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Biomedical subjects

S R Taylor

Publications and source records attributed to S R Taylor.

At least 19 recordsLinked to original sources
PubMed2001

Sleep and 24 hour body temperatures: a comparison in young men, naturally cycling women and women taking hormonal contraceptives.

Body temperature has a circadian rhythm, and in women with ovulatory cycles, also a menstrual rhythm. Body temperature and sleep are believed to be closely coupled, but the influence on their relationship of gender, menstrual cycle phase and female reproductive hormones is unresolved. We investigated sleep and 24 h rectal temperatures in eight women with normal menstrual cycles in their mid-follicular and mid-luteal phases, and in eight young women taking a steady dose of oral progestin and ethinyl oestradiol (hormonal contraceptive), and compared their sleep and body temperatures with that of eight young men, sleeping in identical conditions. All subjects maintained their habitual daytime schedules. Rectal temperatures were elevated throughout 24 h in the luteal phase compared with the follicular phase in the naturally cycling women, consistent with a raised thermoregulatory set-point. Rectal temperatures in the women taking hormonal contraceptives were similar to those of the naturally cycling women in the luteal phase. Gender influenced body temperature: the naturally cycling women and the women taking hormonal contraceptives attained their nocturnal minimum body temperatures earlier than the men, and the naturally cycling women had blunted nocturnal body temperature drops compared with the men. Sleep architecture was essentially unaffected by either menstrual cycle phase or gender. The women taking hormonal contraceptives had less slow wave sleep (SWS), however, than the naturally cycling women. Gender, menstrual cycle phase and hormonal contraceptives significantly influenced body temperature, but had only minor consequences for sleep, in the young men and women in our study.

Body Mass Index↗
PubMed2001

Staircase-like potentiation of calcium release in mouse myotubes during repetitive short-term application of threshold caffeine.

The release of Ca2+ in response to caffeine at threshold concentration (5 mM) was studied in mouse skeletal myotubes. Repeated 5-s applications of caffeine, each followed by a 30-s washout, caused Ca2+ releases of consecutively growing amplitude (staircase phenomenon). Each response declined rapidly and had a slow tail. Repeated applications of threshold caffeine lowered the threshold concentration. The interval between threshold applications could be increased to 30 min without loss of potentiation. When threshold caffeine was applied continuously for up to 10 min, the increase in Ca2+ concentration as seen with staircase potentiation did not occur. Depolarization by elevated [K+] or by voltage-clamp steps potentiated caffeine-induced Ca2+ release rapidly as compared to the slow exponential growth of staircase-like potentiation. Gd3+ prevented the depolarization-induced potentiation, but not the staircase phenomenon. Staircase-like potentiation of Ca2+ release was evident even when the voltage sensors were clamped in their resting state; in contrast, potentiated Ca2+ release and its rapid termination apparently require conversion of the voltage sensors to an activated state. Staircase potentiation was blocked when Ca2+ was omitted from the bath, thus pinpointing the source of Ca2+. We suggest that staircase-like potentiation is conditioned by a caffeine-dependent Ca2+ influx across the plasma membrane.

Animals↗
PubMed2001

Synthesis of phakellistatin 11: a micronesia (Chuuk) marine sponge cyclooctapeptide.

The cyclic octapeptide phakellistatin 11 (1), a constituent of The Federated States of Micronesia (Chuuk) marine sponge Phakellia sp., was synthesized using solid-phase techniques. An initial solution-phase synthesis proved to be inadequate owing to spontaneous deprotection of the Fmoc group at the heptapeptide stage. Using the PAL resin attachment and proceeding from Fmoc-Glu-alpha-allyl ester, linear elongation of the octapeptide was performed until the final unit Pro was added. The allyl ester was removed using Pd(0)[P(C(6)H(5))(3)](4). Cleavage of the final Fmoc group and cyclization with PyAOP provided phakellistatin 11 (1) in 17% overall yield. The synthetic specimen of phakellistatin 11 (1) was found to be chemically but not biologically (cancer cell lines) identical to the natural product. The result suggested a conformational difference or more likely the presence of a trace amount of a highly active antineoplastic agent that binds noncovalently to the natural cyclic octapeptide 1.

Animals↗
PubMed2000

Anaesthesia and saccadic eye movements.

During the last 10 years, there has been a vast increase in day-case surgery under general anaesthesia, but this has not been accompanied by research into the residual cognitive and motor effects during recovery from anaesthesia. Part of the explanation for this phenomenon is the lack of a suitable biophysical monitor of anaesthetic sedation. This review discusses one of the most commonly used of these biophysical monitors - namely saccadic eye movements. In particular, the efficacy of peak saccadic velocity as a monitor of sedation will be evaluated. In addition, the physiology and pharmacology of saccadic eye movements will be discussed within the context of developing other parameters of saccadic eye movements as novel biophysical monitors of anaesthetic sedation.

Anesthesia Recovery Period↗
PubMed1999

A transient and a persistent calcium release are induced by chlorocresol in cultivated mouse myotubes.

The effect of 4-chloro-m-cresol (4-CmC), a stabilizing agent used in commercial preparations of the muscle relaxant succinylcholine, on intracellular free calcium levels in cultivated mouse myotubes was studied. Calcium signals were monitored with an inverted microscope equipped for fluorescence photometry using fura-2 as the calcium indicator. Upon bath application of 500 microM 4-CmC for 90 s, two separate calcium signals, a transient and a sustained one, could be regularly discriminated. First, with a delay of 2 s, the intracellular calcium concentration increased from 41+/-13 to 541+/-319 nM, peaked after 2-5 s and declined within 10 s to nearly resting values (n=36). Then, after a delay of up to 20 s, intracellular calcium rose quickly again to almost the same value and stayed elevated as long as the drug was applied. Upon drug removal, intracellular calcium rapidly decreased to a new level that was always slightly higher than the original base line. At 250 microM 4-CmC, the response was small, whereas at 500 microM it was at its maximum. Thus, the concentration-response curve was very steep. Replacement of extracellular calcium by EGTA and application of calcium channel blockers revealed that, for both the transient and the sustained response, calcium was released from intracellular stores. Pre-treatment with thapsigargin (0.1 microM) or ryanodine (10 microM) abolished both signal components. Repeated short-term applications of 4-CmC suggest that the two components may arise from different systems.

Animals↗
PubMed1998

Opposite effects of cooling on twitch contractions of skeletal muscle isolated from tropical toads (Leptodactylidae) and northern frogs (Ranidae).

Cooling increases the twitch force of frog skeletal muscle (Rana temporaria; Rana pipiens), but decreases the twitch force of tropical toad muscle (Leptodactylus insularis). Action potentials and intramembranous charge movement in frog and toad fibers were slowed identically by cooling. Cooling increased the integral of twitch Ca2+ detected by aequorin in frog fibers (1.4-fold), while also decreasing the peak and slowing the rate of decay. Conversely, cooling decreased the integral (0.6-fold) and the peak of twitch Ca2+ in toad fibers, without affecting the rate of decay. The difference in entire Ca2+ transients may account for cold-induced twitch potentiation in frogs and twitch paralysis in toads. In sustained contractions of toad fibers, cooling markedly decreased maximum force caused by: (i) tetanic stimulation, (ii) two-microelectrode voltage clamp steps, (iii) high [K+], or (iv) caffeine. Maximum force in sustained contractions was decreased moderately by cooling frog fibers. Rapid rewarming and simultaneous removal of high [K+] or caffeine during a sustained contraction, caused toad muscle force to rise towards the value corresponding to the warm temperature. This did not occur after removing high [K+] or caffeine from toad fibers kept in the cold. Transmission electron micrographs showed no relevant structural differences. Parvalbumins are thought to promote relaxation of frog muscle in the cold. The unique parvalbumin isoforms in toad muscle apparently lack this property.

Animals↗
PubMed1998

Revising current two-process accounts of spacing effects in memory.

Memory for repeated items improves when presentations are spaced during study. In Experiment 1A, words were repeated either immediately or after 6 intervening items. Intentional learning occurred under either focused or divided attention. Retention was tested by either free recall or yes-no recognition. Divided attention did not affect the influence of spacing in free recall, whereas it removed the spacing effect in recognition. In Experiment 1B, recognition memory was tested after incidental semantic study of words performed under either focused or divided attention. An equivalent spacing effect occurred in both attentional conditions. In Experiments 2 and 3, recognition memory for unfamiliar faces was assessed. A reliable spacing effect was found under both intentional learning and incidental structural study. These data are, collectively, incompatible with current theories of spacing effects. A theoretical proposal to account for these new findings is outlined.

Attention↗
PubMed1998

Different nocturnal body temperatures and sleep with forced-air warming in men and in women taking hormonal contraceptives.

We studied how forced-air warming, conventionally used to control body temperature during and after anaesthesia, affected the nocturnal rectal temperatures and sleep composition of young men and women. Seven healthy women who were taking oral or injection contraceptives, and six healthy men spent 3 nights in a controlled environment: an adaptation night followed by 2 nights when they slept under either a down duvet (baseline) or a quilt perfused with warm air (hot). Repeated analysis of variance (ANOVA) revealed significant gender differences in the body temperature responses. On the baseline night, despite sleeping under the same conditions, the women did not show a nocturnal drop in body temperature as shown by the men. Forced-air warming increased body temperature to a similar extent in the men and the women, and resulted in enhanced hyperthermia in the women, and blunted the drop in body temperature in the men, compared to their baseline nights. The significant increases in body temperature had no consequences, however, for the subjective sleep quality of either the men or women, and only minor consequences for objective sleep composition. Both men and women had increased amounts of Stage 2 sleep on the hot night (P < 0.04). In addition, the women had reduced rapid eye movement (REM) sleep when compared to their baseline night (P < 0.04). Our results confirm that in a passive thermal environment, women who are taking oral or injection contraceptives have higher nocturnal body temperatures than men. Also, as sleep architecture was minimally affected by the increases in body temperature of between 0.2 and 0.3 degree C on the hot night in the men and women, and subjective sleep quality was unaffected, our results question the existence of a tight association between sleep and body temperature.

Adult↗
PubMed1998

Effects of a low concentration of isoflurane on contrast sensitivity in volunteers.

The effects of 0.15% quasi steady-state end-tidal isoflurane on the contrast sensitivity of five healthy volunteers were investigated by measuring their performance in computer generated letter discrimination tasks. A series of letters were displayed on a computer screen so that the luminance of the letter differed from that of the background. Two protocols were used: in the static protocol, the letter remained displayed on the screen until the subject responded, whereas in the dynamic protocol, the letter was displayed for 1/72 s only. Isoflurane significantly decreased contrast sensitivity in both protocols in all subjects.

Anesthesia Recovery Period↗
PubMed1998

Imaging caffeine-induced Ca2+ transients in individual fast-twitch and slow-twitch rat skeletal muscle fibers.

Fast-twitch and slow-twitch rat skeletal muscles produce dissimilar contractures with caffeine. We used digital imaging microscopy to monitor Ca2+ (with fluo 3-acetoxymethyl ester) and sarcomere motion in intact, unrestrained rat muscle fibers to study this difference. Changes in Ca2+ in individual fibers were markedly different from average responses of a population. All fibers showed discrete, nonpropagated, local Ca2+ transients occurring randomly in spots about one sarcomere apart. Caffeine increased local Ca2+ transients and sarcomere motion initially at 4 mM in soleus and 8 mM in extensor digitorum longus (EDL; approximately 23 degrees C). Ca2+ release subsequently adapted or inactivated; this was surmounted by higher doses. Motion also adapted but was not surmounted. Prolonged exposure to caffeine evidently suppressed myofilament interaction in both types of fiber. In EDL fibers, 16 mM caffeine moderately increased local Ca2+ transients. In soleus fibers, 16 mM caffeine greatly increased Ca2+ release and produced propagated waves of Ca2+ (approximately 1.5-2.5 microns/s). Ca2+ waves in slow-twitch fibers reflect the caffeine-sensitive mechanism of Ca2(+)-induced Ca2+ release. Fast-twitch fibers possibly lack this mechanism, which could account for their lower sensitivity to caffeine.

Animals↗
PubMed1997

Effects of training volume on sleep, psychological, and selected physiological profiles of elite female swimmers.

Excessive training is reported to cause sleep disturbances and mood changes. We examined sleep and psychological changes in female swimmers across a competitive swimming season, that is, at the start of the season (onset), during peak training period (peak), and after a precompetition reduction in training (taper). For each phase, polysomnographic recordings, body composition, psychological parameters, and swimming performance were obtained. A daily training log and sleep diary were maintained for the entire study period. Sleep onset latency (SOL) time awake after sleep onset, total sleep time (TST), and rapid eye movement (REM) sleep times were similar at all three training levels. Slow wave sleep (SWS) formed a very high percentage of total sleep in the onset (26%) and peak (31%) training periods, but was significantly reduced following precompetition taper (16%), supporting the theory that the need for restorative SWS is reduced with reduced physical demand. The number of movements during sleep was significantly higher at the higher training volumes, suggesting some sleep disruption. In contrast to other studies, mood deteriorated with a reduction in training volume and/or impending competition.

Adolescent↗
PubMed1997

The origin of the Earth.

It is not possible to consider the formation of the Earth in isolation without reference to the formation of the rest of the solar system. A brief account is given of the current scientific consensus on that topic, explaining the origin of an inner solar system rocky planet depleted in most of the gaseous and icy components of the original solar nebula. Volatile element depletion occurred at a very early stage in the nebula, and was probably responsible for the formation of Jupiter before that of the inner planets. The Earth formed subsequently from accumulation of a hierarchy of planetesimals. Evidence of these remains in the ancient cratered surfaces and the obliquities (tilts) of most planets. Earth melting occurred during this process, as well as from the giant Moon-forming impact. The strange density and chemistry of the Moon are consistent with an origin from the mantle of the impactor. Core-mantle separation on the Earth was coeval with accretion. Some speculations are given on the origin of the hydrosphere.

Atmosphere↗
PubMed1996

Differences in ultra-endurance exercise in performance-matched male and female runners.

Our study investigated endurance performances in a performance-matched (running 42.2 km) group of females (N = 10) and males (N = 10). The distances examined were 10 km, 21.1 km, 42.2 km, and 90 km. Measurements included VO2max, running economy, lactate accumulation, and running speeds. Although our female subjects performed as well as their male counterparts at 42.2 km (194.8 +/- 12.9 m.min-1 vs 192.6 +/- 16.3 m.min-1), the performance for 90 km was significantly better (P < 0.05) in the female group (171.0 +/- 11.7 m.min-1 vs 155.2 +/- 14.7 m.min-1). The average fraction of the VO2max (F) sustained by each subject indicated that the females achieved their performances by working at a higher (P < 0.01) F (73.4 +/- 5.5% vs 66.3 +/- 3.7% for 42.2 km and 59.8 +/- 6.2% vs 50.2 +/- 3.1% for 90 km). The degree of decline in the fraction of the VO2max sustained as the distance of running increased was significantly less (P < 0.05) in the females. The better performance by the females at 90 km was not related to greater maximal aerobic capacity, running economy, training level, or fatty acid metabolism.

Adult↗
PubMed1996

Origin of the terrestrial planets and the moon.

Our ideas about the origin and evolution of the solar system have advanced significantly as a result of the past 25 years of space exploration. Metal-sulfide-silicate partitioning seems to have been present in the early dust components of the solar nebula, prior to chondrule formation. The inner solar nebula was depleted in volatile elements by early solar activity. The early formation of the gas giant, Jupiter, affected the subsequent development of inner solar system and is responsible for the existence of the asteroid belt, and the small size of Mars. The Earth and the other terrestrial planets accreted in a gas-free environment, mostly from volatile-depleted planetesimals which were already differentiated into metallic cores and silicate mantles. The origin of the Moon by a single massive impact with a body larger than Mars explains the angular momentum, orbital characteristics and unique nature of the Earth-Moon system. The density and chemical differences between the Earth and Moon are accounted for by deriving the Moon from the mantle of the impactor.

Aluminum Silicates↗
PubMed1995

DNA ploidy and clonal selection in ras + myc-induced mouse prostate cancer.

An important goal in prostate cancer research is to define specific molecular and cellular alterations that are associated with malignant progression. The mouse prostate reconstitution model is a relevant and useful system as it allows the study of early events in cancer progression under conditions where oncogene-initiated cells are surrounded by normal tissue. Using this model, activated ras and myc oncogenes are introduced into urogenital sinus cells via the recombinant retrovirus Zipras/myc 9. After 4 weeks' growth as subcapsular renal grafts, poorly differentiated carcinomas are produced in C57BL/6 mice. In this study we examined the temporal relationships between morphological alterations, growth, DNA ploidy status and clonal selection as determined by Southern blotting in ras + myc-initiated carcinomas. Nuclear image analysis demonstrated that the emergence of a cycling DNA tetraploid cell population strongly correlated with growth and histologic progression. These tightly linked events culminated in the outgrowth of mono- or oligoclonal cancer.

Animals↗
PubMed1995

Modulation of caffeine contractures in mammalian skeletal muscles by variation of extracellular potassium.

Caffeine contractures were induced after K(+)-conditioning of skeletal muscles from pigs and mice. K(+)-conditioning is defined as the partial depolarization caused by increasing external potassium (K+0) with [K+]x[Cl-] constant. Conditioning depolarizations that rendered muscles refractory to brief electrical stimulation still enhanced the contracture tension elicited by subsequent direct caffeine stimulation of sarcoplasmic reticulum (SR) calcium release. The effects of K(+)-conditioning on caffeine-induced contractures of intact cell bundles reached a maximum at 15-30 mM K+0 and then progressively declined at higher [K+]0. Conditioning with 30 mM K+ for 5 min, which inactivates excitation-contraction (EC) coupling in response to action potentials, both increased the magnitude of caffeine contractures 2-10-fold and shifted the contracture threshold toward lower caffeine concentrations. Enhanced sensitivity to caffeine was inhibited by dantrolene (20 microM) and its watersoluble analogue azumolene (150 microM). These drugs decreased caffeine-induced contractures following depolarization with 4-15 mM K+ to 25-50% of control tension. The inorganic anion perchlorate (CIO-4), which like caffeine potentiates twitches, increased caffeine-induced contractures approximately twofold after K(+)-conditioning (> 4 mM). The results suggest that CIO-4 and dantrolene, in addition to caffeine, also influence SR calcium release either directly or by mechanism(s) subsequent to depolarization of the sarcolemma. Moreover, since CIO-4 is known to shift the voltage-dependence of intramembrane charge movement, CIO-4 may exert effects on the transverse-tubule voltage sensors as well as the SR.

Animals↗
PubMed1994

Prenatal diagnosis of unilateral megalencephaly by real-time ultrasonography.

Unilateral megalencephaly is a rare anomaly of neuronal cell migration. We recently diagnosed this condition in a fetus at 20 weeks' gestation with ultrasonography and magnetic resonance imaging. The pregnancy was terminated and postmortem magnetic resonance imaging and autopsy confirmed the diagnosis. To our knowledge this represents the first case to be prenatally diagnosed with certainty.

Adult↗