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R S Young

Publications and source records attributed to R S Young.

At least 37 records · Page 2Linked to original sources
PubMed1998

Evidence for genetic heterogeneity in X-linked congenital stationary night blindness.

X-linked congenital stationary night blindness (CSNB) is a nonprogressive retinal disorder characterized by disturbed or absent night vision; its clinical features may also include myopia, nystagmus, and impaired visual acuity. X-linked CSNB is clinically heterogeneous, and it may also be genetically heterogeneous. We have studied 32 families with X-linked CSNB, including 11 families with the complete form of CSNB and 21 families with the incomplete form of CSNB, to identify genetic-recombination events that would refine the location of the disease genes. Critical recombination events in the set of families with complete CSNB have localized a disease gene to the region between DXS556 and DXS8083, in Xp11.4-p11.3. Critical recombination events in the set of families with incomplete CSNB have localized a disease gene to the region between DXS722 and DXS8023, in Xp11.23. Further analysis of the incomplete-CSNB families, by means of disease-associated-haplotype construction, identified 17 families, of apparent Mennonite ancestry, that share portions of an ancestral chromosome. Results of this analysis refined the location of the gene for incomplete CSNB to the region between DXS722 and DXS255, a distance of 1.2 Mb. Genetic and clinical analyses of this set of 32 families with X-linked CSNB, together with the family studies reported in the literature, strongly suggest that two loci, one for complete (CSNB1) and one for incomplete (CSNB2) X-linked CSNB, can account for all reported mapping information.

Female↗
PubMed1998

Something in the air: endotoxins and glucans as environmental troublemakers.

This review provides a clear explanation of the current status of two common airborne contaminants, lipopolysaccharide and (1-->3)-beta-D-glucan, in the induction of indoor air-related disease. A full description of the origin of these two products is given together with information of their structure and function. Details of the biochemical mechanisms by which they interact with human cells and the physiological consequences of these interactions are outlined. Both compounds play a key role in the induction of airway inflammation and this paper highlights the environmental importance in the work place and home of these inhaled agents in terms of respiratory disease.

Air Pollution, Indoor↗
PubMed1996

A chromatic-cancellation property of human pupillary responses.

The pupil exhibits a response property somewhat analogous to perceptual red-green cancellation. Across a limited range of flash intensities near threshold, pupillary constrictions evoked by red flashes can be reduced, if not nulled, by the simultaneous addition of a green flash. The percentage of trials on which a stimulus-evoked response can be correctly discriminated from noise also falls to chance level as a green flash is added to the red flash. In terms of the quanta absorbed by L and M cones, the cancellation can be modelled as a function of magnitude of 0.65*L-M.

Algorithms↗
PubMed1995

Nature of the pupillary responses evoked by chromatic flashes on a white background.

Color flashes on a steady-white background are classically used to isolate the response of the chromatic (color-opponent), as opposed to achromatic (luminance), channel in psychophysical investigations. The present study shows that pupillary responses evoked by such stimuli behave as if they are composed of functionally separable components. One component has a temporally transient waveform and has an action spectrum that is similar to the spectral sensitivity curve of the psychophysical chromatic channel. The present study discusses the possibility that the pupillary response is mediated by phasic (M-like) neurons and/or by tonic (P-like) neurons.

Color Perception↗
PubMed1995

A pupillometric correlate of scotopic visual acuity.

While not easily fit into the classic descriptions of the pupillary light reflex, previous studies reported that changes in the spatial composition of the retinal image can evoke a pupillary response. The present study extends this observation by showing that the pupil constricts in response to scotopic as well as photopic spatial patterns. Moreover, the amplitude of the scotopic response decreases with increasing spatial frequencies suggesting a pupillary spatial acuity of about 3 c/deg. The scotopic pupil acuity is similar to the scotopic perceptual visual acuity measured in the same observers.

Adult↗
PubMed1994

Deletion 5q35.3.

We report on a 15-month-old boy with a de novo deletion of the terminal band of 5q, macrocephaly, mild retrognathia, anteverted nares with low flat nasal bridge, telecanthus, minor earlobe anomalies, bell-shaped chest, diastasis recti, short fingers, and mild developmental delay.

Abnormalities, Multiple↗
PubMed1994

Deletion (2)(q37).

We report on a 5-month-old girl with widely spaced nipples, redundant nuchal skin, coarctation of the aorta, anal atresia with distal fistula, postnatal growth retardation, hypotonia, and sparse scalp hair. Initial clinical assessment suggested the diagnosis of Ullrich-Turner syndrome. Chromosome analysis showed a 46,XX,del(2)(q37) karyotype in peripheral lymphocytes. We compare her findings to those of other reported patients with terminal deletions of 2q.

Chromosome Deletion↗
PubMed1993

Trisomy 22 confirmed by fluorescent in situ hybridization.

We report on a newborn girl with multiple congenital anomalies, whose G-banded chromosome analysis showed complete trisomy 22. Chromosome painting using a whole-chromosome painting probe for chromosome 22 confirmed that neither chromosome 22 was involved in a cryptic translocation.

Abnormalities, Multiple↗
PubMed1993

Fryns syndrome.

We report on a premature female infant with Fryns syndrome who had several less commonly reported anomalies. She had bilateral posterior eventration of the hemidiaphragms instead of the usual diaphragmatic defects with visceral herniation into the chest cavity. She also had a unilateral cleft lip, camptodactyly, duodenal atresia, tracheomalacia, bronchomalacia, and Tetralogy of Fallot.

Abnormalities, Multiple↗
PubMed1993

Transient and sustained components of the pupil response evoked by achromatic spatial patterns.

The present study provides new clues about visual processes underlying the human pupillary responses evoked by achromatic spatial patterns. The pupillary responses can be modeled as a combination of two processes, a temporally transient process which saturates with increasing contrast and a temporally sustained process which varies linearly with increasing grating contrast. The transient process has low-pass, whereas the sustained process has a middle band-pass spatial filter characteristic. the results support the hypothesis that the visual input to the pupillomotor nuclei is composed of phasic and tonic visual neurons that are functionally similar to those in the magno (M)- and parvo (P)- cellular layers in the lateral geniculate nucleus.

Adult↗
PubMed1993

Transient and sustained components of the pupillary responses evoked by luminance and color.

That the pupil reacts to changes in luminance and color, as well as to spatial features in the retinal image raises questions about whether phasic and tonic and/or color and luminance visual pathways project to the pretectal pupillomotor neurons. The present study compares pupillary responses evoked by heterochromatic and achromatic luminance increments to investigate whether the pupillary responses evoked by color and by luminance are independent of one another. Principal component analysis is used to examine the constituents of the pupil responses. The results support the belief that the visual input to the pupillomotor system is organized into phasic and tonic (but not necessarily independent color and luminance) pathways.

Adult↗
PubMed1993

Effect of anoxia on excitatory amino acids in brain slices of rats and turtles: in vitro microdialysis.

Using in vitro microdialysis, we tested the hypothesis that anoxia-induced release of excitatory amino acids is greater in adult rat brain than in turtle brain. Ten minutes of anoxia produced significant elevation of glutamate (from 0.39 +/- 0.03 to 0.90 +/- 0.18 microM dialysate, means +/- SE, P < 0.05), aspartate (from 0.28 +/- 0.12 to 1.20 +/- 0.49 microM, P < 0.05), glycine, and alanine in the rat brain slice. During reoxygenation, alanine and glycine returned toward baseline values, whereas aspartate and glutamate remained elevated. In contrast, prolonged anoxia (60 min) in the turtle brain slice resulted in only minimal increase in aspartate (from 0.06 +/- 0.01 to 0.09 +/- 0.02 microM, P < 0.05) and, interestingly, a decrease in glutamate (from 0.50 +/- 0.11 to 0.33 +/- 0.09 microM, P < 0.05). Levels of glycine, alanine, and taurine were unchanged. We conclude that oxygen deprivation causes marked increase in excitatory amino acids in the anoxia-sensitive rat brain slice, while oxygen deprivation for an even longer period of time in the turtle brain slice produces substantially less change. We speculate that the difference in sensitivity to anoxia between rat and turtle is at least partly attributable to the major difference in interstitial levels of excitotoxic amino acids during oxygen deprivation.

Alanine↗
PubMed1993

Effect of experimental Escherichia coli meningitis on concentrations of excitatory and inhibitory amino acids in the rabbit brain: in vivo microdialysis study.

Excessive extracellular fluid concentrations of the amino acids glutamate and aspartate play an important role in the pathogenesis of neuronal cell damage during hypoxia, hypoglycemia, and seizure. The purpose of these investigations was to test the hypothesis that bacterial meningitis causes progressive increase in excessive extracellular fluid concentrations of excitatory and inhibitory neurotransmitters. To test this hypothesis, Escherichia coli was injected intracisternally in juvenile rabbits after which neurotransmitter concentrations were measured with in vivo microdialysis. The data showed significant elevation of the excitatory amino acids aspartate and glutamate, as well as of the inhibitory neurotransmitters gamma-amino butyric acid and taurine in the excessive extracellular fluid of animals injected with E. coli compared with control animals injected with saline. However, concentrations of these excitatory and inhibitory amino acids rose late in the course of meningitis, at a time when the animals were hypotensive (mean blood pressure < or = 40 mm Hg). These data show that the major increase in excitatory neurotransmitters during experimental meningitis occurs in association with the cerebral ischemia produced by septic shock rather than being produced by the meningitis itself.

Amino Acids↗
PubMed1993

Reading with rods: the superiority of central vision for rapid reading.

PURPOSE: To investigate why the central portion of the visual field is normally the optimal region for pattern recognition. METHOD: The study uses a reading paradigm in which the text can only be seen with rod vision. Reading rates were measured as the text was positioned in different parts of the visual field. RESULTS: Observers obtained the highest reading rates when rod-generated images were viewed at or near the fovea. CONCLUSION: The superiority of the central field for reading is neither linked to some exclusive property of the cone visual system, nor is it primarily related to visual sensitivity or spatiotemporal resolution. The superiority of reading in the central field is associated with some aspect of the visual cortical processes.

Adult↗