Biomaterial Database

Correlated electrophysiology and morphology of the ependyma in rat hypothalamus. 1988

C R Jarvis, and R D Andrew

Department of Anatomy, Queen's University, Kingston, Ontario, Canada.

The ependyma lines the ventricular system of the vertebrate brain and spinal cord. Although its embryology and morphology have been studied extensively, little is known of its physiological properties, particularly in mammals. Tanycytes are modified ependymal cells that are found predominantly lining the floor of the third ventricle, overlying the median eminence. Their processes accompany and enwrap neuroendocrine axons that course from hypothalamic nuclei to terminals in the median eminence, but the significance of this interaction is not yet understood. Intracellular recording and injection techniques were used to study ependymal cells and tanycytes of the rat in the hypothalamic slice preparation after differentiating their respective regions morphologically. With extracellular [K+] = 6.24 mM, the mean membrane potential (+/- SD) for common ependyma was -79.9 +/- 1.40 mV and for tanycytes, -79.5 +/- 1.77 mV. Input resistances (Rin) were very low (much less than 1 M omega). Single-cell injection of Lucifer yellow revealed dye coupling among 2-70 ependymal cells and 5-48 tanycytes. In both freeze-fractured replicas and thin sections, large numbers of gap junctions were found between adjacent ependymal cells and between adjacent tanycytes. The observations of numerous gap junctions, extensive dye coupling and low input resistance demonstrated that both populations are strongly coupled networks. Perhaps for this reason, attempts to uncouple these cells using sodium propionate or CO2 were unsuccessful. Electrical stimulation of the arcuate nucleus did not elicit any detectable synaptic response in impaled tanycytes, so that the functional significance of synaptoid contacts between neuroendocrine neurons and the postsynaptic tanycytes is not yet apparent. Ependymal cells and tanycytes demonstrated a near-Nernstian response to changes in extracellular [K+] between 3 and 20 mM. This finding, as well as their high negative resting potential, low Rin, extensive coupling and absence of spontaneous electrical excitability demonstrate that ependymal cells possess numerous glial characteristics and may therefore have similar functions. In the hypothalamus, ependyma probably take up K+ released from adjacent endocrine neurons and shunt it to the ventricular space.

UI	MeSH Term	Description	Entries
D007031	Hypothalamus	Ventral part of the DIENCEPHALON extending from the region of the OPTIC CHIASM to the caudal border of the MAMMILLARY BODIES and forming the inferior and lateral walls of the THIRD VENTRICLE.	Lamina Terminalis,Preoptico-Hypothalamic Area,Area, Preoptico-Hypothalamic,Areas, Preoptico-Hypothalamic,Preoptico Hypothalamic Area,Preoptico-Hypothalamic Areas
D007365	Intercellular Junctions	Direct contact of a cell with a neighboring cell. Most such junctions are too small to be resolved by light microscopy, but they can be visualized by conventional or freeze-fracture electron microscopy, both of which show that the interacting CELL MEMBRANE and often the underlying CYTOPLASM and the intervening EXTRACELLULAR SPACE are highly specialized in these regions. (From Alberts et al., Molecular Biology of the Cell, 2d ed, p792)	Cell Junctions,Cell Junction,Intercellular Junction,Junction, Cell,Junction, Intercellular,Junctions, Cell,Junctions, Intercellular
D008297	Male		Males
D008564	Membrane Potentials	The voltage differences across a membrane. For cellular membranes they are computed by subtracting the voltage measured outside the membrane from the voltage measured inside the membrane. They result from differences of inside versus outside concentration of potassium, sodium, chloride, and other ions across cells' or ORGANELLES membranes. For excitable cells, the resting membrane potentials range between -30 and -100 millivolts. Physical, chemical, or electrical stimuli can make a membrane potential more negative (hyperpolarization), or less negative (depolarization).	Resting Potentials,Transmembrane Potentials,Delta Psi,Resting Membrane Potential,Transmembrane Electrical Potential Difference,Transmembrane Potential Difference,Difference, Transmembrane Potential,Differences, Transmembrane Potential,Membrane Potential,Membrane Potential, Resting,Membrane Potentials, Resting,Potential Difference, Transmembrane,Potential Differences, Transmembrane,Potential, Membrane,Potential, Resting,Potential, Transmembrane,Potentials, Membrane,Potentials, Resting,Potentials, Transmembrane,Resting Membrane Potentials,Resting Potential,Transmembrane Potential,Transmembrane Potential Differences
D008854	Microscopy, Electron	Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen.	Electron Microscopy
D008855	Microscopy, Electron, Scanning	Microscopy in which the object is examined directly by an electron beam scanning the specimen point-by-point. The image is constructed by detecting the products of specimen interactions that are projected above the plane of the sample, such as backscattered electrons. Although SCANNING TRANSMISSION ELECTRON MICROSCOPY also scans the specimen point by point with the electron beam, the image is constructed by detecting the electrons, or their interaction products that are transmitted through the sample plane, so that is a form of TRANSMISSION ELECTRON MICROSCOPY.	Scanning Electron Microscopy,Electron Scanning Microscopy,Electron Microscopies, Scanning,Electron Microscopy, Scanning,Electron Scanning Microscopies,Microscopies, Electron Scanning,Microscopies, Scanning Electron,Microscopy, Electron Scanning,Microscopy, Scanning Electron,Scanning Electron Microscopies,Scanning Microscopies, Electron,Scanning Microscopy, Electron
D011188	Potassium	An element in the alkali group of metals with an atomic symbol K, atomic number 19, and atomic weight 39.10. It is the chief cation in the intracellular fluid of muscle and other cells. Potassium ion is a strong electrolyte that plays a significant role in the regulation of fluid volume and maintenance of the WATER-ELECTROLYTE BALANCE.
D011919	Rats, Inbred Strains	Genetically identical individuals developed from brother and sister matings which have been carried out for twenty or more generations or by parent x offspring matings carried out with certain restrictions. This also includes animals with a long history of closed colony breeding.	August Rats,Inbred Rat Strains,Inbred Strain of Rat,Inbred Strain of Rats,Inbred Strains of Rats,Rat, Inbred Strain,August Rat,Inbred Rat Strain,Inbred Strain Rat,Inbred Strain Rats,Inbred Strains Rat,Inbred Strains Rats,Rat Inbred Strain,Rat Inbred Strains,Rat Strain, Inbred,Rat Strains, Inbred,Rat, August,Rat, Inbred Strains,Rats Inbred Strain,Rats Inbred Strains,Rats, August,Rats, Inbred Strain,Strain Rat, Inbred,Strain Rats, Inbred,Strain, Inbred Rat,Strains, Inbred Rat
D004805	Ependyma	A thin membrane that lines the CEREBRAL VENTRICLES and the central canal of the SPINAL CORD.	Ependymas
D005614	Freeze Fracturing	Preparation for electron microscopy of minute replicas of exposed surfaces of the cell which have been ruptured in the frozen state. The specimen is frozen, then cleaved under high vacuum at the same temperature. The exposed surface is shadowed with carbon and platinum and coated with carbon to obtain a carbon replica.	Fracturing, Freeze,Fracturings, Freeze,Freeze Fracturings