Polydendrocytes (also known as NG2 glial cells) constitute a fourth major glial cell type in the adult mammalian central nervous system (CNS) that is distinct from other cell types. Although much evidence suggests that these cells are multipotent in vitro, their differentiation potential in vivo under physiological or pathophysiological conditions is still controversial.To follow the fate of polydendrocytes after CNS pathology, permanent middle cerebral artery occlusion (MCAo), a commonly used model of focal cerebral ischemia, was carried out on adult NG2creBAC:ZEG double transgenic mice, in which enhanced green fluorescent protein (EGFP) is expressed in polydendrocytes and their progeny. The phenotype of the EGFP(+) cells was analyzed using immunohistochemistry and the patch-clamp technique 3, 7 and 14 days after MCAo. In sham-operated mice (control), EGFP(+) cells in the cortex expressed protein markers and displayed electrophysiological properties of polydendrocytes and oligodendrocytes. We did not detect any co-labeling of EGFP with neuronal, microglial or astroglial markers in this region, thus proving polydendrocyte unipotent differentiation potential under physiological conditions. Three days after MCAo the number of EGFP(+) cells in the gliotic tissue dramatically increased when compared to control animals, and these cells displayed properties of proliferating cells. However, in later phases after MCAo a large subpopulation of EGFP(+) cells expressed protein markers and electrophysiological properties of astrocytes that contribute to the formation of glial scar. Importantly, some EGFP(+) cells displayed membrane properties typical for neural precursor cells, and moreover these cells expressed doublecortin (DCX)--a marker of newly-derived neuronal cells. Taken together, our data indicate that polydendrocytes in the dorsal cortex display multipotent differentiation potential after focal ischemia.

• MeSH
• Cell Differentiation * MeSH
• Antigens, Differentiation biosynthesis   MeSH
• Brain Ischemia metabolism   pathology   MeSH
• Disease Models, Animal MeSH
• Mice, Transgenic MeSH
• Mice MeSH
• Neuroglia metabolism   pathology   MeSH
• Cell Proliferation * MeSH
• Doublecortin Protein MeSH
• Nerve Tissue Proteins biosynthesis   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Dcx protein, mouse MeSH Browser
• Antigens, Differentiation MeSH
• Doublecortin Protein MeSH
• Nerve Tissue Proteins MeSH

Diffusion in the extracellular space (ECS) of the brain is constrained by the volume fraction and the tortuosity and a modified diffusion equation represents the transport behavior of many molecules in the brain. Deviations from the equation reveal loss of molecules across the blood-brain barrier, through cellular uptake, binding, or other mechanisms. Early diffusion measurements used radiolabeled sucrose and other tracers. Presently, the real-time iontophoresis (RTI) method is employed for small ions and the integrative optical imaging (IOI) method for fluorescent macromolecules, including dextrans or proteins. Theoretical models and simulations of the ECS have explored the influence of ECS geometry, effects of dead-space microdomains, extracellular matrix, and interaction of macromolecules with ECS channels. Extensive experimental studies with the RTI method employing the cation tetramethylammonium (TMA) in normal brain tissue show that the volume fraction of the ECS typically is approximately 20% and the tortuosity is approximately 1.6 (i.e., free diffusion coefficient of TMA is reduced by 2.6), although there are regional variations. These parameters change during development and aging. Diffusion properties have been characterized in several interventions, including brain stimulation, osmotic challenge, and knockout of extracellular matrix components. Measurements have also been made during ischemia, in models of Alzheimer's and Parkinson's diseases, and in human gliomas. Overall, these studies improve our conception of ECS structure and the roles of glia and extracellular matrix in modulating the ECS microenvironment. Knowledge of ECS diffusion properties is valuable in contexts ranging from understanding extrasynaptic volume transmission to the development of paradigms for drug delivery to the brain.

• MeSH
• Diffusion MeSH
• Extracellular Space chemistry   diagnostic imaging   physiology   MeSH
• Quaternary Ammonium Compounds MeSH
• Humans MeSH
• Brain Chemistry physiology   MeSH
• Brain cytology   physiology   MeSH
• Neuroglia physiology   MeSH
• Neurons physiology   MeSH
• Radionuclide Imaging MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Quaternary Ammonium Compounds MeSH
• tetramethylammonium MeSH Browser

[K(+)](e) increase accompanies many pathological states in the CNS and evokes changes in astrocyte morphology and glial fibrillary acidic protein expression, leading to astrogliosis. Changes in the electrophysiological properties and volume regulation of astrocytes during the early stages of astrocytic activation were studied using the patch-clamp technique in spinal cords from 10-day-old rats after incubation in 50 mM K(+). In complex astrocytes, incubation in high K(+) caused depolarization, an input resistance increase, a decrease in membrane capacitance, and an increase in the current densities (CDs) of voltage-dependent K(+) and Na(+) currents. In passive astrocytes, the reversal potential shifted to more positive values and CDs decreased. No changes were observed in astrocyte precursors. Under hypotonic stress, astrocytes in spinal cords pre-exposed to high K(+) revealed a decreased K(+) accumulation around the cell membrane after a depolarizing prepulse, suggesting altered volume regulation. 3D confocal morphometry and the direct visualization of astrocytes in enhanced green fluorescent protein/glial fibrillary acidic protein mice showed a smaller degree of cell swelling in spinal cords pre-exposed to high K(+) compared to controls. We conclude that exposure to high K(+), an early event leading to astrogliosis, caused not only morphological changes in astrocytes but also changes in their membrane properties and cell volume regulation.

• MeSH
• Astrocytes physiology   MeSH
• Potassium pharmacokinetics   MeSH
• Potassium Channels, Voltage-Gated physiology   MeSH
• Glial Fibrillary Acidic Protein metabolism   MeSH
• Gliosis physiopathology   MeSH
• Hypotonic Solutions pharmacology   MeSH
• Immunohistochemistry MeSH
• Hydrogen-Ion Concentration MeSH
• Rats MeSH
• Membrane Potentials drug effects   physiology   MeSH
• Patch-Clamp Techniques MeSH
• Spinal Cord cytology   MeSH
• Osmotic Pressure MeSH
• Rats, Wistar MeSH
• Sodium metabolism   MeSH
• Sodium Channels physiology   MeSH
• Cell Size MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Potassium MeSH
• Potassium Channels, Voltage-Gated MeSH
• Glial Fibrillary Acidic Protein MeSH
• Hypotonic Solutions MeSH
• Sodium MeSH
• Sodium Channels MeSH