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Biomedical subjects

R D Johnson

Publications and source records attributed to R D Johnson.

At least 91 records · Page 5Linked to original sources
PubMed1995

Are routine alpha-fetoprotein and acetylcholinesterase determinations still necessary at second-trimester amniocentesis? Impact of high-resolution ultrasonography.

OBJECTIVE: To audit routine measurement of alpha-fetoprotein (AFP) and acetylcholinesterase in amniotic fluid (AF) samples obtained at second-trimester amniocentesis. METHODS: We reviewed retrospectively 1737 consecutive AF specimens obtained for cytogenetic evaluation over a 4-year period and routinely assayed for AFP and acetylcholinesterase. In all instances, high-resolution ultrasonography was performed before amniocentesis. Details of pregnancy outcome of all cases with AF AFP levels greater than 2.0 multiples of the median and a positive or faint acetylcholinesterase band were obtained. RESULTS: There were 31 abnormal results (1.8%, 1 of 56). Of these, 25 cases had elevated AF AFP and/or positive acetylcholinesterase. Ultrasonography correctly identified all 18 fetuses with anomalies associated with abnormal levels of these biochemical markers, including open neural tube defects and/or anterior abdominal wall defects (17 cases) and fetal hydrops (one). In the remaining seven, no fetal anomalies were detected, and all neonates were structurally normal after birth. In addition, six pregnancies with faint acetylcholinesterase and normal AF AFP showed no fetal abnormalities at ultrasonographic examination and post-delivery. CONCLUSIONS: High-resolution ultrasonography was more accurate than AF biochemistry in the detection of congenital anomalies associated with elevated AFP levels and acetylcholinesterase in the AF. Routine measurement of these biochemical markers in AF samples obtained for cytogenetic analysis appears to have a very low yield and would therefore not be cost-effective in practices where high-resolution ultrasonography is performed before amniocentesis.

Acetylcholinesterase↗
PubMed1995

Opioid involvement in feeding behaviour and the pathogenesis of certain eating disorders.

Incidental findings from animal experiments involving administration of exogenous opioid agonists indicate that there are close links between the endogenous opioid system and feeding behaviour. Subsequent investigations aimed at elucidating the nature of the opioid-feeding relationship led to a wide variety of findings, some of them apparently contradictory. This paper examines the effects of opioid agonists and antagonists on feeding behaviour, and considers the evidence relating levels of endogenous opioids to feeding states, with particular reference to certain eating disorders, including anorexia nervosa, bulimia nervosa, Prader-Willi syndrome, and eating-induced obesity. The receptors which may be involved in opioid-feeding relationships are discussed. Relationships between the endogenous opioid system and other systems, such as the dopaminergic, noradrenergic and hormonal systems, are considered insofar as they may have bearing on the modulation of feeding behaviour. Finally, three theories are briefly outlined which attempt to link the endogenous opioid system with feeding modulation and the pathogenesis of certain eating disorders. The suggestion is put forward that anorexia nervosa may represent a pathological consequence of the triggering of a primitive mechanism for coping with unforeseen food shortages which may have short-term advantages, e.g., for masking or temporarily alleviating a depressed state.

Adaptation, Physiological↗
PubMed1995

Differentiation and growth on a fibrin matrix modulate the cyclooxygenase expression and thromboxane production by cultured human placental trophoblasts.

Preeclampsia is associated with altered placental production of several end-products of cyclooxygenase activity. Thromboxane (TX) is one of these end-products, and trophoblast is a source of villous thromboxane. We cultured term trophoblast in the presence or absence of fibrin to study how differentiation and epithelial-matrix interactions regulate cyclooxygenase expression. The cellular trophoblast present during the first 24 h of culture on uncoated plastic produced TXB2, but little or no TX was produced in cultures grown longer than 24 h when differentiation into syncytial trophoblast occurred. Growth of cells on a fibrin matrix enhanced cellular trophoblast TX production five-fold. Medium containing 10 mumol/l arachidonic acid maximized thromboxane production in cells cultured for less than 24 h, regardless of growth surface, but this medium had little or no effect on TX production by cultures grown for more than 24 h. In contrast, exogenous arachidonic acid enhanced prostaglandin E2 (PGE2) production by both cellular and syncytial trophoblast. Cytochemical staining indicated that changes in cyclooxygenase content occurred with trophoblast differentiation. Western immunoblot analysis of cells cultured in the presence or absence of a fibrin matrix showed cyclooxygenase was induced under both growth conditions. Detectable cyclooxygenase protein disappeared beyond 24 h in cells grown on uncoated plastic. In contrast, cells grown beyond 24 h on fibrin showed sustained expression of cyclooxygenase by Western immunoblotting, and this enzyme protein expression correlated with increased PGE2 production by the differentiated trophoblast.(ABSTRACT TRUNCATED AT 250 WORDS)

Arachidonic Acid↗
PubMed1995

Functional differences and interactions among the putative RecA homologs Rad51, Rad55, and Rad57.

The genes of the Saccharomyces cerevisiae RAD52 epistasis group are required for the repair of ionizing radiation-induced DNA damage. Three of these genes, RAD51, RAD55, and RAD57, have been identified as putative RecA homologs. An important feature of RecA is its ability to bind and hydrolyze ATP. RAD55 and RAD57 contain putative nucleotide binding motifs, and the importance of these motifs was determined by constructing site-directed mutations of the conserved lysine residue within the Walker A-box. Changing the lysine residue to arginine or alanine resulted in a mutant phenotype in DNA repair and sporulation for Rad55 but not for Rad57. Protein-protein interactions among Rad51, Rad55, and Rad57 were tested for by the two-hybrid system. Rad55 was shown to interact with Rad51 and Rad57 but not with itself. Additionally, no interaction between Rad57 and Rad51 or between Rad57 and itself was detected. Consistent with the hypothesis that Rad55 and Rad57 may function within, or stabilize, a protein complex, we found that RAD51 expressed from a high-copy-number plasmid suppresses the DNA repair defect of strains carrying rad55 and rad57 mutations. These data, in conjunction with other reports, demonstrate the importance of protein-protein interactions in the process of DNA repair.

Adenosine Triphosphatases↗
PubMed1995

Selective stimulation of epithelial cells in colonic crypts: relation to active chloride secretion.

Stimulation of Cl secretion by prostaglandin E2 (PGE2) was measured as the short-circuit current (Isc) across isolated epithelium of the rabbit distal colon. Cellular morphology of columnar and goblet cells during secretion was monitored using light and electron microscopy. Stimulation by PGE2 altered epithelial cell morphology only by a reduction of vacuolar space in the apical pole of crypt columnar cells, consistent with release of vacuole contents. Imaging of isolated crypts using differential interference microscopy confirmed the release of material from columnar cells during the onset of secretion. Inhibition of Cl secretion with the loop diuretic bumetanide did not block vacuole release. The actin filament-disrupting agent, cytochalasin, reduced the PGE2-stimulated Isc by 40% and blocked emptying of the vacuolar space. These electrical and morphological results indicate that the process of active ion secretion is associated with release of the macromolecular contents from apical vacuoles through a mechanism involving the cytoskeleton. In addition, this relationship supports the concept that vacuolated columnar cells of the crypts of Lieberkühn are the cell type that secretes Cl in response to PGE2.

Animals↗
PubMed1995

Rescue of motoneuron and muscle afferent function in cats by regeneration into skin. I. Properties of afferents.

1. In this study we investigate the peripheral receptive field properties and spinal cord connections of low-threshold muscle afferent fibers cross-regenerated into the skin to determine whether a cutaneous target can rescue physiological functions lost after chronic axotomy. 2. In adult cats the medial gastrocnemius (MG) muscle nerve was coated with the distal cut end of either the caudal or lateral cutaneous sural nerves and allowed to regenerate into the hairy skin (postoperative period 6-30 mo). During terminal acute experiments we made recordings of single MG afferent fibers in dorsal root filaments and peripheral nerve. Conduction velocity and receptive field characteristics were determined for each fiber. In addition, the MG nerve was stimulated to elicit cord dorsum potentials and monosynaptic excitatory postsynaptic potentials (EPSPs) in heteronymous motoneurons. As controls, studies were carried out after MG nerve axotomy (postoperative period 2.5-12 mo). 3. After innervation of the skin, MG muscle afferent fibers exhibited firing characteristics and proximal segment conduction velocities like those of normal MG afferents. Responses to skin and hair stimulation consisted primarily of slowly adapting, stretch-sensitive, and steady discharge patterns, all common in normal muscle afferents but not in cutaneous afferents. These properties were observed despite the innervation of touch domes and single hairs, suggesting that the peripheral physiology of muscle afferents is a function of the axonal membrane and is not respecified by a cutaneous target and/or receptors. 4. Cord dorsum potentials were characteristic of those elicited by intact muscle afferents rather than skin afferents and showed recovery of configurations lost after chronic axotomy. 5. The monosynaptic EPSPs elicited in lateral gastrocnemius-soleus motoneurons also recovered from the reduction in amplitude observed after chronic axotomy. The configurations of these EPSPs were characteristic of muscle afferents rather than skin afferents. 6. These experiments demonstrate that the peripheral and central physiological properties of muscle afferents are rescued from the axotomy state if the afferents are allowed to reinnervate skin. We found no evidence that respecification had occurred to bring the function of muscle afferents into accord with the new cutaneous target.

Animals↗
PubMed1995

Rescue of motoneuron and muscle afferent function in cats by regeneration into skin. II. Ia-motoneuron synapse.

1. In this study we describe application of high-frequency stimulation to the group Ia afferent-to-motoneuron synapse of cats to determine the extent to which regeneration of axotomized muscle afferents and motoneurons into skin or into muscle rescues their ability to generate excitatory postsynaptic potentials (EPSPs). 2. The medial gastrocnemius (MG) muscle nerve was transected and 1) left chronically axotomized, 2) cross-united to the caudal cutaneous sural (CCS) nerve, or 3) self-united. The ability of the operated MG muscle afferents to generate EPSPs in normal lateral gastrocnemius-soleus (LGS) motoneurons and of normal LGS muscle afferents to generate EPSPs in the operated MG motoneurons was tested 5 wk-30 mo later. 3. EPSPs were generated by bursts of 32 shocks at 167 Hz and averaged in register. In normal cats, EPSP amplitude decreased (negative modulation) during these bursts in type S motoneurons and could increase or decrease in type F motoneurons (positive or negative modulation). 4. After axotomy, EPSPs generated both in axotomized motoneurons and by axotomized afferents showed only negative modulation during the burst, and the negative modulation was much greater than in normal animals. Regeneration of the muscle nerve into skin significantly decreased the negative modulation relative to axotomy. Regeneration of the muscle nerve into muscle restored the EPSP modulation behaviors even more, to essentially normal values. 5. We conclude that the ability of muscle afferents to generate EPSPs in motoneurons in response to high-frequency stimulation, and the ability of motoneurons to express those EPSPs, are both influenced by the target innervated by those neurons. Synaptic efficacy is severely reduced by target deprivation (axotomy), partially rescued by cross-regeneration into skin, and rescued virtually completely by regeneration into the native muscle. We speculate on the role of target-derived neurotrophins in these effects.

Animals↗
PubMed1995

Extreme serum elevations of aspartate aminotransferase.

OBJECTIVE: To determine the frequency, etiology, and associated mortality of extreme elevations of serum AST. METHODS: The medical records were reviewed of all patients with a serum AST over 3000 U/L during 1 full calendar year at a large, tertiary-care hospital. Serum AST, with an upper limit of normal at 35 U/L, is included in the automated, 18-test chemistry profile run on virtually all clinically ill patients admitted to this hospital. RESULTS: Of 23,125 admissions, 56 patients had or developed serum AST concentrations greater than 3000 U/L, an occurrence rate of approximately two per 1000 admissions. Either liver or skeletal muscle was the origin of virtually all such AST elevations. Acute hypotension (ischemic or hypoxic hepatitis) accounted for the majority (29/56) of the cases; toxic (seven) or viral (four) hepatitis together accounted for 11/56 cases. Overall mortality, on this admission, was 31/56 (55%). CONCLUSIONS: Extreme elevations of AST are most often attributable to hypoxic hepatitis. Patients with extreme AST due to hypoxic hepatitis had a 22/29 (75%) mortality compared with 9/27 (33%) for all other causes combined.

Academic Medical Centers↗
PubMed1994

Multiple-site binding interactions in metal-affinity chromatography. I. Equilibrium binding of engineered histidine-containing cytochromes c.

Mechanisms of protein retention in immobilized metal-affinity chromatography (IMAC) have been probed using a set of Saccharomyces cerevisiae iso-1-cytochrome c histidine variants constructed by site-directed mutagenesis. Proteins containing a single accessible histidine exhibit Langmuir-type isotherms with maximum protein binding capacities between 5 and 10% of the maximum copper loading and the capacity of the support to bind imidazole. A simple model that assumes that the copper sites are densely packed and can be blocked by protein adsorption yields binding constants for single-histidine proteins that are similar to the binding constant for free imidazole. Proteins containing multiple accessible histidines do not exhibit simple Langmuir-type behavior; they appear to interact with the support by simultaneous coordination to more than one metal ion, the result of which is to increase the apparent binding affinity by as much as a factor of 1000. The protein binding constant depends on the availability of copper sites: binding is significantly weaker at low surface concentrations of copper that presumably cannot support multiple-site interactions. The protein binding capacity drops to zero at copper loadings less than one-half the maximum, indicating that immobilized iminodiacetic acid ligands are sufficiently close together that two can coordinate a single copper ion, which precludes its interaction with a protein. Protein adsorption via multiple-site coordination has important consequences for the optimization of IMAC separations and the design of new IMAC supports.

Animals↗
PubMed1994

Intraobserver and interobserver reliability of asymptomatic subjects' thoracolumbar range of motion using the OSI CA 6000 Spine Motion Analyzer.

Because spinal range of motion (ROM) is assessed routinely in clinical and research settings, a technique is needed that can be performed comfortably, quickly, and reliably. The purpose of this study was to determine if ROM data from asymptomatic subjects measured with the OSI CA 6000 Spine Motion Analyzer (OSI SMA) are reliable within and between observers. Thoracolumbar ROM, from approximately T7 to S2, was measured in all three planes in eight male and 13 female asymptomatic adult subjects (mean age = 29.7 years, SD = 5.6; mean height = 1.7 m, SD = 3.4, mean weight = 78.25 kg, SD = 34.6). A standardized protocol was used to fit each subject with appropriate hardware. Foot placement at a comfortable foot angle was standardized by the use of a template. Subjects performed three practice trials of flexion, extension, right and left sidebending, and right and left rotation. During testing, subjects performed four trials of each maximal pain-free motion. The hardware was completely removed and replaced by the same examiner, and ROM trials in all three planes were repeated. The same procedure was completed by a second examiner. Repeated measures analysis of variance and intraclass correlation coefficients (ICC [2,1] were used to analyze intra- and interobserver data. Intraobserver ICCs were 0.89 or higher for all motions. Interobserver ICCs were 0.85 or higher for all motions. Measurements of thoracolumbar ROM using the OSI SMA are sufficiently reliable within and between observers for clinical assessment and research purposes.

Adult↗
PubMed1993

Crossed-stranded DNA structures for investigating the molecular dynamics of the Holliday junction.

We have developed a simple and rapid procedure for the synthesis and isolation of figure-eight DNA molecules (figure-8s) beginning with phagemid vectors. The figure-8 molecules generated contain a Holliday junction within 2.9 kb (1 kb = 10(3) bases or base-pairs) of continuous homology connecting the two monomer duplexes. The structure of these molecules was verified by restriction endonuclease analysis, two-dimensional agarose gel electrophoresis, and electron microscopy. Digestion of the figure-8 molecules with a restriction enzyme that cleaves only within the region of DNA sequence homology converted them to X-forms that could dissociate to yield linear monomers. The X-form molecules were stable under physiological conditions, a finding contradicting the notion that spontaneous branch migration is fast.

DNA↗
PubMed1993

Assessment of proteinuria and neuropathy in the nonimmunosuppressed BB diabetic rat after abdominal intratesticular islet transplantation.

Only limited studies are available that assess diabetic complications following islet cell transplantation. Our objectives were to quantitate urine total protein, sural nerve morphometry, and sexual function in the diabetic BB/WOR male rat following islet cell transplantation into the abdominal testis. Success of islet cell transplantation was determined by nonfasting, morning, twice-weekly serum glucose and 12-hr fasting glucose, total glycosylated hemoglobin, and HbA1c after six months of diabetes and prior to death. Results showed that 9 of 16 rats were transplanted successfully for a period of at least six months. Pretransplant glucose was 21.9 +/- 4.67 (SD) mM/L and posttransplant glucose was 6.44 +/- 72 mM/L. The 12-hr fasting glucose ranged from 4.61 to 9.28 mM/L in animals prior to death, and glycosylated hemoglobins were not different from controls. Total urinary protein was significantly (P < 0.01) less than untreated diabetic rats (5.66 +/- 1.96 vs. 16.6 +/- 3.7 mg/24 hr) and not different from controls. Penile reflexes and serum testosterone remained normal in islet cell-transplanted animals. Sural nerve morphometry was normal, with 29.2% fewer abnormalities (paranodal swelling, paranodal demyelination, myelin wrinkling, Wallerian degeneration, and segmental demyelination) than untreated diabetic BB/WOR rats. We conclude that abdominal, intratesticular islet transplantation normalizes fasting blood glucose and glycosylated hemoglobin. In addition, the improvement in metabolic control at six months of diabetes was associated with normal total urinary protein, sural nerve morphometry, and sexual function.

Animals↗
PubMed1993

Rescue of neuronal function by cross-regeneration of cutaneous afferents into muscle in cats.

1. This study investigates the relation between the peripheral innervation of low-threshold cutaneous afferents and the postsynaptic potentials elicited by electrical stimulation of those afferents. 2. In cats deeply anesthetized with pentobarbital sodium, cord dorsum potentials (CDPs) and postsynaptic potentials (PSPs) in spinal motoneurons were elicited by stimulation of the caudal cutaneous sural nerve (CCS), the lateral cutaneous sural nerve (LCS), and the medial gastrocnemius (MG) muscle nerve. We tested 1) unoperated cats, and cats in which CCS has been 2) chronically axotomized and ligated, 3) cut and self-reunited, 4) cut and cross-united with LCS, or 5) cut and cross-united with the MG. Terminal experiments were performed 3-36 mo after initial surgery. 3. In cats in which the CCS had been self-reunited or cross-united distally with LCS, tactile stimulation of the hairy skin normally innervated by the distal nerve activated afferents in the CCS central to the coaptation, indicating that former CCS afferents had regenerated into native or foreign skin, respectively. 4. In cats in which the CCS had been cross-united distally with the MG, both stretch and contraction of the MG muscle activated the former CCS afferents. 5. In unoperated cats, CDPs elicited by stimulation of CCS and of LCS exhibited a low-threshold N1 wave and a higher-threshold N2 wave. These waves were greatly delayed and appeared to merge after chronic axotomy of CCS. Regeneration of CCS into itself, into LCS, or into MG restored the normal latencies and configurations of these potentials. 6. In unoperated cats, stimulation of CCS, of LCS, and of MG each produced PSPs of characteristic configurations in the various subpopulations of motoneurons of the triceps surae. CDPs and PSPs elicited by the CCS cross-regenerated into LCS or MG were typical of those generated by the normal CCS, i.e., there was no evidence of respecification of central synaptic connections to bring accord between center and periphery after cross-regeneration. 7. Chronic axotomy of CCS increased the latencies of PSPs from CCS; regeneration of CCS into the CCS, LCS, or MG restored normal latencies. 8. In summary, CDPs and PSPs in motoneurons from the cutaneous sensory nerve CCS are altered by chronic axotomy of CCS, thus indicating their target dependency. These alterations are restored by regeneration of CCS into not only a native or foreign cutaneous target, but also into skeletal muscle. We conclude that muscle as well as skin is capable of providing trophic support for cutaneous afferents.

Afferent Pathways↗
PubMed1993

A preliminary study of the relationship between central auditory processing disorder and attention deficit disorder.

Fifteen boys aged six to ten who met the criteria for attention deficit disorder (ADD) were compared with ten boys who did not have ADD in a double-blind, placebo-controlled, single-crossover study of methylphenidate. To assess the degree of overlap between ADD and central auditory processing disorder (CAPD), all subjects were assessed on parent and teacher behavior rating scales, as well as a battery of CAPD tests at baseline and after three and six weeks of treatment. Twelve of the 15 subjects with ADD and none of the subjects without ADD met the criteria for CAPD. The subjects with ADD also responded to stimulant treatment on the measures of both ADD and CAPD. The overlap in the symptomatology of these disorders, the finding that the criteria for both disorders were met in 12 of 15 cases and the sensitivity of both ADD and CAPD measures to treatment with methylphenidate suggest that ADD and CAPD are closely related disorders. The implications of these results are three-fold. First, sustained attention is a critical feature of performance on CAPD tests and the current diagnostic criteria for CAPD make a clinical separation of the two disorders problematic. Second, stimulants appear to be a useful treatment for the symptoms of both ADD and CAPD. Third, CAPD tests may be a useful measure of ADD symptomatology and response to stimulants.

Analysis of Variance↗
PubMed1992

Prediction of the volume of distribution of 7-hydroxycoumarin in man from in vitro and ex vivo data obtained in rat.

The essential parameter to estimate the first dose size of a drug in man is the volume of distribution. For a drug that has never been used in man before, estimates of the volume of distribution can only be obtained from animals and in vitro data. The purpose of this study was to compare various approaches presented in the literature for predicting the volume of distribution at steady state (VSS) and the terminal phase volume of distribution (Vd beta) in man. A lipophilic active metabolite of coumarin, 7-hydroxycoumarin (7OHC), was selected for this investigation. This compound is extensively metabolized in both the central and peripheral compartments. Of the six methods evaluated, only an empirical allometric approach yielded a reasonable estimate of VSS. All methods underestimated VSS and none of the applicable methods were able to predict Vd beta. The reason for this discrepancy may be due to the fact that the calculation of VSS in man was done assuming elimination from the central compartment.

Animals↗
PubMed1992

Rural mental health appointment adherence: implications for therapy.

Appointment adherence is a significant concern for community mental health centers. In this investigation adherence, cancellations and non-adherence in a rural county was assessed. Overall, 69.3% of the scheduled appointments were kept, 13.7% canceled, and 17% failed. There were no significant differences found between individuals and couples, females and males, or initial and ongoing contracts. Results are encouraging since they are similar to rates reported for other settings and populations. The present findings highlight the importance of the client-therapist relationship and suggest the need for brief therapy in rural communities.

Appointments and Schedules↗