Search PubMed⌕ Search

Biomedical subjects

W A Gregory

Publications and source records attributed to W A Gregory.

36 records · Page 2Linked to original sources
PubMed1988

Neuronal and glial gap junctions in the goldfish preoptic area, a thin section and freeze-fracture study.

In freeze-fracture, both large macular gap junctions and long thin gap junctions surrounded by a strand of tight junction were found on neurosecretory cells. Preoptic neurons show large areas of soma-to-soma apposition, but thin section showed no evidence for gap junctions between neuronal somata. Neurosecretory cell neurites formed parallel bundles in neuropil lateral to the nucleus, and gap junctions were found between the neurites. These junctions apparently correspond to macular junctions seen on neurosecretory elements in freeze-fracture. Some large macular gap junctions found in freeze-fracture presumably correspond to junctions seen between glial cells in thin section. However, glial membranes lacked characteristics distinguishing them from neuronal membranes. In one instance, a large apparent glial sheet process formed both macular and long thin gap junctions on different surfaces. The long thin gap junctions that were surrounded by a strand of tight junction were formed with a large neurosecretory cell soma. Extensive pinocytosis was observed at some membranes forming gap junctions.

Animals↗
PubMed1988

Gap junctions in goldfish preoptic ependyma: regional variation in cellular differentiation.

Ependyma adjacent to the goldfish preoptic neurosecretory nucleus was examined with transmission electron microscopy. Ependymal cells adjoining the rostroventral end of the nucleus were spindle-shaped with their long axes perpendicular to the ventricular surface. Gap junctions and desmosomes were common near the apical (ventricular) ends of these cells, and less frequent laterally in the ependymal layer. Ependymal cells in more caudodorsal preoptic regions (adjacent to large neurosecretory cells) were progressively more pleomorphic. The frequent occurrence of apparently internalized gap junctions and of gap junction fragments enclosed within lysosome-like organelles indicated extensive turnover of these junctions, or uncoupling. Ependymal cells in the caudodorsal region formed gap junctions on their lateral and basal (abluminal) surfaces with glial processes containing bundles of intermediate filaments. Subependymally, these processes (presumptive radial glia) were parallel to one another and coupled together by gap junctions. Neurites containing dense core vesicles occasionally invaginated into ependymal cells in the caudal region, but did not appear to form gap junctions. Previous observations indicate continuing maturation and growth of the goldfish preoptic area with neurosecretory cell formation rostroventrally and a rostroventral to caudodorsal gradient of maturation. The present findings suggest a parallel and related gradient in preoptic ependyma. Ependymal cell differentiation possibly involves loss of gap junctions, and radial migration or differentiation into underlying neurons and glia.

Animals↗
PubMed1988

Cytology and neuron-glial apposition of migrating cerebellar granule cells in vitro.

In developing mammalian brain, many neurons migrate to their final position by moving in direct apposition to radially oriented glial cells. Glial-guided migration can be visualized in microcultures of mouse cerebellar cells by the combined use of cellular antigen markers and high resolution time-lapse video microscopy (Hatten et al., 1984; Edmondson and Hatten, 1987). Such studies have demonstrated the behavior of migrating cells and revealed a motile leading process on the migrating neuron that resembles an axonal growth cone and grows along extended glial fibers. To study the fine structural details of the migrating neuron and its neuron-glial apposition, we identified and monitored neurons in microcultures with video microscopy and examined the cytology and cellular contacts of the same cells with transmission electron microscopy. The cytology of the soma and leading process of migrating cells closely matches that described for granule cells in intact brain (Rakic, 1971). Newly observed structures include the presence of longitudinally oriented microtubules extending from a basal body in the soma into the leading process, and microfilament-rich filopodia arising from the soma and leading process. The most striking feature of actively migrating neurons is a specialized junction between the neuronal cell soma and apposing glial fibers. At this junction, here termed "interstitial density," the extracellular space is dilated to 20 nm and filamentous material in the intracellular cleft either spans the cleft or runs parallel to the cell membranes. Some interstitial fibrils are contiguous with, or are transmembranous extensions of, submembranous cytoskeletal elements that attach to microtubules. Interstitial junctions were not found between neurons that did not translocate in the observation period before fixation. Instead, stationary cells formed desmosomes (puncta and macula adhaerentia) at appositions with glial processes.

Animals↗
PubMed1987

Oxazolidinones, a new class of synthetic antibacterial agents: in vitro and in vivo activities of DuP 105 and DuP 721.

DuP 721 (p-acetylphenyloxooxazolidinylmethylacetamide) and DuP 105 (a methylsulfinyl derivative) are orally active representatives of the oxazolidinones, a new class of synthetic antibacterial agents. Their antibacterial spectrum includes staphylococci, streptococci, and Bacteroides fragilis strains. The compounds have equal activity against staphylococcal strains susceptible or resistant to beta-lactam antibiotics, including methicillin-resistant strains. The MICs for 90% of the strains (MIC90s) against staphylococcal isolates were 1 to 4 micrograms/ml for DuP 721 and 4 to 16 micrograms/ml for DuP 105, compared with 1 to 2 micrograms/ml for vancomycin, 0.5 microgram/ml for ciprofloxacin, and 2 to greater than 16 micrograms/ml for imipenem. The MIC90s against group D streptococci were 4 micrograms/ml for DuP 721, 16 micrograms/ml for DuP 105, and 2 micrograms/ml for vancomycin, ciprofloxacin, and imipenem. MIC90s against B. fragilis isolates were 4 micrograms/ml for DuP 721, 16 micrograms/ml for DuP 105, and 8 micrograms/ml for cefoxitin. DuP 721 and DuP 105 administered by either the oral or the parenteral route were protective against staphylococcal and streptococcal infections in mice. The 50% effective doses were 2 to 10 mg/kg for DuP 721, 9 to 23 mg/kg for DuP 105, and 2 to 12 mg/kg for vancomycin. These results indicate that further studies of compounds of the oxazolidinone series are warranted.

Animals↗
PubMed1985

Horseradish peroxidase evidence for a spinal projection from the preoptic area of the goldfish, a light and electron microscopic study.

Horseradish peroxidase (HRP) was applied to the transected spinal cord of goldfish labeled neurons in the preoptic area. Since leakage of HRP into the blood could produce the labeling of neurosecretory cells, intraperitoneal (i.p.) injections of HRP were made with a wide range of dosages in order to intentionally label preoptic neurosecretory cells. The distribution of preoptic neurons labeled after spinal HRP application was far more restricted than the labeling via uptake of HRP from the blood, even when cells in the spinal cord-transected fish were intensely labeled. Furthermore, in HRP electron microscopic material, morphological differences were observed between neurons labeled by the two procedures. Large numbers of dense core vesicles and well-developed stacks of rough endoplasmic reticulum, features typical of cells projecting to the pituitary, were not observed in cells labeled via the spinal cord. These findings indicate that in goldfish a direct projection exists from the preoptic area to the spinal cord which could be homologous to one arising from the paraventricular nucleus of mammals. Both i.p. injection and spinal transection also produced labeling of more caudal periventricular diencephalic cells which resemble preoptic cells in efferent projections as well as ultrastructural features.

Animals↗
PubMed1985

Preparation and antiarthritic and analgesic activity of 4,5-diaryl-2-(substituted thio)-1H-imidazoles and their sulfoxides and sulfones.

A series of 4,5-diaryl-2-(substituted thio)-1H-imidazoles was synthesized and evaluated as antiinflammatory and analgesic agents in the rat adjuvant induced arthritis assay and the mouse phenyl-p-benzoquinone writhing (PQW) assay. Several analogues were found to be more potent than phenylbutazone and indomethacin. Structure-activity relationships are discussed. One of the compounds, 4,5-bis(4-fluorophenyl)-2-[(1,1,2,2-tetrafluoroethyl)-sulfonyl]-1H- imidazole (8d, tiflamizole), was found to be 8 times as potent as indomethacin in the rat adjuvant induced arthritis assay and is presently undergoing clinical trial as an antiarthritic drug.

Analgesia↗
PubMed1983

Maturation of the goldfish preoptic area: ultrastructural correlates of position and maturation of neurosecretory cells.

A gradation of small rostral to larger caudal neurosecretory cells is found in the preoptic area of fish. Regional variations in ultrastructural features were assessed in this region of fish ranging widely in size (1.7-283.1 g), some of which had received intraperitoneal injections of horseradish peroxidase in order to label neurons projecting beyond the blood-brain barrier (i.e. neurosecretory cells). In small (less than or equal to 6.6 g) fish, neurosecretory cells of the caudal preoptic area were 10-15 microns in diameter and contained dense core vesicles. More rostral smaller cells had few or no dense core vesicles, but were labeled following intraperitoneal horseradish peroxidase injections. Cells in both areas were progressively larger, with larger nuclei and more granular reticulum in larger fish. In large fish, neurons that contained dense core vesicles ranged from 10 microns in diameter rostrally to 70 microns in diameter caudally. Some intermediate and large cells were extensively vacuolated and contained extremely convoluted and possibly multiple nuclei. Degenerating material was seen in apparently normal large fish. A few neurosecretory cells were extensively surrounded by perineuronal electron-dense glial cells. Most neurosecretory cells were involved in extensive soma-somatic apposition, which was especially pronounced in fish which were removed from cold water in late fall. Gap junctions were also clearly present on the somata of preoptic neurosecretory cells of these fall fish. These data imply that increased capacity for hormone secretion in large fish may be accomplished in part by neuronal hypertrophy. Maturational and seasonal variation in structure suggest that physiological characteristics are also variable in this nucleus.

Animals↗
PubMedDate not supplied

Nucleolar proliferation and cell size changes in rat supraoptic neurons following osmotic and volemic challenges.

Subcutaneous injections of isotonic saline induced nucleolar proliferation in supraoptic neurons in animals sacrificed approximately 5 min postinjection. The magnitude of this proliferation was sustained 4 and 8 hr postinjection. Polyethylene glycol (PG) injections depleted blood volume 4 and 8 hr after the injection, but the percentage of SON cells with multiple nucleoli in these animals was not different from saline-injected controls. The anterior (SOa) portion of the SON in rats given 2% NaCl to drink instead of water for three days contained more cells with multiple nucleoli than controls. This effect was enhanced after five days ingestion, and accompanied by a similar response in the tuberal portion of SON (SOt). Rehydration for ten days after three days of 2% NaCl intake brought the percentage of cells with multiple nucleoli down to control levels. Cell area in SON cells paralleled nucleolar responses during dehydration and rehydration. The results demonstrate the sensitivity of nucleolar proliferation in SON to environmental changes ranging from osmotic to neurogenic stress.

Animals↗
PubMedDate not supplied

Spontaneous and osmotically-stimulated activity in slices of rat hypothalamus.

Single unit activity was recorded from 400-500 mu m thick slices of rat hypothalamus, using either NaCl- or horseradish peroxidase-filled glass micropipettes. Spontaneous activity was present in the following hypothalamic loci: anterior hypothalamic-preoptic area, nucleus circularis, nucleus of the diagonal band of Broca, paraventricular accessory nucleus, paraventricular nucleus (all portions), periventricular regions of the anterior hypothalamus, and the suprachiasmatic nucleus. The supraoptic nucleus was the only major cell group studied to exhibit no spontaneous activity. Cells of the paraventricular and circularis nuclei were spontaneously active, displayed firing rates and patterns of activity similar to those recorded in vivo for magnocellular elements of the hypothalamus, and in some cases responded to increases in the osmolality of the bathing medium with altered firing rates and/or patterns of activity. Many cells in these preparations were characterized by phasic, bursting patterns of activity. Slow, irregular and regular, continuous activity was also frequently observed, as is typical in vivo. Median firing rates were in the range of 4-6 spikes/sec, somewhat faster than the rates usually reported for anesthetized in vivo preparations. These rates are more similar to those observed in unanesthetized monkeys or rats with diencephalic islands. Extracellular HRP marking provided a high degree of localization for many of the recorded cells. These results indicate that the hypothalamic slice preparation is useful for studies in which it is desirable to eliminate extrahypothalamic connections and in which it is necessary to exercise a fine degree of control over the extracellular environment of the cells.

Animals↗
PubMedDate not supplied

Ultrastructure of neurons in the paraventricular nucleus of normal, dehydrated and rehydrated rats.

Previous reports have shown that the percentage of neuronal somatic membrane in soma-somatic apposition (without intervening glia) increased with brief periods of dehydration (4--24 hr) and decreased with rehydration in the rat supraoptic and circularis nuclei. In the present study, the percentage of somal membrane in soma-somatic appositions was found to increase in the primarily vasopressin-containing lateral portion of the rat paraventricular nucleus with twelve hours of dehydration. Further evidence for altered cellular function in this nucleus was a decrease in the number of smaller dense core vesicles (< 2600A) per unit cytoplasmic area during initial dehydration (4--12 hr). No changes were detected, however, in the number of larger dense core vesicles (> 4000 A) or lysosomes (> 4000 A) per unit cytoplasm. Intranuclear membrane-bound vacuoles were found primarily in hydrated and rehydrated animals. No reliable changes were seen in the dilation of granular endoplasmic reticulum. Cilia were found in the neuropil and were occasionally traced to magnocellular somata. Differences in the patterns of morphological responses among the magnocellular hypothalamic nuclei suggest specializations in their roles, and further support a functional significance of neuronal membrane appositions.

Animals↗
PubMedDate not supplied

Effects of heterogeneous layers of composite and time on composite repair of porcelain.

Bond strengths of porcelain/composite resin repair samples, some homogeneous of conventional, hybrid, and microfill materials, some heterogeneous, made by incremental build-up of two of these composites, were evaluated. Samples were allowed to set without disturbance. After storage in 37 degrees C water for intervals of one day, seven days, and 28 days, the test samples were subjected to tensile force until fracture. There were significant differences in bond strengths of homogenous and heterogeneous samples after different storage periods. All mean repair bond strengths were significantly less at seven days than at one or 28 days. Heterogeneous repairs with larger-particle-size composite at the porcelain interface and overlayed with smaller-particle-size composites resulted in higher bond strengths than the homogeneous small-sized composite repairs. Failures of the repairs occurred at the porcelain/composite interface in a statistically significant number, implying that technique exactness at the interface plays an important role in the success of the technique.

Composite Resins↗