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Biomedical subjects

T J Stephens

Publications and source records attributed to T J Stephens.

16 recordsLinked to original sources
PubMed2006

Analysis of optical damage mechanisms in hollow-core waveguides delivering nanosecond pulses from a Q-switched Nd:YAG laser.

Hollow-core waveguides consisting of a glass capillary tube with an internal reflective coating are capable of delivering pulse energies of tens of millijoules with improved focusability compared to step index fibers of similar core diameter. We demonstrate the capability of these fibers to deliver high-power Q-switched pulses at the fundamental (1064 nm), second (532 nm), and third (355 nm) harmonics of a Nd:YAG laser, both in terms of peak power and beam quality delivered. In terms of peak power delivery, the primary limitation is the occurrence of bend-induced optical damage to the reflective coating. The damage mechanism and the influential factors are analyzed, in particular, the dependence upon the number of guided modes, core diameter, coating thicknesses, and input polarization alignment.

Journal Article↗
PubMed2004

5'-aminoimidazole-4-carboxyamide-ribonucleoside-activated glucose transport is not prevented by nitric oxide synthase inhibition in rat isolated skeletal muscle.

1. The nucleoside intermediate 5'-aminoimidazole-4-carboxyamide-ribonucleoside (AICAR) activates skeletal muscle AMP-activated protein kinase (AMPK) and increases glucose uptake. The AMPK phosphorylates neuronal nitric oxide synthase (nNOS)mu in skeletal muscle fibres. There is evidence that both AMPK and nNOSmu may be involved in the regulation of contraction-stimulated glucose uptake. 2. We examined whether both AICAR- and contraction-stimulated glucose uptake were mediated by NOS in rat skeletal muscle. 3. Rat isolated epitrochlearis muscles were subjected in vitro to electrically stimulated contractions for 10 min and/or incubated in the presence or absence of AICAR (2 mmol/L) or the NOS inhibitor NG-monomethyl-L-arginine (L-NMMA; 100 micromol/L). 4. Muscle contraction significantly (P < 0.05) altered the metabolic profile of the muscle. In contrast, AICAR and L-NMMA had no effect on the metabolic profile of the muscle, except that AICAR increased muscle 5'-aminoimidazole-4-carboxyamide-ribonucleotide (ZMP) and AICAR content. Nitric oxide synthase inhibition caused a small but significant (P < 0.05) reduction in basal 3-O-methylglucose transport, which was observed in all treatments. 5'-Aminoimidazole-4-carboxyamide-ribonucleoside significantly increased (P < 0.05) glucose transport above basal, with NOS inhibition decreasing this slightly (increased by 209% above basal compared with 184% above basal with NOS inhibition). Contraction significantly increased glucose transport above basal, with NOS inhibition substantially reducing this (107% increase vs 31% increase). 5'-Aminoimidazole-4-carboxyamide-ribonucleoside plus contraction in combination were not additive on glucose transport. 5. These results suggest that NO plays a role in basal glucose uptake and may regulate contraction-stimulated glucose uptake. However, NOS/nitric oxide do not appear to be signalling intermediates in AICAR-stimulated skeletal muscle glucose uptake.

3-O-Methylglucose↗
PubMed2002

Progressive increase in human skeletal muscle AMPKalpha2 activity and ACC phosphorylation during exercise.

The effect of prolonged moderate-intensity exercise on human skeletal muscle AMP-activated protein kinase (AMPK)alpha1 and -alpha2 activity and acetyl-CoA carboxylase (ACCbeta) and neuronal nitric oxide synthase (nNOSmu) phosphorylation was investigated. Seven active healthy individuals cycled for 30 min at a workload requiring 62.8 +/- 1.3% of peak O(2) consumption (VO(2 peak)) with muscle biopsies obtained from the vastus lateralis at rest and at 5 and 30 min of exercise. AMPKalpha1 activity was not altered by exercise; however, AMPKalpha2 activity was significantly (P < 0.05) elevated after 5 min (approximately 2-fold), and further elevated (P < 0.05) after 30 min (approximately 3-fold) of exercise. ACCbeta phosphorylation was increased (P < 0.05) after 5 min (approximately 18-fold compared with rest) and increased (P < 0.05) further after 30 min of exercise (approximately 36-fold compared with rest). Increases in AMPKalpha2 activity were significantly correlated with both increases in ACCbeta phosphorylation and reductions in muscle glycogen content. Fat oxidation tended (P = 0.058) to increase progressively during exercise. Muscle creatine phosphate was lower (P < 0.05), and muscle creatine, calculated free AMP, and free AMP-to-ATP ratio were higher (P < 0.05) at both 5 and 30 min of exercise compared with those at rest. At 30 min of exercise, the values of these metabolites were not significantly different from those at 5 min of exercise. Phosphorylation of nNOSmu was variable, and despite the mean doubling with exercise, statistically significance was not achieved (P = 0.304). Western blots indicated that AMPKapproximately 2 was associated with both nNOSmu and ACCbeta consistent with them both being substrates of AMPKalpha2 in vivo. In conclusion, AMPKalpha2 activity and ACCbeta phosphorylation increase progressively during moderate exercise at approximately 60% of VO(2 peak) in humans, with these responses more closely coupled to muscle glycogen content than muscle AMP/ATP ratio.

AMP-Activated Protein Kinases↗
PubMed2001

Stimulus characteristics within directives: effects on accuracy of task completion.

Three experiments were conducted in an outpatient setting with young children who had been referred for treatment of noncompliant behavior and who had coexisting receptive language or receptive vocabulary difficulties. Experiment 1 studied differential responding of the participants to a brief hierarchical directive analysis (least-to-most complex stimulus prompts) to identify directives that functioned as discriminative stimuli for accurate responding. Experiment 1 identified distinct patterns of accurate responding relative to manipulation of directive stimulus characteristics. Experiment 2 demonstrated that directives identified as effective or ineffective in obtaining stimulus control of accurate responding during Experiment 1 continued to control accurate responding across play activities and academic tasks. Experiment 3 probed effects of the interaction between the type of directive (effective vs. ineffective) and the reinforcement contingency (differential reinforcement for attempts vs. differential reinforcement for accurate responses) on accurate task completion and disruptive behavior. Results suggested that behavioral escalation from inaccurate responding to disruptive behavior occurred only when ineffective directives were combined with differential reinforcement for accurate task completion. The overall results are discussed in terms of developing a methodology for identifying stimulus characteristics of directives that affect accurate responding.

Child↗
PubMed1999

Fluid ingestion does not influence intense 1-h exercise performance in a mild environment.

PURPOSE: It is generally recommended that fluid be ingested during exercise at a rate that prevents body mass loss and prevents dehydration. It is, however, not known whether these recommendations are valid during intense endurance exercise in a mild environment. The purpose of this study was to examine the effect of fluid ingestion volume on heart rate (HR), rectal temperature, plasma electrolytes, and performance during intense endurance exercise at 21 degrees C. METHODS: Eight well-trained men (26+/-1 yr; 79.6+/-3.5 kg; VO2peak = 5.05+/-0.17 L.min(-1) ; mean+/-SEM) cycled for 45 min at 80+/-1% VO2peak while receiving either no fluid replacement (NF), a volume of water that prevented body mass loss (FR-100 = 1.47+/-0.05 L), or 50% of this volume (FR-50 = 0.72+/-0.03 L). The 45-min exercise bout was followed immediately by a 15-min "all-out" performance ride. RESULTS: NF was associated with a 1.9+/-0.0% body mass loss, while FR-50 and FR-100 resulted in losses of 1.0 = 0.1% and 0.0+/-0.1%, respectively. Although values tended to be higher in NF, fluid ingestion had no significant effect on HR or rectal temperature during exercise. Reductions in plasma volume and increases in plasma sodium and potassium concentrations during exercise were largely unaffected by fluid ingestion. RPE increased to a similar extent during exercise in the three trials while a mild increase in the degree of stomach bloating/fullness was evident in FR-100. Work completed during the 15-min performance ride was similar in the three trials (NF: 273+/-8, FR-50: 267+/-8, FR-100: 269+/-9 kJ). CONCLUSIONS: There appears to be little benefit from ingesting water during intense 1-h cycling exercise in mild environmental conditions since such ingestion has no significant effect on HR, body temperature, plasma volume, plasma electrolytes, or performance.

Adult↗
PubMed1987

Experimental delayed contact sensitization to diazolidinyl urea (Germall II) in guinea pigs.

Diazolidinyl urea (Germall II) is a new preservative recommended for use in certain consumer products. Although 2 reports document the human sensitization rates of this preservative, no publications quantify its sensitization potential in controlled animal experiments. Diazolidinyl urea induced mild sensitization (grade 2) under maximization test conditions. Further, there was evidence of cross-reactions with both imidazolidinyl urea (Germall 115) and formaldehyde in diazolidinyl-urea-sensitized animals. Rechallenge of diazolidinyl-urea-sensitized animals with diazolidinyl urea 4 weeks following the primary challenge only elicited a weak response (0.5) from 1 animal out of 8.

Animals↗
PubMed1984

The prevalence, six-month persistence, and predictive values of laboratory indicators of bacterial vaginosis (nonspecific vaginitis) in asymptomatic women.

The natural course of signs and laboratory test findings indicative of bacterial vaginosis was followed in an observational noninterventive 6-month longitudinal study of 270 asymptomatic women. Only the minority of positive Gardnerella vaginalis cultures (5 of 33), wet mount clue cells (5 of 14), sniff tests (3 of 11), Papanicolaou smear clue cells (0 of 5), and discharge consistent with bacterial vaginosis (11 of 49) persisted in the absence of therapy. While these four laboratory parameters as well as chromatographic succinate/lactate ratios (performed only on the final visit) were abnormal significantly more often in patients with abnormal discharge than in those with normal discharge (p = 0.006, p less than 0.0001, p less than 0.0001, p = 0.0003, and p = 0.002, respectively), all were insensitive predictors of abnormal discharge with sensitivities ranging between 10.6% and 20.2% and abnormal test predictive values between 30.6% and 65.2%. We conclude that G. vaginalis represents indigenous flora in some normal women and that therapy is unwarranted for the incidental finding of a positive laboratory indicator of bacterial vaginosis in the patient without symptoms.

Adolescent↗
PubMed1980

Binding of benzo [a]pyrene to epidermal DNA and RNA as detected by synchronous luminescence spectrometry at 77 K.

The fluorescence associated with benzo[a]pyrene [BP] moieties covalently attached to the nucleic acid (DNA plus RNA) isolated from the epidermis of BP-treated mice was examined at 77 K in frozen aqueous solutions by use of a photon-counting fluorimeter operating in the synchronous scanning mode. The excitation and emission wavelengths were scanned simultaneously with the monochromators set 28 nm apart. This setting coincides with the difference in wavelength between the excitation and emission maxima for the fluorescence of bound BP. Currently the level of detection is in the order of 1 BP residue per 200,000 bases in 40 microgram of nucleic acid. This amount of nucleic acid can be isolated from the skin of a single mouse. The method described here is generally useful for detecting the binding to DNA of nonradioactive carcinogenic polynuclear aromatic which might occur following the topical application to animal skin in vivo of complex hydrocarbon mixtures such as synthetic fuels and crude oils.

Animals↗
PubMed1979

Skin carcinogenicity of synthetic and natural petroleums.

In a series of three separate experiments mice were exposed to various concentrations of fossil liquids obtained from coal, oil shale or natural petroleum. All materials were capable of inducing squamous cell carcinoma, but potency differed substantially. Skin carcinogenicity was markedly greater for both coal or oil shale liquids than for natural petroleums. None of the syncrudes approached the skin carcinogenicity of a pure reference carcinogen, benzo(a)pyrene (BP). It is unlikely that determination of the concentration of an active compound in material applied to the test animal will allow meaningful comparison among the diverse agents of interest to the synthetic fuels industry. To better establish the relationship between actual tissue dose and surface concentration the authors are investigating various in vitro and biochemical measures of hydrocarbon-skin interaction to determine which, if any, could serve as a more definitive measure of surface dose. Results, using BP as a marker carcinogenic hydocarbon, suggest that carcinogenic crudes inhibit both BP metabolism in skin organ culture and the interaction of BP adducts with epidermal DNA, in vivo.

Animals↗
PubMed1977

Chimeric drift in allophenic mice.

The composition of the immune system of 33 allophenic mice of four different types [C57BL/6 in equilibrium DBA/1, C57BL/6 in equilibrium (CBA X CBA/H-T6), C57BL/6 in equilibrium (A X SJL), DBA/1 in equilibrium (CBA X CBA/H-T6)] was studied. It was found that the parental composition of the peripheral white blood cells changed significantly during a two-month interval in 11/33 or 33% of the mice studied. This phenomenon has been termed chimeric drift. The animals were sacrificed between 9 and 16 months of age, and the parental composition of the peripheral white blood cells, spleen white blood cells, and thymocytes was determined on the day of sacrifice. It was foound that the peripheral white blood cell and spleen white blood cell compositions showed a high degree of correlation. However 8/33 or 24% of the mice studied showed discordance of the spleen and thymocyte cell populations. Seven of the 8 mice which showed spleen-thymocyte discordance, had also shown evidence of chimeric drift earlier in their lives. We suggest that this is evidence that chimeric drift may have an immunological basis.

Animals↗
PubMed1977

Chimeric drift in allophenic mice: analysis of changes in red blood cell and white blood cell populations in C57Bl/6 in equilibrium (A X SJL)F1, C57Bl/6 in equilibrium (CBA X CBA/H-T6)F1, and C57Bl/6 in equilibrium DBA/1 mice.

Forty-seven allophenic mice of three different types (C57BL/6 in equilibrium (A X SJL), C57BL/6 in equilibrium (CBA X CBA/H-T6), and C57BL/6 in equilibrium DBA/1) were analyzed for changes in their peripheral white blood cell composition and hemoglobin composition with age. It was found that 10 of the 47 mice showed significant changes termed "chimeric drift" in one or the other or both of these parameters. These 10 mice were classified as unstable chimeras, as opposed to the 37 stable chimeras, which showed no apparent chimeric drift. There was an excellent correlation of peripheral white blood cell and hemoglobin compositions of the stable chimeras. However, the unstable chimeras showed little or no correlation of these two markers. Possible mechanisms of chimeric drift are discussed.

Aging↗