Cellular transfer of macromolecules across the developing choroid plexus of Monodelphis domestica.

Choroid plexus epithelial cells secrete cerebrospinal fluid (CSF) and transfer molecules from blood into CSF. Tight junctions between choroidal epithelial cells are functionally effective from early in development: the route of transfer is suggested to be transcellular. Routes of transfer for endogenous and exogenous plasma proteins and dextrans were studied in Monodelphis domestica (opossum). Pups at postnatal (P) days 1-65 and young adults were injected with biotinylated dextrans (3-70 kDa) and/or foetal protein fetuin. CSF, plasma and brain samples were collected from terminally anaesthetized animals. Choroid plexus cells containing plasma proteins were detected immunocytochemically. Numbers of plasma protein-positive epithelial cells increased to adult levels by P28, but their percentage of plexus cells declined. Numbers of cells positive for biotinylated probes increased with age, while their percentage remained constant. Colocalization studies showed specificity for individual proteins in some epithelial cells. Biotinylated probes and endogenous proteins colocalized in about 10% of cells in younger animals, increasing towards 100% by adulthood. Injections of markers into the ventricles demonstrated that protein is transferred only from blood into CSF, whereas dextrans pass in both directions. These results indicate that protein and lipid-insoluble markers are transferred by separate mechanisms present in choroid plexuses from the earliest stage of brain development, and transfer of proteins from plasma across choroid plexus epithelial cells contributes to the high protein concentration in CSF in the immature brain.

Factors involved in inflammation-induced developmental white matter damage.

Developmental white matter damage is a brain pathology associated with several long-term neurological disorders. An inflammatory insult has been suggested as the major instigating event. This study investigated the relative influence of inflammation, blood-brain barrier permeability and glial ontogeny in white matter damage. Systemic inflammation was induced in Monodelphis domestica (opossum) by serial intraperitoneal injections of lipopolysaccharide at different stages of brain development. Volume of white matter was estimated for the external capsule. Blood-brain barrier permeability was assessed immunocytochemically. Quantitative RT-PCR was used to measure relative levels of mRNA for IL-1beta, IL-6 and COX-2. Developmental changes in numbers and appearance of microglia and astrocytes were estimated. Results showed that in response to systemic inflammation, white matter was reduced in the external capsule during a circumscribed period only. At the same developmental stage blood-brain barrier permeability was altered, cerebral inflammatory response was present and numbers of microglia increased. However, the periods of altered blood-brain barrier permeability and the cerebral inflammatory response were longer than the period of the external capsule's susceptibility to white matter damage, which coincided with the developmental increase in the number of astrocytes in this tract. Thus, the mechanism of white matter damage following systemic inflammation is multifactorial, including cerebral inflammation and breakdown of brain barriers occurring simultaneously at specific stages of glial cell development.