PubMed Health⌕ Search

Biomedical subjects

R McNeil

Publications and source records attributed to R McNeil.

At least 19 recordsLinked to original sources
PubMed2006

Comparing the retinal structures and functions in two species of gulls (Larus delawarensis and Larus modestus) with significant nocturnal behaviours.

Ring-billed gulls (Larus delawarensis) and gray gulls (Larus modestus) are two species active both by day and night. We have investigated the retinal adaptations that allow the diurnal and nocturnal behaviours of these two species. Electroretinograms and histological analyses show that both species have a duplex retina in which cones outnumber rods, but the number of rods appears sufficient to provide vision at night. Their retinas respond over the same scotopic dynamic range of 3.4logcdm(-2), which encompasses all of the light levels occurring at night in their photic environment. The amplitudes of the scotopic saturated a- and b-wave responses as well as the photopic saturated b-wave response and the photopic sensitivity parameter S are however higher in ring-billed gulls than in gray gulls. Moreover, the process of dark adaptation is about 30min faster in gray gulls than in ring-billed gulls. Our results suggest that both species have acquired in the course of their evolution functional adaptations that can be related to their specific photic environment.

Adaptation, Ocular↗
PubMed2005

Comparison of the retinal structure and function in four bird species as a function of the time they start singing in the morning.

We postulated that the retinas of bird species that are the earlier singers are more sensitive to low light conditions than species that sing closer to sunrise. The selected species were the American Robin (Turdus migratorius) and the Hermit Thrush (Catharus guttatus) as early singers, the Common Grackle (Quiscalus quiscula) and the Mourning Dove (Zenaida macroura) which join the dawn chorus near sunrise. Scotopic electroretinogram (ERGs) intensity-response functions were obtained from anesthetized birds, following which the animals were euthanized and their retinas processed for histological analysis. Based on k values, generally considered an adequate measurement of the scotopic (rod) retinal sensitivity, all species yielded comparable night vision capabilities. However, based on the maximal (mixed rod-cone response) amplitude of the scotopic b-wave, our results indicate that robins and thrushes yield larger scotopic ERGs compared with doves and grackles, but unexpectedly do not have higher rod:cone ratios. Increased thickness of the retinal inner nuclear layer and higher numbers of ganglion cells in robins and thrushes compared with doves and grackles suggest a greater number of synaptic connections maximizing vision under low light conditions, and might support their higher retinal responses under scotopic conditions. The higher ERG V(max) of robins and thrushes might also be explained, at least in part, by the optics (i.e., their lower minimum F-numbers), resulting in brighter retinal images, rather than from higher sensitivity of their retina. Our results suggest that an early onset of dawn singing might be correlated with the retinal ability to detect the first dim crepuscular lights.

Animals↗
PubMed2004

Retinal morphology and electrophysiology of two caprimulgiformes birds: the cave-living and nocturnal oilbird (Steatornis caripensis), and the crepuscularly and nocturnally foraging common pauraque (Nyctidromus albicollis).

Oilbirds (Steatornis caripensis) breed in the total darkness of caves and forage at night on fruits. Common pauraques (Nyctidromus albicollis) are crepuscular and nocturnal foragers on flying insects. We examined if their retinal structure and function can be correlated with their types and periods of activity. Electroretinograms (ERGs) were obtained from anesthetized birds in photopic and scotopic conditions to a wide range of light intensities, following which the retinas were processed for histological analysis. Retinal sensitivity is higher in oilbirds than in common pauraques. Under scotopic conditions with maximum flash luminance, the average (+/- 95% CI) b-wave amplitude of oilbirds is double that of common pauraques (500.4 +/- 49.8 and 245.4 +/- 40.9 microV, respectively) but, under photopic conditions, the results are the reverse (common pauraque: 69.4 +/- 18.1; oilbird: 23.0 +/- 4.4 microV). On the other hand, the retina of both species is highly rod-dominated, but rods are highly more numerous in oilbirds than in common pauraques (rods:cones ratio: 123:1 and 5:1, respectively). In oilbirds, rods are largely thinner and their outer segments are 1.0 microm in diameter and 18.6 microm in length. They are distributed over various levels in the photoreceptor layers, an arrangement known for deep-sea fishes, but so far unknown for birds. In common pauraques, rods are patchily distributed and their outer segments are 4.0 microm in diameter and 53 microm in length. The oilbirds rod thinness allows more rods per area unit, and thus to catch more photons per area unit under darkness, while the low cone number suggests that the species has poor daytime vision, which concurs with the species cavernicolous daytime habits. The lower rod number of common pauraques, compared to oilbirds, appears counterbalanced by their patchiness and longer and thicker outer segments to provide high retinal sensitivity. In addition, common pauraques also have a tapetum. These features, combined with a higher proportion of cones, show that common pauraques are well equipped for crepuscular and nocturnal foraging on flying insects in an open environment.

Activity Cycles↗
PubMed1999

Diurnal and nocturnal visual capabilities in shorebirds as a function of their feeding strategies.

Some shorebird species forage with the same feeding strategy at night and during daytime, e.g. visual pecking in the Wilson's Plover (Charadrius wilsonia) or tactile probing in the Short-billed Dowitcher (Limnodromus griseus). The American Woodcock (Scolopax minor) uses tactile probing, by day and by night, but sometimes pecks for insects during daytime. The Black-winged Stilt (Himantopus himantopus) is a visual pecker, both by day and by night, and sometimes forages tactilely on windy (agitated water surface) moonless nights. Territorial Willets (Catoptrophorus semipalmatus) are visual peckers during daylight and on moonlight conditions but switch to tactile feeding under lower light conditions. It could be postulated that some shorebird species would switch from visual feeding during daytime to tactile foraging at night because they have poor night vision compared to species that are always sight foragers irrespective of the time of the day. This issue was examined by comparing retinal structure and function in the above species. Electroretinograms (ERGs) were obtained at different light intensities from anesthetized birds, and the retinae were processed for histological observations. Based on ERGs, retinal sensitivity, and rod:cone ratios, both plovers and stilts are well adapted for nocturnal vision. Although they have low rod density compared to that of stilts and plovers, Willets and woodcocks have a scotopic retinal sensitivity similar to that of stilts and plovers but rank midway between plovers and dowitchers for the b-wave amplitude. Dowitchers have the lowest scotopic b-wave amplitude and retinal sensitivity and appear the least well adapted for night vision. Based on photopic ERGs and cone densities, although stilts, Willets and dowitchers appear as well adapted for daytime vision, plovers occupy the last rank of all species examined. Compared to the nighttime tactile feeders and those that switch from daytime visual pecking to tactile feeding at night, nighttime sight feeders have a superior rod function and, consequently, potentially superior nocturnal visual capabilities.

Animals↗
PubMed1996

Late-onset infections of infants in neonatal units.

OBJECTIVE: To examine regional variations in the incidence of late-onset neonatal infections in Australian and New Zealand neonatal units. METHODOLOGY: A longitudinal, prospective surveillance study of systemic sepsis (septicaemia or meningitis) in 11 neonatal units: 10 in the Australian States of the Northern Territory, New South Wales, Queensland, Victoria and Western Australia, and 1 in Christchurch, New Zealand. The results are reported of late-onset neonatal infection (defined as sepsis after 48 h) for the second year of prospective surveillance, data being collected from 1 October 1992 to 30 September 1993. RESULTS: Data were available on 24535 live births in Australia, representing approximately 10% of all live births in the country. There were 320 episodes of sepsis in Australian units affecting 294 babies. One hundred of these episodes (31%) were early-onset; 3.0% of babies admitted to six tertiary care neonatal units attached to maternity hospitals developed late sepsis, and this rate did not differ between units. The proportion of babies infected was inversely related to birthweight: 22.6% of babies under 1OOOg, but 0.6% over 2000g. Coagulase negative staphylococci were the commonest cause of late-onset sepsis. There were 26 episodes of S. aureus septicaemia, of which only one was due to MRSA. Meningitis occurred in 13 babies (5.9%) with late-onset sepsis. The mortality from late-onset sepsis was 7.7%. CONCLUSIONS: Coagulase-negative staphylococci are the commonest cause of late-onset sepsis of babies in neonatal units. There were no major regional differences in the incidence of, or the organisms causing, late sepsis.

Australia↗
PubMed1996

Impacts of training of village health volunteers in reduction of morbidity from acute respiratory infections in childhood in southern Thailand.

In 1990, the Ministry of Public Health of Thailand started a five-year education program on management of cases with acute respiratory infection (ARI). The objective of this-study was to test whether such a program could reduce the average number of sick days of the target children. 30 villages in the study district were randomly allocated into 15 study and 15 control villages. A 2-day training workshop for village health volunteers from the study villages was conducted. The cohort of children age below 5 years in the two areas were followed-up for 19 week in the peak season of the disease. Among the 664 and 649 target children with 67,083 and 67,984 child-days observed in the study and the control villages, 71 and 41 children, respectively, were free from any episode. The preventive odds ratio of treatment adjusted for age and village effects = 0.88, 95% (CI 0.4-1.95). The median of the average sick periods in the individuals were 27 and 34 days, respectively. After adjusting for age, episodes/month and locality, the ratio of average sick days between children in the study and control villages was 0.89 (95% CI 0.76-1.05) or 11% shorter duration without statistical significance. The adjusted odds ratios of visiting the health center, private clinics, the community hospital and provincial hospital were 0.95 (95% CI 0.69-1.25), 1.43 (95% CI 0.98-2.11), 2.01 (95% CI 1.06-3.82) and 4.71 (95% CI 1.50-14.8), respectively. The training program thus had rather little impact on morbidity of the disease but tended to promote utilization of higher level of health services by the affected children.

Acute Disease↗
PubMed1995

Evaluation of interphase fluorescence in situ hybridization on direct hematological bone marrow smears.

Traditional cytogenetic analysis from bone marrow aspirates is time consuming and frequently suboptimal due to poor viability of cells in culture. Fluorescence in situ hybridization (FISH) with appropriate DNA probes is a potential alternative to routine cytogenetics. Our study examined the reliability of uptake of specific alpha satellite centromere probes from chromosome 18 (D18Z1) and X (DXZ1) and the Yq heterochromatin (pHY3.4) directly from routine hematological bone marrow smears. Altogether 34 separate hybridizations, performed on slides from 20 patients, were scored for fluorescence signals. Cells in interphase were examined with each probe using unstained slides. In addition Giemsa stained slides were destained and then used for interphase FISH. Between 412 and 631 cells were scored for the expected number of signals; 2 for the 18 centromere, 2 for the X centromere in females, one signal for the Yqh in males. The results showed the expected number of signals in 87-97% of cells with the 18 and X probes and 95-97% of cells with the Y probe. Interphase FISH is a reliable, reproducible technique for use on direct bone marrow smears.

Aneuploidy↗
PubMed1982

Potency enhancement of a GnRH agonist: GnRH-receptor microaggregation stimulates gonadotropin release.

Binding of gonadotropin releasing hormone (GnRH, pyro-Glu1-His2-Trp3-Ser4-Tyr5-Gly6-Leu7-Arg8-Pro9-Gly-NH210) to its plasma membrane receptor is the first step leading to pituitary luteinizing hormone (LH) release. In the present study, we have prepared the ethylene glycol bis(succinimidyl succinate) (EGS) dimer of a GnRH agonist, D-Lys6-GnRH; that is, (D-Lys6-GnRH)-EGS-(D-Lys6-GnRH). The bridge length of the EGS is about 15A. This dimer stimulates LH release from pituitary cultures with full efficacy but slightly less potency than D-Lys6-GnRH indicating that the dimerization merely restricts the action of each molecule of D-Lys6-GnRH with respect to the other. When a concentration of the dimer, which alone is too low to evoke substantial LH release, is incubated with pituitary cell cultures in the presence of antibody (AB) against D-Lys6-GnRH, considerable potency enhancement occurs. LH release in response to the AB-dimer conjugate requires extracellular Ca2+ and is blocked by Pimozide. The monovalent form (i.e. reduced pepsin fragment) of AB is ineffective in stimulating release. The addition of antibody to the dimer appears to confer the ability to cross-link receptors and indicates that receptor microaggregation as such is sufficient to activate the effector system in these cells and evoke release.

Animals↗
PubMed1980

Decreased vasopressin content in brain stem of rats with spontaneous hypertension.

The content of arginine vasopressin in the brain stem and neurohypophysis of adult spontaneously hypertensive rats was measured by radioimmunoassay and the values were compared to those measured in normotensive Wistar-Kyoto rats. In the brain stem of hypertensive rats, AVP content was decreased by 77% while neurohypophyseal AVP content was increased by 26%. The results demonstrate that brain stem AVP levels and neurohypophyseal AVP levels may change differentially and they are consistent with the possibility that brain stem AVP may be involved in altering cardiovascular reflex activity.

Animals↗
PubMed1980

Interaction of lysophosphatidylcholine with phosphatidylcholine bilayers. A photo-physical and NMR study.

Several photo-physical methods together with 31P-NMR have been used to investigate the effect of lysophosphatidylcholine on phosphatidylcholine bilayers. 31P-NMR shows that the permeability of the vesicle to Eu3+ increases sharply above approx. 40% lysophosphatidylcholine: fluorescence-quenching studies also show this type of behavior. Similar sharp changes in vesicle properties are observed via the photo-physical technique at this lysophosphatidylcholine/phosphatidylcholine composition. Fluorescence spectra of pyrene and pyrene carboxaldehyde show that increasing lysophosphatidylcholine composition increases the polarity of the environments of these probes up to 40% lysocompound. Above this composition the photo-physical properties of the probes slowly revert to those characteristic of the micellar lyso-compound. The pyrene fluorescence lifetime, the fine structure of the fluorescence, and the case of formation of pyrene excimer in these bilayer mixtures suggest that pyrene complexes weakly with the charged nitrogen of the choline group of the phosphatidylcholine and that the physical state of the system has a striking effect on this complexation process. Similar experiments with simple quaternary compounds lend strong support to this suggestion. The studies monitor in several ways the effect of bilayer composition on movement of molecules in these systems. The degree or site of solubilization of carcinogens is also uniquely affected by composition.

Kinetics↗
PubMed1976

An assessment of the therapeutic potential of azapropazone in rheumatoid arthritis.

A trial to compare the therapeutic potential of 1200 mg. azapropazone daily with 3.9 g. aspirin daily was carried out in 108 out-patients with rheumatoid arthritis over a 14-day period. Analysis of results from the 85 patients with completed assessment data (49 on azapropazone; 36 on aspirin) showed that azapropazone was better than aspirin from the point of view of pain relief, number of days patients were withdrawn prematurely from the trial, and patient satisfaction with treatment. The differences, however, were not statistically significant. The authors compare the results obtained in this trial with those obtained previously from trials with 13 other antirheumatic drugs using the same method.

Administration, Oral↗