PubMed Health⌕ Search

Biomedical subjects

T E Hughes

Publications and source records attributed to T E Hughes.

At least 19 recordsLinked to original sources
PubMed1992

High level expression of human apolipoprotein A-I in transgenic rats raises total serum high density lipoprotein cholesterol and lowers rat apolipoprotein A-I.

To examine the consequences of increased apolipoprotein A-I production on cholesterol and lipoprotein metabolism, we have produced two lines of transgenic rats; one expressing moderate and one very high levels of human apolipoprotein A-I. The rats were produced by microinjection of a 13 kbp DNA fragment containing the human apolipoprotein A-I gene plus 10 kbp of its 5' flanking sequence and 1 kbp of its 3' flanking sequence. Both lines of transgenic rats express human apolipoprotein A-I mRNA in liver and human apolipoprotein A-I in plasma. Sera from these rats contain significantly higher levels of total apolipoprotein A-I, high density lipoprotein cholesterol and phospholipid than sera from non-transgenic littermates. Transgenic rats expressing high levels of human apolipoprotein A-I have reduced levels of serum rat apolipoprotein A-I suggesting a mechanism exists to down-regulate apolipoprotein A-I production. These transgenic rats provide a unique animal model to examine the effects of increased apolipoprotein A-I production on lipid and lipoprotein metabolism.

Animals↗
PubMed1992

Differential expression of glutamate receptor genes (GluR1-5) in the rat retina.

The recent isolation of at least five different cDNAs encoding functional subunits of glutamate receptors (GluR1 to GluR5) has revealed a diversity whose function is not understood. To learn more about how these different receptor subunits are used in the brain, we undertook an in situ hybridization study of the retina to define how the different glutamate receptor genes are expressed. We chose the retina because the glutamate sensitivities of its different cell types have been characterized, and these different neurons reside in different laminae. Hybridization of [35S]UTP-labeled cRNA probes with transverse sections and freshly dissociated cells reveals that all five receptor subunits are expressed in the retina. Hybridization signal is detected in different, but overlapping, sets of cells in the retina. GluR1, GluR2, and GluR5 are expressed by many somata, and GluR4 by a few, in the outer third of the inner nuclear layer, where the horizontal cells reside. Transcripts for GluR1, GluR2, and GluR5 are found in the somata within the middle third of the inner nuclear layer, which is where the bipolar cell somata are located, and GluR2 probes label freshly dissociated rod bipolar cells. All of the probes produce labeling over the cells at the inner edge of the inner nuclear layer, which are probably amacrine cells, as well as over the cell bodies in the ganglion cell layer.

Animals↗
PubMed1992

Gallium nitrate.

OBJECTIVE: To evaluate the therapeutic role of gallium nitrate in the treatment of hypercalcemia associated with malignancy and related disease states. DATA SOURCES: A literature search of English-language studies involving gallium nitrate for the period 1966-1991 using MEDLINE and the bibliographies of relevant articles. STUDY SELECTION: Because of the limited number of studies, all clinical trials were reviewed, with particular emphasis on Phase III comparative trials. Related investigative studies on the pharmacology, pharmacokinetics, and toxicity of gallium nitrate were also reviewed. DATA EXTRACTION: Two appraisers independently abstracted data from available clinical trials and evaluated trial quality. RESULTS OF DATA SYNTHESIS: Two Phase III comparative trials evaluating gallium nitrate in the treatment of hypercalcemia of malignancy have been completed. Gallium nitrate was shown to be superior to both calcitonin and etidronate disodium, based on the comparative percentage of patients achieving normocalcemia and the subsequent duration of normocalcemia. Both trials employed similar methodology. Positive therapeutic effects of gallium nitrate have also been demonstrated in small, noncomparative trials for hypercalcemia associated with parathyroid carcinoma, Paget's disease of bone, and osteolytic bone metastases. CONCLUSIONS: Gallium nitrate is effective in the treatment of hypercalcemia associated with malignancy and is appropriate for formulary addition. In certain clinical situations, it may be clearly advantageous over such agents as calcitonin, plicamycin, and etidronate. Further investigation is needed to define the limitations of nephrotoxicity and the therapeutic potential for other indications. Further comparative clinical trials of gallium nitrate versus bisphosphonates and plicamycin could also help define its relative clinical benefit.

Gallium↗
PubMed1992

Transgenic mice expressing human apolipoprotein A-I have sera with modest trypanolytic activity in vitro but remain susceptible to infection by Trypanosoma brucei brucei.

Although Trypanosoma brucei brucei fatally infects livestock in much of sub-Saharan Africa, humans are innately resistant to infection, apparently because high-density lipoproteins (HDL) in human serum lyse this unicellular protozoan parasite. Recently, we demonstrated that purified human apolipoprotein (apo) A-I, the major protein (M(r) 28,016) constituent of HDL, had full trypanolytic activity in vitro whereas the apoA-I of cattle and sheep was non-lytic. In the present study, we have sought to confirm the trypanocidal capability of human apoA-I by studying four lines of transgenic mice expressing (supra)physiological serum levels of this polypeptide. Although trypanolysis in vitro by sera from transgenic mice (15.1 +/- 1.3% [mean +/- SEM], n = 30) was considerably less than by human sera (typically 60-80%), it was nevertheless significantly greater than by control sera (8.5 +/- 1.1%, n = 10; P < 0.001) and correlated with the concentration of human apoA-I (r = 0.56, P < 0.001). When trypanosomes were incubated at 37 degrees C with human serum or with human apoA-I for 30 min (i.e., within the pre-lytic period) they lost their ability to subsequently infect mice; trypanosomes incubated with transgenic mice serum remained infective. Furthermore, transgenic mice were fully susceptible to infection when inoculated with 10(3) trypanosomes; both the initial detection of trypanosomes in the blood (3-4 days) and the time to death (5-6 days) were no longer than control mice. This apparent paradox between the action of human apoA-I in human serum and in mouse serum was investigated further.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

GABAA receptors in the retina of the cat: an immunohistochemical study of wholemounts, sections, and dissociated cells.

Gamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter used by many neurons of the mammalian retina. To identify the synaptic targets of these cells, we undertook an immunohistochemical study with a monoclonal antibody that recognizes the GABAA receptors (62-3G1, generously donated by A. de Blas). This antibody labels the somata of at least one group of amacrine cells in the inner nuclear layer. It also labels two groups of somata in the ganglion cell layer; one small and the other much larger. The small cells are likely to be displaced amacrine cells based on their size, although some could be gamma ganglion cells. The much larger receptor-positive cells are clearly ganglion cells, based both on their size and the antibody labeling of the initial portion of their axon. In the peripheral retina, the size of these large somata suggests that many are beta ganglion cells. However, at any point across the retina the density of these cells never exceeded 50% of the density of beta cells as a whole. The antibody also labels a dense plexus of processes that extends throughout the inner plexiform layer (IPL), with a marked concentration in the inner third of the layer. This is the portion of the IPL in which the rod bipolar cells terminate. It is difficult to recognize processes of individual cells in the IPL, so retinae were dissociated. The rod bipolar cells were identified by protein kinase C immunoreactivity (Negishi et al., 1988; Karschin & Wäsle, 1990). They were not labeled by the GABAA receptor antibody. This is surprising in light of tight-seal, whole cell voltage-clamp recordings that have shown that the rod bipolars express functional GABAA receptors. One possible explanation is that the antibody recognizes only a subset of the GABAA receptors.

Animals↗
PubMed1991

Altretamine.

Altretamine is a National Cancer Institute-designated group C antineoplastic agent used in the treatment of advanced ovarian cancer. Altretamine is a highly lipid-soluble drug available only for oral administration as a capsule. The drug is activated through metabolic oxidation to intermediate methylol derivatives and formaldehyde. It is unclear which metabolite is the major species responsible for cytotoxicity or the primary mechanism of cytotoxicity. As a single agent in the treatment of ovarian cancer, altretamine demonstrates a response rate similar to other active agents in this disease (21-39 percent). The major utility of altretamine is in combination with other agents such as cyclophosphamide, doxorubicin, fluorouracil, melphalan, and cisplatin. However, few randomized trials have evaluated the contribution of altretamine in these multiagent combinations. Dose-limiting toxicities include gastrointestinal (nausea, vomiting, anorexia), hematologic, and neurotoxic (peripheral neurotoxicity). The therapeutic role of altretamine is limited because of a toxicity profile similar to that of cisplatin, one of the more active agents in ovarian cancer. Its use should be reserved for patients who are not candidates for more standard platinum-based regimens.

Altretamine↗
PubMed1991

The characterization and localization of the glutamate receptor subunit GluR1 in the rat brain.

The cloning of cDNAs that encode functional glutamate receptors makes it possible to produce antibodies that can be used as high-affinity probes for the localization and characterization of these receptors in the mammalian brain. We have made antibodies to different regions of the first cloned member of this family, GluR1, using bacterially overproduced antigen. On Western blots, these antisera detect glycoprotein(s) of 105 kDa present in crude membranes of the hippocampus and cerebellum. The 105-kDa band is associated with postsynaptic densities, and it is observed in cultured cells upon transfection with the GluR1 cDNA. Although glutamate receptors are thought to be the most prevalent excitatory ligand-gated ion channel in the mammalian brain, immunohistochemistry reveals that the receptors recognized by these antisera are localized predominantly in neurons of the cerebellum and some structures of the limbic system, including the hippocampus, the central nucleus of the amygdala, and portions of the septum. This pattern of expression is, in general, consistent with the distribution of GluR1 mRNA as determined by in situ hybridization histochemistry. Our results suggest that glutamate excitatory circuits recognized by these antisera are predominantly found in regions of the limbic system that are reciprocally interconnected.

Animals↗
PubMed1990

A light- and electron-microscopic investigation of the optic tectum of the frog, Rana pipiens, I: The retinal axons.

There are several different groups of ganglion cells in the retina of the frog. Although their axons are thought to terminate in different layers of the optic tectum, little is known about the morphology of their terminal arbors or their synaptic targets. The present paper reports the results of a layer-by-layer study of horseradish peroxidase labeled retinal axons in the optic tectum of Rana pipiens. Light and electron microscopy was used to study the axon's laminar distribution, patterns of arborization, and synaptic contacts. Labeled retinal axons were found in all of the superficial layers of the tectum (A-G). From layer to layer, the retinal axons differed markedly in the diameter of their parent axons (0.2-3.0 microns) and in the morphology and horizontal extent of their terminal arbors. Five classes of synaptic terminals could be distinguished in the tectum. The retinal terminals belonged to a class characterized by round, medium-sized synaptic vesicles. They made synaptic contact with dendrites and other axon terminals in each of the layers. They were always the presynaptic component. The postsynaptic dendrites were often the vertically oriented processes of cells located in the deeper layers. The postsynaptic terminals belonged to a class distinguished by their flat, medium-sized vesicles. These terminals in turn contacted what appeared to be dendrites. In layer eight, the retinal axons were often large, spoon-shaped boutons that ended in apposition with the somata of the layer.

Animals↗
PubMed1990

A light- and electron-microscopic investigation of the optic tectum of the frog, Rana pipiens, II: The neurons that give rise to the crossed tecto-bulbar pathway.

The superficial layers of the frog's optic tectum, Potter's (1969) layers A-G, comprise a complex neuropil made up of many afferent axons, the somata of a few neurons, and many dendrites from the neurons located in the deeper layers. Different types of retinal axons are believed to terminate in different layers (Maturana et al., 1960; Kuljis & Karten, 1988; Sargent et al., 1989), but little is known about the relationships between each type of input and the dendrites of the deep tectal neurons that extend into these superficial layers. The present study used the method of retrograde transport of horseradish peroxidase to study the synaptic contacts on the dendrites of the neurons that give rise to the crossed tecto-bulbar pathway. These cells have apical dendrites that ascend through the superficial retino-recipient layers. The somata of the cells that give rise to the crossed tecto-bulbar pathway are located in the superficial half of layer 6, preferentially clustered along the caudal, lateral, and rostral margins of the tectum. The somata of these cells range from 8-30 microns in diameter. Their axons are large (2-4 microns in diameter) myelinated fibers that arise from either their somata or proximal dendrites. Their axons travel within the deep medullary layer to leave the tectum at the lateral margin. Their dendritic arbors extend obliquely through the superficial layers to reach layer B where they turn and extend within the layer for up to 0.5 mm. The somata of these cells receive only a scant synaptic input. In contrast, their dendrites receive input in every layer, but the nature of this input varies from layer to layer. Synaptic terminals that resemble retinal ganglion cell boutons contact the labeled dendrites in layers B, F, and G. This indicates that the dendrites may receive monosynaptic input from several types of retinal ganglion cells. Terminals with small, flattened vesicles also contact the dendrites of these cells in each layer. In layer F and below, the terminals with flattened vesicles constitute 15% of the contacts; above layer F they constitute only 5-8% of the contacts. Terminals with medium-sized, flattened vesicles also contact the dendrites of these cells in every layer and constitute a large proportion of their input (33-95%). The latter terminals resemble those that are often postsynaptic to retinal terminals.

Animals↗
PubMed1989

Immunohistochemical localization of GABAA receptors in the retina of the new world primate Saimiri sciureus.

A large population of amacrine cells in the retina are thought to use GABA as an inhibitory neurotransmitter in their synaptic interactions within the inner plexiform layer. However, little is known about their synaptic targets; the neurons that express the receptors for GABA have not been clearly identified. Recently, the GABAA receptor has been isolated and antibodies have been raised against it. These antibodies have proven useful for the immunocytochemical localization of the receptor, and two brief reports describing the distribution of GABAA receptor immunoreactivity in the retina have appeared (Richards et al., 1987; Mariani et al., 1987). We used a monoclonal antibody (62-3G1) against the GABAA receptor to study the retina of the New World primate Saimiri sciureus. Labeled somata were found in the inner nuclear layer (INL) and ganglion cell layer (GCL). The staining was confined to what appeared to be the cell's plasmalemma and small cytoplasmic granules. Most of the labeled neurons in the INL had small somata (5-7 microns in diameter) located at the vitreal edge of the layer. They arborized in two laminae (approximately 2 and 4) of inner plexiform layer (IPL). Ventral to the optic disc (2.5 mm) they comprised 29% of the cells present. A few of the labeled neurons appeared to be interplexiform cells or flat bipolar cells, with labeled processes that extended into both the IPL and the inner half of the outer plexiform layer. In the GCL, the labeled somata were among the largest present (13-20 microns in diameter), and 2.5 mm ventral to the optic disc they made up 15% of the cells present. Experiments in which immunoreactive somata were retrogradely labeled following the injection of fluorescent tracers into the optic tract provided a conclusive demonstration that some of the immunoreactive somata were ganglion cells. The antibody often labeled their axons in the optic fiber layer. This suggests that the GABAA receptors are transported anterogradely to the retinal terminal fields. The dendrites of the immunoreactive ganglion cells extended into the 2 laminae of labeled processes in the IPL, and their primary dendritic arbors were, at any given eccentricity, quite similar in appearance. This homogeneity suggests that they comprise a particular subset of the ganglion cells. Sections simultaneously labeled with the monoclonal antibody against the GABAA receptor and antisera against either L-glutamic acid decarboxylase (GAD) or GABA revealed that the GAD/GABA was distributed much more widely in the IPL than the GABAA receptor.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Nonimmunochemical quantitation of mammalian apolipoprotein A-I in whole serum or plasma by nonreducing gel electrophoresis.

A rapid and convenient method for the quantitation of mammalian apoA-I has been developed. The method involves nonreducing sodium dodecyl sulfate gel electrophoresis and Coomassie blue staining, and takes advantage of the relative abundance of apoA-I in whole serum or plasma. ApoA-I was sufficiently resolved to allow quantitation by laser densitometry or spectrophotometry. The assay was linear from 0.25 to 4.0 micrograms of apoA-I. Analytic recovery was 98%. Within-assay variability was 3.1% and between-assay variability was 7.5%. A high degree of positive correlative (r = 0.98) was observed with a human apoA-I radioimmunoassay. For several species investigated, the apoA-I values obtained correlated strongly and positively with high density lipoprotein cholesterol values. When applied to a study of nutritional perturbation in the Mongolian gerbil, the method detected sensible and significant changes in serum apoA-I that paralleled changes in HDL cholesterol.

Animals↗
PubMed1988

Regulation of intestinal apolipoprotein B synthesis and secretion by Caco-2 cells. Lack of fatty acid effects and control by intracellular calcium ion.

To investigate the mechanism of control of intestinal apolipoprotein B (apoB) secretion, we studied the effects of fatty acids and calcium ionophores on the human intestinal model cell line Caco-2. Although treatment with various fatty acids (18:1w9, 18:2w6, and 20:5w3) complexed to bovine serum albumin resulted in a dramatic redistribution of apoB-100 from the low density and high density lipoproteins to the very low density lipoprotein fraction, there was no effect of any of the fatty acids on the overall rate of total apoB (apoB-100 and apoB-48) secretion. Treatment of differentiated monolayers with calcium ionophores A23187 or ionomycin caused dose-specific increases (125% at 1 microM) in the accumulation of total apoB, but not apoA-I, in conditioned medium as measured by specific immunoassays. Incubation studies with 35S-labeled Caco-2 apoB,E-containing low density lipoprotein particles revealed that treatment with ionomycin over a broad concentration range had no effect on the reuptake of secreted apoB-100. The effect on A23187 on total apoB secretion was blocked by prior chelation of medium calcium and was significantly enhanced by the addition of calcium (up to 50 mM) to the medium. The effect of A23187 was significantly blunted by treatment with the calmodulin antagonist trifluoperazine (10 microM). The time course of A23187 action on Caco-2 apoB secretion required at least 6 h to occur. In contrast to the concentration of apoB in the medium, cellular apoB content was not influenced by treatment with ionophore. Pulse-chase experiments demonstrated a significant reduction in the synthesis-secretion interval for apoB-100 and apoB-48 after 24 h of exposure to ionomycin. Neither fatty acid treatment nor stimulation with ionophore affected the ratio of apoB-100 to apoB-48 produced by the cells. These findings with calcium ionophores implicate the involvement of calcium ion in the mechanism of intestinal apoB secretion. A role for calcium-dependent processes in apoB production raises the possibility that, rather than fatty acid flux, calcium-evoked or calcium-dependent hormones may be important regulators of apoB secretion.

Adenocarcinoma↗
PubMed1988

Cholinoceptive neurons in the retina of the chick: an immunohistochemical study of the nicotinic acetylcholine receptors.

Monoclonal antibodies directed against nicotinic acetylcholine receptors (nAChRs) were used to identify and characterize cholinoceptive neurons in the chick retina. Two monoclonal antibodies (mAbs), mAb 210 and mAb 270, stained many neurons in both the inner nuclear layer (INL) and ganglion cell layer (GCL). A class of large labeled cells in the inner INL were positioned at the INL/IPL (inner plexiform layer) border and resembled displaced ganglion cells (DGCs). Their identity was confirmed with injections of rhodamine-labeled microspheres into the ventral tectum and nucleus of the basal optic root (nBOR). Four days after the injection, large nAChR-positive neurons in the inner INL were labeled with beads. The distribution of these cells matched that reported for DGCs in the chicken and pigeon (Reiner et al., 1979; Fite et al., 1981). Many smaller cells in the INL also exhibited nAChR immunoreactivity. These cells were not retrogradely labeled after bead injections into retinal recipient areas. Their processes entered IPL where they arborized in a band comprised of the inner leaflet of lamina 1 and all of lamina 2. In some instances, a process continued inward to lamina 4. These neurons were tentatively identified as amacrine cells because of their position and branching pattern. Approximately 12-18% of the cells in the GCL exhibited nAChR immunoreactivity. Many of these cells could be classified as ganglion cells as their axons were also labeled following exposure to nAChR antibodies. Their distribution mirrored that of all ganglion cells with a higher density of cells in the central retina than in the periphery (Ehrlich, 1981). A "double label" technique was used to compare the distribution of nAChR-positive neurons with that of the choline acetyltransferase-positive (ChAT), cholinergic neurons in the chick retina. The two antigens were visualized with two different fluorophores: FITC and RITC. We were unable to find any cells in either the INL or GCL that exhibited both ChAT- and nAChR-like immunoreactivity. The nAChR-positive cells and the ChAT-positive cells both arborized in two bands within the IPL. The patterns were in perfect register in the inner IPL (lamina 4). But, in the outer IPL, the nAChR-positive dendrites were observed in the inner leaflet of lamina 1 and in all of lamina 2 while the ChAT-positive dendrites did not extend into the innermost portion of lamina 2.

Acetylcholine↗