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Biomedical subjects

D A Jackson

Publications and source records attributed to D A Jackson.

At least 91 records · Page 5Linked to original sources
PubMed1991

The extracellular matrix coordinately modulates liver transcription factors and hepatocyte morphology.

The extracellular matrix (ECM) promotes tissue morphogenesis, cell migration, and the differentiation of a variety of cell types. However, the mechanisms by which ECM causes differentiated gene expression have been unknown. In this report, we show that culturing the hepatocyte-derived cell line H2.35 on an ECM gel changes cell morphology and selectively stimulates the transcription of a subset of liver-specific genes, including serum albumin. Transcriptional activation by ECM also occurs with transfected plasmids bearing the transcriptional enhancer of the albumin gene. ECM substrates of different composition activated the albumin enhancer only when the ECM promoted a cuboidal, differentiated cell morphology. Enhancer activation by the ECM was mediated by two liver transcription factors, HNF3 alpha and eH-TF, which appear to be regulated differently by matrix. Specifically, we found that a collagen gel substratum caused a selective increase in the factor HNF3 alpha at the levels of mRNA accumulation and DNA-binding activity in nuclear extracts, both in H2.35 cells and in the hepatoma cell line HepG2. We conclude that the ECM can stimulate cell differentiation by selectively activating transcriptional regulatory factors and that such regulation occurs coordinately with ECM-promoted changes in cell shape.

Albumins↗
PubMed1991

Ranitidine in the treatment of non-steroidal anti-inflammatory drug associated gastric and duodenal ulcers.

In a multicentre study the effect of ranitidine on healing non-steroidal anti-inflammatory drug (NSAID) associated peptic ulcers was compared in a group of patients who had stopped NSAID treatment with another group who continued with NSAID treatment. A total of 190 patients with confirmed ulcers were randomised to continue or stop NSAID treatment. All patients in addition received ranitidine 150 mg twice daily. Patients were endoscopically monitored at four, eight, and 12 weeks. Gastric ulcers at eight weeks had healed in 63% of those taking NSAIDs compared with 95% of those who had stopped NSAID treatment. For duodenal ulcer the healing rates at eight weeks were 84% in the group continuing NSAIDs compared with 100% in those who stopped NSAIDs. The differences in healing rates were statistically significant for both gastric ulcer (p = 0.001) and for duodenal ulcer (p = 0.006). At 12 weeks, 79% of gastric ulcers and 92% of duodenal ulcers were healed in the group continuing with NSAIDs. All patients with gastric and duodenal ulcers who stopped taking NSAIDs were healed at 12 weeks. The study shows that ranitidine 150 mg twice daily effectively heals NSAID associated peptic ulcers. Healing is more successful when NSAID treatment stops but even if these drugs are continued, substantial healing rates are achievable.

Adult↗
PubMed1990

Attachment of DNA to the nucleoskeleton of HeLa cells examined using physiological conditions.

Although it is widely believed that eukaryotic DNA is looped by attachment to a nucleoskeleton, there is controversy about its composition and which sequences are attached to it. As most nuclear derivatives are isolated using unphysiological conditions, the criticism that attachments seen in vitro are generated artifactually has been difficult to rebut. Therefore we have re-investigated attachments of chromatin to the skeleton using physiological conditions. HeLa cells are encapsulated in agarose microbeads and lysed using Triton in a 'physiological' buffer. Then, most chromatin can be electroeluted after treatment with a restriction enzyme to leave some at the base of the loops still attached. Analysis of the size and amounts of these residual fragments indicates that the loops are 80-90kbp long. The residual fragments are stably attached, with about 1kbp of each fragment protected from nuclease attack. This is very much longer than a typical protein-binding site of 10-20bp.

Chromatin↗
PubMed1990

Does butylphenyl-deoxyguanosine triphosphate differentially inhibit DNA polymerase alpha and delta activities in permeabilized HeLa cells?

In eukaryotic cells, two enzymes, DNA polymerases alpha and delta, are thought to play major roles in DNA synthesis. I have used butylphenyl dGTP (BuPdGTP), a potent inhibitor of purified DNA polymerase alpha, to assess the relative activities of these enzymes in two permeabilized cell systems. In both instances BuPdGTP eliminated all of the activity which was sensitive to aphidicolin. However, no conditions were found where BuPdGTP preferentially inhibited the synthesis of Okazaki fragments--the presumed products of DNA polymerase alpha activity. This implies that DNA polymerase activities on the two sides of the replication fork are unable to operate independently, being just two elements of the integrated replication machinery that undertakes DNA synthesis in permeabilized cells.

Cell Membrane Permeability↗
PubMed1990

Active RNA polymerase I is fixed within the nucleus of HeLa cells.

We have investigated whether active RNA polymerase I, the enzyme responsible for transcribing ribosomal RNA, is immobilized by attachment to a large subnuclear structure in HeLa cells. As unphysiological salt concentrations induce artifacts, we have used isotonic conditions throughout the preparative and analytic procedures. Cells are encapsulated in agarose microbeads and lysed in Triton and a 'physiological' buffer; then soluble proteins and RNA diffuse out through the agarose pores to leave encapsulated chromatin. This can be manipulated without aggregation but is accessible to molecular probes; it retains the replicational and transcriptional activities of the living cell. After treatment with a restriction endonuclease, most chromatin can be removed from beads by electrophoresis: then active ribosomal genes and polymerase I remain behind. Active ribosomal genes are very accessible to nuclease digestion whilst the rest are even more inaccessible than inactive globin genes. Our observations confirm the complex organization of rDNA within nucleoli and are compatible with transcription occurring at fixed sites. A model for transcription involving an attached polymerase is presented.

Cell Nucleus↗
PubMed1990

The size of chromatin loops in HeLa cells.

It is widely believed that the chromatin fibre is organized into loops during interphase, with the loop being implicated as an important unit of nuclear function. However, there remains little direct evidence for looping, with estimates of loop size varying widely. This has led to the suggestion that some loops, or even all of them, arise artefactually during isolation as chromatin aggregates so easily. We have now investigated the effect of isolation procedure on loop size using HeLa cells encapsulated in agarose to allow easy manipulation. Loop size in various derivatives (i.e. nuclei, nucleoids, matrices and scaffolds) critically depended on procedure; some (or all) of their loops are artefacts. The loop size in derivatives isolated using the most 'physiological' conditions was 86 kb; this remained unchanged throughout the cell cycle. This loop size is probably an average of a range of loops of between 5 and 200 kb.

Cell Cycle↗
PubMed1990

Receptor subtypes mediating facilitation by serotonin of excitability of spinal motoneurons.

Serotonin receptor ligands, with differential affinity for subtypes of serotonin (5-HT) receptors, were administered intravenously or iontophoretically to urethane-anesthetized rats and the effects of these compounds on glutamate-evoked firing of spinal motoneurons were tested. The excitability of spinal motoneurons was markedly enhanced after intravenous administration of the selective 5-HT1A ligand 8-hydroxy-2-(di-n-propylamino) tetralin (DPAT) in rats with acute spinal transections at C1. However, local application of DPAT, directly into the ventral horn by microiontophoresis, inhibited the glutamate-evoked firing of motoneurons in direct contrast to the facilitatory effects of iontophoretically applied 5-HT. The DPAT-induced inhibition may have been nonspecific, since it was not antagonized by methysergide. Other 5-HT agonists, with relatively selective affinity for 5-HT1B, 5-HT1C and 5-HT2 receptors, increased the excitability of spinal motoneurons when applied iontophoretically or intravenously. The excitatory effect of iontophoretically applied 5-HT was antagonized by the nonselective 5-HT antagonist, methysergide and by ketanserin and ritanserin, which have relatively selective affinity for 5-HT1C and 5-HT2 receptors. These results indicate that 5-HT1A receptors do not mediate facilitation of excitability of motoneurons produced by local application of 5-HT directly into the vicinity of the motoneurons. However, the marked increase in firing of motoneurons that was caused by intravenous administration of DPAT in spinal transected rats, suggests that 5-HT1A receptors in the spinal cord may participate in 5-HT-induced enhancement of somatomotor outflow, at sites presynaptic to the motoneurons. The iontophoretic results suggest that 5-HT1B, 5-HT1C and 5-HT2 receptors may all play a role in facilitation of the excitability of spinal motoneurons by locally applied 5-HT. Differentiation between these subtypes of receptor awaits the development of more completely selective agonists and antagonists.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1990

Roy in the postanesthesia care unit.

The adaptation model developed by Sister Callista Roy, RN, PhD, was used as the organizing framework for developing a preoperative assessment tool for PACU nurses. The purpose of preoperative assessment of a surgical patient by a PACU nurse is to determine the patient's location on the health-illness continuum. This is done by analyzing data regarding the patient's biopsychosocial needs, evaluating the data, and determining from that information what problems need intervention. Roy's theory advocates assessing the patient's biopsychosocial needs using four different adaptive modes: self-concept, physiological function, role function, and interdependence (level I assessment). After completing the PACU preoperative assessment tool, each mode in level I assessment is identified as either positive (adaptive) or negative (maladaptive) depending on the patient's behavior identified by the tool. If a maladaptive behavior is identified during the preoperative assessment, a level II assessment is made to collect data regarding focal, contextual, and residual stimuli. A nursing diagnosis, expected outcomes, nursing interventions, and evaluation are listed on the patient care plan based on the data obtained from the assessment.

Adaptation, Biological↗
PubMed1989

Relationships between nursing patterns, supplementary food intake and breast-milk intake in a rural Thai population.

Relationships between nursing patterns, supplementary food intake and breast-milk intake were examined in a group of 52 Thai babies under 1 year of age. All data were collected over two consecutive days, 24 h/day. Total sucking time (min/day) and supplementary food intake (kcal/day) were significant predictors of breast-milk intake after allowing for the age of the baby: R-squared is 0.32 for sucking time and 0.39 for supplementary food intake. The two variables were themselves correlated (r is -0.47). The number of breastfeeds per day and their mean duration was determined for each case, counting each episode of attachment to the breast as a separate feed. Number and mean duration of breastfeeds were then evaluated as predictor variables. The duration of feeds had no predictive power. Number of feeds was linearly related to milk intake and combined with age was as good a predictor of milk intake as total sucking time (with R-squared 0.34). These results suggest that a simple count of breastfeeds is as valuable as more complex measures of sucking duration in predicting to breast-milk intake.

Breast Feeding↗
PubMed1989

The bacterial content of infant weaning foods and water in rural northern Thailand.

Samples of weaning food and supplementary water were collected for analysis of bacterial content from among a random sample of 65 infants under the age of 1 year living in a rural area of northern Thailand. Using geometric means, mean total bacterial count of infant's drinking water was 351 organisms/ml (95 per cent CIs 170-770), and the most probable number (MPN) of faecal coliforms/ml was 47 (95 per cent CIs 19-78). Mean total bacterial count of weaning foods was 38,000 (95 per cent CIs 25,000-59,000) organisms/g with 10 per cent recording counts greater than 1,000,000 organisms/g. Bacterial counts were similar to those reported in weaning food and water in other developing countries, and were above internationally recommended 'safe' levels. The bacterial count of water was not affected by boiling, due to poor cleaning and frequent re-use of utensils. Weaning foods were contaminated during preparation, in part through premastication and also via mode of cleaning of utensils.

Colony Count, Microbial↗
PubMed1989

Predictors of breast milk intake in rural northern Thailand.

A random sample of 52 mothers and infants from a rural area of Northern Thailand were studied in their homes for 48 h. Infants were breast fed on demand. Daytime feeds were test weighed with electronic averaging balances and nighttime intake estimated using a new method, Indirect Test Weighing. All feeds, both day and night, were timed to the nearest minute. Other variables measured by direct observation were infant weight, and supplementary food and water intake. Mean 24-h breast milk intake was 579 g (range 78-1,011 g) with a median between day coefficient of variation of 8.8%. The proportion of 24-h breast milk intake consumed at night ranged from 8 to 91%, and increased with increasing infant age. Significant positive associations were found between breast milk intake, and sucking time and infant weight. There were significant negative associations between breast milk intake and age, and supplementary food and water intake.

Body Weight↗
PubMed1989

Thyrotropin-releasing hormone (TRH) effects on spinal cord neuronal excitability.

TRH is found in terminals in the dorsal, lateral, and ventral horns of the spinal cord and apparently has at least a weak facilitatory effect on excitability of neurons in all these locations. These findings suggest that TRH may facilitate transmission in somatosensory pathways, enhance sympathetic outflow from the spinal cord, and facilitate somatic motoneuron excitability, at least transiently. All studies that have examined TRH effects on spinal neuronal excitability have used exogenously administered TRH. Virtually nothing is known about how spinal neuronal functioning might be affected by TRH released from terminals after activation of TRH-containing cell bodies. The acquisition of this knowledge awaits the development of specific TRH antagonists. Preliminary experiments suggest that TRH may have prolonged facilitatory effects on the excitability of developing or damaged spinal cord neurons. Further studies are necessary to determine how TRH interacts with other neuroactive peptides and monoamines to affect excitability of neurons in the developing, damaged, and normal adult spinal cord.

Animals↗
PubMed1989

Methotrexate-induced morphological changes mimic those seen after heat shock.

The survival of cells cultured in medium containing the chemotherapeutic drug methotrexate (MTX) is related directly to drug concentration. Changes in DNA resulting from a severe imbalance in the cells' nucleotide pools are thought to account for this cytotoxicity. We have attempted to clarify the gross biochemical changes that might lead to cell death. DNA strand breaks occur in cells treated with high concentrations of MTX but it is not clear that these are sufficient to account for cytotoxicity at lower doses. We observed dramatic changes in cytoskeletal morphology. Gross reorganization of the cytoskeleton is shown by immunolabelling but is high-lighted dramatically when cells are lysed to leave 'nucleoids'. The nature of the changes seen in MTX-treated cells is characteristic of the cells' general stress response, seen originally following heat shock. This study shows that other factors, such as changes in cytoskeletal function, must be considered together with any contribution from DNA damage, in order to account for the lethal effects of MTX.

Cell Nucleus↗
PubMed1989

Electrodiagnosis of mild carpal tunnel syndrome.

Electrophysiologic tests have been reported to detect mild carpal tunnel syndrome (CTS). Such tests include (i) absolute palmar latency of median wrist segment; (ii) comparison of median and radial distal sensory latencies in digit I; (iii) comparison of median and ulnar distal sensory latencies in digit IV; (iv) comparison of median and ulnar palmar latencies; (v) comparison of median and ulnar sensory potential amplitudes in digits II and V. To clarify the clinical utility of these tests, the parameters of all five tests were determined across four carefully established patient subgroups: group A, controls; group B, CTS referrals with normal nerve conduction studies (NCS) and normal needle electromyography (EMG); group C, CTS referrals with abnormal NCS and normal EMG; group D, CTS referrals with abnormal NCS and abnormal EMG. Special attention was focused on patients in group B who represent the diagnostic dilemma. In group B, tests ii and iii each yielded abnormal results in 44% of hands, while the combination of tests ii and iii yielded abnormal results in 51% of hands.

Adult↗
PubMed1988

Visualization of a filamentous nucleoskeleton with a 23 nm axial repeat.

Whether nucleoskeletons seen after extracting cells are preparative artefacts is controversial. Using an extraction method that preserves vital nuclear functions, we have visualized part of a nucleoskeleton by electron microscopy of thick resinless sections. Cells encapsulated in agarose microbeads are lysed using Triton in a physiological buffer; the agarose coat prevents aggregation and protects fragile cell contents. These extracted cells are accessible to small molecules and transcribe and replicate at rates close to those in vivo. After electroeluting most chromatin after treatment with HaeIII, a skeleton is uncovered which ramifies throughout the nucleus. Individual filaments are approximately 10 nm wide with an axial repeat of 23 nm, characteristic of intermediate filaments.

Cell Nucleus↗
PubMed1988

Thyrotropin releasing hormone (TRH) modified excitability of spinal cord dorsal horn cells.

Thyrotropin releasing hormone (TRH) has been identified recently in fibers and cell bodies in the dorsal horn of the spinal cord, but its function in the dorsal horn is not known. The present study investigated the effects of TRH applied by iontophoresis on the excitability of dorsal horn cells that were responsive to mechanical stimulation of the ipsilateral hindlimb. TRH facilitated glutamate-induced firing of these cells without directly driving the cells in the absence of glutamate. These results suggest that TRH may modulate transmission of somatosensory information in the spinal cord.

Action Potentials↗