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T S Reese

Publications and source records attributed to T S Reese.

136 records · Page 8Linked to original sources
PubMed1969

Junctions between intimately apposed cell membranes in the vertebrate brain.

Certain junctions between ependymal cells, between astrocytes, and between some electrically coupled neurons have heretofore been regarded as tight, pentalaminar occlusions of the intercellular cleft. These junctions are now redefined in terms of their configuration after treatment of brain tissue in uranyl acetate before dehydration. Instead of a median dense lamina, they are bisected by a median gap 20-30 A wide which is continuous with the rest of the interspace. The patency of these "gap junctions" is further demonstrated by the penetration of horseradish peroxidase or lanthanum into the median gap, the latter tracer delineating there a polygonal substructure. However, either tracer can circumvent gap junctions because they are plaque-shaped rather than complete, circumferential belts. Tight junctions, which retain a pentalaminar appearance after uranyl acetate block treatment, are restricted primarily to the endothelium of parenchymal capillaries and the epithelium of the choroid plexus. They form rows of extensive, overlapping occlusions of the interspace and are neither circumvented nor penetrated by peroxidase and lanthanum. These junctions are morphologically distinguishable from the "labile" pentalaminar appositions which appear or disappear according to the preparative method and which do not interfere with the intercellular movement of tracers. Therefore, the interspaces of the brain are generally patent, allowing intercellular movement of colloidal materials. Endothelial and epithelial tight junctions occlude the interspaces between blood and parenchyma or cerebral ventricles, thereby constituting a structural basis for the blood-brain and blood-cerebrospinal fluid barriers.

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PubMed1967

Fine structural localization of a blood-brain barrier to exogenous peroxidase.

Horseradish peroxidase was administered to mice by intravenous injection, and its distribution in cerebral cortex studied with a recently available technique for localizing peroxidase with the electron microscope. Brains were fixed by either immersion or vascular perfusion 10-60 min after administration of various doses of peroxidase. Exogenous peroxidase was localized in the lumina of blood vessels and in some micropinocytotic vesicles within endothelial cells; none was found beyond the vascular endothelium. Micropinocytotic vesicles were few in number and did not appear to transport peroxidase while tight junctions between endothelial cells were probably responsible for preventing its intercellular passage. Our findings therefore localize, at a fine structural level, a "barrier" to the passage of peroxidase at the endothelium of vessels in the cerebral cortex. The significance of these findings is discussed, particularly with reference to a recent study in which similar techniques were applied to capillaries in heart and skeletal muscle.

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PubMedDate not supplied

Quantitative scanning transmission electron microscopy of ultrathin cryosections: subcellular organelles in rapidly frozen liver and cerebellar cortex.

Freeze-dried, ultrathin cryosections of directly frozen mouse liver and brain have been prepared and characterized by low-dose dark-field scanning transmission electron microscopy (STEM). These improved cryosections gave images comparable to those from conventional plastic sections. They were thin enough (< < 1.0 elastic mean free path) to use established dark-field techniques, modified for thickness-dependent nonlinearities, to measure the dry mass fraction of individual organelles, and hence to deduce their water content. Digital STEM imaging in combination with electron and X-ray spectroscopy has important biological applications, as illustrated by studies on calcium regulation in Purkinje neurons. Calcium concentrations per unit dry weight of dendritic compartments were determined by the peak/continuum method of energy-dispersive X-ray spectroscopy (EDXS), which necessarily overstates elemental concentrations because of beam-induced mass loss. The dry mass content of organelles at low dose and the percentage of dry mass retained after analysis at high dose were as follows: mitochondria (46.0 g dry mass/100 g hydrated mass, 67% mass retained); endoplasmic reticulum (27.9 g/100 g, 57%); and cytoplasm (16.3 g/100 g, 41%). These values were used to correct elemental concentrations for mass loss. Results indicated that the major calcium storage organelle in Purkinje cell dendrites is the endoplasmic reticulum, of which there are two types distinguished by their levels of calcium. Parallel electron energy loss spectroscopy of dendritic organelles corroborated EDXS measurements, with an improved sensitivity that indicates the feasibility of quantitative calcium mapping.

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PubMedDate not supplied

Direct visualization of a transmembrane channel associated with ribosomes.

Examination of directly frozen rough endoplasmic reticulum (ER) of retinal pigment epithelial cells by freeze-fracture and freeze-substitution revealed distinct paired transmembrane proteins associated with membrane ribosomes. Ribosomal subunits on intact ER membrane are directly visualized for the first time, providing a global view of the structure of the ribosome and the corresponding structures on the ER membrane. The ribosomal intersubunit cleft appears to be continuous with a cleft between paired transmembrane proteins that extends into the lumen of the ER. This continuous cleft may be the path taken by nascent polypeptides.

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PubMedDate not supplied

Inhibition of phosphatase activity prolongs NMDA-induced modification of the postsynaptic density.

NMDA-induced modification of postsynaptic densities (PSDs) was studied by immunoelectron microscopy. Treatment of cultured hippocampal neurons with NMDA for 2 min promotes a 2.3 fold thickening of the PSD and a 4 fold increase in PSD-associated CaMKII immunolabel. These changes are reversed 5 min after the removal of NMDA and Ca2+ from the medium. In addition, following NMDA treatment, PSDs exhibit a 7.5 fold increase in labeling with an antibody specific to the (Thr286) phospho-form of CaMKII, indicating that CaMKII translocated to the PSD is phosphorylated. When the phosphatase inhibitors, calyculin A or okadaic acid, are included in the medium, the NMDA-induced thickening of the PSD as well as the increase in PSD-associated CaMKII immunolabeling are largely maintained (75% and 88% of the peak values respectively) at 5 min after removal of NMDA and Ca2+ from the medium. These results imply that NMDA receptors can mediate activity-induced changes in the PSD and that phosphatases of type 1 and/or 2A are involved in the reversal of these changes.

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