Neurotoxicology of the brain barrier system: new implications

Brain barrier dysfunction in Cuban epidemic optic neuropathy

BACKGROUND AND PURPOSE

There are practically no references to cerebrospinal fluid (CSF) studies in tropical or nutritional neuropathies. In the present paper we present the results of CSF studies in patients with Cuban Epidemic Optic Neuropathy (CEON) during epidemic and endemic periods, with an appraisal as to the contribution of brain barriers' function in the pathophysiology of this disease.

METHODS

Two hundred and five patients with CEON were studied during the epidemic period (1992-1993) and 12 patients outside the outbreak (1995-1997). CSF protein determination and electrophoresis were carried out, as well as serum and CSF albumin and immunoglobulin G (IgG) quantitation for calculating IgG and Q(alb) indexes, in order to evaluate intrathecal IgG synthesis and the permeability of the blood-CSF barrier (B-CSF B).

RESULTS

One fourth of the patients had increased permeability of the B-CSF B, but damage was more frequent between 16 and 60 days from onset of disease, disappearing after 120 days. B-CSF B dysfunction was more prevalent in patients with severe neurological impairment, although it was not related to the severity of ophthalmological damage. The group of patients studied outside of the outbreak (endemic period) showed similar results.

DISCUSSION

The possible association of increased permeability of the B-CSF B with oxidative stress, which lies on the basis of this epidemic outbreak, is discussed.

Lead and cognitive function in adults: a questions and answers approach to a review of the evidence for cause, treatment, and prevention

Lead has been extensively used worldwide in gasoline, consumer products, commercial applications, and industrial settings. Its use in gasoline and paint has been particularly hazardous to public health leading to widespread population exposure and substantial lifetime cumulative doses in most Americans over age 40 years. Cumulative lead dose can be estimated by measuring the current concentration of lead in tibia bone by X-ray fluorescence. A growing literature has documented that tibia lead levels are associated with decrements in cognitive function and declines in cognitive function over time. Furthermore, there are several interesting lines of biochemical and epidemiological investigation that have demonstrated potential links of lead to neurodegenerative diseases. These studies support the inference that a proportion of what has been termed 'normal' age-related cognitive decline may, in fact, be due to exposure to neurotoxicants such as lead. Well-designed studies of cumulative lead dose and Alzheimer's disease risk should be conducted to follow-up on these leads. The strong and compelling body of literature on lead and cognitive dysfunction and decline also supports a need for intervention studies to prevent lead-related cognitive decline.

Does neurotransmission impairment accompany aluminium neurotoxicity?

Neurobehavioral disorders, except their most overt form, tend to lie beyond the reach of clinicians. Presently, the use of molecular data in the decision-making processes is limited. However, as details of the mechanisms of neurotoxic action of aluminium become clearer, a more complete picture of possible molecular targets of aluminium can be anticipated, which promises better prediction of the neurotoxicological potential of aluminium exposure. In practical terms, a critical analysis of current data on the effects of aluminium on neurotransmission can be of great benefit due to the rapidly expanding knowledge of the neurotoxicological potential of aluminium. This review concludes that impairment of neurotransmission is a strong predictor of outcome in neurobehavioral disorders. Key questions and challenges for future research into aluminium neurotoxicity are also identified.

Pro-oxidant effects in the brain of rats concurrently exposed to uranium and stress

Metal toxicity may be associated with increased rates of reactive oxygen species (ROS) generation within the central nervous system (CNS). Although the kidney is the main target organ for uranium (U) toxicity, this metal can also accumulate in brain. In this study, we investigated the modifications on endogenous antioxidant capacity and oxidative damage in several areas of the brain of U-exposed rats. Eight groups of adult male rats received uranyl acetate dihydrate (UAD) in the drinking water at 0, 10, 20, and 40 mg/kg/day for 3 months. Animals in four groups were concurrently subjected to restraint stress during 2h/day throughout the study. At the end of the experimental period, cortex, hippocampus and cerebellum were removed and processed to examine the following stress markers: reduced glutathione (GSH), oxidized glutathione (GSSG), glutathione reductase (GR), glutathione peroxidase (GPx), superoxide dismutase (SOD), catalase (CAT), thiobarbituric acid reactive substances (TBARS), as well as U concentrations. The results show that U significantly accumulated in hippocampus, cerebellum and cortex after 3 months of exposure. Moreover, UAD exposure promoted oxidative stress in these cerebral tissues. In cortex and cerebellum, TBARS levels were positively correlated with the U content, while in cerebellum GSSG and GSH levels were positively and negatively correlated, respectively, with U concentrations. In hippocampus, CAT and SOD activities were positively correlated with U concentration. The present results suggest that chronic oral exposure to UAD can cause progressive perturbations on physiological brain levels of oxidative stress markers. Although at the current UAD doses restraint scarcely showed additional adverse effects, its potential influence should not be underrated.

Macromolecules involved in production and metabolism of beta-amyloid at the brain barriers

One of the notable features of Alzheimer's disease (AD) is the overabundance of beta-amyloid peptides in brain fluids, leading to the formation and deposition of insoluble amyloid plaques. Previous work in this lab demonstrates that the normal choroid plexus, a primary component of the blood-cerebrospinal fluid barrier, has the capacity to remove beta-amyloid from the cerebrospinal fluid, potentially preventing the formation of beta-amyloid plaques. The purpose of this work was to determine whether the choroid plexus and/or the brain capillaries, a primary component of the blood-brain barrier, possessed the capacity to produce or degrade beta-amyloid peptides. Using quantitative real-time RT-PCR, immunodetection and enzyme activity assays, we demonstrated the presence in brain barriers of several key enzymes involved in beta-amyloid production, namely, amyloid precursor protein and beta-secretase, and in beta-amyloid metabolism and alternate processing, such as insulin degrading enzyme, endothelin-converting enzyme-1, neprilysin and alpha-secretase. Furthermore, beta-amyloid presence, in the absence of its application in culture media, was detected in an immortalized choroidal epithelial cell line, known as Z310 cells. The ability of the choroid plexus to produce and degrade beta-amyloid, in addition to its transport function, suggests a vital role of this tissue in maintaining beta-amyloid homeostasis. Disruption of this homeostasis due to aging, injury or toxicant exposure may contribute to accumulation of beta-amyloid peptides in the brain fluids, leading to AD.

Critical care perspective on immunotherapy in lung transplantation

Lung transplantation is now a viable therapeutic option in the care of patients with advanced pulmonary parenchymal or pulmonary vascular disease. Lung transplantation, however, with chronic posttransplant immunosuppression, creates a uniquely vulnerable population of patients likely to experience significant life-threatening complications requiring intensive care. The introduction of several novel immunosuppressive agents, such as sirolimus and mycophenolate mofetil, in conjunction with more established agents such as cyclosporine and tacrolimus, has greatly increased treatment options for lung transplant recipients and likely contributed to improved short-term transplant outcomes. Modern transplant immunosuppression, however, is associated with a host of complications such as opportunistic infections, renal failure, and thrombotic thrombocytopenic purpura. The main focus of this review is to provide a comprehensive summary of modern immunotherapy in lung transplantation and to increase awareness of the serious and potentially life-threatening complications of these medications.

Adverse health effects of children's exposure to pesticides: what do we really know and what can be done about it

Children may be exposed to pesticides in several ways, such as by transplacental transfer during foetal life, by intake of contaminated breast milk and other nutrients, or by contact with contaminated subjects and areas in the environment such as pets treated with insecticides, house dust, carpets and chemically treated lawns and gardens. Exposure early in life, and particularly during periods of rapid development, such as during foetal life and infancy, may have severe effects on child health and development by elevating the risk of congenital malformations, cancer, malabsorption, immunological dysfunction, endocrine disease, and neurobehavioural deficiencies. As pesticides can also interfere with parental reproductive health, exposure of parents may have consequences for the offspring leading to reduced chance of male birth and increased risk of childhood cancer.

CONCLUSIONS

Current knowledge about tolerable levels and consequences of toxic exposure to pesticides during human development is rather scarce. Owing to the high risk of exposure to pesticides, particularly in less developed countries, further elucidation by well-controlled epidemiological studies in this field it is urgently needed. The Policy Interpretation Network on Children's Health and Environment (PINCHE), which is financed by the EU DG research has suggested actions against pesticide exposure. They have been presented and discussed in this paper. Several suggestions of PINCHE concerning action needed regarding pesticides were presented in the paper.

Pb2+ reduces PKCs and NF-κB in vitro

The mechanism of lead (Pb(2+))-induced neurotoxicity has not yet been fully elucidated. The purpose of this study was to examine the effects of Pb(2+) on several protein kinase C (PKC) isoforms and the nuclear factor-kappaB (NF-kappaB)-I-kappaB kinase-alpha (IKK-alpha) axis in cultured neuronal cells. Neurons were isolated from rat fetal brain at the 18th day of gestation of pregnant Sprague Dawley rats and cultured for 10 days before use. Neurons were exposed to Pb(2+) at concentrations of 10(-10), 10(-9), 10(-8), and 10(-7) mol/L for 14 h and antigens of typical PKC-alpha,beta,gamma; novel PKC (epsilon, delta), atypical PKC (lambda), NF-kappaB (p50), and IKK-alpha were enriched by immunoprecipitation and determined by western blotting. Total, calcium-dependent and independent PKC activities were also determined by counting the transferred gamma-(32) P in the substrate-histone. The results indicated that inorganic Pb(2+) significantly reduced all PKC isoforms (alpha,beta,gamma, epsilon, lambda) except delta, inhibiting the total, calcium-dependent and calcium-independent PKC activities in a dose-dependent manner. Additionally, Pb(2+) gradually reduced NF-kappaB (p50) and IKK-alpha protein levels. This suggests that Pb(2+) exhibits varying preference for individual PKC isoforms but reduces the NF-kappaB-IKK-alpha axis to a similar extent.

Molecular mechanism of distorted iron regulation in the blood-CSF barrier and regional blood-brain barrier following in vivo subchronic manganese exposure

Previous studies in this laboratory indicated that manganese (Mn) exposure in vitro increases the expression of transferrin receptor (TfR) by enhancing the binding of iron regulatory proteins (IRPs) to iron responsive element-containing RNA. The current study further tested the hypothesis that in vivo exposure to Mn increased TfR expression at both blood-brain barrier (BBB) and blood-cerebrospinal fluid (CSF) barrier (BCB), which contributes to altered iron (Fe) homeostasis in the CSF. Groups of rats (10-11 each) received oral gavages at doses of 5 mg Mn/kg or 15 mg Mn/kg as MnCl(2) once daily for 30 days. Blood, CSF, and choroid plexus were collected and brain capillary fractions were separated from the regional parenchyma. Metal analyses showed that oral Mn exposure decreased concentrations of Fe in serum (-66%) but increased Fe in the CSF (+167%). Gel shift assay showed that Mn caused a dose-dependent increase of binding of IRP1 to iron responsive element-containing RNA in BCB in the choroid plexus (+70%), in regional BBB of capillaries of striatum (+39%), hippocampus (+56%), frontal cortex (+49%), and in brain parenchyma of striatum (+67%), hippocampus (+39%) and cerebellum (+28%). Real-time RT-PCR demonstrated that Mn exposure significantly increased the expression of TfR mRNA in choroid plexus and striatum with concomitant reduction in the expression of ferritin (Ft) mRNA. Collectively, these data indicate that in vivo Mn exposure results in Fe redistribution in body fluids through regulating the expression of TfR and ferritin at BCB and selected regional BBB. The disrupted Fe transport by brain barriers may underlie the distorted Fe homeostasis in the CSF.

Effects of prenatal paraquat and mancozeb exposure on amino acid synaptic transmission in developing mouse cerebellar cortex

The goal of this study was to analyze the effects of prenatal exposure to the pesticides paraquat (PQ) and mancozeb (MZ) on the development of synaptic transmission in mouse cerebellar cortex. Pregnant NMRI mice were treated with either saline, 10 mg/kg PQ, 30 mg/kg MZ or the combination of PQ + MZ, between gestational days 12 (E12) and E20. Variation in the levels of amino acid neurotransmitters was determined by HPLC, between postnatal day 1 (P1) and P30. Motor coordination was assessed by locomotor activity evaluation of control and experimental pups at P14, P21 and P30. Significant reductions in the levels of excitatory neurotransmitters, aspartate and glutamate, were observed in PQ-, MZ- or combined PQ + MZ-exposed pups, with respect to control, during peak periods of excitatory innervation of Purkinje cells: between P2-P5 and P11-P15. However, at P30, lower aspartate contents, in contrast with increased glutamate levels, were detected in all experimental groups. During the first two postnatal weeks, delays in GABA and glycine ontogenesis were observed in PQ- and PQ + MZ-exposed pups, whereas notable decrements in GABA and glycine levels were seen in PQ + MZ-exposed animals. Decreased taurine contents were detected at P3 and P11 in PQ- and PQ + MZ-exposed mice. Pups in different experimental groups all showed hyperactivity at P14 and then exhibited reduced locomotor activity at P30. Taken together, our results indicate that prenatal exposure to either PQ or MZ or the combination of both could alter the chronology and magnitude of synaptic transmission in developing mouse cerebellar cortex.

Lithium and ECT--concurrent use still demands attention: three case reports

Bipolar disorders as well as recurrent major depressive episodes can be most effectively treated with electroconvulsive therapy (ECT). Since continuation/maintenance ECT is not well established, prophylactic therapy in recurrent illnesses is more commonly carried out using antidepressive medication alone or more often in combination with lithium. In case of relapse the clinically important question of discontinuation of lithium versus the concurrent use of ECT and lithium may arise. The safety of concurrent use has also to be balanced when lithium treatment is started within an ECT course. Since recent studies have reported no negative interactions with concurrent use, we here report three cases (one case of a prolonged seizure, a serotonin syndrome and a focal seizure) of severe lithium-induced side effects while patients underwent ECT without complications and lithium serum levels were still subtherapeutic. Clinical consequences are discussed and disturbances of the blood brain barrier system as a speculative cause are hypothesized taking previous studies, animal studies and an additional reported clinical case into account.

Immunohistochemical and Ultrastructural Findings Related to the Blood–Brain Barrier in the Blood Vessels of the Cerebral White Matter in Aged Dogs

Immunohistochemical and ultrastructural analysis of canine brain tissue was performed to determine whether cerebral capillaries, which form the blood--brain barrier (BBB), display age-related morphological changes in the white matter (WM). A slight decrease in laminin immunolabelling was detected in the basement membranes (BMs) of capillaries in the WM of old dogs, as compared with that in the brains of young dogs. The Prussian blue DAB post-DAB enhancement method detected iron present in macrophages and astrocytes in the WM. Copper/zinc superoxide dismutase, MT-I and -II and MT-III immunoreactivity was detected mainly in reactive astrocytes in the WM of aged dogs. Ultrastructurally, collagen-like fibrils were detected to a variable degree in the spaces between the BMs of capillary endothelial cells and astrocytes in the WM of some aged dogs. These results suggest that age-related morphological changes in capillaries of the WM are associated with BBB dysfunction, leading to the exudation of serum constituents, including harmful substances (e.g., iron), thereby causing tissue damage by oxidative injury. These factors may play a role in the pathogenesis of severe degenerative changes in the WM of aged dogs.

The effect of stress on the temporal and regional distribution of uranium in rat brain after acute uranyl acetate exposure

Long-term exposure to depleted uranium (DU) has been shown to increase brain uranium and alter hippocampal function; however, little is known about the short-term kinetics of DU in the brain. To address this issue, temporal and regional distribution of brain uranium was investigated in male Sprague-Dawley rats treated with a single intraperitoneal injection of 1 mg uranium/kg as uranyl acetate. Due to the inherent stress of combat and the potential for stress to alter blood-brain barrier permeability, the impact of forced swim stress on brain uranium distribution was also examined in this model. Uranium in serum, hippocampus, striatum, cerebellum, and frontal cortex was quantified by inductively coupled plasma-mass spectrometry (ICP-MS) at 8 h, 24 h, 7 d, and 30 d after exposure. Uranium entered the brain rapidly and was initially concentrated in hippocampus and striatum. While multiple phases of uranium clearance were observed, overall clearance was relatively slow and the uranium content of hippocampus, cerebellum, and cortex remained elevated for more than 7 d after a single exposure. Prior exposure to stress significantly reduced hippocampal and cerebellar uranium 24 h post-exposure and tended to reduce uranium in all brain regions 7 d after exposure. The application of stress appeared to increase brain uranium clearance, as initial tissue levels were similar in stressed and unstressed rats.

Manganese toxicity upon overexposure

Manganese (Mn) is a required element and a metabolic byproduct of the contrast agent mangafodipir trisodium (MnDPDP). The Mn released from MnDPDP is initially sequestered by the liver for first-pass elimination, which allows an enhanced contrast for diagnostic imaging. The administration of intravenous Mn impacts its homeostatic balance in the human body and can lead to toxicity. Human Mn deficiency has been reported in patients on parenteral nutrition and in micronutrient studies. Mn toxicity has been reported through occupational (e.g. welder) and dietary overexposure and is evidenced primarily in the central nervous system, although lung, cardiac, liver, reproductive and fetal toxicity have been noted. Mn neurotoxicity results from an accumulation of the metal in brain tissue and results in a progressive disorder of the extrapyramidal system which is similar to Parkinson's disease. In order for Mn to distribute from blood into brain tissue, it must cross either the blood-brain barrier (BBB) or the blood-cerebrospinal fluid barrier (BCB). Brain import, with no evidence of export, would lead to brain Mn accumulation and neurotoxicity. The mechanism for the neurodegenerative damage specific to select brain regions is not clearly understood. Disturbances in iron homeostasis and the valence state of Mn have been implicated as key factors in contributing to Mn toxicity. Chelation therapy with EDTA and supplementation with levodopa are the current treatment options, which are mildly and transiently efficacious. In conclusion, repeated administration of Mn, or compounds that readily release Mn, may increase the risk of Mn-induced toxicity.

Occupational exposure to welding fume among welders: alterations of manganese, iron, zinc, copper, and lead in body fluids and the oxidative stress status

Welders in this study were selected from a vehicle manufacturer; control subjects were from a nearby food factory. Airborne manganese levels in the breathing zones of welders and controls were 1.45 +/- SD1.08 mg/m and 0.11 +/- 0.07 microg/m, respectively. Serum levels of manganese and iron in welders were 4.3-fold and 1.9-fold, respectively, higher than those of controls. Blood lead concentrations in welders increased 2.5-fold, whereas serum zinc levels decreased 1.2-fold, in comparison with controls. Linear regression revealed the lack of associations between blood levels of five metals and welder's age. Furthermore, welders had erythrocytic superoxide dismutase activity and serum malondialdehyde levels 24% less and 78% higher, respectively, than those of controls. These findings suggest that occupational exposure to welding fumes among welders disturbs the homeostasis of trace elements in systemic circulation and induces oxidative stress.

Occupation and risk of meningioma and acoustic neuroma in the United States

BACKGROUND

Workplace exposures may be related to the development of brain tumors. In this case-control study, we examine occupation as a risk factor for meningioma and acoustic neuroma.

METHODS

A lifetime work history was obtained for 197 incident cases of meningioma, 96 cases of acoustic neuroma and 799 controls with non-malignant diseases enrolled from three hospitals in the United States between 1994 and 1998. Jobs considered to have similar tasks and chemical exposures were assigned to an occupational group. Logistic regression was used to estimate odds ratios (OR) adjusted for study matching factors (hospital, age, sex, race/ethnicity, and proximity of residence to the hospital) and education.

RESULTS

Elevated risk of meningioma was observed for individuals who had ever worked in the following occupational groups: auto body painters, designers and decorators, military occupations, industrial production supervisors, teachers, and managers. For acoustic neuroma, increased risk was noted for having worked as an athlete, gas station attendant, purchasing agent, sales representative, or teacher.

CONCLUSIONS

Although limited by multiple comparisons and the relatively small number of cases and controls in many occupational groups, these results nevertheless provide clues that deserve additional study in future epidemiologic studies.

Pesticides

Pesticides are a broad group of heterogeneous chemicals that have a significant public health benefit by increasing food production productivity and decreasing food-borne and vector-borne diseases. However, depending on the agent and the exposure, they may pose health risks. Because of their behavior, acute accidental toxic exposures occur more commonly in children. Because of the dietary habits and greater intake of foods per kilogram in children and because some infants are breastfed, there is also concern about the effects on them of low-level environmental exposures. In the absence of direct conclusive evidence, consistent and relevant observations have led some investigators to infer that chronic low-dose exposure to certain pesticides might pose a potential hazard to the health and development of infants and children. Other investigators have concluded that such inferences can be neither supported nor refuted at the present time. The pediatrician has a role to play in recognizing the symptoms of acute exposure and to be able to provide appropriate treatment. It is essential to study whether there are subtle neurologic effects that may result from low-level pesticide exposures in individual patients.

Brain capillary endothelium and choroid plexus epithelium regulate transport of transferrin-bound and free iron into the rat brain

Iron transport into the CNS is still not completely understood. Using a brain perfusion technique in rats, we have shown a significant brain capillary uptake of circulating transferrin (Tf)-bound and free 59Fe (1 nm) at rates of 136 +/- 26 and 182 +/- 23 microL/g/min, respectively, while their respective transport rates into brain parenchyma were 1.68 +/- 0.56 and 1.52 +/- 0.48 microL/g/min. Regional Tf receptor density (Bmax) in brain endothelium determined with 125I-holo-Tf correlated well with 59Fe-Tf regional brain uptake rates reflecting significant vascular association of iron. Tf-bound and free circulating 59Fe were sequestered by the choroid plexus and transported into the CSF at low rates of 0.17 +/- 0.01 and 0.09 +/- 0.02 microL/min/g, respectively, consistent with a 10-fold brain-CSF concentration gradient for 59Fe, Tf-bound or free. We conclude that transport of circulating Tf-bound and free iron could be equally important for its delivery to the CNS. Moreover, data suggest that entry of Tf-bound and free iron into the CNS is determined by (i) its initial sequestration by brain capillaries and choroid plexus, and (ii) subsequent controlled and slow release from vascular structures into brain interstitial fluid and CSF.

Brain barrier systems: a new frontier in metal neurotoxicological research

The concept of brain barriers or a brain barrier system embraces the blood-brain interface, referred to as the blood-brain barrier, and the blood-cerebrospinal fluid (CSF) interface, referred to as the blood-CSF barrier. These brain barriers protect the CNS against chemical insults, by different complementary mechanisms. Toxic metal molecules can either bypass these mechanisms or be sequestered in and therefore potentially deleterious to brain barriers. Supportive evidence suggests that damage to blood-brain interfaces can lead to chemical-induced neurotoxicities. This review article examines the unique structure, specialization, and function of the brain barrier system, with particular emphasis on its toxicological implications. Typical examples of metal transport and toxicity at the barriers, such as lead (Pb), mercury (Hg), iron (Fe), and manganese (Mn), are discussed in detail with a special focus on the relevance to their toxic neurological consequences. Based on these discussions, the emerging research needs, such as construction of the new concept of blood-brain regional barriers, understanding of chemical effect on aged or immature barriers, and elucidation of the susceptibility of tight junctions to toxicants, are identified and addressed in this newly evolving field of neurotoxicology. They represent both clear challenges and fruitful research domains not only in neurotoxicology, but also in neurophysiology and pharmacology.

Manganese action in brain function

Manganese, an essential trace metal, is supplied to the brain via both the blood-brain and the blood-cerebrospinal fluid barriers. There are some mechanisms in this process and transferrin may be involved in manganese transport into the brain. A large portion of manganese is bound to manganese metalloproteins, especially glutamine synthetase in astrocytes. A portion of manganese probably exists in the synaptic vesicles in glutamatergic neurons and the manganese is dynamically coupled to the electrophysiological activity of the neurons. Manganese released into the synaptic cleft may influence synaptic neurotransmission. Dietary manganese deficiency, which may enhance susceptibility to epileptic functions, appears to affect manganese homeostasis in the brain, probably followed by alteration of neural activity. On the other hand, manganese also acts as a toxicant to the brain because this metal has prooxidant activity. Abnormal concentrations of manganese in the brain, especially in the basal ganglia, are associated with neurological disorders similar to Parkinson's disease. Understanding the movement and action of manganese in synapses may be important to clarify the function and toxicity of manganese in the brain.

Establishment and characterization of an immortalized Z310 choroidal epithelial cell line from murine choroid plexus

The choroid plexus plays a wide range of roles in brain development, maturation, aging process, endocrine regulation, and pathogenesis of certain neurodegenerative diseases. To facilitate in vitro study, we have used a gene transfection technique to immortalize murine choroidal epithelial cells. A viral plasmid (pSV3neo) was inserted into the host genome of primary choroidal epithelia by calcium phosphate precipitation. The transfected epithelial cells, i.e., Z310 cells, that survived from cytotoxic selection expressed SV40 large-T antigen throughout the life span, suggesting a successful gene transfection. The cells displayed the same polygonal epithelial morphology as the starting cells by light microscopy. Immunocytochemical studies demonstrate the presence of transthyretin (TTR), a thyroxine transport protein known to be exclusively produced by the choroidal epithelia in the CNS, in both transfected and starting cells. Western blot analyses further confirm the production and secretion of TTR by these cells. The mRNAs encoding transferrin receptor (TfR) were identified by Northern blot analyses. The cells grow at a steady rate, currently in the 110th passage with a population doubling time of 20-22 h in the established culture. When Z310 cells were cultured onto a Trans-well apparatus, the cells formed an epithelial monolayer similar to primary choroidal cells, possessing features such as an uneven fluid level between inner and outer chambers and an electrical resistance approximately 150-200 omega-cm(2). These results indicate that immortalized Z310 cells possess the characteristics of choroidal epithelia and may have the potential for application in blood-CSF barrier (BCB) research.