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Biomedical subjects

D L Clark

Publications and source records attributed to D L Clark.

12 recordsLinked to original sources
PubMed1979

Purification and characterization of multiple species (isolectins) of a slime mold lectin implicated in intercellular adhesion.

An improved purification procedure for the carbohydrate-binding proteins (lectins) of cohesive Polysphondylium pallidum cells has been devised. The procedure uses extraction of cells with lactose-containing buffer followed by ammonium sulfate precipitation and affinity chromatography of the redissolved precipitate on a column of acid-treated Sepharose 6B. All hemagglutination activity is adsorbed to the column and recoveries are about 70% of the activity of the starting cell lysate. Sodium dodecyl sulfate-gel electrophoresis of the protein obtained with this procedure resolved three subunits with molecular weights of 26,500 (A), 26,000 (B), and 25,000 (C). Three species are resolved by isoelectric focusing with apparent pI values of 6.4 (I), 7.3 (II), and 7.5 (III) which contain Subunits A, B, and C in the following ratios: I, B:C at 2:1; II, A:B at 2:1, and III, A:B at 1:2. All three isoforms agglutinate rabbit and human type O erythrocytes and are thus isolectins. Isoforms II and III are separated from Isoform I by galactose-gradient elution of the Sepharose 6B column. Isoforms II and III aggregate extensively (nonamers and multiples thereof), but reduction with 2-mercaptoethanol reverses this process yielding a single species of Mr = 73,000 (trimer). Isoform I exists as trimers and hexamers and reduction has no effect on this distribution. Amino acid compositions and tryptic peptide maps of S-[14C]carboxymethyl-isolectins indicate that Subunits A and B are very similar and may represent the same peptide chain, while Subunit C is a peptide quite distinct from A and B.

Amino Acids↗
PubMed1978

Aggression increase and water competition decrease in squirrel monkeys given physostigmine injections.

Six adult squirrel monkeys (Samiri sciureus) were tested in pairs for social dominance in a water competition task. Dominance was defined by two methods: (1) number and direction of aggressive responses, and (2) successful water competition as assessed by latency to the water bottle, latency to accumulate 15 seconds of drinking, and total drinking duration. Monkeys were assigned to pairs on a "round robin" basis so that each monkey was paired with all other monkeys under control, saline, and three levels of physostigmine sulfate (6.25, 12.5, and 25.0 microgram/kg). Under drug conditions only one member of each pair was drugged. The 12.5 microgram/kg dose of physostigmine resulted in a significant increase in aggressive responses. Both drinking duration and general motor activity decreased with increasing dose level of drug. It was also noted that the non-drugged partners of drugged monkeys accumulated 15 seconds of drinking faster and drank more at the 25 and 12.5 microgram/kg dose levels than under control and saline conditions. Physostigmine resulted in an increase in one measure of social dominance and a decrease in the other.

Aggression↗
PubMed1978

Semicircular canal stimulation in cerebral palsied children.

Twelve cerebral palsied children were exposed to 16 sessions of horizontal and vertical semicircular canal stimulation over a four-week period in order to determine the effectiveness of this form of stimulation as a therapeutic procedure. A control group of 11 cerebral palsied children was included. A quantitative evaluation of a series of reflexes and of gross motor skills showed a highly significant degree of improvement following the four weeks of treatment. A qualitative evaluation of each subject corroborated these findings and suggested improvements in fine motor control and in social/emotional behavior. A possible central nervous system mechanism underlying the improvement in motor skills is discussed.

Cerebral Palsy↗
PubMed1977

Vestibular stimulation influence on motor development in infants.

Preambulatory, normal human infants were exposed to sessions of mild semicircular canal stimulation on 2 days per week for 4 weeks. The gross motor ability of each child was assessed before and after the 4-week period. The vestibular stimulation effected a significant improvement in gross motor skills.

Child Development↗
PubMed1977

Mercury and organomercurial resistances determined by plasmids in Pseudomonas.

Mercury and organomercurial resistance determined by genes on ten Pseudomonas aeruginosa plasmids and one Pseudomonas putida plasmid have been studied with regard to the range of substrates and the range of inducers. The plasmidless strains were sensitive to growth inhibition by Hg(2+) and did not volatilize Hg(0) from Hg(2+). A strain with plasmid RP1 (which does not confer resistance to Hg(2+)) similarly did not volatilize mercury. All 10 plasmids determine mercury resistance by way of an inducible enzyme system. Hg(2+) was reduced to Hg(0), which is insoluble in water and rapidly volatilizes from the growth medium. Plasmids pMG1, pMG2, R26, R933, R93-1, and pVS1 in P. aeruginosa and MER in P. putida conferred resistance to and the ability to volatilize mercury from Hg(2+), but strains with these plasmids were sensitive to and could not volatilize mercury from the organomercurials methylmercury, ethylmercury, phenylmercury, and thimerosal. These plasmids, in addition, conferred resistance to the organomercurials merbromin, p-hydroxymercuribenzoate, and fluorescein mercuric acetate. The other plasmids, FP2, R38, R3108, and pVS2, determined resistance to and decomposition of a range of organomercurials, including methylmercury, ethylmercury, phenylmercury, and thimerosal. These plasmids also conferred resistance to the organomercurials merbromin, p-hydroxymercuribenzoate, and fluorescein mercuric acetate by a mechanism not involving degradation. In all cases, organomercurial decomposition and mercury volatilization were induced by exposure to Hg(2+) or organomercurials. The plasmids differed in the relative efficacy of inducers. Hg(2+) resistance with strains that are organomercurial sensitive appeared to be induced preferentially by Hg(2+) and only poorly by organomercurials to which the cells are sensitive. However, the organomercurials p-hydroxymercuribenzoate, merbromin, and fluorescein mercuric acetate were strong gratuitous inducers but not substrates for the Hg(2+) volatilization system. With strains resistant to phenylmercury and thimerosal, these organomercurials were both inducers and substrates.

Chemical Phenomena↗
PubMed1976

Vectorial characteristics of ventricular extrasystoles stimulated during cardiac catheterization.

Ventricular extrasystoles (VES) from different areas of the ventricular muscle mass were obtained by mechanical stimulation of inflow and outflow regions of the right ventricle (RV) and apical and basal portions of the left ventricle (LV) during cardiac catheterization. Cube system vectorcardiogram (VCG) patterns of VES from each location were analyzed to determine the specificity of vector orientation from each site. Transverse plane VCG distinguished between nonseptal LVES and RVES, while a combination of transverse and either sagittal or frontal planes permitted further localization of septal VES to inflow or outflow regions of the RV and apical and basal areas of the LV.

Adult↗
PubMed1976

Effects of vestibular stimulation on nystagmus response and motor performance in the developmentally delayed infant.

The effects were studied of 10 days' exposure to daily repetitive, specific vestibular stimulation on motor performance of children with Down's syndrome and normal children. A quantitative assessment of vestibular function was made in these children including the habituation response of postrotatory nystagmus. Control groups were included. Both the children with Down's syndrome and the normal children who received vestibular therapy demonstrated positive effects when evaluated using a quantitative motor skills assessment test. Control and treatment children showed vestibular habituation, with treatment children evidencing the greater change. This change may reflect the acquisition of an increased level of central nervous system inhibitory control.

Child, Preschool↗
PubMed1976

Hypergravity effects on normal and avulsed developing avian radii.

Rhode Island Red female chicks were subjected to complete closed fracture of the right radius at 2 weeks post-hatching. The animals were allowed to heal for 1 week at either earth gravity or 2 G hypergravity state with control and estrogen-injected groups. Intact and fractured radial length, weight, average epiphysial-diaphysial diameters, and length, width, and weight of healing fracture callus were measured. Daily 2000 IU estrogen administration for 7 d increased intact radial length. Estrogen augments the effects of the 2-G state by inhibiting growth and depleting the mass of both intact and fractured radii and by decreasing the average distal epiphysial diameter of fractured bones. Animals exposed to the hypergravity state without hormonal treatment showed decreased fractured radial length, weight, and smaller proximal epiphysial diameters. The measurable parameters of the fracture callus (width, length, and weight) were depressed by the hypergravity state regardless of whether the animal was untreated or supplemented with estrogen.

Animals↗
PubMed1975

Factors affecting assay of myoglobin by complement fixation or immunodiffusion.

Quantitative micro-scale complement-fixation and semi-quantitative gel immunodiffusion assays for myoglobin have been evaluated experimentally and used to measure myoglobin in the sera of more than 1500 patients. We report certain problems, observations, and methodological improvements. Serum caused enhancement of precipitin lines in the immunodiffusion assay. In the complement-fixation assay, serum interfered both by enhancing or inhibiting complement fixation. Suggested modifications in the complement-fixation assay are: (a) routine threefold or greater dilution of serum with buffer and (b) use of serum-based rather than buffer-based calibration materials in preparing standard curves. Three cycles of freeze-thaw of serum or buffer decreased detectable myoglobin by 50-100%. We conclude that certain serum-related factors and freeze-thaw phenomena are important causes of error in immunological assays for myoglobin.

Complement Fixation Tests↗
PubMedDate not supplied

Behavioral and nystagmus response of a hyperkinetic child to vestibular stimulation.

A five-year-old boy, referred for hyperkinetic behavior, was tested for vestibular function before and after a four-week regime of controlled semicircular canal stimulation. Hyperkinetic behavior was assessed both during and after the four-week treatment period. Initial testing showed that semicircular canal function was normal, but that two measurable central nervous system mechanisms representing integration of the sensory signal were not at a normal level. Behavioral instruments demonstrated an improvement in symptoms of hyperkinetic behavior. It is postulated that the behavioral improvement resulted from an increase in task-relevant arousal in the reticular formation, accompanied by increased cortical inhibition.

Child Behavior↗