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Biomedical subjects

M I Davies

Publications and source records attributed to M I Davies.

At least 19 recordsLinked to original sources
PubMed2001

Investigation of the metabolism of substance P in rat striatum by microdialysis sampling and capillary electrophoresis with laser-induced fluorescence detection.

The metabolism of substance P (SP) was investigated in rat striatum using in vivo microdialysis. Substance P was perfused for 5 h at 0.2 microl/min, and its metabolism was followed for over 13 h. The resulting samples were derivatized precolumn with naphthalene-2,3-dicarboxaldehyde (NDA)/cyanide, separated and detected by cyclodextrin-modified electrokinetic chromatography with laser-induced fluorescence detection (CDMEKC-LIF). Substance P rapidly degraded to form the fragments (3-11), (1-9), (1-4) and, to a lesser extent, (1-7). The metabolites reached steady-state levels 2-3 h after addition of SP.

Animals↗
PubMed2000

Analytical considerations for microdialysis sampling.

Adaptations in microdialysis probe designs have made it possible to obtain samples from the extracellular fluid of a variety of tissues with high temporal resolution. The resulting small volume samples, often with low concentration of the analyte(s) of interest, present a particular challenge to the analytical system. Rapid separations can be coupled on-line with microdialysis to provide near real-time data. By combining microdialysis sampling with a liquid chromatographic or capillary electrophoretic separation and a highly sensitive detection method, a separation-based sensor can be developed. Such sensors have been applied to the investigation of drug entities as well as to study endogenous analytes.

Animals↗
PubMed1998

Thought suppression produces a rebound effect with analogue post-traumatic intrusions.

Attempts to suppress traumatic material may be involved in the development and maintenance of post-traumatic stress disorder (PTSD). In order to investigate this possibility, analogue post-traumatic intrusions were induced in normal participants by means of a distressing film. For comparison, a second film was used to induce intrusions about polar bears. It was hypothesized that the suppression of these intrusions would produce an immediate decrease but a delayed increase ("rebound effect") in their frequency. It was also predicted that the rebound effect would be larger for the analogue traumatic intrusions. Each film was followed by two consecutive time periods during which participants' thoughts were recorded. During the first period, the suppression group was instructed to suppress thoughts about the film whilst the control group merely recorded their thoughts. During the second period, both groups merely recorded their thoughts. The results supported the immediate decrease hypothesis for both types of intrusion. As predicted, there was a rebound effect for analogue traumatic intrusions although not for polar bear thoughts. Several methodological issues relating to the findings are highlighted. The possible implications of a rebound effect with trauma-relevant intrusions are discussed with reference to PTSD.

Adult↗
PubMed1996

Simultaneous microdialysis sampling from multiple sites in the liver for the study of phenol metabolism.

Microdialysis probes of the linear design were implanted in three regions of the liver of anesthetized rats. Probes planted 1 cm apart exhibited no cross communication as demonstrated by continuously perfusing one probe with phenol for over 2 hours while monitoring the other probes for phenol and its metabolites. Regional differences in metabolic profile were observed following intravenous administration of phenol. Significantly lower concentrations of the phase two metabolites, phenol-glucuronide and hydroquinone-glutathione conjugate, were found at the probe implanted at the anterior position relative to the probes at the median and posterior positions. The kinetics of elimination were not significantly different at any of these positions. Phenol was also directly delivered to the liver through the microdialysis probes. No differences in delivery of phenol or formation of metabolites were observed at the three regions.

Animals↗
PubMed1995

Microdialysis sampling for hepatic metabolism studies. Impact of microdialysis probe design and implantation technique on liver tissue.

Microdialysis sampling of liver tissue was performed using several probe geometries. The extent of tissue damage and response in vivo caused by implantation and indwelling of the probe was evaluated by histological examination of the tissue. A linear probe, implanted using fused silica tubing, was less damaging than other probe designs and implantation procedures tested. A series of time points up to 48 hr after implantation ere histologically examined. Infiltration of inflammatory cells, predominantly polymorphonuclear leukocytes (PMNs), was evident adjacent to the probe membrane after approximately 8 hr. Mixed inflammatory infiltration, mainly PMNs but including some macrophages, was observed in tissue slices 18 hr after implantation. At 48 hr, the mixed inflammatory infiltration was still present, with some degeneration of PMNs. In implantations of longer than 12 hr, some necrosis appeared at eh implantation site. The rate of delivery of phenol via the probe was stable for at least 30 hr, despite changes in the surrounding tissue.

Animals↗
PubMed1994

The Thought Control Questionnaire: a measure of individual differences in the control of unwanted thoughts.

Previous research has suggested that unpleasant and unwanted thoughts are a frequent experience in both normal and clinical populations. This paper describes the development and validation of a questionnaire that assesses strategies for controlling such thoughts. Analyses of the Thought Control Questionnaire (TCQ) demonstrated five replicable factors: Distraction; Social Control; Worry; Punishment and Reappraisal. Significant associations were found between the punishment and worry subscales of the TCQ and various measures of emotional vulnerability and perceptions of impaired control over cognition. The implications of these findings are discussed in relation to the literature on thought suppression, worry and mental self-regulation.

Adaptation, Psychological↗
PubMed1978

The effect of gamma radiation and neocarzinostatin on NAD and ATP levels in mouse leukaemia cells.

When mouse leukemia cells are treated with gamma-radiation or neocarzinostatin the intracellular NAD and ATP levels fall rapidly. We have shown that the ATP response is a consequence of the decreased NAD level. We suggest that this low NAD level results in decreased glycolytic activity and that there is a subsequent accumulation of phosphorylated sugars associated with the fall in ATP. Under these extreme conditions, therefore, the NAD level probably regulates the rate of glycolysis in cells which are utilising a rapidly metabolisable sugar as their energy source.

Adenosine Triphosphate↗
PubMed1976

Biological availability of iron supplements for rats, chicks and humans.

Fourteen experiments were concluded on the effect of protein and carbohydrate sources in the assay diets on the relative biological values (RBV) of food grade sodium iron pyrophosphate (NaFePP) and ferric orthophosphate (FePO4) vs. ferrous sulfate (FeSO4) for rats and chicks, using the response in blood hemoglobin to graded levels of supplemental iron as the assay criterion. Two trials were made with volunteers to estimate the RBV of NaFePP and FePO4 for humans, based on the increase in plasma iron 2 hours after ingestion of 100 mg of iron of a test dose following an overnight fast. The RBV of iron from NaFePP and FePO4 for rats were consistently lower when the basal diet contained nonfat dried milk (9 to 16 and 28, respectively, vs. FeSO4=100) than when casein was used (25 to 28 and 49, respectively). The addition of 22% beta-lactose, replacing sucrose in a diet containing casein fed to rats, significantly reduced the RBV of iron from NaFePP from 25 to 15; the addition of 22% alpha-lactose or 40% glucose in place of sucrose had no effect on the RBV of this iron source. The RBV of iron from NaFePP and FePO4 for chicks were 4 to 6 and 4, respectively, with the source of dietary protein having no effect. Very low RBV of iron from NaFePP and FePO4 (4.3 and 5.9, respectively, vs. FeSO4=100) were also obtained with human subjects.

Animals↗
PubMed1975

Effect of particle size on the biological availability of reduced iron.

A sample of reduced iron was separated by air elutriation into several fractions based on particle size; and the relative biological values (RBVs) of 3 fractions containing fine, medium, and coarse particles were determined with rats and chicks, using diets containing either skim milk powder or casein as the major source of protein. The RBV of reduced iron for rats was shown to be dependent on particle size by curative and prophylactic assay procedures, with the source of protein having no marked effect. In contrast to rats, chicks utilized reduced iron to a higher degree, especially the iron from coarse particles. Prophylactic assays with rats indicated that a 3-4 week feeding period from weaning at 21 days of age gave RBVs which were not significantly different from those obtained by repletion of hemoglobin of anemic animals. After 5 weeks on the test diets, however, the rats lost their ability to distinguish between coarse and medium particles of reduced iron when fed with a diet containing casein as the source of protein.

Anemia↗