAG-1/F3 subgroup members, an in situ hybridization analysis was performed in adult and developing rat brain sections with riboprobes specific for BIG-2, BIG-1, TAG-1, and F3. The four AxCAM transcripts displayed cell type-specific expression patterns with overlapping and distinct profiles. In adult hippocampus, for example, we observed BIG-1 mRNA specifically in granule cells of the dentate gyrus, BIG-2 mRNA highly in the CA1 pyramidal cells, TAG-1 mRNA predominantly in the CA3 pyramidal cells, and F3 mRNA in neurons in all of these fields. These results suggest that BIG-2, BIG-1, TAG-1, and F3 may play important roles in the formation and maintenance of specific neuronal networks in the brain.

The ependyma: a protective barrier between brain and cerebrospinal fluid

This review summarizes the current scientific literature concerning the ependymal lining of the cerebral ventricles of the brain with an emphasis on selective barrier function and protective roles for the common ependymal cell. Topics covered include the development, morphology, protein and enzyme expression including reactive changes, and pathology. Some cells lining the neural tube are committed at an early stage to becoming ependymal cells. They serve a secretory function and perhaps act as a cellular/axonal guidance system, particularly during fetal development. In the mature mammalian brain ependymal cells possess the structural and enzymatic characteristics necessary for scavenging and detoxifying a wide variety of substances in the CSF, thus forming a metabolic barrier at the brain-CSF interface.

Serotonin elevates intracellular Ca2+ in rat choroid plexus epithelial cells by acting on 5-HT2C receptors

The effects of serotonin (5-HT) on intracellular calcium activity ([Ca2+]i) in epithelial cells from rat choroid plexuses were examined. Experiments were performed on isolated cells which had been maintained in primary culture. ([Ca2+]i) was measured using micro-spectrofluorimetric techniques and the fluorescent indicator Fura-2. 5-HT was found to increase [Ca2+]i in a dose dependent manner. The [Ca2+]i response was biphasic, with an initial peak of [Ca2+]i (due to release from intracellular stores), followed by an elevated plateau phase (the result of calcium influx). The effect of 1 microM 5-HT was inhibited by mesulergine and mianserin (50 nM), which are antagonists of the 5-HT2C receptor. Spiperone and ketanserin (200 nM), less specific 5-HT2 receptor blockers, caused only a slight reduction in the response to 1 microM 5-HT. The [Ca2+]i response decreased upon repeated challenges with 1 microM 5-HT, probably as a result of receptor desensitisation. Taken together, the data suggest that 5-HT acts at 5-HT2C receptors to increase [Ca2+]i in choroid plexus epithelial cells, both by liberating Ca2+ from intracellular stores and by activating a Ca2+ influx pathway.

Increased cortisol levels in aging and Alzheimer's disease in postmortem cerebrospinal fluid

The hypothalamo-pituitary-adrenal (HPA) axis is activated during aging and even more so in dementia. Increased levels of corticosteroids may be neurotoxic. Therefore we have investigated cortisol levels in cerebrospinal fluid (CSF) of Alzheimer patients and controls. Ventricular postmortem CSF was collected from clinically and neuropathologically well-defined Alzheimer patients (n = 26) and control subjects (n = 21). In the group of Alzheimer patients the mean CSF total cortisol level was 83% higher than that in the controls. In presenile Alzheimer patients (< 65 years of age; n = 13) the CSF-cortisol level was 5 times higher than that of presenile controls (n = 7). In contrast, senile Alzheimer patients (n = 13) and controls of over 65 years of age (n = 14) did not show a significant difference in CSF-cortisol levels. The presence or absence of a difference in the cortisol-CSF levels in, respectively, presenile or senile Alzheimer patients as compared to controls was due to the 3.5-fold rise of CSF-cortisol in control subjects over 65 years of age as compared with controls under 65 years of age. The CSF-cortisol levels in presenile and senile Alzheimer patients were similar. No significant correlation was observed in the Alzheimer patients between age of onset of the dementia and CSF cortisol levels or duration of Alzheimer's disease and CSF cortisol levels. The finding that in senile Alzheimer patients cortisol levels were similar to those of unaffected age-matched controls does not seem to support the cortisol neurotoxicity hypothesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of thyroxine uptake into cerebrospinal fluid and rat brain by hexachlorobenzene and pentachlorophenol

In the present study the effects of hexachlorobenzene (HCB) and the metabolite pentachlorophenol (PCP) were investigated with respect to uptake of thyroxine (T4) into cerebrospinal fluid (CSF) and brain structures of rats. [125I]T4 was taken up into CSF of control rats by a relatively slow process, reaching a steady state after about 3 h. Both repeated dosing of HCB and single doses of PCP caused decreased uptake of [125I]T4 into CSF, total brain tissue as well as specific brain structures, such as occipital cortex, thalamus, and hippocampus. Although HCB-treatment caused a build-up of HCB and PCP levels in serum in brain only HCB was present in significant amounts (16% of the serum level). In CSF, both HCB and PCP concentrations were below detection levels. Separate experiments with PCP showed, however, a dose- and time-dependent uptake of PCP into CSF. The present results indicate that PCP and the parent compound HCB are able to affect brain supply of T4. This may have consequences for an adequate development of the brain or proper brain function in adults. The exact mechanisms of interference of PCP and/or HCB in brain uptake of T4 remain to be established.

An in vivo study of the effect of 5-HT and sympathetic nerves on transferrin and transthyretin mRNA expression in rat choroid plexus and meninges

Brain expression of transferrin (Tf) and transthyretin (TTR) mRNA has been demonstrated in different species, TTR being found only in the choroid plexus. We report here that both these mRNAs are also expressed in the meninges. In vitro studies have shown that Tf secretion by the rat choroid plexus is stimulated by 5-hydroxytryptamine (5-HT) while sympathetic nerves regulate different transport functions in the same tissue. We have used various in vivo models to study the neuroendocrine regulation of Tf and TTR mRNA expression in the choroid plexus and meninges. Destruction of the serotonergic nerves in the brain by either raphe nuclei lesion or intraventricular injections of 5,7-dihydroxytryptamine (5,7-DHT), which both decreased brain 5-HT levels significantly, did not affect Tf or TTR mRNA levels in choroid plexus and meninges, but increased TTR mRNA in liver. Intraventricular injection of 10 or 100 pmol 5-HT did not change the expression of these proteins in any of the tissues studied. Removal of the sympathetic innervation to the choroid plexus by cervical sympathectomy did not affect Tf or TTR mRNA levels in choroid plexus and liver, nor the incorporation of radioactive leucine into protein in various parts of the brain. In conclusion, our results do not support a regulatory role in vivo for neuronally derived 5-HT or sympathetic nerve activity on Tf and TTR mRNA expression in rat choroid plexus and meninges.

Immunocytochemical demonstration of prolactin interaction with choroid plexus in aging and acute hyperprolactinemia

Prolactin (PRL) exerts a direct effect on the central nervous system, reaching the PRL-responsive brain regions via cerebro-spinal fluid (CSF). The hormone enters the CSF by a specific receptor-mediated transport mechanism that is localized on the epithelium of the choroid plexus (CP) of brain ventricles. PRL interactions with the CP in aging were examined in young (3-month) and old (27-month) female Wistar rats using immunocytochemistry (immunogold technique). The enhancement of PRL uptake by the CP in animals at both ages was achieved by the modelling of acute hyperprolactinemia. A great age-related difference was found in the intensity of immunocytochemical reaction under activated conditions, the uptake of PRL by CP being significantly higher in young animals than in old. The character of the colloidal gold particle distribution in different components of CP epithelial cells appeared to be the same in both age groups. The weakening of PRL-transporting capacity in the CP of old animals may constitute one aspect of the alteration of neuroendocrine regulation in the CP-CSF system that occurs during aging.

Endogenous angiotensin II inhibits production of cerebrospinal fluid during posthypoxemic reoxygenation in the rabbit

BACKGROUND AND PURPOSE

The choroid plexus, the major source of cerebrospinal fluid (CSF), contains receptors for angiotensin II and a very high concentration of angiotensin converting enzyme. Circulating angiotensin II decreases blood flow to the choroid plexus and the production of CSF. During recovery from hypoxia, marked increases in circulating angiotensin II have been described in some studies. We tested the hypothesis that CSF production decreases during posthypoxemic reoxygenation and examined related changes in plasma concentrations of angiotensin II. We also determined whether effect of posthypoxic reoxygenation on production of CSF is due to endogenous release of angiotensin II.

METHODS

We measured production of CSF in chloralose-anesthetized rabbits using ventriculocisternal perfusion of artificial CSF containing blue dextran. After control measurements, rabbits were subjected to one of the following interventions: (1) 30 minutes of hypoxia (PaO2 = 36 +/- 1 mmHg [mean +/- SE]) followed by 90 minutes of reoxygenation; (2) 30 minutes of hypoxia (PaO2 = 37 +/- 2 mmHg) followed by 90 minutes of reoxygenation in the presence of the angiotensin II antagonist saralasin; (3) hypoxia for 120 minutes (PaO2 = 35 +/- 1 mmHg); and (4) infusion of vehicle under normoxic conditions for 120 minutes (time control). Plasma concentrations of angiotensin II were also measured (radioimmunoassay) under control conditions, during hypoxia, and during posthypoxic reoxygenation (first intervention) and at corresponding time intervals in time control animals (fourth intervention).

RESULTS

Under control conditions, the rate of production of CSF averaged 6.7 +/- 0.1 microL.min-1. During posthypoxemic reoxygenation, production of CSF decreased by 31 +/- 4% (P < .05). In the presence of sarlasin, CSF production did not change significantly during posthypoxemic reoxygenation (-12 +/- 6%, P > .05). In time control animals and during prolonged hypoxia, CSF production did not change significantly (-12 +/- 5% [P > .05] and 9 +/- 7% [P > .05], respectively). Plasma concentrations of angiotensin were below the threshold of sensitivity of the assay under control conditions and during interventions in animals that were made hypoxic and then reoxygenated and in time control animals.

CONCLUSIONS

CSF production decreases during posthpoxemic reoxygenation. Since plasma concentrations of angiotensin II did not change during posthypoxic reoxygenation, this effect does not appear to be mediated by increases in circulating angiotensin II. We speculate that endogenous release of angiotensin II, perhaps in the choroid plexus epithelium, decreases production of CSF after hypoxic brain injury.

Morphology and distribution of ecto-5'-nucleotidase-positive cells in the rat choroid plexus

The aim of this report was to find out whether adenosine can be produced locally in the choroid plexus of rats. Therefore we investigated the distribution of the enzyme ecto-5'-nucleotidase which hydrolyzes extracellular adenosine monophosphate to adenosine and phosphate. Enzyme activity histochemistry and immunohistochemistry demonstrated that ecto-5'-nucleotidase is present in the stroma but not in the epithelium. The positive cells in the stroma were identified as fibroblasts by their localization and by their shape. Double-labelling immunohistochemistry actually showed that ecto-5'-nucleotidase was absent from MHC class II-positive cells and from vessel walls. These data indicate that adenosine may be produced in the choroid plexus, and specifically in the interstitium. From there, adenosine would have direct access to nerves, immune cells, the epithelium and microvessels. Because adenosine has been reported to modulate blood supply and the rate of production of cerebrospinal fluid, a local control mechanism involving adenosine might operate in the choroid plexus in a similar way to that described in other tissues. Effects of adenosine on nerves and immune cells are discussed. The exclusive presence of ecto-5'-nucleotidase in the fibroblasts that are in contact with choroid plexus epithelium suggests that the expression of the enzyme is controlled by factors produced by epithelial cells, for instance by extracellular nucleotides.

Localization of drug-metabolizing enzyme activities to blood-brain interfaces and circumventricular organs

The brain, with the exception of the choroid plexuses and circumventricular organs, is partially protected from the invasion of blood-borne chemicals by the specific morphological properties of the cerebral micro-vessels, namely, the tight junctions of the blood-brain barrier. Recently, several enzymes that are primarily involved in hepatic drug metabolism have been shown to exist in the brain, albeit at relatively low specific activities. In the present study, the hypothesis that these enzymes are located primarily at blood-brain interfaces, where they form an "enzymatic barrier," is tested. By using microdissection techniques or a gradient-centrifugation isolation procedure, the activities of seven drug-metabolizing enzymes in isolated microvessels, choroid plexuses, meningeal membranes, and tissue from three circumventricular organs (the neural lobe of the hypophysis, pineal gland, and median eminence) were assayed. With two exceptions, the activities of these enzymes were higher in the three circumventricular organs and cerebral microvessel than in the cortex. Very high membrane-bound epoxide hydrolase and UDP-glucuronosyltransferase activities (approaching those in liver) and somewhat high 7-benzoxyresorufin-O-dealkylase and NADPH-cytochrome P-450 reductase activities were determined in the choroid plexuses. The pia-arachnoid membranes, but not the dura matter, displayed drug-metabolizing enzyme activities, notably that of epoxide hydrolase. The drug-metabolizing enzymes located at these nonparenchymal sites may function to protect brain tissue from harmful compounds.

Cl- current activation in choroid plexus epithelial cells involves a G protein and protein kinase A

The involvement of GTP-binding proteins (G proteins) in the regulation of the Cl- conductance in rat choroid plexus epithelial cells was investigated, using the whole cell patch-clamp technique. Intracellular application of a nonhydrolyzable GTP analogue, guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S; 0.1-0.2 mM), evoked a transient increase in the Cl- conductance. The activated Cl- current exhibited inward rectification and was independent of time at hyperpolarizing or depolarizing voltage pulses. The effect of GTP gamma S was inhibited by a nonhydrolyzable GDP analogue, guanosine 5'-O-(2-thiodiphosphate) (2 mM), and by an inhibitor of protein kinase A, H-89, but was not affected by chelation of cytosolic Ca2+ with 5 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid. GTP gamma S failed to activate the current when ATP was omitted from the pipette solution. Intracellular application of adenosine 3',5'-cyclic monophosphate (cAMP; 0.25 mM) or the catalytic subunit of protein kinase A activated a similar Cl- current. These results suggest that G proteins activate Cl- channels via a cAMP-dependent pathway in rat choroid plexus.

Expression of insulin-like growth factor binding protein-4 and -5 mRNAs in adult rat forebrain

Accumulating evidence indicates that the insulin-like growth factors (IGFs) can act as neurotrophic factors. A family of at least six IGF binding proteins (IGFBPs) has been characterized. The IGFBPs prolong the half-life of IGFs in plasma and may modulate IGF action in a cell- or tissue-specific fashion. Two recently characterized IGFBPs, IGFBP-4 and -5, have been shown by northern blot hybridization to be expressed in rat brain, but their cellular sites of synthesis are poorly characterized. Because IGFBP-4 and IGFBP-5 could potentially modulate IGF actions in the brain, we used in situ hybridization histochemistry and 35S-labeled IGFBP-4 and IGFBP-5 riboprobes to localize sites of IGFBP-4 and -5 mRNA expression in adult rat brain. The two IGFBP mRNAs are abundantly expressed within discrete regions of brain. The expression patterns of the two genes are largely nonoverlapping. Notably, IGFBP-4 mRNA is highly expressed within hippocampal and cortical areas, whereas IGFBP-5 mRNA is not detected above background in these areas. Within the hippocampus, abundant IGFBP-4 mRNA expression is detected in pyramidal neurons of the subfields of Ammon's horn and the subiculum and in the granule cell layer of the anterior hippocampal continuation. In the cortex, IGFBP-4 mRNA is widely expressed in most areas and layers. In contrast, IGFBP-5, but not IGFBP-4, mRNA is detected within thalamic nuclei, leptomeninges, and perivascular sheaths. The distinct expression patterns of IGFBP-4 and -5 mRNAs within the brain suggest that these IGFBPs may modulate paracrine/autocrine actions of the IGFs in discrete brain regions or compartmentalization of the IGFs within the brain.

Dominant expression of mRNA for prostaglandin D synthase in leptomeninges, choroid plexus, and oligodendrocytes of the adult rat brain

Glutathione-independent prostaglandin D synthase [prostaglandin-H2 D-isomerase; (5Z,13E)-(15S)-9 alpha,11 alpha-epidioxy-15-hydroxyprosta-5,13-dienoate D-isomerase, EC 5.3.99.2] is an enzyme responsible for biosynthesis of prostaglandin D2 in the central nervous system. In situ hybridization with antisense RNA for the enzyme indicated that mRNA for the enzyme was predominantly expressed in the leptomeninges, choroid plexus, and oligodendrocytes of the adult rat brain. The findings agree with those obtained by immunohistochemical staining with antibodies against the enzyme. It was further revealed that prostaglandin D synthase activity was considerably greater in the isolated leptomeninges (14.2 nmol per min per mg of protein) and choroid plexus (7.0 nmol per min per mg of protein) than the activity in the whole brain (2.0 nmol per min per mg of protein). These results, taken together, indicate that the enzyme is mainly synthesized and located in the leptomeninges, choroid plexus, and oligodendrocytes in the brain.

Endocrinology and the psychiatrist

Objective:Exegetic review of the three areas of common interest to the endocrinologist and the psychiatrist.Method:Literature review through Science Citation Index and references in BMJ, Lancet, Nature, and Science.Findings:Psychiatric symptoms, specific in each condition, may develop in the course of a classical endocrinopathy. Though introduced as a possible diagnostic aid, titration of the hypothalamico-pituitary control of the adrenal and thyroid glands has proved to be a useful research strategy and possible prognostic indicator in affective disorders. Growth in our knowledge of the behaviour effects, distribution, function and pathophysiology of neuropeptides during the last two decades opens a magic casement on their potential value in neuropsychiatric theory and therapy.Conclusion:The psychiatrist ignores endocrinology at his peril, as does the endocrinologist psychiatry, especially in regard to the emerging role of peptides in neuromodulation.

Extracellular and cerebrospinal fluids

The mechanism of formation of extracellular fluid is first described, followed by an explanation of the relation between osmotic force, reflection coefficient and molecular size. The possible mechanism of brain extracellular fluid formation is then proposed in relation to the restriction offered by the blood-brain barrier. The functions and compositions of cerebrospinal fluid (CSF) are then described followed by sections on the process of formation of CSF, the non-electrolytes and proteins in CSF, the drainage mechanisms and protein synthesis by the choroid plexus.