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Biomedical subjects

G R Davis

Publications and source records attributed to G R Davis.

At least 37 records · Page 2Linked to original sources
PubMed1994

Recording mandibular movement: technical and clinical limitations of the Sirognathograph.

It is essential to know the limitations of any equipment used for research or clinical purposes. Clinical electronic equipment is commonly sold for "black box" use without specification of artifacts. This study tested the technical and clinical limitations of the Sirognathograph, which is a device used for recording mandibular movement. From a technical point of view, the Sirognathograph's slow sampling speed and sample artifacts have been shown to be the system's main limitations; however, it was possible to eliminate sampling artifacts by using a customized pulse generator and software for controlled data acquisition. Clinically, the Sirognathograph appears to have some inherent limitations in its accuracy. The effect of cranial movements during mastication can cause a baseline drift with consequent errors in the recording of mandibular position. This problem was controlled in this study by using a headband to stabilize the cranial movements during mastication. Also, the spatial relationships between the aerial and both the cranial base and the magnet were found to be critical for repeatability of the recordings.

Adolescent↗
PubMed1993

Design and synthesis of polyacrylamide-based oligonucleotide supports for use in nucleic acid diagnostics.

Polyacrylamide supports, in a range of pore sizes, were investigated as nucleic acid affinity matrices for the detection of target DNA or RNA sequences using a sandwich hybridization format. Bromoacetyl and thiol oligonucleotide derivatives were covalently linked to sulfhydryl- and bromoacetyl-polyacrylamide supports with greater than 95% end-attachment efficiencies. These polyacrylamide-oligonucleotide supports were further derivatized with anionic residues to provide multi-functional supports which show low non-specific binding for non-complementary nucleic acids. While all the polyacrylamide-oligonucleotide supports capture complementary oligonucleotides with high affinity, the pore size was found to be a critical parameter in sandwich hybridization reactions. The superior hybridization characteristics of the Trisacryl support was ascribed to a combination of its macroporous nature, hydrophilicity and the terminal attachment of its capture oligonucleotides.

Acetates↗
PubMed1993

Time course of anatomical regeneration of descending brainstem neurons and behavioral recovery in spinal-transected lamprey.

In larval lamprey 4 weeks after a spinal transection locomotor patterns were usually complete along the body in whole animals. In in vitro preparations locomotor activity was restricted to a few millimeters below the transection. Retrograde labeling indicated that descending axons from a few brainstem neurons had grown through the transection site and probably directly activate the rostral spinal locomotor networks, but no direct descending projections were found to the caudal spinal cord. Thirty-two weeks after spinal transection locomotor activity was recorded at long distances below the transection in both whole animals and in vitro preparations. The number of brainstem neurons projecting to the rostral spinal cord below the transection appeared near normal while there was a reduced but significant projection to the caudal spinal cord. Thus, at long recovery times it appears that regenerated descending axons can directly activate the motor networks in both the rostral and caudal spinal cord and initiate locomotor activity, as is the case in normal animals.

Animals↗
PubMed1993

Time course of locomotor recovery and functional regeneration in spinal-transected lamprey: kinematics and electromyography.

The time course of recovery of locomotor function was examined with kinematic analysis and muscle recordings in larval lampreys 2-32 weeks after rostral spinal cord transection at the level of the third gill (approximately 10% of body length, BL). Animals began to recover locomotor movements within 2-4 weeks of spinal cord transection, but the amplitude of locomotor movements in the tail region was less than in normal animals. At 2 weeks post-transection, locomotor activity was limited to 20% BL, and at 3 weeks after spinal transection activity could be recorded at least as far as 40% BL. At 4 weeks after spinal transection, well-coordinated locomotor muscle activity was often present as far as 60% BL. At 8 weeks of recovery and longer, well-coordinated locomotor activity was present consistently at least as far as 60% BL, and the amplitudes of locomotor movements were restored to normal values. At each recovery time examined the ranges of locomotor parameters (cycle time, burst proportion, and intersegmental phase lag) overlapped with those in normal animals. Thus, the gradual recovery of the amplitude of locomotor movements in the caudal body is associated with the gradual return of coordinated muscle activity at progressively more caudal levels along the body. The mechanisms responsible for this gradual recovery of locomotor function are discussed in relation to our recent anatomical and in vitro studies.

Animals↗
PubMed1991

Characterization of growth hormone releasing factor analog expression in Saccharomyces cerevisiae.

An analog of growth hormone releasing factor (GRF), [Leu27]GRF(1-40)-OH, has been expressed and secreted in Saccharomyces cerevisiae under the control of the alpha-factor gene promoter and prepro sequence. A single pair of consecutive basic residues served as a processing site between the alpha-factor sequences and the GRF sequences. [Leu27]GRF(1-40)-OH from fermentor broth containing 20-30 mg/L of immunoreactive peptides was shown to be correctly processed and to possess biological activity as measured in vitro and in vivo. Additional peptides purified from broth appear to result from proteolytic degradation of the original translation product. Analysis of the amino acid compositions and sequences of these peptides suggests that processing enzymes may be responsible for some of the degradation.

Amino Acid Sequence↗
PubMed1990

Mauthner cells maintain their lumbar projection in adult frog.

We have used retrograde labeling with horseradish peroxidase (HRP) in the bullfrog. Rana catesbeiana, to determine whether Mauthner (M) cells maintain a projection to the lumbar spinal cord in adult bullfrogs. We found that M cells persist in the adult bullfrog and maintain a projection to the lumbar spinal cord, despite the degeneration of much of their afferent input and of their motoneuronal targets in the spinal cord.

Animals↗
PubMed1990

Detection of human immunodeficiency virus type 1 in AIDS patients using amplification-mediated hybridization analyses: reproducibility and quantitative limitations.

Eighty-six peripheral blood mononuclear cell (PBMC) samples from 30 patients with AIDS were analyzed using a transcription-based amplification system (TAS) and the polymerase chain reaction (PCR). Human immunodeficiency virus type 1 (HIV-1) sequences were detected by amplification-mediated hybridization in 98% of the samples, 52% of which were positive for p24 antigen by ELISA. Neither TAS (93%) nor PCR (95%) detected HIV-1 sequences in all 86 samples. The hybridization-detection methods (slot blot, bead-based sandwich, and solution) used to detect the HIV-1-specific TAS products had a clear influence on the efficiency of detecting and quantitating the levels of HIV-1 present in these samples. The reproducibility of amplification of constant amounts of HIV-1 RNA and beta-globin DNA by TAS and PCR was studied over 3 months. The results indicated that variations of 10- and 5-fold in the HIV-1 sequence levels could be detected between samples by TAS and PCR, respectively. Within the range of sensitivities for each assay used, the administration of zidovudine did not appear to reduce the amount of HIV-1 nucleic acid sequences as observed in PBMC obtained serially from six AIDS patients.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Transcription-based amplification system and detection of amplified human immunodeficiency virus type 1 with a bead-based sandwich hybridization format.

The in vitro amplification of biologically important nucleic acids has proceeded principally by a strategy of DNA replication. Polymerase chain reaction was the first such protocol to achieve this goal. In this report, a transcription-based amplification system (TAS) is described. Each cycle of the TAS is composed of two steps. The first is a cDNA synthesis step that produces one copy of a double-stranded DNA template for each copy of RNA or DNA target nucleic acid. During the course of this cDNA synthesis step, a sequence recognized by a DNA-dependent RNA polymerase is inserted into the cDNA copy of the target sequence to be amplified. The second step is the amplification of the target sequence by the transcription of the cDNA template into multiple copies of RNA. This procedure has been applied to the detection of human immunodeficiency virus type 1 (HIV-1)-infected cells. After four cycles of TAS, the amplification of the vif region of the HIV-1 RNA genome was measured to be, on the average, 38- to 47-fold per cycle, resulting in a 2-5 x 10(6)-fold increase in the copy number of the original target sequence. This amplification by the TAS protocol allows the detection of fewer than one HIV-1-infected CEM cell in a population of 10(6) uninfected CEM cells. Detection of the TAS-generated RNA from HIV-1-infected cells can easily be accomplished by means of a bead-based sandwich hybridization protocol, which provides additional specificity for the identification of the amplified HIV-1-specific sequence.

Cell Line↗
PubMed1988

Jitter correction: a computer algorithm for reduction of the velocity recovery function artifact.

The measurement of neuromuscular jitter in single fiber electromyography may be artifactually raised by a component of interdischarge interval (IDI)-dependent jitter caused by the velocity recovery function (VRF) in muscle fibers. We have developed a computer algorithm for on-line mathematical correction for this artifact, thus improving the reliability of neuromuscular jitter estimates. The method, based on a modeling technique, was validated using intramuscular stimulation in order to either exclude an IDI-dependent component (using regular stimulation) or to include an IDI-dependent component (using pseudorandom stimulation). In 10 normal subjects the distribution of 106 corrected jitter values obtained using voluntary activity showed no difference from the measured values. This finding implies that previously published values for normal jitter are not likely to have been influenced by the VRF effect.

Action Potentials↗
PubMed1988

Patterns of selective involvement of thigh muscles in neuromuscular disease.

In 14 patients with limb girdle muscular dystrophy, polymyositis, and type 3 spinal muscular atrophy, CT scans of the thigh muscles were correlated with single fiber EMG studies in vastus lateralis, semimembranosus and biceps femoris muscles. There was a relation between the extent of CT scan abnormality and increased fiber density in the three muscles studied, except in the most severely affected muscles in which in some muscles the fiber density values were lower than expected. These results were independent of the underlying pathology. Correlative CT/SFEMG studies provide insights into the pattern of selective involvement of certain muscles in neuromuscular disorders.

Adult↗
PubMed1988

Dose-response, meal-stimulated gastric antisecretory study of prostaglandin E1 analog, misoprostol, in man.

In a randomized, double-blind, crossover trial, the effects of 50-, 100-, and 200-micrograms doses of misoprostol on meal-stimulated gastric acid secretion were compared with placebo in 16 healthy male subjects. Compared with placebo, the 100- and 200-microgram doses produced significant reductions in acid output for 2 and 3 hr, respectively, following the test meal (P = 0.05). Misoprostol did not influence either the fasting or postprandial serum gastrin levels as compared with placebo. No adverse experiences were reported by any of the subjects. One subject experienced a transient rise in SGPT as compared with baseline, which may have been due to ethanol intake. This study provides a scientific rationale on which to base additional trials of misoprostol in patients with disease related to gastric acid production.

Adult↗
PubMed1987

Hybridization properties of immobilized nucleic acids.

The 5'-end attachment of oligonucleotides to dextran supports facilitates the study of the hybridization properties of an immobilized oligonucleotide system. The hybridization properties which were studied include: hybridization capacity and kinetics, hybridization-complex stability, and reagents influencing hybridization efficiency. Results of these experiments reveal that the hybridization efficiencies of support-bound oligonucleotides were 75-80% and 40-50% for single-stranded oligonucleotide targets and long double-stranded targets, respectively. These hybridization efficiencies are dependent upon prehybridizing the support-bound oligonucleotides with dextran sulfate. In addition, comparisons of the relative hybridization efficiencies of the support-bound oligonucleotide and nitrocellulose-based systems have been made which indicate a retention of 13-28% of target sequences on the filters and a detection efficiency of 8-20%.

Acrylic Resins↗
PubMed1987

The double collision technique: a new method for measurement of the motor nerve refractory period distribution in man.

A new, double collision, technique is described for non-invasive measurement of the motor nerve refractory period distribution for human peripheral nerves. In contrast to previous collision techniques, this method is independent of the transient changes in nerve and muscle fibre conduction which can distort test muscle responses. The end-point of the distribution is determined by a null response; this permits accurate identification of those nerve fibres with the longest refractory periods. We have used the double collision technique to measure the refractory period distributions for the median nerve at the wrist in 20 normal subjects aged between 22 and 58 (mean 35) years. 150% maximal stimuli were used with a controlled limb temperature of 35 degrees C. Following a conditioning stimulus, the mean latencies for recovery of 5%, 50%, 95% and 99% of motor nerve fibres were 0.94, 1.03, 1.12 and 1.23 msec respectively. Data are also presented for the ulnar and peroneal nerves. The results show that the human motor nerve refractory period distribution is much less dispersed than has been previously supposed.

Adult↗
PubMed1987

Motor nerve conduction velocity distributions in man: results of a new computer-based collision technique.

A new computer-based collision technique for direct measurement of the human motor nerve conduction velocity distribution is described. In contrast to previous collision techniques, the test muscle response is progressively cancelled to a null using an arrangement of proximal and distal stimuli which eliminates distortion of the test response caused by transient changes in nerve and muscle fibre conduction. The increased sensitivity of this new technique permits accurate measurement of the slowest 1% of alpha motor nerve fibres. We have used our modified collision technique to determine motor nerve conduction velocity distributions for the median nerve in 20 normal subjects aged between 19 and 59 (mean 35) years. 150% maximal stimulus intensities were used, with a controlled limb temperature of 35 degrees C. Group mean velocities (+/- S.D.) for the fastest (95%), mean (50%) and slowest (5% and 1%) motor fibres were 59.1 +/- 3.0, 56.9 +/- 2.9, 52.7 +/- 3.1 and 51.2 +/- 3.7 m/sec respectively. Data are also presented for the ulnar and peroneal nerves.

Action Potentials↗
PubMed1986

Tularemic hepatitis presenting as obstructive jaundice.

A 56-yr-old man was admitted for evaluation of fever, chills, jaundice, and alcoholic stools. Laboratory studies suggested a cholestatic process. Ultrasonography, computed tomography, and transhepatic cholangiography failed to reveal any abnormalities. Acute infection with Francisella tularensis was confirmed serologically, and a liver biopsy revealed cholestatic hepatitis with focal coagulative necrosis. Recovery was coincident with antibiotic therapy.

Cholangiography↗
PubMed1986

Introduction and expression of the bacterial PaeR7 methylase gene in mammalian cells.

An approach is devised for studying the role of DNA methylation in eukaryotic gene expression. The approach is based on the expression of site-specific bacterial methylase genes in animal cells. A model system using the cloned PaeR7 (an isoschizomer of Xho I) methylase gene was constructed to test the feasibility of this approach. Expression plasmids for the PaeR7 methylase gene were introduced into mouse Ltk- cells by cotransfection with the cloned chicken thymidine kinase (tk) gene. Several of the cell strains derived from Tk+ colonies were found to express the PaeR7 gene as judged by four criteria: the cellular DNA of these strains showed increased resistance to cleavage by Xho I; these strains contained cellular proteins that comigrated with pure PaeR7 methylase protein, as visualized by immunoblotting; PaeR7 methylase activity was found in vitro in crude extracts of total cellular protein from these strains; and murine adenovirus genomes grown on cells expressing PaeR7 methylase showed resistance to cleavage to PaeR7 endonuclease. The potential applications of this approach for the study of cellular and viral gene regulation, DNA repair, and restriction modification are discussed.

Animals↗
PubMed1985

The effect of continuous voluntary activation on neuromuscular transmission: a SFEMG study of myasthenia gravis and anterior horn cell disorders.

In normal subjects the neuromuscular jitter does not increase during continuous voluntary activation. In patients with myasthenia gravis, spinal muscular atrophy and motor neurone disease we have found that the neuromuscular jitter may increase during recordings of several minutes of continuous voluntary activation at steady innervation rates. In some units this led to impulse blocking, and in other units an initially normal jitter increased beyond the normal range. Measurement of jitter during continuous voluntary activation at steady innervation rates provides relevant information in the evaluation of neuromuscular transmission and fatigue in these disorders.

Adult↗