Search PubMed⌕ Search

Biomedical subjects

D Roberts

Publications and source records attributed to D Roberts.

At least 199 records · Page 11Linked to original sources
PubMed1994

Sperm increase inositol 1,4,5-trisphosphate mass in Xenopus laevis eggs preinjected with calcium buffers or heparin.

Although it is known that all fertilization events are due to elevated intracellular calcium ([Ca2+]i), it is not known how sperm induce an increase in zygote [Ca2+]i. We report that sperm can increase inositol 1,4,5-trisphosphate in Xenopus laevis eggs that have been preinjected with calcium buffers to prevent the increase in [Ca2+]i (both the initial increase and the subsequent wave) after fertilization. After buffering [Ca2+]i to levels well below basal, IP3 production was not blocked, whereas IP3 metabolism may be inhibited. Also, heparin (an inhibitor of inositol 1,4,5-trisphosphate action and the fertilization response) does not prevent a normal increase in IP3 after fertilization. Conditions that produce various levels of polyspermy are associated with IP3 increases similar to those noted after monospermic fertilization. These data suggest a specific order of fertilization events: sperm utilize an initial production of inositol 1,4,5-trisphosphate to produce the [Ca2+]i increase at fertilization.

Animals↗
PubMed1994

Short-term vestibulo-ocular reflex adaptation in humans. I. Effect on the ocular motor velocity-to-position neural integrator.

We investigated the effect of short-term vestibulo-ocular reflex (VOR) adaptation in normal human subjects on the dynamic properties of the velocity-to-position ocular motor integrator that holds positions of gaze. Subjects sat in a sinusoidally rotating chair surrounded by an optokinetic nystagmus drum. The movement of the visual surround (drum) was manipulated relative to the chair to produce an increase (x 1.7 viewing), decrease (x 0.5, x 0 viewing), or reversal (x (-2.5) viewing) of VOR gain. Before and after 1 h of training, VOR gain and gaze-holding after eccentric saccades in darkness were measured. Depending on the training paradigm, eccentric saccades could be followed by centrifugal drift (after x 0.5 viewing), implying an unstable integrator, or by centripetal drift [after x 1.7 or x (-2.5) viewing], implying a leaky integrator. The changes in the neural integrator appear to be context specific, so that when the VOR was tested in non-training head orientations, both the adaptive change in VOR gain and the changes in the neural integrator were much smaller. The changes in VOR gain were on the order of 10% and the induced drift velocities were several degrees per second at 20 deg eccentric positions in the orbit. We propose that (1) the changes in the dynamic properties of the neural integrator reflect an attempt to modify the phase (timing) relationships of the VOR and (2) the relative directions of retinal slip and eye velocity during head rotation determine whether the integrator becomes unstable (and introduces more phase lag) or leaky (and introduces less phase lag).

Adaptation, Physiological↗
PubMed1994

Short-term vestibulo-ocular reflex adaptation in humans. II. Error signals.

We oscillated humans sinusoidally at 0.2 Hz for 1 h, using various combinations of rotations of the head and visual surround to elicit short-term adaptation of the gain of the vestibulo-ocular reflex (VOR). Before and after each period of training, the gain of the VOR was measured in darkness, in response to a position step of head rotation. A small foveal target served as well as a full-field stimulus at driving VOR adaptation. Oscillation of the visual surround alone produced a substantial increase in the VOR gain. When the visual scene was rotated in phase with the head but with a larger amplitude to produce a reversal of the VOR, the VOR gain increased if the movement of the visual scene was much greater than that of the head, otherwise the gain decreased. We interpreted these results with a model of VOR adaptation that uses as its "error signal" the combination of motion of images on the retina (retinal slip) and any additional slow-phase eye velocity, beyond that generated by the VOR through the vestibular nuclei, necessary to prevent such retinal slip during head rotation. The slow phase velocity generated by the VOR is derived from "inferred head rotation", a signal based on the discharge of neurons in the vestibular nuclei that receive both labyrinthine and visual (optokinetic) inputs. The amplitude and sign of the ratio of the "error signal" to "inferred head velocity" determined the amplitude and the direction (increase or decrease) of VOR gain adaptation.

Adaptation, Physiological↗
PubMed1994

Increasing opportunities for requesting in classrooms serving children with developmental disabilities.

Evaluated an intervention package for increasing requesting opportunities in special education classrooms. Five teachers, serving 26 children with moderate to severe disabilities, received in-service training, consultation, and feedback on the use of three strategies designed to create opportunities for requesting (i.e., missing item, interrupted chain, delayed assistance). Observations were conducted in a multiple-baseline across classrooms design to record the number and types of opportunities provided by each teacher. During baseline, few opportunities for requesting were observed. The number of opportunities for requesting and the number of correct student responses increased during intervention. Opportunities continued to be provided during generalization and follow-up sessions. The study demonstrated an effective strategy for helping teachers incorporate opportunities for functional communication into the natural environment.

Adolescent↗
PubMed1994

Opportunities for communication in classrooms serving children with developmental disabilities.

Documented the number and types of opportunities for communication provided by teachers in seven classrooms for children with developmental disabilities and by teachers of nonhandicapped preschoolers in a day care center. In the special education settings, less than 14% of the more than 6,000 observation intervals contained an opportunity for communication. Most opportunities involved naming an object or event followed in frequency by opportunities to request, answer, and imitate. Similar results were obtained in the day care center. In the special education classrooms, a strong positive correlation was found between a child's existing communication skills and the number of opportunities received. Results suggest that these teachers did incorporate opportunities for communication into classroom activities.

Adolescent↗
PubMed1994

Effects of high volume and/or intense exercise on selected blood chemistry parameters.

The goal of athletic training is to provide the body with a stimulus to adapt, increasing the capacity of the various systems to perform increased work loads. However, the magnitude of the stress must be large enough to induce the synthesis of new enzymes, tissues, and yet not so large that the biochemical and physiological processes of recovery are depressed. As each individual undergoes this process at a different rate, objective evaluation of the level of fatigue and adaptation is of enormous value in directing the training program of an athlete. The role of iron in the body is such that this element can be used as a marker of both adaptation to training and as an indicator of an acute inflammatory response to exercise. The various clinical measurements of iron in transport, storage, and in hematological parameters are discussed in this paper, relative to athletic populations. In addition expected changes in the level of the acute inflammatory protein, alpha 1-antitrypsin are also discussed relative to acute and chronic training protocols. Data is presented indicating that measurement of serum iron, transferrin, serum ferritin, and alpha 1-antitrypsin can be used to differentiate between an inflammatory response to tissue damage and infection. These parameters can also provide information as to the state of recovery, or lack thereof, experienced by an athlete to both acute and chronic training programs. The use of biochemical markers can help to avoid an overstress situation.

Acute-Phase Reaction↗
PubMed1994

Quantification of oil and water in preserved reservoir rock by NMR spectroscopy and imaging.

Reservoir rock analysis by proton NMR requires separation of the response into brine and crude oil components. Tests on preserved core from a North Sea chalk reservoir show that spin-lattice relaxation time distributions can be used to distinguish the two fluids. NMR estimates of oil and water saturations for 1.5" diameter core examined in a 10 MHz Bruker Minispec spectrometer closely match fluid contents determined by distillation. The spin-lattice relaxation contrast mechanism developed for core samples can be applied in the quantitative analysis of NMR images. The relaxation data are compared with data from chemical shift imaging on the same core sample. The results indicate that it will be possible to monitor changes in fluid distributions, in this and similar systems, under dynamic conditions such as in a waterflood.

Calcium Carbonate↗
PubMed1994

Wegener's granuloma--presenting as a unilateral parotid swelling.

Wegener's granuloma is a systemic necrotizing vasculitis which predominantly affects the upper and lower respiratory tracts and kidneys. The nose and paranasal sinuses are often the first or main sites to be affected. Equally ear involvement is common and a recognized early manifestation of the disease. Salivary gland involvement is rare and is usually part of more widespread systemic involvement. We present a 34-year-old female with a six-week history of hearing loss and a unilateral parotid swelling. One year previously she was diagnosed as having myalgic encephalomyelitis following a long period of post-viral malaise. The case points to the difficulties encountered when Wegener's granuloma presents in an unusual and varied way. A high index of suspicion coupled with early diagnosis and treatment is essential. The patient made a good recovery.

Adult↗
PubMed1994

Lipoma of the left tonsillar fossa.

Lipomas are common benign connective tissue tumours composed of adult adipose tissue. They are relatively rare in the upper aerodigestive tract, although they occur with considerable frequency in other areas, particularly in the subcutaneous tissues of the neck. Although there are several reports of this tumour occurring in the oropharynx, there is no recorded case of a lipoma of the tonsillar fossa. An 83-year-old man with a left tonsillar fossa lipoma is presented. Clinical presentation, management and a literature review are discussed.

Aged↗
PubMed1994

Altered stability of etoposide-induced topoisomerase II-DNA complexes in resistant human leukaemia K562 cells.

K562 leukaemia cells were selected for resistance using 0.5 microM etoposide (VP-16). Cloned K/VP.5 cells were 30-fold resistant to growth inhibition by VP-16 and 5- to 13-fold resistant to m-AMSA, adriamycin and mitoxantrone. K/VP.5 cells did not overexpress P-glycoprotein; VP-16 accumulation was similar to that in K562 cells. VP-16-induced DNA damage was reduced in cells and nuclei from K/VP.5 cells compared with K562 cells. Topoisomerase II protein was reduced 3- to 7-fold and topoisomerase II alpha and topoisomerase II beta mRNAs were each reduced 3-fold in resistant cells. After drug removal, VP-16-induced DNA damage disappeared 1.7 times more rapidly and VP-16-induced DNA-topoisomerase II adducts dissociated 1.5 times more rapidly in K/VP.5 cells than in K562 cells. ATP (1 mM) was more effective in enhancing VP-16-induced DNA damage in nuclei isolated from sensitive cells than in nuclei from resistant cells. In addition, ATP (0.3-5 mM) stimulated VP-16-induced DNA-topoisomerase II adducts to a greater extent in K562 nuclei than in K/VP.5 nuclei. Taken together, these results indicate that resistance to VP-16 in a K562 subline is associated with a quantitative reduction in topoisomerase II protein and, in addition, a distinct qualitative alteration in topoisomerase II affecting the stability of drug-induced DNA-topoisomerase II complexes.

Antineoplastic Agents↗
PubMed1994

Using vehicle-mounted nets for studying activity of Arabian sand flies (Diptera: Psychodidae).

Vehicle-mounted nets were used on 15 nights in northern Oman to collect 2,216 sand flies. The composition of the catch was compared with that of 100 sticky traps, which were used twice a month over a 15-mo period to collect 3,099 sand flies. Sticky trap catches showed no obvious seasonal change in abundance. The vehicle nets collected up to 260 flies per night, with a mean of 148. This compared with the catch of the 100 sticky traps, which had an overall mean of 115 flies per night. The vehicle nets collected seven species of sand flies (four Phlebotomus and three Sergentomyia). Phlebotomus alexandri Sinton, the presumed vector of visceral leishmaniasis in Oman, made up 29% of the catch. In contrast, the sticky traps collected mainly Sergentomyia spp., and P. alexandri was only 4% of the catch. Overall, catch of both methods had a sex ratio of 1:1, but both collected a higher proportion of female P. alexandri. The vehicle nets collected only a few blood-fed flies, the greatest number being 33 P. alexandri (8% of the females for this species). However, some females were collected at each stage of the gonotrophic cycle; the smallest number was in stage II. All the flies developing eggs beyond stage II had had a blood meal, so that there was no sign of autogeny in these species. Ten percent of the females were parous. The vehicle-mounted net placed on the side of the vehicle at 0.3 to 1.8 m above the ground caught a greater number of Sergentomyia clydei Sinton than an identical net mounted on top of the vehicle at 1.8 to 2.8 m, in which the rest of the species, including P. alexandri, mainly were caught.

Animals↗
PubMed1994

The surgical management of congenital coronary artery fistula.

BACKGROUND: Congenital coronary artery fistula (CAF) is a very rare cardiovascular anomaly and only 400 cases have been reported. The purpose of this study was to analyse the experience of surgical treatments in CAF and evaluate the surgical indications, techniques and long-term results. METHODS: A retrospective study reviewing 20,000 cardiovascular surgical cases from 1978 to 1993 was carried out, from which 14 patients with CAF were identified and diagnosis was confirmed by both coronary angiography (CAG) and echocardiography. Twelve patients had heart-related symptoms. CAG revealed that fistulous channels arose from the right coronary artery (RCA) in seven patients, and from the left coronary artery (LCA) in six patients. One patient had multiple fistulae, from both RCA and LCA. The surgical managements and late follow-up were assessed. RESULTS: Surgery was performed on 13 patients; one had died before surgery. Cardiopulmonary bypass (CPB) was performed in 11 patients. The presence of coronary aneurysm was treated by reduction plasty of the aneurysm (four patients). Other procedures were coronary artery bypass grafting (CABG; four patients), ventricular septal defect (VSD) and patent ductus arteriosus (PDA) closure (one patient), and one patient had mitral valve replacement. The mean follow-up time was 7.2 years and all symptomatic patients improved their New York Heart Association (NYHA) functional class (average 1.2 classes). Although there were no surgical deaths in our group, one late death (6 months after surgery) was caused by acute myocardial infarction; this resulted in an annual mortality rate of 1%. CONCLUSIONS: Surgical closure of CAF can be recommended because it is a low-risk procedure and leads to good long-term results. The problems with myocardial protection, residual fistula prevention and surgical techniques must be emphasized. For these purposes, special surgical techniques that have been introduced are described.

Adolescent↗
PubMed1994

Growth phase variation of integration host factor level in Escherichia coli.

We have measured the intracellular abundance of integration host factor (IHF), a site-specific, heterodimeric DNA-binding protein, in exponential- and stationary-phase cultures of Escherichia coli K-12. Western immunoblot analysis showed that cultures that had been growing exponentially for several generations contained 0.5 to 1.0 ng of IHF subunits per microgram of total protein and that this increased to 5 to 6 ng/microgram in late-stationary-phase cultures. IHF is about one-third to one-half as abundant in exponentially growing cells as HU, a structurally related protein that binds DNA with little or no site specificity. Wild-type IHF is metabolically stable, but deletion mutations that eliminated one subunit reduced the abundance of the other when cells enter stationary phase. We attribute this reduction to the loss of stabilizing interactions between subunits. A mutation that inactivates IHF function but not subunit interaction increased IHF abundance, consistent with results of previous work showing that IHF synthesis is negatively autoregulated. We estimate that steady-state exponential-phase cultures contain about 8,500 to 17,000 IHF dimers per cell, a surprisingly large number for a site-specific DNA-binding protein with a limited number of specific sites. Nevertheless, small reductions in IHF abundance had significant effects on several IHF-dependent functions, suggesting that the wild-type exponential phase level is not in large excess of the minimum required for occupancy of physiologically important IHF-binding sites.

Amino Acid Sequence↗