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A J Miller

Publications and source records attributed to A J Miller.

At least 73 records · Page 4Linked to original sources
PubMed1995

In situ characterization of Clostridium botulinum neurotoxin synthesis and export.

A monoclonal antitoxin/colloidal gold probe and sequential centrifugation were used to study synthesis, translocation and export of Clostridium botulinum strain 62A neurotoxin (NT). Exponential growth occurred after 5 h of anaerobic incubation of spores and continued for 15-16 h. NT was detected at 15 h using the probe and transmission electron microscopy (TEM), 2 h earlier than the first detection by the mouse bioassay. During exponential growth, the probe localized NT primarily in the cytoplasm, on the inner side of the cytoplasmic membrane and in the cell wall. During stationary and death phases, the NT was located within the cytoplasm, cell wall and extracellularly. NT was released from the cell during cell wall exfoliation. Cells retained NT after repeated gelatin-phosphate washes and sequential centrifugations, consistent with the TEM observation that the NT is bound to the cell wall. These observations indicate that the process of Cl. botulinum type A NT production follows a sequence of synthesis, translocation across the cytoplasmic membrane and export through the cell wall.

Animals↗
PubMed1995

Further analysis of the mechanisms underlying the tracheal relaxant action of SCA40.

1. SCA40 (1nM-10 microM), isoprenaline (1-300 nM) and levcromakalim (100 nM-10 microM) each produced concentration-dependent suppression of the spontaneous tone of guinea-pig isolated trachea. Propranolol (1 microM) markedly (approximately 150 fold) antagonized isoprenaline but did not antagonize SCA40. The tracheal relaxant action of SCA40 was unaffected by suramin (100 microM) or 8-(p)-sulphophenyltheophylline (8-SPT; 140 microM). 2. An isosmolar, K(+)-rich (80 mM) Krebs solution increased tracheal tone, antagonized SCA40 (approximately 60 fold), antagonized isoprenaline (approximately 20 fold) and very profoundly depressed the log concentration-effect curve for levcromakalim. Nifedipine (1 microM) did not itself modify the relaxant actions of SCA40, isoprenaline or levcromakalim. However, nifedipine prevented the rise in tissue tone and the antagonism of SCA40 and isoprenaline induced by the K(+)-rich medium. In contrast, nifedipine did not prevent the equivalent antagonism of levcromakalim. 3. Charybdotoxin (100 nM) increased tracheal tone, antagonized SCA40 (approximately 4 fold) and antagonized isoprenaline (approximately 3 fold). Nifedipine (1 microM) prevented the rise in tissue tone and the antagonism of SCA40 and isoprenaline induced by charybdotoxin. 4. Quinine (30 microM) caused little or no change in tissue tone and did not modify the relaxant action of isoprenaline. However, quinine antagonized SCA40 (approximately 2 fold). Nifedipine (1 microM) prevented the antagonism of SCA40 induced by quinine. 5. Tested on spontaneously-beating guinea-pig isolated atria SCA40 (1 nM-10 microM) increased the rate of beating in a concentration-dependent manner. Over the concentration-range 1 microM-10 microM, SCA40 also caused an increase in the force of atrial contraction. 6. Intracellular electrophysiological recording from guinea-pig isolated trachealis showed that the relaxant effects of SCA40 (1 micro M) were often accompanied by the suppression of spontaneous electrical slow waves but no change in resting membrane potential. When the concentration of SCA40 was raised to 10 micro M, its relaxant activity was accompanied both by slow wave suppression and by plasmalemmal hyperpolarization.7. SCA40 (10 nM- 100 micro M) more potently inhibited the activity of cyclic AMP phosphodiesterase (PDE)than that of cyclic GMP PDE derived from homogenates of guinea-pig trachealis. Theophylline(1 micro M- 1O mM) also inhibited these enzymes but was less potent than SCA40 in each case and did not exhibit selectivity for inhibition of cyclic AMP hydrolysis.8. Tested against the activity of the isoenzymes of cyclic nucleotide PDE derived from human blood cells and lung tissue, SCA40 proved highly potent against the type III isoenzyme. It was markedly less potent against the type IV and type V isoenzymes and even less potent against the isoenzymes types I and II.9. It is concluded that the tracheal relaxant action of SCA40 (1 nM- 1 micro M) does not involve the activation of beta-adrenoceptors or P1 or P2 purinoceptors. Furthermore, this action is unlikely to depend upon the opening of BKca channels with consequent cellular hyperpolarization and voltage-dependent inhibition of Ca2+ influx. The tracheal relaxant action of SCA40 (up to 1 micro M) is more likely to depend upon its selective inhibition of the type III isoenzyme of cyclic nucleotide PDE. At concentrations above 1 micro M, SCA40 exerts more general inhibition of the isoenzymes of cyclic nucleotide PDE and may then promote the opening of BKca channels.

Animals↗
PubMed1995

Effect of maturation on 31P magnetic resonance spectroscopy of the rabbit masseter muscle.

This work studies the dynamic metabolic changes of the rabbit masseter muscle during post-natal development. The composition and proportion of oxidative and glycolytic muscle fibers alter during maturation. The masseter muscle, as most muscles of the craniofacial region, exhibits unusual development in composition of isoforms of myosin. The effect of this unusual composition on the dynamic metabolic properties of the masseter muscle have not been assessed. The metabolism of the rabbit masseter muscle was studied by means of 31P-nuclear magnetic resonance (NMR) spectroscopy. Contraction was elicited by electrical stimulation of the muscle in the anesthetized animal. Five animals were studied at 8 weeks and 24 weeks so that both the juvenile and adult stages could be evaluated. The dynamic biochemical changes in the masseter muscle were studied by the analysis of NMR spectra. A single-turn surface coil (copper) was used, and the original signal was treated with Fourier transforms to obtain 31P spectra. The low signal-to-noise ratio required averaging 16 acquisitions (acquisition time = 400 msec, repetition rate = 1.8 sec) in 30 sec and then obtaining continuous spectra for 27 min. Each averaged spectrum demonstrated five peaks: inorganic phosphate (Pi), creatine phosphate (PCr), and three peaks related to adenosine triphosphate (ATP). The protocol involved recording an initial three-minute rest period, stimulating the muscle at 5 Hz for 3 min twice, separated by three-minute rest periods, and stimulating the muscle at 50 Hz twice for 3 min separated by rest periods. The Pi/PCr ratio increased significantly in the adult masseter during both 5-Hz stimulations, evoking twitching, and the first 50-Hz stimulation, evoking tetany (repeated ANOVA, P < 0.05). The resting pH (6.96 +/- 0.13) was significantly lowered during both twitching (6.85 +/- 0.10; P < 0.0038) and tetany (6.55 +/- 0.13; P < 0.0001), but only in the adult masseter muscle. These finding suggest that the adult masseter muscle possesses more glycolytic fibers as it modifies its metabolism during postnatal development.

Adenosine Triphosphate↗
PubMed1995

Development and histologic characterizations of an animal model of antigen-induced arthritis of the juvenile rabbit temporomandibular joint.

Children with juvenile rheumatoid arthritis or juvenile chronic arthritis often exhibit temporomandibular joint (TMJ) involvement accompanied by pain, dysfunction, and growth abnormalities. Despite the severe functional and developmental consequences of this disease, its pathogenesis remains poorly understood, but important insights may be provided by a suitable animal model of this disease. The purpose of this study was to develop and histologically characterize a juvenile animal model of antigen-induced arthritis of the TMJ. Arthritis was induced with an intra-articular administration of ovalbumin in previously sensitized 10-week-old male New Zealand white rabbits. Sham-treated and untreated rabbits were used as controls. The TMJs were retrieved en bloc at 5, 10, 15, 35, and 55 days post-challenge for histology and matrix histochemistry. Antigen-treated joints demonstrated severe arthritis, including mononuclear cell infiltration, synovial lining and villous hyperplasia, and pannus formation, as early as 5 days after challenge; the arthritis was maintained up to 55 days post-challenge. A decrease in the area of the TMJ disc that stained positively for glycosaminoglycans was observed throughout the experimental period. Loss of collagen staining was primarily localized to sites at the junction of the synovium with bone and fibrocartilage. The histopathologic features of this model of antigen-induced arthritis of the juvenile rabbit TMJ are similar to those observed previously in adult animal models of experimental arthritis and in human rheumatoid arthritis. This animal model will be useful for understanding the pathogenesis of juvenile rheumatoid arthritis of the TMJ, and for exploring the mechanisms for aberrant craniofacial growth.

Analysis of Variance↗
PubMed1995

The lymphatic drainage of the parietal pericardium in man.

Parietal pericardial lymphatics were visualized by indirect and direct India ink injections in 35 human cadavers. Studies included examination of cleared specimens under the dissecting microscope and standard light microscopy. The lymphatic vessels of the ventral pericardial surface most often pass along the phrenic nerves cranially to terminate in the anterior right and left and transverse mediastinal nodes, or caudally to the diaphragm or prepericardial lymph nodes. The lymphatics draining the lateral parts of pericardium pass to the anterior mediastinal, tracheobronchial, lateropericardial, prepericardial and posterior mediastinal (juxtaesophageal) lymph nodes. The posterior part of the pericardium drains to the juxtaesophageal and tracheobronchial nodes. Lymphatics from the diaphragmatic part of the pericardium pass to the right lateropericardial and prepericardial, juxtaesophageal and tracheobronchial nodes. The pericardial cupula is anteriorly drained to the anterior mediastinal nodes, and posteriorly to the tracheobronchial nodes. In cleared specimens two networks of lymphatic vessels are seen to surround the pericardial space. On the ventral surface, the lymphatics of the parietal pericardium connect to lymphatics in the pericardial fat and areolar tissue. On the lateral and posterior surfaces, the lymphatics of the parietal pericardium anastomose with lymphatics of the reflected mediastinal pleura. These anatomical observations offer new insights into the mechanisms of turnover of pericardial fluid and into the mechanisms of occurrence of chylopericardium.

Adolescent↗
PubMed1994

31P-magnetic resonance spectroscopy of the rabbit masseter muscle.

Dynamic biochemical changes in the masseter muscle were studied in 14 New Zealand adult male rabbits by 31P-nuclear magnetic resonance (NMR) spectroscopy. NMR spectra were obtained during rest and electrical stimulation of the muscle in the anaesthetized animal at 33 recording sessions. Electrical stimulation was applied by a pair of copper wires placed separately with hypodermic needles into the muscle. NMR spectra were acquired with a 2 x 3 cm, double-turn, copper transmit/receive coil. Sixteen spectra were averaged over 30 s to obtain averaged spectra continuously during a 30-min recording. The spectra were processed automatically using a non-linear 'least-squares' fitting program on the spectrometer. A Lorentzian line shape was assumed for the peaks, and values of peak height, area and chemical shifts were generated. Each averaged spectrum consisted of five peaks: inorganic phosphate (Pi), creatine phosphate (PCr), and three peaks related to ATP. Data were analysed as to absolute changes in Pi and PCr, in the ratio of Pi/PCr, and the shift of Pi to PCr to estimate pH. Several protocols were used in which ranges of frequency, intensity and duration of electrical stimulation were tested. The protocol for detailed studies involved stimulating the muscle twice at 5 Hz for 3 min separated by a 3-min rest period, then stimulating twice at 50 Hz for 3 min separated by a rest period. During contraction of the muscle, there was a significant increase in the Pi/PCr ratio (p < 0.05) as compared to the resting level. The ratio reached a plateau over a 3-min contraction using 5-Hz stimulation, then increased significantly more with the 50-Hz stimulation but decayed during the 3 min. Sustained stimulation with 50 Hz for 15-45 min evoked an initial sharp change in Pi/PCr, which then reached a steady plateau that remained over the entire stimulation. These findings indicate that the rabbit masseter muscle is relatively fatigue resistant in maintaining a steady-state equilibrium in the relation of Pi to PCr.

Adenosine Triphosphate↗
PubMed1994

Vancomycin penetration into biofilm covering infected prostheses and effect on bacteria.

To evaluate the adequacy of penetration of antibiotics into biofilm, a novel in vitro model for prosthesis-related infection was developed. Sterile stainless steel orthopedic nuts were incubated with slime-producing Staphylococcus epidermidis. Biofilm-covered nuts were exposed to varying concentrations of vancomycin; then biofilms were harvested. Vancomycin levels in biofilm, as measured by fluorescent polarization immunoassay, far exceeded the MIC and MBC of vancomycin for the organism. Bacterial growth in biofilm was inversely related to vancomycin concentration in biofilm, but even extremely high drug concentrations did not eradicate bacteria embedded in biofilm. The MICs and MBCs for bacteria recovered from biofilm did not differ from those for incubating organisms. Thus, failure of glycopeptide antibiotics to cure prosthesis-related infection is not due to poor penetration of drugs into biofilm but likely due to diminished antimicrobial effect on bacteria in the biofilm environment.

Bioprosthesis↗
PubMed1994

Disruptive effects of protein on performance of liquid membrane-based ion-selective microelectrodes.

The effects of addition of protein [bovine serum albumin (BSA)] to the calibration solutions of various liquid membrane-based ion-selective microelectrodes have been assessed. Protein at typically cytosolic levels of 100 mg/ml had no effect on the response of Na(+)-, K(+)-, Mg(2+)-, Ca(2+)-, H(+)-, NO3(-)-, and Cl(-)- selective microelectrodes at ion concentrations well above the respective detection limits. By contrast, this level of protein resulted in a pronounced increase in the detection limits of Na(+)-, K(+)-, Mg(2+)-, Ca2+, and Cl(-)-selective microelectrodes; H+ and NO3- microelectrodes were largely unaffected by the protein. The effect of BSA on detection limit is independent of pH and ionic strength, nor is it due to hysteresis, to binding of ions to the protein, or to the generation of junction potentials. More extensive studies on Na(+)-selective microelectrodes revealed that other proteins and large molecules (e.g., polyethylene glycol) also increase detection limits, with the extent of this effect apparently correlated positively with the molecular weight. Because biological macromolecules at physiological concentrations can influence the properties of alkali- and alkali earth cation-selective microelectrodes, care must be taken if the use of these electrodes entails cytosolic measurements close to their detection limits.

Equipment Failure↗
PubMed1994

The efficacy of choline magnesium trisalicylate (CMT) in the management of metastatic bone pain: a pilot study.

Twenty-six patients with painful, bony metastases were recruited into a randomized, double-blind, single dose, two-treatment, three-part crossover study of choline magnesium trisalicylate (CMT) and placebo. Assessments were made prior to and at one, two, three and four hours after dosing. Bone pain caused by metastatic cancer was significantly relieved one hour after the administration of 1500 mg CMT (p = 0.04). At all four time points the pain was less than baseline with CMT and at three time points greater than baseline with placebo but these results did not reach statistical significance. The summed pain intensity difference for patients was greater with CMT than with placebo, but this also did not reach significance. The incidence of volunteered side-effects was similar for both treatments. The results suggest that a nonacetylating, nonsteroidal anti-inflammatory drug may have a role complementary to that of an opioid in the management of metastatic bone pain.

Adolescent↗
PubMed1994

The heterologous expression of H(+)-coupled transporters in Xenopus oocytes.

The Xenopus oocyte has become a convenient and robust system for the expression of many different animal transport proteins and it has now been demonstrated that oocytes can also translate, process and target plant membrane proteins. Here we review the background to this expression system and discuss how it can be used to express plant transporters. A H+/hexose cotransporter (STP1) from Arabidopsis thaliana has been successfully expressed in oocytes and further characterization has shown the transporter to have properties similar to the same transporter expressed in yeast. However, the expression of H(+)-coupled transporters may present problems for oocyte intracellular pH regulation, because the influx of protons during their operation may acidify the cell. To investigate this possibility, proton-selective microelectrodes have been used to measure intracellular pH during symport of H+ and hexose in oocytes expressing STP1. These measurements showed that oocyte cytosolic pH is unaltered during H+/glucose cotransport, but is sensitive to changes in external pH.

Animals↗
PubMed1994

The lymphatics of the canine parietal pericardium.

A careful anatomical study of the lymphatic drainage from the parietal pericardium reveals a complicated network that is notably different from that defined by the instillation of markers into the pericardial sac. The pericardial cupola and the posterior (dorsal) area of the parietal pericardium drain directly to the cardiac lymph node in the right upper mediastinum by relatively short lymphatics. The lymphatics of the anterior and lateral areas of the parietal pericardium pass to collecting vessels that travel cranially or caudally along the phrenic nerves. The former traverse specific lymph nodes and then enter the right or left venous angles. The latter pass caudally and then drain to the major collecting systems from the area of the diaphragm.

Animals↗
PubMed1993

The search for the central swallowing pathway: the quest for clarity.

As the work of Dr. Martin Donner has brought a clarity to understanding swallowing, so has the work of various neuroscientists, including that of a Nobel Laureate, in providing us with a better comprehension of this complex motor pattern. Understanding the neural control of swallowing has been a process that has occurred during this century in which several investigators, primarily from Europe, Japan, Canada, and the United States, have brought their perspectives in applying particular techniques to decipher how the central and peripheral nervous system control swallowing. Swallowing represents a complex muscular response of the oral, pharyngeal, and esophageal regions which are integrated to provide an effective functional pattern that prepares and transports food while simultaneously protecting the airway. This adaptation of the upper gastrointestinal tract in mammals has been extensively studied peripherally by two methods: recording from the peripheral nerves and muscles, and stimulating peripheral nerves and their receptive fields that can induce the pharyngeal and esophageal phases of swallowing. The study of the peripheral nervous system has provided insight into the sensory receptive fields that evoke or facilitate swallowing, and has established the first serious evidence of the all-or-none sequential contraction pattern of the oropharyngeal and esophageal muscles. It has been these electromyographic studies of the muscles that has established much of the criteria for evaluating the central swallowing pathway. Five techniques have been applied to the central nervous system to study swallowing and include lesioning or destroying discrete regions to determine how swallowing is impaired or modified, electrically stimulating the central neural tissue to determine the type of effects on swallowing, recording from the central neural tissue with macro- and microelectrodes to ascertain when neurons respond in timing to the peripheral muscle activity during swallowing, applying pharmacological agents through micropipettes which could mimic or inhibit potential transmitters, and using immunochemical techniques to tag specific chemicals that could be transmitters used by the neurons in the central swallowing pathway. These various techniques have provided insight into how the central swallowing pathway is organized but the details of the central control are still in the process of being defined and will require as much effort this next century as has been previously developed over the past 90 years.

Brain Stem↗
PubMed1993

The use of power images to perform quantitative analysis on low SNR MR images.

Zero-mean noise introduced into quadrature detected MRI signals is generally rectified by the reconstruction algorithm to give a nonzero background intensity in the displayed image. In low signal-to-noise ratio (SNR) images, this background will inflate region of interest (ROI) signal measurements, leading to improper T2 and diffusion fits. A method is described here which separates signal from noise by computing power images from traditional magnitude data. Parameters measured from such power images show closer agreement with true values that do those derived from magnitude images. Because the correction algorithm is the same for all pixel intensities, it can be used with regions of interest with heterogeneous values.

Humans↗
PubMed1993

Beta-adrenoceptor subtypes and the opening of plasmalemmal K(+)-channels in bovine trachealis muscle: studies of mechanical activity and ion fluxes.

1. Studies of mechanical activity and 86Rb+ efflux have been made in bovine isolated trachealis with the objectives of: (a) identifying which of the beta-adrenoceptor subtypes mediates the opening of plasmalemmal K(+)-channels, (b) gaining further insight into the properties of the novel, long-acting beta 2-adrenoceptor agonist, salmeterol and (c) clarifying the role of K(+)-channel opening in mediating the mechano-inhibitory actions of agonists at beta-adrenoceptors. 2. In bovine trachealis muscle strips precontracted with histamine (460 microM), isoprenaline (0.1 nM-1 microM), procaterol (0.1-10 nM) and salmeterol (0.1-10 nM) each caused concentration-dependent relaxation. 3. ICI 118551 (10 nM-1 microM) antagonized isoprenaline, procaterol and salmeterol in suppressing histamine-induced tone of the isolated trachealis muscle. The antagonism was concentration-dependent. In contrast, CGP 20712A (10 nM-1 microM) failed to antagonize isoprenaline, procaterol or salmeterol. 4. Salmeterol (1-10 microM) antagonized isoprenaline in relaxing strips of bovine trachea which had been precontracted with carbachol (1 microM). 5. Cromakalim (10 microM), isoprenaline (100 nM-10 microM), procaterol (10 nM-1 microM) and salbutamol (100 nM-10 microM) each promoted the efflux of 86Rb+ from strips of bovine trachealis muscle preloaded with the radiotracer. In contrast, salmeterol (100 nM-10 microM) failed to promote 86Rb+ efflux. 6. CGP 201712A (1 microM), ICI 118551 (100 nM) and salmeterol (1 microM) did not themselves modify 86Rb+ efflux from trachealis muscle strips, nor did they affect the promotion of 86Rb+ efflux induced by cromakalim (10 microM). In contrast, CGP 20712A (1 microM) and ICI 118551 (100nM) were each able to inhibit the promotion of 86Rb+ efflux induced by isoprenaline (1 microM) or procaterol (100 nM). Furthermore,salmeterol (10 microM) inhibited isoprenaline (1 microM)-induced promotion of 86Rb+ efflux.7. It is concluded that, in bovine trachealis, activation of either beta l- or beta 2-adrenoceptors can promote the opening of 86Rb+-permeable K+-channels in the plasmalemma. The failure of salmeterol to promote plasmalemmal K+-channel opening may reflect, not its selectivity in activating beta 2- as opposed to beta 1-adrenoceptors, but rather its low intrinsic efficacy at beta 2-adrenoceptors. The opening of plasmalemmal K+-channels plays a supportive rather than a crucial role in mediating the mechano-inhibitory effects of agonists at beta-adrenoceptors acting on trachealis muscle.

Adrenergic beta-Agonists↗
PubMed1993

Metoclopramide in the treatment of reflux oesophagitis: a comparison of normal and controlled-release formulations.

Twenty patients with reflux oesophagitis were recruited into a randomized, single (investigator)-blind, two-part crossover study of controlled-release metoclopramide ('Gastrobid Continus' tablets) 15 mg given twice daily, and normal-release metoclopramide ('Maxolon'), 10 mg given 4-times daily. Both treatment regimens were efficacious in reducing the severity of heartburn, the incidence of waking at night due to pain from heartburn and the severity of gastro-intestinal symptoms. The incidence of volunteered and sought side-effects/symptoms was similar on both treatments. More patients preferred the controlled-release than the normal-release formulation. It is concluded that 15 mg controlled-release metoclopramide twice daily and 10 mg normal-release metoclopramide 4-times daily are equally effective and well-tolerated treatment regimens, but that the controlled-release formulation has the advantage of a smaller dose and twice daily administration.

Administration, Oral↗