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Biomedical subjects

D A Samuelson

Publications and source records attributed to D A Samuelson.

47 records · Page 3Linked to original sources
PubMed1984

Maturation of the retina of the canine neonate as determined by electroretinography and histology.

Retinal potentials were obtained by electroretinography from birth to maturity of dogs. Amplitudes, time latency, and flicker fusion frequencies under scotopic conditions were compared to the histologic development of the retina. There was no electroretinogram (ERG) recorded during the 1st week of life, but in the 2nd week, a small negative wave (not exceeding 5 microV) was detected. Small ERG waveforms appeared in dogs at 3 weeks of age; these markedly increased in amplitude and latency between the 3rd and the 4th weeks of age. Additional changes in the ERG amplitudes were evident in the 5th to the 8th weeks of life approximating amplitudes of the adult dog. Similarly, the greatest changes in flicker fusion frequencies occurred between the 3rd and the 5th weeks and the 7th and the 8th weeks. Latency of the a-wave indicated little change in the age groups studied. The greatest decrease in latency occurred in the b- and c-waves between the 3rd and 5th weeks of age. The rod and cone inner and outer segments were first observed microscopically in the 3rd week after the dogs were born. Further differentiation of the rod and cone segments and other retinal layers occurred from the 5th to the 8th weeks.

Aging↗
PubMed1983

Biometry and clinical characteristics of congenital cataracts and microphthalmia in the Miniature Schnauzer.

Forty-two Miniature Schnauzer pups and adults with congenital cataracts and microphthalmia were evaluated by serial ophthalmic examinations, slit lamp biomicroscopic photography, and A-scan ultrasonography. The cataracts were evident when the eyelids opened at 2 weeks, affecting predominantly the lens nucleus and posterior cortex. Lenticonus was evident in 19% of the cataractous lenses. Progression of the cataracts was variable and related to involvement of the equatorial and posterior cortices. Lens-induced uveitis developed in some adult dogs with advanced hypermature cataracts. The globe and lens were smaller than normal in the cataractous eyes, as ascertained by A-scan ultrasonography. Age-matched comparisons of clear lens carrier Miniature Schnauzers and normal Beagles with the cataractous Miniature Schnauzers indicated affected globes and cataractous lenses were reduced 10% to 20% in their anteroposterior lengths. The microphthalmia appeared related to the congenital microphakic cataract.

Animals↗
PubMed1983

Effects of phacoemulsification and extracapsular lens removal on corneal thickness and endothelial cell density in the dog.

Twenty-one dogs were used to study the effects of phacoemulsification and extracapsular lens removal on corneal endothelium and corneal thickness. Specular microscopy revealed preoperative cell morphology and cell densities similar to man. After surgery endothelial cell counts significantly decreased 22% (central) and 13% (periphery) with phacoemulsification and 34% (central) and 31% (periphery) with extracapsular lens removal. Corneal thickness increased with both procedures. Endothelial cell pathology included cellular enlargement, increased pleomorphism, and focal cellular degeneration. Phacoemulsification time did not correlate with the degree of cell loss. Dog corneal endothelium responds to surgical trauma in a manner similar to man and maintains a functional monolayer via cellular enlargement and migration. The dog, therefore, represents a good animal model for the study of corneal endothelial disease in man.

Animals↗
PubMed1983

Inheritance of congenital cataracts and microphthalmia in the Miniature Schnauzer.

Congenital cataracts and microphthalmia in the Miniature Schnauzer were inherited as an autosomal recessive trait. Eighteen matings of affected X affected Miniature Schnauzers resulted in 87 offspring with congenital cataracts and microphthalmia (49 males/38 females). Two matings of congenital cataractous and microphthalmic Miniature Schnauzers (2 females) X a normal Miniature Schnauzer (1 male) yielded 11 clinically normal Miniature Schnauzers (7 males/4 females). Eighteen matings of congenital cataractous and microphthalmic Miniature Schnauzers (6 males) X carrier Miniature Schnauzers (9 females) produced 81 offspring; 39 exhibited congenital cataracts and microphthalmia (20 males/19 females) and 42 had clinically normal eyes (17 males/25 females).

Animals↗
PubMed1982

Effects of alpha chymotrypsin on the canine eye.

Injection of 150, 500, or 750 U of alpha chymotrypsin into the posterior chamber of clinically normal Beagles resulted in changes in intraocular pressure and iridocyclitis. In the 6 eyes treated with 500 or 750 U, lens subluxation occurred in 4 eyes, retinal detachment in 1 eye, retinal degeneration in 1 eye, and optic nerve degeneration in 6 eyes. Scanning electron microscopic changes included dose-related zonulolysis and zonulary remnants within the aqueous humor outflow pathways. Ultrastructural changes by transmission microscopy of the optic nerve degeneration revealed loss of axoplasm and organelles and disruption of the myelin sheaths. Retinal and optic nerve changes may represent the direct toxic effects of alpha chymotrypsin and/or the indirect effects of increased intraocular pressure.

Animals↗
PubMed1977

Concentric bodies in two species of he loculoascomycetes.

Concentric bodies were found in vegetative and pycnidial cells of Podoxythium tricothecium and in ascostromal paraphyses of Rhytidhysterium rufulum, two representatives of the Loculoascomycetes. They averages 185 nm in diameter in P. trichothecium and 255 nm in R. rufulum and consisted of three zones.

Ascomycota↗
PubMedDate not supplied

X-ray microprobe analysis of the retina and RPE in sheep with ovine ceroid-lipofuscinosis.

Ovine ceroid-lipofuscinosis (OCL) is one animal model for the human condition, and because autofluorescent lipopigments are prominent in the brain and eye, it may also prove useful as a model for aging. For example, a progressive decline in electrical recording from brain and retina are observed in both aging and OCL. Samples of retinal and retinal pigment epithelial (RPE) tissues were obtained from a young control. 2 animals with OCL and a normal aged sheep. Specimens were cryo-fractured and examined by scanning electron microscopy/x-ray microanalysis. Measurements made of 6 individual cells in the ganglion layer of OCL specimens, the remainder of the retina, and RPE showed age-related changes in zinc, iron, and copper which were associated with lipopigment accumulation in the RPE. There was marked decrease in phosphate, sulfur, and manganese levels, as photoreceptor cells and their outer segments are lost in the disease process. This is the first report of metal analysis in the retina and RPE in a disease entity, and as a function of normal aging.

Aging↗
PubMedDate not supplied

Comparative morphology of the tapetum lucidum (among selected species).

OBJECTIVES: The phenomenon of 'eye-shine' is seen in a variety of animal species, and is generally thought to be related to the presence of an intraocular reflecting structure, the tapetum lucidum. The tapetum lucidum is a biologic reflector system that is a common feature in the eyes of vertebrates. It normally functions to provide the light-sensitive retinal cells with a second opportunity for photon-photoreceptor stimulation, thereby enhancing visual sensitivity at low light levels. The tapetum lucidum is presented here according to a classification based on the location, as well as the composition, of this reflective layer. Finally, the physical and chemical properties, as well as the origins of the different tapeta lucida, are discussed and compared. METHODS: The anatomic and biochemical aspects of the tapetum lucidum in various vertebrates are examined. Morphologic observations were made from paraffin and plastic embedded specimens. Specimens were treated with traditional stains and observed by light and transmission electron microscopy. RESULTS: Some species (primates, squirrels, birds, red kangaroo and pig) do not have this structure and they usually are diurnal animals. In vertebrates, the tapetum lucidum exhibits diverse structure, organization and composition. Therefore, the retinal tapetum (teleosts, crocodilians, marsupials, fruit bat), the choroidal guanine tapetum (elasmobranchs), the choroidal tapetum cellulosum (carnivores, rodents, cetacea), and the choroidal tapetum fibrosum (cow, sheep, goat, horse) are described. CONCLUSIONS: The tapetum lucidum represents a remarkable example of neural cell and tissue specialization as an adaptation to a dim light environment and, despite these differences, all tapetal variants act to increase retinal sensitivity by reflecting light back through the photoreceptor layer. These variations regarding both its location and structure, as well as the choice of reflective material, may represent selective visual adaptations associated with their feeding behavior, in response to the use of specific wavelengths and amount of reflectance required.

Animals↗
PubMedDate not supplied

Glutamine synthetase: a key enzyme for intestinal epithelial differentiation?

BACKGROUND: We have previously shown that glutamine synthetase protein and mRNA are concentrated in the crypt region of the rat small intestine and that the activity of this enzyme is highest around the time of weaning. This anatomical location and time of peak activity are sites and periods of active enterocyte differentiation. This led to our current hypothesis that glutamine synthetase is important in the differentiation of enterocytes. METHODS: To test our hypothesis, we treated Caco-2 cells with physiologic (0.6 mM) glutamine concentrations in cell culture medium. The experimental group was treated with methionine sulfoximine, an irreversible glutamine synthetase inhibitor, and the control group with phosphate buffered saline. Three standard and well-defined markers of intestinal differentiation-sucrase-isomaltase activity, microvillus formation, and electrical impedance in transwell plates-were compared between the two groups. RESULTS: The methionine-sulfoximine-inhibited group was found to have lower sucrase-isomaltase activity, a lower density of microvilli, and lower electrical impedance values over time compared with the control group. CONCLUSION: The experimental group was found to be less differentiated by all three markers of differentiation. Therefore, glutamine synthetase is important for Caco-2 cell differentiation.

Caco-2 Cells↗