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W S Warren

Publications and source records attributed to W S Warren.

At least 37 records · Page 2Linked to original sources
PubMed1993

Generation of impossible cross-peaks between bulk water and biomolecules in solution NMR.

Intermolecular multiple-quantum coherences between bulk water and a glycoprotein fragment at modest concentration (20 mM) have been experimentally produced and detected, although such coherences are inconceivable in the normal theoretical framework of nuclear magnetic resonance. A density matrix treatment explains these results by including the long-range dipolar interaction between spins and by discarding the high-temperature approximation. These results imply that peak intensities (critical for structural determinations) can be distorted in many gradient experiments, and show that magic-angle gradients provide substantial improvements with reduced gradient strengths. They also suggest methods for contrast enhancement in magnetic resonance imaging.

Fibronectins↗
PubMed1993

Pinealectomized rats entrain and phase-shift to melatonin injections in a dose-dependent manner.

Previous work has shown that daily injections of the pineal hormone melatonin (N-acetyl, 5-methoxytryptamine) entrain the free-running locomotor rhythms of rats held in constant darkness (with a median effective dose [ED50] of 5.45 +/- 1.33 micrograms/kg) and in constant bright light. The present experiments determined the dose-response characteristics of entrainment and phase shifting to daily and single melatonin injections in both sham-operated (SHAM) and pinealectomized (PINX) rats. The data indicated an ED50 of 332 +/- 53 ng/kg and 121 +/- 22 ng/kg for SHAM and PINX rats, respectively, during the entrainment experiment. The ED50's for the entrainment experiment were considerably lower than doses previously employed, and much lower than doses employed in reproductive and metabolic studies in rats and hamsters. The data indicated that no partial entrainment occurred; nor were there differences in phase angle, length of activity, or period among all effective doses. Next, a single injection of 1 mg/kg melatonin has previously been shown to cause a phase advance of approximately 45 min when administered at about circadian time (CT) 10. We found that both SHAM and PINX animals phase-advanced, in a dose-dependent manner to a single melatonin injection given at CT 10. The data for the phase-shifting experiment indicated an ED50 of 8.19 +/- 0.572 micrograms/kg and 2.16 +/- 0.326 micrograms/kg for SHAM and PINX animals, respectively, with an average phase advance of 40 min for both groups. Together, the data suggest that the presence of the pineal gland is not necessary for the effects of melatonin on the rat circadian system, and that PINX animals are marginally more sensitive to melatonin than their SHAM controls.

Adaptation, Physiological↗
PubMed1993

Melatonin, the pineal gland, and circadian rhythms.

Amniote circadian organization derives from the interactions of circadian oscillators and photoreceptors located in the hypothalamic suprachiasmatic nuclei (SCN), the pineal gland, and the eyes. In mammals, circadian organization is dominated by the SCN, which serve as "master pacemakers" in the control of a wide array of behavioral and physiological rhythms (including locomotion, sleep-wake, thermoregulation, cardiovascular function, and many endocrine processes). Among the rhythms under SCN control in mammals are the circadian synthesis and secretion of the pineal hormone melatonin, which relies on a multisynaptic pathway via the sympathetic nervous system to maintain and entrain rhythmicity in this hormone. Several studies have indicated that pineal melatonin feeds back on SCN rhythmicity to modulate circadian patterns of activity and other processes. However, the nature and system-level significance of this feedback are unknown. Recently published work indicates that although pinealectomy does not affect rat circadian rhythms in light-dark cycles or constant darkness, wheel-running activity rhythms are severely disrupted in constant light. These data suggest that either (1) pineal feedback regulates the light sensitivity of the SCN, and/or (2) it affects coupling among circadian oscillators within the SCN or between the SCN and its output. Research in our laboratory is currently addressing each of these hypotheses.

Animals↗
PubMed1992

Laser-enhanced NMR spectroscopy.

Experimental studies show that optical irradiation far from any absorption bands can shift the resonances in a nuclear magnetic resonance (NMR) spectrum without significant heating. This effect may lead to increased dispersion in NMR studies of complex molecules.

Camphor↗
PubMed1988

Effects of pulse shaping in laser spectroscopy and nuclear magnetic resonance.

Pulsed excitation fields are routinely used in most laser and nuclear magnetic resonance (NMR) experiments. In the NMR case, constant amplitude (rectangular) pulses have traditionally been used; in laser spectroscopy the exact pulse shape is often unknown or changes from shot to shot. This article is an overview of the effects of radio-frequency and laser pulse shapes and the instrumental requirements for pulse shaping. NMR applications to selective excitation, solvent suppression, elimination of phase roll, and reduced power dissipation are discussed, as are optical applications to soliton generation, velocity selective excitation, and quantitative population transfer.

Lasers↗
PubMed1988

FRODO pulse sequences: a new means of eliminating motion, flow, and wraparound artifacts.

Magnetic resonance images of the spine, chest, abdomen, and pelvis are commonly degraded by ghost artifacts. The authors have developed a new technique named FRODO (Flow and Respiratory artifact Obliteration with Directed Orthogonal pulses) to suppress these artifacts. Signal from tissues responsible for the artifacts is eliminated by use of radio frequency pulses specifically optimized for high selectivity to saturate proton magnetization over one or more independently defined slabs (large rectangular volumes) of tissue. Ghost artifacts from pulsatile flow in the heart and blood vessels, as well as from respiratory motion and swallowing, are suppressed. Additional applications of this technique include elimination of intraluminal signal in blood vessels and suppression of wraparound artifact along the phase-encoding axis. Preliminary clinical experience suggests that the FRODO technique, in conjunction with other flow compensation methods, may provide a definitive solution to the problem of motion in spine imaging. FRODO pulse sequences may also prove useful for imaging of blood vessels, heart, abdomen, and other areas where motion, flow, or wraparound artifacts limit image quality.

Abdomen↗
PubMed1985

Bacterial tracheitis, diagnosis and treatment.

During a 22-month period, 5 children, 6-13 months of age, presented with an acute obstructive upper airway infection which resembled both croup and epiglottitis. All 5 failed to respond to standard treatment for croup, including aerosolized racemic epinephrine. In all patients, direct laryngoscopy revealed minimal or no change in the epiglottis and aryepiglottic folds but severe subglottic swelling and copious purulent tracheal secretions. Gram stains of the purulent secretions revealed many polymorphonuclear leukocytes with gram-positive cocci (3 patients) and small gram-negative rods (2 patients). Cultures subsequently confirmed the presence of S. Aureus and H. Influenzae. Initial therapy for all patients included endotracheal intubation, antibiotic therapy for both S. Aureus and H. Influenzae and frequent tracheal suctioning. Hospitalization varied from one to 3 weeks. We reported findings in these patients because: the initial diagnosis was unclear due to confusion caused by clinical features common to both croup and epiglottitis and bacterial tracheitis requires a prompt accurate diagnosis and aggressive antibiotic and airway management in order to prevent unnecessary morbidity and mortality.

Airway Obstruction↗
PubMed1981

Intrafamilial transmission of Epstein-Barr virus infections.

Intrafamilial transmission of Epstein-Barr virus infections was studied in 35 familial. After infectious mononucleosis was diagnosed in an index child, all siblings were tested for antibodies to EBV. Susceptible children were retested in four to eight weeks. In five families, a concurrent seroconversion was detected in an asymptomatic younger child. Two of 35 seronegative siblings developed clinical IM, confirmed serologically, during the study period. Overall, there evidence of spread in 7 (20%) of the 35 families. We conclude that there is significant intrafamilial transmission of IM. Our findings are compatible with an incubation period of four to six weeks.

Adolescent↗
PubMed1981

Congenital right diaphragmatic hernia. A case report and review of the literature.

Congenital right diaphragmatic hernia can present a difficult diagnostic problem. An illustrative case is reviewed in which the diagnosis was not considered during the initial hospitalization because chest radiographs were interpreted as showing an atelectatic and pneumonic process. Once suspected, the diagnosis was made by fluoroscopy, which showed an immobile right hemidiaphragm, and by liver scan, which demonstrated herniation of the liver into the right thorax. The tendency of congenital right diaphragmatic hernias to present after the neonatal period and to mimic pulmonary parenchymal disease is discussed. Several alternative means of diagnosis of right diaphragmatic hernias are reviewed.

Female↗