Search PubMed⌕ Search

Biomedical subjects

S R Young

Publications and source records attributed to S R Young.

At least 55 records · Page 3Linked to original sources
PubMed1986

Embryogenesis of arborization pattern and topography of individual axons in N. laminaris of the chicken brain stem.

This study examined the development of individual axon terminal fields in n. laminaris (NL) of the chicken brainstem. In their mature form axons from the nucleus magnocellularis (NM), second-order auditory neurons in the chicken brainstem, project bilaterally onto the NL. Axons from the ipsilateral and contralateral NM neurons form spatially segregated, elongated arbors in the dorsal and ventral neuropil of NL, respectively. The long axes of these arbors correspond to physiologically defined isofrequency bands. To assess the development of this stereotyped arborization pattern, 6-17-day embryonic chicken brain stems were maintained in vitro while injecting horseradish peroxidase into small groups of axons. Three-dimensional reconstructions were made from serial sections and projected onto a cartesian plane for quantitative analyses. At embryonic day 6 (E6), the ventral axons already course beneath the recently migrated NL neurons. The arrival of the dorsal NM axon branches is delayed and their paths are indirect. They first loop dorsally into the the ventricular layer, where they seem to make specific connections with migrating NL neurons and use these as guides to their appropriate positions in the NL. During the period from E9 to E17 the dorsal and ventral terminal fields become similar, each adopting properties of the other's initial pattern. The dorsal terminal fields extend to form bands similar to the early ventral terminal fields, while the ventral terminal fields narrow and appear to shift position in order to achieve the tonotopic specificity characteristic of the early dorsal terminal fields. The results show that a complex, mature pattern of neuronal connections can be formed during development by the combination and reorganization of two simple patterns--each shaped, in turn, by its respective axonal trajectory.

Animals↗
PubMed1985

Results of a double running suture in penetrating keratoplasty performed on keratoconus patients.

Parallel running 10-0 and 11-0 nylon sutures were used in 76 consecutive penetrating keratoplasties on patients with keratoconus. Removal of the 10-0 suture at eight to 12 weeks allowed for early visual rehabilitation postoperatively. The use of various trephine sizes and the use of a bridle suture versus a scleral ring were evaluated by several visual parameters. The incidence of complications with the double running suture was not greater than that obtained with other suture techniques.

Astigmatism↗
PubMed1984

The eye of the humboldt penguin, Spheniscus humboldti: visual fields and schematic optics.

Construction of a schematic eye indicates that the eye of Spheniscus humboldti is aquatic in design. The lens has a power of 100 dioptres (D) while (in air) the cornea has a power of 29 D. In air, the eye is myopic (approximately 28 D) but in water it is emmetropic. Minimum pupil size would seem insufficient to allow the pupil to function as a stenopaic aperture and increase depth of focus sufficiently to overcome the eye's aerial myopia. Entry into water reduces maximum image brightness by approximately three times. In air, the maximum width of the retinal binocular field is 45 degrees and this occurs approximately 10 degrees above the line of the bill. The bill intrudes into the retinal field and binocular field width in the plane containing the bill and the optic axes is 28 degrees. The vertical extent of the binocular field is 125 degrees. In the plane containing the optic axes the cyclopean field equals 282 degrees and the optic axes diverge by 116 degrees. In this plane the mean uniocular field is 155 degrees with the temporal hemifield approximately 11 degrees larger than the nasal hemifield. Entry into water reduces the widths of the visual fields such that maximum binocular field width is only 17 degrees and the vertical extent is reduced to about 80 degrees. Binocular vision is lost in the plane of the bill, and the uniocular retinal field is reduced by 32 degrees and the cyclopean field by 36 degrees.

Air↗
PubMed1984

Optics of retinal oil droplets: a model of light collection and polarization detection in the avian retina.

A wave optical model was used to analyse the scattering properties of avian retinal oil droplets. Computations for the near field region showed that oil droplets perform significant light collection in cone photoreceptors and so enhance outer segment photon capture rates. Scattering by the oil droplet of the principal cone of a double cone pair, combined with accessory cone dichroic absorption under conditions of transverse illumination, may mediate avian polarization sensitivity.

Animals↗
PubMed1983

The results of one thousand consecutive prenatal diagnoses.

From 1976 to 1982, prenatal diagnosis was performed on more than 1,000 patients at the Richland Memorial Hospital. This report analyzes the experience of our unit with the first 1,000 consecutive studies. The integration of geneticist and clinician is stressed. A total of 77.7% of referrals were because of maternal age with the next most common indication being a prior child with a neural tube defect. There were 18 chromosomal abnormalities discovered, and no cases of open neural tube defect were detected. In all cases of elective termination of pregnancy in which follow-up was possible, the diagnosed abnormality was confirmed.

Adult↗
PubMed1983

The retinal binocular field of the pigeon (Columba livia: English racing homer).

An ophthalmoscopic reflex technique has shown that in sedated pigeons maximum retinal binocular field width occurs approximately 20 degrees above the bill. The binocular field has a maximum width of 27 degrees and extends vertically by 130 degrees (90 degrees above the bill, 40 degrees below it). Both the bill and cere intrude into the binocular field. Maximum optical binocularity also occurs approximately 20 degrees above the bill. The plane containing the optic axes of each eye coincides with the bill.

Animals↗
PubMed1983

Frequency-specific projections of individual neurons in chick brainstem auditory nuclei.

Nucleus magnocellularis and nucleus laminaris in the avian brainstem contain second- and third-order auditory neurons thought to be homologous to the mammalian anteroventral cochlear nucleus and medial superior olivary nucleus, respectively. Nucleus laminaris in the chicken is a tonotopically organized sheet of bipolar neurons; each of these neurons receives spatially segregated bilateral innervation from the two magnocellular nuclei. In the present study, this projection was studied at the single cell level by analyzing the pattern of terminal arborizations of individual horseradish peroxidase-filled axons. Reconstruction of the terminal arborizations of nucleus magnocellularis axons revealed that each axon forms an elongated band of endings, the long axis of which is parallel to the physiologically defined isofrequency bands. Within a band, the individual terminal collaterals form distinct patches separated by areas without endings. We suggest that the elongated terminal fields provide the basis of the tonotopic organization observed in nucleus laminaris and that the trajectories of the ipsilateral and contralateral axons may provide differential conduction delays that are important for binaural integration of acoustic information.

Animals↗
PubMed1982

Immune function in pure iron deficiency.

Immunologic studies were performed in ten iron-deficient children, aged 12 to 30 months, before and after iron replacement. Chronic infection, malnutrition, and vitamin deficiency were excluded. Mean hemoglobin levels went from 8.2 +/- 0.2 (SEM) to 12.3 +/- 0.3 g/dL after iron replacement. Mean T-cell percentage increased from 50% +/- 3.0% to 58% +/- 3.7%. Absolute numbers of T cells were unchanged. Three children converted negative in vitro proliferative responses to Candida or tetanus antigen. Mean stimulation indexes increased for Candida (6.8 +/- 1.7 to 17.9 +/- 6.7) and tetanus (19.5 +/- 6.0 to 31.7 +/- 8.5). Nine of 16 delayed hypersensitivity skin tests were positive before and ten of ten were positive after iron therapy. The IgG and IgA levels did not change significantly, but IgM levels decreased from 181 +/- 13 to 128 +/- 5 mg/dL. We conclude that T-cell immunity is slightly impaired in pure iron deficiency and that these subtle defects can be corrected with oral iron replacement.

Anemia, Hypochromic↗
PubMed1978

Confirmation of regional assignment of nucleoside phosphorylase (NP) on chromosome 14 by gene dosage studies.

Gene dosage studies yielded results consistent with assignment of the locus for nucleoside phosphorylase to band 14q13. The red blood cells from a patient with the karyotype 47,XX,+der(14),t(8;14)(8qter leads to 8q24::14q21 leads to 14pter)pat had enzyme activity 50% higher than red cells from 47 normal controls, two trisomies involving chromosomes other than 14, and five balanced translocations involving chromosome 14. On the other hand, the red cells of a case with a karyotype 45,XX,-14,-22+der(22),t(14;22)(14qter leads to 14q11 or 14q12::22p11 leads to 22qter)mat and a case with a a karyotype 47,XX,+der(14),t(14;16)(14pter leads to 14q11::16q24 leads to 16qter)mat had normal activity

Child, Preschool↗