Biomedical subjects

D L Johnson

Publications and source records attributed to D L Johnson.

At least 73 records · Page 4Linked to original sources

PubMed1999

Estimation of heritabilities and correlations associated with milk color traits.

The objective of this study was to estimate the genetic parameters associated with milk color traits of dairy cattle. The data consisted of test day records of 9516 first lactation dairy cows and the records of 6358 of these cows that went on to produce a second lactation. Friesians, Jerseys, and crossbred cows were included in the data. Test day records included measures of milk, fat, and protein as well as milk color measured as absorbance at 450 nm. From these measurements, fat color and beta-carotene yield were calculated. Analyses were performed both within and across breeds. Jerseys produced more beta-carotene than did Friesians, and milk and fat from Jerseys had more intense color. Lactation model estimates for the heritabilities of milk color traits ranged from 0.33 to 0.44 (across breed), 0.40 to 0.49 (Friesians), and 0.17 to 0.31 (Jerseys). In all analyses, the heritability estimates associated with beta-carotene yield were lower than the estimates associated with the color of milk or fat. Genetic correlations between beta-carotene yield and the production traits were positive, but genetic correlations between fat color and production traits were generally negative. Genetic correlations between milk color and milk and protein yields were negative, and the correlations with fat yield were close to zero.

Animals↗

PubMed1999

Pathological and physiological responses of ring-necked pheasant chicks following dietary exposure to the fungus Metarhizium flavoviride, a biocontrol agent for locusts in Africa.

Metarhizium flavoviride, a fungal pathogen of grasshoppers and locusts, appears to be an effective, non-chemical insecticide (mycoinsecticide) for control of grasshoppers and locusts. This study, conducted during June and July, 1997, examined the pathogenic potential of this entomopathogenic fungus to non-target avian species that encounter infected insect prey items or contaminated food sources. Ring-necked pheasant (Phasianus colchicus) chicks were exposed to one of three diets, (spore-coated feed, infected insects, or untreated feed), either from 4 to 9 days of age, or, from 35 to 40 days of age. Necropsies were conducted on birds 10 days and 46 days old, respectively. Neither consumption of infected insects, nor of spore-coated feed, resulted in pathological changes, or significant changes in weight, growth rate, behavior, or mortality rate. Histological examination of organs indicated either no changes related to treatment, or normal tissue responses to antigenic challenge.

Analysis of Variance↗

PubMed1999

Meniscal reconstruction. Part I: indications, techniques, and graft considerations.

Menisci are specialized structures capable of bearing loads, absorbing shock, stabilizing, and lubricating the knee joint. Increased knowledge of meniscal anatomy and function, as well as studies of chronic anterior cruciate ligament-deficient and -reconstructed knees, have indicated that loss of meniscal function is associated with progression of degenerative changes within the knee. Meniscal reconstruction has been developed to preserve those functions prior to the development of significant degenerative changes in patients who have undergone meniscectomy. Indications are still being defined. Meniscal reconstruction has been achieved by either arthroscopically assisted or open techniques. Anatomic placement and secure fixation of the graft are requirements to allow the optimal revascularization needed for successful incorporation of the graft. Part I of this review will discuss the anatomy and function of the meniscus, followed by the indications, techniques, and graft considerations for meniscal allograft reconstruction. In Part II, which will be published in the May 1999 issue, we will review the results, potential complications, and future directions of meniscal allograft reconstruction.

Anterior Cruciate Ligament↗

PubMed1999

Meniscal reconstruction. Part II: Outcome, potential complications, and future directions.

Currently, magnetic resonance imaging and second-look arthroscopy are the only methods available to objectively evaluate the outcome of meniscal reconstruction. While clinical studies indicate progressively improving outcomes of meniscal reconstruction, longer follow-up is needed to determine whether the natural history of joint degeneration can be altered. Part I of this comprehensive review, published in the April 1999 issue, discussed the anatomy and function of the meniscus, followed by the indications, techniques, and graft considerations for meniscal allograft reconstruction. Part II reviews the results, potential complications, and future directions of meniscal allograft reconstruction.

Animals↗

PubMed1999

Does pulsed low intensity ultrasound allow early return to normal activities when treating stress fractures? A review of one tarsal navicular and eight tibial stress fractures.

We sought to evaluate the efficacy of daily pulsed low intensity ultrasound (LIUS) with early return to activities for the treatment of lower extremity stress fractures. Eight patients (2 males, 6 females) with radiographic and bone scan confirmed tibial stress fractures participated in this study. Additionally, a case report of a tarsal navicular stress fracture is described. All patients except one were involved in athletics. Prior to the study, subjects completed a 5 question, 10 cm visual analog scale (VAS) regarding pain level (10 = extreme pain, 1 = no pain) and were assessed for functional performance. Subjects received 20-minute LIUS treatments 5 times a week for 4 weeks. Subjects maintained all functional activities during the treatment period. Seven patients with posterior-medial stress fractures participated without a brace. Subjects were re-tested after 4 weeks of treatment. Mann-Whitney U tests (VAS data) and paired t-tests (functional tests) assessed statistical significance (p<0.05). Although the intensity of practice was diminished in some instances, no time off from competitive sports was prescribed for the patients with the tibial stress fractures. The patient with the anterior tibial stress fracture underwent tibial intramedullary nailing at the conclusion of a season of play. In this uncontrolled experience, treatment of tibial stress fractures with daily pulsed LIUS was effective in pain relief and early return to vigorous activity without bracing for the patients with posterior-medial stress fractures.

Basketball↗

PubMed1999

Crossover cutting during hamstring fatigue produces transverse plane knee control deficits.

OBJECTIVE: To assess the effects of eccentric work-induced hamstring fatigue on sagittal and transverse plane (axial) knee and ankle biodynamics and kinetics during a running crossover cut directional change (functional pivot shift). DESIGN AND SETTING: A pretest-posttest, single-group intervention experimental design was employed. All data were collected in a biodynamics laboratory. SUBJECTS: Twenty healthy athletic females were trained for 3 weeks in crossover cutting before testing. MEASUREMENTS: Data were sampled during 3 unfatigued and 3 fatigued (20% eccentric isokinetic knee-flexor torque reduction) crossover cut trials. Three-dimensional kinematic and ground reaction-force data were sampled at 200 Hz and 1000 Hz, respectively, and joint moment estimates were calculated. Data were standardized to initial force-plate heelstrike for comparisons of mean differences between conditions using paired t tests with Bonferroni adjustments. Pearson product-moment correlations compared kinematic and eccentric hamstring-torque relationships. RESULTS: During internal rotation phase 1, between heelstrike and impact absorption, mean internal rotation velocity increased by 21.2 degrees /s +/- 114 degrees /s. During internal rotation phase II, mean peak transverse plane knee rotation during propulsion decreased by 3.1 degrees +/- 9 degrees . During internal rotation phase II, mean peak ankle plantar flexor moment onsets occurred 12.7 +/- 53 milliseconds earlier, and this activation demonstrated a moderately positive relationship with the onset of mean peak knee internal rotation during propulsion and a weak negative relationship with mean peak hamstring torque/lean body weight. CONCLUSIONS: The increased knee internal rotation velocity during phase I indicates transverse plane dynamic knee-control deficits during hamstring fatigue. Earlier peak ankle plantar-flexor moments and decreased internal rotation during phase II in the presence of hamstring fatigue may represent compensatory attempts at dynamic knee stabilization from the posterior lower leg musculature during the pivot shift portion of the crossover cut. The weak relationship between decreased hamstring torque/lean body weight and delayed knee internal rotation during propulsion further supports greater dependence on ankle plantar flexors for dynamic knee stabilization compensation.

Journal Article↗

PubMed1999

Urolithiasis in dogs V: regional comparisons of breed, age, sex, anatomic location, and mineral type of calculus.

OBJECTIVE: To determine extent and nature of regional differences in distribution of canine urinary calculi. SAMPLE POPULATION: 13,552 calculus specimens: 7,056 (52.1%) from females, 6,492 (47.9%) from males, and 4 from dogs of unrecorded sex. Procedure Records were used to compile information from all specimens submitted between July 1981 and December 1995. Results from mixed-breed and various breeds of stone-forming dogs were analyzed. Interrelations of breed, sex, and age of dogs, and anatomic location and mineral composition of specimens were analyzed and compared for 6 US geographic regions. RESULTS: Struvite-, apatite-, and urate-containing calculi were reported significantly most often from female dogs of the Mountain/Pacific region. Oxalate-, silica-, and brushite-containing calculi were reported significantly most often from male dogs in the New England/mid-Atlantic (NEMA) region. Cystine-containing calculi were reported most frequently from the NEMA and South Central (SC) regions. Dogs from the NEMA region were oldest in average age at diagnosis. Significant regional differences in distribution were found for several breeds. Sex distribution of renal calculi in 11 breeds of dogs (Lhasa Apso, Yorkshire Terrier, Shih Tzu, Basset Hound, Pug, Mastiff, Bichon Frise, Doberman Pinscher, Dalmatian, English Bulldog, and Pekingese) reported to be at high risk of renal lithiasis differed among the 6 geographic regions. Renal and ureteral calculi were reported significantly most often from dogs in the South Atlantic region, and bladder and urethral calculi were reported most often from dogs in the SC region. CONCLUSIONS: Wide regional differences exist in distribution of stone-forming dogs by sex, average age at diagnosis, breed, and minerals contained within and anatomic location of calculi.

Age Factors↗

PubMed1998

Identification of a 13 amino acid peptide mimetic of erythropoietin and description of amino acids critical for the mimetic activity of EMP1.

To obtain information about the functional importance of amino acids required for effective erythropoietin (EPO) mimetic action, the conserved residues of a peptide mimetic of EPO, recently discovered by phage display, were subjected to an alanine replacement strategy. Further, to identify a minimal mimetic peptide sequence, a series of truncation peptides has been generated. One EPO mimetic peptide sequence, EMP1, was targeted and more than 25 derivatives of this sequence were evaluated for their ability to compete with [125I]EPO for receptor binding and for their ability to support the proliferation of two EPO-responsive cell lines. Two hydrophobic amino acids, Tyr4 and Trp13, appear essential for mimetic action, and aromatic residues appear to be important at these sites. These findings are consistent with the previously reported X-ray crystal structure of EMP1 complexed with the extracellular domain of the EPO receptor (EPO binding protein; EBP). In our efforts to define the structural elements required for EPO mimetic action, a 13 amino acid peptide was identified which possesses mimetic properties and contains a minimal agonist epitope. The ability of this peptide to effectively serve as a mimetic capable of the induction of EPO-responsive cell proliferation appears to reside within a single residue, equivalent to position Tyr4 of EMP1, when present in a sequence that includes the cyclic core peptide structure. Although these peptides are less potent than EPO, they should serve as an excellent starting point for the design of compounds with EPO mimetic activity.

Alanine↗

PubMed1998

Working with native American families.

Family education is a respectful approach to working with Native American families. When clinicians are informed about tribal ways, families can contribute greatly to accurate diagnosis and effective treatment and rehabilitation.

Family↗

PubMed1998

The human glenohumeral joint. A proprioceptive and stability alliance.

The glenohumeral joint, because of its relatively poor osseous and capsuloligamentous stability, depends upon the proprioceptive and stabilizing capabilities of musculotendinous structures more than any other joint in the human body. The purpose of this review is to compare the morphology, histology, and sensorimotor functional relationships of the human glenohumeral joint with the more abundant animal research data. From a synthesis of this information, a proprioceptive and stability alliance is proposed for the human glenohumeral joint which is initiated by mechanoreceptor activation from capsuloligamentous and musculotendinous structures, resulting in reflex-mediated protective muscular responses that are ultimately under the bias and sensitivity control of upper levels of the central nervous system hierarchy. The clinical impact of these findings as they relate to rehabilitation and conditioning strategies, surgical intervention, aging, and injury are discussed in addition to future research directions.

Aging↗

PubMed1998

Effect of antibiotic pretreatment on immunogenicity of human heart valves and component cells.

BACKGROUND: For many years valves have been sterilized with high-dose antibiotics before implantation, but now there is an increasing trend to using "homovital" valves, which have been exposed to very low dose antibiotics. METHODS: To investigate the immunogenicity of valve tissue, before and after exposure to high- and low-dose antibiotics, peripheral blood mononuclear cells and human allogenic T cells were cocultured with antibiotic-treated valve discs, cultured valve endothelial cells, and fibroblasts. Proliferation was measured by uptake of thymidine labeled with hydrogen 3. RESULTS: Untreated tissue pieces stimulate peripheral blood mononuclear cells (4,080+/-980 cpm) at day 0 with similar results after 1 day in Hank's balanced salt solution (4,272.4+/-1,307 cpm) reducing to 2,442+/-926 cpm after 3 days and 1,111+/-255 cpm after 5 days; antibiotic-treated pieces are less immunogenic after 1 (2,560+/-403 cpm), 3 (1,550+/-60 cpm), 5 (717+/-295 cpm), and 7 days (633+/-174 cpm) in homovital solution, whereas sterilized pieces are not immunogenic (184+/-96 cpm) after only 1 day in strong antibiotics. Histologic analysis showed that this corresponds to a reduction of class I and class II expression by human valve endothelial cells. Human valve endothelial cells but not fibroblasts are capable of causing direct stimulation of CD4+ T cells. However, human valve endothelial cells poorly stimulate CD4+ T cells after incubation in homovital solution for 24 hours. CONCLUSIONS: This study shows that valve tissue is immunogenic and this immunogenicity is mediated mainly by endothelial cells. However, the immunostimulatory potential of the valve can be reduced by incubating the solution in an antibiotic cocktail.

Anti-Bacterial Agents↗

PubMed1998

Quadrupled semitendinosus-gracilis autograft fixation in the femoral tunnel: a comparison between a metal and a bioabsorbable interference screw.

Although semitendinosus-gracilis (SG) grafts for anterior cruciate ligament reconstruction have many potential benefits, effective fixation remains a challenge. This study assessed differences between the maximum pullout forces needed to detach a quadrupled SG graft from a femoral tunnel when secured by either a metal or a bioabsorbable interference screw. Sixteen paired fresh frozen quadrupled SG autografts (x, 8.4 mm; range, 7-10 mm) from 8 donors were anchored into cadaveric femoral tunnels by either a 7-mm metal or a 7-mm bioabsorbable screw after bone mineral density (BMD) assessment and before undergoing a longitudinal 20 mm/min traction force. Statistical analysis compared BMD (gm/cm2), insertional torque (N-m), and maximum load at pullout (N) between screw types. Insertional torques (.28-1.21, N-m range) did not correlate (P>.05) to BMD or maximum load at pullout (x +/- S.D.) 242 +/- 90.7 N (metal screw) and 341.1 +/- 162.9 N (bioabsorbable screw). Differences did not exist between the maximum load at pullout for bioabsorbable or metal screw fixation (P = .16). Careful graft preparation, sizing, and matched tunnel placement enables interference fit and fixation capable of reliably withstanding the low-level rehabilitation loads to which the graft is exposed until bony ingrowth occurs.

Absorption↗

PubMed1998

An antagonist peptide-EPO receptor complex suggests that receptor dimerization is not sufficient for activation.

Dimerization of the erythropoietin (EPO) receptor (EPOR), in the presence of either natural (EPO) or synthetic (EPO-mimetic peptides, EMPs) ligands is the principal extracellular event that leads to receptor activation. The crystal structure of the extracellular domain of EPOR bound to an inactive (antagonist) peptide at 2.7 A resolution has unexpectedly revealed that dimerization still occurs, but the orientation between receptor molecules is altered relative to active (agonist) peptide complexes. Comparison of the biological properties of agonist and antagonist EMPs with EPO suggests that the extracellular domain orientation is tightly coupled to the cytoplasmic signaling events and, hence, provides valuable new insights into the design of synthetic ligands for EPOR and other cytokine receptors.

Amino Acid Sequence↗

PubMed1998

A mixture model approach to the mapping of quantitative trait loci in complex populations with an application to multiple cattle families.

A mixture model approach is presented for the mapping of one or more quantitative trait loci (QTLs) in complex populations. In order to exploit the full power of complete linkage maps the simultaneous likelihood of phenotype and a multilocus (all markers and putative QTLs) genotype is computed. Maximum likelihood estimation in our mixture models is implemented via an Expectation-Maximization algorithm: exact, stochastic or Monte Carlo EM by using a simple and flexible Gibbs sampler. Parameters include allele frequencies of markers and QTLs, discrete or normal effects of biallelic or multiallelic QTLs, and homogeneous or heterogeneous residual variances. As an illustration a dairy cattle data set consisting of twenty half-sib families has been reanalyzed. We discuss the potential which our and other approaches have for realistic multiple-QTL analyses in complex populations.

Animals↗

PubMed1998

Effects of familiarity and temporal organization on memory for event schemas in aged and Alzheimer subjects: implications for clinical management.

Individuals with Alzheimer disease (AD) often forget how to perform everyday activities. To understand better this type of memory loss, the effects of familiarity and temporal organization on memory for event schemas was investigated in college students, elderly controls, and individuals with AD. Participants were asked to read short stories describing common activities. Both recall and recognition memory were assessed immediately after reading the story. The number of items correctly remembered and the error types were recorded and analyzed. Both familiarity and temporal organization were found to play a role in memory for event schemas. All groups remembered the most information when the stories were familiar and sequentially organized. Elderly participants were more likely to remember items associated with, but included in, the stories than were the other groups. The AD group was the only group to recall or recognize items not associated with the story. It was concluded that event schema memory in AD participants is moderated by the same factors that influence memory in healthy young and elderly participants. These results suggest that individuals with AD will be best able to perform common everyday activities when they are familiar and when daily activities follow a predictable sequential pattern.

Activities of Daily Living↗

PubMed1998

Pharmacologic pain. Management for cancer patients at home.

Pain management is one of the most important responsibilities of the home care nurse serving cancer patients. Patients and caregivers often fear uncontrolled pain, and need frequent reassurance that effective pain control can be achieved. This article discusses the etiology and types of cancer pain, pain assessment, pharmacologic pain management interventions, and evaluation of pain management for home care patients.

Analgesics↗

PubMed1998

Regulation of RNA polymerase I-dependent promoters by the hepatitis B virus X protein via activated Ras and TATA-binding protein.

The hepatitis B virus (HBV) X protein is essential for viral infectivity, and evidence indicates that it is a strong contributor to HBV-mediated oncogenesis. X has been shown to transactivate a wide variety of RNA polymerase (Pol) II-dependent, as well as RNA Pol III-dependent, promoters. In this study, we have investigated the possibility that X modulates RNA Pol I-dependent rRNA transcription. In both human hepatoma Huh7 and Drosophila Schneider S2 cell lines, X expression stimulated rRNA promoter activity. Extracts prepared from X-expressing cells stably transfected with an X gene also exhibited an increased ability to transcribe the rRNA promoter. The mechanism for X transactivation was examined by determining whether this regulatory event was dependent on Ras activation and increased TATA-binding protein (TBP) levels. Our previous studies have demonstrated that X, and the activation of Ras, produces an increase in the cellular levels of TBP (H.-D. Wang, A. Trivedi, and D. L. Johnson, Mol. Cell. Biol. 17:6838-6846, 1997). Expression of a dominant negative form of Ras blocked the X-mediated induction of the rRNA promoters, whereas expression of a constitutively activated form of Ras mimicked the enhancing effect of X on rRNA promoter activity. When TBP was overexpressed in either Huh7 or S2 cells, a dose-dependent increase in rRNA promoter activity was observed. To analyze whether the increase in TBP was modulating rRNA promoter activity indirectly, by increasing activity of RNA Pol II-dependent promoters, a Drosophila TBP cDNA was constructed with a mutation that eliminated its ability to stimulate RNA Pol II-dependent promoters. Transient expression of wild-type TBP in S2 cells increased the activities of specific RNA Pol I- and Pol II-dependent promoters. Expression of the mutant TBP protein failed to enhance the activity of the RNA Pol II-dependent promoters, yet the protein completely retained its ability to stimulate the rRNA promoter. Furthermore, the addition of recombinant TBP to S2 extracts stimulated rRNA promoter activity in vitro. Together, these results demonstrate that the HBV X protein up-regulates RNA Pol I-dependent promoters via a Ras-activated pathway in two distinct cell lines. The enhanced promoter activity can, at least in part, be attributed to the X- and Ras-mediated increase in cellular TBP, a limiting transcription component.

Animals↗

PubMed1998

Severe pediatric head injury: myth, magic, and actual fact.

Reports of low mortality rate for severely head-injured children have led to the myth that children have a better outcome than adults after severe head injury. This was examined in the present study by comparing the outcome of 4,041 severely head-injured children with 14,789 adults from five Level I trauma centers in the Pennsylvania Trauma Systems Foundation from 1986 to 1996. Severe head injury was defined as GCS <8, and outcome was defined by mortality. The overall mortality rate for children (<18 years) was 36.5% and for adults 47. 6%. However, for patients involved in motor vehicle accidents, there was no clinically significant difference between children age 3-11 years (35%), age 12-18 years (31.4%) and adults (32.5%). The unprecedented low mortality rate for severe head injury in children was probably due to the selection bias of the patient population. We conclude that children involved in motor vehicle accidents are just as likely to die from severe head injury as adults.

Accidents, Traffic↗