Choline and PAH transport across blood-CSF barriers: The effect of lithium

The components of the blood-CSF barrier responsible for the transport of p-aminohippuric acid (PAH) and choline from CSF to blood were identified using in vitro preparations of frog choroid plexus and arachnoid membranes. Choline was transported out of CSF across the arachnoid, while PAH was transported out across the choroid plexus. Probenecid and ouabain blocked both processes. The effect of Li on these transport processes was tested by the addition of 5 mM LiCl to the incubation media. Li increased, by a factor of two, choline transport across the arachnoid, but there was no effect of Li on PAH transport across the plexus. Lithium was passively transported across the choroid plexus, and we suggest that the major transport pathway is through the tight junctions. The steady-state distribution of Li between the choroidal epithelium and the incubation medium was only half that expected for passive distribution. This suggests the existence of sodium/lithium countertransport in these epithelial cell membranes.     

In vitro studies on the uptake and incorporation of natural amino acids in rabbit choroid plexus

Isolated rabbit choroid plexus was incubated aerobically at 37 °C in artificial cerebrospinal fluid (CSF) medium containing 1 mg/ml glucose and trace amounts of [¹⁴C]leucine. The uptake of leucine occurred against a concentration gradient, was saturable, energy dependent and inhibited by natural amino acids. Of the total amount accumulated after 1 h, in the presence of trace levels of [¹⁴C]leucine, approximately 80% of the leucine was found to be in the bound form. A similar free to bound distribution was observed for isoleucine, phenylalanine, tyrosine, histidine and proline. Classic inhibitors of cytoplasmic protein synthesis inhibited the incorporation of leucine into protein but did not prevent [¹⁴C]leucine from being actively taken up into the choroid plexus tissue water. Our in vitro studies on leucine uptake are in general agreement with previous in vivo data and help support the view that the choroid plexus plays a role in the regulation of cerebrospinal fluid and cerebral amino acids.     

Early postnatal development of transport functions in the rabbit choroid plexus

The development of transport functions in the rabbit choroid plexus was followed postnatally up to 2 months after birth. The activity of ouabain-sensitive Na+, K+-ATPase in newborn rabbit choroid plexus composes about one-fourth (lateral and third ventricle) to one-half (fourth ventricle) of the activity in the adult animal, and it increases markedly within the first 3 weeks of early life. A similar profile of postnatal changes is observed for the capacity to take up and accumulate the organic base choline, which is about three to five times higher for the adult rabbit than for the newborn animal. This coincides with the maturation of the epithelial cells as well as with the development of the sympathetic nerve supply in the choroid plexus. The results suggest that energy-dependent translocation systems influenced by local sympathetic nerves in the choroid plexus, at the interface between blood and CSF, have a functional role shortly after birth.     

Pre-operative embolisation of choroid plexus tumours in children. Part II. Observations on the effects on CSF production

Objective

Choroid plexus tumours are one of the few causes of hydrocephalus secondary to increased CSF production. Operative treatment aided by pre-op embolisation is being used in our institution as a primary option of treatment. Our aim was firstly to quantify the effects of embolisation on CSF production and secondly to assess whether the use of pre-operative embolisation would lead to reduction of CSF production thus reducing the need for CSF diversion procedures in the perioperative and long term.

Methods

From 1996 till 2009, 30 patients (mean age, 2.25 years) underwent surgical treatment for 24 choroid plexus papillomas and 6 choroid plexus carcinomas. Thirteen underwent pre-operative super-selective embolisation of the feeding vessels with Histoacryl glue. The need for CSF diversion—external ventricular drain (EVD)/shunt—was recorded together with the daily CSF production between the two groups (embolised: EMB+ vs. not embolised: EMB?)

Results

The embolisation was successful in 13 of 15 (86.6 %) patients. The average post-op daily CSF production between the EMB+ and EMB? groups was (67 vs. 135 ml/day; p?=?0.005). EVD days in situ post-operatively was 7.9 vs. 12.1 (p?=?0.033). However, the need for permanent CSF diversion was similar in both groups (five vs. six).

Conclusion

We have established the safety of pre-operative embolisation as an adjunct to operative treatment of choroid plexus tumours. As we expected, this technique, by removing the tumour's blood supply, reduces the rate of CSF production. This has had a positive impact on the post-operative management of these patients. We cannot say the same for the need of permanent CSF diversion in our study.     

Anandamide levels in cerebrospinal fluid of first-episode schizophrenic patients: impact of cannabis use

BACKGROUND: Previous studies have shown that cerebrospinal fluid (CSF) from schizophrenic patients contains significantly higher levels of the endogenous cannabinoid anandamide than does CSF from healthy volunteers. Moreover, CSF anandamide levels correlated inversely with psychotic symptoms, suggesting that anandamide release in the central nervous system (CNS) may serve as an adaptive mechanism countering neurotransmitter abnormalities in acute psychoses. In the present study we examined whether cannabis use may alter such a mechanism. METHODS: We used liquid chromatography/mass spectrometry (LC/MS) to measure anandamide levels in serum and CSF from first-episode, antipsychotic-na?ve schizophrenics (n=47) and healthy volunteers (n=81). Based on reported patterns of cannabis use and urine delta9-tetrahydrocannabinol (delta9-THC) tests, each subject group was further divided into two subgroups: 'low-frequency' and 'high-frequency' cannabis users (lifetime use < or = 5 times and > 20 times, respectively). Serum delta9-THC was investigated to determine acute use and three patients were excluded from the analysis due to detectable delta9-THC levels in serum. RESULTS: Schizophrenic low-frequency cannabis users (n=25) exhibited > 10-fold higher CSF anandamide levels than did schizophrenic high-frequency users (n=19, p=0.008), healthy low-frequency (n=55, p<0.001) or high-frequency users (n=26, p<0.001). In contrast, no significant differences in serum anandamide levels were found among the four subgroups. CSF anandamide levels and disease symptoms were negatively correlated in both user groups. CONCLUSIONS: The results indicate that frequent cannabis exposure may down-regulate anandamide signaling in the CNS of schizophrenic patients, but not of healthy individuals. Thus, our findings suggest that alterations in endocannabinoid signaling might be an important component of the mechanism through which cannabis impacts mental health.     

Simultaneous and continuous measurement of choroid plexus blood flow and cerebrospinal fluid production: effects of vasoactive intestinal polypeptide

Using laser-Doppler flowmetry during ventriculocisternal perfusion with inulin-[14C]carboxylic acid, choroid plexus blood flow (CPBF) and CSF production were measured simultaneously in rats during periods of 3 h. Blood flow and CSF production decreased only slightly during control experiments. The effect of vasoactive intestinal polypeptide (VIP) was studied at different concentrations of the peptide given either intraventricularly or intravenously. Intraventricular administration of VIP (10(-9) or 10(-7) M) resulted in a decrease in CSF production of up to 30%, while CPBF increased by 20%, also demonstrating that CSF production and blood flow are not directly coupled in the choroid plexus. When infused intravenously, VIP (10 or 100 pmol/kg/min) increased CPBF, an effect partly antagonized at higher concentrations owing to a VIP-induced systemic hypotension. No effect of VIP on CSF production could be seen with intravenous administration.     

Sympathetic influence on sodium-potassium activated adenosine triphosphatase activity of rabbit and rat choroid plexus

Ouabain-sensitive Na+-K+-ATPase was measured spectrophotometrically in the lateral choroid plexuses of rabbit and rat. In the rabbit, a significant increase in the enzyme activity was seen at one week after unilateral sympathectomy (removal of the superior cervical ganglion), but not at three days or two weeks postoperatively, as compared with the intact, contralateral plexus. Unilateral sympathetic denervation of the rat's choroid plexus induced a nearly 40% decrease in Na+-K+-ATPase activity at 6 days after the operation, while no effect was seen after 12 days. The results agree with a local sympathetic inhibition of CSF production in rabbit (corresponding studies on rat have not been performed), and favor the assumption that the adrenergic nerves in the choroid plexus mediate direct effects on transport functions in the plexus epithelium.     

Role of choroid plexus epithelium in the removal of valproic acid from the central nervous system

Previous experiments suggest the primary route of valproic acid (VPA) removal from the rabbit central nervous system (CNS) is by probenecid-sensitive transporters at the blood-brain barrier but not at the choroid plexus. The purpose of this study was to determine if other transport mechanisms at the choroid plexus played a significant role in the removal of VPA from the CNS. In six rabbits, silicone oil was perfused into both cerebral ventricles and out through the cisterna magna to physically block exchange of VPA between cerebrospinal fluid (CSF) and blood and between brain and CSF. In six control rabbits, perfusion was performed with mock CSF. Both groups received a loading dose followed by continuous intravenous infusion of VPA for 2.10 min. Ventriculocisternal perfusion with silicone oil had no significant effect on the steady-state brain concentrations or brain-to-plasma concentration ratios of VPA, further confirming that efflux of VPA at the choroid plexus is negligible.     

Cerebrospinal fluid glucose and leukocyte responses in experimental meningitis

The fall in cerebrospinal fluid (CSF) glucose and CSF leukocyte response was studied in cats with experimental meningitis. Klebsiella pneumoniae or Streptococcus pneumoniae were injected intracisternally, and the latter organisms were incubated with CSF in vitro. When 10(6)-10(9)K. pneumoniae were incubated with 4 ml of CSF, the time time necessary for the glucose to decrease to less than 10 mg/dl ranged from 6.5 to 2.5 h, at a rate proportional to the size of the inoculum. When the same numbers of bacteria were injected intracisternally, the time ranged from 9 to 3 h, and the CSF leukocyte response did not exceed 1200 WBC/mm3. At this time, only minimal histological changes in brain and choroid plexus were seen. Twenty hours after intrathecal K. pneumoniae, large numbers of leukocytes (up to 4 X 10(4)/mm3) were recovered from the CSF. Regardless of the number of leukocytes, however, hypoglycorrhachia occurred when the CSF contained more than 10(7) bacteria/ml. At this interval, large numbers of leukocytes were seen invading the stroma of the choroid plexus, leptomeninges and perivascular spaces. When 10(8) S. pneumoniae were injected intracisternally, CSF glucose concentration decreased as rapidly as with K. pneumoniae. The spinal fluid leukocyte response to S. pneumoniae was, however, greater than that to K. pneumoniae. These results suggest that under the conditions of these studies, hypoglycorrhachia of bacterial meningitis is the result of metabolism of the bacteria with little contribution from the leukocytes.     

Transthyretin: a choroid plexus-specific transport protein in human brain. The 1986 S. Weir Mitchell award

Plasma transthyretin (TTR, formerly called prealbumin) is a 55-kd protein that participates in the plasma transport of both thyroxine and retinol (vitamin A). TTR concentrations are disproportionately high in human ventricular CSF, suggesting that TTR is either selectively transported across or synthesized de novo within the blood-CSF barrier. To address this question, we adopted a molecular genetic approach; after isolating a cDNA clone encoding human TTR, we previously demonstrated specific TTR messenger RNA (mRNA) synthesis in rat choroid plexus. We have now extended these investigations to the human brain. Northern analysis of postmortem brain homogenates revealed abundant TTR mRNA in choroid plexus, but not in cerebellum or cerebral cortex. Choroid plexus mRNA was readily translated into TTR preprotein in an in vitro translation system. An immunocytochemical survey of human postmortem brain sections revealed the presence of TTR protein specifically and uniquely in the cytoplasm of choroid plexus epithelial cells; these results were corroborated at the mRNA level by an extensive survey of whole rat-brain sections by in situ hybridization. Therefore, within the mammalian CNS, TTR is the first known protein synthesized solely by the choroid plexus, suggesting a special role for TTR in the brain or CSF. Whether this function differs from its established plasma transport functions is presently unknown.     

Hydrocephalus due to cerebrospinal fluid overproduction by bilateral choroid plexus papillomas

Case report A 10-month-old boy, with congenital deafness and blindness associated with chromosomal deletion [46XY, del(13)(q32)], presented with intractable ascites 9 months after ventriculo-peritoneal shunting for congenital hydrocephalus. Revision of the ventriculo-atrial shunt resulted in shunt failure 1 month later. External ventricular drainage revealed cerebrospinal fluid (CSF) overproduction (2,000 ml/day). Magnetic resonance imaging showed marked lobular enlargement of the bilateral choroid plexuses extending from the trigone to the body and inferior horn of the lateral ventricle. Multi-staged resection was performed via bilateral temporo-occipital transcortical approaches, and CSF production significantly decreased to 100 ml/day postoperatively. Histological assessment of the villous surface suggested villous hyperplasia of the choroid plexus and thorough evaluation including the proximal portion of the lobular lesion near the attachment revealed choroid plexus papilloma. He was discharged after ventriculo-peritoneal shunting without additional neurological deficits except for hyperreflexia of the left extremities.Conclusion CSF overproduction caused by bilateral choroid plexus papillomas can result in hydrocephalus. Radical resection of the bilateral ventricular lesions should be considered for this entity. Thorough evaluation of the surgical specimen is recommended because histological examination of only the lobular surface of the choroid plexus lesion may fail to identify choroid plexus neoplasm.     

Multiple isoforms of the tumor protein p73 are expressed in the adult human telencephalon and choroid plexus and present in the cerebrospinal fluid

p73, a homolog of the p53 tumor suppressor, codes for full-length transactivating (TA) and N-terminally truncated (DeltaN) isoforms, with pro- and anti-apoptotic activities, respectively. We examined the expression of the main p73 isoforms in adult human and mouse telencephalon and choroid plexus by immunohistochemistry on paraffin sections, and immunoblotting (IB) of tissue extracts and cerebrospinal fluid (CSF), using antibodies against different protein domains. Cortical neurons expressed TAp73 predominantly in the cytoplasm and DeltaNp73 mainly in the nucleus, with partial overlap in the cytoplasm. Highest expression was found in the hippocampus. IB showed an array of TAp73 variants in adult human cortex and hippocampus. IB of human choroid plexus and CSF using TAp73-specific antibodies revealed the presence of a approximately 90-kDa protein whose molecular weight was reduced after N-deglycosylation, suggesting that glycosylated TAp73 is exported into the CSF. In the mouse, high expression of TAp73 was also detected in the subcommissural organ (SCO), an ependymal gland absent in adult humans. TAp73 colocalized with anti-fibra-Reissner-antibody (AFRU), which is a marker of Reissner's fiber, the secreted SCO product. p73-deficient mice had generalized cortical hypoplasia and hydrocephalus; in addition, we observed a dramatic size reduction of the choroid plexus. However, the SCOs were apparently unaltered and continued to secrete Reissner's fiber. Our findings point to complex and widespread p73 activities in the maintenance of adult cortical neurons and in brain homeostasis. TAp73 in the CSF may play important roles in the maintenance of the adult ventricular wall as well as in the development of the proliferating neuroepithelium.     

Choroid plexus blood flow in the sheep

Choroid plexus blood flow was measured in 29 adult female sheep using the radioactive microsphere technique. Basal blood flow, response to change in arterial carbon dioxide tension, and response to change in mean arterial blood pressure were determined. The results were compared to cerebral cortical blood flow values in the same sheep. Mean choroid plexus blood flow was 601 ml/100 g/min under basal conditions. Choroid plexus blood flow fell 31% with hypocarbia, a reduction comparable to that seen in cortex. With hypercarbia choroid plexus blood flow rose only 27% whereas cortical blood flow increased by 199%. Unlike cortical blood flow, choroid plexus blood flow fell significantly with pharmacogenic hypertension. The latter finding may reflect the absence of a blood-brain barrier in choroid plexus.     

Neuroendocrine regulatory mechanisms in the choroid plexus-cerebrospinal fluid system

The CSF is often regarded as merely a mechanical support for the brain, as well as an unspecific sink for waste products from the CNS. New methodology in receptor autoradiography, immunohistochemistry and molecular biology has revealed the presence of many different neuroendocrine substances or their corresponding receptors in the main CSF-forming structure, the choroid plexus. Both older research on the sympathetic nerves and recent studies of peptide neurotransmitters in the choroid plexus support a neurogenic regulation of choroid plexus CSF production and other transport functions. Among the endocrine substances present in blood and CSF, 5-HT, ANP, vasopressin and the IGFs have high receptor concentrations in the choroid plexus and have been shown to influence choroid plexus function. Finally, the choroid plexus produces the growth factor IGF-II and a number of transport proteins, most importantly transthyretin, that might regulate hormone transport from blood to brain. These studies suggest that the choroid plexus-CSF system could constitute an important pathway for neuroendocrine signalling in the brain, although clearcut evidence for such a role is still largely lacking.     

Modification of protein transfer across blood/cerebrospinal fluid barrier in response to altered plasma protein composition during development

A developmentally regulated protein-specific transfer mechanism across choroid plexus epithelial cells has previously been proposed to contribute to the characteristically high concentration of protein in cerebrospinal fluid (CSF) in the immature brain. Here we demonstrate that this mechanism is sensitive to protein variations in plasma resulting in changed numbers of transferring cells for individual proteins and altered transfer into the CSF. Pups of Monodelphis domestica at postnatal day (P)9, P65 and P110 were injected intraperitoneally with either adult Monodelphis plasma or exogenous bovine fetuin. Samples of CSF, blood and brain were collected from terminally anaesthetized animals 3-48 h later. The concentration of total protein was measured and levels of albumin, hemopexin, α-fetoprotein and bovine fetuin were estimated by western blotting. Numbers of lateral ventricular choroid plexus cells positive for total and individual plasma proteins were counted in paraffin sections of brains stained with appropriate antibodies. Following intraperitoneal injections, the content of proteins in the CSF increased at all three ages, but the concentration increased only in the CSF of older animals. The total numbers of plexus cells positive for plasma protein did not change significantly, but cells positive for individual proteins did. Fetuin was detected in all protein-positive cells, but apparently displaced α-fetoprotein and, to a lesser degree, hemopexin. The results indicate that protein transfer across the blood/CSF barrier appears to be regulated by a molecular recognition mechanism that is probably saturable but may not be as specific for individual proteins as previously suggested.     

The stability of the hippocampal slice preparation: An electrophysiological and ultrastructural analysis

To determine if canine and rat choroid plexus Na+,K+-ATPase can be localized by immunoperoxidase staining after fixation and embedding, we prepared rabbit antiserum to purified canine kidney medulla Na+,K+-ATPase. When sodium dodecylsulfate polyacrylamide electrophoretic gels of purified canine kidney Na+,K+-ATPase and canine kidney microsomes were treated with antiserum followed by [125I]protein A and autoradiography, the canine microsomes and purified Na+,K+-ATPase showed a prominent radioactive band coincident with the alpha-, beta- and gamma-subunits of the purified canine kidney enzyme. When the rabbit immunoglobulin that was purified from the Na+,K+-ATPase antiserum through DEAE-cellulose ion exchange chromatography was used for immunoperoxidase staining of the choroid plexus fixed with Bouin's fixative, intense immunoreactive staining was present on the epithelial cells of both choroid plexuses but was not found in the tissue around the vessel. The staining was especially confined to apical surfaces of the epithelial cells. The same procedure was performed in the canine kidney, and immunostaining was obtained in the tubules where Baskin and Stahl described the enzyme localization. No staining was seen with pre-immune serum of the normal rabbit. We concluded that both the canine and rat choroid plexus are rich in Na+,K+-ATPase, which plays an important role in cerebrospinal fluid (CSF) secretion.     

In situ formation of immune complexes in the choroid plexus of rats by sequential injection of a cationized antigen and unaltered antibodies

The deposition of cationized human serum albumin (HSAED) in the choroid plexus of rats was compared to deposition in renal glomeruli. Initial deposition in the choroid plexus required a higher dose of antigen than deposition in glomeruli. The optimal dose for deposition in the choroid plexus was 50 mg/kg of HSAED. With this dose the antigen was still present in the choroid plexus at eight days after injection, whereas the glomeruli became largely negative by one day. Immune complex formation and persistence was examined in the choroid plexus by injecting rabbit antibodies to HSA at varying times after the injection of HSAED. When a limited amount of antibody was injected, it localized preferentially to glomeruli as compared to the choroid plexus. When sufficient antibodies were injected, the antigen and antibodies persisted in a comparable manner in the choroid plexus and glomeruli. By the eighth day after injection of foreign proteins, rat IgG deposited in both organs, indicating an endogenous immune response. The formed deposits were still present at 28 days, containing HSA, rabbit IgG, and rat IgG, but not rat C3. These results indicate that immune deposits readily form in the choroid plexus after injecting a cationized antigen. Differences, however, exist in the formation of immune deposit in the choroid plexus and the glomeruli.     

Antiepileptic and prophylactic effects of tetrahydrocannabinols in amygdaloid kindled cats.

Acute administration of delta8-tetrahydrocannabinol (delta8-THC) or delta9-THC failed to affect partially developed or fully developed kindled amygdaloid seizures in cats. However, delta9-THC was quite effective in suppressing focal AD in the stimulated amygdala when administered very early in kindling, before the development of any clinical manifestations. This finding suggested that chronic administration of delta9-THC during kindling might block the process of seizure development, which was supported by the observation that three of four cats failed to kindle when treated with the drug. The cat that failed to be protected by delta9-THC was also insensitive to the general electroclinical effects of moderately high doses of delta9-THC. The prophylactic activity of delta9-THC is in contrast to the ineffectiveness of diphenylhydantoin, a drug whose anticonvulsant activity is often compared with that of THC.     

Human choroid plexus growth factors: What are the implications for CSF dynamics in Alzheimer's disease?

The choroid plexus plays a key role in supporting neuronal function by secreting cerebrospinal fluid (CSF) and may be involved in the regulation of various soluble factors. Because the choroid plexus is involved in growth factor secretion as well as CSF dynamics, it is important to understand how growth factors in CSF interact with the brain parenchyma as well as with cells in direct contact with the flowing CSF, i.e., choroid plexus and arachnoid villi. While the existence of growth factors in the choroid plexus has been documented in several animal models, the presence and distribution of growth factors in the human choroid plexus has not been extensively examined. This study describes the general distribution and possible functions of a number of key proteins in the human choroid plexus and arachnoid villi, including basic fibroblast growth factor, FGF receptor, and vascular endothelial growth factor. FGF and VEGF could both be readily demonstrated in choroid plexus epithelial cells. The presence of FGF and VEGF within the choroid plexus was also confirmed by ELISA analysis. Since Alzheimer's disease (AD) is known to be associated with a number of growth factor abnormalities, we examined the choroid plexus and arachnoid villi from AD patients. Immunohistochemical studies revealed the presence of FGF and VEGF within the AD choroid plexus and an increased density of FGFr in both the choroid plexus and the arachnoid villi of AD patients. No qualitative changes in the distribution of FGF and VEGF were observed in the AD choroid plexus. The appearance of FGFr in AD arachnoid was associated with robust amyloid and vimentin immunoreactivity. These findings confirm the presence of FGF and VEGF within the normal and AD choroid plexus and suggest that the alteration of growth factors and their receptors may contribute to the pathogenesis of the hydrocephalus ex vacuo that is characteristically seen in AD.     

Choroid plexus: biology and pathology

The choroid plexus is an epithelial–endothelial vascular convolute within the ventricular system of the vertebrate brain. It consists of epithelial cells, fenestrated blood vessels, and the stroma, dependent on various physiological or pathological conditions, which may contain fibroblasts, mast cells, macrophages, granulocytes or other infiltrates, and a rich extracellular matrix. The choroid plexus is mainly involved in the production of cerebrospinal fluid (CSF) by using the free access to the blood compartment of the leaky vessels. In order to separate blood and CSF compartments, choroid plexus epithelial cells and tanycytes of circumventricular organs constitute the blood–CSF–brain barrier. As non-neuronal cells in the brain and derived from neuroectoderm, choroid plexus epithelia are defined as a subtype of macroglia. The choroid plexus is involved in a variety of neurological disorders, including neurodegenerative, inflammatory, infectious, traumatic, neoplastic, and systemic diseases. Aβ and Biondi ring tangles accumulate in the Alzheimer’s disease choroid plexus. In multiple sclerosis, the choroid plexus could represent a site for lymphocyte entry in the CSF and brain, and for presentation of antigens. Recent studies have provided new diagnostic markers and potential molecular targets for choroid plexus papilloma and carcinoma, which represent the most common brain tumors in the first year of life. We here revive some of the classical studies and review recent insight into the biology and pathology of the choroid plexus.