Search PubMed⌕ Search

Biomedical subjects

J R Thomas

Publications and source records attributed to J R Thomas.

At least 163 records · Page 9Linked to original sources
PubMed1989

Repeated exposure to moderate cold impairs matching-to-sample performance.

To study effects of moderate cold (5 degrees C) on complex cognitive performance, subjects were exposed to cold while responding on a conditional discrimination task. The task required a correct choice of which of two simultaneously presented matrices matched a previously presented sample matrix. The effects of task performance in cold and ambient temperatures was examined on three repeated occasions, one pair of conditions per week. Responses accuracy was consistently impaired in each cold session. In addition, choice response latencies lengthened and sample response latencies decreased in all cold exposures. The data show that even moderate cold exposure that does not produce core hypothermia can impair performance of a complex cognitive task and that the magnitude of performance change is not attenuated by a brief series of cold exposures.

Adult↗
PubMed1988

Locations and contexts of sequences that hybridize to poly(dG-dT).(dC-dA) in mammalian ribosomal DNAs and two X-linked genes.

Sequences located several kilobases both 5' and 3' of the stably transcribed portion of several genes hybridize to radio-labeled pure fragments of the alternating sequence poly (dG-dT) (dC-dA) ["poly(GT)"]. The genes include the ribosomal DNA of mouse, rat, and human, and also human glucose-6-phosphate dehydrogenase (G6PD) and mouse hypoxanthine-guanine phosphoribosyl transferase (HPRT). HPRT has additional hybridizing sequences in introns. Fragments that include the hybridizing sequences and up to 300 bp of adjoining DNA show perfect runs of poly(GT) (greater than 30bp) in all but the human 5' region of rDNA, which shows a somewhat different alternating purine:pyrimidine sequence, poly(GTAT) (36bp). Within 150 bp of these sequences in various instances are found a number of other sequences reported to affect DNA conformation in model systems. Most marked is an enhancement of sequences matching at least 67% to the consensus binding sequence for topoisomerase II. Two to ten-fold less of such sequences were found in other sequenced portions of the nontranscribed spacer or in the transcribed portion of rDNA. The conservation of the locations of tracts of alternating purine:pyrimidine between evolutionarily diverse species is consistent with a possible functional role for these sequences.

Animals↗
PubMed1988

The precise midline forehead flap as a musculocutaneous flap.

The forerunners of the midline forehead flap date back to ancient India. The flap, as modified in this presentation, is often the treatment of choice for reconstructing significant full-thickness defects of the nose. The flap described is designed as a musculocutaneous flap incorporating skin, subcutaneous tissue, muscle, and aponeurosis. The enhanced vascularity of this flap allows precise thinning and tailoring at the distal end. A stepwise description of flap design is outlined.

Forehead↗
PubMed1988

The beta adrenoceptor blocker tertatolol causes vasodilatation in the isolated perfused vasoconstricted rat kidney.

The activity of the beta adrenoceptor antagonist tertatolol on renal vasoconstrictions was investigated. Infusion of increasing concentrations of tertatolol (10(-8) to 10(-5) M) progressively inhibited the constrictor responses to bolus injections of norepinephrine and to electrical stimulation in isolated perfused kidneys of both normotensive and spontaneously hypertensive rats. Also, in kidneys of normotensive rats the vasoconstrictions caused by serotonin and barium chloride were inhibited by tertatolol. During sustained vasoconstrictions induced by infusion of norepinephrine (6 X 10(-7) M) increasing doses of tertatolol (2.5 X 10(-7) g to 2 X 10(-5) g) caused rapid, reversible dilatations in the rat kidneys. The inhibitory responses caused by tertatolol were not antagonized by propranolol, atropine, hexamethonium, SCH23390, metoclopramide, mepyramine, cimetidine, naloxone, cocaine or indomethacin. During constrictions caused by norepinephrine, methylene blue significantly inhibited the renal vasodilatations caused by tertatolol, acetylcholine, papaverine and nitroglycerin but not those caused by atrial natriuretic factor. Unlike the other vasodilators, tertatolol did not inhibit the constrictions induced by prostaglandin F2 alpha (5 X 10(-6) M) in the rat kidneys. In canine renal arteries with endothelium, tertatolol (10(-9) to 10(-5) M) did not cause relaxations during contractions induced by norepinephrine, electrical stimulation or prostaglandin F2 alpha. Our data illustrate that tertatolol has potent vasodilator properties in the isolated perfused vasoconstricted rat kidney. The dilator response to the beta blocker cannot be inhibited by a variety of classical receptor blockers but ultimately seems to depend on the formation of cyclic GMP.

Adrenergic beta-Antagonists↗
PubMed1987

Structure of Plant Cell Walls : XIX. Isolation and Characterization of Wall Polysaccharides from Suspension-Cultured Douglas Fir Cells.

The partial purification and characterization of cell wall polysaccharides isolated from suspension-cultured Douglas fir (Pseudotsuga menziesii) cells are described. Extraction of isolated cell walls with 1.0 m LiCl solubilized pectic polysaccharides with glycosyl-linkage compositions similar to those of rhamnogalacturonans I and II, pectic polysaccharides isolated from walls of suspension-cultured sycamore cells. Treatment of LiCl-extracted Douglas fir walls with an endo-alpha-1,4-polygalacturonase released only small, additional amounts of pectic polysaccharide, which had a glycosyl-linkage composition similar to that of rhamnogalacturonan I. Xyloglucan oligosaccharides were released from the endo-alpha-1,4-polygalacturonase-treated walls by treatment with an endo-beta-1,4-glucanase. These oligosaccharides included hepta- and nonasaccharides similar or identical to those released from sycamore cell walls by the same enzyme, and structurally related octa- and decasaccharides similar to those isolated from various angiosperms. Finally, additional xyloglucan and small amounts of xylan were extracted from the endo-beta-1,4-glucanase-treated walls by 0.5 n NaOH. The xylan resembled that extracted by NaOH from dicot cell walls in that it contained 2,4- but not 3,4-linked xylosyl residues. In this study, a total of 15% of the cell wall was isolated as pectic material, 10% as xyloglucan, and less than 1% as xylan. The noncellulosic polysaccharides accounted for 26% of the cell walls, cellulose for 23%, protein for 34%, and ash for 5%, for a total of 88% of the cell wall. The cell walls of Douglas fir were more similar to dicot (sycamore) cell walls than to those of graminaceous monocots, because they had a predominance of xyloglucan over xylan as the principle hemicellulose and because they possessed relatively large amounts of rhamnogalacturonan-like pectic polysaccharides.

Journal Article↗
PubMed1987

Steps for a safer method of osteotomies in rhinoplasty.

Knowledge of osteotomy technique is essential to rhinoplasty. Using cadaver specimens, in addition to clinical observation, a safer method of osteotomy was acquired. Discussion of anatomy with reference to medial and lateral osteotomy follows. Several safety tips for each type of osteotomy are given.

Humans↗
PubMed1987

References for motor tasks--gender differences across age in motor performance: a meta-analysis.

In 1985 we published a meta-analysis of gender differences across age in motor performance in Psychological Bulletin, but it did not include an indexing of each motor task to the references from which it was obtained. This paper provides a table listing the 20 motor tasks and the references from which data for each task were taken. The range of tasks was from fundamental movements (e.g., catching, jumping, running, throwing) to motor fitness (e.g., agility, arm hang, balance, grip strength) to perceptual-motor abilities (e.g., anticipation timing, fine eye-motor coordination, pursuit-rotor tracking, reaction time). The arm hang was represented in the fewest papers (n = 2) while the dash and long jump were most frequently referenced (n = 21).

Aging↗
PubMed1986

A specific curriculum in facial plastic surgery. Effect on residency training.

There has been a dramatic change in the degree of exposure to facial plastic surgery by the otolaryngology resident in the past decade. The amount of this exposure and the method of presentation of aesthetic concepts and procedures varies. We favor a specific curriculum in facial plastic surgery for the residency training program. The effect of this curriculum is measured by statistical analysis of resident-generated aesthetic surgery cases in one year following the introduction of this curriculum into the teaching program. These data are compared with the same period one year prior to the initiation of the program. Tympanoplasty, mastoidectomy, and tonsillectomy case numbers served as controls for statistical comparison over the same time period. These data serve as a guide to residency programs in determining the most effective means of providing optimum facial plastic surgery exposure to their trainees.

Curriculum↗
PubMed1986

Low-intensity magnetic fields alter operant behavior in rats.

The present study demonstrates that operant behavior is affected by a combination of a 60-Hz magnetic field and a magnetostatic field 2.6 X 10(-5) T (about half the geomagnetic field). Rats exposed to this combination for 30 min consistently exhibited changes in the rate and pattern of responding during the differential reinforcement of low rate (DRL) component of a multiple fixed ratio (FR) DRL reinforcement schedule. By contrast, there were no measurable changes following exposure to the static field alone or to the oscillating field alone, even with a 10-fold increase in intensity (5 X 10(-5) to 5 X 10(-4) Trms). A cyclotron resonance mechanism has been suggested as a possible explanation for the observation that weak static magnetic fields modify the response of in vitro brain tissue to low-frequency magnetic fields. The choice of static field intensity Bo and frequency nu in the present study follows from the cyclotron resonance condition nu = (1/2 pi)(q/m)Bo, for singly charged lithium, an element in extensive use in the clinical treatment of affective disorders in humans. The present research is consistent with a cellular cyclotron resonance mechanism and tends to imply a functional dependence of behavior on the geomagnetic field.

Animals↗
PubMed1986

The relationship of lateral osteotomies in rhinoplasty to the lacrimal drainage system.

Damage to the lacrimal drainage system is a potentially complicating factor in rhinoplasty utilizing lateral osteotomies. The authors present data from osteotomies performed on a series of fresh cadavers. Following completion of the osteotomies, the lacrimal sac and nasal lacrimal ducts were identified and cannulated. Soft tissue was dissected to demonstrate the osteotomy site. The specimen was inspected to delineate involvement (if any) of the lacrimal duct or sac. The proximity of the osteotomy site to the lacrimal drainage apparatus components was measured in each specimen. Various parameters were observed, including the effect of curved vs. straight osteotomies, guarded vs. unguarded osteotomies, and the effect of various widths of osteotomies. Likewise, the degree of risk to the lacrimal system was evaluated, and the technique of the novice and resident surgeon was compared to that of the experienced rhinoplastic surgeon. A low, curved osteotomy, performed with a sharp osteotome without subperiosteal tunnels, provides the safest maneuver. Lateral osteotomies, properly performed, prove to be an unusual cause of lacrimal drainage dysfunction.

Cadaver↗
PubMed1986

Classification of nasal defects: a practical guide for reconstruction.

Nasal defects are among the most complicated problems frequently facing the otolaryngologists--head and neck surgeon. The complex role of the nasal structure and its anatomy makes a practical guide for reconstruction particularly attractive. The nose, as a unique facial component, must ideally perform important airway functions, while also having an acceptable appearance. A range of reconstructive problems from simple defects to total nasal loss is addressed.

Female↗