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Biomedical subjects

J B Phillips

Publications and source records attributed to J B Phillips.

At least 37 records · Page 2Linked to original sources
PubMed1995

Characterization of an ultraviolet photoreception mechanism in the retina of an amphibian, the axolotl (Ambystoma mexicanum).

Spectral sensitivity measurements from the retina of the Mexican salamander Ambystoma mexicanum (the 'axolotl') were used to provide evidence for and to characterize an amphibian ultraviolet-sensitive photoreception mechanism. Electroretinograms (transretinal voltage responses) were recorded from open eye cup preparations to analyze the spectral sensitivity of the retina. Both dark-adapted and white light-adapted preparations exhibited a peak in sensitivity between 360-370 nm. Under selective chromatic adaptation with long-wavelength light the eye cups continued to exhibit a peak sensitivity around 360 nm. These data confirm the presence of ultraviolet-sensitive cones in the retina of Ambystoma salamanders. The possible relevance of these results to the development and behavior of this group of salamanders is briefly discussed.

Ambystoma mexicanum↗
PubMed1994

Gas chromatographic column for the storage of sample profiles.

The concept of a sample retention column that preserves the true time profile of an analyte of interest is studied. This storage system allows for the detection to be done at convenient times, as opposed to the nearly continuous monitoring that is required by other systems to preserve a sample time profile. The sample storage column is essentially a gas chromatography column, although its use is not the separation of sample components. The functions of the storage column are the selective isolation of the component of interest from the rest of the components present in the sample and the storage of this component as a function of time. Using octane as a test substance, the sample storage system was optimized with respect to such parameters as storage and readout temperature, flow rate through the storage column, column efficiency and storage time. A 3-h sample profile was collected and stored at 30 degrees C for 20 h. The profile was then retrieved, essentially intact, in 5 min at 130 degrees C.

Atmosphere↗
PubMed1994

MRI cisternography, and the localization of CSF fistulae.

Accurate localization of CSF fistulae not only makes the planning of surgery easier, but it also increases the chances of successful dural repair and eliminates negative exploration. CSF fistulae localization has been a problem for many years, and several methods have been used to pin-point the site of CSF leakage with variable degree of success. Recently, contrast CT cisternography (CCTC) has replaced radio-isotope cisternography (RIC) in many centres. However, both methods are invasive, time consuming, contraindicated in patients with intracranial mass lesions and insensitive in detecting inactive CSF leaks. Furthermore, in both, ionizing radiation is used and both techniques may lead to allergic reactions or seizures. On the other hand, T2-weighted Magnetic Resonance Imaging (MRI) shows the CSF as a high signal without the need to inject contrast media intrathecally. Furthermore, MRI demonstrates the intracranial anatomy and pathology in detail in multiple planes within a relatively short time. MRI does not involve ionizing radiation and therefore is safely repeatable. MRI using T2-weighted sequences should be an ideal tool to locate precisely the site of CSF fistulae. This paper describes our experience with MRI cisternography in CSF fistulae localization. Eleven patients with inactive CSF fistulae were investigated. MRI cisternography localized the site of fistula in each case. All patients were explored surgically and the site of CSF fistula was confirmed and repaired intradurally with a pericranial graft and fibrin glue without recurrence or meningitis.

Adolescent↗
PubMed1993

Scotopic spectral sensitivity of the optomotor response in the green treefrog Hyla cinerea.

Amphibians are unusual among vertebrates in having two spectral classes of rod photoreceptors, unique amphibian "green" rods and typical vertebrate "red" rods. Although amphibians have been the subject of extensive research on visual function, it is not known whether possession of two classes of rods is a general feature of Amphibia, nor is it clear to what behaviors each class of rods contributes. The Hylidae comprise one of the largest families within Amphibia but have been little studied with respect to visual function. Here, we demonstrate the presence of green and red rods in Hyla cinerea by microspectrophotometry and provide evidence for the contribution of green rods to one visually based behavior, the optomotor response. In addition, we discuss the role of green and red rods in visually based behavior in light of apparently conflicting demands resulting from the need to maximize absolute sensitivity, visual acuity, and color sensitivity.

Animals↗
PubMed1993

Wavelength-dependent effects of light on magnetic compass orientation in Drosophila melanogaster.

1. Wildtype Oregon-R Drosophila melanogaster were trained in the ambient magnetic field to a horizontal gradient of 365 nm light emanating from one of the 4 cardinal compass directions and were subsequently tested in a visually-symmetrical, radial 8-arm maze in which the magnetic field alignment could be varied. When tested under 365 nm light, flies exhibited consistent magnetic compass orientation in the direction from which light had emanated in training. 2. When the data were analyzed by sex, males exhibited a strong and consistent magnetic compass response while females were randomly oriented with respect to the magnetic field. 3. When tested under 500 nm light of the same quantal flux, females were again randomly oriented with respect to the magnetic field, while males exhibited a 90 degree clockwise shift in magnetic compass orientation relative to the trained direction. 4. This wavelength-dependent shift in the direction of magnetic compass orientation suggests that Drosophila may utilize a light-dependent magnetic compass similar to that demonstrated previously in an amphibian. However, the data do not exclude the alternative hypothesis that a change in the wavelength of light has a non-specific effect on the flies' behavior, i.e., causing the flies to exhibit a different form of magnetic orientation behavior.

Animals↗
PubMed1991

Necrotizing enterocolitis in very low birth weight infants: biodemographic and clinical correlates. National Institute of Child Health and Human Development Neonatal Research Network.

We studied the occurrence of necrotizing enterocolitis in 2681 very low birth weight infants during an 18-month period to characterize the biodemographic and clinical correlates. Proven necrotizing enterocolitis (Bell stage II and beyond) occurred in 10.1% of study infants; necrotizing enterocolitis was suspected in 17.2% of study infants. Positivity of blood cultures was related to necrotizing enterocolitis staging. The mortality rate increased only for stage III necrotizing enterocolitis (54% died). Logistic regression identified medical center of birth, race, gender, birth weight, maternal hemorrhage, duration of ruptured membranes, and cesarean section as significant risk factors. For one center the odds ratio was 3.7, whereas for another center it was only 0.3. For black boys, the odds ratio was 2.3 relative to nonblack boys; for girls, race did not affect prevalence of necrotizing enterocolitis. Age at onset was related to birth weight and gestational age. Intercenter differences in necrotizing enterocolitis prevalence were related to time required to regain birth weight and other indicators of fluid management. Gram-positive organisms predominated in positive blood cultures for stage I and II necrotizing enterocolitis; enteric bacteria were isolated more frequently in infants with stage III disease. We conclude that necrotizing enterocolitis prevalence varies greatly among centers; this may be related to early clinical practices of neonatal care.

Birth Weight↗
PubMed1991

Olfactory cues perceived at the home loft are not essential for the formation of a navigational map in pigeons.

Deflector lofts consist of a 'pinwheel' arrangement of four stationary deflector panels attached to the sides of a cube-shaped cage. These panels are made of wood and Plexiglas and rotate incoming winds in either a clockwise or counterclockwise direction. When released at a distant site, homing pigeons (Columbia livia) raised in deflector lofts exhibit a shift in orientation relative to controls which corresponds to the clockwise or counterclockwise rotation of winds in their loft, suggesting the involvement of wind-borne olfactory cues in pigeon navigation. As part of a long-term study designed to test whether orientation cues other than odors might also be involved in creating the deflector-loft effect, we carried out experiments in upstate New York, USA, in which deflector lofts were modified to reverse the direction of light reflected from the Plexiglas panels while leaving the rotation of winds unchanged. The results indicate that the orientation of pigeons raised as permanent residents of these altered deflector lofts is not influenced by reflected light cues; i.e. they exhibit the same orientation bias as birds raised in the lofts with normal panels. This is in direct contrast to our previous findings that non-resident pigeons kept in the altered lofts for short periods exhibit a reversal of initial orientation compared to birds from the lofts with normal panels. However, when permanent-resident birds are prevented from having a direct view of the horizon sky by the addition of 'anti-cheating' slats (which prevent the birds from seeing beyond the end of each panel), the deflections are either greatly reduced or eliminated entirely, contrary to the predictions of olfactory navigation models. This disappearance of the deflector-loft effect in the presence of anti-cheating slats suggests that the positions of the deflector panels in the two experimental lofts must be differentially influencing important visual orientation cues reaching the birds housed inside. We believe that these cues are probably derived from polarized skylight emanating from the horizon, and that the obstruction of specific regions of horizon skylight by the deflector panels in the two experimental lofts is responsible for a miscalibration of the pigeon's sun compass. This miscalibration, in turn, generates the orientation bias observed for deflector-loft birds. Our findings force us to conclude that, at least for pigeons raised in New York (and perhaps those from other geographical locations as well), olfactory cues perceived at the home loft do not contribute to the formation of the navigational map.

Animals↗
PubMed1987

An analysis of ambulance accidents in Tennessee.

In an effort to improve our program for ambulance crash and related injury prevention, we analyzed 102 consecutive ambulance accidents. Incidents reported included those that resulted in human injury or in which property damage exceeded $200. Multiple logistic regression was used to determine the association between circumstances reported at the time of the accidents and the risk of injury. Twenty-nine accidents contributed to a total of 65 injured victims, with one death. The variable most strongly associated with the probability of an injury-accident was use of a passenger restraint device. Darkness and occurrence at an intersection were variables showing increased risk, but were not statistically significant. The interaction of variables did not have a combined influence on the incidence of injury. The mean delay to hospital care after an accident was 9.4 minutes. Based on our data, we conclude that passenger restraints for both ambulance attendants and passengers should be mandatory, and we suggest that traffic signals be strictly heeded at intersections and speed limits in urban settings be obeyed.

Accidents, Traffic↗
PubMed1987

Laboratory studies of homing orientation in the eastern red-spotted newt, Notophthalmus viridescens.

The orientation behaviour of adult male eastern red-spotted newts (Notophthalmus viridescens) was studied in laboratory tests. Newts were collected from ponds located 10-30 km from the laboratory, and housed in water-filled, all-glass aquaria located in a greenhouse or outdoors adjacent to the laboratory building. The aquaria were aligned on the magnetic north-south axis. Newts were tested in a dry, enclosed arena in four magnetic fields: the ambient magnetic field (magnetic north at North) and three altered fields (magnetic north rotated to East, West or South). Newts tested during January-March exhibited weak bimodal magnetic orientation along the axis of the holding tank. However, during the spring migratory period (April until early May), the bimodal response shifted to coincide with the direction of the pond from which the newts had been collected. Much stronger unimodal orientation was elicited by elevating the water temperature to 33-34 degrees C immediately prior to testing. If newts were held in a training tank with an artificial shoreline at one end and exposed to elevation of water temperature after several days of stable water temperatures, they exhibited unimodal shoreward orientation and did not show the seasonal switch to homing behaviour observed in the earlier tests. If, however, the elevation of water temperature followed a period of fluctuating water temperature (over a 20 degrees C range), the newts exhibited strong unimodal orientation in the direction of the pond from which they had been collected. These results suggest that newts possess a navigational system that enables them to home from distances in excess of 20 km. Moreover, these experiments provide the first opportunity to examine the sensory basis of navigational ability in any animal under controlled laboratory conditions.

Animals↗
PubMed1986

Two magnetoreception pathways in a migratory salamander.

Male eastern red-spotted newts (Notophthalmus viridescens) under controlled laboratory conditions exhibit unimodal magnetic compass orientation either in a trained compass direction or in the direction of their home pond. If the vertical component of the magnetic field is inverted, newts exhibiting the simple-compass response undergo a 180 degree reversal in orientation, whereas newts orienting in the home direction are unaffected by this treatment. These results indicate that newts use an axial compass mechanism for simple-compass orientation similar to that found in migrating birds. However, a distinct magnetoreception pathway with polar response properties is involved in homing and is possibly linked in some way to the navigational map.

Adaptation, Physiological↗