Biomedical subjects

S A McFadden

Publications and source records attributed to S A McFadden.

4 recordsLinked to original sources

PubMed1996

Phenotypic variation in xenobiotic metabolism and adverse environmental response: focus on sulfur-dependent detoxification pathways.

Proper bodily response to environmental toxicants presumably requires proper function of the xenobiotic (foreign chemical) detoxification pathways. Links between phenotypic variations in xenobiotic metabolism and adverse environmental response have long been sought. Metabolism of the drug S-carboxymethyl-L-cysteine (SCMC) is polymorphous in the population, having a bimodal distribution of metabolites, 2.5% of the general population are thought to be nonmetabolizers. The researchers developing this data feel this implies a polymorphism in sulfoxidation of the amino acid cysteine to sulfate. While this interpretation is somewhat controversial, these metabolic differences reflected may have significant effects. Additionally, a significant number of individuals with environmental intolerance or chronic disease have impaired sulfation of phenolic xenobiotics. This impairment is demonstrated with the probe drug acetaminophen and is presumably due to starvation of the sulfotransferases for sulfate substrate. Reduced metabolism of SCMC has been found with increased frequency in individuals with several degenerative neurological and immunological conditions and drug intolerances, including Alzheimer's disease, Parkinson's disease, motor neuron disease, rheumatoid arthritis, and delayed food sensitivity. Impaired sulfation has been found in many of these conditions, and preliminary data suggests that it may be important in multiple chemical sensitivities and diet responsive autism. In addition, impaired sulfation may be relevant to intolerance of phenol, tyramine, and phenylic food constituents, and it may be a factor in the success of the Feingold diet. These studies indicate the need for the development of genetic and functional tests of xenobiotic metabolism as tools for further research in epidemiology and risk assessment.

Carbocysteine↗

PubMed1987

The binocular depth stereoacuity of the pigeon and its relation to the anatomical resolving power of the eye.

The stereoacuity of the pigeon was measured by finding the smallest depth difference discriminable between two arrays of elements, each array confined to one of two parallel planes in space. For both the human and the pigeon, the depth between the two planes was not discriminable under stationary monocular conditions. The mean binocular depth acuity for five human subjects was 4 arc sec, reflecting hyperacuity. In the pigeon, the binocular stereoacuity was between 0.8-1.8 arc min, allowing each eye to discriminate a visual angle of at most 0.89 min of arc. This value is less than the anatomical resolving power of the retina as predicted by sampling theory. The area of the pigeon retina involved in this binocular depth judgement is likely to be the area dorsalis, a specialised region that does not contain a fovea. The pigeon is a granivorous bird with laterally placed eyes, thus we demonstrate that lifestyle and binocular field width do not predict stereoscopic vision quality.

Animals↗

PubMed1986

Binocular depth perception in the pigeon.

By means of a discrete-trial simultaneous discrimination procedure, pigeons were trained to respond differentially to visual arrays that were identical except that one of them contained a circle displaced in depth when viewed stereoscopically. Performance was severely disrupted when one eye was occluded. The monocular deficit was peculiar to the depth task, inasmuch as no such decrement was seen on a pattern discrimination. The results imply that presence of the displaced circle was discriminated on the basis of a binocular cue. It was also found that pigeons could discriminate the direction of the displacement. Discrimination of depth was independent of the global form and still occurred when elements of the array were randomly displaced in depth. Performance was not disrupted when the absolute convergence angle of the depth stimulus was changed. The cue that consistently accounted for the behavior seen was the detection of the relative angles of convergence--that is, the retinal disparity of the two planes in depth. Thus, despite the lateral position of the eyes of the pigeon, a small binocular field mediates the binocular discrimination of near objects in depth.

Animals↗

PubMed1985

A further look at the binocular visual field of the pigeon (Columba livia).

The binocular visual field of the pigeon, measured ophthalmoscopically, is ovoid in shape. It is 114 degrees in vertical extent and centered and widest (37 degrees) about the eye-beak axis (i.e. the line passing through the straight edge of the beak and the midpoint of a line connecting the centres of the pupils). The area dorsalis projects 10 degrees-15 degrees below the eye-beak axis where the field is 35 degrees wide. The stereotyped peck response of the pigeon entails birds pausing twice. At the first fixation, the image of a grain is on the area dorsalis and at the final fixation the grain is centered within the widest part of the binocular field.

Animals↗