Biomedical subjects

A B Fulton

Publications and source records attributed to A B Fulton.

At least 91 records · Page 5Linked to original sources

PubMed1987

Oscillatory potentials of visually inattentive children.

The oscillatory potentials (OPs) are probably generated in the proximal retina. The OPs of 20 visually inattentive infants and children were recorded. All 20 had evidence of abnormalities of the visual parts of the brain. The a- and b-waves, indices of distal retinal function, were normal in 10 patients, abnormal in the other 10. Among the patients with abnormal, attenuated a- and b-waves, OP amplitudes were more attenuated than among those with normal a- and b-waves. However, the timing of the OP wavelets was not correlated with distal retinal activity. These results suggest that in humans OP amplitude may be determined by inputs from the distal retina, but OP latency and periodicity are governed by processes within the proximal retina.

Adult↗

PubMed1987

The relationship of retinal sensitivity and rhodopsin in human infants.

During dark adaptation after full field, greater than or equal to 90% bleaches recovery of sensitivity and regeneration of rhodopsin were studied using electroretinographic and pupillographic techniques in both 10-week-old infants and adults. The courses of scotopic sensitivity recovery and rhodopsin regeneration of infants and adults were similar and were reasonably well fit by single exponentials having tau = 400 sec. For both infants and adults log scotopic sensitivity was linearly related to the proportion of rhodopsin present during dark adaptation. It is concluded that by age 10 weeks human distal retinal processes that occur after photolysis are equivalent to those of adults.

Adult↗

PubMed1987

"Self-screening" of rhodopsin in rod outer segments.

Microspectrophotometry (MSP) shows rhodopsin highly concentrated (about 3.0 mmol/l) in rod outer segments (ROS). Calculation of the in vivo absorption spectrum of human rhodopsin from such data reveals a striking failure to agree with the action spectrum of human rod vision. Agreement is good between the spectral distribution of absorption coefficients and the action spectrum, but the "concentration-broadening" (or "self-screening") introduced by the high end on absorbance at this concentration results in a misfit among the largest in the 93 years comparisons of this kind have been made! To deal with this anomaly, it has been suggested that "concentration-broadening" is inappropriate for rhodopsin in rod vision. This proposal was tested by comparing rod action spectra of 15-day-old and adult rats, since the lengths of ROS increase by a factor of about two in maturation. Three lines of evidence are inconsistent with it. Although the conundrum remains unexplained, it cannot be dismissed by supposing "self-screening" inappropriate for night vision.

Aging↗

PubMed1987

Special diagnostic and therapeutic modalities in pediatric ophthalmology.

Ophthalmology is a specialty rich in instrumentation used for special diagnostic and therapeutic functions. Many of these special modalities are appropriate to pediatric ophthalmology, and this article discusses them in summary fashion for those who may wish to know about the procedures but who may not be involved directly in their use.

Child↗

PubMed1987

Cotranslational assembly of myosin heavy chain in developing cultured skeletal muscle.

To examine how nascent myosin heavy chains associate with the cytoskeletons of developing muscle cells, we used pulse labeling, cell fractionation, and immunoprecipitation. More than 80% of nascent myosin heavy chains associate with the cytoskeleton. More than one-third of these nascent chains are not released by puromycin and/or RNase. The fraction of nascent heavy chains that resists release increases during development of muscle cells in culture. Treatment with cytochalasin D but not nocodazole decreases myosin heavy chain cotranslational assembly. These results indicate that (i) cotranslational assembly of myosin heavy chains is developmentally regulated, (ii) structures containing actin and not microtubules may mediate initial association of the heavy chains with the cytoskeleton, and (iii) the site of translation dictates where a significant fraction of the heavy chains will be inserted into the cytoskeleton.

Animals↗

PubMed1987

Concurrence of congenital ocular motor apraxia and other motor problems: an expanded syndrome.

The records of all cases of congenital ocular motor apraxia diagnosed by the Ophthalmology Department at the Children's Hospital, Boston, over the past 25 years were reviewed to ascertain other problems with motor organization. There were eight boys and two girls, ranging in age from eight months to 2 1/2 years at diagnosis. Eight of the 10 had evidence of oral motor planning problems which significantly affected their speech output. Five had evidence of awkwardness or clumsiness, suggesting difficulties with gross motor organization as well. This concurrence of motor planning problems in at least two spheres, ocular motor and oral motor, suggests more general difficulties with motor organization in this syndrome. In all cases for whom data were available the ocular motor problems resolved but oral motor problems persisted.

Apraxias↗

PubMed1986

Background adaptation in human infants.

Human infants' thresholds for detecting 10 degrees diameter 50 and 1000 msec stimuli in the dark adapted condition and in the presence of steady red backgrounds were determined using a preferential looking method. Dark adapted sensitivity and the slope of the linear portion of the increment threshold function increased with age. The slope was 0.5 at 4 weeks, but by 10 weeks it was not different from the adult value (approximately 1.0). At all ages the eigengrau was approximately the same as that of adults (-2.3 log scot. td). These results suggest that visual mechanisms involved in detection of flashes and adaptation to steady background lights mature postnatally.

Adult↗

PubMed1986

A simple trypsin resistance assay for muscle and other cell fusion.

Muscle cells fusing in vitro have long provided biologists with a tool to study development and gene expression. However, many such studies used morphological assays of cell fusion. We present here a method for assaying fusion at a specific, operationally defined step. Muscle cells grown in monolayer are exposed to trypsin-EDTA solution at 37 degrees C; the trypsin is inactivated, the cells fixed in Lugol's iodine, and 200 to 300 nuclei are counted as being single or multiple. The presence of EDTA is important under standard conditions for muscle culture; however, little difference is seen in divalent cation-depleted cultures. Therefore, for consistency EDTA can be included in all assays. Samples are stable for over 24 hr, with no cell loss from trypsinization or fixation. This assay exploits a specific stage of muscle fusion, trypsin-resistant contact, to provide a rapid, simple, and observer-independent assay for an early state of muscle fusion. The assay can be used to measure fusion between any nucleated cells.

Animals↗

PubMed1986

Assessment of acuity of amblyopic subjects using face, grating, and recognition stimuli.

For amblyopic subjects, square-wave gratings, such as those used in preferential looking tests of infants' vision, yield more optimistic estimates of visual acuity than complex stimuli such as letters. A complex stimulus--a schematic face pattern--has recently been shown (Harris et al, IOVS 25:782, 1984) to permit preferential looking estimates of acuity of infants with normal eyes. In the present study, older amblyopic subjects had acuities measured with the face stimulus as well as gratings and standard recognition tests. Acuities measured with the face stimulus agreed better with the results of the standard recognition tests than did those obtained with gratings. Thus, if amblyopia of infants and young children affects spatial vision in a manner similar to that of older children and adults, one would anticipate that complex stimuli, such as the face pattern, would complement current assessments of young pediatric patients.

Adolescent↗

PubMed1986

Pupillary changes during dark adaptation in human infants.

Pupillary diameter of 10 infants (age 10 weeks) and four adult subjects was measured during 30 min of dark adaptation following exposure to a full-field adapting light. Adult results confirm that, under these conditions, the course of pupillary recovery was reasonably well described by an exponential time course (t0 = 408 sec; SD = 42 sec), as is rhodopsin regeneration. Pupillary recovery of infants also could be described by an exponential course (average t0 = 399 sec; SD = 31 sec). These results, demonstrating similarities between adaptive functions of infants and adults, suggest that pupillographic techniques can be used to investigate dynamic processes accompanying dark adaptation in preverbal children.

Adult↗

PubMed1985

Retinal degenerations and brain abnormalities in infants and young children.

Of 51 infants and children who presented with visual impairment, developmental delays, and suspected brain abnormalities, 28 (55%) had clinical, electroretinographic, and cranial computed tomographic results indicative of cerebroretinal disorders. This report concentrates on the electroretinographic and psychophysical results from 12 patients who had evidence of progression of both brain and retinal disease. We believe these patients represent human cerebroretinal degenerative disorders that have yet to be completely characterized.

Brain↗

PubMed1985

Treadmilling, diffusional exchange and cytoplasmic structures.

Microfilaments and microtubules exchange monomers from solution by at least two mechanisms; treadmilling and diffusional exchange. Refined kinetic analysis of both mechanisms shows that this exchange may be nonlinear under certain conditions. The two mechanisms of exchange differ in some of their predictions for the behaviour of cytoplasmic structures. Studies of assembly of cytoplasmic structures in vivo suggest that diffusional exchange is probably predominant for steady-state structures and further suggest that additional mechanisms may be operating in the cell.

Actin Cytoskeleton↗

PubMed1985

Assessment of young amblyopes. Array vs. single picture acuities.

A linear array of intact and "jumbled" symbols suitable for testing young children has been used to evaluate 35 young amblyopes. Acuities with the jumbled array test were poorer than those obtained with single symbols: the discrepancy between the jumbled array and single picture acuities was greater for large acuity deficits than small deficits. The depth of amblyopia, indexed by the interocular difference in acuity, was greater for the jumbled array than single pictures. For the patients who could be tested with lines of Snellen letters the jumbled array acuities were closer to line letter acuities than single picture or grating acuities. These results suggest that the jumbled array provides a more sensitive test of amblyopia in young children than single symbols or gratings, possibly because the jumbled array presents contour interactions that exploit the crowding phenomenon.

Amblyopia↗

PubMed1985

The specificity and stability of the triton-extracted cytoskeletal framework of gerbil fibroma cells.

Cellular meshworks and topography of gerbil fibroma cells can be preserved by gentle extraction procedures using Triton X-100. We determined the stability and specificity of these cytoskeletal frameworks by measuring extraction rate and its sensitivity to exogenous protein. Two buffers were used, which mimicked the intracellular and extracellular ionic environments. With both buffers, extraction was nearly complete at 5 min. This pattern of extraction was seen both in 5- and 9-day-old cultures. The same pattern of extraction was seen when three different dilutions of cells were examined the second day after plating. Thus, extraction rate was largely independent of minor variations in ionic composition, age in culture, or cell density. Specificity of the cytoskeletal frameworks so produced was determined by competition with two different exogenous proteins (bovine serum albumin or ovalbumin), which did not remove any additional material from the cytoskeletal frameworks, even with over 10% exogenous protein in the extraction buffer. This pattern of extraction is not unique to gerbil fibroma cells. A similar pattern of extraction was seen for a series of cells: mouse 3T3 cells, 3T6 cells and SVPY 3T3 cells. These experiments indicate that the cytoskeletal framework produced by Triton extraction under appropriate conditions is stable after extraction for a period of 10 min or longer, and that the structures are specific, in that they are not disrupted by the presence of exogenous proteins.

Animals↗

PubMed1985

Visual acuity of infants and children with retinal degenerations.

Visual acuity for gratings was studied in 18 infants and children with generalized retinal degenerations using preferential looking (PL) procedures. Diagnoses were Leber's congenital amaurosis (12), Laurence-Moon-Bardet-Biedl-like syndromes (4) and metabolic disorders (2). ERG's were extinguished in 11 patients and much attenuated in seven patients. Acuities at all ages (two months to 12 years) were significantly poorer than normal, and patients with extinguished ERG's had the poorest acuity. Neurological abnormality or mental retardation, present in ten patients, was as likely in patients with 6/60 or poorer grating acuity as in patients with better than 6/60 acuity. A comparison group of 12 infants and children with oculocutaneous albinism showed significantly better grating acuities than the patients with retinal degeneration. Relatively good grating acuity in infants with no anatomic fovea (oculocutaneous albinism) and much poorer acuities of infants with generalized retinal degeneration suggest that parafoveal or peripheral retina is necessary and sufficient for normal, behaviorally-obtained grating acuity in infancy.

Adolescent↗

PubMed1985

Preferential looking grating acuities of infants at risk of amblyopia.

Preferential looking (PL) has been successful in the assessment of visual acuity of infants with eye disorders that place them at risk of amblyopia, such as non-alternating strabismus, anisometropia, and complete unilateral cataracts. However, PL acuities do not always conform to clinical expectations. In most esotropic infants, even untreated esotropes with a strong fixation preference, differences in acuity between eyes are minimal. PL interocular acuity differences are marked, however, in optically corrected, severe anisometropia and, after surgery and with contact lens in place, in unilateral cataracts. A different neural basis for infant PL acuities in strabismic amblyopia vs. anisometropic and stimulus deprivation amblyopia is proposed based on the dominance of extrafoveal neural elements in detecting PL grating stimuli.

Age Factors↗

PubMed1984

Retinal degeneration in vitamin B12 disorder associated with methylmalonic aciduria and sulfur amino acid abnormalities.

A 33-month-old boy with an inborn error of vitamin B12 metabolism characterized by methylmalonic aciduria, homocystinuria, cystathioninuria , and hypomethioninemia had poor vision and a progressive retinal pigmentary degeneration. The child had early growth retardation with microcephaly, developmental delay, and a megaloblastic anemia. The retinal lesions were first noted when he was 1 year of age and, by ophthalmoscopy and by electroretinographic testing, have progressed. Treatment with hydroxocobalamin and L-methionine improved the anemia and the biochemical abnormalities but apparently did not halt the retinal degeneration. We believe the retinopathy is a feature of this disease, particularly in patients with infantile involvement. The retinal lesion may be caused by an unidentified abnormality of sulfur amino acid metabolism.

Amino Acid Metabolism, Inborn Errors↗

PubMed1984

Grating and recognition acuities of pediatric patients.

Acuities for gratings obtained by preferential looking (PL) that differed from expectations based upon the ophthalmologic examination prompted this study. Older pediatric patients (124 patients; mean age, 6.5 years) were tested by the PL grating test and a test of recognition acuity (pictures or letters). On the average, grating acuity was better than recognition acuity. In patients with dense amblyopia or foveal abnormalities, very large discrepancies between grating and recognition acuities were found. In nonamblyopic patients, acuities were no more discrepant than for children with normal eyes. Amblyopia was less dense by grating acuities than by recognition acuities; grating acuities were sensitive, however, to refractive and organic amblyopia but not to strabismic amblyopia. Possible explanations include the heterogeneity of patients' eye disorders, single vs. linear acuity, stimulus size and relative complexity of stimuli. These results can aid in evaluating PL grating acuities of preverbal patients, and suggest modifications of stimuli to investigate amblyogenesis.

Adolescent↗