ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
Its importance cannot be overstated: the bloodstream contains very many chemicals: some are required by the brain for effective functioning (such as GLUCOSE) and some act as information signals to the brain (such as HORMONES), but there are many chemicals that are not required by brain (and would be dangerous if present there) and of course DRUGS delivered into the bloodstream deliberately, either for therapeutic or recreational purposes, may or may not be wanted in brain. Those substances that need to be excluded are effectively barred by the blood-brain barrier; those that need access generally have to have that access regulated. (For example, the concentration of glucose in the blood fluctuates dramatically during the day. Brains need to be protected against surging levels of glucose, requiring instead a regulated and controlled flow.)Chemicals that cross the blood-brain barrier typically have a low MOLECULAR WEIGHT and high solubility in LIPIDS, or they cross by virtue of an active transport mechanism. In drug discovery research it is always important to know whether a compound can cross the blood-brain barrier: an agent intended to treat a neurological condition would normally be expected actually to enter brain tissue. The existence of a barrier was noted first by Paul Ehrlich in the nineteenth century: he injected dye into the bloodstream and noted that it stained all tissues except the brain. The same dye injected into the cerebral VENTRICLES did stain brain tissue, indicating that something normally obstructed the passage of chemicals from blood to brain. The term blood-brain barrier was coined in 1900 by Lewandowski. The blood-brain barrier is formed by complex tight junctions between cells which physically prevent movement of fluids across the membranes. There are a number of places where specialized barriers are formed: (1) the ENDOTHELIUM of blood vessels in brain form tight junctions to prevent fluid escaping from the bloodstream into the brain interstitial fluid. (2) The CHOROID PLEXUS is CONNECTIVE TISSUE found in the VENTRICLES of the brain. It is here that CEREBROSPINAL FLUID (CSF) is formed, this accumulating in the ventricles and flowing out into the extracellular spaces around the NEUROPIL of the brain. A barrier in the choroid plexus epithelium prevents direct exchange of fluids between blood and CSF. (3) The NEUROTHELIUM is a barrier formed in the ARACHNOID MEMBRANE: cells form a barrier on the outside of the arachnoid membrane to prevent blood from vessels in the DURA MATER escaping into brain. (4) There are specialized sites known as the CIRCUMVENTRICULAR ORGANS where exchange between brain and blood can take place. Such sites are critically involved in monitoring the composition of the blood-stream, but nevertheless possess a form of barrier that allows the required communication to take place while preventing non- selective influx of material into brain. This barrier is made of TANYCYTES, specialized ependymal cells. All of these—blood vessel endothelium, choroid plexus endothelium, neurothelium, tanycytes—show formation of tight junctions to prevent unwanted movement of fluid. Clearly though, blood contains substances such as glucose that need to be extracted by the brain. Specialized transport mechanisms exist to take such substances from the bloodstream and divert them to the required brain sites. ASTROCYTES are involved in this process: they make contact with blood vessels and, using specialized transporter mechanisms, effect passage of required substances into brain in a controlled manner.
Choroid Plexus Tumors and Meningiomas
David A. Walker, Giorgio Perilongo, Roger E. Taylor, Ian F. Pollack in Brain and Spinal Tumors of Childhood, 2020
CPTs are rare central nervous system (CNS) tumors derived from choroid plexus epithelium. The choroid plexus is well-perfused neuroepithelial tissue located mainly in the lateral, third, and fourth ventricles. The choroid plexus has an enormous surface area, approximately 25–50% the size of the inner capillary surface area of the brain. The choroid plexus is responsible for secretion of the cerebrospinal fluid (CSF) (generating intracranial pressure), maintaining CSF ion homeostasis, and providing micronutrients, proteins, and hormones for neuronal and glial development. The choroid plexus has roles in brain immunity, protection from toxins, and absorption and removal of waste products. CPTs are distributed in proportion to the density of the choroid plexus itself, with 50% occurring in the lateral ventricle, followed by 40% in the fourth ventricle, and 5% in the third ventricle. About 5% of CPTs are multifocal. In adults (mean age of 35.5 years), an infratentorial location is slightly more common, with the fourth ventricle being the most common site. In children (mean age of 1.5 years), supratentorial location is more common, including the lateral and third ventricles. In a meta-analysis of 566 CPTs, Wolff et al. found that, as patients became older, tumors were located more caudally (Figure 19.1). Patients with tumors arising in the lateral and third venticles presented at a median age of 1.5 years, whereas patients with tumors of the fourth ventricle and cerebellopontine angle had median ages of 22.5 and 35.5 years, respectively. Rarely, extraventricular locations for CPT have been described.
Extrahepatic Synthesis of Acute Phase Proteins
Andrzej Mackiewicz, Irving Kushner, Heinz Baumann in Acute Phase Proteins, 2020
The structure of the brain is not homogeneous. It seemed unlikely that the expression of the transthyretin gene would be distributed evenly throughout the brain. The choroid plexus is known to produce most of the cerebrospinal fluid (for a review, see Reference 52). The most likely site for the expression of a protein in the brain for secretion into the cerebrospinal fluid would therefore seem to be the choroid plexus. RNA was prepared from choroid plexus, the “rest of brain” (i.e., brain from which choroid plexus had been removed), and the liver. This RNA was analyzed by dot-blot hybridization with cDNA probes for various rat plasma proteins, as shown in Figure 8. One gram of choroid plexus contained far more transthyretin mRNA than 1 g of liver. Transferrin mRNA was present in choroid plexus and liver in roughly similar amounts per gram of tissue. Messenger RNAs for albumin, the β-subunit of fibrinogen, thiostatin, and α-acid glycoprotein were detectable in liver only.
Rapid evolution of a choroid plexus papilloma in an infant
Published in British Journal of Neurosurgery, 2009
Aimun A. B. Jamjoom, Momen A. Sharab, Abdulhakim B. Jamjoom, Mohamed B. Satti
Choroid plexus papilloma (CPP) is primarily found in children less than 2 years of age but can also be diagnosed prenatally. The presentation of a large CPP during infancy is not uncommon and surgical excision is usually recommended without delays. As a result, information about the growth rate of CPP during infancy is lacking. We report a preterm infant who presented with a choroid plexus papilloma that grew from being undetected on MRI to reaching a large size in 5 months. The case is unique in that it provides documentation of the rapid growth potential of this benign tumour in infancy. A possible explanation for this occurrence is discussed.
Nodular Lesions of Choroid Plexus in Hurler Disease
Published in Fetal and Pediatric Pathology, 2011
Neuropathologic examination of six brains from children with Hurler disease revealed nodular lesions in the glomus of choroid plexus caused by proliferation of vacuolated pericytes, fibroblasts, and arachnoid cells on the background of collagenized and myxoid stroma. This localization of lesions can be explained by the presence of a rich vascular network, as well as cellular heterogeneity greater in the glomus than in other parts of the choroid plexus or in the brain parenchyma. The development of nodules did not correlate with the age, severity of hydrocephalus, or the degree of expansion of the perivascular spaces in the brain.
Choroid Plexus Transporters for Drugs and Other Xenobiotics
Published in Journal of Drug Targeting, 2002
Jean-FranÇois Ghersi-Egea, Nathalie Strazielle
The transporter mediated uptake of various drugs and toxic compounds by choroid plexuses has been extensively described over the last decades. In conjunction with several other specific features of the choroidal tissue such as its drug metabolism and antioxidant capacities, these transport activities contribute to the neuroprotective functions attributed to the choroid plexus. Recently, the molecular identity and localization of the proteins responsible for the influx and efflux of drugs and metabolites at the choroid plexus has started to be deciphered, thus allowing a better understanding of the directionality and significance of the transport processes observed at the choroid plexus. Transport of drugs and metabolites involves mainly the SLC (solute carrier) and ABC (ATP-Binding Cassette) transporter super-families. In this review, we describe the identity and mechanism of transport of the SLC and ABC members so far characterized at the choroid plexus.
Related Knowledge Centers
- Blood Vessels
- Cerebrospinal Fluid
- Pons
- Third Ventricle
- Medulla Oblongata
- Brain
- Cerebral Ventricles