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Biomedical subjects

M C Johnson

Publications and source records attributed to M C Johnson.

At least 73 records · Page 4Linked to original sources
PubMed1994

An investigation of habituation in the jellyfish Aurelia aurita.

Three experiments were conducted to examine the effectiveness of different forms of tactile stimulation, probe and stream, and interstimulus intervals (ISI) in producing habituation in the polypoid sessile stage of the jellyfish Aurelia aurita. Results from Experiment 1 showed that polyps significantly decreased their responsiveness to both forms of tactile stimulation with 30-s ISI across 60 trials. Response to a novel stimulus indicated that the response decrement had not been due to fatigue. When the ISI was lengthened to 6 min in Experiment 2, response to the probe form of tactile stimulation did not significantly decrease across 20 trials. Using an ISI of 1 min in Experiment 3, response to the probe form of tactile stimulation decreased significantly across 40 trials. A significant increase in response to the original stimulus (dishabituation) following presentation of a novel stimulus indicated that response decrement was due to habituation or a habituation-like process rather than simple effector fatigue or sensory adaptation.

Animals↗
PubMed1994

Severe diffuse axonal injury in adults and children.

Diffuse axonal injury (DAI) occurs in 30% of all fatal head injuries. DAI is identified on autopsy as microscopic lesions that commonly appear in the splenium of the corpus callosum, rostral brainstem and frontal and temporal lobes of the cerebrum. Clinical presentation of severe DAI includes patients with no lucid interval and decorticate or decerebrate posturing. Diagnostic studies describe concurrent pathologic anatomy associated with DAI. The most common mechanism for DAI is motor vehicle accidents. The neuroscience nurse needs to have an understanding of DAI anatomy and physiology, including the differences and similarities in the clinical presentation and neurologic functional outcome in both adult and pediatric populations.

Accidents, Traffic↗
PubMed1993

Repair of coarctation of the aorta in infancy: comparison of surgical and balloon angioplasty.

Surgical repair of coarctation of the aorta in infancy has recently been challenged by some investigators who suggest that balloon angioplasty results in a lower mortality rate and similar risk of restenosis. Over a 44-month period, 37 consecutive infants with a mean age of 33 days (median, 15 days; range, 1 to 200 days) and mean and median weight of 3.7 kg (range, 2.4 to 5.4 kg) underwent surgical repair of coarctation of the aorta with either an end-to-end anastomosis (24 patients) or subclavian flap angioplasty (13 patients). There were no operative deaths (95% confidence interval, 0% to 10%). Four patients died late (> 30 days) after surgery (11%). Four patients (11%) (95% confidence interval, 3% to 25%) had residual gradients greater than 20 mm Hg. A review of the recent literature on treatment of native coarctation in infants with surgical repair (18 reports, 1189 patients) and balloon angioplasty (8 reports, 57 patients) reveals a similar early mortality rate but a much higher rate of recoarctation in infants who were treated with balloon dilation (57%) as compared with those who underwent surgical repair (14%). Because of the incidence of restenosis, balloon dilation as compared with surgical repair does not yet offer an improved outcome for native coarctation of the aorta in infancy.

Abnormalities, Multiple↗
PubMed1992

Small atrial natriuretic peptide analogues: design, synthesis, and structural requirements for guanylate cyclase activation.

Structure/activity studies on atrial natriuretic peptide ANP (1-28) have highlighted three portions of the native molecule as necessary for its biological responses. We have linked these three regions and excised the remaining segments to produce a family of small analogues (less than half the size of the parent) which demonstrate the full range of ANP's actions. Importantly, these compounds act at both major types of ANP receptor. Two critical modifications lead to more potent analogues; both involve expanding the cyclic portion of the molecule. Further optimization of one of these modified structures leads to A68828, a full ANP agonist which shows promise as a preventative agent against acute renal failure.

Acute Kidney Injury↗
PubMed1992

Klippel-Feil syndrome revisited: diagnostic pitfalls impacting neurosurgical management.

Klippel-Feil syndrome in its most basic definition includes several anomalous conditions of the cervicomedullary junction and suboccipital region. Pediatric neurosurgeons are often involved in surgical palliation of this syndrome, without realizing how the accompanying anomalies may obfuscate management in the older child. A brief review of the embryology of the rhombencephalon helps to clarify the etiology of some of these symptoms which may cause confusion and, occasionally, inappropriate treatment. Illustrative cases will demonstrate some of these pitfalls. Appropriate early intervention, such as posterior fossa decompression, ventricular shunting, and fundal plication, may help to avoid needless morbidity. The advent of magnetic resonance scanning has helped to clarify the diagnosis and resulted in more appropriate treatment in these cases.

Female↗
PubMed1992

Nucleotide and amino acid sequence of pap-gene (pediocin AcH production) in Pediococcus acidilactici H.

N-terminal analysis of purified pediocin AcH produced a partial sequence of 23 amino acids. This sequence matched perfectly with a segment of 23 amino acids in a 62 amino acid molecule generated from the 186 nucleotide sequence open reading frame in a Hind III fragment in pSMB74 encoding pap-gene (pediocin AcH production). It is suggested that the molecule is translated as inactive prepediocin AcH of 62 amino acids. Then through enzymatic modifications the leader segment of 18 amino acids is removed from the NH2-terminal. The remaining segment of 44 amino acids is active pediocin AcH of 4628 M(r).

Amino Acid Sequence↗
PubMed1992

Novel method to extract large amounts of bacteriocins from lactic acid bacteria.

Antimicrobial peptides, bacteriocins, produced by lactic acid bacteria were adsorbed on the cells of producing strains and other gram-positive bacteria. pH was a crucial factor in determining the degree of adsorption of these peptides onto cell surfaces. In general, between 93 and 100% of the bacteriocin molecules were adsorbed at pHs near 6.0, and the lowest (< or = 5%) adsorption took place at pH 1.5 to 2.0. On the basis of this property, a novel isolation method was developed for bacteriocins from four genera of lactic acid bacteria. By using this method we made preparations of pediocin AcH, nisin, sakacin A, and leuconocin Lcm1 that were potent and concentrated. This method produced a higher yield than isolation procedures, which rely on precipitation of the bacteriocins from the cell-free culture liquor. It is simple and can be used to produce large quantities of bacteriocins from lactic acid bacteria to be used as food biopreservatives.

Adsorption↗
PubMed1992

Studies on the mechanism of the novel stimulatory effect of angiotensin-II on adenylate cyclase in rat fetal skin fibroblasts.

In contrast to other systems in which angiotensin-II (AII) inhibits adenylyl cyclase, in fetal skin fibroblasts the peptide stimulates cAMP accumulation. The mechanism of this novel effect was studied by analysis of the actions of AII and other regulators on the adenylyl cyclase system in cultured cells. In the presence of phosphodiesterase inhibitors, AII, isoproterenol (ISO), choleratoxin (CTx), and forskolin (Fk) stimulated cAMP accumulation by 2.0 +/- 0.26-, 26 +/- 0.9-, 75 +/- 5.6-, and 88 +/- 3.3-fold, respectively. AII potentiated the stimulatory effect of ISO and CTx by 1.5 +/- 0.1- and 1.25 +/- 0.03-fold, respectively, but had no effect on that of Fk. Preincubation of the cells with PTx did not prevent the stimulatory effect of AII on basal and ISO- and CTx-stimulated cAMP, indicating that the effect of AII was not due to interaction with Gi. Unexpectedly, pretreatment of the cells with PTx for 18 h inhibited cAMP production stimulated by ISO and Fk. Similar inhibition by PTx was observed in adult rat skin fibroblasts, but not in adult human fibroblasts, in which pretreatment with PTx resulted in potentiation of Fk-stimulated cAMP production. ADP ribosylation studies showed that the optical density of the band corresponding to Gs was less than 20% that of Gi and Go in rat fetal cells, suggesting that excess release of the beta-gamma-subunit is responsible for the inhibition of cAMP production by PTx. However, immunoblot analysis of G-proteins showed that the content of Gs alpha was similar to that of Gi alpha and Go alpha in rat and human, fetal and adult cells. In contrast to the effect in intact cells, AII had no effect on basal or stimulated adenylyl cyclase activity in cell homogenates, suggesting that the stimulatory effect observed in intact cells is indirect. The stimulatory action of AII on cAMP production was not blocked by indomethacin, indicating that the effect is not mediated by prostaglandin formation. The stimulation of cAMP by AII was mimicked by 10-min incubation with phorbol 12-myristate 13-acetate (PMA), and prevented after cellular protein kinase-C (PKC) depletion by 4- or 6-h preincubation with PMA. However, the stimulation was not prevented by the PKC inhibitors staurosporine and H7 or 24-h preincubation with PMA, suggesting that the effect is not mediated by a traditional PKC-dependent mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenylyl Cyclases↗
PubMed1991

The role of fitness on VO2 and VCO2 kinetics in response to proportional step increases in work rate.

The purpose of this study was to determine the effect of fitness and work level on the O2 uptake and CO2 output kinetics when the increase in work rate step is adjusted to the subject's maximum work capacity. Nine normal male subjects performed progressive incremental cycle ergometer exercise tests in 3-min steps to their maximum tolerance. The work rate step size was selected so that the symptom-limited maximum work rate would be reached in four steps at 12 min in all subjects. Oxygen consumption (VO2) and carbon dioxide production (VCO2) were calculated breath by breath. For the group, the time (mean, SEM) to reach 75% of the 3-min response (T0.75) for VO2 increased significantly (P less than 0.01) at progressively higher work rate steps, being 53.3 (5.5) s, 63.5 (4.6) s, 79.5 (5.0) s, and 94.5 (5.8) s, respectively. In contrast, T0.75 for VCO2 did not change significantly [74.9 (7.4) s, 75.6 (5.0) s, 85.1 (5.3) s, and 89.4 (6.3) s, respectively]. VCO2 kinetics were slower than VO2 kinetics at the low fractions of the subjects' work capacities but were the same or faster at the high fractions because of the slowing of VO2 kinetics. The first step showed the fastest rise in VO2. While VO2 kinetics slowed at each step, they were faster at each fraction of the work capacity in the fitter subjects. The step pattern in VO2 disappeared at high work rates for the less fit subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Influence of Growth Conditions on the Production of a Bacteriocin, Pediocin AcH, by Pediococcus acidilactici H.

The influence of growth parameters on the production of pediocin AcH by Pediococcus acidilactici H was studied. This strain produced large quantities of pediocin AcH in TGE broth (Trypticase [1%], glucose [1%], yeast extract [1%], Tween 80 [0.2%], Mn [0.033 mM], Mg [0.02 mM] [pH 6.5]) within 16 to 18 h at 30 to 37 degrees C (final pH, 3.6 to 3.7). Pediocin AcH production was negligible when the pH of the medium was maintained at 5.0 or above, even in the presence of high cell mass.

Journal Article↗
PubMed1991

Angiotensin-II receptor subtypes and coupling to signaling systems in cultured fetal fibroblasts.

Angiotensin-II (AII) receptors and their coupling to signaling transduction systems were studied in fetal skin fibroblasts using the receptor subtype-specific antagonists Dup753 (type 1) and PD123177 (type 2). In primary cultures, total binding per cell remained constant from days 2-6 of culture, but after subculture levels were initially decreased, then increased until the cells reached confluence. In freshly isolated cells more than 90% of the receptors were type 2, and only a minor fraction were type 1, findings that are consistent with autoradiographic analyses and membrane binding assays. The proportions tended to reverse during culture, with type 1 receptors accounting for 60-80% and type 2 for 20-40% by day 6 of culture. In secondary culture, subtype 1 was about 50% on day 1 and increased to 70% by day 6. At subsequent passages, the proportion of receptor subtypes remained constant up to 6 days, with 90% being of the type 1 variety and 10% of type 2. Scatchard analysis of binding in the presence of the selective antagonists showed similar binding affinities for both subtypes, and the changes in receptor subtype during culture were due primarily to changes in receptor number. Treatment of primary cultures with actinomycin-D for 24 h prevented the transition from AII receptor type 2 to type 1 by increasing the absolute number of type 2 receptors, suggesting that receptor synthesis is regulated at the posttranscriptional level. Stimulation of the cells with 100 nM AII resulted in increases in inositol phosphate accumulation, an effect that was prevented by the type 1 antagonist, but not by the type 2 antagonist. In contrast with other systems in which AII inhibits adenylate cyclase, in fetal fibroblasts AII stimulate cAMP production. The increases in cAMP were more pronounced in secondary cultures in which type 1 receptor content is higher, and the effect was prevented by the type 1, but not the type 2, antagonists. These findings demonstrate the presence of both AII receptor subtypes in fetal fibroblasts, but only the type 1 receptors are coupled to a known intracellular signalling system. The changes in AII receptor subtypes may be the consequence of alterations in intercellular communication, endocrine, or paracrine factors during culture.

Angiotensin II↗
PubMed1991

Effect of exercise testing protocol on parameters of aerobic function.

Four different patterns of increasing work rate (ramp and 1-min, 2-min, and 3-min steps) to maximum tolerance were studied in eight normal male subjects during cycle ergometer exercise testing to determine the effect of the work rate protocol on the parameters of aerobic function. The overall rate of work rate increase was kept constant. Measurements included VO2max, anaerobic threshold (AT), and the O2 uptake increase with respect to work rate increase (delta VO2/delta WR). VO2, VCO2, VE, respiratory exchange ratio (R), PETCO2, and PETO2 were calculated breath-by-breath. No significant difference was found in VO2max, AT, AT/VO2max, and delta VO2/delta WR among the four work rate protocols. Other measurements such as total work, maximal work rate, VCO2, VE, R, HR, O2 pulse, and the VO2 at which VE increases disproportionately to VCO2 (ventilatory compensation point) were also similar among the four protocols. Both the ramp and 1-min step work rate tests had no step pattern in either VO2 or VCO2, and the step pattern for the 2-min and 3-min step tests was attenuated or disappeared at work rates above AT. We conclude that the parameters of aerobic function, and other physiological responses at maximum work rate, were independent of the pattern of work rate increase, provided that the overall rate of work rate increase was the same.

Adult↗
PubMed1990

Estimates of psychological distress among Vietnamese refugees: adolescents, unaccompanied minors and young adults.

This study focuses on the assessment of psychological distress among three subgroups of Vietnamese refugee youth: adolescents, unaccompanied minors, and young adults. Using translated and backtranslated instruments, data was gathered in refugee camps in the Philippines in order to provide baseline measurement for future comparisons, as well as to begin to develop normative standards for these populations. A rationale for the choice of instruments (Vietnamese Depression Scale, Hopkins Symptom Checklist-25 and General Health Questionnaire) is offered and mean scores and percentages scoring above established clinical cut-offs are presented. Results indicate relatively high levels of depression and anxiety for the young adult group, although anxiety appeared high across all three groups. All three groups also scored poorly on self-reports of general health, with the young adults and unaccompanied minors being especially overrepresented in the clinical range. Significant method problems were noted regarding construct validity in the assessment of depression, and instructional set differences that may account for the relatively low intercorrelations between seemingly similar measures.

Adolescent↗
PubMed1990

Chronic ethanol exposure before injury produces greater immune dysfunction after thermal injury in rats.

Chronic alcoholics constitute a small but significant subgroup of burned patients. The effects of chronic alcohol exposure on immune function in burned patients has not to our knowledge been studied. This study was designed to determine the effect of chronic alcohol exposure before burn injury on immune function after injury in rats. Immune function assessed by in vivo chemotaxis and responsiveness of non-adherent splenocytes to both a T-cell mitogen, concanavalin A, and a B-cell mitogen, lipopolysaccharide, was measured at 4 days after a 20% BSA full-thickness burn injury and/or gavage of 2.4 gm/kg/day of ethanol for 14 days. Chronic ethanol ingestion before burn injury produced significant suppression in chemotaxis and response to lipopolysaccharide but not in response to concanavalin A. These results suggest that chronic alcohol exposure before injury can contribute to further impaired immune function after injury, and may lead to increased susceptibility to infection and increased mortality.

Alcoholism↗
PubMed1990

Antigenic property of pediocin AcH produced by Pediococcus acidilactici H.

Pediocin AcH, a bacteriocin of Pediococcus acidilactici H, inhibits the growth of several food spoilage and pathogenic bacteria. The antigenic property of partially purified pediocin AcH was tested by immunizing mice and a rabbit. Pediocin AcH was not immunogenic in these animals as determined by immunoblotting even after conjugation to bovine serum albumin. The non-immunogenic nature of pediocin AcH, its non-toxicity to laboratory animals and its hydrolysis by gastric proteolytic enzymes may be considered favourably in its possible use as a food preservative.

Animals↗