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Biomedical subjects

S M Johnson

Publications and source records attributed to S M Johnson.

At least 19 recordsLinked to original sources
PubMed1992

Excitatory effects of thyrotropin-releasing hormone on neurons within the nucleus ambiguus of adult guinea pigs.

The electrophysiological effects of thyrotropin-releasing hormone (TRH) on neurons within the nucleus ambiguus (NA) of adult guinea pigs were studied using an in vitro brain stem slice preparation. In 0.01-1.0 micron TRH, NA neurons depolarized (25/39), expressed enhanced postinhibitory rebound (8/8 tested), or exhibited oscillations of the membrane potential (17/39). Because the amplitude of postinhibitory rebound in tetrodotoxin (TTX) at various membrane potentials was not altered by TRH, it suggests that TRH enhanced postinhibitory rebound indirectly by depolarizing the cell membrane. The membrane potential oscillations in NA neurons were persistent in TTX and their frequency was dependent on the membrane potential, suggesting that these oscillations were due to intrinsic membrane properties and not to synaptic inputs. The excitation of NA neurons in vitro by TRH suggests that endogenous TRH may modulate the activity of neurons involved in the regulation of respiratory and autonomic function.

Action Potentials↗
PubMed1992

Measuring marital distress in couples with chronically ill children: the Dyadic Adjustment Scale.

The idea that couples with chronically ill children are particularly at risk for marital distress has been supported by clinical observation and empirical research. Three recent controlled studies, however, did not find evidence for this increased risk. A possible explanation for the discrepant findings is that these three studies employed Spanier's Dyadic Adjustment Scale (DAS) as a unidimensional measure of marital adjustment. To develop a better understanding of the discrepant findings of risk for marital distress in couples with chronically ill children, the present study examined both the appropriateness of the DAS's published norms as well as the criterion validity of the DAS for use in this population of couples. Three hundred and sixteen parents (158 couples) from a large urban pediatric health care setting completed a survey investigating interest and need to participate in an intervention program for marital distress. Results indicated that this instrument can reliably predict marital distress in this population of couples, however, mean DAS scores are higher than those established by Spanier.

Adaptation, Psychological↗
PubMed1992

Teaching the process of obtaining informed consent to medical students.

This paper describes a unit on the informed consent process taught to 119 first-year students at the Michigan State University College of Osteopathic Medicine in 1988-89. The unit consisted of a pretest and a posttest, a lecture, readings, small-group discussions, a model videotaped interview, and the students' videotaped interviews with one of two simulated patients. In the interviews, the students were most successful in establishing rapport and engaging the patients in discussions of treatment alternatives, and were less successful in perceiving the patients as unique individuals and in dealing with situations that involved conflict or confrontation. The authors suggest that curricula can be enhanced by focusing on the importance of patients' participation in the informed consent process.

Curriculum↗
PubMed1992

The coccidioidal complement fixation and immunodiffusion-complement fixation antigen is a chitinase.

Culture filtrates and autolysates of Coccidioides immitis have provided suitable crude antigens for the serodiagnosis and prognosis of coccidioidomycosis. One of these, a heat-labile antigen which participates in the immunodiffusion reaction corresponding to the complement fixation reaction (IDCF), has been characterized as a 110-kDa native protein that, when subjected to reducing conditions and heat, yields a 48-kDa component. The present report provides serologic and biochemical evidence that this antigen is a chitinase. This chitinase, isolated from 48-h culture filtrate of the spherule-endospore-phase C. immitis by affinity adsorption to chitin, formed a line of identity with the IDCF reference antigen and participated in the complement fixation reaction with human serum. It lost its enzymatic as well as antigenic activity when heated, but when not heated it retained its enzymatic activity even when precipitated with coccidiodal antibody present in human serum. This chitinase represents a significant serodiagnostic substance and may be important in the morphogenesis of C. immitis.

Antigens, Fungal↗
PubMed1992

Passive smoking: directions for health education among Malaysian college students.

This study investigated knowledge, attitudes, and preventive efforts of Malaysian college students regarding health risks associated with passive smoking, as well as possible directions for intervention and health education programs. Students responded anonymously to a structured written questionnaire. Statistical analyses were conducted to examine (1) differences in knowledge, attitudes, and preventive efforts between smokers and nonsmokers and between men and women; (2) the relationship between smoking by parents, siblings, and friends, and students' knowledge, attitudes, and preventive efforts; and (3) relationships between knowledge, attitudes, and preventive efforts. Peer groups and siblings had a substantial influence on students' attitudes toward passive smoking and their preventive efforts when exposed to passive smoke. A regression analysis revealed a statistically significant linear dependence of preventive efforts on knowledge and attitudes, with the attitude component playing the dominant role. This research suggests that educational efforts on passive smoking, directed toward young college students in developing countries such as Malaysia, should concentrate heavily on changing attitudes and reducing the effects of peer group and sibling influences.

Adult↗
PubMed1992

Membrane potential in myenteric neurons associated with tolerance and dependence to morphine.

Chronic treatment of guinea pigs with morphine produces subsensitivity (tolerance) of the longitudinal smooth muscle-myenteric plexus preparation to a variety of inhibitory agonists (e.g., mu opioid, alpha adrenoceptor and adenosine receptor agonists) and supersensitivity (dependence) to a variety of excitatory agonists (e.g., nicotine, 5-hydroxytryptamine and potassium ions). The present investigation was to determine if these changes in sensitivity could be related to changes in electrical properties of the S and AH neurons in the myenteric plexus. S neurons from morphine-implanted animals were significantly depolarized (7 mV) relative to those from placebo-implanted animals, whereas the membrane potential of AH neurons was unchanged. Approximately 60% of S neurons were hyperpolarized by morphine. In this subset of neurons, membranes were significantly depolarized but the threshold was unchanged in morphine-implanted animals. This means that resting potentials of S neurons from tolerant preparations are closer to threshold. The hyperpolarization produced by morphine (0.1 microM) was similar in preparations from morphine- and placebo-implanted animals. Thus, the partially depolarized state of S neurons in the myenteric plexus is the cause of the subsensitivity and supersensitivity to agonists and can explain both tolerance and dependence. Changes in opioid receptors or their coupling to potassium channels do not appear to contribute to tolerance in the longitudinal smooth muscle-myenteric plexus.

Action Potentials↗
PubMed1992

Stability of ceftazidime in plastic syringes and glass vials under various storage conditions.

The stability of ceftazidime solutions (100 and 200 mg/mL) in plastic syringes and glass vials under various storage conditions was examined. Solutions of ceftazidime 100 and 200 mg/mL in sterile water were placed in polypropylene plastic syringes or glass vials and stored (1) at 21-23 degrees C for up to 8 hours, (2) at 4 degrees C for up to 96 hours, (3) at -20 degrees C for 28 days and then 21-23 degrees C for up to 8 hours, (4) at -20 degrees C for 28 days and then 4 degrees C for up to 96 hours, (5) at -20 degrees C for 91 days and then 21-23 degrees C for up to 8 hours, or (6) at-20 degrees C for 91 days and then 4 degrees C for up to 96 hours. Samples were withdrawn from each syringe and vial at designated times and assayed by high-performance liquid chromatography. Solutions were judged to be stable if drug concentrations remained above 90% of the initial values. The number of particles in each container under each storage condition was also evaluated. Ceftazidime was stable under all storage conditions. In all containers, particulate matter was within USP specifications for small-volume injections, with no change in particle count as a result of the freezing and thawing. Ceftazidime in sterile water in either glass vials or plastic syringes is stable for 8 hours at room temperature or 96 hours at 4 degrees C when such storage occurs (1) immediately after constitution, (2) after 28 days of frozen storage, or (3) after 91 days of frozen storage.

Ceftazidime↗
PubMed1991

Electrophysiological properties of neurons within the nucleus ambiguus of adult guinea pigs.

1. The purpose of this study was to determine the electrophysiological properties of neurons within the region of the nucleus ambiguus (NA), an area that contains the ventral respiratory group. By the use of an in vitro brain stem slice preparation, intracellular recordings from neurons in this region (to be referred to as NA neurons, n = 235) revealed the following properties: postinhibitory rebound (PIR), delayed excitation (DE), adaptation, and posttetanic hyperpolarization (PTH). NA neurons were separated into three groups on the basis of their expression of PIR and DE: PIR cells (58%), DE cells (31%), and Non cells (10%). Non cells expressed neither PIR nor DE and no cells expressed both PIR and DE. 2. PIR was a transient depolarization that produced a single action potential or a burst of action potentials when the cell was released from hyperpolarization. In the presence of tetrodotoxin (TTX), the maximum magnitude of PIR was 7-12 mV. Under voltage-clamp conditions, hyperpolarizing voltage steps elicited a small inward current during the hyperpolarization and a small inward tail current on release from hyperpolarization. These currents, which mediate PIR, were most likely due to Q-current because they were blocked with extracellular cesium and were insensitive to barium. 3. DE was a delay in the onset of action potential firing when cells were hyperpolarized before application of depolarizing current. When cells were hyperpolarized to -90 mV for greater than or equal to 300 ms, maximum delays ranged from 150 to 450 ms. The transient outward current underlying DE was presumed to be A-current because of the current's activation and inactivation characteristics and its elimination by 4-aminopyridine (4-AP). 4. Adaptation was examined by applying depolarizing current for 2.0 s and measuring the frequency of evoked action potentials. Although there was a large degree of variability in the degree of adaptation, PIR cells tended to express less adaptation than DE and Non cells. Nearly three-fourths of all NA neurons adapted rapidly (i.e., 50% adaptation in less than 200 ms), but PIR cells tended to adapt faster than DE and Non cells. PTH after a train of action potentials was relatively rare and occurred more often in DE cells (43%) and Non cells (33%) than in PIR cells (13%). PTH had a magnitude of up to 18 mV and time constants that reflected the presence of one (1.7 +/- 1.4 s, mean +/- SD) or two components (0.28 +/- 0.13 and 4.1 +/- 2.2 s).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1991

Nonspecific tolerance in ileal circular muscle-myenteric plexus preparations from morphine-pretreated guinea pigs.

Guinea pigs were treated for 6 to 8 days by s.c. implantation of pellets, each containing a mixture of morphine base (120 mg) and morphine hydrochloride (35 mg). Each guinea pig received one pellet. Circular muscle-myenteric plexus preparations from the pretreated animals exhibited 6.1-fold tolerance to the inhibitory effects of morphine on nerve-mediated contractions of the circular muscle. Morphine-tolerant tissues were also tolerant to the inhibitory effects of another mu agonist, (D-Ala2-N-Me-Phe4,Gly5- ol)enkephalin (2.7-fold), the selective kappa agonist, dynorphin (4.0-fold), the adrenoceptor agonist, clonidine (22-fold) and the adenosine receptor agonist, 2-chloroadenosine (43-fold). That is, tissues were tolerant to four inhibitory agents that acted via four distinct receptors. Tolerance therefore cannot be explained by a change in the opioid receptor that was occupied chronically by morphine. Nonspecific tolerance would result if an intracellular effector mechanism that was shared by each agonist was altered by morphine pellet implantation. Alternatively, tolerance could be a consequence of the neuronal hyperexcitability that is induced by chronic exposure to morphine. As such, inhibitory agents, irrespective of the receptors or intracellular mechanisms that they activate, may be less effective in reducing the excitability of myenteric neurons and hence less effective in decreasing transmitter release.

2-Chloroadenosine↗
PubMed1991

Carotid endarterectomy: a review.

The carotid endarterectomy procedure has provided an invaluable option in the management of patients with symptomatic atherosclerotic carotid artery disease. The criteria for surgical interventions vary from different institutions as well as the mortality and morbidity, but, for a select patient population, it is a viable alternative to conservative medical management.

Arteriosclerosis↗
PubMed1991

The effect of interferon-alpha on the ecto 5'-nucleotidase of human lymphoblastoid B-cell lines depends on the class of immunoglobulin secreted.

Thirteen immunoglobulin-secreting mycoplasma-free human cell lines were treated with increasing concentrations of lymphoblastoid interferon-alpha (IFN-alpha) in order to study the activity of their CD73 ecto-5'-nucleotidase (5'N), their rate of growth and their immunoglobulin (Ig) production. Although IFN-alpha did not immediately affect the activity of the 5'N on the cell plasma membranes, the class of Ig secreted by the cell lines determined whether culturing the cells in the presence of IFN-alpha gave a small increase in the 5'N enzyme activity (IgM), or had no effect (IgE), or showed a marked decrease in activity (IgG). The 5'N activity of two IgG4-secreting clones was more suppressed by IFN-alpha than that of the four IgG1-secreting clones. The clone with the highest 5'N was killed by IFN-alpha. A high 5'N activity inhibited the growth rate of the cells, since the rate of growth of the three IgG-producing lines with high 5'N was increased when their 5'N was inhibited by increasing concentrations of IFN-alpha. The growth rate of three other Ig-producing lines was uninhibited by up to 10(5) U/ml IFN-alpha, whereas the rest were partially or strongly inhibited. Excluding the clone which died, 10/11 lines or cultures increased their Ig/cell by a mean of 25% at 100 U/ml IFN-alpha; their total Ig production also increased despite any growth inhibition. One IgG-secreting clone decreased its Ig production at 100 U/ml IFN-alpha by 11%. The Ig/cell of 4/5 of the cell lines increased with IFN-alpha concentrations up to at least 10(4) U/ml. The increase in Ig/cell was not related to the class of Ig, the growth rate of the cells or the amount of 5'N.

5'-Nucleotidase↗
PubMed1991

Marital therapy: issues and challenges.

This paper outlines the advances made in the field of marital therapy in the last decade. The present status of clinical intervention, empirical research and theoretical conceptualization is reviewed. In addition, the challenges the field now faces are outlined, and proposals made for future directions, which would enable marital intervention to become a more comprehensive and systematic endeavor.

Adaptation, Psychological↗
PubMed1990

Opioid inhibition of cholinergic transmission in the guinea-pig ileum is independent of intracellular cyclic AMP.

This study examined whether the inhibitory actions of opioids in the guinea-pig ileum were influenced by agents which mimic or elevate intracellular cyclic adenosine 3',5'-monophosphate (cyclic AMP) levels. In longitudinal muscle-myenteric plexus preparations, the mu agonist, [D-Ala2,NMePhe4,Gly-ol5]enkephalin (DAGO) and the kappa agonist, dynorphin A-(1-13) depressed contractions of the longitudinal muscle evoked by electrical stimulation of myenteric neurons. Mean IC50 values were 19 and 2.8 nM for DAGO and dynorphin, respectively. Neither forskolin, cholera toxin nor dibutyryl cyclic AMP affected significantly the IC50s for the opioid agonists. The experiments suggest that mu and kappa agonists inhibit excitatory cholinergic transmission to the longitudinal muscle by intracellular effector mechanisms that do not involve cyclic AMP.

1-Methyl-3-isobutylxanthine↗
PubMed1990

Hyperpolarization of myenteric neurons by opioids does not involve cyclic adenosine-3',5'-monophosphate.

To investigate the role of cyclic adenosine-3'5'-monophosphate on the inhibitory actions of opioids in guinea-pig ileum, we made intracellular recordings from the two electrophysiologically defined classes of neurons (S and AH) in the myenteric plexus. The selective opioid mu agonist (D-Ala2,N-Me-Phe4,Gly5-ol)-enkephalin caused a membrane hyperpolarization in 34 out of 67 S neurons but did not affect the membrane potential of AH neurons. The mean amplitude (+/- S.E.M.) of the hyperpolarization was 8.2 +/- 0.8 mV. Forskolin, which activates adenylate cyclase and increases intracellular cyclic adenosine-3',5'-monophosphate levels, caused a membrane depolarization in AH neurons (9.4 +/- 1.9 mV) but did not alter the resting membrane potential of S neurons. Similarly, neither the phosphodiesterase inhibitor, isobutylmethylxanthine, nor the membrane permeable analogue of cyclic adenosine-3',5'-monophosphate, dibutyryl cyclic adenosine-3'-5'-monophosphate, altered the resting membrane properties of S neurons. Furthermore, none of these agents affected significantly the amplitude of the hyperpolarization of S neurons by (D-Ala2,N-Me-Phe4,Gly5-ol)-enkephalin. The experiments indicate that changes in intracellular cyclic adenosine-3',5'-monophosphate are not important in the processes that link occupation of mu receptors to the opening of potassium channels on myenteric neurons.

1-Methyl-3-isobutylxanthine↗
PubMed1979

The composition and fluidity of normal and leukaemic or lymphomatous lymphocyte plasma membranes in mouse and man.

The lymphocyte surface membranes from normal and leukaemic or lymphomatous cells from man and mouse were isolated, characterized, and analyzed both biochemically and by diphenyl hexatriene fluorescence polarization. The cholesterol/phospholipid molar ratio for all the pure lymphocyte plasma membranes was 0.45--0.50, and the fluorescence polarization results showed that values much higher than this were not credible. The lipid composition of all the plasma membranes was remarkably similar, except for the concentration of free fatty acids and glycerides. The latter two were particularily high in the mouse lymphoma membrane and these, rather than a low cholesterol concentration, were responsible for the increased fluidity of the cells. The most prominent protein in most of the plasma membrane preparations was actin. This is found only by some authors, and its presence probably depends on the method of lymphocyte disruption.

Adult↗
PubMed1979

Hemodynamic effects of oxprenolol and propranolol in hypertension.

Oxprenolol is a beta-adrenergic blocker with intrinsic sympathomimetic activity. Such drugs are not currently available in the United States, although they have the advantage of less negative inotropic effect than the available propranolol. In 18 patients with mild essential hypertension, oxprenolol (9 patients) or propranolol (9 patients) was added to thiazide in random double-blind fashion and continued for 7 wk during which supine heart rate, blood pressure, and noninvasively measured cardiac output (by CO2 rebreathing) were determined weekly. With thiazide dosage constant throughout, maximal dose titration to 386. +/- 52.1 (SEM) mg/day of oxprenolol and 360.0 +/- 45.4 mg/day of propranolol was achieved over the first 5 wk. Blood pressure fell with both (141.8 +/- 4.8/96.0 +/- 2.3 to 128.0 +/- 5.1/87.2 +/- 1 mm Hg on oxprenolol, p less than 0.01; 150.8 +/- 5.5/98.0 +/- 1.7 to 129.9 +/- 5.5/86.8 +/- 3.4 mm Hg on propranolol, p less than 0.01). Cardiac output fell from 6.85 +/- 0.63 to 5.77 +/- 0.45 1/min (p less than 0.01) on oxprenolol, and from 6.79 +/- 0.61 to 5.37 +/- 0.37 1/min (p less than 0.02) on propranolol. Oxpranolol. Oxprenolol reduced heart rate from 76.4 +/- 2.0 to 65.6 +/- 2.1 beats/min (p less than 0.001) and it fell from 82.0 +/- 3.8 to 65.3 +/- 3.7 beats/min (p less than 0.001) with propranolol; the fall in heart rate was less but not significantly so for oxprenolol (-14.2 +/- 1.8% and -19.8 +/- 2.8%, p less than 0.1). Thus oxprenolol is equivalent to propranolol in antihypertensive action; minor hemodynamic differences between the two drugs might reflect intrinsic sympathomimetic activity of oxprenolol. Oxprenolol should be considered as an alternative to propranolol.

Adult↗